激光功率对Q235钢接头组织和力学性能的影响

Effect of laser power on the microstructure and mechanical properties of Q235 steel joint

摘要:

采用不同的激光功率，对2 mm厚的Q235钢进行了激光焊（Laser beam welding，LBW）．通过光学显微镜、扫描电子显微镜、显微硬度计、室温拉伸和室温弯曲实验等表征手段，研究了激光功率对接头组织和力学性能的影响．结果表明：接头横截面，包括母材（Base metal, BM）、临界热影响区（Critical heat affected zone, ICHAZ）、细晶热影响区（Fine-grain heat-affected zone, FGHAZ）、粗晶热影响区（Coarse-grain heat-affected zone, CGHAZ）和熔合区（Fusion zone, FZ）；激光焊接功率增大时，ICHAZ区铁素体（F）晶粒变大，珠光体（P）被分解；FGHAZ区的晶粒被细化，部分细颗粒状碳化物在F中弥散分布，其余部分碳化物与F在晶界机械混合；CGHAZ区主要为等轴状马氏体（M），晶界存有少量粒状贝氏体（BG）、板条马氏体（ML）和块状马氏体（MB）；FZ区以马氏体（M）、针状铁素体和贝氏体（B）为主；在激光功率3535 W和3830 W下焊缝的硬度高于HAZ区和BM；当激光功率为3535 W时，接头抗拉强度为514.8 MPa、延伸率23.4%，FZ硬度平均值约为360 HV，获得了综合力学性能优良的接头．

Abstract:

Laser beam welding （LBW） was conducted on the butt joints of 2 mm thickness Q235 steel by utilizing different laser powers. Optical microscope， scanning electron microscope， microhardness testing， tensile testing and bend testing at room temperature were used to investigate the effects of laser power on the microstructure and mechanical properties of the joints. Results show that the joint cross section consists of base metal （BM）， critical heat affected zone （ICHAZ）， fine-grain heat-affected zone （FGHAZ）， coarse-grain heat-affected zone （CGHAZ） and fusion zone （FZ）. In the case of higher laser power， for the ICHAZ， ferrite （F） becomes coarser and pearlite （P） is decomposed. The grains in FGHAZ are refined， some fine granular carbides are characterized by dispersed distribution in F， and the rest carbides are mechanically mixed with F at the grain boundaries. In the CGHAZ， equiaxed martensite （M） is dominant， a small amount of granular bainite （BG）， lath martensite （ML） and massive martensite （MB） can be observed at grain boundaries. FZ is mainly consist of martensite（M）， acicular ferrite and bainite （B）. For the cases of 3535 W and 3830 W， the microhardness of the FZ is much higher than that of other zones. When the laser power is 3535 W， the tensile strength and elongation of the joint are 514.8 MPa and 23.4%， respectively. The average microhardness of FZ is 360 HV. Thus， the joint with excellent comprehensive mechanical properties was obtained.