2023 Volume 109 Issue 7 Pages 638-648
The effect of combined addition of V and Mo on hydrogen trapping was investigated using tempered martensitic steels (0.3%C-1.2%Cr-0.5%Mo-0.4%V, 1.5%Mo-0.2%V or 2.0%Mo-0.1%V in mass%), for the purpose of improving hydrogen embrittlement strength. The trapped hydrogen content and the hydrogen trapping energy were evaluated under various tempering conditions and compared with the single addition 0.2%V and 1.0%Mo steels in the previous paper. The trapped hydrogen content and the hydrogen trapping energy of 0.5%Mo-0.4%V and 1.5%Mo-0.2%V steels were higher at 650°C tempering temperature for 1 hour than at 600°C. On the other hand, those values of 0.2%V and 1.0%Mo steels were lower at a tempering temperature of 650°C than at 600°C. This was presumed to be due to the some interaction between V and Mo at a tempering temperature of 650°C. In the 0.5%Mo-0.4%V and 1.5%Mo-0.2%V steels at tempering temperatures of 600°C and 650°C for 1 hour, the plate-shaped Cr enriched cubic (Mo, V)C fine carbides with a width of about 1nm and a length of about 20nm or less were precipitated, and there was no significant difference in the number density. The V/Mo peak ratio of the fine carbides by EDS analysis was higher at a tempering temperature of 650°C than at 600°C and the length of fine carbides was slightly longer. The 2.0%Mo-0.1%V steel was estimated to have less trapped hydrogen content at a tempering temperature of 650°C than at 600°C, similar to single addition steels, because of the smaller V/Mo mole ratio.
