非调质钢中MnS分布对轧材横向塑性的影响

Effect of MnS distribution on transverse ductility of rolled non-quenched and tempered steel

为了探究实际生产中非调质钢轧材横向塑性波动较大的原因,利用电子显微镜对比研究了连铸坯、轧材和拉伸试样断口中MnS夹杂物形貌及其演变行为,并对轧材横纵截面MnS夹杂物的尺寸、数量以及分布特征进行定量化表征,发现MnS夹杂物的分布特征是影响轧材横向塑性的关键。MnS夹杂物聚集分布,拉伸试样在受力过程中大量微裂纹在局部同时萌生,导致试样提前断裂,形成木质状的断口形貌,轧材表现出较差的横向塑性。当MnS夹杂物分布较为均匀时,拉伸试样受力相对均匀,应力集中小,轧材横向塑性较好。轧材中MnS夹杂物的分布行为主要取决于铸态下MnS夹杂物的形貌。减少铸态下II类树枝状MnS数量,是改善最终轧材横向塑性的关键。

The transverse ductility of rolled non-quenched and tempered steel fluctuates greatly in actual production.In order to figure out the reason,the morphologies and evolution behavior of MnS in continuous casting blooms,rolled bars and tensile samples were studied by electron scanning microscope.The size,number and distribution characteristics of MnS inclusions in the rolled bars were quantitatively characterized.It was found that the distribution characteristics of MnS inclusions were the key to affect the transverse ductility of the rolled bars.When MnS inclusions were aggregated,a large number of microcracks in the tensile specimen were locally inoculated during the stretching process,which caused the specimen to fracture in advance,forming a woody fracture morphology,and the rolled material showed poor transverse ductility.When the distribution of MnS inclusions was relatively uniform,the tensile sample was relatively uniformly stressed,the stress concentration was small,and the transverse ductility of the rolled material was good.The distribution behavior of MnS inclusions in rolled bars was mainly determined by the morphology of MnS inclusions in the as-cast state.Reducing type II dendritic MnS inclusions in the as-cast state was the key to improve the transverse ductility of the final rolled products.