Vacuum-arc Nitriding of Carbon Steels Having Low Tempering Temperature

Abstract

Studies have been made into a new possibility of modifying the surface of steels having a low tempering temperature by nitriding them in a vacuum-arc gas discharge followed by heat treatment (heating, quenching and tempering). Generally, nitriding of hardened steels takes place at a temperature of about 500°C, and thus this process appears impossible for steels with tempering temperatures of the order of 200... 300°C. It is demonstrated here that a single ion-plasma nitriding of high-carbon steel with the composition of 0.9% C, 1% Cr, 1% Si, followed by heat treatment, provides the nitrided layer of 2.5 mm in depth, with the hardness between 9 and 11 GPa. Within the range of X-rays penetration, the nitride-hardened layer of the surface is defined as the nitrogen austenite-alpha ferrite mixture, which shows high wear resistance and impact toughness. This layer contributes, in particular, to three-/four-foldin crease in the operational life of cutting punches (made of this steel and used in the manufacture of metal sieves) as opposed to the punches that have undergone conventional heat treatment. After repeated nitriding of the same steel and its subsequent heat treatment according to standard technologies the nitrided layer thickness becomes nearly twice as large, and that allows for multiple regrinding of steel tools. A computer analysis of related publications entered into three International Databases (INIS, MSCI, SCOPUS) has been carried out.