THE LOW-PRESSURE RF PLASMA AS A MEDIUM FOR NITRIDING IRON AND STEEL

This study compares the nitriding efficiency of a low-pressure pure-ni trogen rf plasma for the materials AISI-316 stainless steel, 99.8% iro n and the low-alloy steels AISI 4140 and En41B. The process temperatur e was 400 degrees C; a range of gas pressures and biasing conditions w as explored. The treated samples were examined using instrumented micr ohardness measurements; proton backscattering, X-ray diffraction and o ther diagnostics. The degree of nitriding is enhanced by increased bom bardment by excited neutral molecules. Ion bombardment assists in the nitriding of iron and the low-alloy steels studied, apparently by aidi ng the production of Fe2-3N. This phase does not form in the nitriding of 316 stainless steel, and therefore treatment of this material is n ot assisted by ion bombardment. In comparing low-pressure rf plasmas t o procedures involving higher pressures and temperatures, the process described here is more appropriate for hardening austenitic stainless steel, but perhaps less appropriate for the other materials.