STRESS RELAXATION TEST WITH SINGLE IMPLANT FOR REHEAT CRACKING TENDENCY ASSESSMENT OF LOW ALLOY STEELS

During isothermal stress-relaxation test performed to assess the reheat cracking tendency of materials,failures were encountered owing to premature yielding of thes amples if Murry's formula (σ₀=0.8σ_SE_T/E_RT) is employed to determine the initiate stress.Repeated tests made on several HSLA steels show that the proper formula for choosing the initiate testing stress is σ₀/σ_S=1.37-0.0016T.The requirement of the same initiate strain for stress relaxation at different temperatures is met and "C-shaped curves" of rupture time can be plotted.A creep plastic criterion (σ₀-σ_r) for assessing the reheat cracking tendency of materials and an expression (σ₀²-σ_r²) for indicating the amount of the absorbed elastic energy by materials during stress relaxation have been suggested.It is considered that the results obtained can more truly reflect the reheat cracking tendency of materials.