It is the intentions of the authors of this paper to focus attention on the tests used to determine the susceptibility to intergranular attack of stainless alloys. It is pointed out that a large number of variables exist in the present testing practice and that a standard practice should be inaugurated.
Using an acidified copper sulfate solution, a series of tests was made on type 316 heats to determine the effects of the stabilizing heat-treatment temperature (1550 and 1650 F.), stabilizing heat-treatment time and the cooling rate after the stabilizing heat treatment. It is shown that the cooling rate after stabilizing is important since it can effect sensitization of the alloy. Another series of tests was made to study the effects of sensitizing type 316 heats at 800 and 900 F. for 500 hr. after the stabilizing heat treatment. In these tests the regular type 316 alloys failed. However most of the low-carbon (0.03 per cent carbon maximum) type 316 heats sustained the sensitizing treatment at 800 and 900 F. for 500 hr. and exhibited immunity to intergranular attack.
Some tests were made on type 316 Cb2 in order that some comparison could be made with the low-carbon type 316.
In another series of tests, specimens of low-carbon type 316 and type 316 Cb were sensitized at 900 and 1020 F. for times up to 1000 hr.
The results of these tests show that the low-carbon type 316 alloy will sensitize at the low temperature if held for a sufficient length of time.