Effect of Strain Aging on Tensile Properties of X80 Large-Diameter Pipeline Steel

Aging treatment at room temperature and 200, 230, 250℃, respectively, was conducted on X80 large-diameter pipeline steel specimens after stretching to strains of 0.5%-3.5% and then unloading; the effects of tensile pre-strain and aging temperature on tensile properties of the tested steel were studied. The tested steel was made into pipe by longitudinal submerged arc welding at pipe-making expanding ratios of 0.5%-0.8%; the effect of pipe-making expanding ratio on tensile properties of the tested steel was investigated. The results show that after tensile at a certain strain and then aging or pipe-making expanding, the strain aging occurred in the tested steel; the yield strength of the tested steel increased, the tensile strength changed little, and the yield ratio increased. The pipe-making expanding ratio had bigger influences on the yield strength increment and yield ratio increment than the tensile pre-strain had. Tensile pre-strain was the main factor that improved the yield strength and yield ratio after room-temperature strain aging. The effect of strain aging at 200-250℃ on tensile properties was stronger than that at room temperature. The variation of aging temperatures between 200-250℃ had little effect on the tensile properties.