Elsevier

Applied Surface Science

Volume 298, 15 April 2014, Pages 243-250
Applied Surface Science

Surface properties of nitrided layer on AISI 316L austenitic stainless steel produced by high temperature plasma nitriding in short time

https://doi.org/10.1016/j.apsusc.2014.01.177Get rights and content

Highlights

  • The 8 μm nitrided layer was produced on the surface of AISI 316L stainless steel by plasma nitrided at high temperatures (540 °C) within 1 h.

  • The nitrided layer consisted of nitrogen expanded austenite and possibly a small amount of free-CrN and iron nitrides.

  • It could critically reduce processing time compared with low temperature nitriding.

  • High temperature plasma nitriding could improve pitting corrosion resistance of the substrate in 3.5% NaCl solution.

Abstract

It has generally been believed that the formation of the S phase or expanded austenite γN with enough thickness depends on the temperature (lower than 480 °C) and duration of the process. In this work, we attempt to produce nitrogen expanded austenite layer at high temperature in short time. Nitriding of AISI 316L austenitic stainless steel was carried out at high temperatures (>520 °C) for times ranging from 5 to 120 min. The microstructures, chemical composition, the thickness and the morphology of the nitrided layer, as well as its surface hardness, were investigated using X-ray diffraction, X-ray photoelectron spectroscopy, optical microscopy, scanning electron microscopy, and microhardness tester. The corrosion properties of the untreated and nitrided samples were evaluated using anodic polarization tests in 3.5% NaCl solution. The results confirmed that nitrided layer was shown to consist of γN and a small amount of free-CrN and iron nitrides. High temperature plasma nitriding not only increased the surface hardness but also improved the corrosion resistance of the austenitic stainless steel, and it can critically reduce processing time compared with low temperature nitriding.

Introduction

The austenitic stainless steels are widely used in many industrial fields because of their very high general corrosion resistance [1], [2], [3]. Unfortunately, their low hardness and poor wear resistance seriously limit these applications [4], [5], [6], [7], [8], [9]. Low temperature nitriding can improve the hardness and wear resistance of austenitic stainless steels without losing corrosion resistance by producing a layer of supersaturated nitrogen solid solution phase which is usually called ‘expanded austenite’ γN, or S-phase [2], [10], [11], [12], [13], [14], [15], [16], [17]. Many nitriding techniques were used to produce this phase layer: glow discharges plasma nitriding, RF plasma nitriding, plasma immersion ion implantation, plasma-based low-energy ion implantation, and active screen plasma nitriding [4], [12], [18], [19]. Table 1 is data on the low temperature nitriding of austenitic stainless steels collected from the literature and including some important experiments.

In order to avoid the drop in corrosion resistance of austenitic stainless steels, these nitriding techniques are characterized by treatment temperatures (<480 °C). At temperatures above 480 °C, hardness continues to increase but corrosion resistance is affected, due to the mobilization of Cr and formation of CrN precipitates. Li [42] also stated that the precipitation of CrN occurs, above the nitriding treatment temperatures of 470–490 °C for the AISI 316L steels.

In most of the published results, long nitriding times are necessary to obtain the sufficient thickness γN phase layers for low temperature nitriding techniques. From Table 1, it can be seen that the formation of about 5–6 μm thickness γN layer commonly requires 2 h or longer. We report a study of high temperature (520–560 °C) nitriding of AISI 316L austenitic stainless steel carried out in the plasma atmosphere enclosed by bilayer active screen. The results show that high temperature nitriding can also nitrogen expanded austenite layer with the thickness of 6 μm within 60 min. The aim of this work is to study the influence of high temperature nitrided on the microstructure, morphology, hardness and the corrosion behaviour in NaCl aqueous solutions of the AISI 316L austenitic stainless steel.

Section snippets

Experiments

The samples used in this work were AISI 316L austenitic stainless steel with the following chemical compositions (wt.%.): Cr (17.10–17.80), Ni (10.10–11.20), Mo (2.16–2.30), C (<0.03), Si (<0.80), and Fe balance. Samples (15 mm × 15 mm × 4 mm) were cut from a hot rolling plate, ground and mirror polished then cleaned with acetone before nitriding.

The nitriding was carried out in an ion nitriding furnace and the details of which had been described elsewhere [43]. The discharge current and voltage

Results and discussion

Fig. 1 presents the cross-section optical micrographs of the samples nitrided at various temperatures and times. For all samples nitrided at 520 °C and 540 °C, it could be seen that the nitrided layers are resistant to the etching reagent, so that it appears ‘bright’ under an optical microscope. The thickness of the ‘bright’ layer ranged from1.5 to 10 μm, depending on processing temperature and time. With increasing temperature at 540 °C, some dark spots became visible in the nitrided layer. It can

Conclusions

The nitrided layer mainly composed of nitrogen expanded austenite phase was formed on the surface of AISI 316L austenitic stainless steel by plasma nitriding at high temperatures (>520 °C) in short time (15–60 min). In case of the sample nitrided at 540 °C for 60 min, the nitrided layer with a thickness of 8 μm was produced in the surface. The surface microhardness was about 980 HV0.05, nearly 4.5 times higher in compared with the untreated substrate.

All the nitrided samples showed better corrosion

Acknowledgment

The authors gratefully acknowledge the National Natural Science Foundation of China (Nos. 51301149 and 51179017) for financial support of this research work.

References (54)

  • F.Y. Dong et al.

    Materials Science and Engineering A

    (2013)
  • L.-H. Lin et al.

    Applied Surface Science

    (2011)
  • K.H. Lo et al.

    Materials Science and Engineering R: Reports

    (2009)
  • S. Corujeira Gallo et al.

    Applied Surface Science

    (2011)
  • A. Devaraju et al.

    Wear

    (2012)
  • C.M. Lepienski et al.

    Materials Science and Engineering A

    (2008)
  • D. Zeng et al.

    Applied Surface Science

    (2012)
  • E. Menthe et al.

    Surface and Coatings Technology

    (1995)
  • T.-S. Shih et al.

    Applied Surface Science

    (2011)
  • A. Martinavičius et al.

    Acta Materialia

    (2012)
  • M. Asgari et al.

    Materials Science and Engineering A

    (2011)
  • L. Gil et al.

    Surface and Coatings Technology

    (2006)
  • Y. Sun

    Materials Science and Engineering A

    (2005)
  • T. Czerwiec et al.

    Surface and Coatings Technology

    (2000)
  • A. Saeed et al.

    Applied Surface Science

    (2013)
  • Y. Sun et al.

    Heat Treatment of Metals

    (1999)
  • A. Fossati et al.

    Surface and Coatings Technology

    (2006)
  • F. Borgioli et al.

    Surface and Coatings Technology

    (2005)
  • B.-Y. Jeong et al.

    Surface and Coatings Technology

    (2001)
  • E. Skolek-Stefaniszyn et al.

    Vacuum

    (2010)
  • H. Dong et al.

    Materials Science and Engineering A

    (2006)
  • N. Karimzadeh et al.

    Applied Surface Science

    (2013)
  • M. Olzon-Dionysio et al.

    Surface and Coatings Technology

    (2008)
  • O. Öztürk et al.

    Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

    (2009)
  • J.C. Stinville et al.

    Surface and Coatings Technology

    (2010)
  • G.A. Collins et al.

    Surface and Coatings Technology

    (1998)
  • J.M. Priest et al.

    Thin Solid Films

    (1999)
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