Carbon Surface Modification for Enhanced Corrosion Resistance
NAVAL RESEARCH LAB WASHINGTON DC
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Case hardening by carburization has long been recognized to produce wear-resistant surfaces in steels. Historically, case hardening has not been applicable to chromium-containing alloys such as stainless steels SS, due to chromium carbide formation that significantly degraded corrosion performance. As a result, the availability of case-hardened and consequently wear-resistant alloys for applications in corrosive environments was extremely limited. A new low-temperature 450 deg-500 deg C paraequilibrium carburization technique has been developed for introducing carbon into stainless steel surfaces without formation of carbides.1,2 This surface modification technique has been termed Low-Temperature Colossal Supersaturation LTCSS. Paraequilibrium refers to the concept that the diffusion of substitutional solutes metal atoms, such as Cr and Ni in the alloy is slower than the diffusion of interstitial solutes atoms such as carbon, that fit between metal alloy atoms. Substitutional solutes are effectively immobile under LTCSS treatment conditions, whereas carbon can diffuse considerable distances into the alloy.
- Properties of Metals and Alloys