Abstract：Large-sized inclusions formed in steelmaking and mold casting have a significant effect on the metallurgical quality of steel. Stainless steel AISI 431 produced by a domestic steel plant has severe defects,and these defects were found to be large-sized oxide inclusions after microscopic analysis. In order to investigate the source of large-sized inclusions in AISI 431 stainless steel bars, the inclusion evolution mechanism during production was investigated in this study based on full process sampling analysis. OTSInca inclusion analysis system and commercial thermodynamic software FactSage 8.2 were employed to investigate and analyze inclusions in every production process. It was found that the inclusions at the end of AOD were mainly CaO-SiO2-Al2O3 complex inclusions with high SiO2 content,which transformed to spinel and calcium aluminate after Al deoxidation at the beginning of LF. After the casting process,the decrease of dissolved Al concentration in steel is very obvious,and new large-sized Al2O3 and Na- and K-containing SiO2-based complex inclusions can be detected in steel. Al2O3 originated from a new aluminum-oxygen reaction in the molten steel after contact with air,and Na- and K-containing SiO2-based complex inclusions is from the entrapment of mold flux. During the subsequent process,the maximum size of both types of inclusions further increased. Al2O3was elongated as long lines along the rolling direction,while the Na- and K-containing SiO2-based complex inclusions were deformed and broken. Analysis of the defects in AISI 431 stainless steel bars further verified that these two types of large size inclusions can directly lead to bar defects. Finally,this study proposes to consider process optimization in terms of reducing the exposure time of the steel flow,controlling the intensity of the gas supply during casting,the design of the casting mold flow field and the control of LF soft blowing argon.
王举, 李阳, 姜周华, 孙萌, 毛昀惬, 马帅. AISI 431不锈钢生产过程夹杂物转变机理[J]. 钢铁, 2023, 58(7): 54-63.
WANG Ju, LI Yang, JIANG Zhouhua, SUN Meng, MAO Yunqie, MA Shuai. Inclusion transformation mechanism of AISI 431 stainless steel during production[J]. Iron and Steel, 2023, 58(7): 54-63.
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