The influence of temperature on the Austenite grain size and microstructure of 4140 steel
Rui Zhang and Richard D. Sisson, Jr
Center for Heat Treating Excellence, Worcester Polytechnic Institute, Worcester, Massachusetts, 01609, U.S.A
Abstract
Grain growth during heat treatment can affect mechanical properties. A large grain size can result in a lower strength and susceptibility to brittle failure. In order to control the Austenite grain size, the effect of Austenitizing temperatures and holding times on the grain size and hardness in 4140 steel was experimentally investigated. Samples were heat treated at 900°C, 1000°C and 1100°C, and held for 1, 4, and 9 hours in air. After Austenitizing, samples were cooled in the furnace to 850°C before they were quenched in water at room temperature. Each sample was cut, mounted and polished. Rockwell hardness and micro-hardness tests were performed on each sample. A Picric etch was used for grain size analysis. E112 Standard Test Methods for Determining Average Grain Size was followed to measure the grain size. It was found that the Austenite grain size increased with temperature and time according to a standard grain growth model, it was also found that the as-quenched hardness decreased with an increase in grain size.