Q550高强钢焊接接头强韧性匹配

Strength matching on mechanical properties of welded joint of Q550 high strength steel

在不预热条件下采用不同合金成分焊丝焊接Q550高强钢,试验研究焊丝中合金对焊缝组织、接头抗拉强度及冲击韧性的影响.结果表明,使用MK.G60-1焊丝可获得以针状铁素体为主的焊缝组织.焊缝中沿晶界分布的先共析铁素体在承受拉应力时易萌生裂纹,提高焊缝中针状铁素体含量可以提高接头抗拉强度和韧性.采用MK.G60-1焊丝接头抗拉强度接近母材的抗拉强度,断裂发生在熔合区.接头热影响区的冲击吸收功最高,而熔合区的抗拉强度和韧性最低.焊缝冲击断口纤维区均以穿晶断裂为主,断口韧窝产生的机理是微孔聚集型,针状铁素体区对应的韧窝较大,先共析铁素体对应的韧窝较小.

Q550 high strength steel was welded by means of gas metal arc welding process without pre-heating.The effects of welding wires with different composition and strengths on the microstructure of weld metal and the mechanical properties of the joints were studied.Results indicate that acicular ferrite is the dominant microstructure in the weld metal produced by using MK·G60-1 welding wire.When the joint is subjected to tensile stress,cracks occur easily at pro-eutectoid ferrite presenting along the prior austenite grain boundaries.Both the tensile strength and impact toughness in weld metal and fusion zone are improved with the increasing of the content of acicular ferrite.The tensile strength of the joint made by MK·G60-1 wire is close to that of Q550 steel,and tensile samples fracture at the fusion zone.For both ER50-6 and MK·G60-1 weld metals,impact toughness is the best in the heat-affected zone and the worst in the fusion zone.Transgranular fracture with the mechanism of micro-void coalescence appears in fibrous zone in the fractured surfaces of impact specimens.It can be concluded from microstructure and fractographs that acicular ferrite corresponds to relatively large dimples while pro-eutectoid ferrite corresponds to the small ones.