Elsevier

Surface and Coatings Technology

Volume 201, Issue 6, 4 December 2006, Pages 2796-2801
Surface and Coatings Technology

Wear and corrosion properties of a low carbon steel processed by means of SMAT followed by lower temperature chromizing treatment

https://doi.org/10.1016/j.surfcoat.2006.05.019Get rights and content

Abstract

A duplex lower temperature chromizing treatment at 600 °C for 120 min followed by 860 °C for 90 min was performed on a low carbon steel plate with a nanostructured surface layer, induced by surface mechanical attrition treatment (SMAT) [Z.B. Wang, J. Lu, K. Lu, Acta Mater. 53 (2005) 2081]. Microhardness, wear and corrosion resistances of the chromized SMAT sample were measured, in comparison with those of the chromized coarse-grained counterpart and the as-annealed coarse-grained sample. Experimental results showed that these properties were improved markedly. The much enhanced properties of the chromized SMAT sample relative to the chromized coarse-grained counterpart might originate from its superior microstructures, i.e., a much thicker chromized surface layer with smaller grains and more homogenous phase-distribution, due to the employed processes of the SMAT and the duplex lower temperature chromizing treatment.

Introduction

Chromizing is one of the widely used surface coating technologies to economically improve the performance of components. The chromized surface layer can substantially improve the surface hardness, wear resistance, corrosion resistance and high-temperature oxidation resistance of ferrous alloys [2], [3], [4]. However, nearly all conventional chromizing processes are carried out at temperatures above 1000 °C, limited by the diffusion and reaction kinetics involved. The thermochemical treatment of some ferrous alloys at these temperatures will induce serious distortion of the workpieces and severe degradation of the mechanical properties [5], [6]. To prevent these negative effects and to widen the application of chromizing techniques to a larger variety of materials, it is a must to lower the treating temperatures.

In a previous work [1], lower temperature chromizing process was investigated on a low carbon steel plate after surface mechanical attrition treatment (SMAT) [7], [8]. Due to the much enhanced atomic diffusivities [9] and chemical reaction kinetics [10] in the resultant nanostructured surface layer, a thicker chromized layer was formed in the SMAT sample than in the coarse-grained counterpart, especially at the temperature below 600 °C. Meanwhile, carbides and nitrides of chromium were formed predominantly in the surface layer at the temperature above 700 °C. To fabricate a much thicker chromized surface layer containing a large volume fraction of compounds, a duplex lower temperature chromizing process at 600 °C for 120 min followed by 860 °C for 90 min has been developed to chromize the SMAT low carbon steel [1]. The lower temperature process would allow an effective diffusion of Cr along grain boundaries, while keeping the nanostructures relatively stable, and the following higher temperature process would enhance the growth kinetics of the compounds layer. In this study, the hardness, the resistances to wear and corrosion of the low carbon steel sample processed by means of SMAT followed by the duplex lower temperature chromizing treatment were evaluated, in comparison with those of the chromized coarse-grained counterpart and the as-annealed coarse-grained specimen. The effects of the microstructure formed by the process of SMAT followed by chromizing on these properties were discussed.

Section snippets

Experimental

A commercial low carbon steel plate, with compositions (wt.%) of Fe, 0.11C, 0.01Si, 0.39Mn, 0.024S (max), 0.01P (max), was used for the investigation. The as-received sample was submitted to annealing to obtain homogeneous coarse grains, followed by the SMAT. The details of set-up and SMAT processing were described previously [7], [8]. The resultant microstructures were characterized in detail in [1]. In brief, a nanostructured surface layer of about 20 μm thick was achieved. The average grain

Microstructure characterization of the chromized surface layer

Detailed microstructural characterization of the surface layer of the SMAT sample after the duplex chromizing treatment by SEM, TEM observations and XRD analyses, together with the underlying enhanced chromizing kinetics of diffusion and phase formation due to numerous grain boundaries with a high excess stored energy in the nanostructured surface layer induced by SMAT, can be found in [1]. Fig. 1(a) and (b) show the cross-sectional SEM morphologies of the chromized SMAT sample (sample A) and

Summary

A chromized surface layer of about 20 μm thick was produced on the SMAT sample after a duplex chromizing process at 600 °C for 120 min followed by 860 °C for 90 min. Microhardness, resistances to wear and corrosion of the chromized SMAT sample were investigated, in comparison with those of the chromized coarse-grained counterpart and the as-annealed coarse-grained sample. It was demonstrated that the chromized SMAT sample showed larger hardness and superior resistances to wear and corrosion.

Acknowledgements

The authors are indebted to Mr. B. Guelorget and Dr. Y. Li for their cooperation in the nanoindentation and the corrosion experiments, respectively. Financial support from the National Science Foundation of China (Grants 50071061 and 50021101) and the French Ministry of Research (Grant 2001882, CPER EN2040) is acknowledged.

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