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金属学报  2015, Vol. 51 Issue (12): 1489-1499    DOI: 10.11900/0412.1961.2015.00294
  本期目录 | 过刊浏览 |
保护气对1000 MPa级熔敷金属组织及力学性能的影响*
安同邦1,2,田志凌2(),单际国1,魏金山2
1 清华大学机械工程系, 北京 100084
2 钢铁研究总院, 北京 100081
EFFECT OF SHIELDING GAS ON MICROSTRUCTURE AND PERFORMANCE OF 1000 MPa GRADE DEPOSITED METALS
Tongbang AN1,2,Zhiling TIAN2(),Jiguo SHAN1,Jinshan WEI2
1 Department of Mechanical Engineering, Tsinghua University, Beijing 100084
2 Central Iron & Steel Research Institute, Beijing 100081
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摘要: 

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.

关键词 1000 MPa级熔敷金属保护气强韧性马氏体/贝氏体板条分布形态氧化物夹杂    
Abstract

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.

Key words1000 MPa grade deposited metal    shielding gas    strength and toughness    martensite/bainite lath    distributed morphology    oxide inclusion
    

引用本文:

安同邦,田志凌,单际国,魏金山. 保护气对1000 MPa级熔敷金属组织及力学性能的影响*[J]. 金属学报, 2015, 51(12): 1489-1499.
Tongbang AN, Zhiling TIAN, Jiguo SHAN, Jinshan WEI. EFFECT OF SHIELDING GAS ON MICROSTRUCTURE AND PERFORMANCE OF 1000 MPa GRADE DEPOSITED METALS. Acta Metall Sin, 2015, 51(12): 1489-1499.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2015.00294      或      https://www.ams.org.cn/CN/Y2015/V51/I12/1489

Shielding gas C Si Mn Ni+Cr+Mo Ti O N Fe
Ar+5%CO2 0.097 0.52 1.67 3.88 0.070 0.021 0.0034 Bal.
Ar+10%CO2 0.089 0.48 1.54 3.83 0.065 0.027 0.0032 Bal.
Ar+20%CO2 0.089 0.47 1.46 3.80 0.045 0.032 0.0036 Bal.
Ar+30%CO2 0.087 0.43 1.38 3.69 0.043 0.040 0.0034 Bal.
表1  熔敷金属的化学成分
图1  保护气对熔敷金属力学性能的影响
图2  不同保护气下末层焊道熔敷金属显微组织的OM像
图3  不同保护气下熔敷金属显微组织的TEM像和残余奥氏体SAED分析
图4  不同保护气熔敷金属板条块亚结构EBSD图和反极图
图5  熔敷金属中夹杂物尺寸分布
Shielding gas Average inclusion diameter / μm Maximum inclusion size / μm Number density of inclusion / 104 mm-2 Area fraction of inclusion / %
Ar+5%CO2 0.3316 1.118 10.0 0.08
Ar+10%CO2 0.4023 1.365 9.8 0.13
Ar+20%CO2 0.4137 1.408 12.3 0.20
Ar+30%CO2 0.4338 1.447 12.9 0.22
表2  不同保护气熔敷金属中夹杂物统计
图6  不同保护气下末层焊道熔敷金属显微组织彩色OM像
图7  熔敷金属的贝氏体相变体积分数为50%时的温度B50和马氏体相变开始温度Ms随保护气中CO2含量的变化关系
图8  夹杂物处形核长大的贝氏体板条TEM像和SEM像
图9  Ar+30%CO2熔敷金属冲击断口中以夹杂物为起裂源形成的解理形貌
Shielding gas Mn Si Ti Al S O
Ar+5%CO2 29.57 1.89 48.87 5.73 0.39 13.55
Ar+10%CO2 34.11 3.52 40.19 7.81 0.53 13.84
Ar+20%CO2 36.68 11.17 32.97 4.80 0.95 13.43
Ar+30%CO2 37.65 9.80 31.82 3.55 1.66 15.52
表3  熔敷金属中夹杂物化学成分
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