INFLUENCE OF POSTWELD HEAT-TREATMENT ON CREEP-PROPERTIES OF 1CR0.5MO AND 2.25CR1MO WELDMENTS

The creep properties of simulated heat-affected zone, weld metal and c ross-weld specimens of 1Cr0.5Mo and cross-weld specimens of 2.25Cr1Mo have been studied with reference to the effect of postweld heat treatm ent (PWHT). A reduction in the creep rupture strength of up to 20% has been observed after PWHT. Contrary to what has been previously propos ed, PWHT was in the present investigation found to have only a margina l influence on the creep ductility. The creep rate can increase by up to a factor of 2-4 after postweld heat treatment, probably because of carbide coarsening during the heat treatment. Preheating at 200-degree s-C did not affect the creep properties of 2.25Cr1Mo. Overheating, on the other hand, at 650-degrees-C for 1000 h reduced the rupture time o f 1Cr0.5Mo by almost an order of magnitude. The tensile strength and y ield strength of 1Cr0.5Mo were significantly reduced after postweld he at treatment. Reductions of up to 100-200 MPa were observed both at ro om temperature and at 550-degrees-C in some cases.