Effect of Boron Concentration in the Fe-Cr-Mo-(B,C) Hardfacing Alloys on the Microstructure and Mechanical Properties

This study presents the production of Fe-Cr-Mo-(B,C)-based hardfacing coatings containing a Mo2FeB2 phase on low-carbon DIN St37 steel using a gas tungsten arc (GTA) welding process. The effects of the B content on the phase distribution, microstructure, microhardness and wear rate of the coatings were systematically studied. An x-ray analysis showed that the coating microstructures consisted of Mo2FeB2, alpha-(Fe-Cr), M6C, M-2,M-3(B,C), M-23(C,B)(6), martensite and M-7(C,B)(3) (M=Fe,Cr,Mo) phases. Microstructural examination revealed a hypoeutectic microstructure in the boron-free and 10% boron-containing coatings. For the coatings with 20 and 30% boron contents, the microstructure completely changed and became hypereutectic. The hardness values of the coatings significantly increased with increasing boron content. The measured row hardness values of the coating layers were 754.67 +/- 28.80-1811 +/- 25 HV0.3. The measured macrohardness values from the surface were 834.53 +/- 22.84-1215.72 +/- 51.13 HV1. Increasing the amount of added boron decreased the wear rate of the coatings. The S3 (Fe7Cr3Mo3B6C) sample had the best wear performance among the produced coating layers and the highest boron content for all wear loads.