JPS596315A - Manufacture for stainless steel - Google Patents

Abstract

PURPOSE:To obtain the super clean steel containing extremely low oxygen by converting MnO.SiO2, MnO.Cr2O3 series inclusions generated at deoxidizing reaction into the CaO series inclusions which may be easily removed, by adding CaO, etc. in the refining final period for stainless steel may be easily removed. CONSTITUTION:In the refining of Ni series stainless steel, molten steel is deoxidized by adding Si and/or Mn. Next, to this molten steel, 0.2% Ca or Ca alloy is added, and the MnO.SiO2 series inclusions generated in the preceding deoxidation are converted into the CaO series inclusions which may be easily removed. Then, this CaO series inclusions are separately floated up and removed. Thus, the oxygen content in the steel is extremely decreased and the super clean steel may be obtained.

Description

[Detailed description of the invention] and provides an alternative method to obtain ultra-clean steel.

Inclusions in steel are the starting point for corrosion, especially in stainless steel, which is characterized by its corrosion resistance.

I want to reduce it as much as possible. When a product has a mirror finish, it also has a commercial value based on its appearance.

This demand is strong.

Since the problematic inclusions are mainly oxide-based inclusions, the number of inclusions can be reduced by reducing the oxygen content in the steel. However, in the past, stainless steel with high purity and oxygen content of 100 ppp were used.
m or less. The concentration was only 50 ppm, and it was difficult to manufacture anything lower than that.

The present inventors investigated the reason why there is a limit to the reduction of oxygen content in steel.
'IO-SIOz system and/or MnOCr203
It was found that this was due to the formation of CaO-based inclusions that tend to remain in the steel, whereas CaO-based inclusions are relatively easy to remove. The present invention was achieved by discovering that the above-mentioned limitations can be overcome by knowing the fact that the former is true and converting the former to the latter.

The method for producing stainless steel of the present invention, which has an ultra-low oxygen content and is therefore ultra-clean, uses Si and/or Mn to perform deoxidation during refining, and if necessary, performs refining such as slag desulfurization. At the end of the process, Sl and M
Adding Ca or Ca alloy, which has a stronger affinity for oxygen and sulfur than n. Ca
Converted into O-based inclusions.

This makes it easy to remove oxide inclusions and significantly reduces the oxygen content in the steel.

When adding Ca or Ca alloy, the oxygen content in the steel is reduced to 200 pp by deoxidation with Sl and (still) Mn.
m or less, preferably 100 ppm or less. Thereby, excessive consumption of Ca can be avoided and the desired purpose of super deoxidation can be achieved. Needless to say, Ca is expensive, so consuming large quantities is not economically disadvantageous; however, if the oxygen content is high when Ca is added, ultra-clean steel cannot be produced even if a large amount is added. I experienced something difficult.

If the above conditions of oxygen content of 200 ppm or less are met. The amount of Ca or Ca alloy added is . It is sufficient that Ca content is at least 0.2% of the weight of the steel, and with a maximum of 3% or less, an oxygen content of 30 ppm or less can be achieved.

As art engineers are well aware. Since Ca is easily flammable and has a low specific gravity, even when added as an alloying element, it is difficult to effectively introduce it into molten steel, and the yield inevitably becomes low.

This problem still persists in the present invention, and it is necessary to take measures that have been tried in the past, such as adding Ca by casting it in steel or adding it in the form of an alloy with other metals. .

From this point of view, for example, 9ONi-10Ca or 95%N
It is preferable to add it as an alloy of i-5%Ca.
Therefore, the method of the present invention. This is particularly advantageous when producing ultra-clean Ni-based stainless steel containing approximately 5 to 20% NI.

As mentioned above, the stainless steel manufacturing method of the present invention has been mainly described in terms of realizing ultra-low oxygen content, but the effect of the combined use of Si and/or Mn and Ca is not limited to deoxidation, but also This is also remarkable in denitrification and dephosphorization, as shown in the examples below. The result is stainless steel that contains only small amounts of non-metallic components.
Its corrosion resistance can be fully demonstrated.

Example 1 In refining stainless steel, deoxidation was performed using sl and Mn, and the oxygen content in molten steel was set to 100 ppm. At the final stage of refining. Ca is cast in mild steel.
Ca was added in an amount equivalent to 0.5% of the weight of the steel, and the generated inclusions were sufficiently floated and separated before casting.

The content and removal rate of nonmetallic impurities in the obtained steel ingot were as follows.

ON P content 24ppm 0.007% 0.023
% removal rate 76.0% 36.4% 26.9
% Example 2 In the refining of 18-8 stainless steel, Sl and Mn
After deoxidation, Ca was added at 0.2% of the steel in the form of a 9ONi-10Ca alloy.

The results at this time are as follows.

ON P content 27ppm, 0.025% 0.0
29% removal rate 76.1% 24.2% 12
．． 1% Example 3 In Example 2, the added Ni-Ca alloy was increased to 1% of the steel in terms of Ca. An extremely clean steel was obtained.

ON P content 5ppm 0.015% 0.
017% removal rate 95.6% 55.9% 4
85% Patent Applicant Daido Steel Co., Ltd. Agent Patent Attorney Souo Suga

Claims (1)

[Claims] 11) When refining stainless steel, Si and (
Or) Mn is used for deoxidation, and Ca is removed at the final stage of refining.
However, by adding Ca alloy, the remaining MnO in the steel can be removed.
-5iOz-based and/or Mn0-Cr2O3-based inclusions are converted into CaO-based inclusions, thereby facilitating the removal of oxide-based inclusions and significantly reducing the oxygen content in the steel. A method of manufacturing stainless steel. (2) The stainless steel is Ni-based stainless steel, and C
The manufacturing method according to claim 1, wherein a Ni--Ca alloy is added as the a-alloy. The manufacturing method according to claim 1, wherein 0.2% or more of +31 Ca or Ca-based alloy is added to the steel. (4) The manufacturing method according to claim 1, which reduces the oxygen content in the steel to 30 ppm or less.