Effects of Carbide Forming Elements on Hydrogen Attack and Embrittlement in 2 1/4 Cr-1Mo Steel

Abstract

2 1/4Cr-1Mo steel was alloyed with various elements and its resistance to hydrogen attack and hydrogen embrittlement was investigated. The results are as follows:
1) Hydrogen attack resistance is improved by V addition of more than 0.2 %. Nb, Ti, or Zr addition of less than 0.05 % also has strong beneficial effect. However, W is useless and 0.5 % Ni is harmful.
2) Hydrogen embrittlement resistance is also improved by V addition of more than 0.2 %. However, Nb, W, and Ni are useless and Ti and Zr are harmful.
3) Carbides in 2 1/4Cr-1Mo-0.26V steel consist of Cr, Mo, Fe and V, and many fine carbides containing 10-60 % V are formed. These V-rich carbides are thought to be responsible for fining and stabilizing of carbides, which improve resistance to hydrogen embrittlement and attack, respectively.
4) Nb and Ti are not detected in Cr-Mo-Fe carbides in 0.045%Nb or 0.028%Ti containing steel. This suggests that the beneficial effect on hydrogen attack is due to stabilizing carbon through NbC and TiC formation. However, since solubility of Nb and Ti in austenite is small, fine carbides whose particle number enough to suppress hydrogen embrittlement are not formed.