NEAR-SURFACE ELEMENTAL CONCENTRATION GRADIENTS IN ANNEALED 304 STAINLESS-STEEL AS DETERMINED BY ANALYTICAL ELECTRON-MICROSCOPY

Elemental concentration profiles in the near surface region of 304 stainless steel resulting from hot-band annealing have been investigated with scanning transmission electron microscopy-energy dispersive X-ray spectrometry (STEM/EDS). A severe Cr depletion in the top 100 nm of the steel surface was observed, and a Ni enrichment was present at depths less than 1 mu m. The maximum Cr depletion depth, which was approximated by an error function relationship, was in excellent agreement with the Cr depletion depth maximum determined experimentally. The oxide-alloy interfacial Cr concentration projected from the parabolic depletion profile of the 304 stainless steel at depths greater than 400 nm was also in reasonable agreement with the calculated value. The oxide/metal interfacial (within 50 nm) Cr concentration determined experimentally was, however, substantially lower than the calculated values.