نیتروژن دهی یون-پلاسمایی فولاد ابزار ماشین آلات و قطعات

Ion-plasma nitriding of machines and tools parts instrumental steels

نیتروژن دهی یون - پلاسمایی فولاد ابزار ماشین آلات و قطعات 

ABSTRACT

Here introduced features of formation diffusion bond during ion nitriding in glow discharge plasma in gaseous mediums (mixture of nitrogen and argon). It is shown, that argon existing in saturated medium changes the nitriding process kinetics and the phase composition of the outer zone. Here presented investigation results on ion-plasma nitriding of instrumental steels, focused on microstructure and tool areas phase composition change, operating in most difficult conditions.

 

میکروساختار و خواص سایشی فولاد ابزار

Microstructure and wear properties of AISI M2 tool steel

on RF plasma nitriding at different N2–H2 gas compositions

میکروساختار و خواص سایشی فولاد ابزار AISI M2

نیتروژن دهی پلاسمایی RF شده در ترکیب های مختلف از گازهای N2–H2

ABSTRACT

Wear behavior of quenched-tempered AISI M2 tool steel samples has been studied after plasma nitriding at different N2–H2 plasma gas flows containing 25, 50 and 75 sccm N2. Plasma nitriding was performed at 450 °C for 8 h under floating potential using a plasma reactor equipped with a radio frequency power generator. Microstructure, phase composition, nitrided layer thickness, hardness and surface roughness of the samples were studied using optical microscopy, X-ray diffraction, microhardness and surface profilometry measurements. Dry sliding wear resistance of samples was determined by performing ball-on-disc wear testes. The results revealed formation of mainly a diffusion zone at the 25 sccm N2–75 sccm H2 gas flow and mono-phase ε-Fe2–3N compound layer at higher N2 concentrations. Plasma nitriding increases near surface hardness up to 50% (about 1600HV0.025) irrespective of the N2:H2 ratio, where nitrided layer depth and surface roughness increase with increasing the N2 flow rate in the plasma gas. Depending on the nitrogen content, sliding wear resistance may be improved between 20 and 90% with respect to the un-nitrided substrate. Among the nitrided samples the maximum and minimum wear resistance was obtained at plasma gases containing higher and lower H2 fractions, respectively. Decreasing wear resistance with increasing N2 flow rate in the plasma gas attributed to formation of the hard and brittle compound (white) layer on the sample surface and development of residual stress profiles.