Effect of pre-strain on impact fracture behavior of X80 pipeline steel
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摘要: 开展了预应变对X80管线钢冲击断裂行为影响的研究，采用OM、SEM、EDS能谱对断口形貌及夹杂物进行分析，利用EBSD获取断口横截面上二次裂纹附近晶体学特征。结果表明，预应变对最大冲击载荷没有显著影响，但当材料中存在预应变时，材料脆性断裂趋势增加、缺口敏感度增加、裂纹形成功和材料对裂纹的止裂能力降低；在冲击断裂过程中，预应变导致材料内部位错相互缠结，位错运动受到阻碍，当受到外力时易发生脆性断裂，同时材料内部的脆性夹杂物也是裂纹源。由于相邻晶粒之间存在取向差，裂纹扩展遇到晶界时，裂纹的扩展路径进入下一个晶粒时发生偏转。此外对横截面近断口区晶体取向进行分析，发现X80管线钢的主要解理面为{100}，其次为{211}。Abstract: The influence of pre-strain on the impact fracture behavior of X80 pipeline steel was studied. Fracture morphology and inclusions were analyzed by OM, SEM, EDS spectroscopy, and the crystallographic characteristics near the secondary crack on the fracture cross-section were obtained by EBSD. The results show that the pre-strain has no significant effect on the maximum impact load, but pre-strain will increase brittle fracture tendency and notch sensitivity, which leads to decreasing the crack formation energy and crack resistance. In the process of impact fracture, the pre-strain causes the internal dislocations of the material to become entangled with each other, and dislocation movement is hindered. Therefore, brittle fracture is easy to occur when the material is subjected to external force, and the brittle inclusions inside the material also act as the source of cracks. Due to the misorientation between adjacent grains, when the crack propagation encounters the grain boundary, the crack propagation path is deflected when it enters the next grain. In addition, analysis on the crystal orientation of the cross-section near the fracture area indicated that the main cleavage plane of X80 pipeline steel was {100}, followed by {211}.
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Key words:
- X80 pipeline steel /
- impact fracture /
- pre-strain /
- cleaved surface
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图 1 断口横截面金相EBSD观察示意
Figure 1. Schematic diagram of sampling for metallographic and EBSD observation
图 3 不同应变量冲击试验下载荷-位移曲线
(a)0； (b)2%
Figure 3. Load-displacement curve under impact test with different stress variables
图 4 断口横截面处典型二次裂纹
(a)(b)裂纹沿直线扩展； (c)(d)裂纹沿曲线扩展
Figure 4. Secondary crack at cross section of fracture
图 5 不同变形量下冲击断口宏观形貌
Figure 5. The macro morphology of impact fracture under different deformation amounts
(a) 0；(b) 2%
图 6 不同变形量下冲击断口SEM形貌
Figure 6. The SEM morphology of impact fracture under different deformation amounts
(a)0；(b)2%
表 1 焊缝处化学成分
Table 1. Chemical composition of the weld
% C Si Mn P S V+Nb+Ti Cu Ni Cr Mo Fe 0.057 0.11 1.37 0.01 0.0004 0.022 0.001 1.7 0.07 0.03 Bal. 
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