焼もどし脆化した中炭素鋼の破壊靱性(<特集>鉄鋼材料の破壊靱性)

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In order to find a clue to establish the relationship between fracture toughness and metallurgical factors, macroscopic energy (G_<IC>) for intergranular fracture of temper embrittled 0.3%C-1%Mn-1%Cr-0.02%P-0∿3%Ni steels was investigated and it was compared with the surface energy of a crack (γ : true surface energy, γ_p : plastic strain energy in front of a crack) introduced from Griffith-Orowan's thermodynamic and/or microscopic criterion. To obtain the exact fracture toughness (G_<IC>) corresponding to intergranular fracture due to temper embrittlement, it is required not only to exclude the influence of stretched zone formation or normal rupture in front of fatigue pre-crack, but also to consider the influence of pre-crack path on fracture toughness. Fractographic studies were carried out in detail with a scanning electron microscope to find the exact energy for intergranular fracture mentioned above. It was found that fracture toughness (G_<IC>) corresponding to intergranular fracture due to temper embrittlement was in the order of 10^3 J. m^<-2>. G_<IC> was much bigger than γ_S (surface energy) and γ_B (grain boundary energy), and it was found to be close to γ_P. If it is assumed that G_<IC> corresponds to γ_P, the reasons for the increase of degree of embrittlement (⊿FATT) and the decrease of G_<IC> with Ni content in embrittled steels (P content is constant) are considered as follows. Intergranular fracture due to temper embrittlement is mainly caused by the decrease of γ_P, and the decrease of γ_P is considered, from AES analysis, to be due to the segregation of impurity elements and to the segregation of alloying elements such as Ni and Mn to austenite grain boundaries.
社団法人日本鉄鋼協会の論文
1978-06-01

焼もどし脆化した中炭素鋼の破壊靱性(<特集>鉄鋼材料の破壊靱性)

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