JP5680451B2 - High thermal expansion Fe-Ni-Cr alloy for bimetal and method for melting the same - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a high thermal expansion Fe—Ni—Cr alloy used for a bimetal, and specifically, a high thermal expansion Fe—Ni—Cr alloy for bimetal excellent in hot workability and surface properties and a method for melting the same. It is about.

  Bimetals widely used in electrical products as temperature sensors and temperature compensation parts join two types of metal plates with different thermal expansion coefficients by mechanical pressure welding, diffusion, welding, etc., and bend due to differences in thermal expansion coefficients. It is a composite material to be awakened. Generally, Fe-Ni alloy containing about 36 mass% of Ni is used as the low thermal expansion metal plate, while Cr is added to Fe-20 to 25% Ni alloy as the high thermal expansion metal plate. Stainless steel having an austenite single phase structure is used.

By the way, the high thermal expansion metal plate satisfies the physical characteristics that the thermal expansion coefficient α in the temperature range of 30 to 100 ° C. is 18 × 10 ⁻⁶ / ° C. or more and the electric resistance ρ is 70 μΩ · cm or more. In addition, it is necessary to have excellent manufacturability and surface properties. However, the conventional Fe—Ni—Cr-based alloy has a problem that workability is poor, ear cracks are likely to occur during hot rolling, and surface defects due to inclusions are likely to occur on the product plate surface. When the above-mentioned ear cracks occur, both end portions of the hot-rolled sheet must be cut off and removed, which causes a decrease in product yield and a decrease in productivity. In addition, when surface defects occur on the product plate surface, not only the appearance as a product but also the quality characteristics as a bimetal are adversely affected.

  Therefore, as a solution to this problem, Patent Document 1 discloses that in Fe—Ni—Cr alloy containing Ni: 8 to 30 wt%, Cr: 0.5 to 14 wt%, S is 0.08 wt% or less, and P is Regulated to 0.040 wt% or less, and further added one or more of B: 0.001 to 0.030 wt%, Ti: 0.05 to 2 wt%, Zr: 0.001 to 1 wt% By doing so, it is disclosed that a high expansion alloy for bimetals excellent in hot workability can be obtained. However, in the technique of this patent document 1, the surface property has not been studied.

In addition, as a technique for preventing surface defects due to inclusions, some of the Fe—Ni alloys used in the same field are disclosed. For example, Patent Document 2 discloses Ni: 30 to 50 wt%. In the Fe-Ni alloy containing Ni, the inclusions are stabilized by deoxidation control by reducing the Al content of the added alloy as much as possible and inclusion composition control in which refining is performed with slag in the pan in which the slag composition is controlled. It has been disclosed that a low-melting point, stretched and refined by hot rolling and cold rolling, and a high-quality high Ni alloy having excellent cold workability and no inclusion physical surface defects and internal defects can be obtained. . Patent Document 3 discloses that in a Fe—Ni alloy containing Ni: 20 to 50 wt%, the composition of non-metallic inclusions is basically MnO—SiO ₂ —Al ₂ O ₃ system, and MnO is 5 to 5%. 50 wt%, SiO ₂ is 30 to 60 wt%, Al ₂ O ₃ is 5 to 30 wt%, and CaO and MgO contained therein are controlled to silicate-based nonmetallic inclusions with a total of 30 wt% or less. It is disclosed that an Fe—Ni alloy having excellent surface properties and etching properties can be obtained.

Japanese Patent Laid-Open No. 06-093381 JP-A-11-315354 JP 2002-004006 A

As described above, in the Fe—Ni—Cr alloy, a technique for improving the hot workability is disclosed, but a technique for improving the surface properties is hardly studied.
Further, according to the investigation by the inventors, B and Ti, which are recognized to have an effect of improving the hot workability in the technique of the above-mentioned Patent Document 1, may deteriorate the hot workability. Became clear.

  Therefore, the present invention was developed to solve the above-described problems of the prior art, and the purpose thereof is an Fe-Ni-Cr alloy excellent in hot workability and surface properties, and an advantageous melting method thereof. Is to propose.

  The inventors diligently conducted various experiments to solve the above problems. As a result, the decrease in hot workability in the Fe—Ni—Cr alloy is caused by S mixed as an impurity in the steel, but the decrease in hot workability due to the addition of B or Ti In order to improve the hot workability in the Fe—Ni—Cr alloy in order to reduce the grain boundary strength by bonding with N to Ti and precipitate at the grain boundaries, the inclusion of S and N In addition to reducing the amount, it has been found that it is necessary to limit the amount of addition of B and Ti.

In addition, the deterioration of the surface properties in the Fe-Ni-Cr alloy is caused by non-metallic inclusions inferior in the extensibility existing in the steel. Therefore, in order to improve the surface properties, the non-metallic inclusions are made to be extensible. Therefore, it is necessary to control the MnO—SiO ₂ —Al ₂ O ₃ —MgO—CaO system, which is excellent in the process, and for that purpose, it is effective to control the component composition of the slag generated in the refining process within an appropriate range. I found it.

That is, the present invention is C: 0.05-0.30 mass%, Si: 0.05-0.40 mass%, Mn: 0.05-0.60 mass%, S: 0.0001-0.005 mass%, P: 0.040% or less, Ni: 20~26mass%, Cr: 1~6mass%, N: 0.02mass% or less, B: less than 0.001% and Ti: containing less than 0.05 mass%, further Mg: 0.001 mass% or less, Ca: 0.0001 to 0.002 mass%, Al: 0.0001 to 0.01 mass%, and O: 0.0001 to 0.005 mass%, the balance being Fe and inevitable has a component composition consisting of impurities, non-metallic inclusions contained in the alloy _is a _{MnO-SiO 2 -Al 2 O 3} -MgO-CaO system, Component _{composition, MnO: 0.1~10mass%, SiO 2} : 10~40mass%, Al 2 O 3: 5~40mass%, MgO: 5~40mass%, CaO: bimetal for Fe is 10～40Mass% -Ni-Cr alloy.

In the present invention, a melting raw material using iron scrap, ferronickel, and pure Ni is melted in an electric furnace, and then oxidized and refined using AOD and / or VOD to dephosphorize and decarburize, and Si and / or Or, after adding Si alloy iron to deoxidize and finish desulfurize, after adding a raw material melted in an electric furnace by adding Cr to have the component composition according to claim 1 , AOD and / or Using VOD, oxidative refining to dephosphorize and decarburize, add Si and / or Si alloy iron to deacidify and finish desulfurize, then add Cr to make the component composition described above We propose a method for melting Fe-Ni-Cr alloys for bimetals.

Further, the present invention is a method in which an iron furnace , a stainless steel scrap, ferronickel, ferrochrome, and pure Ni are used to dissolve a low phosphorus melting raw material having a P content of 0.06 mass% or less in an electric furnace, and then AOD and / or Using VOD, oxidative refining and decarburization, adding Si and / or Si alloy iron to reduce Cr, deoxidation and finish desulfurization to have the above- described component composition A method for producing an Fe-Ni-Cr alloy is proposed.

Moreover, melting process of bimetal for Fe-Ni-Cr alloy of the present invention, in the deoxidation step of introducing the Si and / or Si alloy iron, the slag generated by the basicity (CaO / SiO ₂₎ is 1 To CaO—SiO ₂ —Al ₂ O ₃ —MgO—F system in which MgO is ₂ to 10 mass% and Al ₂ O ₃ is 0.2 to 10 mass%, and Si in the molten steel is controlled to 0. It is characterized by being controlled in the range of 05 to 0.40 mass%.

  According to the present invention, the hot workability of the high thermal expansion Fe-Ni-Cr alloy for bimetal can be remarkably improved, and surface defects caused by inclusions can be greatly reduced. Contributes not only to improved yield but also to improved bimetal quality.

It is the microstructure picture which compared the grain boundary precipitate of Fe-Ni-Cr alloy (steel ingot) with and without B addition.

An experiment that triggered the development of the present invention will be described.
According to Patent Document 1, S is an element that degrades hot workability, and N is an element that degrades hot workability when contained in a large amount. It is said that it needs to be reduced to 2 wt% or less. Therefore, the inventors first conducted an experiment to confirm the technique of Patent Document 1.

In the above experiment, an Fe—Ni—Cr alloy containing Ni: 22 mass% and Cr: 3 mass% was dissolved in a magnesia crucible using a high frequency induction furnace, and CaO—SiO ₂ —Al ₂ O ₃ —MgO—F was dissolved. 1 kg of slag is added, and Si and Mn are further added for deoxidation, and desulfurization is performed to reduce S to 0.005 mass% or less, and further, the invasion of N from the atmosphere is suppressed, and N: 0.00. Fe-22Ni-3Cr alloy (B: 0.0003 mass%, N: 0.001 mass%) reduced to 05 mass% or less, and Fe-22Ni in which B is added to the above alloy in order to improve hot workability Two types of alloys of -3Cr alloy (B: 0.0022 mass%, N: 0.022 mass%) were melted and cast into 20 kg steel ingots. Next, after the above two types of steel ingots were heated to 1200 ° C. and hot rolled to evaluate the workability, the hot workability of the alloy to which B was not added was good. It became clear that the added alloy produced large ear cracks and was not at a practical level.

  Therefore, in order to investigate the cause of the occurrence of the above-mentioned ear cracks, a microstructure observation was performed on the steel ingot of the alloy added with B and the steel ingot of the alloy without addition of B. As shown in FIG. In the added alloy, it was found that huge BN was precipitated at the grain boundaries. From this result, it was speculated that the decrease in hot workability due to the addition of B was due to the formation of voids starting from the BN that had precipitated enormously at the grain boundaries and causing the grain boundary fracture. As a result of conducting the same investigation with the Ti-added alloy, the same ear cracks as with the B-added alloy occurred. Furthermore, precipitation of TiN at the grain boundaries has also been confirmed, and it is considered that hot workability has decreased due to the same cause.

  From the results of the above experiments, B and Ti have been conventionally considered to be elements that improve hot workability. However, in alloys containing N, addition of B or Ti causes the addition of BN or TiN grains. S: 0.005 mass% or less, N: 0.005%, in order to promote boundary precipitation and, on the other hand, impair hot workability, and thus improve hot workability in Fe—Ni—Cr alloys. In addition to reducing to 02 mass% or less, it was also found that the addition amount of B and Ti should be reduced as much as possible, and limited to B: less than 0.001 mass% and Ti: less than 0.05 mass%, respectively.

Next, in order to investigate the composition of the non-metallic inclusions that impair the surface properties, the inventors used a high frequency induction furnace to form an Fe-22% Ni-3% Cr alloy in a magnesia crucible as in the above experiment. After dissolution, 1 kg of CaO—SiO ₂ —Al ₂ O ₃ —MgO—F-based slag is added, and Si and Mn are further added to deacidify and desulfurize. The basicity of the slag generated during deoxidation (CaO / SiO ₂ ) and the component composition were changed to melt and cast an alloy in which the component composition of the nonmetallic inclusions produced in the steel was variously changed and cast into a 20 kg steel ingot. Thereafter, the steel ingot is heated to 1200 ° C., hot-rolled, the scale on the surface is removed, cold-rolled to obtain a cold-rolled sheet having a thickness of 1 mm, and the surface of the cold-rolled sheet is visually observed. An experiment was conducted to investigate the presence or absence of wrinkles.
As a result, the basicity (CaO / SiO ₂ ) of the slag generated during deoxidation by adding Si and Mn is set to 1 to 6, the component composition of the slag is MgO: _{2 to} 10 mass%, Al ₂ O ₃ : 0.2. MnO—SiO ₂ —Al ₂ O ₃ —MgO— which has excellent stretchability of inclusions in the steel by adjusting Si in the molten steel at that time: 0.05 to 0.40 mass% It was possible to control to CaO system and found out that surface flaws were not generated.

Here, the reason why Si in the molten steel is 0.05 mass% or more is that when it is less than 0.05%, deoxidation is insufficient, O in the molten steel exceeds 0.0050 mass%, and the amount of inclusions increases. This is because the size is increased at the same time and surface defects are easily generated. On the other hand, the reason for setting it to 0.40 mass% or less is that when Si exceeds 0.40 mass%, the reduction of MgO and Al ₂ O _{3 in} the slag proceeds too much, and the composition of inclusions formed in the molten steel is This is because MgO.Al ₂ O ₃ and Al ₂ O ₃ systems that are inferior in stretchability are generated and surface defects are generated. In addition, the MgO · Al ₂ O ₃ and Al ₂ O ₃ inclusions cause surface flaws even if they fall on the inner wall of the immersion nozzle in continuous casting. There is a need to.

Furthermore, according to the results of the above experiment, the MnO—SiO ₂ —Al ₂ O ₃ —MgO—CaO-based inclusion has a component composition of MnO: 0.1 to 10 mass%, SiO ₂ : 10 to 40 mass%. _{, Al 2 O 3: 5~40mass%} , CaO: 10~40mass%, MgO: by controlling the range of 5～40Mass%, without large inclusions are formed, moreover, are drawn by hot rolling It has also been found that surface flaws are less likely to occur because they are finely divided by cold rolling.
The present invention has been developed by further studying the above findings.

Next, the component composition that the Fe—Ni—Cr alloy of the present invention should have will be described.
C: 0.05-0.30 mass%
C is an element effective for increasing the strength of steel by solid solution strengthening and the like, and is also an austenite generating element. In order to obtain an austenite single phase structure at room temperature and to secure a high thermal expansion coefficient necessary for bimetal, it is necessary to add 0.05 mass% or more of C. On the other hand, the addition of C exceeding 0.30 mass% produces a large amount of carbides and decreases the hot workability. Therefore, C is set to a range of 0.05 to 0.30 mass%. Preferably it is 0.05-0.25 mass%, More preferably, it is the range of 0.05-0.20 mass%.

Si: 0.05-0.40 mass%
Si is an element added as a deoxidizer and a desulfurizer, and it is necessary to contain 0.05 mass% or more. However, if added over 0.40 mass%, the reduction of MgO and Al ₂ O _{3 in} the slag produced during refining proceeds too much, and the composition of inclusions formed in the molten steel is MgO · Al ₂ O _3. And Al ₂ O ₃ type, surface flaws are generated. Therefore, Si is set to 0.05 to 0.40 mass%. Preferably it is the range of 0.05-0.35 mass%.

Mn: 0.05 to 0.6 mass%
Mn is an austenite generating element, and is an element that fixes S segregated at grain boundaries as MnS and contributes to improvement of hot workability. In order to acquire such an effect, addition of 0.05 mass% or more is required. On the other hand, if it exceeds 0.6 mass%, the corrosion resistance is lowered. Therefore, Mn is in the range of 0.05 to 0.6 mass%. Preferably it is 0.10-0.6 mass%, More preferably, it is the range of 0.20-0.6 mass%.

S: 0.0001 to 0.005 mass%
S is an extremely harmful element that lowers the hot workability of the Fe—Ni—Cr alloy, and it is desirable to reduce it as much as possible. When it contains exceeding 0.005 mass% especially, hot workability will fall remarkably and will come to produce an ear crack at the time of hot rolling. On the other hand, in order to ensure the punchability and weldability for producing the bimetal, S needs to be contained in an amount of 0.0001 mass% or more. Therefore, in the present invention, S is in the range of 0.0001 to 0.005 mass%. Preferably, it is 0.0001-0.003 mass%, More preferably, it is the range of 0.0001-0.002 mass%.

P: 0.040 mass% or less P, like S, is a harmful element that impairs hot workability, and it is desirable to reduce it as much as possible. In particular, when it exceeds 0.040 mass%, the hot workability is lowered. Therefore, P is set to 0.040 mass% or less. Preferably it is 0.030 mass% or less, More preferably, it is 0.025 mass% or less.

Ni: 20 to 26 mass%
Ni is an austenite-forming element and needs to be added in an amount of 20 mass% or more in order to obtain an austenite single-phase structure at room temperature and ensure a necessary high thermal expansion coefficient. On the other hand, when it is added in excess of 26 mass%, the thermal expansion coefficient is decreased. Therefore, Ni is set to a range of 20 to 26 mass%.

Cr: 1 to 6 mass%
Cr is an element necessary for ensuring a high coefficient of thermal expansion, and is added by 1 mass% or more. However, if it is added in excess of 6 mass%, the coefficient of thermal expansion decreases. Therefore, Cr is set to a range of 1 to 6 mass%.

N: 0.02 mass% or less N, like C, is an austenite-forming element. However, N is an element that combines with B, Ti, or the like to form a nitride and significantly reduce the hot workability. Therefore, it is desirable to reduce it as much as possible when adding a small amount of B or Ti. . Therefore, in the present invention, N is limited to 0.02 mass% or less. Preferably it is 0.018 mass% or less, More preferably, it is 0.016 mass% or less.

B: Less than 0.001 mass% B is an element effective for improving hot workability. However, according to the study by the inventors, in the Fe-Ni-Cr alloy, when 0.001 mass% or more is added, it combines with N in the steel to form B nitride, and the hot workability is significantly reduced. Will come to let you. Therefore, in the present invention, B is limited to 0.001 mass% or less. Preferably it is 0.0008 mass% or less, More preferably, it is 0.0006 mass% or less.

Ti: Less than 0.05 mass% Ti is an element effective for improving hot workability. However, according to the research by the inventors, Ti, like Fe, in Fe—Ni—Cr alloy, when added in an amount of 0.05 mass% or more, Ti combines with C and N in the steel and Ti (C, N ) To significantly reduce hot workability. Therefore, in the present invention, Ti is limited to less than 0.05 mass%. Preferably it is 0.045 mass% or less, More preferably, it is 0.04 mass% or less.

The Fe—Ni—Cr alloy of the present invention preferably further contains Mg, Ca, Al and O in the following ranges in addition to the essential components.
Mg: 0.001 mass% or less Mg is an element supplied into molten steel by reducing MgO in slag and refractory during the refining process, and the inclusion composition is MnO—SiO ₂ —Al ₂ O _3. In order to make it a -MgO-CaO system, it is preferable to contain 0.001 mass% or less. Although it does not limit, it is preferable to contain 0.0001 mass% or more at least. On the other hand, when Mg exceeds 0.001 mass%, the main component of nonmetallic inclusions is a hard MgO.Al ₂ O ₃ system, which causes surface defects. Therefore, Mg is preferably contained in an amount of 0.001 mass% or less, but more preferably in the range of 0.0001 to 0.0008 mass%.

Ca: 0.0001 to 0.002 mass%
Ca is an element supplied into molten steel by reducing CaO contained in slag in the deoxidation process of the refining process, and the non-metallic inclusion composition is changed to hard MgO.Al ₂ O ₃ or Al. prevented from becoming ₂ O _3, because of the effect of the _{MnO-SiO 2 -Al 2 O 3} -MgO-CaO -based, preferably contains more than 0.0001mass%. On the other hand, when Ca exceeds 0.002 mass%, CaO in the non-metallic inclusions rises and adversely affects the corrosion resistance. Therefore, Ca is preferably contained in the range of 0.0001 to 0.002 mass%.

Al: 0.0001 to 0.01 mass%
Since Al has a function of controlling the composition of non-metallic inclusions to the MnO—SiO ₂ —Al ₂ O ₃ —MgO—CaO system, it is preferably contained in an amount of 0.0001 mass% or more. On the other hand, if the content exceeds 0.01 mass%, the non-metallic inclusions become hard MgO.Al ₂ O ₃ or Al ₂ O ₃ and cause surface defects. Therefore, it is preferable to contain Al in the range of 0.0001 to 0.01 mass%.

O: 0.0001 to 0.005 mass%
O is an element present in steel as an oxide-based non-metallic inclusion, and if it exceeds 0.0050 mass%, the amount of non-metallic inclusion increases and the occurrence frequency of large inclusions increases. Drought begins to occur. On the other hand, when O becomes less than 0.0001 mass%, it is excessively deoxidized, and Al ₂ O ₃ and MgO in the slag are reduced, and the nonmetallic inclusions generated in the steel are hard MgO · Al ₂ O _3. And Al ₂ O ₃ inclusions are the main components, which causes surface flaws. Therefore, in the present invention, O is preferably contained in the range of 0.0001 to 0.005 mass%. In order to control the O content within the above range, it is effective to control the deoxidizing elements Si, Mn, and Al within the above composition range.

Next, nonmetallic inclusions present in the Fe—Ni—Cr alloy of the present invention will be described.
Nonmetallic inclusions present in the Fe-Ni-Cr alloy of the present invention are easily dispersed finely by stretching and breaking in hot rolling and cold rolling, and do not generate surface defects when formed into a product plate. For that purpose, it is preferably a MnO—SiO ₂ —Al ₂ O ₃ —MgO—CaO-based non-metallic inclusion having a component composition described below.

MnO: 0.1-10 mass%
When MnO is less than 0.1 mass%, the stretchability of the non-metallic inclusions is remarkably lowered, so that surface flaws are generated. On the other hand, the content of MnO exceeding 10 mass% corresponds to the case where the content of O exceeds 0.0050 mass%. Therefore, the amount of non-metallic inclusions increases, and surface flaws are generated. Therefore, it is preferable that the MnO in the non-metallic inclusion is in the range of 0.1 to 10 mass%. In addition, in order to make the composition of MnO in the above range, the Al and Mg contents in the steel are controlled to the above-mentioned ranges, or the basicity of slag (CaO / SiO ₂ ) is controlled to the range of 1 to 6. Is effective.

SiO _2: 10~40mass%
When SiO ₂ is less than 10 mass% or exceeds 40 mass%, the melting point of the non-metallic inclusion increases, the stretchability decreases, and surface defects are generated. Thus, SiO ₂ of the non-metallic inclusions is preferably in the range of 10~40mass%. In addition, in order to make the composition of SiO _{2 in} the above range, the basicity of slag (CaO / SiO ₂ ) is controlled in the range of 1 to 6, and the Si and Al contents in the steel are controlled in the range described above. Is effective.

Al ₂ O _3: 5~40mass%
When Al ₂ O ₃ is less than 5 mass%, the melting point of the non-metallic inclusions increases and the stretchability decreases. On the other hand, when it exceeds 40 mass%, nonmetallic inclusions are easily clustered rapidly, or become hardened and cannot be stretched by hot rolling, causing surface defects. Therefore, it is preferable _Al 2 _{O 3} of nonmetallic inclusions is in the range of 5~40mass%. In addition, in order to make the composition of Al ₂ O _{3 in} the above range, the Al content in the steel is controlled to the above-described range, or the Al ₂ O ₃ in the slag is controlled to a range of 0.2 to 10 mass%. Is effective.

MgO: 5 to 40 mass%
In both cases where MgO is less than 5 mass% or exceeds 40 mass%, the melting point of the non-metallic inclusions increases, the stretchability decreases, and surface defects are generated. Therefore, MgO in the nonmetallic inclusion is preferably in the range of 5 to 40 mass%. In addition, MgO is a component supplied into molten steel by reducing MgO in slag and refractory in the refining process. To make the MgO composition within the above range, the Mg content in steel is It is effective to control to the above-mentioned range or to control the composition of MgO in the slag to a range of 2 to 10 mass%.

CaO: 10 to 40 mass%
When CaO is less than 10 mass% or exceeds 40 mass%, in any case, the melting point of the nonmetallic inclusions is increased, and the stretchability may be lowered to cause surface defects. Therefore, CaO in the nonmetallic inclusion is preferably in the range of 10 to 40 mass%. If so, the melting point of the non-metallic inclusions is increased, and the stretchability may be reduced. In addition, CaO is a component supplied in molten steel by reducing CaO in slag in a deoxidation process, and in order to make the composition of CaO into the said range, Ca content in steel was mentioned above. It is effective to control to the range or to control the basicity (CaO / SiO ₂ ) in the slag to the range of 1-6.

The non-metallic inclusions contained in the alloy of the present invention contain 10 mass% or less of FeO, Cr ₂ O _{3 and the} like in addition to the above MnO, SiO ₂ , Al ₂ O ₃ , MgO and CaO. May be. Preferably, it is 5 mass% or less.

Next, a method for melting the Fe—Ni—Cr alloy of the present invention will be described.
Methods for melting the Fe—Ni—Cr alloy of the present invention include method A and method B described below, and either method may be used.
<Method A>
Dissolving raw materials mainly composed of Fe and Ni, that is, melting raw materials such as iron scrap, ferronickel, pure Ni, etc. are melted in an electric furnace, and then oxidatively refined and dephosphorized and decarburized with AOD and / or VOD. After demineralizing, add quick lime and fluorite, add Si and / or Si alloy iron, deoxidize, finish desulfurize and add Cr, and then add the final ingredients in ladle refining A method of adjusting to obtain the above-described component composition of the present invention.
<Method B>
Dissolving raw materials mainly containing low phosphorus Fe with a P content of 0.06 mass% or less and Cr, Ni, ie, molten raw materials such as selected iron scraps, stainless scraps, ferronickel, ferrochrome and pure Ni After melting in a furnace, etc., after oxidative refining and decarburization with AOD and / or VOD, quick lime and fluorite are added, and further Si and / or Si alloy iron is added to reduce and deoxidize Cr. A method of desulfurizing and then adjusting the final component by ladle refining to obtain the above-described component composition of the present invention.

Here, in any of the melting methods A and B, the slag to be generated is preferably a CaO—SiO ₂ —Al ₂ O ₃ —MgO—F system. SiO ₂ in the slag is generated from Si and / or Si alloy iron introduced in the deoxidation step. CaO and F are generated from quicklime and fluorite that are input as flux. Further, MgO can be added to the slag when the refractory containing MgO such as dolomite or MgO-C is used as the refractory for the AOD and VOD smelting furnaces. Further, Al ₂ O ₃ may be added by flux, but may be formed by oxidizing a small amount of Al contained in the Si alloy iron used for deoxidation.

The CaO—SiO ₂ —Al ₂ O ₃ —MgO—F-based slag produced in the deoxidation step has a basicity (CaO / SiO ₂ ) of 1 to 6 for the reason described below. The MgO contained in the slag is preferably ₂ to 10 mass%, the Al ₂ O ₃ is 0.2 to 10 mass%, and the Si in the molten steel is preferably controlled to be in the range of 0.05 to 0.40 mass%.

Slag basicity _(CaO / SiO 2): 1~6
When the basicity of the slag is less than 1, deoxidation does not proceed sufficiently and the O content exceeds 0.0050 mass%, so that nonmetallic inclusions increase and cause surface defects. On the other hand, if the basicity exceeds 6, the activity of MgO in the slag becomes too high, and Mg in the molten steel exceeds 0.001 mass%, so that the inclusions produced are mainly MgO · Al ₂ O ₃ , This is because it causes surface defects. Therefore, the basicity is preferably controlled to 1-6. Preferably it is 1.5-4, More preferably, it is the range of 1.7-3.5.

MgO: 2 to 10 mass%
If MgO in the slag is less than 2 mass%, MgO cannot be supplied into the produced inclusions, and the stretchability of the inclusions is lowered, causing surface defects. On the other hand, if it exceeds 10 mass%, Mg in the molten steel exceeds 0.001 mass%, so that the inclusions produced are mainly MgO.Al ₂ O ₃ , which also causes surface defects. Therefore, it is preferable to control MgO in the slag within a range of 2 to 10 mass%. Preferably it is 2.4-9.5 mass%, More preferably, it is the range of 3.5-9.0 mass%.

Al ₂ O ₃ : 0.2 to 10 mass%
If Al ₂ O ₃ in the slag is less than 0.2 mass%, the Al content in the molten steel is less than 0.0001 mass%, and it becomes impossible to supply the required amount of Al ₂ O ₃ in the inclusions generated in the steel. The stretchability of inclusions is hindered and causes surface defects. On the other hand, if it exceeds 10 mass%, Al ₂ O ₃ in the inclusions exceeds 40 mass%, and the melting point is increased to deteriorate the stretchability. Therefore, _Al 2 _{O 3} in the slag is preferably controlled in the range of 0.2~10mass%.

Si: 0.05-0.40 mass%
Si in the molten steel in the deoxidation step is an element added as a deoxidizer and a desulfurizer and needs to be 0.05 mass% or more. However, if added over 0.40 mass%, the reduction of MgO and Al ₂ O _{3 in} the slag proceeds too much, and MgO · Al ₂ O ₃ and Al ₂ O ₃ inclusions are formed in the molten steel. Cause surface flaws. Therefore, Si is set to 0.05 to 0.40 mass%. Preferably it is the range of 0.05-0.35 mass%.

In the method A or B described above, Fe—Ni—Cr having the component composition shown in Table 1 was melted by an electric furnace-AOD or VOD process and continuously cast to obtain a steel slab.
Specifically, in the method A, a melting raw material mainly composed of Fe and Ni such as iron scrap, ferronickel, pure Ni, etc. is melted in a 60-ton electric furnace, oxidized and refined by AOD, and dephosphorized and decarburized. After that, it is removed, and thereafter quick lime and fluorite are added, and Si and / or Si alloy iron is added to deoxidize and finish desulfurize, then Cr is added, and finally, ladle refining After adjusting the temperature and the final component by adjusting to the component composition shown in Table 1, a steel slab was obtained by a continuous casting method. In addition, what made the dolomite refractory was used for said AOD.
In Method B, melting raw materials mainly composed of low phosphorus (P ≦ 0.06 mass%) Fe, Cr and Ni such as iron scrap, stainless steel scrap, ferronickel, ferrochrome, and pure Ni are melted in a 60-ton electric furnace. Then, after decarburization by oxidation refining with VOD, quick lime and fluorite are added, and Si and / or Si alloy iron is added to reduce Cr, and further, Ar is stirred to deoxidize and finish desulfurize. Finally, temperature adjustment and final component adjustment were performed by ladle refining to adjust the component composition shown in Table 1, and then a steel slab was formed by a continuous casting method. In addition, the said VOD used what used MgO-C as a refractory.
In both methods A and B, the slag composition during deoxidation was controlled to a CaO—SiO ₂ —Al ₂ O ₃ —MgO—F system.
Moreover, the component composition of the alloy was measured by fluorescent X-ray analysis. However, C was performed by an infrared absorption method, and oxygen was performed by an inert gas impulse melting infrared absorption method. Moreover, the component composition of the slag was measured by fluorescent X-ray analysis.

  Thirty non-metallic inclusions included in the positions of the width direction 1/4 and the thickness direction 1/4 of each steel slab obtained as described above were extracted at random, and the components were analyzed by EDS. The average component composition was determined.

The steel slab was then heated to 1200 ° C. and then hot rolled to obtain a hot rolled sheet having a thickness of 4.0 mm, and then further cold rolled to obtain a cold rolled sheet having a thickness of 1 mm. . At this time, for the hot-rolled sheet, the presence or absence and the size (depth of the ear crack) of the edge portion of the steel plate was visually inspected, and those having an ear crack depth of less than 10 mm had good hot workability ( (Circle)) The thing of 10 mm or more was evaluated as inferior hot workability (x). For cold-rolled sheets, the steel sheet surface is visually observed, the occurrence rate per unit area of surface flaws having a length of 15 mm or more is measured, and the average occurrence rate over the entire length of the product coil is less than 1 piece / m ² The surface quality was good (◯), and those having 1 / m ² or more were evaluated as poor surface quality (×).

The measurement results are shown in Table 2. From Table 2, the alloys (Nos. 1 to 7) of the inventive examples having the component composition suitable for the present invention and melted by controlling the slag during refining to the component composition suitable for the present invention, No cracking occurs in the hot-rolled sheet, and the hot-rolled sheet is excellent in hot workability, and the surface flaw generation rate in the cold-rolled sheet is small and the surface property is excellent.
On the other hand, in the alloys of comparative examples (Nos. 8 to 13) in which the component composition (S, N, B, Ti) of the alloy is out of the present invention, large ear cracks occur in the hot-rolled plate in all cases. Furthermore, in the comparative alloys (Nos. 10 to 13) in which the composition of the slag during refining is out of the present invention, the incidence of surface defects on the cold-rolled sheet is high.
From the above results, it can be confirmed that the present invention is extremely effective in improving the hot workability and surface properties of the Fe—Ni—Cr alloy.

  The technology of the present invention is not limited to a high thermal expansion Fe—Ni—Cr alloy. For example, low thermal expansion materials, stainless steel, Fe—Ni alloys, magnetic materials, etc. Can also be applied.

Claims (4)

C: 0.05-0.30 mass%,
Si: 0.05-0.40 mass%,
Mn: 0.05-0.60 mass%,
S: 0.0001 to 0.005 mass%,
P: 0.040 mass% or less,
Ni: 20 to 26 mass%,
Cr: 1 to 6 mass%,
N: 0.02 mass% or less,
B: less than 0.001 mass% and Ti: less than 0.05 mass% ,
Mg: 0.001 mass% or less, Ca: 0.0001 to 0.002 mass%, Al: 0.0001 to 0.01 mass%, and O: 0.0001 to 0.005 mass%, the balance being Fe and inevitable Having a component composition consisting of impurities ;
Nonmetallic inclusions contained in the alloy are MnO—SiO ₂ —Al ₂ O ₃ —MgO—CaO system, and the component composition thereof is MnO: 0.1 to 10 mass%, SiO ₂ : 10 to 40 mass%, A Fe—Ni—Cr alloy for bimetals having Al ₂ O ₃ : 5 to 40 mass%, MgO: 5 to 40 mass%, and CaO: 10 to 40 mass% . After melting raw materials using iron scrap, ferronickel, and pure Ni in an electric furnace, AOD and / or VOD are used to oxidize and refine, dephosphorize, decarburize, and introduce Si and / or Si alloy iron Then, after deoxidizing and finishing desulfurizing, Cr is added to obtain the component composition according to claim 1 , and the method for producing an Fe—Ni—Cr alloy for bimetals. A low phosphorus- melting raw material containing iron scrap, stainless steel scrap, ferronickel, ferrochrome, and pure Ni and having a P content of 0.06 mass% or less is melted in an electric furnace, and then oxidized using AOD and / or VOD. Refining and decarburization, adding Si and / or Si alloy iron to reduce Cr, deoxidation and finish desulfurization to obtain the component composition according to claim 1, characterized in that Fe-Ni- for bimetal Method for melting Cr alloy. In the deoxidation step in which Si and / or Si alloy iron is added, the slag to be generated has a basicity (CaO / SiO ₂ ) of 1 to 6, MgO of ₂ to 10 mass%, and Al ₂ O ₃ of 0.2. controls the _{CaO-SiO 2 -Al 2 O 3} -MgO-F system is ~10mass%, claim 2, characterized by controlling the Si in the molten steel to a range of 0.05～0.40Mass% Alternatively, the method for melting the bimetallic Fe—Ni—Cr alloy according to 3 .

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