Principles of certification of metals for susceptibility to brittleness by the criterion of critical strength

Abstract

Problem definition. Existing evaluation system of liability to brittle fracture is based on specifying the critical temperature T_c of ductile/brittle transition for specimens with stress concentrator (SC) and uses relative values of impact toughness (KCV, KCU) and widening (ψ_к). Thus the T_c becomes relative and it is not possible to measure brittleness or embrittlement degree for specimens with SC. Paper purpose. Neutralize the system faults of evaluation system of liability to brittle fracture of constructional alloys with SC. The concept is to change the KCV (KCU) or ψ_к  parameters by critical strength parameter (ϭ_0,2с at T_c). Conclusions. Fracture of the specimen with SC (ϭ_NF) on YTS (ϭ_0,2с) at T_c (or room T_R) as embrittlement criterion is proposed instead of relative values of (KCV, KCU) and (ψ_к). The ϭ_NF / ϭ_0,2 = B_rNF ratio is a degree of reliability for specimen with SC (B_rNF > 1) or embrittlement measure (B_rNF < 1). The B_rNF value is a quantitative measure of the fracture resistivity of the specimen with SC or crack. Correlation ratio between B_r and B_rNF  for each type of SC has been found. It allows to use the calculation of embrittlement liability based on metal strength for test of metals without full scale tests of metal specimens with SC.

Keywords: embrittlement; fracture degree; fracture resistivity; critical temperature; critical strength; strength
reliability of the specimen with SC