The Effect of Stress on Degradation of 1Cr-1Mo-1/4V Steel at Elevated Temperatures

The creep tests for the specimens aged and stress-aged in the temperature range from 550 to 700°C have been carried out at 550°C-28 kgf/mm2 to determine quantitatively the degree of degradation of a 1Cr-1Mo-1/4V steel. The decrease in creep resistance due to aging has been discussed in terms of two microstructural changes: (i) a homogeneous change; the coarsening of intragranular carbides, and (ii) a heterogeneous change; the formation of subgrains or ferrite grains along prior austenite grain boundaries.When the stress-aged specimens were compared with the specimens aged without stress at the same hardness level, the creep resistance of the former was substantially lower than that of the latter and the amount of subgrains or ferrite grains for the former was significantly greater than that for the latter. The decrease in the creep resistance was proportional to the increase in the width of recovered area, which was defined as a parameter representing the amount of subgrains or ferrite grains along the prior austenite grain boundaries.The loss of the creep resistance during elevated temperature exposure is caused not by the homogeneous microstructural change of the carbide coarsening, but by the marked local recovery along the prior austenite grain boundaries.