微量铋合金对易切削钢中MnS形貌的影响

 利用Q500图像分析仪和JSM6480LV型扫描电镜研究了微量元素Bi对S-Bi易切削钢中的MnS长宽比的影响规律。结果表明，Bi在易切削钢中以3种形态存在：单独存在于钢基体中、被硫化物包裹和介于钢基体与硫化物之间。S-Bi易切削钢铸锭中w（TO）分别为0.032%，0.022%和0.024%，Bi质量分数分别为0.0002%、0.0010%和0.0020%时，MnS的长宽比均在1.0~1.6，低于硫系易切削钢的1.2~3.2（w（TO）为0.030%）。在锻造比为2.25时，钢中MnS的长宽比增长率低于1.0，且MnS夹杂物的变形率随Bi含量增加而降低。钢中Bi金属在钢锭锻造过程中可起到抑制硫化物变形的作用。

Effect of Trace Bi on Inclusion Morphology in Free-Cutting Steel

The influence of trace element Bi on MnS inclusions aspect ratio in S-Bi free-cutting steel was investigated through using Q500 image analyzer and JSM6480LV SEM. The results show that there are three existing forms of Bi in free-cutting steel: exist alone in steel, be packaged by sulfide and between steel and sulfide. The aspect ratio of MnS in S-Bi free-cutting steel ingot, with w（TO） = 0.032%, 0.022% and 0.024%, w(Bi) = 0.0002%, 0.0010% and 0.0020%, is during 1.0-1.6, which is lower than 1.2-3.2 in w（TO）=0.030% S free-cutting steel. The growth rate of inclusion aspect ratio is less than 1.0 when forging ratio is 2.25. Deformation rate MnS inclusions will decrease when Bi content rising up. It is found that Bi in steel can prevent MnS deformation during forging process.