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本文报导了三种具有不同显微组织状态的电渣重熔钢的断裂韧性和疲劳裂纹扩展数据。在这三种组织状态中,两种是经过淬火加回火但各自晶粒度不同的全马氏体组织,第三种为原始马氏体材料在重新加热后经不完全淬火和回火处理的组织。经不完全淬火的组织是由马氏体基体中含35％左右的下贝氏体所组成,所有三种显微组织状态均经回火,以获得相同的抗拉强度。 不完全淬火钢的断裂韧性(K_(1c))高于粗晶粒的全马氏体材料。但是,经进一步试验证实,不全完淬火材料的断裂韧性之所以高,原因仅在于奥氏体晶粒的细化。所有三种显微组织状态下的疲劳裂纹扩展性能都很相似。扫描电镜显微检验表明,裂纹扩展的第二区表现出“常规”的条纹状,因此其结果可采用形式为da/dN=c△K~m的Paris-Erdogom定律表达。基于本研究工作的结果,提出如下观点:下贝氏体组织降低了经淬火、回火处理的0.36C Ni—Cr-Mo钢的断裂韧性。裂纹扩展速率高于10~(-5)毫米/次时,则不受微观组织状态或晶粒度的影响。
This paper reports the fracture toughness and fatigue crack growth data of three kinds of ESR steels with different microstructures. Of the three organizational states, two are all-martensite structures that have been quenched and tempered but have different grain sizes, respectively, and the third, incomplete quenching and tempering of the original martensitic material after reheating Of the organization. The incompletely quenched structure consists of a lower bainite with about 35% martensite matrix, and all three microstructures are tempered to achieve the same tensile strength. The fracture toughness (K_ (1c)) of incompletely hardened steel is higher than that of the whole-martensite material of coarse grains. However, further tests confirm that the reason why the fracture toughness of incomplete quenching material is high is only because of the refinement of austenite grains. The fatigue crack growth behavior is similar in all three microstructures. Scanning electron microscopy revealed that the second zone of crack propagation exhibited a “regular” streak, so the results can be expressed using the Paris-Erdogom’s law of the form da / dN = cΔK ~ m. Based on the results of this study, the following observations were made: Lower bainite reduces the fracture toughness of 0.36C Ni-Cr-Mo steels treated by quenching and tempering. Crack propagation rate higher than 10 ~ (-5) mm / time, it is not affected by the microstructure or grain size.