Effects of P, Sn, As, Sb, Si, and Cu on the Formation of Bubbles by Hydrogen Attack in 2.25Cr-1Mo Steel

Abstract

Effects of impurities P, S, As, and Sb and those of alloying elements Si and Cu on the density and growth of methane bubbles formed on grain boundaries in 2.25Cr-1Mo steel by hydrogen attack were investigated.
The results are summarized as follows:
(1) The addition of 0.016 wt%Sn to the high-purity steel increased the bubble density and diameter by factors of 2.7 and 1.15 respectively.
(2) The addition of 0.016 wt%Sb increased the bubble density by a factor of 2 to 3, but reduced the bubble diameter to 0.8.
(3) The addition of either 0.016wt%P or 0.017wt%As decreased the bubble density by a factor of 0.750.5, while the growth rate was unchanged.
(4) Phosphorus and arsenic, however, could not relieve the above effects of tin and antimony.
(5) The bubble density and diameter of 0.26wt%Si steel were 1.3 and 1.4 times those of 0.016 wt%Si steel respectively, where both the steels contained all of the impurities by 0.01wt% each.
(6) The addition of 0.2wt%Cu decreased the bubble density but could not relieve the effects of tin and antimony when added together, while it increased the growth rate.
(7) Temper-embrittlement treatment further reduced the bubble density in 0.016wt%P steel magnifying the effect of phosphorus, while the effect of tin was not magnified by the treatment in 0.016 wt%Sn steel.