Kinetics and wear behaviour of M50NiL steel plasma nitrided at low temperature

Abstract

The quenched M50NiL steel was plasma nitrided at 460°C for different time to investigate the effects of the duration time on the microstructure, microhardness and wear resistance of the nitrided layers. The results show that the plasma nitrided layer depth increases with increasing nitriding time. The plasma nitrided layer includes only the diffusion layer without compound layer. The main phases in the nitrided surface layer are nitrogen expended α ′ -Fe and γ ′ -Fe 4 N. The microstructure of the nitrided layer is refined. The wear resistance of the nitrided samples can be improved significantly by plasma nitriding. The sample nitrided for 4 h possesses the highest wear resistance, due to its relatively smooth surface and ultra-fine grains in the nitrided layer.

EFFECT OF NITROGEN HYDROGEN RATIO ON PLASMA NITRIDING FOR 38CrMoAl

“…It clearly indicates that the surface hardness of specimen with nitrogen hydrogen ratio of 1:5 is the highest, though the thickness of effective hardening layer is a little thinner. which is much more brittle than the underneath diffusion layer due to the different characteristics, including different crystal lattices, therefore, the compound layer is easy to crack upon subjecting impact loads [10] . Moreover, the big difference of elasticity modulus between compound layer and diffusion layer results in uncoordinated deformation, especially upon subjecting cyclic loads [10,11] , which makes the compound layer have a tendency to crack and peel off from the surface, and thus result in premature failure.…”

“…which is much more brittle than the underneath diffusion layer due to the different characteristics, including different crystal lattices, therefore, the compound layer is easy to crack upon subjecting impact loads [10] . Moreover, the big difference of elasticity modulus between compound layer and diffusion layer results in uncoordinated deformation, especially upon subjecting cyclic loads [10,11] , which makes the compound layer have a tendency to crack and peel off from the surface, and thus result in premature failure. Therefore, though the compound layer can provide high surface hardness and excellent wear resistance, it is of significant value for 38CrMoAl high-pressure valve to get a nitriding layer without compound layer for preventing its premature failure in real applications.…”

“…To meet the technical requirements, surface modification of high-pressure valves is necessary [3][4][5], and plasma nitriding is one of the most widely used surface modification techniques in industry, since a modified layer with high surface hardness and excellent wear resistance can be obtained [6][7][8][9]. Unfortunately, during conventional plasma nitriding, a hard and brittle compound layer (also called white layer) is generally produced, which is easy to crack and peel off from the surface during the service life of 38CrMoAl steel high-pressure valve upon subjecting the severe impact and cyclic load [10][11][12], and thus leading to premature failure of the components. Hence, it is of significant value to control the formation of compound layer during plasma nitriding for highpressure valve.…”

Acceleration effects of rare earths on salt bath nitriding: diffusion kinetics and first-principles calculations

“…It is generally accepted that in salt bath nitriding, rare earth elements can improve the microstructure of the nitrided layers [3][4][5], accelerate the diffusion process, and facilitate the formation of thick nitride layers [6]. In recent years, to study the mechanism by which rare earth elements accelerate nitridation, much research has focused on determining how rare earth elements speed up the diffusion of nitrogen atoms into substrate materials through experiments and calculations; for instance, kinetic calculations have been performed based on changes in the thickness [7] or weight [8] of nitrided layers. Dai et al [9] investigated the depths of compound layers formed after 2 h in nitride salts with or without 5% of the rare earth element La at different temperatures and pointed out that the diffusion activation energy decreased from 183 to 136 kJ mol −1 after La addition.…”

Improvement of stamping performance of H13 steel by compound-layer free plasma nitriding

“…Plasma nitriding is a kind of surface modification technology widely used for steels to improve their surface combined properties [9][10][11][12][13][14][15]. Generally, the nitriding layer formed during normal plasma nitriding is composed of compound layer and diffusion layer.…”