Effect of ceramic heat insulating paste on degree of sensitisation of AISI type 304 stainless steel

Double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests and oxalic acid etch tests were conducted to evaluate the effect of a ceramic heat insulating paste on the degree of sensitisation of AISI type 304 stainless steel. Steel strips in the as received condition, partially and totally protected with the ceramic heat insulating paste, were heat treated in a furnace at 700 degrees C for intervals of 15, 30, and 60 min. Measurements of the ratios of the reactivation current to the anodic current indicated that the ceramic heat insulating paste effectively prevented sensitisation of the steel for the first 15 min at 700 degrees C and reduced the degree of sensitisation for specimens heat treated for 30 and 60 min. Microstructural examination of specimens after DL-EPR tests and oxalic acid etch tests provided additional evidence for the effectiveness of the ceramic paste. The decreased degree of protection at 30 and 60 min was due to dehydration and subsequent cracking the protective paste layer on the steel surfaces.