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17-4PH钢在不足时效和正常时效状态下从马氏体基体中析出的ε-Cu为近乎球形,呈细小弥散任意分布。在579℃过时效和650℃太过时效状态下从马氏体中析出的ε-Cu仍为近乎球形,亦呈细弥散任意分布,而从逆变奥氏体中析出的ε-Cu却比较粗大,为圆滑的短棒状,呈相互垂直的取向,且具有同一取向的ε-Cu按一定间隔线性排列的倾向。 在不足时效和正常时效状态下,甚至在太过时效(650℃)状态下从马氏体基体中析出的细小分散分布的ε-Cu对位错有钉扎作用,但从逆变奥氏体中析出的较粗大的分布较稀疏的ε-Cu对位错作用较小,或几乎没有作用。在650℃太过时效状态下从逆变奥氏体中析出的呈短棒状的粗大ε-Cu对位错完全没有作用。这就是过时效状态的17-4PH钢中逆变奥氏体量,或淬火后的17-4PH钢中残余奥氏体量过多时屈服强度降低的根本原因。
The ε-Cu precipitated from the martensite matrix in the under-aged and normal-aged state of 17-4PH steel is nearly spherical with small dispersion and random distribution. Ε-Cu precipitated from martensite at 579 ℃ overexposure and 650 ℃ overestimation state is still nearly spherical, and is also finely dispersed and randomly distributed, whereas ε-Cu precipitated from the transformed austenite is compared Coarse, smooth and short rod-shaped, were perpendicular to each other, and with the same orientation of ε-Cu at a regular interval of linear alignment. In the under-aged and normal-aged states, the finely dispersed ε-Cu precipitated from the martensite matrix even at the too-aging (650 ° C) pinned the dislocations, but from the reverse austenite The more coarsely distributed ε-Cu precipitates have little or no effect on dislocations. The coarse rod-shaped coarse ε-Cu precipitated from the transformed austenite at 650 ° C is too ineffective at dislocation. This is the root cause of the loss of yield strength when the amount of retained austenite in the 17-4PH steel over-aged or the amount of retained austenite in the quenched 17-4PH steel is excessive.