高硅铸钢残余奥氏体分布形态及其对力学性能的影响

采用透射电子显微镜(TEM)对高硅铸钢等温淬火热处理后的显微组织以及残余奥氏体分布形态进行了研究,对等温淬火组织中残余奥氏体量进行了测定.结果表明,残余奥氏体呈薄膜状及块状两种分布形态.薄膜状分布的残余奥氏体与贝氏体铁素体间的位向符合K-S关系,对钢的综合力学性能特别是韧性有积极的作用;而呈块状分布的残余奥氏体,由于其机械稳定性差,对钢的各项力学性能有不利的影响.要获得具有优异综合力学性能的高硅铸钢,薄膜状残余奥氏体与块状残余奥氏体体积分数量的比值Vγ-F/Vγ-B要大于1.0.

Morphology of Retained Austenite and Its Effects on the Mechanical Properties of High Silicon Cast Steel

The microstructure and morphology of retained austenite of the austempered high silicon cast steel after various austempering combinations are investigated by TEM, and the volume fraction of retained austenite is also studied by XRD method. The experiments indicate that the retained austenite present at the isothermal transformation temperature has two typical morphologies, film shaped and blocky retained austenite. There are K-S orientation relationship between interface of film shaped retained austenite and bainite ferrite. The film shaped retained austenite is conductive to both high strength and good toughness, while the blocky retained austenite has poor stability and thus is detrimental to the mechanical properties of the steel. It is suggested that the ratio of volume fraction of the film shaped/blocky retained austenite must exceed about 1.0 for optimum mechanical properties.