改善QT20CrMo含硫齿轮钢A类夹杂物的优化中心偏析的工艺实践

对A类夹杂物超标（A细>3.0级,A粗>2.5级）含硫齿轮钢QT20CrMo（/%:0.20C,0.020S,0.020Al,0.95Cr,0.20Mo）Φ16 mm轧材和150 mm×150 mm铸坯中的MnS央杂进行了分析,得出铸坯中心区域的大尺寸MnS夹杂物是轧材中超标A类夹杂物的来源,并且中心偏析严重是铸坯中心区域形成大尺寸MnS夹杂物的主要原因。通过将二次冷却比水量从0.37 L/kg提高到0.59 L/kg后,铸坯中心碳偏析指数由1.12~1.44降低至0.99~1.23,硫偏析指数由1.28~1.70降低至1.01~1.31,最大网状MnS尺寸由2 000μm降低至1 000μm。QT20CrMo钢轧材A类夹杂物合格率达100%,A细类央杂物≤2.0级的比例由25.0%提高至97.0%。

Practice of Process for Optimized Center Segregation to Improve A-Type Inclusions in Sulfur-Bearing Gear steel QT20CrMo

Based on analysis on MnS in 016 mm rolled products and in 150 mm x 150 mm casting billet of sulfur-bearing gear steel QT20CrMo (/%：0. 20C,0. 020S,0.020Al,0. 95Cr,0. 20Mo) to get the factors to occur non-qualified rating of A-type inclusions (Anne >3 rating and Aeuaret. >2. 5 rating) in steel, it is obtained that the large size MnS inclusions occurring in central zone of casting billet are source of non-qualified rating A-type inclusions in rolled products and the serious center segregation is main reason of formed large size MnS inclusions in central zone of casting billet. With increasing secondary cooling water rate from 0. 37 L/kg to 0. 59 L/kg, the billet central carbon segregation index decreases from 1. 12 ~ 1. 44 to 0. 93 ~ 1. 23, the sulfur segregation index decreases from 1. 28 ~ 1. 70 to 1. 01 ~ 1. 31 and the size of max network MnS decreases from 2 000μm to 1 000μm. As a result the qualified rate of rating of A-type inclusions in steel QT20CrMo rolled products is up to 100% , and the ratio of ≤2. 0 rating of A-type thin inclusions increases from 25. 0% to 97. 0%.