KR980009473A - Refining method of low carbon, low nitrogen stainless steel - Google Patents

Abstract

The present invention relates to a method for refining low-carbon and low-nitrogen stainless steel, wherein the carbon concentration of the stainless steel molten steel charged into the refining furnace is adjusted to 1.8% to 2.0% by weight, A lancing lance is used at a carbon concentration of 1.8-2.0 wt% up to 0.7-0.8 wt%, and a lance is used at a carbon concentration of 1.8-2.0 wt%, using only a transversal tuyere Thereby reducing the nitrogen concentration without causing a problem in reducing the carbon concentration of the stainless steel. As a result, the clogging phenomenon of the deposition nozzle by the TiN during continuous casting is remarkably improved .

Description

Refining method of low carbon, low nitrogen stainless steel

The present invention relates to a refining method for lowering the nitrogen concentration in an AOD refining furnace in the production of low-carbon and low-quality Ti-stabilized stainless steels.

Carbon and nitrogen in stainless steels are known as harmful elements because they degrade various mechanical properties of steel products such as elongation during processing and decrease in toughness of welded parts. Since stainless steel contains a large amount of elements with high affinity for carbon and nitrogen, such as chromium and manganese, it is very important to remove carbon and nitrogen during refining of stainless steel. In particular, the steel containing Ti, such as STS409L steel, has to be different in the concentration of the two components because carbon and nitrogen form carbide or nitride, respectively. Especially, in case of nitrogen, TiN is formed during the solidification process, Or causing surface defects of the hot-rolled coil, the nitrogen concentration in the molten steel must be actively reduced.

Figure 1 shows the relationship between [Ti] and [N] in molten steel with temperature in 11.5% Cr-containing stainless steels. It can be seen that the concentration of dissolved nitrogen decreases with increasing Ti concentration. If nitrogen in the molten steel is higher than the dissolved nitrogen concentration, nitrogen becomes TiN and precipitates, and TiN causes all of the problems described above. Also, as the molten steel temperature decreases at the same Ti concentration, the nitrogen concentration also decreases. That is, the temperature of molten steel gradually decreases until casting after casting the molten steel in the refining furnace. As nitrogen dissolved in high temperature precipitates into TiN, the nitrogen concentration of STS409L is higher than that of STS409L at the coagulation temperature (1505 ° C) (About 100 ppm at 0.15% Ti).

The percentages used in this specification are understood to mean, by weight, unless otherwise indicated.

When producing stainless steel by the electro-furnace (Argon Oxygen Decarburization) process, it dissolves ferroalloys and ordinary scrap using an electric furnace. Nitrogen in air is dissolved in the molten steel by arc discharge, The nitrogen concentration in the molten steel is increased by the absorption of nitrogen by the contact of the molten steel and the air, and the nitrogen concentration before the AOD charging is about 200-250PPM. In AOD, carbon is removed from the stainless steel molten steel produced in an electric furnace by using a mixture gas of oxygen and argon. Nitrogen in stainless steel is known to be removed by CO gas bubbles and argon gas bubbles generated during the decarburization process, Since it is not possible to reduce the nitrogen concentration in the process subsequent to the AOD refining furnace, the nitrogen concentration in the refining furnace must be sufficiently lowered.

The denitrification of molten steel can be considered in the following five sub-processes.

FIG. 1 is a graph showing the relationship between Ti and N in 11.5% Cr STS steel. FIG.

FIG. 2 is a graph showing the relationship between the nitrogen concentration at the end point of the refining furnace and the nitrogen concentration of the product. FIG.

FIG. 3 is a graph showing the influence of the loading carbon concentration on the nitrogen concentration. FIG.

FIG. 4 is a graph showing the relationship between the charging carbon concentration and the carbon pickup amount; FIG.

FIG. 5 is a graph showing the relationship between the carbon concentration and the nitrogen concentration at the extreme lance end point. FIG.

Table 2 shows the carbon and nitrogen concentration in the end point of the refining furnace and product of STS409L produced by the application of the present invention, and it is made possible to lower the carbon and nitrogen concentration to an extremely low level. As a result, It is possible to remarkably improve the clogging of the immersion nozzle.

An object of the present invention is to provide a stainless steel refining method capable of effectively lowering the nitrogen concentration in molten steel without causing a problem of carbon concentration control during the production of low carbon and low nitrogen Ti stabilized stainless steels.

Claims (1)

In the refining method for lowering the nitrogen concentration in the production of the low carbon and low nitrogen Ti stabilized stainless steel, the carbon concentration of the stainless steel molten steel charged into the refining furnace is adjusted to 1.8% to 2.0% by weight and the carbon is removed in the decarburization process of the refining furnace As a method for blowing oxygen to be supplied to a ship, a lance is used at a carbon concentration of 1.8-2.0 wt% to 0.7-0.8 wt%, and a lance is used at a carbon concentration of 1.8-2.0 wt% Wherein the concentration of nitrogen in the stainless steel is lowered without causing a problem in the reduction of the carbon concentration of the stainless steel. ※ Note: It is disclosed by the contents of the first application.