球状石墨铸铁焊缝冷裂纹萌生与扩展动态观察

Dynamic observation of cold crack initiation and propagation in SG cast iron weld

利用自制拉伸装量在光学显微镜下对球状石墨铸铁焊缝冷裂纹的萌生与扩展进行了动态观察.在拉应力作用下,塑性变形集中在铁素体区.裂纹的萌生部位有:(a)铁素体应变集中处,特别是近邻球状石墨之间的基体桥及表层下存在球状石墨的薄层铁素体处;(b)铁素体与珠光体交界处;(c)珠光体应变集中处.裂纹选择铁素体比例大的区域,穿过球状石墨间的基体桥,连接距离较近的球状石墨扩展.

Dynamic observation of crack initiation and propagation in SG cast iron weld was carried out using a self-made uniaxial tensile device and optical microscope. Plastic deformation concentrates at the ferrite area under the tensile stresses. The areas where cracks initiate are as follows: (1) the ferrite areas with high strain concentration, especially the ferrite bridges among close graphite nodules and the thin ferrite areas with underface graphite nodules; (2) the ferrite-pearlite interface; (3) the pearlite areas with high strain concentration. The cracks tend to propagate in the area of high ferrite proportion through fracturing matrix bridges among graphite nodules and linking up the close nodules.