JP2009120884A - Method for refining stainless steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover Cr-oxide shifted to slag by decarburization in a stainless steel-refining into the molten steel. <P>SOLUTION: In the operation for recovering the Cr-oxide shifted to the slag into the molten steel by reducing with ferro-Si alloy after oxygen-blowing to make the carbon to be ≤0.03%; the ferro-Si alloy is added the charging quantity pre-calculated as a function of the total blowing quantity. This calculated method is as the followings, that before the actual operation, the pre-operations having different total blowing quantities, are performed at the plurality of times and in one pre-operation, the refining is performed with the ferro-Si alloy of the arbitrary amount. In the case of remaining the Cr-oxide exceeding the prescribed content in the slag, the original charging quantity is calculated by summing up the further needing ferro-Si alloy and the already charged ferro-Si alloy, and the refining is performed in the other pre-operation by the ferro-Si alloy of the arbitrary amount. When the Si content in the molten alloy exceeds a prescribed concentration caused by excessive charging quantity of the ferro-Si alloy, the original charging quantity for making the Si concentration in the molten steel below into a prescribed concentration is calculated from the difference between the added ferro-Si alloy and the excessive Si concentration of the molten steel, and in the respective pre-operation, blowing quantity and the ferro-Si alloy charging quantity is obtained as a regression formula. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for refining stainless steel in the Argon Oxygen Decarburization (hereinafter abbreviated as AOD) method, and relates to a technique for reducing the use of expensive Si alloy iron and efficiently reducing Cr. In particular, the present invention relates to a method for refining stainless steel having a low Si content.

  The decarburization and refining of stainless steel is generally performed by an AOD method or a vacuum oxygen decarburization (hereinafter abbreviated as VOD) method. In the case of the AOD method, the raw materials are usually melted in an electric furnace, the carbon content is adjusted to approximately 1 to 2.5%, transferred to AOD, blown with oxygen or argon-oxygen mixed gas, and decarburized and refined. enter.

  At this time, the Cr component, which is a valuable metal, is not less oxidized by the blown oxygen and moves into the slag. Therefore, after decarburization refining, Si alloy iron is added to the slag in order to reduce this Cr oxide and recover it in the molten alloy. In the case of a relatively general-purpose stainless steel such as SUS304, the Si input amount (Si basic unit) is set as a constant value.

  However, in the case of stainless steel containing a high concentration of Cr and Mo, if the Si content in the molten alloy increases, an intermetallic compound formed of Cr, Fe, Mo, etc., called a sigma phase, is likely to be formed. The resulting alloy may be extremely brittle. In such an alloy, it is necessary to control the Si content that promotes the formation of the sigma phase to be low.

  Since Si is an alloy element and a Cr reducing agent in AOD, control of Si is important. In the case of stainless steel having a relatively high Cr content, there was a problem of insufficient reduction of Cr oxide due to insufficient introduction of Si alloy iron, and conversely, there was a problem of excessive addition of Si.

  Furthermore, stainless steel containing high concentrations of Cr and Mo (0.1 to 0.4 mass% in some cases) is often used for high corrosion resistance, and suppresses the formation of carbides that reduce corrosion resistance. In order to achieve this, decarburization is performed to an extremely low carbon region in the AOD. Due to the high Cr, the blending amount of FeCr containing a large amount of carbon increases, and for that reason as well, the carbon concentration immediately after blending is higher than the normal carbon concentration.

  Therefore, in AOD, since a relatively high C concentration is lowered to an extremely low carbon region, a larger amount of oxygen blowing is required than usual, and the concentration of Cr oxide that is oxidized and moves into slag also increases. End up. For this reason, the subsequent reduction of Cr was also difficult. If the Cr reduction is insufficient, the oxygen and sulfur concentrations are increased, resulting in a problem that hot workability is lowered and cracking occurs during hot rolling.

  Looking at the conventional technology, in order to strengthen the Cr reduction and sufficiently proceed with deoxidation and desulfurization, the amount of Fe-Si alloy corresponding to the amount of Cr and Mn transferred into the slag and further in the molten alloy A technique for setting the Si concentration to 0.4% or more is disclosed (for example, see Patent Document 1). However, this technique cannot produce alloys with a low Si content of less than 0.4%.

Further, a technique is disclosed in which the S concentration is controlled to 20 ppm or less by reducing (Cr ₂ O ₃ ) + (MnO) + (T.Fe) in the slag after Cr reduction to 3% or less (for example, patents) Reference 2). However, there is no specific measure for how to achieve a total amount of 3% or less of (Cr ₂ O ₃ ) + (MnO) + (T.Fe), and the present application is intended. Not applicable to stainless steel.

JP-A-4-99215 JP-A-7-62418

  In the present invention, in the refining of stainless steel, Cr oxide transferred into slag by oxygen blowing in the decarburization step is efficiently and accurately reduced and recovered in the molten alloy using Si alloy iron. Provide technology. In particular, it is an object of the present invention to provide a technique that does not cause excessive addition of Si while avoiding insufficient Cr reduction due to insufficient addition of Si alloy iron with respect to Cr reduction of high Cr-containing stainless steel in which the Si content is limited to be low.

  In the present invention, in order to solve the above-mentioned problems, the present inventors have intensively analyzed the results of Cr reduction with AOD. The analysis was advanced with particular emphasis on SUS312L, SUS329J3L, and SUS329J4L, which are high Cr-containing stainless steels. These steel types are obtained by melting raw materials such as ferrochrome (high carbon ferrochrome alloy is preferable for inexpensive production), iron scrap, Ni, stainless steel scrap, ferromolybdenum, etc. in an electric furnace according to the target composition, and then converting to AOD. The hot water is transferred, decarburized with oxygen, a mixed gas of oxygen and Ar, or a mixed gas of nitrogen and oxygen, and Cr reduction, deoxidation, and desulfurization are performed. Thereafter, the temperature and trace components are adjusted by ladle refining, and the slab is manufactured by casting with a continuous casting machine.

  A very large variation was observed in the Si concentration after Cr reduction and the Cr oxide concentration in the slag. This is presumed to be one of the reasons why these steel types are extremely low carbon steels that require C to be reduced to about 0.03 mass% or less by decarburization. We conducted earnest operation analysis through trial and error. When Cr reduction was insufficient, the Si basic unit required for the Cr oxide in the slag to be a predetermined content (3% for SUS312L, SUS329J3L, and SUS329J4L, which differ for each steel type) was determined. When the amount of Si alloy iron input is excessive and the Si concentration in the molten alloy exceeds a predetermined Si concentration, the amount of added Si alloy iron and the excess Si concentration in the molten alloy (excess Si is melted) The difference between the Si concentration in the alloy and the predetermined Si concentration is shown.) The amount of Si alloy iron input that should have been originally input to suppress the Si concentration in the molten alloy to the predetermined Si concentration is obtained. It was. As a result of various analyzes for calculating the necessary Si basic unit, a good correlation with the oxygen basic unit was obtained. That is, it was found that the Si basic unit needs to be increased as the oxygen basic unit increases. This is because the amount of oxygen blowing is different due to the difference in the initial state (temperature, carbon concentration, Si concentration) in the AOD, and the amount of Cr oxide formed changes accordingly. That is, the higher the oxygen basic unit, the greater the amount of Cr oxide formed and the greater the amount of Si required. In this analysis, it is necessary to plot about 10 points or more in order to maintain accuracy.

FIG. 1 shows SUS329J3L (Fe-5 mass% Ni-22.5 mass% Cr-3.2 mass% Mo-0.16 mass% N), SUS329J4L (Fe-6 mass% Ni-25 mass% Cr-3.3 mass% Mo-0). .15 mass% N) oxygen basic unit and Si basic unit, FIG. 2 shows the oxygen content of SUS312L (Fe-18 mass% Ni-20 mass% Cr-6 mass% Mo-0.8 mass% Cu-0.2 mass% N). The relationship between the basic unit and the Si basic unit is shown. Above the straight line in the figure is a region where the amount of Si input is excessive. In particular, in the present invention, in order to finally proceed with deoxidation and desulfurization using Al, when Al is added, SiO ₂ in the slag is reduced by the reaction represented by the following formula (1), and the molten alloy Inside Si picks up.

3 (SiO ₂ ) +4 Al = 2 (Al ₂ O ₃ ) +3 Si (1)
In formula (1), () indicates that it is in slag, (Underlined part) indicates that it is in metal.

  As described above, Si promotes the formation of sigma phase in the stainless steel of the present application. Therefore, if not suppressed to less than 0.4% after Cr reduction, by adding Al finally, 0.6% It becomes too high and becomes a problem. On the contrary, under the straight line, due to insufficient reduction, it was a region where oxygen and sulfur could not be effectively reduced due to weak deoxidation.

Thus, it was decided to calculate and add using the function indicated by the straight line in the figure. That is, the function is expressed as follows when the Si basic unit (kg / t) is y and the oxygen basic unit (Nm ³ / t) is x.

y = 0.78x-6.14 (in the case of SUS329J3L, SUS329J4L)
y = 0.70x + 2.21 (for SUS312L)

  When the Si basic unit calculated according to the oxygen basic unit is added, Cr reduction is performed, and then limestone and fluorite are added as appropriate, and the components are adjusted together with deoxidation and desulfurization. And deoxidation did not become poor. Subsequently, Al was added to control the oxygen concentration to a preferable level of 30 ppm or less. Since deoxidation proceeded without problems, desulfurization proceeded and the sulfur concentration could be reduced to 0.005% or less. In this way, since the oxygen and sulfur concentrations could be controlled low without adding excessive Si, a slab with excellent hot workability could be obtained without forming a sigma phase that would cause embrittlement. It was. The present invention has been developed based on the above findings.

  That is, the present invention solves the above problems, and the method for refining stainless steel according to the present invention comprises melting a raw material to form a molten alloy, and in a decarburization step in AOD, oxygen, argon-oxygen mixed gas, or nitrogen In an operation in which oxygen mixed gas is blown into a molten alloy to reduce the carbon concentration to 0.03% or less, and Cr oxide transferred into slag by blowing is reduced by Si alloy iron and recovered in the molten alloy. , Si alloy iron is to add the input amount calculated in advance as a function of the total oxygen blown amount in the decarburization process, and the calculation method of the Si alloy iron input amount is the same as before the main operation of refining stainless steel. In addition, multiple preliminary operations with different total oxygen blowing rates are performed, and in one preliminary operation of multiple preliminary operations, an arbitrary amount of Si alloy iron is introduced and refined, for each steel type. If Cr oxide exceeding the determined Cr oxide content remains in the slag, further addition is necessary to keep the residual Cr oxide in the slag below the predetermined Cr oxide content The total amount of Si alloy iron input and the amount of Si alloy iron input that has already been added are summed up to obtain the amount of Si alloy iron input that should have been originally input, and it is optional in other preliminary operations among multiple preliminary operations When the amount of Si alloy iron is excessive and the Si concentration in the molten alloy exceeds a predetermined Si concentration, the amount of added Si alloy iron and In order to suppress the Si concentration in the molten alloy below the predetermined Si concentration from the difference in the excess Si concentration in the molten alloy (excess Si indicates the difference between the Si concentration in the molten alloy and the predetermined Si concentration). Of the amount of Si alloy iron that should have been originally introduced In addition, an optimum Si concentration in the molten alloy after reduction of Cr oxide is obtained according to a condition in which a function of oxygen blowing rate and Si alloy iron input is set as a regression equation by a plurality of preliminary operations. Further, the deoxidation and desulfurization are performed by adding 2 to 10 kg / t of Al.

  In this invention, it is set as the preferable aspect that Si concentration in the molten alloy after Cr reduction | restoration is less than 0.4%. The chemical components of stainless steel are: C: 0.003 to 0.03%, Si: 0.1 to 0.6% or less, S: 0.005% or less, Cr: 11 to 35%, Ni: 40 % Or less, Al: 0.005 to 0.1%, balance iron or unavoidable impurities is a preferred embodiment. Furthermore, Mo: 1 to 18%, Cu: 3% or less, W: 5% or less, and Co: 3% or less may be included. In addition to the above, it is preferable that B: 5 to 70 ppm and oxygen: 30 ppm or less.

  According to the present invention, since the oxygen concentration and sulfur concentration of stainless steel can be effectively reduced, a slab with good workability can be obtained. As a result, cracks do not occur during hot rolling, and the product yield can be kept high.

The best mode for carrying out the present invention will be described.
FIG. 3 is a schematic diagram showing an alloy manufacturing process in the present invention. Reference symbol A denotes an electric furnace (EF), and as a melting step, raw materials such as ferrochrome, iron scrap, Ni, and stainless scrap are melted in accordance with a target composition. As a refining process, the melted raw material is transferred from electric furnace A to oxygen blowing furnace B (AOD) and decarburized with oxygen or a mixed gas of oxygen and Ar (in some cases, a mixed gas of nitrogen and oxygen). , Cr reduction, deoxidation and desulfurization are performed, and then the temperature and trace components are adjusted by ladle refining.

  Subsequently, the molten alloy is cast into the casting pot of the casting machine to perform casting. The code | symbol C of FIG. 3 is a schematic diagram of a continuous casting machine (Continuous Casting Machine, CCM). The casting machine shown in FIG. 3 is a vertical casting machine in which a molten alloy is supplied from above and a slab is sent downward. Since many elements are added in high alloys, cracks tend to easily occur when bent when cooled and hardened. However, in a vertical type device, it is difficult to apply an unreasonable force and is suitable for high alloys. Used as However, the continuous casting machine is preferably a vertical type, but is not limited thereto.

  Finally, a molten alloy is cast by the CCM shown in FIG. 3 to produce a slab. In FIG. 3, reference numeral 10 denotes an pouring pan, and the molten alloy 20 that has undergone the melting process and the refining process is put into the pouring pot 10. Subsequently, the molten alloy 20 is supplied to the mold 12 through the tundish 11 provided on the downstream side of the pouring pan 10 and is put into the mold. The molten alloy 20 poured into the mold is solidified by passing through a spray cooling zone 13 provided on the downstream side, and is drawn by the pinch roll 14 to obtain a slab 21 having a predetermined thickness. Moreover, the slab 21 is cut | disconnected by the torch 15 in a predetermined position, and a final product is obtained through required processes, such as rolling.

This invention relates to the operation method of Cr reduction | restoration after the decarburization in AOD among the said processes, and demonstrates it in detail below.
In the decarburization process in AOD, after oxygen and argon oxygen mixed gas is blown, the carbon concentration targeted by the present application is reduced to 0.03% or less. Thereafter, Si alloy iron is used as a reducing agent in order to reduce the Cr oxide transferred into the slag and recover it in the molten alloy. As described above, when the Si input amount is insufficient, the Cr oxide is not sufficiently reduced and recovered in the molten alloy. Conversely, when the Si input amount is excessive, The Si concentration increases, which is not preferable. Thus, it is not preferable that the Si input amount is too large or too small, and since strict control is required, the Si input amount is calculated as a function of the total oxygen blowing amount in the decarburization process, and is necessary. Add sufficient amount.

The method of deriving the regression equation as the function is as follows.
The preliminary operation for deriving this function is performed several times before the main operation. The number of preliminary operations is required to be at least about 10, and the function of the required Si input amount is analyzed using the result. In the preliminary operation, an arbitrary amount of Si alloy iron is put into operation and the slag is analyzed. As a result, when excessive Cr oxide remains in the slag, that is, Cr reduction by Si is insufficient. If it is found that the residual Cr oxide in the slag is less than a predetermined content (determined for each steel type, 3% for SUS312L, SUS329J3L, and SUS329J4L), the amount of Si input that needs further addition From the sum of the amounts of Si that had already been added, the basic unit of Si that was originally required was determined.

  Conversely, in other preliminary operations, similarly, an arbitrary amount of Si alloy iron is put into operation, and as a result, when too much Si alloy iron is thrown in, that is, excess Si is transferred to the molten alloy. If the Si concentration in the molten alloy exceeds the predetermined Si concentration, the Si concentration in the molten alloy is determined from the difference between the added Si amount and the excess Si concentration in the molten alloy after Cr reduction. The originally required Si basic unit that effectively acted on Cr reduction while being suppressed below the predetermined Si concentration was determined.

At that time, limestone and fluorite are appropriately added to form a slag having an appropriate fluidity. By this operation, the Cr oxide in the slag is reduced to 8% or less, and the Si concentration at the time when the Cr reduction is completed can be controlled to less than 0.4%. If it is 0.4% or more, subsequently added Al will reduce SiO ₂ in the slag, and the Si concentration in the molten alloy will eventually exceed 0.6%. The slag formed at this time may be temporarily discarded. In case of excretion, add limestone and fluorite again to make slag.

After Cr reduction by Si, 2 to 10 kg / t of Al is added for deoxidation and desulfurization. The slag composition is a system composed of CaO, SiO ₂ , MgO, Al ₂ O ₃ , and F. MgO is mixed due to erosion damage of dolomite or magcro, which is an AOD refractory. A CaO / SiO ₂ ratio of 2 or more is preferable in promoting deoxidation and desulfurization.

  As described above, the critical concentration of Cr oxide in the slag targeted by the operation for obtaining the regression equation for calculating the Si basic unit is 3% for SUS312L, SUS329J3L, SUS329J4L, for example. Is different for each steel type. Table 1 shows the critical concentration of Cr oxide for each steel type. As shown in Table 1, for example, in the case of SUS304, this concentration is 1%. Therefore, in a preliminary operation for creating a regression equation, an arbitrary amount of Si alloy iron is introduced and the slag is reduced. As a result of the analysis, when Cr reduction by Si was insufficient, from the sum of the Si input amount that needs to be further added to reduce the residual Cr oxide in the slag to 1% or less and the Si input amount that has already been added, The Si basic unit that was originally necessary is obtained, and a regression equation is created. The critical concentration of Cr oxide is an indicator of the concentration set in order to reduce the Cr oxide by introducing Si alloy iron and keep the Si concentration at less than 0.1% in the molten alloy. .

  Also, the above-mentioned predetermined Si concentration means that when the Cr oxide remaining in the slag after the reduction of Cr oxide exceeds the predetermined critical concentration of Cr oxide, the Si concentration in the molten alloy remains in the slag. This is an index when Si alloy iron is added until the Cr oxide to be obtained reaches a predetermined Cr oxide critical concentration.

Next, chemical components of the stainless steel of the present invention will be described.
C: 0.003 to 0.03%
C is an element necessary for ensuring the strength of stainless steel. However, if it exceeds 0.03%, Cr carbide is formed and the corrosion resistance is lowered. Therefore, it was set as 0.003 to 0.03%. Preferably, it is 0.005 to 0.025%.

Si: 0.1-0.6%
Si is an element necessary for Cr reduction and deoxidation. However, excessive addition exceeding 0.6% promotes sigma phase formation that embrittles the steel. Therefore, it was determined as 0.1 to 0.6%. By calculating the Si basic unit using the above regression equation and introducing Si, the upper limit of 0.6% or less can be satisfied by suppressing the Si concentration to less than 0.4% after Cr reduction. Preferably, it is 0.2 to 0.55%, more preferably 0.25 to 0.55%.

S: 0.005% or less Since S is an element that decreases hot workability, the content is set to 0.005% or less. It can be controlled by reducing Cr by the above operation and deoxidizing by adding 2 to 10 kg / t of Al. Preferably, it is 0.004% or less, more preferably 0.003% or less.

Cr: 11-35%
Cr is an element necessary for generating a non-conductive film on the surface of steel and ensuring corrosion resistance. If it is less than 11%, the effect cannot be obtained, and if it exceeds 35%, the hot strength becomes remarkably high and hot working becomes difficult. Therefore, it was set to 11 to 35%. In addition, this invention is more effective in the 19 to 30% region where the Cr content is relatively high.

Ni: 40% or less Since Ni is an element that stabilizes the austenite phase, it may be added within a range of 40% or less.

Al: 0.005 to 0.1%
Al is an element necessary for the progress of deoxidation and desulfurization. However, excessive addition exceeding 0.1% may form AlN and reduce hot workability. Further, SiO ₂ in the slag is excessively reduced, and the Si concentration is increased to more than 0.6%. Therefore, it was set as 0.005 to 0.1%. After reduction of Cr by Si, this range can be controlled by adding 2 to 10 kg / t of Al. Preferably, it is 0.01 to 0.07%, more preferably 0.01 to 0.06%.

Other element components In addition to the above elements, Mo: 1 to 18%, Cu: 3% or less, W: 5% or less, Co: 3% or less, from the viewpoint of corrosion resistance It may be contained. Furthermore, B may contain 5 to 70 ppm for the purpose of improving hot workability. Since oxygen reduces hot workability, it is preferable that oxygen be low, and it is preferable to suppress it to 30 ppm or less.

  An example is shown concretely and the effect of the present invention is explained. In addition, the Example described here is about SUS329J3L, SUS329J4L (FIG. 1), and SUS312L (FIG. 2).

  In a 60-ton electric furnace, raw materials such as ferrochrome, iron scrap, Ni and stainless steel scrap are melted to the desired composition, then transferred to AOD, decarburized with oxygen or a mixed gas of oxygen and Ar, Cr Reduction, deoxidation, and desulfurization were performed. In the decarburization step in AOD, the carbon concentration was lowered to 0.03% or less after blowing oxygen and argon-oxygen mixed gas. Thereafter, in the operation of reducing the Cr oxide transferred into the slag and recovering it in the molten alloy, a ferrosilicon alloy is used as the reducing agent, and the amount of Si input is calculated as a function of the total oxygen blowing rate in the decarburization process. And added.

  The method of deriving the regression equation as the function was as follows. Preliminary operations were performed 10 times, and the results were used for analysis. When Cr reduction was insufficient, the Si basic unit necessary for the Cr oxide in the slag to be 3% was determined. Conversely, when too much reducing agent Si was added, the Si basic unit that effectively acted on Cr reduction was determined from the difference in Si concentration between the added Si and the molten alloy after Cr reduction.

In the Cr reduction operation, limestone and fluorite were appropriately added to form slag having appropriate fluidity. The slag formed at this time was once discarded, and limestone and fluorite were added again as appropriate to form slag. The slag composition was a system composed of CaO, SiO ₂ , MgO, Al ₂ O ₃ , and F. Thereafter, Al was added to proceed with deoxidation and desulfurization. In some comparative examples, there was an example that was not intentionally added.

  After refining at AOD, temperature and trace components were adjusted by ladle refining, and cast by a continuous casting machine to produce a slab. The surface of the slab was ground and hot rolled to form a hot rolled sheet. After this hot-rolled sheet was pickled, the state of occurrence of lashes was visually inspected. The position where the lashes are generated is mainly 100 to 300 mm from the end of the coil. FIG. 4 shows a typical wing photographed from the surface. The feature is that it has a cover shape.

Each measurement and evaluation method was as follows.
Slug in the Cr ₂ O ₃ concentration after the reduction: After slag is collected grinding, making the tablet, was determined by X-ray fluorescence analysis.
-Si concentration after reduction: A molten alloy was collected and determined by fluorescent X-ray analysis.
-Final component: A molten alloy sample was collected, and other than N and O were determined by fluorescent X-ray analysis. N and O were determined by an inert gas impulse melting infrared absorption method.
-Appearance on hot-rolled sheet: Evaluated by the frequency of occurrence of lashes. ◎: 10 or less in the coil, ○: More than 10 in the coil, but can be removed by coil grinding, ×: Degradable that cannot be removed by coil grinding

[Example 1]
SUS329J3L
Table 2 shows examples of SUS329J3L. Invention Example No. 1 to 4 were all within the scope of the present invention, Si unit, Cr ₂ O ₃ concentration in the slag after reduction, Si concentration after reduction, and Al unit. Therefore, both S and O of the final component were lowered, and the appearance on the hot-rolled sheet was good, i.e., ◎ or ○.

  On the other hand, in the comparative example, since one of the conditions was not met, many defects were observed in the hot rolled sheet. In Comparative Examples 1 and 3, since the Si basic unit was lower than the oxygen basic unit, the reduction was insufficient, and both oxygen and sulfur were high. Comparative Example 1 was higher in oxygen than Comparative Example 3 because Al was not further added. In Comparative Examples 2 and 4, since the Si basic unit was higher than the oxygen basic unit, the Si concentration after the reduction exceeded 0.4%. Therefore, the final Si concentration was also higher than 0.6%, and it became brittle due to sigma phase formation, resulting in defects in the hot-rolled sheet.

[Example 2]
SUS329J4L
Table 3 shows examples of SUS329J4L. Invention Example No. 5 to 10 were all within the scope of the present invention, including Si basic unit, Cr ₂ O ₃ concentration in the slag after reduction, Si concentration after reduction, and Al basic unit. Therefore, both S and O of the final component were lowered, and the appearance on the hot-rolled sheet was good, i.e., ◎ or ○.

  On the other hand, in the comparative example, since one of the conditions was not met, many defects were observed in the hot rolled sheet. In Comparative Examples 6, 7, 8, and 10, since the Si basic unit was lower than the oxygen basic unit, the reduction was insufficient and both oxygen and sulfur were high. In Comparative Examples 7 and 10, since Al was not further added, the oxygen concentration was higher than the others. In Comparative Examples 5 and 9, since the Si basic unit was higher than the oxygen basic unit, the Si concentration after the reduction exceeded 0.4%. Therefore, the final Si concentration was also higher than 0.6%, and it became brittle due to sigma phase formation, resulting in defects in the hot-rolled sheet.

[Example 3]
SUS312L
Table 4 shows examples of SUS312L. Invention Example No. Nos. 11 to 14 were all within the scope of the present invention, including Si basic unit, Cr ₂ O ₃ concentration in the slag after reduction, Si concentration after reduction, and Al basic unit. Therefore, both S and O of the final component were lowered, and the appearance on the hot-rolled sheet was good, i.e., ◎ or ○.

  On the other hand, in the comparative example, since one of the conditions was not met, many defects were observed in the hot rolled sheet. In Comparative Examples 11 and 13, the Si basic unit was high, the Si concentration after reduction was higher than 0.4%, and the final Si concentration was also higher than 0.6%. Therefore, it became brittle due to sigma phase formation, resulting in defects in the hot rolled sheet. In Comparative Examples 12 and 14, on the contrary, the Si basic unit was low, and the oxygen and sulfur concentrations were high. Particularly in Comparative Example 12, since no Al was added, the oxygen and sulfur concentrations were particularly high.

  As described above, in the method for refining a stainless alloy of the present invention, a preliminary operation is performed before the main operation to obtain a regression equation indicating the relationship between the Si basic unit and the oxygen basic unit. Therefore, it is not necessary to analyze the components for each operation, and the necessary and sufficient amount of Si alloy iron can be determined according to the regression equation.

  It is possible to efficiently produce a high Cr-containing stainless steel alloy in which the Si concentration is reduced and sigma phase formation is suppressed.

It is a graph which shows the relationship between the Si basic unit and oxygen basic unit of SUS329J3L and SUS329J4L in this invention. It is a graph which shows the relationship between Si basic unit and oxygen basic unit of SUS312L in this invention. It is a schematic diagram which shows the manufacturing process of the stainless alloy of this invention. It is an optical microscope photograph of the baldness produced at the time of rolling of a stainless alloy.

Explanation of symbols

A Electric furnace B Oxygen blowing furnace C Continuous casting machine 10 Pouring pan 11 Tundish 12 Mold 13 Spray cooling zone 14 Pinch roll 15 Torch 20 Molten alloy 21 Slab

Claims (6)

A method for refining stainless steel, in which a raw material is melted to form a molten alloy, and in the decarburization process in AOD, oxygen, argon-oxygen mixed gas, or nitrogen-oxygen mixed gas is blown into the molten alloy to reduce the carbon concentration. In the operation of reducing to 0.03% or less and reducing the Cr oxide transferred into the slag by the above blowing to the molten alloy by reducing with the Si alloy iron,
The Si alloy iron is to add the input amount calculated in advance as a function of the total oxygen blowing amount in the decarburization step,
The calculation method of the input amount of the Si alloy iron is as follows:
Prior to the main operation of refining the stainless steel, a plurality of preliminary operations with different total oxygen blowing rates are performed,
In one preliminary operation of the above-mentioned multiple operations, an arbitrary amount of Si alloy iron is introduced and refined, and Cr oxides exceeding a predetermined Cr oxide critical concentration determined for each steel type are slag. In the case where the residual Cr oxide remains in the slag, the amount of Si alloy iron that needs to be further added to bring the residual Cr oxide in the slag to the above-mentioned critical Cr oxide critical concentration is combined with the amount of Si alloy iron that has already been added. Then, the amount of Si alloy iron input that should have been originally input is obtained,
In other preliminary operations among the plurality of preliminary operations, an arbitrary amount of Si alloy iron is charged and refining is performed. The amount of Si alloy iron input is excessive and the Si concentration in the molten alloy is a predetermined value. When the Si concentration was exceeded, it should have been originally introduced in order to suppress the Si concentration in the molten alloy to a predetermined Si concentration from the difference between the amount of added Si alloy iron and the excess Si concentration in the molten alloy. Determine the amount of Si alloy iron input,
According to the conditions in which the function of the oxygen blowing amount and Si alloy iron input amount is a regression equation by each of the plurality of preliminary operations, an optimum Si concentration in the molten alloy after Cr oxide reduction is obtained,
Furthermore, the refining method of stainless steel characterized by adding 2-10 kg / t of Al, and deoxidizing and desulfurizing.   The method for refining stainless steel according to claim 1, wherein a predetermined Si concentration used in a preliminary operation for obtaining the regression equation is 0.1%.   3. The method for refining stainless steel according to claim 1, wherein the Si concentration in the obtained molten alloy after reduction of the Cr oxide is less than 0.4% under the condition of the regression equation.   The chemical composition of the stainless steel is C: 0.003 to 0.03%, Si: 0.1 to 0.6%, S: 0.005% or less, Cr: 11 to 35%, Ni: 40% or less, The method for refining stainless steel according to any one of claims 1 to 3, comprising Al: 0.005 to 0.1%, balance iron or inevitable impurities.   The stainless steel contains one or more of Mo: 1 to 18%, Cu: 3% or less, W: 5% or less, and Co: 3% or less. The method for refining stainless steel as described. 6. The method for refining stainless steel according to claim 4, wherein the stainless steel contains B: 5 to 70 ppm and oxygen: 30 ppm or less.

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