SUS 304鋼の高温高圧純水中の応力腐食割れにおけるPの役割

抄録

Effect of P content on stress corrosion cracking (SCC) has been studied for SUS304 stainless steel in high temperature water at 562K. SCC test was carried out using slow strain rate testing (SSRT) technique at 4.17×10^-6s^-1.
For the solution-treated specimens with 0.008%P to 0.10%P, the corrosion rate by Huey test increased with increasing P content, and that correlated with segregation of P at the grain boundaries. But, intergranular stress corrosion cracking (IGSCC) hardly occured.
The precipitation of M₂₃C₆ by sensitization treatment at 723K increased with increasing P content, Because it is considered that phosphorus was inserted in the M₂₃C₆, and carbides precipitated as M₂₃(C, P)₆.
IGSCC in high temperature water increased with increasing P content, because of the increase of M₂₃(C, P)₆ at the grain boundary.
The specimens sensitized after solution treatment at 1373K occured IGSCC more than that at 1573 K, because of the increase of M₂₃(C, P)₆ at the grain boundary.