Behaviour at Nitriding in Fluidized Layer of Austenitic Stainless Steels at the Temperature of 450 °C

Résumé

Stainless austenitic steels have a good corrosion resistance but reduced abrasion strength due to low strength below 200 HV₅. By nitriding one may ensure the obtaining of a superficial layer with increased strength that should maintain unaltered the corrosion resistance. The nitriding in fluidized layer applied at 450 ºC allowed the obtaining of diffusion layers formed of nitrogen enriched austenite with certain nitride separations. For the CrNi, CrNiMo usual steels, the obtained strengths have been higher than 1000 HV₀₀₅. In the case of steel X1CrNiMoCu20.18.7 with more than 50% of alloying elements, the strengths did not exceed 500 HV₀₀₅ due to the low nitrogen concentration, much below the saturation limit determined by the reduced diffusion speed. The corrosion test in saline mist indicates the maintaining of corrosion resistance, the materials ranging in the group of Perfectly resistant. Also, the abrasion strength increased 2-3 times due to the limited diffusion speed at low temperature. The favourable property assembly allows the usage of the treatment for some practical applications.