Investigation of compound layer formed during ion nitriding of AISI 4140 steel

Low alloy AISI 4140 steel was ion nitrided at temperatures of 500, 550 and 600 degrees C for various times in a 50%N-2-50%H-2 gas mixture. The nature of the compound layer formed was studied by X-ray diffraction and optical metallography. The X-ray analysis shows the existence of a gamma-Fe4N compound zone on the surface at all three temperatures. The thickness of the compound layer increases with increasing time at 500 and 550 degrees C; however, it begins to decrease with increasing time at 600 degrees C.