保护气体对440MPa HSLA钢GMAW焊缝组织及韧性的影响

采用不同保护气体对440 MPa级低合金高强钢(HSLA钢)进行气保焊焊接,通过光学显微镜(OM)、透射电镜(TEM)、扫描电镜(SEM)和电子背散射衍射技术(EBSD)对焊缝微观组织及夹杂物形貌进行了观察,研究了保护气体组成对焊缝组织及韧性的影响,并分析了不同成分保护气体对焊缝夹杂物大小、数量及其成分的影响.结果表明,保护气体为100％ CO2,焊缝金属韧性较差；保护气体(体积分数)为80％ Ar+20％ CO2和90％ Ar+ 10％ CO2,焊缝金属韧性较好.100％ CO2气体保护焊焊缝组织主要为铁素体和贝氏体,混合气体保护焊(20％ CO2和10％ CO2)焊缝组织主要为针状铁素体和少量侧板条铁素体.随着保护气体中CO2含量的减少,焊缝金属中夹杂物数量、尺寸均降低,且成分发生变化.对于440 MPa级HSLA钢,合理的保护气体组成可以得到良好的焊接质量.

Effects of shielding gas composition on microstructure and toughness of 440 MPa HSLA steel weld metals with gas metal arc welding

The 440 MPa HSLA steel was welded with gas metal arc welding (GMAW),and the microstructure of weld metals and the morphology of inclusions were analyzed with OM, TEM,SEM,and EBSD.The effects of shielding gas on the microstructure, impact toughness of the weld metals and the size, quantity,compositions of inclusions were investigated.The results show that impact toughness of weld metal is bad with 100% CO₂ as shielding gas,and weld metals with good impact toughness can be obtained with 80% Ar+20% CO₂ and 90% Ar+10% CO₂ (volume fraction) as shielding gas.The microstructure of weld metal of 100% CO₂ GMAW is made up of ferrite and bainite,and that of both 20% CO₂ GMAW and 10% CO₂ GMAW are predominantly acicular ferrite with small areas of ferrite side plates.With the increasing of the proportion of CO₂ in shielding gas,the amount and dimension of inclusions increase,and the compositions of its main ingredients change.For 440 MPa HSLA steel,welding with proper gas composition can produce welded joints with good properties.