Observations Related to Etching 316 Stainless Steel and 304 Stai

Summer 1987

Observations Related to Etching 316 Stainless Steel and 304 Stainless Steel in Partially Consumed Ferric Chloride as a Function of Free Acid Content

Earlier work done by Dr. David Allen of the Cranfield Institute of Technology on the etching of AISI 304 stainless steel showed that unusual effects were achieved in etched rates and surface textures as a function of free hydrochloric acid content. Carl Whinery reported at our recent PCMI meeting in Rochester good results in etching 304 S/S, copper and most other alloys but very poor results on 316 SIS when run concurrently in a partially consumed bath of ferric chloride.

This author had seen similar results with 316 S/S at Chemart Company. It was always our experience to add additions of hydrochloric acid when poor qualitative etching results were obtained. This generally resolved the problem. The poor results were manifested by erratically etched areas in which unetched areas were scattered throughout as though some type of scum retarded the etch; or alloy segregation had taken place within the grain boundaries that appeared to cause a different rate of etch, or in some cases would not etch at all.

Richard Beaupre, Chemart Company