论文部分内容阅读
本文综述了近年来人们对球铁等温转变组织构成的新认识。铸铁中的贝氏体,长期以来被认为是由铁素体和渗碳体(或碳化物)的混合物所组成。然而,直至70年代末和80年代初才被否定,重新确定铸铁等温转变贝氏体是由铁素体和奥氏体混合物所组成。在等温转变过程中,会发生两种不同的贝氏体反应,一种是形成贝氏体型铁素体—奥氏体组织,韧性好;另一种是脆性反应,使韧性降低,并随等温时间的延长而发生。因此,为了获得高强韧球铁,存在一个有限的时间规范。着重讨论了等温贝氏体转变机理以及热处理参数和合金元素对贝氏体转变动力学的影响。合金化推迟了脆性反应,使高强度高韧性球铁有一个较宽的处理规范。降低奥氏体化温度,增加第一阶段转变的驱动力,提高第一阶段的反应速率。而等温温度对第一阶段转变速率没有明显的影响。
This article summarizes the recent new understanding of the structure of ductile iron ductile iron. Bainite in cast iron has long been thought to consist of a mixture of ferrite and cementite (or carbide). However, it was not until the late 1970s and early 1980s that redefined cast iron isothermally transformed bainite consisted of a mixture of ferrite and austenite. During the isothermal transformation, two different bainitic reactions occur, one is the formation of bainitic ferrite - austenite, good toughness; the other is a brittle reaction, the toughness decreases, and with the isothermal The extension of time takes place. Therefore, there is a limited time specification for obtaining high toughness ductile iron. The mechanism of isothermal bainite transformation as well as the influence of heat treatment parameters and alloying elements on the kinetics of bainite transformation are emphatically discussed. Alloying delayed the brittle reaction, so that a high strength and ductile ductile iron has a wider processing specifications. Reduce the austenitizing temperature, increase the driving force of the first phase of transformation, and increase the reaction rate in the first stage. The isothermal temperature has no significant effect on the first-stage transition rate.