LBW与MAG焊接14MnMoNbB低合金高强钢接头组织及力学性能对比研究

Comparative Study on Microstructure and Mechanical Properties of 14MnMoNbB High Strength Low Alloy Steel Joints Using LBW and MAG Welding

分别采用激光焊接(LBW)和熔化极活性气体保护焊(MAG),焊接板厚为10mm的14MnMoNbB低合金高强钢对接接头,并对两种焊接接头的显微组织及力学性能进行了对比分析研究。研究结果表明,两种焊接方法在优化焊接工艺条件下都实现了全熔透焊,且得到了正反表面成型良好,无裂纹、气孔等宏观缺陷的焊接接头;激光焊接焊缝显微组织主要为板条马氏体,热影响区为由细小的板条马氏体淬火区和铁素体加贝氏体组成的二次回火区组织,而MAG焊缝主要为细小的针状铁素体组织,热影响区主要由粗大的板条马氏体组成,两种接头热影响区晶粒尺寸都沿熔合线到母材方向逐渐减小,但LBW接头的平均晶粒尺寸明显小于MAG焊接;激光焊接接头焊缝处显微硬度明显高于母材,无接头软化现象,而MAG焊接头焊缝处显微硬度低于母材,且热影响区硬度高于母材;激光焊接接头拉伸强度与母材相当,试样断裂位置位于远离焊缝的母材,而MAG焊接接头拉伸强度略低于母材,断裂于焊缝区;两种焊接接头都有良好的冲击性能,但激光焊接接头的冲击性能要略优于MAG焊。

The butt joints of 10 mm thickness 14 MnMoNbB high strength low alloy steel were obtained by laser beam welding（LBW）and metal active gas（MAG）arc welding respectively.The microstructure and mechanical properties of the two welded joints were compared and analyzed.The results show that two kinds of methods have achieved full penetration welding under the optimized welding conditions,and have obtained the welded joints with good forming in positive and negative surface,no cracks,holes and other macroscopic defects.The microstructure of the laser weld is mainly composed of lath martensite,and the heat affected zone is composed of fine lath martensite quenching zone and ferrite plus bainite secondary tempering zone.The MAG weld is mainly composed of tiny acicular ferrite,the heat affected zone is mainly composed of coarse lath martensite.The grain size of heat affected zone of the two welded joints is decreasing along the fusion line to the base metal.But the average grain size of LBW joints is obviously smaller than that of MAG welding.The microhardness of the laser welded joint is significantly higher than that of the base metal,no joint softening phenomenon,and the microhardness of MAG welded joints is lower than the base metal,and the microhardness of heat affected zone is higher than the base metal.The tensile strength of the laser welded joints is equivalent to that of the base metal,and the fracture position of the specimen is located away from the base metal of the weld.The tensile strength of the MAG welded joints is slightly lower than that of the base metal,and is broken in the weld zone.Both welded joints have good impact performance,but the impact of laser welding joints is slightly better than MAG welding.