Surface characterization and investigation of mechanical properties of pack-borided AISI 304l steel with microwave hybrid and conventional heating

In this study, AISI 304L austenitic stainless steel was pack-borided at 850 °C, 900 °C and 950 °C for 2, 4 and 6 hours with microwave hybrid and conventional heating method. The microstructural, mechanical and tribological properties of the boride layers formed after pack-boriding with two different heating methods were compared. It was observed that both thicknesses of FeB and Fe2B phases increased as the process temperature and time increased in microwave hybrid and conventional method. X-ray diffraction (XRD) patterns were showed that there are FeB, Fe2B, Cr2B ve Ni2B phases in the boride layers. The B activation energy was determined as 255.90 kJ/mol for pack-borided AISI 304L stainless steel with conventional heating method, but it has decreased to 154.35 kJ/mol with microwave hybrid heating method. While the highest hardness was obtained as 2074.8 HV0.05 at 950 °C for 4 hours with microwave hybrid heating, the highest hardness value of the pack-borided sample with conventional heating method was 1947.5 HV0.05. After the fracture toughness tests conducted by the Vickers indentation method, the values of fracture toughness of pack-borided samples with microwave hybrid heating and conventional heating system 1.304 MPa·m1/2 and 1.417 MPa·m1/2, respectively. According to the results of Daimler-Benz Rockwell-C adhesion tests, the adhesive strength between the boride layer and the substrate of all samples is high except for some samples. As a result of the corrosion tests in 2% HNO3 solution of the pack-borided samples with microwave hybrid heating, it was observed that the corrosion resistance of the samples borided at 950 °C for 6 hours was 95 times higher than that of the untreated samples. Microwave hybrid heating can make a 2-hour gain in process time based on the same boriding temperature, or a higher thickness boride layer can be obtained even if boriding conducted at 50 degrees lower process temperature. Keywords: Microwave hybrid heating, conventional heating, pack-boriding, adhesion strength, fracture toughness, corrosion.