JP6855940B2 - How to remove the oxidation scale - Google Patents

Description

The present invention provides an oxidation scale generated in the heating process of a steel material containing 0.3 to 1.5% Ni and 0.001 to 0.5% Si, particularly a brake disc material, before hot working. It is related to how to remove by descaling.

Ni is widely used as an alloying element because it has actions such as increasing the strength of steel materials, improving toughness, improving corrosion resistance, and improving plating adhesion. For example, Ni-containing steel is widely used in liquid tanks and the like as a steel material for welding structures for low temperatures, and is also used as a brake disc material.

By the way, iron oxides (scales) containing alloying elements are generated in the heating process and rolling process of alloy steel. If the scale is hot-worked while remaining on the steel surface, the scale is pushed into the steel and becomes a scale defect, deteriorating the surface quality of the product.

In particular, in a steel material containing Ni, since Ni has an effect of enhancing the adhesion between the scale generated during heating and the steel, there is a problem that it is difficult to remove the scale even if descaling with high-pressure water is performed. When hot forging a brake disc material containing about 1% Ni, if the scale cannot be removed before forging, it causes scale defects after forging.

In relation to this problem, in Patent Document 1, the surface of Ni-containing steel, which is difficult to descale, is mechanically ground, and then an antioxidant is applied, heated, and rolled to generate an oxide scale itself. We are proposing a method to suppress. However, Patent Document 1 has not solved the problem that it is difficult to remove the generated oxidation scale, although the oxidation scale is reduced.

Patent Document 2 relates to a problem that a steel material containing Si has a low descaling property. The cause of the low descaling property is considered to be the oxide of Fe-Si generated in the scale of the steel material containing Si, and Fe-Si is obtained by reheating the steel material after descaling once. It is proposed to generate a new FeO layer (easy to descale) between the oxide and steel of the above and to descale again. Patent Document 2 does not describe whether or not Ni-containing steel can be descaled, because the operation is complicated and the cost is likely to increase because the second descaling and reheating for that purpose are required. ..

Patent Document 3 proposes applying an antioxidant paint to Ni-containing steel to prevent the generation of oxidation scale in a high-temperature oxidizing atmosphere (1100 ° C. or lower) such as in a heating furnace. In Patent Document 3, as a matter of course, the antioxidant effect can be obtained only at the place where the antioxidant paint is applied. Also, Patent Document 3 has not solved the problem that it is difficult to remove the generated oxidation scale.

Japanese Unexamined Patent Publication No. 2006-212671 Japanese Unexamined Patent Publication No. 6-269841 Japanese Unexamined Patent Publication No. 11-22564

In view of the above, it is an object of the present invention to propose a novel method for improving the descaling property of a Ni-containing steel material and suppressing the occurrence of surface defects. In particular, when a Ni-containing steel material is heat-treated, a scale having a thickness of 3 mm or more may be generated on the surface of the steel sheet by the heat treatment. It is also an object of the present invention to propose a novel method for improving the descaling property of a Ni-containing steel material having a scale having a thickness of 3 mm or more on the surface and suppressing the occurrence of surface defects.

As a result of diligent studies, the present inventor places a mixture of a predetermined Si-containing material and at least one of Fe-containing material, B-containing material, P-containing material, and S-containing material on the surface of Ni-containing steel and heats the mixture. As a result, it was found that the descaling property was remarkably improved on the entire surface of the Ni-containing steel, and the present invention was completed.

The present invention provides the following means.
[1] Heating a steel material containing 0.3 to 1.5% by mass of Ni and 0.001 to 0.5% by mass of Si at a temperature of 1170 ° C. or higher and 1300 ° C. or lower for 1 hour or more and 10 hours or less. It is a method to remove the oxidation scale generated in the process of
A Si-containing material having a Si content of 400 to 1200 g / m ^{2 per surface area of the steel material and}
Fe content of 0.3 to 20% of the amount of Si in mass%,
^{B content of 4 to 40 g / m 2} as the amount of B per surface area of the steel material,
A P-containing material having a P amount of 8 to 80 g / m ^{2 per surface area of the steel material.}
At least one of the S-containing substances having an S amount of 8 to 80 g / m ^{2 per surface area of the steel material was mixed with each other.}
The mixture is placed on the surface of the steel material and
The steel material is heated to the extent that the steel material is heated.
A method for removing oxidation scale, which is characterized by subsequent descaling.
[2] The Fe-containing substance is iron oxide or iron hydroxide, the iron oxide is ustite, magnetite, hematite, margemite, or a mixture thereof, and the iron hydroxide is iron hydroxide. The method for removing an oxide scale according to [1], which is (II), iron (III) hydroxide, gaesite, akaganite, lepidoclosite, ferrooxyheite, or a mixture thereof.
[3] The method according to [1] or [2], wherein the arrangement is performed on the entire surface of the steel material.
[4] The method according to any one of [1] to [3], wherein the steel material is a brake disc material.
[5] The method according to any one of [1] to [4], wherein the oxidation scale has a thickness of 3 mm or more on the surface of the steel material.

According to the present invention, it is possible to easily perform descaling of Ni-containing steel, which has been difficult in the past, particularly Ni-containing steel having a scale having a thickness of 3 mm or more on the surface. Therefore, scale defects can be suppressed in the subsequent processing. Further, as the Si-containing material, easily available SiO ₂ or the like can be used, and as the Fe-containing material, an easily available Fe-containing material (iron oxide or iron hydroxide) can be used, and the B-containing material and P-containing material can be used. Since easily available S-containing substances can be used, they can be operated at low load and low cost.

Schematic diagram of the oxidation scale produced in Ni-containing steel. The schematic diagram which shows the removal state of the oxide scale at the time of normal descaling of Ni-containing steel. The schematic diagram which shows the removal state of the oxide scale when descaling a Ni-containing steel using this invention. The schematic diagram which shows the removal state of the oxidation scale at the time of descaling using the substance other than the Si-containing substance.

According to the present invention, a steel material containing 0.3 to 1.5% by mass Ni and 0.001 to 0.5% by mass Si is heated at a temperature of 1170 ° C. or higher and 1300 ° C. or lower for 1 hour or more and 10 hours or less. It is a method of removing the oxidation scale generated in the process of
A Si-containing material having a Si content of 400 to 1200 g / m ^{2 per surface area of the steel material and}
Fe content of 0.3 to 20% by mass of the Si amount as the Fe amount,
^{B content of 4 to 40 g / m 2} as the amount of B per surface area of the steel material,
A P-containing material having a P amount of 8 to 80 g / m ^{2 per surface area of the steel material.}
At least one of the S-containing substances having an S amount of 8 to 80 g / m ^{2 per surface area of the steel material was mixed with each other.}
The mixture is placed on the surface of the steel material and
The steel material is heated to the extent that the steel material is heated.
A method for removing oxidation scale, which is characterized by subsequent descaling, is provided.

Although not bound by a specific theory, the reasons why descaling of Ni-containing steel is difficult are considered to be as follows.
When a Ni-containing steel material is heated in an oxygen atmosphere, a scale as shown in FIG. 1 is generated. The best feature is that the steel and scale form an intricate internal oxide layer. An outer scale and an inner scale are generated above it. The outer layer scale is a scale grown mainly by the outward diffusion of iron and has a dense structure, whereas the inner layer scale is a scale grown mainly by the inward diffusion of oxygen and is inside. Has many voids. The internal oxide layer is a layer in which oxygen is diffused into steel (bare metal) and iron oxide is precipitated.

In the internal oxide layer, since Ni is noble than Fe, Fe is selectively oxidized, and Ni is left behind and gradually concentrated. Since Fe, which is more easily oxidized than Ni, is oxidized in the Ni-enriched layer, an internal oxide layer in which Fe is dispersed as an oxide is formed in the Ni-enriched layer. Since the internal oxide layer remains in the form of the internally oxidized Fe oxide biting into the Ni-enriched steel, the scale is in a state of biting in the search direction of the base iron, and this internal oxide layer (especially the concentrated part) ) Holds the scale to the steel (anchor effect).
As a result, it becomes difficult to remove the scale, and even if descaling with high-pressure water is performed, it is difficult to descale the entire scale including the outer layer scale and the inner layer scale (Fig. 2).

According to the present invention, a Si content having an amount of ^{400 to 1200 g / m 2} of Si per surface area of the steel material is provided on the surface of the steel material.
Fe-containing material (iron oxide or iron hydroxide) in which the amount of Fe is 0.3 to 20% by mass of the amount of Si,
^{B content of 4 to 40 g / m 2} as the amount of B per surface area of the steel material,
A P-containing material having a P amount of 8 to 80 g / m ^{2 per surface area of the steel material.}
After arranging a mixture of at least one S-containing material having an S amount of 8 to 80 g / m ² per surface area of the steel material, the steel material is heated at a temperature of 1170 ° C. or higher and 1300 ° C. or lower for 1 hour or more and 10 hours or less. As a result, the scale can be changed to a structure that is easy to descale. Explaining with reference to schematic FIG. 3, a mixture of Si-containing material and at least one of Fe-containing material, B-containing material, P-containing material, and S-containing material is heated to a sufficient amount in the scale. To generate the liquid phase component of. The liquid phase component permeates into the scale and weakens the bond at the grain boundary of the scale, so that the scale composed of the outer layer scale and the inner layer scale can be easily peeled off. (Fig. 3) As a guide, the amount of the liquid phase component sufficient to obtain good descaling property is 50% or more in volume fraction with respect to the total amount of the inner layer scale.

The liquid phase component is a Si—Fe-based oxide derived from Si in the Si-containing material and Fe in the Fe-containing material (iron oxide or iron hydroxide) or Fe in the steel material. The Si-containing material placed on the surface of the steel material is oxidized in the process of heating the steel material to produce _{silica (SiO 2).} Silica (SiO ₂ ) reacts with wustite (FeO) to form Si—Fe-based oxides. Wüstite (FeO) is produced from the Fe-containing material arranged on the surface of the steel material, and is also produced by the oxidation of Fe in the steel material. Even if the Fe-containing material is an iron oxide other than wustite (FeO), it is reduced to produce wustite (FeO) in the above heating temperature range. Further, even if the Fe-containing material is iron hydroxide, dehydration occurs in the above heating temperature range and is reduced to produce wustite (FeO). When the Si-containing material and the Fe-containing material arranged on the surface of the steel material are mixed, they easily react to form a Si—Fe-based oxide. That is, since the Si-containing substance and the Fe-containing substance are mixed, the effect of rapidly advancing the liquid phase formation reaction can be obtained. On the other hand, even when the Si-containing substance reacts with Fe in the steel material instead of the Fe-containing substance, Fe that diffuses outward from the steel material in the scale forms a new scale (FeO) on the scale surface, and FeO. Is formed to take in Si-containing substances, so that they react steadily to form Si—Fe-based oxides. Since the eutectic point of FeO and Fe ₂ SiO ₄ is 1170 ° C., the Si—Fe-based oxide becomes a liquid phase component at 1170 ° C. or higher. Therefore, the lower limit of the heating temperature is set to 1170 ° C. The upper limit of the heating temperature is not particularly limited as long as the Si—Fe-based oxide is in the liquid phase, but is set to 1300 ° C. The reason is that if the temperature exceeds 1300 ° C., the internal oxide layer (particularly the concentrated portion) is melted, and descaling is easier, but the scale loss becomes large and the heat energy is lost, which is not preferable. Because.

When at least one of the B-containing material, the P-containing material, and the S-containing material is mixed with the Si-containing material, the B-containing material, the P-containing material, and the S-containing material lower the eutectic point temperature, and the liquid phase formation reaction occurs. The effect of progressing from an early stage during heating can be obtained. In other words, even at the same heating temperature (for example, 1170 ° C.), when at least one of B-containing material, P-containing material, and S-containing material is contained, the liquid phase is compared with the case where they are not contained. It produces more and is easier to descale.

In the present invention, at least one of the Fe-containing material, the B-containing material, the P-containing material, and the S-containing material is mixed with the Si-containing material, so that the mixture is the Fe-containing material, the B-containing material, and the P-containing material. A mode containing two or more S-containing substances is also included. The effect that the liquid phase formation reaction proceeds rapidly due to the inclusion of the Fe-containing substance in the mixture, and the eutectic temperature due to the inclusion of at least one of the B-containing substance, the P-containing substance, and the S-containing substance in the mixture. It is possible to synergistically obtain the effect of reducing the temperature and allowing the liquid phase formation reaction to proceed from an early stage during heating.

When a mixture of a Si-containing material and at least one of Fe-containing material, B-containing material, P-containing material, and S-containing material is placed on the surface of the steel material before heating, it easily reacts at 1170 ° C. or higher to obtain Si. -Fe-based liquid phase oxide is produced. On the other hand, since Fe diffused outward from the steel material in the scale forms a new scale on the scale surface, Si—Fe-based liquid phase oxide is incorporated into the scale, and Si—Fe-based liquid phase oxide is incorporated into the scale. The liquid phase oxide can be infiltrated. Then, this Si—Fe-based liquid phase oxide can easily move in the scale and permeates into the scale / steel (internal oxide layer) interface. In order to sufficiently heat the steel material to the center, if the temperature is 1170 ° C., the heating time needs to be 1 hour or more. The heating time is not particularly limited as long as it is 1 hour or more, but the upper limit is 10 hours. Even if it is made longer than that, the effect is saturated and it is considered that heat energy is lost. Further, when heating is performed at 1170 ° C. or higher and 1300 ° C. or lower for 1 hour or more and 10 hours or less, the scale may grow and a scale having a thickness of 3 mm or more may be generated.

The mixture of the Si-containing material and at least one of the Fe-containing material (iron oxide or iron hydroxide), B-containing material, P-containing material, and S-containing material should be arranged as widely as possible on the surface of the steel material. Since the formation reaction of Si—Fe-based liquid phase oxide is likely to proceed, it is desirable to carry out the reaction on the entire surface.
However, since the Si—Fe-based liquid phase oxide has a property of easily moving in the scale, it can move at a distance of about several tens of centimeters. Therefore, it is not always necessary to uniformly apply or attach the mixture of the Si-containing substance to be permeated into the scale and at least one of the Fe-containing substance, the B-containing substance, the P-containing substance, and the S-containing substance on the entire surface of the steel material. However, when it is arranged on a part of the surface of the steel material, the descaling property of the entire surface of the steel material can be improved even when it is sprayed unevenly. Therefore, the degree of arrangement of the mixture may be 99% or less in terms of the area ratio with respect to the surface area of the steel sheet. On the other hand, as described above, the mixture of the Si-containing material and at least one of the Fe-containing material (iron oxide or iron hydroxide), B-containing material, P-containing material, and S-containing material is on the surface of the steel material. It is easier for the formation reaction of a sufficient amount of Si—Fe-based liquid phase oxide to proceed when it is arranged as wide as possible. Therefore, the degree of arrangement of the mixture is preferably 50% or more in terms of the area ratio with respect to the surface area of the steel sheet. Unless otherwise specified, in the present invention, the steel material surface refers to the upper surface (front surface) of the steel material when the steel material is placed in a horizontal position, and does not include the side surface or the lower surface (back surface) of the steel material.

In the present invention, as shown in FIG. 3, when the mixture is placed on the surface of the steel material before heating, a sufficient amount of Si—Fe liquid phase oxidation occurs in the scale while heating at a high temperature of 1170 ° C. or higher for 1 hour or longer. The material penetrates through the grain boundaries of the scale and is distributed throughout the scale and to the scale / steel (internal oxide layer) interface. Therefore, the outer layer scale and the inner layer scale can be removed by the subsequent descaling. Further, the descaling in the present invention refers to a method of removing scale on the surface of a steel material by injecting water from a nozzle onto the surface of the steel material having a high temperature of 900 ° C. or higher. The water pressure is preferably 3 MPa or more and 100 MPa or less.

On the other hand, when a substance other than a mixture of the Si-containing substance and at least one of the Fe-containing substance, the B-containing substance, the P-containing substance, and the S-containing substance is used, that is, a sufficient amount of liquid phase oxide is used. When a substance that does not have the property of infiltrating the liquid phase oxide into the scale is used, as shown in FIG. 4, the substance placed before heating is placed between the outer layer scale and the inner layer scale. Stay. This is because the outer layer scale has the property of growing outward due to the diffusion of Fe ions, the inner layer scale has the property of growing by the inward movement of oxygen, and the molten liquid phase oxide cannot move within the scale. is there. When descaling is performed in such a state, the liquid phase oxide and the outer layer scale above it can be removed, but it is difficult to remove the inner layer scale.

It should be noted that conventional antioxidants are used to prevent the surface of a steel material from oxidizing during heating, and its basic principle is to block oxygen from the surface of the steel material. Therefore, it is necessary to apply the antioxidant uniformly to the entire surface of the portion where oxidation is not desired. Generally, the antioxidant is applied not only to the upper surface (front surface) of the steel material, but also to the side surface and the lower surface (back surface) of the steel material. In addition, the antioxidant needs to have high adhesion. This is because oxygen may infiltrate and reach the surface of the steel material even from a slight crack, so it is necessary to prevent fine peeling after application and the foaming of the antioxidant during heating ( For example, see Patent Document 3). As described above, since the antioxidant is used in close contact with the steel material, it is not assumed that the antioxidant is used as a liquid phase and moved in the scale.

The amount of Si contained in the mixture arranged on the surface of the steel material is 400 to 1200 g / m ² as the amount of Si per surface area of the steel material. Here, the surface area of the steel material is the area of the upper surface (front surface) of the steel material when the steel material is placed in a horizontal position. The amount of Si is an amount defined by the amount of Si content (g / m ² ) × (total atomic weight of Si per molecule of Si content ÷ molecular weight of Si content). If the amount to be arranged ^{is less than 400 g / m 2} , the permeation of the Si—Fe-based liquid phase oxide into the entire scale and the scale / steel (internal oxide layer) interface may not be sufficient, and the descaling property may not be improved. is there. From the viewpoint of improving the descaling property, the larger the Si-containing content, the more preferable, and the upper limit of the amount to be arranged is not particularly limited. However, if the amount to be arranged ^{exceeds 1200 g / m 2} , it may be difficult to arrange the material on the surface of the steel material, or the Si-containing material may not be sufficiently in contact with the atmosphere and the liquid phase formation reaction may not proceed easily. Therefore, the amount of the Si-containing material to be arranged is limited to ^{1200 g / m 2.}

The Si-containing material is not particularly limited as long as it contains Si, and any one or a combination of _{metal Si, SiC, SiCN, and SiO 2 can be used. Silica (SiO 2} ) may be used because it is stable, easy to handle, easily available, and inexpensive. Further, the Si-containing material is preferably in the form of a paste. Since it is in the form of a paste, it has an appropriate viscosity, and it is easy to increase the arrangement amount of the Si-containing material and the Fe-containing material to be mixed without spilling from the steel material, and it is easy to apply it to the surface of the steel material.

The Fe-containing material may be iron oxide or iron hydroxide. Iron oxides or iron hydroxides (Fe-containing substances) include ustite, magnetite, hematite, margemite, iron hydroxide (II), iron hydroxide (III), gesite, akaganite, lepidocrosite, ferrooxyheit, Alternatively, it may be a mixture thereof. It is desirable because wustite easily forms a liquid phase, but other iron oxides are also reduced to wustite, and the same effect can be obtained. Iron hydroxides are also dehydrated by heating at high temperatures and reduced to wustite. Further, the iron oxide or iron hydroxide (Fe-containing substance) is preferably in the form of powder in order to easily mix with the Si-containing substance.

The appropriate amount of Fe-containing material (iron oxide or iron hydroxide) is 0.3 to 20% of the amount of Si in the Si-containing material in mass%. The Fe content is an amount defined by Fe content content (g / m ² ) × (total atomic weight of Fe per molecule of Fe content ÷ molecular weight of Fe content). If the amount of Fe is less than 0.3%, the liquid phase formation reaction is not promoted and the descaling property may not be improved. On the other hand, if the amount of Fe is more than 20%, the viscosity may be improved to the extent that it becomes difficult to mix the mixture with the Si-containing substance and arrange the mixture. Further, if the upper limit of either the Si-containing substance or the Fe-containing substance contained in the mixture is exceeded, the steel material surface is likely to spill into the heating furnace, which not only does not contribute to the improvement of descaling performance, but also the spilled liquid phase. Oxides can damage refractories in the heating furnace.

When B-containing substances, P-containing substances, and S-containing substances are mixed, the amount of each element per surface area of the steel material is 4 to 40 g / m ² per surface area of the steel material, and 8 to 8 to P amount per surface area of the steel material. 80 g / ^{m 2,} are mixed in 8~80g / ^{m 2} as the amount of S per the steel surface.
The lower limit of the mixed amount of the B-containing material, the P-containing material, and the S-containing material is set based on the following idea.
B, P, and S have the effect of lowering the eutectic point between _{FeO and Fe 2} SiO _4. In the case of B, the present inventor has found that the concentration in the range of 1 cm from the surface of the steel material needs to be 0.005% by mass or more in order to obtain the effect. It is also known that in the case of P and S, the concentration needs to be 0.01% by mass or more. Based on this finding, B, S, and P in a depth range of 1 cm from the surface of the steel material are supplied from the B-containing material, the P-containing material, and the S-containing material. In that case, based on the fact that the density of Fe, which is the main component of the steel material, is 7.9 g / cm ³ , the lower limit of the mixing amount of each content is set as follows. (In the case of B, 7.9 g / cm ³ × 1 cm × 0.005% = 3.95 × 10 ^-4 g / cm ² ≈ 4 g / m ² , and in the case of P and S, 7.9 g / cm ³ × 1 cm × 0.01% = 7.9 × 10 ^-4 g / cm ² ≒ 8 g / m ² )
On the other hand, the upper limit is set based on the following idea. In general, the larger the amount of each of these elements added, the greater the effect of lowering the eutectic point. However, if the amount added is too large, it may affect the material of the steel material, so the upper limit is set within the range of the concentration that does not affect the material of the steel material. B is said to be an element effective for strengthening grain boundaries and increasing the strength of steel, but if the content is too large, workability may decrease, and the upper limit concentration is 0.05% by mass. There is. If the content of S is too large, the workability may decrease, and 0.1% by mass is set as the upper limit concentration. For P, grain boundary embrittlement is likely to occur and workability may deteriorate, and the upper limit concentration is 0.1% by mass. This effect is considered to extend to a depth of 1 cm from the surface of the steel material, ^{and based on the density of Fe, which is the main component of the steel material, being 7.9 g / cm 3} , B-containing material, P-containing material, and S-containing material. The upper limit of the mixing amount of substances is set as follows. (In the case of B, 7.9 g / cm ³ × 1 cm × 0.05% = 39.5 × 10 ^-4 g / cm ² ≈ 40 g / m ² , and in the case of P and S, 7.9 g / cm ³ × 1 cm × 0.1% = 79 × 10 ^-4 g / cm ² ≒ 80 g / m ² )

The B-containing compound is not particularly limited as long as it is a compound containing B, but B ₂ O ₃ (boron oxide) may be used in consideration of availability and handleability. The S-containing substance is not particularly limited as long as it is a compound containing S, but CuS (copper sulfide), FeS (iron sulfide), and MnS (manganese sulfide) may be used in consideration of availability and handleability. You may use it. The P-containing compound is not particularly limited as long as it is a compound that contains P, availability, considering the handleability may be used P 2 _O 5 _(phosphorus pentoxide).

The mixing method of the Si-containing material and at least one of the Fe-containing material, the B-containing material, the P-containing material, and the S-containing material is not particularly limited as long as the materials can be mixed homogeneously, for example, a mixer. , A shooter, an excavator or the like may be used for batch mixing, or a hopper or the like may be used for continuous mixing.

The steel material handled in the present invention contains 0.3 to 1.5% by mass of Ni. The higher the Ni content, the more difficult it is to descale, but if the Ni content is less than 0.3%, it can be descaled by a general descaling method without using the present invention. .. When the Ni content is 0.3% or more, descaling becomes difficult and the effect of the present invention is clearly shown. If the Ni content exceeds 1.5%, descaling is difficult even with the present invention.

The steel material handled in the present invention contains 0.001 to 0.5% by mass of Si. Si is an element added to steel materials from the viewpoint of ensuring strength and improving weldability, and may be appropriately added depending on the required performance. However, since the cost increases in order to reduce the Si content to less than 0.001%, this is set as the lower limit. Further, when Si contains more than 0.5%, the descaling property is good at 1170 ° C. or higher without using the present invention. This is because when the steel material is heated to form scale, the Si content contained in the steel material forms a Si—Fe-based liquid phase oxide, which improves the descaling property. Therefore, the upper limit of the Si content of the steel material handled in the present invention is 0.5% by mass.

The chemical components contained in the steel other than these are 0.001 to 1.0% in C, 0.001 to 2% in Mn, 0.001 to 0.1% in P, and 0. in S in mass%. If the composition is in the range of 001 to 0.1% and B of 0.001% to 0.05%, the descaling property of the present invention range is not affected, and the action of the present invention can be enjoyed.
C is an element that is effective for ensuring strength at low cost, but it is set to 0.001 to 1.0% because processability decreases as the amount added increases.
Mn is also an element added to improve the strength. The strength improving effect of Mn increases as the Mn content increases. However, even if the Mn content exceeds 2%, the strength increases with the addition amount, but the processability deteriorates. Therefore, the Mn content is set to 0.001 to 2%.
P is also an alloy element effective for improving the strength, and the P-based oxide lowers the eutectic temperature and increases the liquid phase, so that the scale peelability is good. However, even if the content exceeds 0.1%, the effect on the peelability of the scale is saturated, and grain boundary embrittlement is likely to occur and the workability is deteriorated. Therefore, the upper limit is set to 0.1%.
S is originally an impurity, and if it is contained in a large amount, it impairs cold or hot workability. Therefore, it is preferable that S is as small as possible. There is no problem.
B is an element having an action of improving the hardenability of steel, and 0.001% or more is required to obtain the effect. Therefore, the B content may be 0.001% or more. If the B content exceeds 0.05%, not only the above effect is saturated and the cost increases, but also the manufacturability during hot rolling is hindered, so that the B content is 0.05% or less. ..

The heating of the present invention may also serve as heating for hot working. The steel material is often hot-worked so that the steel material has the desired shape and properties. When heated at 1170 ° C. or higher and 1300 ° C. or lower for 1 hour or more and 10 hours or less, scales may grow and scales having a thickness of 3 mm or more may be generated. According to the present invention, after arranging a mixture of a Si-containing material and at least one of Fe-containing material, B-containing material, P-containing material, and S-containing material on the surface of the steel sheet, the steel sheet is heated and descaled. After that, even scales, especially scales having a thickness of 3 mm or more, are removed. Further, the temperature of the steel material after descaling can often be maintained at the temperature required for hot working. Therefore, after descaling, hot working is possible without separate heating, and since the scale is sufficiently removed, scale defects do not occur during processing. The type of hot working is not particularly limited, and examples thereof include hot rolling, hot forging, and hot extrusion.

The steel material may be a brake disc material. Generally, brake discs are formed by hot forging Ni-containing steel. In hot forging, a steel material is heated to make it soft, and then pressure is applied by a press or the like to form a die. The heating temperature range for softening the steel material can be a temperature that overlaps with or is lower than the above-mentioned temperature range of 1170 ° C. or higher and 1300 ° C. or lower. Therefore, by applying the present invention to hot forging of a brake disc material, a brake disc without an oxide scale can be easily and efficiently obtained.

The arrangement amount of the mixture of the Si-containing material and at least one of the Fe-containing material, the B-containing material, the P-containing material, and the S-containing material may be changed according to the heating time of the steel material. This is to secure a certain amount of Si-Fe-based oxide in the liquid phase in the scale to ensure higher descaling property, and to prevent the generation of Si-Fe-based oxide in the liquid phase more than necessary. This is because it leads to cost reduction. That is, the amount of Si to be arranged and the amount of at least one of Fe-containing material, B-containing material, P-containing material, and S-containing material are controlled according to the expected scale production amount. Generally, the amount of scale produced depends on the heating time above 1170 ° C. That is, the longer the heating time, the larger the amount of scale generated. Therefore, the amount of the mixture may be changed according to the heating time. In order to ensure good descaling property, it is a guideline to secure a liquid phase Si—Fe-based oxide amount having a volume fraction of 50% or more with respect to the total amount of the inner layer scale. The scale properties and the condition of the Ni-enriched layer may change depending on the steel composition and the oxidation conditions, and the arrangement amount of the mixture may be adjusted according to these conditions.

Prepare the steel materials with the chemical components shown in Table 1 below, heat them in the combustion gas atmosphere of LPG with the air ratio set to 1.1 at the specified temperature and time shown in Table 2, and remove them from the furnace. The steel material temperature is 1175 ° C. After descaling (descaling water pressure 150 kg / cm ² ), hot forging (press pressure 2000 kg / cm ² ) was performed.
As an example and a comparative example, a mixture of a Si-containing substance and an Fe-containing substance (iron oxide or iron hydroxide) was prepared by changing their mass, form, and arrangement position (see Table 2) before heating. After arranging on a steel material, heating, descaling, and hot forging, the presence or absence of surface defects (scale defects) was determined. In the comparative example, the Si-containing substance, the Fe-containing substance, and the arrangement position were adopted so as to be outside the scope of the present invention.
Further, a mixture of the Si-containing material and at least one of the B-containing material, the P-containing material, and the S-containing material is made into a steel material before heating by changing their mass, form, and arrangement position (see Table 3). After arranging, heating, descaling, and hot forging, the presence or absence of surface defects (scale defects) was determined. In the comparative example, the mass and the arrangement position of the B-containing material, the P-containing material, and the S-containing material were adopted so as to be outside the scope of the present invention.
Judgment of surface defects is x when visually confirming that there is a problem with the surface quality of the product, △ when it is confirmed by cross-sectional observation that there is no problem with quality, and there is no surface defect. Was confirmed by visual inspection and cross-sectional observation as ◯.
The placement conditions and the results of surface defects are shown in Tables 2 and 3.

(About Si content)
In Examples 1 to 22 of the present invention, Si-containing substances are arranged in an amount within the range of the present invention, and at least one of Fe-containing substances, B-containing substances, P-containing substances, and S-containing substances is arranged within the range of the present invention. However, heating was performed at a temperature and time within the range of the present invention, and in each case, the scale was sufficiently removed by descaling, and subsequent forging did not cause unacceptable defects in surface quality.
In Comparative Example 2, even if the Si content was arranged in an amount smaller than the range of the present invention and descaling was performed, the scale was not sufficiently removed, and subsequent forging caused a defect that caused a problem in surface quality (×). ). In Comparative Example 5, the Si content was 1300 g / m ² (outside the range of the present invention), and no surface flaws occurred after forging, but the mixture containing excess Si content spilled from the surface of the steel material, and the heating furnace. It was deposited inside.

(About Fe content)
Here, the ratio of the amount of Fe contained in the Fe-containing material (iron oxide or iron hydroxide) to the amount of Si contained in the Si-containing material will be considered.
In Comparative Examples 1, 3 and 4, the Fe ratio was less than the lower limit value (0.3%) of the present invention, a sufficient liquid phase oxide could not be obtained, and the descaling property was not improved. In Example 6 of the present invention, the Fe ratio was 0.3%, the scale was sufficiently removed by descaling, and subsequent forging did not cause unacceptable defects in surface quality. In Example 7 of the present invention, the ratio of Fe was 20%, and forging did not cause unacceptable defects in surface quality, but the viscosity of the mixture of the Si-containing substance and the Fe-containing substance was higher, and Fe was higher than this. It was suggested that increasing the ratio of the above would reduce the workability of the mixing work and the work of arranging the mixture on the surface of the steel material.

(About B-containing material, P-containing material, S-containing material amount)
Here, the case where at least one of the B-containing substance, the P-containing substance, and the S-containing substance is mixed with the Si-containing substance will be considered. In Comparative Examples 6, 7 and 8, the amounts of B, P and S were less than the lower limit of the present invention, a sufficient liquid phase oxide could not be obtained, and the descaling property was not improved. Separately, when the amounts of B, P, and S were the upper limit values of the present invention, the descaling property was good and no surface defects were observed after forging.

(About heating temperature and heating time)
In Examples 11 and 18 of the present invention, the heating temperature was set to 1300 ° C. and the heating time was set to 10 hours to generate a thick scale of 9 mm. However, in this case as well, the scale was sufficiently removed by descaling, and the surface was forged thereafter. There were no unacceptable defects in quality. That is, the result was obtained that the present invention is effective even when heated at a high temperature for a long time. Further, in Example 12 of the present invention, the heating temperature was set to 1180 ° C. and the heating time was set to 1 hour to generate a scale having a thickness of 3 mm. No unacceptable flaws occurred. That is, it was confirmed that the effect of the present invention is exhibited even at a heating temperature and a heating time near the lower limit of the range of the present invention.

(About the placement position of the mixture)
In Invention Examples 8, 9 and 20, the mixture of the Si-containing material and the Fe-containing material or the S-containing material was arranged so as to cover 40% (area ratio) of the steel material surface, not the entire surface of the steel material. That is, 60% (area ratio) of the surface of the steel material was descaled by heating the steel material without arranging the mixture. Surface defects after forging could not be visually confirmed, and cross-sectional observation confirmed that there was no problem in quality (Δ). Invention Example 4 is an example performed under the same conditions as Invention Example 8 except that the mixture is arranged on the entire surface of the steel material. In Invention Example 4 in which the mixture was arranged on the entire surface of the steel material, surface defects after forging were not confirmed not only visually but also by cross-sectional observation (◯).

(About the form of Fe-containing substances (iron oxides and iron hydroxides))
Used FeO powder as invention example 1～4,8,9,12 the Fe-containing material, using the _Fe 3 _{O 4} powder as Fe-containing material in the invention examples 5～7,11, water as the invention example 10, Fe-containing material Iron (III) oxide powder was used. In any of the invention examples, forging after descaling did not cause unacceptable defects in surface quality.

Claims (4)

A process of heating a steel material containing 0.3 to 1.5% by mass of Ni and 0.001 to 0.5% by mass of Si at a temperature of 1170 ° C. or higher and 1300 ° C. or lower for 1 hour or more and 10 hours or less. It is a method of removing the oxidation scale generated in
A Si-containing material having a Si content of 400 to 1200 g / m ^{2 per surface area of the steel material and}
Fe content of 0.3 to 20% of the amount of Si in mass%,
Boron oxide of 4 to ^{40 g / m 2} as the amount of B per surface area of the steel material,
Diphosphorus pentoxide having a P amount of 8 to 80 g / m ² per surface area of the steel material,
At least one, were mixed in,
The mixture is placed on the surface of the steel material and
The steel material is heated to perform the heating.
Then descaling and
The Si-containing material is any one of metal Si, SiC, SiC, SiO ₂ , or a combination thereof.
The Fe-containing material is iron oxide or iron hydroxide, the iron oxide is ustite, magnetite, hematite, margemite, or a mixture thereof, and the iron hydroxide is iron (II) hydroxide. A method for removing iron oxide scale, which is iron (III) hydroxide, gesite, akaganite, lepidoclosite, ferrooxyheite, or a mixture thereof. The method according to claim 1, wherein the arrangement is performed on the entire surface of the steel material. The method according to claim 1 or 2 , wherein the steel material is a brake disc material. The method according to any one of claims 1 to 3 , wherein the oxidation scale has a thickness of 3 mm or more on the surface of the steel material.

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