Effects of Heat Treatment on Phase Transformation and Corrosion Resistance of Boride Layer on Austenitic Stainless Steel
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NTRODUCTION
STAINLESS steels, especially austenitic stainless steels, possess an excellent corrosion resistance with acceptable strength. Accordingly, they are widely used in various industrials. Roughly 60 to 70 pct of stainless steel used by industries, e.g., storage tanks, accessory parts in the chemical, petrochemical, and food industries, is austenitic stainless steels.[1,2] However, complicated applications requiring high loading with contact surface have been in increased demand in recent years. Therefore, the need for improved wear resistance for enhanced service lifetime is often called for. Boronizing process is a thermochemical surface treatment that provides an excellent wear resistance for various metallic materials including austenitic stainless steels.[3–10] Double-phase (FeB and Fe2B) boride layers with smooth morphology are normally detected for high alloy steels. Normally, the single-phase Fe2B boride layer is appropriate for practical applications because the boron-rich FeB phase in particular is harder and more brittle than the Fe2B phase.[11–13] The conventional heat treatment is a simple method to diminish FeB phase on the double-phase boride layer.[14–16] Therefore, in this research, the phase transformation of the boride layer of the
P. NAEMCHANTHARA and P. JUIJERM are with the Department of Materials Engineering, Faculty of Engineering, Kasetsart University, 50 Ngamwongwan Rd., Ladyao, Jatujak, Bangkok, 10900, Thailand. Contact e-mails: [email protected], [email protected] Manuscript submitted January 26, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
boronized austenitic stainless steel AISI 304 will be presented after heat treatment at a temperature range of 800 °C to 900 °C for 2 hours. An optical microscope and X-ray diffractometer (XRD) were used to characterize the microstructure of the boride layers. In general, the adequate corrosion resistance of the austenitic stainless steel AISI 304 is an important expectation of end users. Therefore, the corrosion resistances of the boronized austenitic stainless steel AISI 304 with and without heat treatment were investigated and compared with the untreated one using electrochemical techniques. Finally, the effects of heat treatment on the microstructure and corrosion resistance of the boronized austenitic stainless steel AISI 304 were clarified.
II.
MATERIALS AND EXPERIMENTAL PROCEDURES
The metallic material investigated in this research was an austenitic stainless steel AISI 304. The chemical composition is 0.045 pct C, 1.60 pct Mn, 0.43 pct Si, 0.031 pct P, 0.003 pct S, 18.26 pct Cr, and 8.65 pct Ni (all values in wt pct). Cylindrically shaped samples 12.5 mm in diameter and 10 mm in length were prepared. All specimens were ground up to 600 grit silicon carbide (SiC) paper to clean and obtain a good surface before carrying out the boronizing process. Boronizing process was carried out using a solid boronizing medium of Ekabor-I powder procured from BorTec GmbH, Germany. Specimens were packed as well as buried with Ekabor-I powder in a st
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