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This study compares the nitriding efficiency of a low-pressure pure-nitrogen rf plasma for the materials AISI-316 stainless steel, 99.8% iron and the low-alloy steels AISI 4140 and En41B. The process temperature was 400 C; a range of gas pressures and biasing conditions was explored. The treated samples were examined using instrumented microhardness measurements, proton backscattering, X-ray diffraction and other diagnostics. The degree of nitriding is enhanced by increased bombardment by excited neutral molecules. Ion bombardment assists in the nitriding of iron and the low-alloy steels studied, apparently by aiding the production of Fe 2-3 N. This phase does not form in the nitriding of 316 stainless steel, and therefore treatment of this material is not assisted by ion bombardment. In comparing low-pressure rf plasmas to procedures involving higher pressures and temperatures, the process described …