2 1/4Cr-1Mo鋼の水素脆性に及ぼす焼もどし脆化の影響

抄録

The effect of temper embrittlement on hydrogen embrittlement was investigated on 2 1/4 Cr-1Mo steel for high-temperature and high-pressure vessels. The threshold stress intensity, K_IH, for hydrogen-stress cracking (HSC) was determined by immersing modified 1T-WOL specimens with and without stepcooling heat treatment into a H₂S-saturated 0.5% acetic acid solution.
The results obtained are summarized as follows :
(1) Temper embrittlement enhances the susceptibility to hydrogen embrittlement of grain boundary.
(2) The K_IH value decreases with increase of fracture surface transition temperature, vTrs(°C), grain size, d(mm), and hydrogen content, C(ppm).
(3) The K_IH value has a good correlation with the hydrogen embrittlement susceptibility factor, Φ, denoted by
Φ=0.05d^-1/5 (vTrs + 133) + 4 (log d² + C^1/3)
(4) On the basis of the relation between K_IH and Φ and some diagrams to determine the maximum residual hydrogen content in a pressure vessel wall, a safety estimation method for preventing HSC during hydrostatic test of pressure vessels after the service was proposed.