Nd:YAG激光焊接800 MPa TRIP钢的接头组织与性能

Microstructures and properties of Nd:YAG laser welded 800 MPa TRIP steel

采用Nd:YAG激光对强度为800MPa,厚度为1.2mm的TRIP钢板进行焊接.研究焊接速度对焊缝外观和截面成形的影响及接头的组织特点、硬度、强度和成形能力.激光功率相同,焊接速度较低时焊缝易产生气孔,速度较高时易发生飞溅;焊接速度对焊缝熔深及熔宽也有影响.焊缝组织主要由马氏体构成,从焊缝、热影响区到母材,组织中马氏体含量下降,接头的最高硬度出现在焊缝或热影响区.在平行于焊缝方向,焊接接头的抗拉强度高于母材,垂直于焊缝方向,接头的抗拉强度与母材相当.由于焊缝中出现马氏体,接头的塑性和韧性降低,板材的冲压成形能力下降.

Nd:YAG laser welding of cold rolled TRIP steel sheet with tensile strength of 800 MPa and thickness of 1.2 mm was carried out. The effects of welding speed on bead morphologies and cross-section shape were investigated. The microstructures of welded joint were observed. The hardness distribution,tensile strength and formability of the welded joint were tested. The results show that for the same laser power,blowholes occur on weld bead at low welding speed and spatters occur at high welding speed. In addition,welding speed also has influence on penetration and bead width. The weld metal is mainly composed of martensite due to high cooling rate of laser welding. The amount of martensite decreases rapidly approaching base metal from weld bead center. Therefore,the weld metal or heat-affected zone has maximum hardness for the whole welded joint. The tensile strength of the welded joint perpendicular to the weld line is equal to that of the base metal,but the tensile strength of welded joint parallel to the weld line is higher than that of the base metal. The plasticity and formability of the welded joint are impaired because of the formation of martensite in the weld metal.