Volume 14, Issue 1 (January 1986)
A Modified Metallographic Method to Detect Sensitization in Type 316 Stainless Steel
For detecting susceptibility to intergranular corrosion (IGC) in austenitic stainless steels, ASTM Recommended Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels (A 262), Practice A (metallographic test), serves as a screening test. Alloys showing “step” or “dual” structures are considered to have passed the test. When a “ditch” structure is obtained, the material needs further testing by one of the immersion tests (Practices B, C, D, or E). It has been observed that the electro-etching parameters of Practice A are rather severe, leading to the development of “ditch” structures in nonsensitized materials which are not susceptible to IGC. A modified etching technique has been developed in which nonsensitized samples of Type 316 stainless steel as detected by Practice E show step structure or no structure at all; ditch structure is developed only in the cases of samples heat treated close to or within the sensitization range. Use of this technique could result in a reduction of the number of specimens that must be tested by one of the other practices in ASTM A 262.