抄録
Stress corrosion cracking behavior of SUS 304 and SUS 316 stainless steels was investigated in terms of concentration and temperature of MgCl2 solutions with or without dissolved oxygen. The potential-MgCl2concentration relation between SCC and pitting corrosion was also studied by constant potential method under the applied stress of 25 kg/mm2.
As dissolved oxygen becomes necessary to cause SCC with decreasing the concentration or the temperature of MgCl2 solutions, SUS 316 becomes much more resistant to SCC than SUS 304. The crack is often observed originating at the bottom of a pit.
The lower limit of MgCl2 concentration above which cracks develop at 80°C is about 20% for SUS 304 and about 25% for SUS 316, while the critical SCC potential of SUS 316 is about 50 mV more noble than that of SUS 304. Above the lower limit of MgCl2 concentration, the corrosion mode shifts from SCC to pitting corrosion as the applied potential is raised and the SCC potential range widens with increasing MgCl2 concentration. Below that, only pitting corrosion occurs.
