研究了不同保护气(Ar+5%CO₂, Ar+10%CO₂, Ar+20%CO₂和Ar+30%CO₂)对1000 MPa级高强熔敷金属组织及强韧性的影响. 结果表明, 当CO₂含量为20%时, 熔敷金属力学强韧性最佳, 屈服强度为980 MPa, 室温冲击功为72.6 J, -40 ℃冲击功为52 J. 组织观察和分析结果表明, 随着保护气中CO₂含量增加, 熔敷金属组织中贝氏体板条含量增多, 且贝氏体板条分布形态由平行状向交织状转变, 交织状贝氏体板条分割细化原奥氏体晶粒, 从而细化马氏体板条. 贝氏体含量和马氏体/贝氏体板条的分布形态是决定熔敷金属力学性能的根本原因. 贝氏体含量并非越多越好, 存在最佳含量比例; 随着保护气CO₂含量的进一步增加, 熔敷金属夹杂物数量增加, 尺寸增大, 且主要成分含量发生变化. 当保护气中CO₂含量为30%时, 出现较大尺寸的夹杂物, 导致熔敷金属韧性降低.

The use of high strength low alloy steels provides several potential advantages including lower weight, lower manufacturing costs, and ease of handling and transport. The progress in steel manufacturing technology has continually called for new developments in welding processes and consumables to produce weld metal deposits with mechanical properties essentially equivalent to the base metal. Controlling the weld metal microstructures as well as raising the welding productivity is critical factor for the development of weld metal of high strength steel to secure satisfactory mechanical properties and to reduce production costs. In order to meet the demand to apply 1000 MPa class steel to the fabrication of large scale steel structures, a weld wire for the 1000 MPa class steel has been under development to obtain the required strength and toughness, which depend primarily on the microstructure. In this work, the effects of shielding gas composition on the microstructure and properties of 1000 MPa grade deposited metals produced by metal active gas (MAG) welding have been investigated. The shielding gas employed was a mixture of argon (Ar) and carbon dioxide (CO₂) (5%~30%), and the weld heat input was 13 kJ/cm. The properties of deposited metal with shielding gas of 80%Ar+20%CO₂ is the best, the yield strength is 980 MPa, meanwhile, its Charpy absorbed energy at room temperature and -40 ℃ are 72.6 and 52 J, respectively. The results show that the microstructure of the deposited metal, consisting primary of low carbon martensite and a few parallel bainite plate, became more interweaved bainitic packets as the CO₂ content of the shielding gas was increased. The initial bainite nucleated at austenite grain boundaries and subsequent bainite plates can form at the oxide inclusions of intragranular, which presented an intersected configuration and the microstructure was refined. The content of bainite palte and distribution morphology of martensite/bainite is the intrinsic reason attributed to mechanical properties of deposited metals. The content of bainite for deposited metal has an optimal proportion and more isn't necessarily better. It was also found that the area fraction, the size and the compositions of oxide inclusions in deposited metals were changed with increasing CO₂ content. The deposited metal as using 70%Ar+30%CO₂ has the minimum toughness because more large size oxide inclusions formed which are known to be harmful to the toughness.