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着重从断裂机制研究了两种基体钢a_K和K_(1C)数值矛盾的原因。断口观察表明,在最高强化状态a_K和K_(1C)试样的断裂机制相同,都是准解理机制。透射电镜观察表明,准解理断裂的解理面主要是孪晶马氏体的内孪晶界{112}晶面。高于500℃回火,由于渗碳体转变使合金的塑性和断裂强反σ_f提高,因而a_K随二次硬化过程发展而提高,但K_(1C)却降低。作者认为在评定高合金工模具钢的韧性时,a_K和K_(1C)是同样重要的两个判据。
The reasons for the contradiction between the values of a_K and K_ (1C) of the two kinds of base steel are studied emphatically from the fracture mechanism. Fracture observations show that the fracture mechanisms of a_K and K_ (1C) specimens are the same in the highest strengthening state and are quasi-cleavage mechanisms. Transmission electron microscopy showed that the cleavage plane of the quasi-cleavage fracture was mainly the twinned {112} crystal plane of twinned martensite. Higher than 500 ℃ tempering, due to cementite transformation of the alloy plasticity and strong fracture σ_f increase, so a_K with secondary hardening process to improve, but K_ (1C) is reduced. The authors believe that a_K and K_ (1C) are two equally important criteria when assessing the toughness of high alloy tool steels.