368K希薄硫酸ナトリウム溶液中における鋭敏化SUS304鋼の粒界型応力腐食割れの発生と伝播に及ぼす電位の影響

抄録

The effects of potential and sodium sulfate concentration on the initiation and growth of IGSCC of sensitized 304 stainless steel in 0.01-1kmol/m³ sodium sulfate solutions at 368K have been investigated. A slow strain rate test apparatus was used to make direct observations of crack generation and propagation during the test. The initiation and growth of IGSCC were found to occur for potentials from -500mV_Ag/AgCl to -200mV_Ag/AgCl and the IGSCC susceptibility reached a maximum at approximately from -400mV_Ag/AgCl to -300mV_Ag/AgCl. The initial crack generation time was a minimum around -400mV_Ag/AgCl and the crack growth rate increased monotonously with increasing potential. Therefore, the SCC test results indicated that the maximum IGSCC susceptibility emerged at approximately from -400mV_Ag/AgCl to -300mV_Ag/AgCl, suggesting that the susceptibility of IGSCC must be determined as a function of the synergistic effect of the crack generation frequency and the crack growth rate. The initial crack generation time decreased with increasing sodium sulfate concentration. The crack growth rate was independent of the crack generation time and showed approximately a constant value. The crack generation time were distributed at random. Therefore, it was considered indispensable to evaluate IGSCC resistance of various austenitic stainless steel by statistical methods.