Relaxation behavior of 2 1/4 Cr--1 Mo steel under multiple loading

Multiple-loading relaxation data for annealed 2/sup 1///sub 4/ Cr-1 Mo steel are reported for times to 100 hr and for temperatures in the range 450 to 566/sup 0/C. At 450 and 482/sup 0/C the relaxation strength rises with the plastic flow stress, and recovery phenomena are not very significant in the time span of concern. At 510, 538, and 566/sup 0/C the relaxation behavior during the first loading is unusual in the sense that for a period the relaxation rate is almost independent of stress. This behavior is thought to be associated with a strain-induced aging process, which depletes the proeutectoid ferrite of solid-solution strengtheners. At 510/sup 0/C and above the plastic flow stress partially recovers during the relaxation process. At 566/sup 0/C there is clear recovery in the sense that the relaxation rates after the first loading depend on the current value of stress and not on history. Multiple loading tests at 566/sup 0/C on material in the normalized-and-tempered condition show no unusual behavior