调质处理对G520钢焊接接头组织及性能的影响

Influence of Quenching and Tempering on Microstructure and Properties of Welded Joints of G520 Martensitic Steel

对G520马氏体不锈钢进行焊条电弧焊接和调质处理,利用OM、SEM、EBSD、XRD以及拉伸、冲击等实验研究了调质顺序对焊接接头组织及性能的影响。结果表明,焊前调质处理下焊接接头各区域组织差别较大,焊缝粗大柱状组织呈长条状分布且含有大量δ-铁素体;焊后调质处理焊接接头组织为均匀细小的板条马氏体。与焊前调质相比,焊后调质处理的焊接接头具有更优异的强韧性。焊缝经调质处理后,δ-铁素体得以溶解,粗大柱状组织分解成较小的马氏体板条块,在板条马氏体边界和原始奥氏体晶界形成一定量的逆变奥氏体,使大角度晶界比例增加,有效改善了焊缝金属强韧性。

As a low carbon martensitic precipitation hardening stainless steel,G520 steel has been widely used in heavy load and corrosion-resistant components such as compressor impeller due to its high strength with reasonable toughness,ductility and corrosion resistance.Although heat treatment usually presents a tendency to promote a improvement of mechanical properties,it may cause unpredictable changes in the microstructure and properties of high strength steel weldment,which is extremely complicated and normally very sensitive to heat.Based on this scenario,the influence of quenching and tempering on the mechanical and microstructural properties of G520 steel weld metals obtained by shielded metal arc welding(SMAW)was studied in this work.Tensile test,impact test and metallographic examination by OM,XRD,SEM and EBSD were performed for mechanical and microstructural characterization.The results indicate that,the welded joints after quenching(at 850℃,oil cooling)and tempering(at 520℃,air cooling)have better strength and toughness than the pre-weld quenching and tempering.Moreover,the quenching and tempering treatment of the weld metal,breaks down the columnar microstructure into smaller martensite sub-blocks.Meanwhile,it form a certain amount of inversion austenite at the prior austenite grain boundary and the boundary of the lath martensite.As above,the proportion of the large angle grain boundary is increased,which effectively improves the toughness of the weld metal.