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 prior 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, 1000, and 1100 °C, and held for 1, 4, and 9 hours. 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 microhardness tests were performed on each sample. A Picric etch was used for grain size analysis. The grain size was measured following the E112 standard test method. It was found that the prior austenite grain size increased with temperature and time according to the standard grain growth model. It was also found that the as-quenched hardness decreased with an increase in grain size.
