本文研究了淬火温度对4330M钢在蒸馏水中的应力腐蚀裂纹扩展速率的影响。实验表明,淬火温度从870℃上升到1100℃时,裂纹扩展速率da/dt显著下降(相差一个数量级);从1100℃上升到1200℃时,裂纹扩展速率da/dt却稍提高,在1100℃处,da/dt有一最小值。断口分析表明,随淬火温度升高,应力腐蚀的断裂方式有所改变,870,1000℃淬火的试样系沿晶断裂,而1100,1200℃淬火试样则是穿晶准解理断裂。 用饱和苦味酸溶液腐蚀显示奥氏体晶界,通过奥氏体晶界腐蚀沟槽深度估算出杂质磷在奥氏体晶界的平衡偏聚浓度,它和淬火加热温度之间的关系符合Mclean的平衡偏聚理论。磷在奥氏体晶界的偏聚是造成应力腐蚀裂纹扩展速率da/dt变化的主要原因。 采用杂质原子偏聚和氢对脆性断裂影响的理论,对各种实验现象加以解释,并认为杂质原子在晶界偏聚和氢共同作用的氢脆断口是沿晶断裂型,而单纯氢起作用的氢脆断口是穿晶准解理断裂型。
The effect of quenching temperatures on the rate of stress corrosion crack propagation of 4330M steel in distilled water has been investigated. The rate of crack propagation, da/dt, decreased rapidly as the increase of quenching temperature in the range of 870—1100℃, while increased slightly from 1100 to 1200℃. The fracture mode changed from intergranular separation along prior austenite grain boundary in the specimens quenching at 870 and 1000℃ to transgranular quasicleavage in that quenching at 1100℃ and 1200℃. The segregation concentration of P at prior austenite grain boundaries has been measured with selective etching and found to be related to quenching temperature fitting McLean's theory of equilibrium segregation. The change of propagation rate with quenching temperature was found to be mainly due to the P segregation at prior austenite grain boundaries and can be rationalized with an interactional effect between H_2 and grain boundary P segregation. It is concluded that stress corrosion cracking of 4330M steel without grain boundary impurity segregation in distilled water is transgranular,while intergranular cracking is a result of impurity segregation at the grain boundraies.
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