Abstract
Creep rupture tests in high pressure hydrogen and argon of 200 kgf/cm2 at 525 and 550°C were performed on two 2 1/4 Cr-1Mo steels indicated as P and Sn steels which have low and high density of voids by hydrogen attack, respectively. The results are as follows:
1) Marked decrease in reduction of area was observed in hydrogen atmosphere after a certain rupture time in a stress-rupture time diagram. However, the decrease on Sn steel was observed at earlier rupture time than on P steel.
2) Contrast to intragranular ductile fractrure in argon atmosphere, whole fracture surface of Sn steel consisted of grain boundaries with coalescent voids in hydrogen atmosphere. In the case of P steel, since only a few voids were grown on grain boundaries, micro cracks occurring around triple point of grain boundaries could not propagate along grain boundaries but combined with intragranular ductile fracture. This indicates that the number of voids are not increased under applied stress and the ductility loss in hydrogen atmosphere is determined by hydrogen attack resistance of steels.
3) Applied stress accelerated void growth rate by 3-4 times. This can be understood by taking methane pressure to be 1 000-2 000 kgf/cm 2 and applying this value to a theoretical equation. The carbon activity corresponding to the methane pressure is 0.04-0.10.
