低碳Ni-Cr-Mo铜中M/A岛及回火特性

采用现代高分辨电子－光学分析技术及光学显微镜等，对低碳Ｎｉ－Ｃｒ－Ｍｏ钢（Ｃ≥０．０６％）中Ｍ／Ａ岛及其回火特性进行分析。结果表明，有两种类型的Ｍ／Ａ岛，一种为可聚成团状的小尺寸Ｍ／Ａ岛（即粒状贝氏体中的Ｍ／Ａ岛），它所在的铁素体基体呈胞状结构，位错密度较高，胞状之间为小角度关系；另一种为孤立的块状Ｍ／Ａ岛（类似双相钢中的Ｍ／Ａ岛），它所在的铁素体基体与多边形铁素体类似，位锗密度较低，透射电镜下没有看到亚结构。前者Ｍ／Ａ岛碳含量较高，回火后析出的碳化物尺寸较粗大。而且前者Ｍ／Ａ岛中残留奥氏体量比后者高，故粒状贝氏体回火抗力较大是由于残留奥氏体量较多的缘故。

M/A ISLAND IN LOW CARBON Ni-Cr-Mo STEEL AND TS CHARACTERISTICS OF TEMPERING

The paper examines martensite and austenite constituent in low carbon Ni, Cr, Mo steel during continuous cooling and its characteristics of tempering using modern high resolution electron-optical analytical techniques and optical microscope. It is found that there are two morphologies of M/A island in tested steel. One is small size M/A island which is presented as getting together in matrix (named granular bainite), and TEM shows that ferritic matrix in which such M/A islands dispersed consists of fine crystals, containing high densities of dislocations, separated by low-angle boundaries. Another is massive M/A island which is presented alone and its size is larger than the former. In the ferritic matrix such M/ A island dispersed characterized by very low dislocation densities and absence of substructure under TEM. Carbon content which is contained in the former M/A island is higher than that in the later and the size of carbides after tempering is coarser. Tempering resistance of granular bainite is higher due to more retained austenite.