分别对TRIP800钢板母材、点焊接头进行疲劳试验, 获得了载荷与疲劳寿命曲线, 并对其显微组织、硬度、疲劳寿命和疲劳断口形貌进行了研究。结果表明: 点焊接头的熔核区组织为板条状马氏体, 热影响区为马氏体、铁素体及高温回火贝氏体组织, 与母材的有较大差异; 熔核区和热影响区的硬度比母材的高; TRIP钢点焊接头缺口效应严重以及大量脆性马氏体组织的存在, 使得点焊接头的疲劳寿命明显降低, 只有母材的1/10左右; 母材的疲劳源均位于试样外表面的缺陷处; 而由于缺口应力集中作用, 点焊接头的疲劳源位于缺口附近的微观缺陷处, 夹杂物的存在仍然是裂纹萌生的主要原因; 母材的疲劳扩展区表现为韧性断裂, 点焊接头表现为脆性断裂, 瞬断区都表现为脆性断裂。

A series of fatigue tests were carried out for TRIP800 steel and spot welded joints to obtain load versus fatigue life curves, and the microstructure, hardness, fatigue life and fatigue fracture were studies as well. The results show the microstructure on the fusion zone of the spot weld nuclear was lath martensite while it was martensite and ferrite and high temperature tempering bainite on heat affected zone, which was quite different with the base metal. The hardness of both nuclear fusion zone and heat affected zone was higher than that of the base metal. The serious gap effect of TRIP steel spot welded joint and the existence of a large number of brittle martensite structure made the spot weld fatigue life significantly reduce to about 1/10 of the base metal fatigue life. The fatigue source of base metal located at the surface defects, but the fatigue source of spot welded joint was at the micro defect near the gap due to gap and stress concentration effect. The existence of inclusions is still the main reason for the crack initiation. The fracture mechanism was characterized by ductile fracture for base metal fatigue extension area, but it was characterized by brittle fracture for spot welded joint and the crack transient breaking area.