Effects of grain size on fracture toughness in transition temperature region of Mn–Mo–Ni low-alloy steels
Effects of grain size on fracture toughness in transition temperature region of Mn–Mo–Ni low-alloy steels
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DOI：
10.1016/s0921-5093(03)00344-7
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发表时间：
2003-10
期刊：
影响因子：
6.4
通讯作者：
Sangho Kim;Sunghak Lee;Bongsang Lee
中科院分区：
文献类型：
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作者：
Sangho Kim;Sunghak Lee;Bongsang Lee
研究了核压力容器用Mn-Mo-Ni低合金钢在转变温度区晶粒尺寸对断裂韧性的影响。通过改变Al和N含量制备了3种不同奥氏体晶粒尺寸的钢，并对其显微组织和力学性能进行了研究。根据ASTM E1921标准测试方法，通过预裂纹夏比V形缺口（PCVN）样本的三点弯曲测试来确定弹塑性解理断裂韧性KJc。当AGS降低时，碳化物总数增加，而尺寸和长径比减小。局部断裂应力，估计从理论应力分布在裂纹尖端的前面，被发现主要是由92nd%的尺寸的碳化物。观察断裂面下的横截面积，以了解影响解理裂纹扩展行为的微观结构特征。结果表明，解理断裂单元比AGS小，表明在解理裂纹扩展过程中，包晶界和奥氏体晶界起着重要作用。根据电子背散射衍射（EBSD）结果，解理断裂单元也可以与取向差容差角25°确定的有效晶粒尺寸相匹配。
An investigation was conducted into the effect of grain size on fracture toughness in the transition temperature region of Mn–Mo–Ni low-alloy steels used for nuclear pressure vessels. Three kinds of steels with different austenite grain sizes (AGS) were fabricated by varying the contents of Al and N, and their microstructures and mechanical properties were examined. Elastic–plastic cleavage fracture toughness, KJc, was determined by three-point bend tests of precracked Charpy V-notch (PCVN) specimens according to ASTM E1921 standard test method. When the AGS decreased, the total number of carbides increased, while the size and the aspect ratio of carbides decreased. Local fracture stresses, estimated from a theoretical stress distribution in front of a crack tip, were found to be mainly determined by the 92nd% size of carbides. Cross-sectional areas beneath fracture surfaces were observed to understand microstructural features to affect the cleavage crack propagation behavior. The results showed that measured cleavage fracture units were smaller than AGSs, indicating that packet boundaries as well as austenite grain boundaries played an important role in the cleavage crack propagation. Based on the electron back-scatter diffraction (EBSD) results, the cleavage fracture units could also be matched with the effective grain sizes determined by the misorientation tolerance angle of 25°.