热输入对DP600激光焊组织和力学性能的影响

摘要：为了研究DP600钢的焊接性能，采用5种不同的激光焊接工艺进行焊接试验。结果表明，焊接接头表面成形质量良好，随着热输入的增加，上下熔宽逐渐增大；熔融区均为板条状马氏体组织，当热输入高于33J/mm时热影响区组织为马氏体、铁素体和少量的回火马氏体；当热输入低于33J/mm时，热影响区组织为马氏体和铁素体。在低热输入条件下，回火时间很短，马氏体未发生分解；在高的热输入条件下，回火时间较长，马氏体分解显著，热影响区中出现M3C型碳化物，碳化物形貌以球状和片状为主。从熔融区到母材，显微硬度值逐渐降低；焊接接头静态拉伸失效位置均在母材，拉伸断口为韧性断口，DP600钢激光焊接接头不存在软化现象。

Effect of heat input on microstructure and mechanical properties of laser welded DP600 steel

In order to study the welding performance of the DP600 steel, welding tests with five different laser welding processes were conducted. The results reveal that the quality of welded joint is good, and the upper and lower width of weld zone gradually increases with increasing heat input. The fusion zone is composed of lath martensite; when the heat input is more than 33J/mm, the heat affected zone (HAZ) is composed of martensite, ferrite, and a small amount of tempered martensite; when the heat input is less than 33J/mm, the microstructure of the HAZ is determined to be martensite and ferrite. When the heat input is low, martensite does not decompose due to the short tempering time. When the heat input is high, martensite decomposes remarkably with longer tempering time, and M3C carbides with spherical and flaky morphology are found in the HAZ. The microhardness are found to decrease gradually from fusion zone to base metal. The static tensile failure of welded joints are all occurred in the base metal and are found to be ductile fracture, and no softening zones are observed in DP600 welded joints.