Conversion electron and X-ray Mössbauer studies of boronized low-carbon steel under corrosion and oxidation conditions

Abstract

Iron-boride layers on low-carbon steel were produced by thermochemical diffusion process. The surface interaction products: Fe₂B, FeB, FeB_x (x>1) and a solid solution of iron in boron were identified by surface Mössbauer spectroscopy (CEMS and XMS). Samples of original and boronized steel were subjected to corrosion process by immersion in HCl (0.1 N) solution for 150 h. While the steel sample was strongly corroded, none corrosion product was found on the boronized sample surface. However, significant changes in relative percentages of the various iron boride phases were detected. Also, samples of original and boronized steel were subjected to oxidation process by heat-treatment in air at 300°C for 8 h and 500°C for 4 h. At 300°C, while bulk Fe₃O₄ and α-Fe₂O₃ were formed on the steel surface, none iron oxide was detected on the boronized surface. At 500° C, while only pure bulk α-Fe₂O₃ was detected on the steel surface, a particle size distribution ofγ-Fe₂O₃, with particle size of about 100 Å, was probably formed on the boronized surface, as evidenced by CEMS.