HIGH-NITROGEN STEEL POWDER FOR THE PRODUCTION OF NEAR NET SHAPE PARTS

The Plasma-Rotating-Electrode-Process is a powder metallurgical proces s for the production of high nitrogen steel utilizing the activated, i onized or dissociated state of the nitrogen in plasma for the nitrogen ization of steel. The powder produced is characterized by its high nit rogen level far in excess of the nitrogen content under normal conditi on and its nearly ideal spherical form. The influences of rotational s peed and nitrogen content in the plasma gas on powder sizes and nitrog en content of the powders respectively are pointed out. The microstruc ture of the powder has been investigated at different heat treatment c onditions. The initial material (before nitrogenization) was an austen itic steer grade 304. After a solution heat treatment the powder is al most free of precipitates. After an annealing treatment at moderate te mperatures (600 to 800 degrees C) different forms of nitrides occur in dependence of temperature and time. The observed nitrides are describ ed. 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 sol ution. The powder is well adapted for extrusion process.