Investigation of corrosion and wear behaviors of boronized AISI 316L stainless steel

AISI 316 L austenitic stainless steel has a wide usage area in various sectors of the industry (in chemistry, petro-chemical industry, paper industry, nuclear engineering, milking house equipments) because of its high corrosion resistance at high temperatures. Furthermore, because of biocompability and high corrosion resistance, it is also used in the field of medicine as an implant material. Besides these superior properties, the areas of usage are limited because of its low surface hardness and wear performance. Therefore, as a result of technological developments and expectation of more superior properties for the materials, the surface modification of the materials inservice are highlighted. Boronizing process is the first method that comes into mind because of being applicable for most of the metallic materials and having superior features such as high surface hardness and low friction coefficient, high corrosion and high wear resistance among the thermo chemical treatments.In this study, AISI 316 L austenitic stainless steel samples have been boronized by means of pack boronizing for 2, 4 and 6 hours at 800, 850 and 900 °C inside the commercial Ekabor®-2 powder. The sections of the boronized samples have been used in the micro-structure examinations after being prepared using metallographic methods. The surface morphology and phase analysis of the boride layers formed after the boronizing process have been performed with the techniques of optical, scanned electron microscope and X-ray diffraction analysis. The surface hardness of the formed boride layers has been measured by means of micro-knoop hardness methods. Growth kinetics of boride layers has been calculated by using equation of Arrhenius. Adhesion of the boride layers has been determined by means of Rockwell-C indentation method. Corrosion behaviors of the boronized samples have been inspected in different solutions (1M HCl, 1M NaOH, simulation body fluid (SBF) and %0.9 NaCl) for different immersion times (1 and 168 hours) using Tafel extrapolation and linear polarization methods. Furthermore, wear behaviors have been realized using ball-on-disk method under 5 N load and 0.3 m/s sliding speed in dry and liquid (SBF) medium.The metallographic studies have revealed that the boron layer formed on the AISI 316 L austenitic stainless steel has a flat and smooth morphology. Using XRD analysis, it has been determined that the boron layer formed on the steel surface comprised FeB, Fe2B, CrB, Cr2B, NiB and Ni2B phases. It has been determined that the boride layer thickness increased with increasing in both boronizing temperature and time. Similarly, it has been observed that the boronizing process also increased the surface hardness of the materials. As a result of the corrosion experiments, it is found that boronizing process significantly increased the corrosion resistance of the material in 1M HCl medium. While no positive effect of the boride layer was observed in the other mediums, the corrosion resistance of the borided samples has been observed to be increased in solution media with the increase of the waiting periods. The friction coefficient of AISI 316 L austenitic stainless steel has decreased after the boronizing process. With the increase of the boronizing temperature, the corrosion rate decreased both in dry and wet medium. In conclusion, by means of obtaining low friction coefficients with high surface hardness of AISI 316 L austenitic stainless steel using boronizing process, the wear and corrosion behaviors are improved.