Structural and mechanical properties of different hard welded coatings for impact plate for ventilation mill

Abstract

Ventilation mill for grinding coal is one of the main steam power plants in the system that makes a significant influence on the level of energy efficiency with its work. Working parts of the device during exploitation are dominantly exposed to intensive abrasive and erosive wear and also to impact loading at elevated temperatures, which can lead to damage and fracture of homogeneous materials, thus shortening their working life. The consequences are the reduction in mill production capacity and its ventilatory effects compared to the projected value, as well as frequent delays due to parts replacements, that significantly affects the productivity, economy and energy-efficiency of the system. In order to determine the optimal technology for revitalization of the damaged impact plates the experimental model-hardfacing was engaged and different technologies and additional materials were used. Three technologies archardfacing were applied (MMA, SMAW and gas welding - G) and eight additional materials with different chemical composition and properties (Fe-Cr-C-Si, Fe-Cr-C-Si-Ti, Fe- C-W-Co-Ni-Si, Fe-Cr-W-B-Nb-Mo-C, W-Fe-C and WC-Ni- Cr-Si-B). The aim of this paper is to make the selection of optimum welding procedures and additional materials and hardfacing technology definition based on the results of structural and mechanical properties of samples of experimental model hardfacing. Cutting the samples for mechanical and structural tests is performed with water jet cutting using hardfaced test plan. Investigation of its macrostructure has been done, diagrams of distributions of hardness have been made, zone of the surface layer and HAZ-a, and the degree of mixing for all hardfaced samples have been defined. In addition, microstructural analyses were obtained with optical (OM) and scanning electron microscopy (SEM). The choice of additional materials and hardfacing procedures which were applied in the hard facing impact plates ventilation mill has been made based on the results of this research paper.