The mechanical anisotropy and effects of MnS inclusions configuration on the local ductility in hot rolled bars with 0.03% sulphur were experimentally investigated and statistically regression analyzed. Results show that the elongation and reduction of area decline significantly as the angle between the gauge length and the transverse direction decreases, while the tensile strength and yield strength vary little. The reduction of area in transverse tensile tests of various rolled bars ranges widely from 6.5% to 38.1% and the differences in engineering stress–strain curve profile are mainly reflected in the local deformation stage. MnS inclusions configuration in the surface adjacent to fracture were classified into three types according to the morphology and three-dimensional distribution. When the type of MnS transitions from C to A to B, the reduction of area decreases obviously and area of ribbon-like fractures where most local deformation performs declines as well. Multiple linear regression of the parameters of MnS inclusions shows that the reduction of area is more sensitive to the length of single MnS inclusion or aggregation of tiny MnS inclusions and the local density of MnS inclusions. Voids in matrix tends to nucleate between the parallel MnS inclusions and along the line connecting two MnS inclusions with rounded or blunt tips and then grow and link up to form cracks. Besides, cracks can also be directly induced by the sharp tips of tiny MnS inclusions. In conclusion, the aggregated tiny MnS inclusions of type B should be avoided and the evenly distributed spindle-shaped MnS inclusions of type C are expected in steels requiring favorable transverse mechanical properties.

实验研究了硫含量为0.03％的热轧钢筋的力学各向异性和MnS夹杂物形态对局部塑性的影响，并进行了统计回归分析。结果表明，随着长度和横向的夹角的减小，伸长率和断面收缩率显着下降，而抗拉强度和屈服强度变化不大。各种轧制钢筋的横向拉伸试验中面积的减小范围从6.5％到38.1％，工程应力-应变曲线轮廓的差异主要反映在局部变形阶段。根据断口的形貌和三维分布，将断裂附近的MnS夹杂物构型分为三类。当MnS的类型从C转变为A再转变为B时，面积的减少明显减少，且带状裂缝的局部变形最大的区域也减少了。MnS夹杂物参数的多元线性回归表明，面积的减小对单个MnS夹杂物的长度或微小MnS夹杂物的聚集以及MnS夹杂物的局部密度更为敏感。基质中的空洞倾向于在平行的MnS夹杂物之间并沿着连接两个带有圆形或钝头的MnS夹杂物的线形核，然后生长并连接形成裂纹。此外，细小的MnS夹杂物的尖锐尖端也可以直接引起裂纹。总之，应避免聚集B型微小的MnS夹杂物，并且在需要良好的横向机械性能的钢中，应预期C型的均匀分布的纺锤形MnS夹杂物。