材料期刊网

本文应用金属薄膜试样的透射电子显微镜的分析方法,以及扫描电镜和光学显微镜的分析方法,研究调质状态40Mn钢拉伸加载过程变形度对位错结构和裂纹萌生的影响。 条状铁素体和渗碳体试样在拉伸加载过程中随延伸率δ的增加,铁素体中的位错网很快演变为高密度的位错缠结和拉长的位错胞。显微组织特征直接影响裂纹的萌生部位。微孔往往在铁素体与渗碳体的界面处和条状铁素体间的边界处萌生,开裂的早期阶段主要是形成微孔群。

The process of deformation and crack initiation of high temper (550℃) medium-carbon steel 40Mn has been investigated using smooth tensile specimens. The midgage length part of the specimen was spark cut into 0.3mm thick sheets. The direct transmission observation of thin foil specimens was carried out on TEM. The evolution of the dislocation structure with elongation in the steel of hardened and tempered condition was studied. In the lath ferrite, the feature of dislocation structure is irregular network. At the stage of comparatively small elongation (δ=0.2-2.7％), near the interface of ferrites and the ferrite-cementite interface, regular dislocation networks appear and the dislocation density increases. At the deformation stage of δ=4.7％, the dislocations tangle and desify. At the deformation stage of δ=6.8-10％, the feature of dislocation structure becomes elongated dislocation cells. The crack nucleation in hardened and tempered steel has been observed by SEM and optical microscope. When the deformation attains δ=4.7％, the submicroscopic cracks are initiated at interface of metal matrix and inclusion. At the deformation stage of δ=6.8％, the submicrocrack initiated at interface of lath ferrites and interface of ferritecementite. The submicroscopic crack propagated through the formation and joining up of void groups.