Effect of austempering temperatures on surface hardness of AISI 4140 steel

Abstract

AISI 4140 steel is widely used in various engine elements, such as connecting rods, crankshafts, axles, piston rods, and sprockets. The purpose of this study was to determine the hardness value and microstructure using temperature variations in the austempering process. The test results show that after the austempering process with temperature variations changed the hardness. The austempering process can increase the hardness value, but after the temperature is raised, the hardness value decreases. The greatest hardness value at 350°C was 264.4 BHN. After increasing the temperature to 400°C, the hardness decreased to 239.1 BHN. At a temperature of 450°C, the hardness was 226.7 BHN. Microstructure observations showed that the bainite is more uniform with increasing temperature. The test results show that the austempering temperature affects the hardness value and microstructure. When the austempering temperature is increased, the hardness value decreases.