大方坯连铸42CrMoAH钢皮下夹杂物控制

 针对苏钢42CrMoAH钢大方坯（260mm×340mm）浇注存在的铸坯皮下夹杂物问题，分析了夹杂物的主要类型及其来源，研究了精炼渣组成对钢洁净度的影响，同时讨论了连铸工艺条件对铸坯皮下40mm以内的夹杂物数量、尺寸、组成的影响。研究表明：铸坯中的夹杂物主要来源于以A12O3为主的脱氧产物及以MnO·Cr2O3，FeO·Cr2O3等尖晶石类为主的二次氧化产物；由于精炼渣吸收A12O3夹杂物能力不足，再加上拉速低等因素导致结晶器内钢液上循环流弱，不利于脱氧及二次氧化产生的微小夹杂物在结晶器内碰撞聚合后上浮、排除，以致铸坯中尺寸为20~50μm的夹杂物达到总量的45%左右；采取提高精炼渣炉渣碱度、w(CaO)/w(Al2O3)值，及采用双侧孔型水口以加强结晶器内上循环流等措施后，铸坯皮下20~50μm的夹杂物降低了64%。

Control of Subsurface Inclusion in 42CrMoAH Steel Cast by Bloom Caster

In order to control the subsurface inclusions existing in 42CrMoAH steel made by a 260mm×340mm bloom caster in Su Steel, the main type and origin of inclusions was analyzed, the effect of refining slag system on steel cleaness was investigated and subsurface inclusions about 40mm beneath the surface were investigated, including inclusions amount, size distribution and compositions. It shows that the inclusions are mainly deoxidation products (Al2O3) along with reoxidation products (MnO·Cr2O3, FeO·Cr2O3) and the inclusions size between 20μm and 50μm takes about 45% of the total inclusion amount. According to the result, two main factors are found to have great contributions on the bloom subsurface inclusions: poor inclusion (Al2O3) absorbing ability of refining slag; weak upward flow in the mold. Trials were conducted by increasing the basicity and w(CaO)/w(Al2O3) ratio of the refining slag and controlling the casting condition. The industrial results show that the amount of subsurface inclusions with size from 20 to 50μm is reduced about 64%.