Surface Deoxidation Mechanism during Vacuum Heat Treatment of Stainless Steels AISI 304 and 446

A process of removal of surface oxides from stainless steels AISI 304 and 446 that involves reduction by residual carbon, followed by the formation and desorption of carbon monoxide, is studied by investigation of thermal desorption with quadrupole mass spectrometry (QMS) and secondary ion mass spectrometry (SIMS). Carbon monoxide desorption is studied as a function of time and temperature by QMS, and carbon diffusion due to heat treatment is studied with SIMS—twice as much carbon monoxide desorbs from AISI 304 overall and desorption sets in at 900 °C as opposed to 1100 °C for AISI 446. In samples heated to 900 °C, carbon shows surface enrichment in AISI 304 but depletion in AISI 446.