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 350C was 264.4 BHN. After increasing the temperature to 400C, the hardness decreased to 239.1 BHN. At a temperature of 450C, 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.

AISI 4140 钢广泛用于各种发动机元件，如连杆、曲轴、车轴、活塞杆和链轮。本研究的目的是利用等温回火过程中的温度变化来确定硬度值和微观结构。测试结果表明，经过温度变化的等温回火过程后，硬度发生了变化。等温处理可以提高硬度值，但温度升高后，硬度值降低。350C 时的最大硬度值为 264.4 BHN。升温至400℃后，硬度下降至239.1 BHN。在450℃的温度下，硬度为226.7 BHN。显微组织观察表明，随着温度的升高贝氏体更加均匀。试验结果表明，奥氏体回火温度影响硬度值和显微组织。当等温回火温度升高时，硬度值降低。