Some Observations on Corrosion Tests of Cr-Ni Stainless Steels

Abstract

In the study of steels used in corrosive environment, the experimental values of corrosion tests are scattered over wide range, so it is very important to know the variation of the experimental results under various test conditions in order to compare the corrosion resistance of specimens.Studies were made on type 316 stainless steel in boiling 5% H₂SO₄ to examine the variation of experimental results and to analyse statistically the effects of surface conditions, solution-treatment temperature and cold rolling on the corrosion resistance. An investigation was also made on the effect of σ ferrite on the intercrystalline corrosion.
The following results were obtained.
i) The variation of the experimental results decreased and the corrosion resistance increased as the surface texture of the specimens became finer.
ii) The loss in weight in boiling 5% H₂SO₄ was minimum in the specimen as solutiontreated at 1200°C.
iii) The loss in weight increased remarkably with an increasing reduction ratio between 10 and 30% but it was almost invariable above 30%.
iv) The variation of the experimental results in the test for two hours in boiling 5% H₂SO₄ was wider than that in the test for six hours.
v) In Huey test, the steels used in this experiment were attacked over the whole surface. But σ ferrite seemed to have a favourable effect on the corrosion resistance to boiling 65% HNO₃.
vi) In all specimens, the electric resistance did not change after Strauss test.
vii) In this experiment, any definite conclusion about the effect of σ ferrite on the intercry-stalline corrosion was not obtained.It is necessary to select the steel and to find the optimum testing method for investigation of the effect of σ ferrite on the intercrystalline corrosion.