JPH0499215A - Production of stainless steel for mirror-like finishing - Google Patents

Abstract

PURPOSE:To reduce Al2O3 type inclusions by reducing the total content of Al in a raw material for electric furnace melting and reducing Al content in a molten crude stainless steel. CONSTITUTION:A crude stainless steel is prepared by carrying out electric furnace melting while blending the raw material so that the total content of Al in the raw material for melting is regulated to <=0.020kg per ton of molten crude steel. The molten crude steel is subjected to AOD decarburization, and reduction is performed in the course of this carburization. The content of Si in the molten steel after the completion of reduction stage is regulated to >=0.40%. In a finishing stage, metallic Al is not used for deoxidation regulation, and heat elevation by means of Si addition is not exerted. The resulting refined stainless steel is subjected to continuous casting at 0.67-0.80m/min pouring rate.

Description

[Detailed description of the invention]

(Industrial Application Field) This invention relates to a method for manufacturing stainless steel that is used after being cold-rolled to a mirror finish. Concerning a method of manufacturing steel. (Prior art) Mirror-finished stainless steel used for decorative layers, reflective mirrors, etc. Using steel equivalent to LIS 5US304, etc., it is usually melted in an AOD smelting furnace, then continuously cast, and after the surface of the slab is treated, it undergoes the processes of hot rolling, pickling, cold rolling, and bright annealing. Finally, it is manufactured by performing puff polishing. As mentioned above, mirror-finished stainless steel sheets are finally pub-polished, so even minor scratches appear on the surface and are easy to detect, so the quality grade required for cold-rolled sheets is extremely high. The occurrence of underground formations is said to be caused by Al zfh inclusions generated during the melting process that remain undeformed even during rolling. This A
l Gos-based inclusions are difficult-to-process inclusions and exist in clusters without being stretched or divided by rolling. Therefore, it is necessary to reduce the Al gos-based inclusions present in steel as much as possible, and in particular, in order to obtain high-quality mirror-finished stainless steel sheets, it is necessary to reduce the underground occurrence rate caused by Al-O inclusions. It needs to be made smaller. (Problem B to be solved by the invention) The problem of the present invention is to provide mirror-finished stainless steel.
The purpose is to manufacture steel with less underground formation, and the specific purpose is to provide a new method for manufacturing stainless steel with fewer Al x Ch inclusions by improving the process from melting and refining to casting. There is a particular thing. (Means for Solving Problem 1) The present inventors have discovered that it is possible to reduce the amount underground by improving the electric furnace melting process, the AOD refinement process, and the continuous casting process. The gist of the present invention is a method for producing mirror-finishing stainless steel characterized by the following (1) to (2). ■ The total A2 content of the molten raw materials is 0.0% per ton of crude molten steel.
Crude molten stainless steel is obtained by melting in an electric furnace with a raw material composition of 0.020 kg or less. ■ The crude stainless steel molten steel is subjected to AOD decarburization, and during the process, reduction is performed. ■ After the reduction process? [SI] in 8 steels shall be 0.40% or more. ■ In the finishing process, metal Al is not used for deoxidation adjustment and S
Do not raise the temperature by adding i. ■ Stainless steel refined by the above method is 0.67~0.
．． Continuous casting is performed at a casting speed of 80 m/min. Normal AOD refining of stainless steel is performed in the following steps. Melting mouth! Charge high carbon ferrochrome such as charged chromium, ferronickel or nickel oxide, ferrosilicon, stainless steel scrap and ordinary steel scrap mixed according to LCR and Ni content into an electric furnace, and add lime for slag making. Dissolve by applying electricity. To reduce metal oxidation loss during melting,
The amount of Si added is usually about 0.5%, and the lime for slag is melted at the minimum amount necessary to adjust the basicity to 1.0 to 1.5. Crude stainless molten steel melted in a needle steam coal-fired electric furnace, etc. is transferred to an AOD furnace, and 0□ gas or a mixed gas of 0□ and Ar or N is blown at the bottom to generate a CO reaction, and the temperature is increased to a predetermined value. decarburize up to ■-” L: In the decarburization process, Cr generated by simultaneous oxidation with Cr in molten steel
This is a step of reducing oxides of Mn and Mn, using ferrosilicon as a reducing agent, and blowing Ar gas from the bottom to proceed with the reduction reaction while strongly stirring the molten steel. Phantom-ILk-Step After completion of the reduction, use ferrosilicon or Al to lower the (0) level in the molten steel and adjust the components and temperature. If it is necessary to raise the temperature of the molten steel, ferrosilicon is added and 0□ gas is blown from the bottom to oxidize and heat up the molten steel (St), so-called Si blowing. is carried out,
In the electric furnace melting process, the ferroalloy to be melted is (1,01-0
,02% by weight of A1, and since some scraps contain Al, A1 is added to the crude stainless steel after melting.
I! , is dissolved and remains, and in the next decarburization process, it is oxidized and most of it becomes Affi 10. Therefore, it is included in the steel. In the reduction process, dirosilicon (usually used as a reducing agent) contains AI! is contained in an amount of about 2%, and a portion of it is dissolved in the molten steel after reduction. In the molten steel after reduction (Si
) is low or when Si blowing (01 blowing) is performed in the finishing process? Of the 8 ropes

When the [0] level becomes high, the trace amount of remaining CA1 in the molten steel is oxidized, resulting in AN, 0. generate. As mentioned above, under conventional refining conditions, AQ generated in molten steel during the refining process is 0. A part of the steel remains in the solidified steel, causing ground pressure in the cold-rolled plate (this ground pressure is not so much of a problem with normal (non-mirrored) plates, but
This is a problem for mirror-finished plates that are subjected to puff polishing. (Operation) Compared with the conventional refining process described above, the characteristics of the refining process of the method of the present invention are in the above-mentioned points 1 to 2. These will be explained in detail below. ■ By keeping the total A1 content of the raw material melted in the electric furnace low and reducing the [1] content in the crude stainless steel molten steel, 1□0. Inclusions in the system can be reduced. Figures 1 and 2 show 18% Cr-8% Ni steel (J
IS-5US304 equivalent) mirror-finished steel sheets were manufactured under the conditions shown in the examples below, and the total Al content of the raw material charged in the electric furnace and the ^2□0. These are the results of investigating the relationship between *t and underground occurrence tendency. As shown in Figure 1, when the total Al content of the raw material charged in the electric furnace increases, the amount of [^N] in the crude molten stainless steel increases, and the amount of [^N] (Af) in the melting atmosphere or the blowout during the decarburization process increases. Since it combines with the included O and remains in the steel, A l , 0. The generation of system inclusions increases. In addition, Al2o generated by oxidation of Al in the charged raw material
s is mainly removed by floating to the surface of the molten steel during stirring of the molten steel by the CO gas generated during the decarburization process, and its residual rate is approximately 19 to 35.
%. In addition, as shown in Figure 2, when the total Al content of the raw material charged in the electric furnace is high and there are many He2□03-based inclusions, the underground grade will be lower than 3, causing problems in practical use as a specular plate. is occurring. Furthermore, underground results 1, 2.3.4 and 5 are as follows:
The underground % defined by the following formula is 0~2% and 3~
4%, 5-6%, 7-9%, and 10% or more, underground performance of 1.2 is ranked A, 3 is ranked B, and up to this point is evaluated as underground with no practical problems as a mirror plate. ing. However, A is a count number in which the coil is divided into sections of 2 m, and 1 is the case where there is an underground section. That is, for example, if there is one underground part in a 200 m long coil, the underground percentage is 1%. In the method of the present invention, the stainless steel scraps and ferroalloys to be charged into the electric furnace are selected from those with a known AN content, and are all self-generated stainless steel scraps that do not use ordinary steel scraps that normally contain Al. We have taken measures such as reducing the amount of charged chromium with a high A2 content and reducing the amount of AI used in charging raw materials for electric furnaces. Content: 0.020kg/crude molten steel 1. It should be kept below. ■ In the method of the present invention, AOD decarburization step (for example, (C)
In the middle of decarburization (decarburization) from = 1.50 wt.% to 0.06 wt.%, for example, at CC = 0.4 wt.%, the 02 blowing was interrupted, and the carbon was oxidized by the 02 blowing in low Al ferrosilicon. After preliminary reduction of the CrzO*, the CrzO* was reduced to 0. By blowing, for example, [C]=0°0
Decarburize to 6% by weight. This reduces the amount of low Al ferrosilicon used in the final reduction step. AIV in low Al ferrosilicon added during intermediate reduction
, again generates Al goz during decarburization, but as mentioned above, the CO gas produced during decarburization? 8 Steel floats to the surface of the molten steel by stirring, and the amount of production is 120. On the other hand, AN in low-Al ferrosilicon, which is added in the reduction process after decarburization is complete, remains in the molten steel.
0) to produce A N , 0. However, since the stirring of the molten steel is weak at this time, they tend to remain as 1.0° inclusions. Therefore, if the amount of low Af ferrosilicon used in the final reduction process is reduced during the intermediate reduction, low Al ferrosilicon will be produced. The amount of Af, O, produced by AN in silicon is reduced, and the amount of Al remaining in molten steel during casting is reduced to 0. The amount of inclusions in the system is smaller than when no intermediate reduction is performed. In addition, in the method of the present invention, in order to prevent Al zch inclusions from remaining in the molten steel, metal A2 is not used for de#ing adjustment in the finishing process for the same reason as described above. ■ and ■ By keeping [S1] above a certain value after the reduction process, the oxygen [0] level in the molten steel is lowered, and a trace amount of [A/!] remains in the molten steel after reduction. ] A produced by reacting with
The amount of generated tCh-based inclusions is reduced. Figure 3 shows 18% Cr-8% Ni steel (JIS-SIJ
This is the result of investigating the relationship between the amount of Sil and the underground generation tendency after the completion of the reduction process by manufacturing a mirror-finished steel plate (equivalent to S304) under the conditions shown in the example below. As shown in Figure 3. As the value of , after reduction (Si) increases, the tendency for underground generation decreases.In addition, O in the figure indicates that the heating by adding 51 was not carried out in the finishing process of smelting. If the value after reduction (Si) is 0.40% or more, the ground scratch score will be 3 or less, and there will be no problem in practical use as a mirror plate. As shown in the figure, if Si blowing heat raising is performed after Si addition in the finishing process (even if the Si3 content is 0.40% or more, underground formation will occur more often). The oxidation reaction heat of the blown (Si) is used, but the trace amount of (AA) remaining in the steel and the blown 02
The reaction is A i! This is thought to be because gos is generated. Therefore, in the method of the present invention, Si blowing heating is not performed during the finishing period. A specific method for increasing (Si) to 0.40% or more after the reduction process is to calculate the oxidation amount of (Cr) and (Mn) from the (Cr) and [PIN] contents in the molten steel before and after decarburization. The total amount of ferrosilicon, which is the amount of ferrosilicon required to reduce the metal oxide and the amount of ferrosilicon required to make (Si) in the molten steel 0.40% or more, is removed. It is added to molten steel after charcoal is finished. By securing (Si) 20.40% in this way, the (0) level during refining is reduced, resulting in A/!
, 0. The total number of inclusions in the system is reduced. By taking the above-mentioned measures to (3), the underground density caused by Az, O, and inclusions can be significantly reduced. Next, the conditions for continuous casting mentioned above will be explained. ■ Figure 4 shows the CrlB%-N48% steel (JIS 5
Mirror finish (equivalent to US304)! These are the results of examining the relationship between the casting speed of continuous casting and the tendency for underground formation by refining a ll plate under the conditions of the method of the present invention shown in the examples below. As shown in FIG. 4, if the pouring speed of continuous casting is increased, the tendency to order underground becomes smaller. Casting speed is 0.67m
/min or more, the base paper score of the mirrored board will be 3 or less. This is thought to be due to the fact that by increasing the casting speed, the flow rate of molten steel in the mold was kept high, and the cleaning effect of the solidified shell was increased. If the casting speed is less than 0.67 m/min, a sufficient cleaning effect of the solidified shell cannot be obtained;
．． If the speed is 80m/min, there is a risk of flaking out. (Example) Raw materials having the composition shown in Table 1 were charged into an electric furnace and melted to produce crude stainless steel molten steel having the composition shown in Table 2. After that, it is refined in an AOD furnace under the two operating conditions shown in Table 3.
Steel equivalent to JIS-5tlS304 having the composition shown in the table was manufactured. (Hereafter, blank space) After AOD scouring, 1200mm width, 2
06--thickness of slabs from 0.67 to 0.8 in the method of the present invention
Casting was performed at a casting speed of 0 m/min and 0.60 to 0.65 m/min for the comparative method, and after surface treatment, it was heated to 1200°C and rolled to a thickness of 3.6 mm using a continuous hot rolling mill. This hot-rolled sheet was pickled and firstly cold-rolled to a thickness of 1.51 in a continuous cold rolling mill, bright annealed, and then secondly cold-rolled in a temper mill to a thickness of 1.49.
A 5m thick thin steel plate was manufactured. The steel plate thus obtained was puff polished under #700 conditions, and the rate of ground pressure generation was investigated. The results are shown in Table 5. In Table 5, the examples of the present invention refer to steel plates manufactured by the method of the present invention shown in Tables 1 and 3, and the comparative examples refer to steel plates manufactured by the comparative method. It is. Table 5 (Effects of the Invention) According to the production method of the present invention, Aj'ZOY system intervention@! I!
This can reduce the ground pressure caused by this. the result,
It becomes possible to manufacture high-quality mirror-finished stainless steel sheets. Note that the reduction in ground pressure also helps improve the workability and plating properties of mirror-finished plates.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the total 1 content of the raw material charged in the electric furnace and the AltOff content lid in the molten stainless steel before casting. Figure 3 is a diagram showing the relationship between C3l) after the end of the reduction process and the presence or absence of Si blowing heat raising and the direction of ground pressure generation around 1. Figure 4 is a diagram showing the relationship between the generation tendency and FIG. As shown in Table 5, in the examples of the present invention, the ground pressure generation rate is extremely small. Applicant Nippon Stainless Co., Ltd. Representative Patent Attorney Terutada Hogami (and 1 other person) Chilling damage to drawings Figure 1 (defective) Cleaning of drawings Figure 2 Total AL content in electric furnace melting raw materials t (kg/ton of crude molten steel) ) Total A4 content of raw materials melted in electric furnace (kg/ton crude molten steel) Procedural amendment (November 22, 1990, 1990 Patent Application No. 210641 2, Title of invention: Manufacture of stainless steel for mirror finishing) Method 3: Relationship with the case of the person making the amendment Patent Applicant Address: 8-2 Motoshio-cho, Shinjuku-ku, Tokyo Name: Nippon Stainless Co., Ltd. 7 Contents of the amendment Figures 1 to 4 will be amended as shown in the attached sheet. 8. Revised catalog of attached documents Figures 1, 2, 3 and 4. 4. Agent

Claims (1)

[Claims] The total Al content of the molten raw material is 0.02 per ton of crude molten steel.
Crude stainless steel molten steel melted in an electric furnace with a raw material composition of 0 kg or less is decarburized by AOD, and reduction is performed midway through the AOD decarburization process to reduce [Si] in the molten steel to 0.40% after the reduction process is completed.
With the above, in the finishing process, metal Al is not used for deoxidation adjustment, and refining is performed without heating by adding Si, and 0.67
A method for producing stainless steel for mirror finishing, characterized by continuous casting at a casting speed of ~0.80 m/min.