铈和铌改性对DP780双相钢焊缝冲击性能的影响

 双相钢中铁素体马氏体两相性能差异会导致焊接接头软化,在使用过程中温度较低时,冲击功下降,使材料由韧性状态变为脆性状态。为研究铈和铌添加量对改善DP780焊缝低温脆性的问题,利用低温冲击试验与拉伸试验,开展了不同铈和铌添加量对DP780焊缝的力学性能的研究。利用金相显微镜、SEM等方法阐明了试验钢在添加不同铈和铌后的焊缝组织与形貌变化。结果表明,在-40 ℃时,无铈和铌添加时组织中出现部分残余奥氏体,焊缝冲击功为0.465 J,解理台阶面出现大量河流花样,属于脆性断裂;随铈与铌质量分数变化,焊缝冲击功与铈和铌的添加量呈现非线性关系。当铈与铌占熔敷金属质量分数分别为0.35%和0.15%时焊缝的综合性能最佳,冲击功达到3.9 J,熔敷金属组织晶界紧密,撕裂棱周围出现韧窝,呈混合断裂特征。试验研究表明,加入的适量的铈与铌,焊缝中形成的稀土化合物可增加断裂变形阻力与消耗能量,从而有效阻碍裂纹的扩展,显著提高DP780的低温冲击韧性而不会大幅降低其抗拉强度,保证双相钢焊接质量。但铈与铌影响焊缝性能无固定函数关系可循且试验样本量少,无法精确到任意添加量探究。在后续研究中可引入算法对DP780焊缝力学性能进行预测,在生产之前建立模型,寻找最佳铈和铌添加量,提高安全性能。

Effect of Ce and Nb modification on weld impact properties of DP780 duplex steel

The two-phase performance difference of ferrite and martensite in dual-phase steel,caused the welded joint to soften. When the using temperature was low, the impact energy decreased,caused the material change from a ductile state to a brittle state. In order to research the Ce and Nb addition on the brittleness with low temperature improvement of DP780 weld,used low temperature impact test and tensile test,to study mechanical properties of DP780 weld with different Ce and Nb addition. Used metallographic microscope,SEM and other methods, clarified the changes in weld microstructure and morphology which added different Ce and Nb. The results showed that at -40 ℃,residual austenite appeared in the microstructure without Ce and Nb,the impact energy of the weld was 0.465 J. And a large number of river patterns appeared on the cleavage step surface,which belonged to brittle fracture. As the Ce and Nb mass percents changed,the impact energy of the weld was nonlinear with Ce and Nb addition. When the mass percent of Ce and Nb was 0.35% and 0.15% of the deposited metal,the weld had the best overall performance,the impact energy of the weld reached to 3.9 J. The deposited metal structure had dense grain boundaries,and dimples appeared around the tearing edge,showed mix fracture characteristics. It appeared that add appropriate amount of Ce and Nb,rare earth compounded form in welds,could increase the fracture deformation resistance and energy consumption. Thereby effectively retard the crack propagation,significantly improved the low-temperature impact toughness of DP780,and would not greatly reduce its tensile strength,ensured the welding quality of dual-phase steel. But there was no fixed function relationship between Ce and Nb on weld performance,and the sample size was small,could not be accurate to any addition amount. In the follow-up research,algorithms could be introduce to predict the mechanical properties of DP780 welds,build the model before production,to find the best addition of cerium and niobium,improved safety performance.