热输入对1200MPa级HSLA钢焊缝组织性能的影响

Effect of Heat Input on Microstructure and Property of Weld Joints of a 1200 MPa Grade HSLA Steel

为了研究焊接工艺条件对焊缝金属组织性能的影响,采用不同热输入对1200 MPa级低合金高强钢进行熔化极气体保护焊,利用OM、SEM、TEM观察并分析不同焊接热输入对焊缝组织及力学性能的影响规律。结果显示,当热输入为16、20、25 k J/cm时,焊缝组织主要以针状铁素体为主,并含有少量M-A组元以及粒状贝氏体。随焊接热输入增大,针状铁素体组织有所增多且板条宽度逐渐增大,而粒状贝氏体组织减少。焊缝内非金属夹杂物类型多为促进针状铁素体形核的Ti-Mn-Al-O-S系复合氧化物夹杂。焊缝金属硬度、冲击韧性及焊接接头强度随热输入增大基本呈下降趋势,并且各焊接热输入条件下焊缝金属具有良好的强韧性匹配。随热输入增大,焊缝金属断裂特征由韧性、脆性混合型断裂向脆性断裂转变。热输入为20 k J/cm时,焊接接头综合性能最佳。

A 1200 MPa grade high-strength low-alloy （HSLA） steel was welded by metal active gas （MAG） welding method with filler material of GHS50NS welding wire by three different heat inputs. And then the effect of heat input on microstructure and property of the weld joints was investigated by means of optical microscopy, scanning electronmicroscopy, transmission electron microscopy and mechanical tests. The results indicate that the microstructure of weld joints consists mainly of acicular ferrite, a granular bainite and small amount of M-A by different heat inputs. With the increasing heat input, the amount of acicular ferrite was increased and its lath width was coarsened while the amount of granular bainite decreased, and the type of non metallic inclusions which promote the nucleation of acicular ferrite in weld joints was a complex oxide-sulfide Ti-Mn-Al-O-S. The strength and hardness of the welded joint decreases with the increase of heat input, but it has a good combination of strength and toughness. Along with the increase of heat input, the morphology of the impact fracture of the weld joint changed from fracture with mixed mode to brittle fracture. When the heat input is 20 kJ/cm, the comprehensive performance of the welded joint is the best.