690 MPa级ULCB熔敷金属组织与强韧化规律

 采用传统的高强钢焊接材料焊接690 MPa级低碳铜沉淀强化钢时,仍需严格控制热输入、预热温度、层间温度,这使得低碳铜沉淀强化钢的优良性能和可节约生产成本的优势得不到很好地发挥。通过采用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电镜(TEM)等表征方法,研究了不同质量分数的Si/Mn/Ni配比对690 MPa级超低碳贝氏体(ULCB)熔敷金属的组织及强韧性能的影响,为690 MPa级低碳铜沉淀强化钢配套的焊接材料的工程化应用提供一定的技术支持和积累。结果表明,690 MPa级超低碳贝氏体(ULCB)熔敷金属组织主要由板条贝氏体、粒状贝氏体和针状铁素体组成。当Si质量分数为0.16%、Mn质量分数为1.46%时,熔敷金属组织细化,冲击韧性得以提升,但Si含量过低易使贝氏体铁素体呈块状,导致韧性提升有限。而当Si质量分数为0.29%、Mn质量分数为1.02%时,Ni含量增加,贝氏体铁素体板条呈细长条状,显微组织相互交错分布,使熔敷金属冲击韧性显著改善。相变位错强化受贝氏体开始转变温度(B_s)影响,这是影响ULCB熔敷金属强度的主要原因。ULCB熔敷金属中夹杂物主要分布在贝氏体铁素体的板条亚结构间,少量成为针状铁素体的形核质点,促进针状铁素体形核,因此,对熔敷金属中的夹杂物进行控制,可进一步发挥超低碳贝氏体熔敷金属的潜力,提高其韧性。

Microstructure and strength-toughness mechanism of 690 MPa grade ULCB deposited metals

When using traditional welding materials for high-strength steels to carry out extensive welding testing of 690 MPa grade copper precipitation strengthening steel,it was still necessary to strictly control the heat input,preheating temperature,and interpass temperature,which makes the excellent performance of copper precipitation strengthening steel and the advantage of saving production cost cannot be brought into full play. The effect of Si,Mn,Ni on the microstructure and mechanical properties of the 690 MPa grade ultra-low carbon bainite (ULCB) deposited metal was investigated by OM,SEM,TEM,in order to provide technical accumulation for domestic production of non-preheating welding materials for copper precipitation strengthening steel. Experimental results showed that the microstructure of deposited metal was primarily comprised of granular bainite (GB),lath bainite (LB),and acicular ferrite (AF). The microstructure of the deposited metal with 0.16% Si and 1.46% Mn was refined, leading to the improvement of impact toughness. However,the Si content was too low to make the width of the bainite ferrite (BF) substructure decreased,resulting in the improvement of toughness was limited. The microstructure of deposited metal with 0.29% Si,1.02% Mn and more Ni content was interlocked,and the lath width of the bainite ferrite decreased,contributing to impact toughness improved significantly. Phase transformation dislocation strengthening was affected by the bainite onset temperature (B_s),which was the main reason that affects the strength of ULCB deposited metal. Inclusions were mainly distributed between the bainite ferrite,and a small amount become the nucleation points of the acicular ferrite. Therefore,a greater increase in impact toughness would be realized by reduction in inclusion density and size of the deposited metal.