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在-20和-60℃对X80管线钢进行Charpy冲击实验,用SEM-EDS对断口进行形貌和夹杂物成分分析,并将断口切开进行金相和EBSD观察,研究X80管线钢的冲击断裂行为.结果表明:温度对X80管线钢最大冲击载荷影响较小,但随实验温度降低,裂纹形成功、裂纹扩展功和止裂后吸收的能量显著减小.在冲击断裂过程中强烈的拉应力作用使断口附近产生变形带,晶粒沿与主裂纹垂直的方向被拉长,原始奥氏体晶界几乎不变形,因而产生应力集中,并产生沿晶界的断裂.同时,钢中的脆性第二相粒子也是裂纹源.在裂纹扩展过程中,强烈的内应力使主裂纹附近的晶粒产生剧烈的变形,拉长直至破裂,并形成新晶粒;新形成的晶界表现为大角晶界.裂纹扩展区附近的晶粒尺寸较原始组织细小而大角晶界比例有所增加.-20℃冲击断口裂纹扩展区附近的晶粒尺寸比原始组织小得多,而-60℃断口裂纹扩展区附近的晶粒尺寸与原始组织相差不大.
The Charpy impact test of X80 pipeline steel was carried out at -20 and -60 ℃. The morphology and inclusions of the X80 pipeline steel were analyzed by SEM-EDS. The fractures were cut and analyzed by metallography and EBSD. The impact fracture The results show that the temperature has little effect on the maximum impact load of X80 pipeline steel, but with the decrease of the experimental temperature, the energy of crack formation work, crack extension work and absorption after the crack arrest is significantly reduced.The intense tensile stress The effect is that the deformation zone is generated near the fracture, the grains are elongated in the direction perpendicular to the main crack, the original austenite grain boundaries hardly deform, resulting in stress concentration and fracture along the grain boundaries. Meanwhile, the brittleness The second phase particles are also the source of cracks. During the crack propagation, the strong internal stress causes the grains near the main crack to undergo severe deformation, elongate until they rupture and form new grains. The newly formed grain boundaries appear as large angle crystals The grain size near the crack growth zone is smaller than that of the original structure and the ratio of the large-angle grain boundaries is increased.Crystallization grain size near the crack propagation zone at 20 ℃ is much smaller than the original structure, while the crack growth at -60 ℃ District attached The grain size of the original organization or less.