1. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
2.School of Mechanical Engineering, Xiangtan University, Xiangtan 411105, China
Cr-Mo low alloy heat-resistant steel has been widely used in energy, chemicals and other large equipment manufacturing industries by welding. The strength, toughness, creep properties of welding joints are of very strict requirement. But the welding joint consists of the welding metal, fusion, zone, harden area of based metal, and soft zone with significant differences in chemical composition, organization, and performance, with the mechanical behavior of the welding joint showing obvious differences with homogeneous materials, so tests are needed to find the weak links of the welding joint, which can reflect the mechanics characteristics of different zones at the same time. In this paper, a three-point bending test including different zones was made on the narrow-gap multi path/multi layer welding joints of the typical 2.25Cr-1Mo steel, with the secondary crack found near the fusion zone. The fracture surface observation, optical observation, micro-hardness test and numerical simulation were carried out to study what causes the secondary crack. The results show that the fusion zone has some soft ferrites, and the coarse grain zone has some harden martensites, with non-uniform hardness found near the secondary crack. The results of finite-element analysis reveal that stress concentration exists at the boundary with non-uniform hardness, which leads to the secondary crack in the fused zone. The results has are of significance to adjust the matched types of welding joints and the welding technology.
林尚扬, 于丹, 于静伟. 压力容器焊接新技术及其应用[J]. 压力容器, 2010, 26(11): 1-6. LIN Shangyang, YU Dan, YU Jingwei. New welding technologies for pressure vessel manufacturing[J]. Pressure Vessel Technology, 2010, 26(11): 1-6. (in Chinese)
[2]
叶小松, 刘应虎, 田洪波, 等. 采用窄间隙埋弧焊焊接2. 25Cr-1Mo-0. 25V钢的试验及应用研究[J]. 大型锻件, 2009(5): 30-33, 37. YE Xiaosong, LIU Yinghu, TIAN Hongbo, et al. The experiment and application study for 2.25Cr-1Mo-0.25V steel by narrow submerged arc welding[J]. Heavy Castings and Forgings, 2009(5): 30-33, 37. (in Chinese)
[3]
Rojko D, Gliha V. Simulations of transformation kinetics in a multi-pass weld[J]. Materials and Manufacturing Processes, 2005, 20: 833-849.
[4]
JANG Jae-Il, LEE Jng-Suk, UU Jang-Bog, et al. Determination of microstructural criterion for cryogenic toughness variation in actual HAZs using microstructure-distribution maps[J]. Materials Science and Engineering, 2003, 351(1-2): 183-189.
[5]
周志良, 刘书华, 谢明. 局部脆性区对直接淬火回火钢焊接热影响区断裂韧性的影响[J]. 焊接学报, 1998, 19(3): 147-153. ZHOU Zhiliang, LIU Shuhua, XIE Ming. Effect of local brittle zones on HAZ fracture toughness of direct quenched and tempered steel[J]. Transactions of the China Welding Institution, 1998, 19(3): 147-153. (in Chinese)
FANG Huizhen, SU Yi, LU Anli. The influence of austenitic metal on the fracture behavior of 9% Ni steel welded joints [C]// The International Welding Congress in Conjunction with ASM Materials Week' 85. 1985: 131-141.
[8]
于启湛, 史春元. 耐热金属的焊接 [M]. 北京: 机械工业出版社, 2009.
[9]
Saxenaa S, Ramakrishnanb N. An improved method for numerical determination of SZW using FEM[J]. Nuclear Engineering and Design, 2009, 239: 1207-1211.
[10]
孙慧敏, 王国珍, 轩福贞, 等. 焊接接头延性裂纹扩展的数值模拟[J]. 焊接学报, 2010, 31(8): 105-108, 112. SUN Huimin, WANG Guozhen, XUAN Fuzhen, et al.Numerical simulation of ductile crack propagation in weld joint[J]. Transactions of the China Welding Institution, 2010, 31(8): 105-108, 112. (in Chinese)
[11]
陈伯蠡. 焊接冶金原理 [M]. 北京: 清华大学出版社, 1991.
[12]
Nowacki J, Lukojc A. Microstructural transformations of heat affected zones in duplex steel welded joints[J]. Materials Characterization, 2006, 56: 436-441.
2014, Vol. 54 
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