Key Technology Research On Taishan Steel TSR Converter Process Of 430 Stainless Steel Making

In 2014 the total output of 400 series Stainless Steel is 21.69 million tons in China, among which 430 as the most widely used ferritic stainless steel, is 2.67 million tons. Many Chinese domestic Stainless Steel manufacturers, such as Baosteel, TISCO, and JISCO and so on, have all produced 430 Stainless Steel as a main steel production for ferritic stainless steel. The above companies adopt AOD and K-OBM-S as the decarburization device of 430 Stainless Steel. However the oxygen supplying intensity at high-carbon stage is weaker and volume-capacity ratio is smaller, during the operation of above equipment. This would make the decarburization rate slower and lead to lower heat efficiency. In this case, we have to employ the EAF to help the steel refining, in order to reduce the load of AOD and K-OBM-S during decarburization operation, as well as chromium loss. Therefore, it is the only method to introduce two-step process of 430 Stainless steel making for Baosteel, TISCO and JISCO before their second phase revamp, which would lead to longer production cycle and bigger refractory consumption. Under this circumstance, the technical revamp of "Hot Metal Pretreatment+TSR Converter" process with completely hot metal, is carried out and achieved successfully in Taishan Steel Group Co., Ltd. in 2011. After the revamp, the one-step production method on "DE-P Hot Metal+TSR Converter+LF" process of 430 Stainless Steel is accomplished. Through years of practice, there still have several problems as follows:(1) Initial content of phosphorus in hot metal is higher, and dephosphorization rate is lower; (2) The design of gas supplying curve for 430 Stainless Steel is not reasonable, chromium loss is higher, and endpoint oxygen content is also higher; (3) Slag-forming procedure at Oxidation Stage is not reasonable, with higher slag basicity and bigger chromium loss. The consumption of slagging and deoxidizing material at Reduction Stage is bigger; (4) Deoxidization is not sufficient with silicon iron at TSR Reduction Stage, which would lead to resulfurization in LF, and couldn’t meet the variety and quality requirements because of inclusion, and result in a poor surface quality of Cold-Rolled Coils/sheets.Focusing on the above problems, the "hot metal desiliconization and desulfurization+TSR Converter+LF" steel-making process of 430 Stainless Steel is mainly studied. And theoretical analysis & calculation, and local industrial experiments research on Hot Metal Desulphurization, Gas Supplying Curve in TSR Converter, Top Lance Position Control, Slagging Procedure during Oxidization and Reduction Stage, Deoxidization and Desulphurization at Reduction Stage, and Plasticization Control of Inclusions and so on, are carried out. As a result, [P] is reduced from the initial value of 0.15-0.20%, to lower than 100x10-6; average oxygen availability in TSR reaches 64%; chromium yield is up to 99%; [O] is controlled to about 100×10-6 at blowing endpoint; [O] is further reduced to 1.95×10-6 while [S] reduced to 19.8×10-6 at the end of Reduction Stage in TSR; and inclusion composition is controlled to low melting point zone of CaO-MgO-Al2O3 ternary system, which efficiently solves the surface defects such as lamination and so on.