超高碳钢超级贝氏体转变及组织与性能

Superbainite transformation in ultrahigh carbon steel and its microstructure and properties

研究了碳含量1.26wt%的超高碳钢在等温淬火后的组织及其对拉伸力学性能的影响。结果表明,超高碳钢的等温淬火组织为超级贝氏体(superbainite)+残留碳化物的复相组织。超级贝氏体的形成是因为超高碳钢中的高碳成分及铝元素的添加。由于原奥氏体晶粒细化,超级贝氏体的形核率增加,长大路径缩短,使转变速率加快。形貌观察表明,贝氏体铁素体片和残留奥氏体薄膜的厚度只随着等温温度的降低而减小;奥氏体化温度对贝氏体铁素体片厚度没有影响,但超级贝氏体组织的尺寸会随奥氏体化温度提高而增加。拉伸试验结果表明,随着等温时间的延长,抗拉强度逐渐升高,但断后伸长率却先增加后减小;等温温度或奥氏体化温度升高均会引起抗拉强度降低,但伸长率增加。

The austempering microstructure of ultrahigh carbon steel with 1.26wt% carbon content and its effect on tensile properties were studied.The results show that a duplex structure of superbainite and residual carbide in ultrahigh carbon steel is obtained after austempering . The formation of superbainite is due to the high carbon content and addition of aluminum .Because of the grain refinement of prior austenite , the nucleation rate of superbainite increases and its growth path shortens , which is helpful to accelerate the transformation rate .Morphological observation shows that the thickness of the laminar bainite ferrite ( BF) and retained austenite film decrease with the decrease of austempering temperature.Austenitizing temperature plays little role on the thickness of BF , but the superbainite size enlarges with the increase of austenitizing temperature .The tensile test results show that the tensile strength increases when the austempering time is prolonged , while the elongation first increases and then decreases .Increasing austempering temperature or austenitizing temperature will lead to decrease of tensile strength and increase of elongation .