排气系统用耐热不锈钢夹杂物控制理论与实践

doi:10.13228/j.boyuan.issn0449-749x.20220598

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Abstract In order to increase the oxidation resistance of the material, a kind of austenitic heat-resistant stainless steel used in the automobile exhaust system contains more than 1.5%Si element. The silicate inclusions with diameter larger than 50 μm were formed by ferrosilicon deoxidation during AOD process. Due to the high alloy composition, the viscosity of the molten steel is high, therefore, the large particle silicate inclusions cannot be removed by LF bottom blowing gas stirring method. The inclusions in continuously cast strands was deformed greatly during rolling process, and the grade was exceeding level 2.0 in the austenitic heat-resistant stainless steel cold rolled plate for the exhaust system, which seriously affects the high temperature fatigue and creep resistance of the product and reduces the service life of the product. Aiming at the higher requirements of inclusions in heat-resistant stainless steel cold rolled sheet for automobile exhaust system, starting from the basic thermodynamic theory, according to the actual smelting process and the composition of molten steel, the thermodynamic conditions for the formation of SiO₂, Al₂O₃and MgO·Al₂O₃ inclusions in the smelting process and the thermodynamic basis of Ca modified high melting point MgO·Al₂O₃ inclusions were calculated. LF refining process were improved according to the thermodynamic results, and the following conclusions were obtained. When the mass percent of Al in molten steel is more than 0.003%, the inclusions in molten steel are mainly Al₂O₃, and MgO·Al₂O₃ inclusions are easily formed. Ca can modify high melting point MgO·Al₂O₃ inclusions into low melting point composite inclusions. At 1 500 ℃, when the mass percent of Al in molten steel is 0.04%, the critical mass percent of Ca that begins to modify MgO·Al₂O₃inclusions is 0.000 4%. In actual LF refining production process, the technology of modifying large-size silicate inclusions into small-size plastic inclusions is adding 0.1 kg aluminum shot and 1.5 kg aluminum powder per ton steel, and feeding 3 m calcium wire per ton steel after aperiod of reaction. The total oxygen mass percent of austenitic heat-resistant steel cold-rolled sheet for automobile exhaust system produced after LF refining process adjustment is less than 0.002 5%, and the inclusions grade is less than level 1.0.

Key words： exhaust system heat resistant stainless steel inclusion thermodynamic calculation composition controlling

Received: 16 September 2022

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	ZHUANG Ying
	LI Guo-ping

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ZHUANG Ying,LI Guo-ping. Inclusion control theory and practice of heat resistant stainless steel for exhaust system[J]. Iron and Steel, 2023, 58(3): 151-157.

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http://www.chinamet.cn/Jweb_gt/EN/10.13228/j.boyuan.issn0449-749x.20220598 OR http://www.chinamet.cn/Jweb_gt/EN/Y2023/V58/I3/151

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