Austenite grain growth during hot forging of medium carbon engineering steels with or without V–Ti microalloying

Abstract

Medium carbon engineering steels which are used for automotive and machine components are usually forged at rather high temperatures and subsequently quenched and tempered or controlled cooled. The austenite grain structure at the beginning of the γ-α transformation greatly determines the transformation process. Two commercial steel grades (about 0·4%C) with and without V–Ti microalloying were investigated using hot compression tests to simulate forging. The development of austenite grain structure during reheating, forging, and subsequent holding or cooling to the transformation temperature was evaluated. On reheating of both steels, a narrow range of temperature close to l000°C was found in which formation of a mixed austenite grain structure was observed. After forging, the higher the hot strain the faster the grain growth after recrystallisation. In the microalloyed steel, onset of abnormal grain growth was observed after heavy deformation at 1200°C, presumably due to strain induced coalescence of grain growth inhibiting particles.MST/1362