Effect of Zr on austenite grains growth behaviour of high strength Ti microalloyed low carbon steel

The isothermal grain growth behaviour for three Ti microalloyed steels with different Zr contents (0-0.039 wt-%) at different reheating temperatures (1100, 1150, 1200 and 1250 degrees C) and for holding times (10, 60, 600 and 1800 s) was investigated. Austenite growth model was established to analyse and predict the functional relationship between austenite grains size and austenitising temperature and time during the isothermal austenitising process in the three tested steels, and the influence of Zr was discussed. The results indicate that the activation energy Q and time index n of austenite grains boundary migration in the tested steels decrease with the increase of Zr content. The addition of Zr can inhibit the growth of primary austenite grains at high temperatures. With the increase of Zr content, the trend of average grain size growth of primary austenite becomes smoother. The addition of Zr improves the high-temperature stability of precipitates, resulting in smaller precipitates and stronger pinning effect for austenite grains boundary in Ti-Zr microalloyed steel compared to that in Ti microalloyed steel at high temperatures.