Comparative Study of Heat Treatment Effects Performed with Solar Energy and Electric Furnace on EN 1.4848 Stainless Steel Alloyed with Co, W, Cu and Mo

摘要

This paper presents a comparative study of the microstructure characteristics resulted from heat treatments performed with solar energy and with electric resistance furnace of EN 1.4848 steel alloyed with Co-W-Cu- Mo. In order to increase the hardness characteristics, mechanical strength and fatigue, this steel was previously alloyed with 6.15 wt% Co, 1.8 wt% W, 0.3 wt% Cu and 0.2 wt% Mo. The alloying with Co and W aimed at increasing the hardness, while Cu was added to improve the tensile strength and Mo to increase the fatigue strength. The thermal treatment of EN 1.4848 austenitic stainless steel alloyed with Co-W-Cu-Mo consisted in solid solution quenching in liquid, after heating the samples at 1050°C, maintaining the plateau temperature for about 10 min and subsequently cooling in water or oil. The purpose of this treatment was to dissolve the compounds possibly formed during the production of steel, if any, and to form supersaturated solid solutions, stable at low temperatures and in corrosive environments. The microstructural aspects, microhardness, and Differential Scanning Calorimetry (DSC) results were highlighted, in order to emphasize the solid phase transformations, on both heat treatment variants. The microstructure consists of high-alloy austenite, supersaturated with carbon, with small proportions of delta ferrite with interdendritic precipitations and various intermetallic compounds, very stable and without showing phase transformations up to negative temperatures (- 75 C). Comparing the solar quenched samples to the electric-quenched one, regarding to the differential scanning calorimetry (DSC) analysis, showed that independently of the applied cooling process (in water or oil) the phase transformation temperature is lower for the solar-quenched samples compared to the electric-quenched ones.