1991 Volume 77 Issue 8 Pages 1320-1327
The effect of the prior-austenite grain size on the hydrogen attack of 2 1/4 Cr-1Mo steel was studied. Austenite grain size was varied by alloying of V, Nb, Ta, Ti or Al up 0.05 mass% to 2 1/4Cr-1Mo steel and by a change of the austenitizing temperature between 950°C and 1250°C. Steels were quenched and tempered, then exposed to hydrogen at 600°C and 29.4 MPa for 1000 h.
The volume of bubbles per unit volume and the number of bubbles along prior austenite grain boundaries per unit area of polished surfaces were decreased by raising of the austenitizing temperature, and furthermore by coarsening of austenite grains. They were little affected by the addition of V, Nb, Ta and Ti, but increased by Al addition.
A small addition of Nb, Ta and Ti and the lowering of the austenitizing temperature decreased the volume of bubbles per unit area of prior austenite grain boundaries and the number of bubbles per unit length of prior austenite grain boundaries. This result is considered to be originated from the refining of austenite grains. On the other hand, the addition of Al increased them, and in Al alloyed steels the lowering of the austenitizing temperature was inffective for the decrease of them. The latter behavior was due to the acceleration in bubble formation by the unidissolved AlN at the lower austenitizing temperature.
