High nitrogen steel powder for the production of near net shape parts

Abstract

The Plasma-Rotating-Electrode-Process is a powder metallurgical process for the production of high nitrogen steel utilizing the activated, ionized or dissociated state of the nitrogen in plasma for the nitrogenization of steel. The powder produced is characterized by its high nitrogen level far in excess of the nitrogen content under normal condition and its nearly ideal spherical form. The influences of rotational speed and nitrogen content in the plasma gas on powder sizes and nitrogen content of the powders respectively are pointed out. The microstructure of the powder has been investigated at different heat treatment conditions. The initial material (before nitrogenization) was an austenitic steel grade 304. After a solution heat treatment the powder is almost free of precipitates. After an annealing treatment at moderate temperatures (600 to 800°C) different forms of nitrides occur in dependence of temperature and time. The observed nitrides are described. The microhardness of the powder increases with increasing nitrogen content. In the solution heat treated state the corrosion resistance of the powder increase if the nitrogen can be kept in interstitial solution. The powder is well adapted for extrusion process.