高强厚板S620Q桥梁用钢焊接接头组织及力学性能

Properties and microstructure of welded joint of high strength thick plate S620Q bridge steel

采用实芯80%Ar+20%CO2气体保护焊对40 mm厚S620Q桥梁用钢板进行多层多道焊接,利用光学显微镜和扫描电镜等分析手段研究焊接接头组织及力学性能。结果表明,从X形焊根到盖面焊道,焊缝组织由针状铁素体(AF)+粒状贝氏体(GB)转变为粗大AF+GB,强度先增大后减小。粗晶热影响区(CGHAZ)主要组织为板条状贝氏体、马氏体和GB。二次热循环温度在(α+γ)临界区时,粗晶区晶界处生成了不规则、岛状M-A和贝氏体,部分淬火区晶界处为GB。-20℃接头CGHAZ冲击韧性值高于焊缝,焊缝断口形貌为韧窝+少量解理,CGHAZ纤维区为大的韧窝,放射区为解理+少量韧窝,在小的撕裂刻面上有二次裂纹。CGHAZ晶界处不规则、岛状M-A对韧性损害较小,脆性解理断裂起源于晶内,而不是晶界。

Weldability experiments of S620 Q bridge steel plate with 40 mm thickness were carried out by using the solid wire 80% Ar +20% CO2 shielded multi-pass welding technology. Microstructural characteristics and mechanical properties of welded joint were investigated by means of optical microscope and scanning electron microscopy( SEM). Results indicate that from the X shape welding root to cover welding pass,microstructure of the weld is changed from acicular ferrite( AF) and granular bainite( GB) to coarse AF and GB,and strength increases first and then decreases. The main microstructure of coarse grain heat affected zone( CGHAZ) is composed of lath martensite,bainite and GB. When the second peak temperature is up to the( α + γ) critical region,the irregular,granular M-A islands and bainitic ferrite are formed in the boundaries of CGHAZ,and only GB is distributed in the boundaries of partial quenching zone. The-20 ℃ impact toughness of CGHAZ is higher than that of the weld with the fracture morphology characterized by dominant dimples and a small amount of cleavage. While in CGHAZ large dimples are observed in the fibrous zone,and the radical zone is composed of cleavage with a small amount of dimple,moreover,there exists secondary crack in the small cleavage facets. The irregular,granular M-A islands along the grain boundary of CGHAZ have little effect on toughness,and brittle cleavage fracture is initiated in grain,rather than at grain boundary.