JP6794652B2 - Method for manufacturing heat-treated steel pipe and heat-treated steel pipe - Google Patents

Description

The present invention relates to the production how heat treatment for steel and heat treatment steel pipe, and more particularly relates to the production how suitable heat treatment for steel available and heat treatment steel as an automobile member.

In recent years, in consideration of the global environment, steel materials for automobile structures are strongly required to be lightweight, have a tensile strength of 780 MPa or more, and have a high strength of 900 MPa or more, which is a completely different level from the conventional one. Requested. In addition, in order to improve the safety of the vehicle body at the time of a collision and improve the safety, development for enhancing the energy absorption characteristics of the automobile members at the time of a collision is also being promoted. In particular, an invention is disclosed in which a steel pipe or a steel plate is used as a material, for example, a molded product having an optimum shape having a wide variety of bending shapes in which a bending direction changes in an arbitrary direction.

According to Patent Document 1 below, even in the case of continuous bending in which the bending direction of the steel material changes three-dimensionally, the roller dies that are movably arranged in three dimensions can be used for efficient bending, and further. A bending method for quenching a steel material at the same time as the bending process (in the present specification, such a bending method is abbreviated as "3DQ: 3 Dimensional hot bending and Quench") is disclosed. In 3DQ, a steel material, which is a work material, is rapidly heated to an Ac3 transformation point or higher in the atmosphere by a high-frequency heating coil, and then immediately cooled and baked, and at the same time, it is heated to a high temperature and its deformation resistance is reduced. A bending moment is applied to the steel by a movable roller die to cause plastic deformation.

On the other hand, zinc-based plated steel materials such as hot-dip galvanized steel sheets, alloyed hot-dip galvanized steel sheets, and electrogalvanized steel sheets are often used as automobile members because they have necessary and sufficient corrosion resistance in the usage environment and are excellent in terms of cost. Will be done. Among them, the alloyed hot-dip galvanized steel sheet in which the steel plate is continuously hot-dip galvanized and then heat-treated at a temperature of about 500 to 550 ° C. to change the entire plating layer into an intermetallic compound layer of Fe-Zn is hot-dip zinc. Compared with the plated steel plate and the hot-dip galvanized steel plate, the plating layer becomes somewhat noble and the sacrificial anticorrosion ability is slightly reduced, but the adhesion of the plating layer to the coating film is improved. Therefore, such alloyed hot-dip galvanized steel sheets are often used for automobile members used after being subjected to chemical conversion treatment and electrodeposition coating.

Therefore, if an alloyed hot-dip galvanized steel material can be used as the work material in 3DQ, it is expected that a plated heat-treated steel material having high corrosion resistance can be provided by preventing oxidation of the work material due to heating. However, (1) when the alloyed hot-dip galvanized steel is heated above the Ac3 transformation point, the zinc vapor pressure rapidly increases with the temperature rise, for example, 200 mmHg: 788 ° C. and 400 mmHg: 844 ° C. Zinc oxidation occurs with heating in the atmosphere, and (2) the alloyed hot-dip galvanized steel material decomposes at 600 ° C or higher, especially in the Γ phase (Fe ₃ Zn ₁₀ ). When heated to a temperature exceeding 660 ° C., the dissolution phenomenon of Zn in the ferrite of the steel base becomes remarkable, and the plating layer may be lost. Therefore, as a plating layer, There is a risk of loss of function.

In this way, the problem in mass-producing automobile parts by 3DQ using alloyed hot-dip galvanized steel as the work material is to heat the zinc-based plated steel, which is the base material, to about 870 ° C or higher for quenching. In addition to the need, the alloyed hot-dip galvanized film disappears at about 950 ° C., so that the allowable range of the heating temperature of the work material is as narrow as about 870 to 950 ° C.

In Patent Document 2 below, an alloyed hot-dip galvanized steel sheet or induction-hardened steel sheet is cooled to an induction temperature of Ar3 transformation point or more and 1000 ° C. or less and 350 ° C. from the start of heating. A method for manufacturing a reinforcing member by induction hardening is disclosed, in which the heat cycle time up to is limited to 60 seconds or less (about 3 seconds in the embodiment of the same document) to heat and cool. However, in Cited Document 2, the rate of temperature rise and the rate of cooling are not disclosed.

According to the method disclosed in Reference 2, even if a zinc-based plated steel sheet using a quenching steel sheet as a base plate is used as an induction hardening strengthening member and induction hardening is performed on a portion whose strength is to be improved, quenching is performed. The plating layer can be left in the inlet, and the Fe concentration in the plating layer is controlled to 35% or less (in the present specification, "%" means "mass%" unless otherwise specified). Although it is said that an automobile member having excellent coatability and corrosion resistance can be provided, Patent Document 2 discloses only the use of hot-dip zinc plating as a plating material, and similarly to Patent Document 1 above. There is a problem of plating hardening.

According to Patent Document 3, the present inventors have described that at least a part of a steel material having a 55% Al-Zn-1.5% Si hot-dip plating film on at least one side has a heating rate of 10 ° C./sec or more above the Ac3 transformation point. By heating with a cooling rate of 30 ° C./sec or higher before the liquid phase is present on the surface of at least a part of the heated part, at least a part of the heated part is heated and cooled. A plated heat-treated steel material is formed on the surface by forming a zinc and / or oxide layer and a solid-dissolved phase in which iron-aluminum is alloyed, which has corrosion resistance and can secure a lubricating function at high temperatures. The invention to be manufactured is disclosed. Even if the plated heat-treated steel material is heat-treated under the above-mentioned conditions, it has proper corrosion resistance after painting as an automobile member, can suppress the generation of scale due to the heat treatment, and further suppresses the generation of scale. In addition to being able to do so, it exhibits excellent lubricity even when processed at high temperatures because it is hard.

Here, when the product disclosed in Patent Document 3 is used for an automobile part, it is required to have good chemical conversion processability as in the case of a press-molded steel product. At that time, it is conceivable to apply the 3DQ method disclosed in Patent Document 1 to the product disclosed in Patent Document 3.

However, the steel material disclosed in Patent Document 3 has a drawback that a strong alumina film is formed on the plating surface after 3DQ heating because the plating layer contains a large amount of Al, and the chemical conversion treatment property is inferior. The chemical conversion treatment is a treatment for forming a phosphate crystal film on the surface of a steel material as a base treatment for painting in automobile parts. In addition, poor chemical conversion treatment means that a healthy phosphate crystal film is not formed under the current chemical conversion treatment conditions.

In Patent Document 4, a layer containing ZnO is formed on the upper layer of an Al-plated steel plate, heated in a furnace, and pressed with a mold at room temperature to simultaneously perform molding and quench hardening by cooling the mold. A method for ensuring subsequent chemical conversion processability by the effect of a layer containing ZnO is disclosed.

International Publication No. 2006/093006 Japanese Unexamined Patent Publication No. 2000-248338 JP-A-2010-265515 Patent No. 4590025

However, the method disclosed in Patent Document 4 is considered to have no problem in the so-called hot stamping method, but the 3DQ method disclosed in Patent Document 1 probably has a high rate of temperature rise, so that the coating amount is large. There is a problem that is presumed to be excessive. Further, there is a problem that the above-mentioned Patent Document 4 does not specify compounds other than ZnO.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is that the 3DQ method can be applied even when the Al content of the plating layer is large. There, and capable of realizing excellent chemical conversion treatability is to provide a manufacturing how heat treatment for steel and heat treatment steel.

In order to obtain a member having excellent corrosion resistance at the time of heat treatment, chemical conversion treatment and electrodeposition coating, the type, particle size and content of metal oxide and resin components in the film before heat treatment. Etc. must be selected appropriately. However, the film before the heat treatment undergoes various processes such as heat treatment, chemical conversion treatment, and electrodeposition coating before being applied to the actual member, and is affected by the temperature of the heat treatment and the components of the chemical conversion treatment liquid in the chemical solution. By combining various factors such as the difference in etching force due to the difference and slight fluctuations in the treatment conditions in electrodeposition coating, the film at the time of product changes in various ways. Therefore, it is very difficult to limit the present invention without omission by analysis at the time of becoming a member. In addition, it is extremely time-consuming and impractical to individually identify the characteristics of each of the films that have changed due to various factors. Therefore, in the present invention described in detail below, the heat treatment steel pipe that defines the film of the steel material before heat treatment is defined, the heat treatment method using the heat treatment steel pipe, and the specific heat treatment for the heat treatment steel pipe. It specifies the parts manufactured by applying the method.

The present inventor has obtained the following invention as a result of further detailed examination of a heat-treated steel material made of a steel material having a 55% Al-Zn-1.5% Si hot-dip galvanized layer disclosed in Patent Document 3. ..

( 1 ) A plating film layer located on at least one of the inner and outer surfaces of a steel pipe and containing 50% by mass or more of Al per side, and a plating film layer located on the plating film layer and containing granular metal compounds. The granular metal compound including a surface film layer is one or more of Mg compound, ZrO, CaO, TiO ₂ or SiO ₂ , and the Mg compound is MgO, which is per one side of the MgO. coating weight, as ^Mg, a ^{0.2g / m 2 ~2.4g / m 2} , the particle size of the MgO is 5 nm to 100 nm, heat treatment for steel pipes.
( 2 ) A plating film layer located on at least one of the inner and outer surfaces of the steel pipe and containing 50% by mass or more of Al per one side, and a granular metal compound located on the plating film layer. The granular metal compound comprising a surface film layer is one or more of Mg compound, ZrO, CaO, TiO _{2 and} SiO ₂ , and the Mg compound is magnesium chloride, magnesium nitrate, or magnesium sulfate. is any one of, said magnesium chloride, magnesium nitrate, or the coating weight of either per surface of magnesium sulfate as ^Mg, is ^{0.2g / m 2 ~2.4g / m 2} , heat treatment Steel pipe.
( 3 ) A plating film layer located on at least one of the inner and outer surfaces of a steel pipe and containing 50% by mass or more of Al per side, and a plating film layer located on the plating film layer and containing granular metal compounds. The granular metal compound including the surface film layer is one or more of Mg compound, ZrO, CaO, TiO ₂ or SiO ₂ , and the amount of ZrO adhered to one side is 0. was ^{4g / m 2 ~2.0g / m 2} , the ZrO has particle sizes of 10 nm to 200 nm, heat treatment for steel pipes.
( 4 ) A plating film layer located on at least one of the inner and outer surfaces of a steel pipe and containing 50% by mass or more of Al per side, and a granular metal compound located on the plating film layer. The granular metal compound comprising a surface film layer is a mixture of ZrO and CaO or a mixture of ZrO and MgO, and the amount of adhesion of the mixture per side is Zr and Ca, or Zr and Mg. as ^{a 0.4g / m 2 ~2.0g / m 2} , the heat treatment for steel pipes.
( 5 ) A plating film layer located on at least one of the inner and outer surfaces of a steel pipe and containing 50% by mass or more of Al per side, and a granular metal compound located on the plating film layer. comprising a surface film layer, a metal compound of the particulate _is, TiO 2, SiO _2, or a mixture of TiO ₂ and SiO _2, per side of the _TiO 2, SiO ₂ or TiO ₂ and mixtures of SiO ₂ The amount of adhesion of Ti, Si, or the total of Ti and Si is 0.4 g / m ^{2 to} 2.0 g / m ² , and the particle sizes of TiO ₂ and SiO ₂ are 5 nm to 30 nm. there, the heat treatment for the steel pipe.
( 6 ) The surface coating layer contains a resin component and / or a silane coupling agent in addition to the granular metal compound, and the content of the resin component and / or the silane coupling agent is The heat treatment steel pipe according to any one of (1) to ( 5 ), which is 5 % by mass to 35% by mass with respect to the mass of the granular metal compound.
( 7 ) The above-mentioned one of (1) to ( 6 ), wherein the plating film layer is composed of (50 to 60) mass% Al-Zn- (1 to 2.5) mass% Si hot-dip galvanized. Steel pipe for heat treatment.
( 8 ) The steel pipe for heat treatment according to any one of (1) to ( 6 ), wherein the plating film layer is made of Al- (0 to 15) mass% Si hot-dip galvanized.
( 9 ) A method for manufacturing a heat-treated steel pipe using the heat-treated steel pipe according to any one of (1) to ( 8 ), wherein at least a part of the heat-treated steel pipe is hardened. It has a quenching step, and in the quenching step, an average rise of 100 ° C./sec or more from 100 ° C. to the maximum heating temperature on at least one surface of the heat treatment steel pipe having the plating film layer and the surface film layer. It is heated to the maximum heating temperature within the temperature range of 850 ° C. to 1300 ° C. at a temperature rate, cooling is started within 2 seconds after being heated to 850 ° C. or higher, and from the maximum heating temperature to 350 ° C., an average of 1000 A method for manufacturing a heat-treated steel pipe that cools to a temperature range of 350 ° C or lower at a cooling rate of ° C / sec or higher.
( 10 ) A plating film layer located on at least one of the inner and outer surfaces of a steel pipe and containing 50% by mass or more of Al per side, and a granular metal compound located on the plating film layer. The granular metal compound comprising a surface film layer is a method for producing a heat-treated steel tube using a heat-treated steel tube which is ZnO, and quenching is performed on at least a part of the heat-treated steel tube. It has a quenching step, and in the quenching step, on at least one surface of the heat treatment steel tube having the plating film layer and the surface film layer, the temperature rises from 100 ° C. to the maximum heating temperature by an average of 100 ° C./sec or more. It is heated to the maximum heating temperature within the temperature range of more than 1000 ° C. and 1300 ° C. or lower at a temperature rate, cooling is started within 2 seconds after being heated to 850 ° C. or higher, and from the maximum heating temperature to 350 ° C. on average. A method for manufacturing a heat-treated steel tube, which cools to a temperature range of 350 ° C. or lower at a cooling rate of 1000 ° C./sec or higher.
(11) In the heat treatment for steel pipe before being subjected to the quenching step, coating weight per one surface of the ZnO as Zn, a ^{0.2g / m 2 ~7g / m 2} , wherein the ZnO is The method for producing a heat-treated steel pipe according to ( 10 ), which has a particle size of 50 nm to 300 nm.
( 12 ) In the heat treatment steel pipe before being subjected to the quenching step, the surface coating layer contains a resin component and / or a silane coupling agent in addition to the granular metal compound, and said. The heat-treated steel pipe according to ( 10 ) or ( 11 ), wherein the content of the resin component and / or the silane coupling agent is 5% by mass to 35% by mass with respect to the mass of the granular metal compound. Production method.
( 13 ) In the heat treatment steel pipe before being subjected to the quenching step, the plating film layer is composed of (50 to 60) mass% Al-Zn- (1 to 2.5) mass% Si hot-dip galvanized. , ( 10 ) to ( 12 ), the method for producing a heat-treated steel pipe according to any one of ( 12 ).
( 14 ) In the heat treatment steel pipe before being subjected to the quenching step, the plating film layer is any of ( 10 ) to ( 12 ) made of Al− (0 to 15) mass% Si hot dip galvanizing. The method for manufacturing a heat-treated steel pipe according to one.
( 15 ) The method for producing a heat-treated steel pipe according to any one of ( 9 ) to ( 14 ), wherein the heat-treated steel pipe is bent at a temperature of 850 ° C. or higher.

As described above, according to the present invention, it is possible to apply the 3DQ method even when the Al content of the plating layer is high, and it is possible to realize excellent chemical conversion processability. possible, it is possible to provide a manufacturing how heat treatment for steel and heat treatment steel.

It is explanatory drawing which illustrates the structure of the manufacturing apparatus for manufacturing the coated heat-treated steel material which concerns on embodiment of this invention. It is sectional drawing which illustrates the outline of the structure of the high frequency heating coil and the cooling apparatus in the manufacturing apparatus for manufacturing the coated heat-treated steel material which concerns on embodiment of this invention. It is explanatory drawing which illustrates the shape of the movable roller die which can be used for manufacturing the coated heat-treated steel material which concerns on embodiment of this invention, and shows the case which is composed of two pressure rolls. It is an SEM photograph of a chemical conversion crystal film after chemical conversion treatment of the steel material of this invention and a comparative example.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

According to the present invention described in detail below, a (50 to 60)% Al-Zn- (1 to 2.5)% Si hot-dip galvanized film layer or an Al- (0 to 15)% Si hot-dip galvanized film layer is provided. Further, by using a steel tube having a surface film layer containing a metal compound on the surface of these plating film layers as a material to be processed and producing a heat-treated steel tube by a 3DQ method, a plated heat-treated steel material having excellent chemical conversion treatment properties. Can be obtained.

<About steel pipes for heat treatment>
First, the heat-treated steel pipe used for the heat-treated steel pipe according to the embodiment of the present invention will be described.

(Main pipe of steel pipe for heat treatment)
As the mother pipe which is the material of the steel pipe for plating heat treatment according to the present embodiment, for example, a high-strength steel pipe can be adopted. After adopting such a high-strength steel pipe, providing the following plating film layer on the surface of the steel pipe, and then heating and cooling according to the conditions described in detail below, the surface of the steel pipe is coated with a base film as an automobile member. And by applying a coating film, it is possible to obtain a high-strength plated heat-treated steel pipe steel material having corrosion resistance after coating.

Further, as the mother pipe, for example, a hardenable steel pipe steel material can be used. Using such a low-strength steel pipe as a starting material, the following plating film layer is provided on the surface of the steel pipe, and then quenching is performed by heating and cooling under the conditions described in detail below to increase the tensile strength to, for example, 1200 MPa or more. It can also be a high-strength plated heat-treated steel pipe steel material.

As a steel tube steel material having such hardenability, for example, the chemical composition thereof is C: 0.1% or more and 0.3% or less, Si: 0.01% or more and 0.5% or less, Mn: 0 in mass%. .5% or more and 3.0% or less, P: 0.003% or more and 0.05% or less, S: 0.05% or less, Cr: 0.1% or more and 0.5% or less, Ti: 0.01% It contains 0.1% or less, Al: 1% or less, B: 0.0002% or more and 0.004% or less, N: 0.01% or less, and the balance is composed of Fe and impurities. Examples thereof include steel pipes containing one or more selected from Cu: 1% or less, Ni: 2% or less, Mo: 1% or less, V: 1% or less, and Nb: 1% or less. To.

(Plating film layer)
On at least one of the inner surface or the outer surface of the mother tube (before the 3DQ method is applied) as described above, for example, (50 to 60)% Al-Zn- (1 to 2.5)% Si hot-dip galvanized film. Alternatively, the Al− (0 to 15)% Si hot-dip galvanized film is formed as the plating film layer according to the present embodiment.

The amount of plating adhered to the (50 to 60)% Al-Zn- (1 to 2.5)% Si hot-dip galvanized film layer or the Al- (0 to 15)% Si hot-dip galvanized film layer is 30 g / side. It is preferable that the content is m ^{2 to} 200 g / m ² from the viewpoint of sufficiently ensuring the corrosion resistance after coating after the heat treatment. The amount of the (50 to 60)% Al-Zn- (1 to 2.5)% Si hot-dip galvanized film layer or the Al- (0 to 15)% Si hot-dip galvanized film layer adhered is more preferably 40 g. / M ² or more and 80 g / m ² or less.

All of the plating films composed of the above components are superior to hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets in terms of residual plating at high temperatures, but when such plating films are heated to high temperatures as they are, alumina films form on the surface. It forms and does not show excellent chemical conversion processability. Therefore, in the present embodiment, the chemical conversion treatment property is improved by applying 3DQ after forming a layer containing a metal compound on the plating film layer.

The plating applied to the mother tube according to the present embodiment is the above-mentioned (50 to 60)% Al-Zn- (1 to 2.5)% Si hot-dip galvanizing or Al- (0 to 15)% Si. The plating is not limited to hot-dip galvanizing, and any plating containing 50% by mass or more of Al can be appropriately used.

(Surface film layer)
Further, on the surface of the (50 to 60)% Al-Zn- (1 to 2.5)% Si hot-dip galvanized film or the Al- (0 to 15)% Si hot-dip galvanized film, a granular metal compound is applied. The contained film is coated. Hereinafter, the coating layer coated on the surface of the plating coating layer as described above will be referred to as a “surface coating layer”. In the heat treatment steel pipe according to the present embodiment, the granular metal compound contained in the surface coating layer is preferably any one or more of ZnO, Mg compound, ZrO, CaO, TiO ₂ or SiO ₂ .

[Surface film layer containing ZnO]
ZnO can be used as the granular metal compound contained in the surface film layer. Coating weight per one side of such a ZnO as Zn, is preferably ^{0.2g / m 2 ~7g / m 2} , ZnO particle size (average particle diameter) is preferably 50 nm to 300 nm. Further, in addition to the above ZnO, a resin component and / or a silane coupling agent may be contained in the surface film layer in a mass ratio of 5% to 35% with respect to ZnO.

The ZnO-containing surface film layer can be formed on the plating film layer by, for example, applying a coating material containing ZnO particles and then performing a curing process by baking and drying after the application. The method for applying ZnO is not particularly limited, and for example, a method in which a sol containing ZnO and a predetermined organic binder are mixed and applied to the surface of the plating film layer, powder coating And the like. Examples of the predetermined organic binder include polyurethane-based resin, polyester-based resin, acrylic-based resin, and silane coupling agent. These are preferably water-soluble so that they can be dissolved in a sol containing ZnO. The coating liquid thus obtained is applied to the surface of the plated steel sheet.

The coating amount per one side of the ZnO (i.e., coating weight per one surface of ZnO), as described above, in terms of Zn, is preferably ^{0.2g / m 2 ~7g / m 2} . If the amount of ZnO adhered is less than 0.2 g / m ² , the chemical conversion processability cannot be ensured, which is not preferable. Further, when the amount of ZnO adhered exceeds 7 g / m ² , coating unevenness is likely to occur, which is not preferable. In the above Patent Document 4 have been defined as ^{0.5g / m 2 ~7g / m 2} , heat treatment of the present application, as described in detail below, the temperature as compared with the heat treatment of the patent document 4 Since the heating rate is high and the heating is performed for a short time, the lower limit values are different. Incidentally, coating weight per one surface of ZnO is more preferably ^{0.5g / m 2 ~3g / m 2} .

The particle size of the fine particles of ZnO is preferably 50 nm to 300 nm in diameter. There are two types of ZnO particle size, the particle size of the powder itself and the particle size in the sol when the powder is made into a sol, and these are described as the diameter in the sol. Generally, the particle size in the sol is larger than the particle size of the powder itself because the secondary agglutination of the fine powder occurs in the sol. When the particle size of the powder itself is less than 50 nm, not only is it difficult to knead, but also secondary agglutination is likely to occur, and as a result, the diameter in the sol becomes coarse. Therefore, it is practically difficult to make the diameter in the sol less than 50 nm. Further, when the particle size in the sol exceeds 300 nm, precipitation is likely to occur, so that unevenness also occurs. The particle size of ZnO in the sol is more preferably about 50 to 150 nm.

The baking / drying method after coating is not limited to a specific method as long as it can volatilize the dispersion medium (mainly water). For example, a hot air furnace, an induction heating furnace, or a near-infrared furnace. Etc. may be used, or these may be used in combination. Here, if the surface treatment layer is heated at an excessively high temperature, the uniformity of the surface treatment layer may be lowered, and conversely, if the surface treatment layer is heated at an excessively low temperature, the productivity may be lowered. Therefore, in order to stably and efficiently produce a surface-treated layer having excellent properties, it is necessary to heat the coated surface-treated layer at a temperature of about 80 ° C. to 150 ° C. for about 5 seconds to 20 seconds. preferable. At this time, depending on the type of binder used for coating, curing treatment with, for example, ultraviolet rays or electron beams may be performed instead of baking / drying after coating. Examples of the predetermined organic binder include polyurethane, polyester, acrylic and silane coupling agents. However, the method for forming the surface coating layer containing ZnO is not limited to the above examples, and various methods can be used.

[Surface film layer containing MgO]
MgO can be used as the granular metal compound contained in the surface film layer. The coating weight per one side of such MgO, (in terms of ^Mg) as Mg, is preferably ^{0.2g / m 2 ~2.4g / m 2} , MgO having a particle size (average particle diameter), It is preferably 5 nm to 100 nm. Further, in addition to the above MgO, a resin component and / or a silane coupling agent may be contained in the surface film layer in a mass ratio of 5% to 35% with respect to MgO.

Here, coating weight per one surface of MgO, more preferably ^{0.5g / m 2 ~1g / m 2} .

Unlike ZnO, the particle size of MgO is not the diameter in the sol, but the particle size of the raw material (that is, the primary particle size) of 5 nm to 100 nm. When the primary particle size is less than 5 nm, the secondary agglutination becomes remarkable, and as a result, it becomes coarse and does not uniformly disperse in the coating film. On the other hand, when the primary particle size exceeds 100 nm, precipitation is likely to occur, causing unevenness and shortening the life of the dispersion liquid. The primary particle size of MgO is more preferably 10 nm to 50 nm.

The surface film layer containing MgO can be formed in the same manner as the surface film layer containing ZnO.

[Surface film layer containing Mg chloride, Mg nitrate or Mg sulfate]
As the granular metal compound contained in the surface film layer, any one of magnesium chloride, magnesium nitrate or magnesium sulfate can be used. Such chloride Mg, the adhesion amount of any per surface nitrate Mg or sulfuric Mg is (in terms of ^Mg) as Mg, is preferably ^{0.2g / m 2 ~2.4g / m 2} . Adhesion amount of any per side chloride Mg, nitrate Mg or sulfuric Mg is more preferably ^{0.5g / m 2 ~1g / m 2} . Further, in addition to the above Mg compounds, a resin component and / or a silane coupling agent may be contained in the surface film layer in a mass ratio of 5% to 35% with respect to these Mg compounds.

The surface film layer containing these Mg compounds can be formed in the same manner as the surface film layer containing ZnO.

[Surface film layer containing at least ZrO]
As the granular metal compound contained in the surface film layer, either ZrO, a mixture of ZrO and CaO, or a mixture of ZrO and MgO can be used. Coating weight per one side of the metal compounds, Zr, the sum of Zr and Ca, or, preferably as a sum of Zr and ^Mg, it is ^{0.4g / m 2 ~2.0g / m 2} , these The particle size (average particle size) of the metal compound is preferably 10 to 200 nm. Further, in addition to the above metal compounds, a resin component and / or a silane coupling agent may be contained in the surface film layer in a mass ratio of 5% to 35% with respect to these metal compounds.

Here, ZrO, a mixture of ZrO and CaO, or the coating weight per one surface of a mixture of ZrO and MgO ^is more preferably ^{0.5g / m 2 ~1.0g / m 2} .

The particle size of ZrO is preferably 10 nm to 200 nm as the diameter in the sol (that is, as the secondary particle size). When the particle size of ZrO is less than 10 nm, secondary agglutination becomes remarkable, and as a result, it becomes coarse and does not uniformly disperse in the coating film. Further, when the particle size of ZrO exceeds 200 nm, precipitation is likely to occur, causing unevenness and shortening the life of the dispersion liquid. The secondary particle size of ZrO is more preferably 20 nm to 50 nm.

The surface film layer containing a mixture of ZrO, ZrO and CaO, or a mixture of ZrO and MgO can be formed in the same manner as the above-mentioned surface film layer containing ZnO.

[Surface film layer containing TiO ₂ or SiO ₂ ]
As the granular metal compound contained in the surface coating layer, any one of TiO ₂ , SiO ₂ , or a mixture of TiO ₂ and SiO ₂ can be used. Coating weight per one side of the metal compounds, respectively, Ti, Si, or, as the sum of Ti and ^Si, is preferably ^{0.4g / m 2 ~2.0g / m 2} , these metal compounds The particle size (average particle size) is preferably 5 nm to 30 nm. Further, in addition to the above metal compounds, a resin component and / or a silane coupling agent may be contained in the surface film layer in a mass ratio of 5% to 35% with respect to these metal compounds.

_Here, TiO 2, SiO _2, or the coating weight of either per surface of the mixture of TiO ₂ and SiO ₂ is more preferably ^{0.5g / m 2 ~1g / m 2} .

The particle size of TiO _{2 and} the particle size of SiO ₂ are preferably 5 nm to 30 nm as the diameter in the sol (that is, as the secondary particle size). When the particle size of TiO ₂ or SiO ₂ is less than 5 nm, secondary agglutination becomes remarkable, and as a result, it becomes coarse and does not uniformly disperse in the coating film. Further, when the particle size of TiO ₂ or SiO ₂ exceeds 30 nm, precipitation is likely to occur, causing unevenness and shortening the life of the dispersion liquid. The secondary particle size of TiO ₂ and SiO ₂ is more preferably 10 nm to 20 nm.

The surface coating layer containing any of TiO ₂ , SiO ₂ , or a mixture of TiO ₂ and SiO ₂ can be formed in the same manner as the above-mentioned surface coating layer containing ZnO.

The surface coating layer according to the present embodiment has been described in detail above.

<Measurement method of adhesion amount and particle size>
The method for measuring the amount of adhesion of the plating film layer according to the present embodiment is not particularly limited, and can be measured by, for example, a gravimetric method or a fluorescent X-ray method. The gravimetric method is a method in which after measuring the weight of a plating sample having a defined area, only the plating layer is dissolved with hydrochloric acid or the like, and the amount of adhesion is obtained from the difference from the weight after dissolution. The fluorescent X-ray method is a method in which a calibration curve is prepared in advance from a sample having a known adhesion amount by a means such as a gravimetric method, and the adhesion amount is calculated from the fluorescence X-ray intensity of the sample of interest.

Further, the method for measuring the amount of adhesion of the surface coating layer according to the present embodiment is not particularly limited, and for example, the cross-sectional energy dispersion indicates that the compound contained in the surface treatment layer is the above-mentioned compound. Measurement is possible by confirming by type X-ray (Energy Dispersive X-ray: EDX) analysis or the like, dissolving the film, and using ICP (Inductively Coupled Plasma) emission spectroscopic analysis or the like. ..

Further, the particle size (primary particle size or secondary particle size) of the metal compound used for the surface film layer according to the present embodiment can be measured by using a known device such as a laser diffraction type particle size measuring device. It is possible.

<Manufacturing method of heat-treated steel pipe>
Subsequently, a method for manufacturing a heat-treated steel pipe using the heat-treated steel pipe according to the present embodiment as described above will be described in detail.

In the method for producing a heat-treated steel pipe according to the present embodiment, at least a part of the heat-treated steel pipe as described above is subjected to a quenching step of quenching to obtain a heat-treated steel pipe. This quenching step comprises a heating step and a cooling step, as described in detail below.

More specifically, (50 to 60)% Al-Zn- (1 to 2.5)% Si hot-dip plating film layer or Al- (0 to 15)% Si hot-dip on at least one of the inner and outer surfaces. A steel tube (heat treatment steel tube) in which a plating film layer is formed and a surface film layer containing a granular metal compound is formed on the surface of these plating film layers is subjected to a heating step and a cooling step in sequence, and then plated and heat-treated. It is called a steel pipe (heat-treated steel pipe).

In the heating step, the heat-treated steel pipe having the plating film layer and the surface film layer is heated to the Ac3 transformation point or higher as a temperature range in which quenching is possible. The heat treatment pattern at this time is to heat the surface temperature of the plating layer from 100 ° C. to the maximum heating temperature at an average heating rate of 100 ° C./sec or more to the maximum heating temperature within the temperature range of 850 to 1300 ° C. .. The cooling step is started within 2 seconds after the steel pipe is heated to 850 ° C. or higher. In the subsequent cooling step, the temperature is cooled from the maximum heating temperature to 350 ° C. at an average cooling rate of 1000 ° C./sec or more to 350 ° C. or lower.

If the heating rate is less than 100 ° C./sec on average, the processing accuracy is lowered, which is not preferable, and if the cooling rate is less than 1000 ° C./sec on average, quenching cannot be performed, which is not preferable.

The time from when the steel pipe is heated to 850 ° C. or higher until cooling is started is within 2 seconds. In other words, the time from heating to 850 ° C. or higher until the refrigerant (cooling water) comes into contact with the steel pipe is within 2 seconds. If the temperature of the steel pipe is 850 ° C. or higher for a long time, the plating film evaporates or an intermetallic compound with iron is formed, which causes a problem that the corrosion resistance is lowered.

When the plated heat-treated steel pipe according to the present invention is manufactured by the 3DQ method based on the invention disclosed in Patent Document 1 described above, this heat treatment is performed on the steel pipe as a material in the longitudinal direction thereof, as in Patent Document 1. While feeding the steel pipe intermittently or continuously toward, the steel pipe is supported by the first supporting means, and the pressure roll is arranged downstream of the first supporting means and its position is two-dimensional or tertiary. It is rotatably supported by a second support means that is originally movable, and further, the heating of the steel pipe is between the second support means and the first support means, and is on the outer periphery of the steel pipe. It is desirable that the heating is performed by the heating means arranged apart from the steel pipe and the cooling is performed by the cooling means arranged between the heating means and the second supporting means. Further, the heated portion of the steel pipe is bent (and the corresponding portion is hardened) to obtain a heat-treated steel pipe that has been bent two-dimensionally or three-dimensionally.

The plating film layer of the heat-treated steel tube according to the present embodiment produced as described above has a (50 to 60)% Al-Zn- (1 to 2.5)% Si hot-dip galvanizing film or Al-. Regardless of which of the (0 to 15)% Si hot-dip galvanized films is used, Fe-Zn intermetallic compounds (so-called ζ phase, δ ₁ phase, Γ phase, etc.) do not exist. This is because Zn does not exist in Al-Si hot-dip galvanizing Al- (0 to 15)% Si hot-dip galvanizing, and (50 to 60)% Al-Zn- (1 to 2.5)% Si hot-dip galvanizing. in a heating temperature of 900 ° C. exceeded, FeZn intermetallic compound in which ζ phase (FeZn _13), δ ₁ phase (FeZn _7), Γ ₁ phase _(Fe 5 _{Zn 21)} and gamma-phase (Fe _It is understood that these layers are decomposed during heating because they are higher than any melting point or decomposition temperature of ₃ Zn ₁₀ ).

Here, the basis weight of the plating film layer of a heat treatment steel according to the present embodiment ^is preferably ^{32g / m 2 ~1000g / m 2} . Further, it is exemplified that the Fe content of the plating film layer is 5% to 80% with respect to the mass of the entire plating film layer. The basis weight of the plating film layer of the heat-treated steel pipe according to the present embodiment is more preferably 45 g / m ^{2 to} 320 g / m ² , and the Fe content of the plating film layer is more preferably 10% to 75%. is there.

The heat-treated steel pipe according to the present invention may be such that at least a part of the steel pipe satisfies the conditions specified in the present invention. For example, in the heat-treated steel pipe according to the present invention, when a bending member for an automobile is assumed as its use, it is not necessary to perform bending or quenching on all of the members. For example, a member that is neither bent nor hardened at the end of the steel pipe is also a target of the heat-treated steel pipe according to the present invention. In such a case, a part of the member is bent or hardened (for example, by the 3DQ method), but it is not necessary to have the film specified in the present invention in all the parts of the member. .. That is, only the surface or portion that is particularly important as a member is included in the heat-treated steel pipe according to the present invention if the conditions specified in the present invention are satisfied.

In the method for producing a heat-treated steel pipe according to the present embodiment, for example, as a steel pipe as a material, (50 to 60)% Al-Zn- (1) is applied to one or both of the inner surface and the outer surface. A steel pipe for heat treatment having a ~ 2.5)% Si hot-dip plating film layer and a film containing ZnO on the surface of the plating film layer is used as a material for long members for automobiles, and after quenching or heating. The heat-treated steel pipe according to the present embodiment is manufactured by simultaneously performing bending or quenching and bending by 3DQ.

<About 3DQ method>
FIG. 1 is an explanatory diagram illustrating the configuration of a manufacturing apparatus 7 for manufacturing the heat-treated steel pipe 1b according to the present embodiment.

In the manufacturing apparatus 7 illustrated in FIG. 1, the plating film layer of the welded steel pipe using the work material 1 as a material, for example, (50 to 60)% Al-Zn- (1 to 2.5)% Si hot-dip plated steel sheet. A heat-treated steel pipe (hereinafter, simply referred to as “heat-treated steel pipe”) on which a surface coating layer containing a granular metal compound is formed is formed, and the heat-treated steel pipe 1a, which is a work material, is sequentially and continuously heated. The heat-treated steel pipe 1b is manufactured by causing plastic deformation of the locally heated portion by using the movable roller die 4 and cooling immediately after that.

Therefore, a feed device 3 for intermittently or continuously feeds and moves the heat treatment steel pipe 1a is arranged on the upstream side of the support roll 2, which is two sets of rotatable support means for supporting the heat treatment steel pipe 1a. Will be done. On the other hand, on the downstream side of the two pairs of support rolls 2, a movable roller die 4 for supporting the heat treatment steel pipe 1a and controlling the support position and / or the moving speed is arranged. As shown in FIG. 1, the movable roller die 4 includes pressure rolls 4a and 4b, which are hole-shaped rolls that come into contact with the surface of the heat treatment steel pipe 1a.

On the entrance side of the movable roller die 4, a high-frequency heating coil 5 is arranged on the outer periphery of the heat-treating steel pipe 1a so as to be separated from the heat-treatment steel pipe 1a, and the heat-treatment steel pipe 1a is partially and rapidly heated, and high-frequency heating. A cooling device 6 for rapidly cooling the heat treatment steel pipe 1a by injecting a cooling medium onto the heat treatment steel pipe 1a rapidly heated by the coil 5 is arranged.

FIG. 2 is a cross-sectional view illustrating an outline of the configuration of the high frequency heating coil 5 and the cooling device 6 in the manufacturing apparatus 7. An annular high-frequency heating coil 5 is arranged on the outer periphery of the heat-treating steel pipe 1a on which the heating portion is to be formed so as to be separated from the heat-treatment steel pipe 1a. The heat-treated steel pipe 1a rapidly heated by the high-frequency heating coil 5 is rapidly cooled by injecting a cooling medium (for example, water or the like) from the cooling device 6 as needed. In this heating-cooling process, conditions such as the output and feed rate of the heating coil are optimized, and the temperature history on the outer surface side of the steel pipe is set as the above-mentioned conditions.

Further, at this time, the heat treatment steel pipe 1a that has passed through the two sets of support rolls 2 is supported by the pressure rolls 4a and 4b of the movable roller die 4, and the high frequency heating coil 5 and the cooling device are arranged on the outer periphery of the heat treatment steel pipe 1a. While locally heating and cooling the heat treatment steel pipe 1a using No. 6, the position and inclination of the movable roller die 4 are controlled, and the moving speed thereof is also adjusted as appropriate. As a result, the bending moment can be applied to the partially hot portion of the heat treatment steel pipe 1a to perform the bending process, and the heating rate and heating temperature by the heating device 5 and the cooling rate by the cooling device 6 are appropriately adjusted. By doing so, the desired portion of the heat treatment steel pipe 1a can be hardened. As a result, it is possible to manufacture a heat-treated steel pipe 1b having a desired high strength and a two-dimensional or three-dimensional bending portion having a desired curvature.

FIG. 3 is an explanatory view illustrating the shape of the movable roller die 4 that can be used in the production of the heat-treated steel pipe 1b according to the present invention. FIG. 3A schematically shows a case where the movable roller die 4 is composed of two rolls when the heat treatment steel pipe 1a is a closed cross-section material such as a round pipe. FIG. 3B schematically shows a case where the movable roller die 4 is composed of two rolls when the heat treatment steel pipe 1a is a closed cross-section material such as a rectangular pipe or an open cross-section material such as a channel. There is. FIG. 3C schematically shows a case where the movable roller die 4 is composed of four rolls when the heat treatment steel pipe 1a is a closed cross-section material such as a rectangular pipe or a deformed cross-section material such as a channel. There is.

As shown in FIG. 3A, the movable roller die 4 is composed of two pressure rolls 4a and 4b to support the heat treatment steel pipe 1a. The pressure roll 4a in the movable roller die 4 contacts and drives the surface of the heat treatment steel pipe 1a, and holds the heat treatment steel pipe 1a while feeding the heat treatment steel pipe 1a in the longitudinal direction thereof. Even if the surface properties of the plating film layer and the surface film layer on the surface of the heat treatment steel pipe 1a deteriorate due to the high temperature region, the surface of the heat treatment steel pipe 1a can be pressed while applying a pressing force using the pressure roll 4a. it can. Thereby, the surface roughness Ra of the surface coating layer can be adjusted. As a result, the roughness of the film of the heat-treated steel pipe 1b in which the plating film layer and the surface film layer remain on the surface can be within a desired range. When adjusting the roughness of the surface of a bent steel pipe in a separate process, if the position of the roll and the bending of the steel pipe deviate from each other, processing will be hindered, whereas in the case of adjusting the roughness with a movable roller die, there is no such risk.

Here, as shown in FIG. 3B, when the movable roller die 4 is composed of two pressure rolls 4c and 4d, or as shown in FIG. 3C, the movable roller die 4 is Even in the case of being composed of four pressure rolls 4e, 4f, 4g, and 4h, it is possible to improve the surface texture of the film of the heat-treated steel pipe 1b by performing the processing in the same manner as described above.

Further, the movable roller die 4 is provided with a vertical shift mechanism, a horizontal shift mechanism, a vertical tilt mechanism, or a horizontal tilt mechanism, preferably further in the front-rear direction. By providing the moving mechanism, the steel pipe 1a for heat treatment can be supported three-dimensionally, and a bending moment can be applied if necessary.

In order to adjust the surface roughness of the surface coating layer of the heat treatment steel pipe 1a by pressurizing with the movable roller die 4 shown in FIG. 3, specifically, the pressing force of the pressure roll 4a on the heat treatment steel pipe 1a is controlled. You can do it by doing. When the roll diameter of the pressure roll 4a is about 30 mm, the pressing pressure at that time is, for example, 1 kgf / mm or more and 100 kgf / mm or less as a linear load (here, 1 kgf is about 9.8 N). ) Is preferable. For example, the pressing force is controlled by mounting a hydraulic cylinder or an air cylinder on the movable roller die 4.

In this way, according to the present embodiment, even when the heat treatment steel pipe 1a is heat-treated by high-temperature heating and cooling, the plating film layer having a predetermined plating adhesion amount and texture and a predetermined metal compound The surface film layer containing the above can be left, and thus the surface texture (surface roughness Ra) of the heat-treated steel pipe 1b can be improved. The heat-treated steel pipe 1b produced in this way can ensure appropriate corrosion resistance after painting as an automobile member.

As described above, the 3DQ method that can be suitably used in the method for producing the heat-treated steel pipe according to the present embodiment has been described in detail with reference to FIGS. 1 to 3.

<About heat-treated steel pipe>
Subsequently, the heat-treated steel pipe manufactured according to the above-mentioned method for manufacturing the heat-treated steel pipe will be briefly described by using the heat-treated steel pipe according to the present embodiment as described above.

The heat-treated steel pipe according to the present embodiment is a martensite provided with an Al alloy plating film layer on the surface by performing the above-mentioned specific quenching step using the above-mentioned predetermined heat-treated steel pipe. It becomes a steel pipe with a structure. In such a heat-treated steel pipe, the hardened portion exhibits the characteristics as described in detail below.

That is, the hardened portion of the heat-treated steel pipe according to the present embodiment is moved from the outermost surface of the hardened portion to a deeper portion than the outermost surface by glow discharge emission spectroscopy (GDS) or the like. The content of each element is measured up to a depth of 0.1 μm. In this case, the content (average content) of elements other than oxygen in the measurement range is mass% and Al: 20% or less. Further, the content (average content) of Zn, Mg, Zr, Ti or Si in such a measurement range is preferably 50% or more in mass%.

For example, in a heat-treated steel pipe used for manufacturing a heat-treated steel pipe, when ZnO is contained in the surface film layer, the content of elements other than oxygen in such a measurement range is Al: 20% or less and Zn: It will be 50% or more.

Similarly, in the heat-treated steel pipe used for manufacturing the heat-treated steel pipe, when MgO is contained in the surface film layer, the content of elements other than oxygen in such a measurement range is Al: 20% or less and Mg. : 50% or more, and when the surface film layer contains ZrO in the heat-treated steel pipe used for manufacturing the heat-treated steel pipe, the content of elements other than oxygen in such a measurement range is Al: 20% or less. Moreover, Zr: 50% or more.

Further, in the heat-treated steel pipe used for manufacturing the heat-treated steel pipe, when TiO ₂ is contained in the surface coating layer, the content of elements other than oxygen in such a measurement range is Al: 20% or less and Ti. : 50% or more, and when the surface film layer contains SiO ₂ in the heat-treated steel pipe used for manufacturing the heat-treated steel pipe, the content of elements other than oxygen in such a measurement range is Al: 20% or less. And Si: 50% or more.

The heat-treated steel sheet according to the present embodiment exhibits excellent chemical conversion treatment property when the average content of Al is 20% or less in the measurement range as described above. In the measurement range as described above, the lower limit of the average content of Al is not particularly specified, and the lower the average content of Al, the more preferable the chemical conversion treatment property. Further, in the measurement range as described above, the average content of Al is preferably 10% or less.

The heat-treated steel pipe according to the present embodiment has been briefly described above.

<About strength members for automobile bodies>
Subsequently, a strength member for an automobile body manufactured by using the heat treatment steel pipe according to the present embodiment as described above will be briefly described.

By using the heat-treated steel pipe according to the present embodiment as described above and appropriately performing heat treatment according to the method for producing the heat-treated steel pipe as described above, a strength member for an automobile body can be manufactured. Such strength members for automobile bodies are not particularly limited, and examples thereof include front pillars, seat cloths, and seat frames.

Hereinafter, the heat-treated steel pipe, the method for producing the heat-treated steel pipe, and the heat-treated steel pipe according to the present invention will be specifically described with reference to Examples and Comparative Examples. The examples shown below are merely examples of the heat-treated steel pipe, the method for manufacturing the heat-treated steel pipe, and the heat-treated steel pipe according to the present invention, and the heat-treated steel pipe, the method for manufacturing the heat-treated steel pipe, and the heat-treated steel pipe according to the present invention are described below. It is not limited to the example of.

(Mother tube)
In this test example, as the steel material, C: 0.22%, Si: 0.21%, Mn: 1.25%, P: 0.012%, S: 0.002%, Al: 0.040%, Zn-55% Al-1.6% Si galvanized melt using a steel sheet having a chemical composition consisting of Cr: 0.25%, Ti: 0.030%, B: 0.0015, balance Fe and impurities as a plating base material. Using a plated steel sheet (grain size: 50.1 g / m ² ) and an Al-10% Si hot-dip aluminum plated steel sheet (grain size: 70 g / m ² ), both ends of the plated steel sheet are welded to form a welded steel pipe. did. The obtained welded steel pipe was used as a mother pipe for a steel pipe for heat treatment. In Table 1 below, the plating type of "GL" corresponds to Zn-55% Al-1.6% Si galvanium hot-dip galvanizing, and the plating type is "Al-Si". It corresponds to Al-10% Si hot-dip aluminum plating.

(Metal compound)
Fine particles of a predetermined compound having a predetermined particle size were purchased from a reagent manufacturer. Alternatively, a reagent in a sol state already dispersed in a solvent having a predetermined sol diameter was purchased. (Resin: Urethane-based resin emulsion (Daiichi Kogyo Seiyaku Co., Ltd. Superflex (registered trademark) E-2000), cross-linking agent (silane coupling agent: Chisso Co., Ltd. Sila Ace S510)) The surface film layer is formed by mixing the predetermined compound reagent with the resin and the cross-linking agent so as to have the values shown in Table 1 in terms of the mass ratio of the solid matter, applying the mixture to the surface of the mother tube with a bar coater, and baking at about 80 ° C. Formed. The details and average particle size of the purchased metal compound are as follows.

ZnO: Sigma-Aldrich, sol particle size 70 nm (catalog value)
MgO: Sigma-Aldrich, primary particle size 50 nm (catalog value)
Magnesium chloride: manufactured by Sigma-Aldrich, particle size 70 nm (catalog value)
Magnesium nitrate: manufactured by Sigma-Aldrich, particle size 70 nm (catalog value)
Magnesium sulfate: manufactured by Sigma-Aldrich, particle size 70 nm (catalog value)
ZrO (1): manufactured by Sigma-Aldrich, sol particle size 50 nm (catalog value)
ZrO (2): manufactured by Sigma-Aldrich, sol particle size 500 nm (catalog value)
CaO: Sigma-Aldrich, primary particle size 50 nm (catalog value)
TiO ₂ (1): manufactured by Sigma-Aldrich, sol particle size 10 nm (catalog value)
TiO ₂ (2): Sigma-Aldrich, sol particle size 100 nm (catalog value)
SiO ₂ (1): manufactured by Nissan Chemical Industries, Ltd., sol particle size 10 nm (catalog value)
SiO ₂ (2): manufactured by Nissan Chemical Industries, Ltd., sol particle size 100 nm (catalog value)

The obtained surface film layer was analyzed, and the amount of the metal compound adhered was measured by the film dissolution-ICP solution analysis method. Further, the mass ratio of the metal compound in the surface coating layer and the binder (that is, the resin and the cross-linking agent) is determined by comparing the mass of the surface coating layer with the mass before and after coating, and the amount of the metal compound is determined by the film dissolution-ICP solution analysis method. Measured by. The results obtained are summarized in Table 1.

(Manufacturing of heat-treated steel pipe)
Using the manufacturing apparatus 7 as shown in FIGS. 1 to 3, the manufacturing apparatus 7 is heated from 100 ° C. to the maximum heating temperature at an average heating rate of 300 ° C./s to the maximum temperature shown in Table 1, held for 0.1 seconds, and then water-cooled. Was done. At this time, a part of the test material was bent before the cooling was started. The average cooling rate from the maximum heating temperature to 350 ° C. was 1000 ° C./s or higher.

Heat-treated steel materials (Nos. 1 to 53) were prepared as described above, and the chemical conversion processability was evaluated as follows.

(Evaluation methods)
For chemical conversion treatment, the test material was degreased and washed with water, and then the surface was adjusted to perform chemical conversion treatment. The chemical conversion treatment liquid used was Surfdyne 6370 manufactured by Nippon Paint Co., Ltd. Then, the amount of chemical crystals adhered to the bent portion was measured with a fluorescent X-ray analyzer, and the surface of the test material was observed with a scanning electron microscope (SEM) to photograph the morphology of the crystals.

Here, the chemical adhesion amount of 2.5 g / m ² or more was regarded as acceptable. Regarding the crystal morphology, if the chemical crystal densely covered the test material, it was judged as acceptable, and if it was not covered, it was rejected. If both the amount of chemical conversion adhered and the crystal morphology were acceptable, a circle was entered in the “chemical conversion processability” column of Table 1 shown below, and if any of them was unacceptable, a cross was entered. The results obtained are shown in Table 1 below.

As is clear from Table 1 above, the test material corresponding to the comparative example did not have excellent chemical conversion treatment property, whereas the test material according to the example of the present invention could realize excellent chemical conversion treatment property. You can see that there is.

Further, FIG. 4 shows an SEM photograph of the chemical conversion crystal film prepared in this test example. As is clear from FIG. 4, No. 1 which is a reference example of the present invention. It can be seen that the surface of No. 3 is densely covered with the plate-shaped chemical crystal film, but the surface of No. 1, which is a comparative example, is not densely covered with the plate-shaped chemical crystal film.

Next, using a test material that has been subjected to the 3DQ process and has not been chemically converted, the mass ratio of each element in the depth direction from the surface is measured by GDS, and oxygen is added in the range up to a depth of 100 nm. The average concentration of Zn, Al, Fe, and Si was determined without including. The results obtained are shown in Table 2 below.

As is clear from Table 2 above, No. 1 which is a reference example of the present invention. In the test material of No. 3, Zn is 50% or more and Al is 20% or less in the range from the surface to a depth of 100 nm, and it is estimated that the surface of this test material is mainly ZnO. On the other hand, No. In the test material of No. 1, Zn is less than 50% and Al is more than 20% in the range from the surface to a depth of 100 nm, and it is estimated that the surface of this test material is mainly composed of alumina. .. Similarly, No. 1 which is an example of the present invention. 6, No. 11, No. 16, No. 21, No. In the test materials of 23, Zn, Mg, Zr, Ti, and Si are 50% or more and Al is 20% or less in the range from the surface to the depth of 100 nm, respectively, and the surfaces of these test materials are each. , ZnO, MgO, ZrO, TiO ₂ and SiO ₂ are presumed to be the main components. On the other hand, No. In the test material of No. 5, Zn, Mg, Zr, Ti, and Si are less than 50% and Al is more than 20% in the range of 100 nm from the surface, and the surface of this test material contains alumina. Presumed to be the subject. It is presumed that such a difference in the main components is the reason why the chemical conversion processability differs between the example of the present invention and the comparative example.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that anyone with ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

1 Work material 1a Heat-treated steel pipe 1b Heat-treated steel pipe 2 Support roll 3 Extruder 4 Movable roller die 5 High-frequency heating coil 6 Cooling device 7 Manufacturing equipment

Claims (15)

A plating film layer located on at least one of the inner and outer surfaces of the steel pipe and containing 50% by mass or more of Al per side.
A surface film layer located on the plating film layer and containing a granular metal compound,
With
The granular metal compound is any one or more of Mg compound, ZrO, CaO, TiO ₂ or SiO ₂ .
The Mg compound is MgO and
Coating weight per one surface of the MgO are as ^Mg, a ^{0.2g / m 2 ~2.4g / m 2} ,
The particle size of the MgO is 5 nm to 100 nm, heat treatment for steel pipes. A plating film layer located on at least one of the inner and outer surfaces of the steel pipe and containing 50% by mass or more of Al per side.
A surface film layer located on the plating film layer and containing a granular metal compound,
With
The granular metal compound is any one or more of Mg compound, ZrO, CaO, TiO ₂ or SiO ₂ .
The Mg compound is either magnesium chloride, magnesium nitrate, or magnesium sulfate.
The magnesium chloride, magnesium nitrate, or the coating weight of either per surface of magnesium sulfate as ^Mg, is ^{0.2g / m 2 ~2.4g / m 2} , the heat treatment for steel pipes. A plating film layer located on at least one of the inner and outer surfaces of the steel pipe and containing 50% by mass or more of Al per side.
A surface film layer located on the plating film layer and containing a granular metal compound,
With
The granular metal compound is any one or more of Mg compound, ZrO, CaO, TiO ₂ or SiO ₂ .
Coating weight per one surface of the ZrO as ^Zr, was ^{0.4g / m 2 ~2.0g / m 2} ,
The ZrO has particle sizes of 10 nm to 200 nm, heat treatment for steel pipes. A plating film layer located on at least one of the inner and outer surfaces of the steel pipe and containing 50% by mass or more of Al per side.
A surface film layer located on the plating film layer and containing a granular metal compound,
With
The granular metal compound is a mixture of ZrO and CaO, or a mixture of ZrO and MgO.
Coating weight per one surface of said mixture, Zr and Ca, or as Zr and ^Mg, it is ^{0.4g / m 2 ~2.0g / m 2} , the heat treatment for steel pipes. A plating film layer located on at least one of the inner and outer surfaces of the steel pipe and containing 50% by mass or more of Al per side.
A surface film layer located on the plating film layer and containing a granular metal compound,
With
The granular metal compound is TiO ₂ , SiO ₂ , or a mixture of TiO ₂ and SiO ₂ .
Coating weight per one surface of the _TiO 2, SiO ₂ or TiO ₂ and mixtures of SiO ₂ is, Ti, Si, or, as the sum of Ti and ^Si, at 0.4g / ^{m 2} ~2.0g / m 2 Yes,
The particle size of the TiO ₂ and SiO ₂ are 5 nm to 30 nm, heat treatment for steel pipes. The surface coating layer contains a resin component and / or a silane coupling agent in addition to the granular metal compound.
The content of the resin component and / or the silane coupling agent is 5% by mass to 35% by mass with respect to the mass of the granular metal compound, according to any one of claims 1 to 5. Steel pipe for heat treatment. The heat treatment steel pipe according to any one of claims 1 to 6 , wherein the plating film layer is made of (50 to 60) mass% Al-Zn- (1 to 2.5) mass% Si hot-dip galvanized. The heat treatment steel pipe according to any one of claims 1 to 6 , wherein the plating film layer is made of Al- (0 to 15) mass% Si hot-dip galvanizing. A method for manufacturing a heat-treated steel pipe using the heat-treated steel pipe according to any one of claims 1 to 8 .
It has a quenching step of quenching at least a part of the heat treatment steel pipe.
In the quenching process,
On at least one surface of the heat treatment steel pipe having the plating film layer and the surface film layer, the temperature range from 100 ° C. to the maximum heating temperature is within the temperature range of 850 ° C. to 1300 ° C. at an average heating rate of 100 ° C./sec or more. Heat to the maximum heating temperature of
Cooling started within 2 seconds after being heated to 850 ° C or higher,
A method for producing a heat-treated steel pipe, which cools a heat-treated steel pipe from the maximum heating temperature to 350 ° C. at an average cooling rate of 1000 ° C./sec or more to a temperature range of 350 ° C. or lower. A plating film layer located on at least one of the inner and outer surfaces of a steel pipe and containing 50% by mass or more of Al per side, and a surface film layer located on the plating film layer and containing granular metal compounds. The granular metal compound is a method for producing a heat-treated steel pipe using a heat-treated steel pipe which is ZnO.
It has a quenching step of quenching at least a part of the heat treatment steel pipe.
In the quenching process,
On at least one surface of the heat treatment steel pipe having the plating film layer and the surface film layer, a temperature of more than 1000 ° C. and 1300 ° C. or lower at an average heating rate of 100 ° C./sec or more from 100 ° C. to the maximum heating temperature. Heat to the maximum heating temperature in the region,
Cooling started within 2 seconds after being heated to 850 ° C or higher,
A method for producing a heat-treated steel pipe, which cools a heat-treated steel pipe from the maximum heating temperature to 350 ° C. at an average cooling rate of 1000 ° C./sec or more to a temperature range of 350 ° C. or lower. In the heat treatment for steel pipe before being subjected to the quenching step, coating weight per one surface of the ZnO as Zn, a ^{0.2g / m 2 ~7g / m 2} , the ZnO may have a particle size The method for producing a heat-treated steel pipe according to claim 10 , which has a diameter of 50 nm to 300 nm. In the heat treatment steel pipe before being subjected to the quenching step, the surface coating layer contains a resin component and / or a silane coupling agent in addition to the granular metal compound.
The production of the heat-treated steel pipe according to claim 10 or 11 , wherein the content of the resin component and / or the silane coupling agent is 5% by mass to 35% by mass with respect to the mass of the granular metal compound. Method. The claimed steel pipe for heat treatment before being subjected to the quenching step, wherein the plating film layer comprises (50 to 60) mass% Al-Zn- (1 to 2.5) mass% Si hot-dip galvanized. The method for producing a heat-treated steel pipe according to any one of 10 to 12 . The method according to any one of claims 10 to 12 , wherein in the heat treatment steel pipe before being subjected to the quenching step, the plating film layer is made of Al- (0 to 15) mass% Si hot-dip galvanizing. A method for manufacturing a heat-treated steel pipe. The method for producing a heat-treated steel pipe according to any one of claims 9 to 14 , wherein a bending process is performed on a portion of the heat-treated steel pipe at 850 ° C. or higher.