Evaluation of Microstructure and Wear Behavior of Iron-based Hard - facing Coatings on the Mo۴۰ Steel

Mo۴۰ low-alloy steels are mostly used to produce industrial components such as crane wheels which are exposed to abrasive wear. However, during working conditions, their wear resistance is reduced after a while due to its low hardness. With increasing abrasive wear, the dimensions of components decrease and they need to be repaired for surface modification. In this regard, hard overlay coatings are applied by hard-facing process for reusing these components. This work deals with the surface analysis, hardness and wear behaviors of the clad layers made of the Fe-Cr-C based hard-facing on the Mo۴۰ low-alloy steel by submerged arc welding method. The overlay coatings are performed by two ways of welding: ۱. rods of UP۶-GF-۵۰ (۳۰۷ kavosh joosh standard number), and ۲. UP۶-GF-۵۰-C (۴۲۰ kavosh joosh standard number) regarding the Din ۸۵۵۵ standard, in single and double passes. According to the X-ray diffraction analysis and microstructure characteristics, both martensite with retained austenite phases and the (Fe, Cr)۲۳ C۶ carbides were identified within the overlay coatings. The presence of the carbon and chromium elements in hard surfaced specimens (as denoted by ۳۰۷ and ۴۲۰) produced by single and double pass were increased. The wear resistance in the coatings of ۳۰۷ and ۴۲۰ produced by double pass are higher than the coatings produced by single pass. In addition, the amount of average hardness in the coatings of ۳۰۷ and ۴۲۰ produced by single and double passes increases from ۳۶ to ۳۸ HRC and from ۳۹ to ۴۲ HRC, respectively. Based on the scanning electron microscopy micrographs, the wear mechanisms of specimens with high hardness are adhesive and tribochemical wear.

Keywords:

Mo۴۰ steel , Submerged arc welding , Coating , Hard-facing , Wear resistance