Effect of gas pressure on active screen plasma nitriding response

An austenitic stainless steel AISI 304 was active screen plasma nitrided using a 304 steel screen to investigate the effect of the gas pressure on the nitriding response. The sample was treated for 18 ks at 723 K in 25 % N2 + 75 % H2. The gas pressure was changed to 100, 600, and 1200 Pa. The distance between the screen and the sample was also changed to 10, 30, and 50 mm. The nitrided samples were characterized by observing their appearance and surface roughness by optical microscopy, X-ray diffraction, and microhardness testing. After nitriding, polygonal particles with a normal distribution were observed at the center and edges of all the nitrided sample surfaces. The particles on the sample surface became finer with an increase in the gas pressure. The nitrided layer with a greater and homogeneous thickness was obtained at a low gas pressure of 100 Pa. Copyright © 2011 by ASTM International.