【摘要】 通过附带EDS的FEGSEM、EBSD、TEM等实验方法,研究了保护气成分（Ar+5%CO₂、Ar+10%CO₂、Ar+20%CO₂、Ar+30%CO₂,体积分数）对1000 MPa级高强熔敷金属组织特征的影响,阐明了保护气成分对组织转变的影响机制。结果表明,随着保护气中CO₂含量增加,1000 MPa级熔敷金属强度略有下降,而冲击韧性先升高后降低。不同保护气熔敷金属均由马氏体/贝氏体混合组织及板条间残余奥氏体组成。随着保护气中CO₂含量增加,熔敷金属中贝氏体相变体积分数为50%时的温度(B₅₀)与马氏体相变开始温度（M_s）相变温度区间增大,适宜贝氏体形核的夹杂物数量增多,随贝氏体含量（体积分数）由8%增加到29.6%,其形核位置从原始奥氏体晶界向原始奥氏体晶界及晶内夹杂物处共同形核转变,熔敷金属组织形貌由"平行状"向"交织状"转变,分割细化组织,有利于高强熔敷金属强韧性的改善。更多还原

【Abstract】 In recent years, high and ultra-high strength steels have been developed and used in light-weight constructions such as the structural members of mobile equipment in order to reduce weight and fabrication costs and to enhance the performance. Welding of steels with yield strength of more than 900 MPa is particularly challenging because of the toughness requirements for the weld metal, which calls for welding consumables of high strength and good toughness. Weld metals have been produced for a variety of welding methods with yield strength up to or above 1000 MPa, but their impact toughness remained only at medium yield strengths. Proper microstructure is the key to meeting this requirement,and its final microstructure depends on the chemical composition and cooling rate. For the deposited metal produced by gas metal arc welding（GMAW）, the composition is dependent on the welding wire and shielding gas. The cooling rate of the weld metal is controlled by a combination of heat input and heat extraction. It is known that the addition of CO₂ to argon based shielding gas is effective for improvement of productivity in GMAW welding of steel. Through the chemical reaction in the welding arc, CO₂ in the shielding gas can affect the chemical composition of the weld metal, and its microstructure. The 1000 MPa grade deposited metals was welded with GMAW, and the effects of shielding gas composition（Ar+（5%～30%）CO₂,volume fraction） on the general compositional and microstructural characteristics of deposited metals, including nonmetallic inclusions, were experimentally characterized with SEM, EBSD and TEM. The microstructure of the deposited metals is mainly composed of martensite and bainite. With the increase of CO₂ content（5%～30%）, the strength of the deposited metals decrease slightly and the impact toughness increases first and then decreases. Meanwhile, the transformation range(B₅₀-M_s) of the deposited metal increases, the bainite content increases（8%～29.6%） with the quantity of inclusions that are suitable for bainite nucleation increases, and the nucleation position changes from the original austenite grain boundary to the common nucleation on the original austenite grain boundary and inclusions within the grain. At the same time, the microstructure morphology of the deposited metal changes from parallel to intertexture, which presented an intersected configuration and microstructure refinement.更多还原