硫含量对中碳非调质钢中硫化物及组织的影响

利用真空感应炉冶炼了不同硫含量的中碳非调质钢,研究了S含量对非调质钢中硫化物形态分布及显微组织的影响.结果表明：在0.025%~0.065%范围内,随S质量分数的增加,非调质钢中硫化物的数量增多,偏聚分布现象加重；晶内铁素体比例随之升高,组织得到细化.通过热力学计算及相图信息研究了硫化物的类型转变. S含量增加时第Ⅲ类MnS在凝固末期以离异共晶形式较早析出,剩余液相中的S在凝固结束时以共晶形式析出为第Ⅱ类MnS.单独MnS以及MnS- V( C, N)复合硫化物均可作为晶内铁素体的有效形核核心,促进铁素体的生成.

Effect of sulfur content on sulfide inclusions and microstructure in medium carbon non-quenched and tempered steel

Medium carbon non-quenched and tempered steels with different S contents were smelted with a vacuum induction fur-nace. Several experiments were conducted to study the effect of S content on the morphology of sulfides and microstructure in the steels. The results show that with the increase of S content from 0. 025 wt% to 0. 065 wt%, the number of sulfide inclusions increa-ses, and the aggregation of sulfide inclusions is promoted, while the microstructure becomes finer due to the increasing area ratio of in-tragranular ferrite. Thermodynamic calculations and phase diagram information were employed to explain the transition of MnS from type Ⅱ to type Ⅲ. The angular type Ⅲ MnS is resulted from divorced eutectic reaction before the solidification completes, and the rod-like type Ⅱ MnS is derived from normal eutectic reaction at the end of the solidification process. Both MnS and MnS- V( C,N) complex inclusions are found to act as effective nucleation sites to improve the formation of intragranular idiomorphic ferrite.