球粒化程度对S50C钢热处理相变和性能的影响

Effects of Spheroidization Levels on Phase Transformation and Property of S50C Steel During Heat Treatment

采用冷轧和退火的方法制备了不同球粒化程度的S50C钢样,比较了在同一淬回火工艺时球粒化程度对淬回火相变和力学性能的影响,检测了淬回火前后的拉伸断口形貌,并采用马氏体转变驱动力公式分析了球粒化对马氏体相变的影响。结果表明:S50C钢的球粒化程度随着退火次数的增加而提升,球粒化程度越高淬回火后的组织越均匀;相同淬火工艺下,450℃回火比400℃回火组织均匀细小,抗拉强度随着厚度规格从3.0mm减少到2.0mm,先上升后下降,而伸长率先下降后上升;球粒化程度越高断口的韧窝数量越多、越均匀,淬回火后脆性断裂趋向增强;马氏体转变驱动力公式分析表明,粒化程度增加了铁原子和碳的活度系数,促进了马氏体转变,从而提升产品的综合性能。

The samples of S50C steel with different spheroidization levels were prepared by the way of cold rolling and annealing, the effects of spheroidization levels on the phase transformation and mechanics property were contrasted in the same quenching tempering process, and the tensile fracture morphologies before and after quenching tempering were studied. Furthermore, the influence of spheroidization and martertsitic phase transformation was ana- lyzed, using the driving force formula of martensitic transformation. The results show that the spheroidization levels were improved with the increase of annealing times for S50C steel, which raised the uniformity of the quenching tem- pering microstructures ; The microstructure under the tempering temperature of 450℃ was more even and fine than that of 400℃ in the same quenching process, and the tensile strength was first increased and then decreased along with the increasing of thicknesses from 3.0mm to 2.0mm, while the elongation was opposite, The spheroidization levels could increase the number of dimple and improve the uniformity of fracture, but the trend of brittle fracture was increased after quenching tempering; The analysis results of the driving force formula showed that the spheroidization levels increased the activity coefficients of iron and carbon atoms, which promoted martensitic transformation, then the properties of products were improved.