热输入对电弧增材制造船用高强钢组织与力学性能的影响

Effect of Heat Input on Microstructure and Mechanical Properties of Marine High Strength Steel Fabricated by Wire Arc Additive Manufacturing

采用冷金属过渡(CMT)技术+脉冲(P)电弧增材制造工艺制备了不同热输入的590 MPa(屈服强度)级船用高强钢构件,利用OM、SEM、EBSD和TEM等方法研究了热输入对成形构件组织与力学性能的影响。结果表明,热输入为5.6 kJ/cm时,构件显微组织主要为上贝氏体和粒状贝氏体,马氏体-奥氏体(M-A)组元面积分数约为14.82%,有效大角度晶界(晶界角度α>45°)长度占比为36.3%,构件在横向和纵向的抗拉强度分别达到843和858 MPa,平均硬度为286 HV,但其-50℃冲击吸收功分别仅为15和16 J;而当热输入增加至13.5 kJ/cm时,低冷却速率和高有效夹杂物(夹杂物尺寸d>0.4μm)含量促使增材制造构件组织中形成大量针状铁素体,同时还出现了板条贝氏体和少量粒状贝氏体,M-A组元面积分数降低至4.21%,有效大角度晶界长度占比增至52.4%,构件在横向和纵向的抗拉强度分别降低至723和705 MPa,与此同时,构件平均硬度也降低至258 HV,但其低温冲击吸收功大幅提高,分别达到了109和127 J,约是低热输入条件下构件低温冲击吸收功的7~8倍,冲击断裂特征也由准解理断裂转变为典型的韧性断裂。

Marine-grade high strength steel(yield strength=590 MPa)is a low-carbon,low-alloy steel characterized by high strength and toughness,excellent weldability,and seawater corrosion resistance.Thus,it is suitable for structural applications and widely used in the shipbuilding industry.Recently,wire arc additive manufacturing(WAAM)has attracted significant attention worldwide because of its high deposition rates and material utilization ratios,low material and equipment costs,and good structural integrity.However,the research on WAAM of 590 MPa marine-grade high strength steel is limited.In this work,590 MPa marine-grade high strength steel components were produced by cold metal transfer and pulse-arc additive manufacturing(CMT+P-WAAM).The effect of the heat input on the microstructures and mechanical properties of the developed steel were investigated using several techniques,including OM,SEM,EBSD,and TEM.The results indicate that at a heat input of 5.6 kJ/cm,the microstructures of the WAAM deposited metals are mainly upper bainite and granular bainite,the area fraction of the martensite-austenite(M-A)constituents accounts for about 14.82%,the length ratio of the effective highangle grain boundary(grain boundary angleα>45°)is 36.3%,the tensile strength of the deposited metals are 843 and 858 MPa in the horizontal and vertical directions,respectively,and the average microhardness is about 286 HV.However,its impact absorbed energy at-50oC is only 15 and 16 J in the horizontal and vertical directions,respectively.At a heat input of 13.5 kJ/cm,the low cooling rate and the high inclusion(inclusion size d>0.4μm)content promote the formation of a large quantity of acicular ferrites with lath bainites and a small amount of granular bainites.The area fraction of the M-A constituents is reduced to 4.21%,and the length ratio of the effective high-angle grain boundary is increased to 52.4%.The tensile strength of the deposited metals in the horizontal and vertical directions is reduced to 723 and 705 MPa,respectively.Similarly,the average microhardness is also reduced to 258 HV,but the lowtemperature impact absorbed energy is greatly improved,reaching 109 and 127 J,respectively,which is 7-8 times that of the WAAM deposited metal at a low heat input.The impact fracture characteristics also changed from a quasi-cleavage fracture to a typical ductile fracture.