易切削钢9SMn28定向凝固过程中夹杂物的研究

Inclusions in 9SMn28 free-cutting steel during directional solidification process

应用B ridgm an区域熔炼定向凝固设备制备出不同抽拉速度下的定向凝固易切削钢9SMn28。利用光学显微镜、扫描电镜及电子探针显微分析仪对所得试样中的夹杂物及树枝晶进行了观察,并通过凝固理论对其进行了计算和分析。研究发现,9SMn28钢中的夹杂物主要以MnS的形式存在,普遍聚集在树枝晶间隙之中,其形态以球形为主,在二次枝晶臂周围也存在少量纺锤状和条状的夹杂物,其尺寸随抽拉速度的增大而减小。二次枝晶臂间距的计算结果与测量结果比较吻合,同样随抽拉速度的增大而减小。

The 9SMn28 free-cutting steel samples were prepared under different with drawal velocity using Bridgman zone melting directional solidification apparatus.The inclusions and dendrites of which were observed by OM（optical microscope）,SEM（scanning electron microscope） and EPMA（electron probe microanalyzer） were calculated and analyzed by applying solidification theory.The results show that the inclusions are mainly manganese sulfides and gathered in the space among dendrites arms in 9SMn28 steel ingots.Manganese-sulfide inclusions are almost spherical,as a small amount of elliptoid and rod-like inclusions are found around the secondary dendrite arms.And the size of inclusions decreases with increasing the with drawal velocity.The calculation result of secondary dendrite arm spacing is in agreement with that of the test,which both decreases as withdrawal velocity increases.