700 MPa微合金高强钢焊接软化机理及解决方案

Mechanism and solution of welding softening for 700 MPa microalloyed high strength steel

700 MPa级Ti-Nb成分体系控轧控冷高强钢以其生产成本低、高强韧性以及优良的可焊性,近年来在专用车轻量化领域得到广泛应用。采用80%Ar+20%CO_2(体积分数)混合气体保护焊,对高Ti、Nb元素析出强化高强钢进行了焊接强度实验研究。结果表明,随着焊接热输入增大,焊接接头强度有降低趋势,焊接热影响区较母材硬度降低,存在软化行为,其软化机理表现在细晶强化、变形强化和析出强化效果的丧失。通过母材的B微合金化、控制焊接热输入等措施可有效缓解软化倾向,可为此种高强钢进一步推广应用提供技术参考。

Currently,Ti-Nb microalloyed high-strength steel with thermo-mechanical control process has been widely used in the field of light weight applications on special vehicles,owing to its characteristics of low production cost,high strength,high toughness,and excellent welding ability.The welding strength of Ti-Nb microalloyed high strength steel was studied by using metal active gas welding(80 vol.%Ar+20 vol.%CO2).The results show that the strength of welded joint decreases with the increasing welding heat input.The hardness of the heat-affected zone(HAZ)is lower than that of the base metal,which indicates the existence of softening behavior in HAZ.The softening mechanism is manifested in the loss of fine grain strengthening,deformation strengthening and precipitation strengthening.Microalloying of B in the base metal and controlling welding heat input can effectively alleviate the softening tendency,and provide technical reference for the further promotion and application of this kind of high-strength steel.