Low-temperature plasma nitriding of sintered PIM 316L austenitic stainless steel

Abstract

This work reports experimental results on sintered PIM 316L stainless steel low-temperature plasma nitriding. The effect of treatment temperature and time on process kinetics, microstructure and surface characteristics of the nitrided samples were investigated. Nitriding was carried out at temperatures of 350, 380, 410 and 440 °C , and times of 4, 8 and 16 h, using a gas mixture composed by 60% N 2 + 20% H 2 + 20% Ar, at a gas flow rate of 5.00 × 10 -6 Nm 3 s −1, and a pressure of 800 Pa. The treated samples were characterized by scanning electron microscopy, X-ray diffractometry and microhardness measurements. Results indicate that low-temperature plasma nitriding is a diffusion controlled process. The calculated activation energy for nitrided layer growth was 111.4 kJmol -1 . Apparently precipitation-free layers were produced in this study. It was also observed that the higher the treatment temperature and time the higher is the obtained surface hardness. Hardness up to 1343 HV 0.025 was verified for samples nitrided at 440 °C. Finally, the characterization of the treated surface indicates the formation of cracks, which were observed in regions adjacent to the original pores after the treatment.

Martensitic Stainless Steels Low-temperature Nitriding: Dependence of Substrate Composition

“…For this purpose, lowtemperature plasma-assisted techniques is among of the most studied techniques for this steel class. If processing parameters are conveniently chosen, it is possible to obtain a treated surface presenting higher hardness and corrosion resistance than the untreated surface [7][8][9][10][11][12][13][14] . However, if the process parameters are not correctly selected, the treated surface can present a corrosion resistance lower than that expected for the bulk material after adequate solution treatment, which must be strongly avoided particularly on the case of stainless steels.…”

Nitrogen Surface Enrichment of Austenitic Stainless Steel ISO 5832-1: SHTPN vs Low-temperature Plasma Nitriding

“…This fact, allied to low hardness and tribological properties, limits their applicability. Several techniques are being used to improve the surface characteristics of these steels, like plasma nitriding at low temperatures [1][2][3][4] , ion implantation 5 , and high temperature gas nitriding (HTGN) 6 . More recently, the so-called "Solution Heat Treatment after Plasma Nitriding" (SHTPN) process was proposed as a new method for surface enrichment of nitrogen in solid solution, with good results regarding improvement of corrosion resistance of stainless steels 7,8 .…”

“…Hence, the use of plasma nitriding is limited to the low temperature range, where only the formation of the S-phase (also called expanded austenite -γ N ) occurs 1,12,13 . The S-phase formation on austenitic stainless steels by advanced nitriding treatments has been the subject of several studies [1][2][3][4][5][6][7][8][9][10][11][12][13] . Theo focus of this work is not the study of the S-phase itself, rather the SHTPN process as an alternative to low temperature plasma nitriding.…”

Wear resistance of AISI 304 stainless steel submitted to low temperature plasma carburizing

“…However, if the temperature is higher than 450ºC, the S phase may decompose, resulting in precipitation of carbides such as Cr 23 C 6 and Cr 7 C 3 that reduce wear and corrosion resistance. The combined improvement in hardness, wear properties, and excellent corrosion resistance are responsible for making the S phase one of the most significant recent developments in stainless steels (Sun and Bell, 1993;Bell, 2002;Sun and Bell, 2002;Cheng et al, 2005;Mendes et al, 2014). When temperature or treatment time are increased, the S phase thickness also increases, but the possibility of forming carbides is higher.…”