Effects of Heat Treatments on Mechanical Properties, Specific Wear and Corrosion Rate of HQ 809 Steel for Machinery Components Application

Abstract

HQ (High Quality) 809 steel is a HSLA (High Strength Low Alloy) steel and it is equivalent to AISI 4140, JIS SCM440, DIN 42CrMo4. HQ 809 is a chromium molybdenum alloy steel for applications requiring a high tensile strength, good hardenability, ductility, toughness, wear resistance and good fatigue strength. HQ 809 is commonly used for heavy-duty shafts, gears, axles, couplings, pins, bolts, nuts, impellers of centrifugal compressors. The objective of this research is to characterize the effects of heat treatment such as quenching and tempering processes on mechanical properties (hardness, impact energy), specific wear and corrosion rate of HQ 809 steel in 3.5 % NaCI solution. Quenching process has been conducted by heating the samples at the austenite temperature of 950 °C with a soaking time of 2 hours and then these samples were cooled rapidly in oil medium. Tempering processes were done at temperatures of 150, 200, 250, 300, 350, 400, 450, 500, 550 and 600 °C with a holding time of 2 hours. The sample properties such as hardness, impact energy, specific wear and have been characterized by a micro Vickers hardness test, Charpy impact, disk-on-block wear test respectively. Corrosion rate was characterized by potential polarization. All tests were performed at room temperature and test parameter was tempering temperature variations. The results show that the tempering temperature variations generate significant effect on HQ 809 properties. In general, the Vickers microhardness decreases, however, the specific wear and impact energy increase if tempering temperatures of the samples increase. The raw material of HQ 809 has a hardness of 270 VHN (Vickers Hardness Number) and the quenched sample has the highest hardness of 370 VHN. But, tempering temperatures do not have significant effects on the corrosion rate of HQ 809. The tempering temperature of 500 °C produces a more cathodic sample compared to other tempering temperatures.