Effect of Mn content on microstructure and properties of wear-resistant bainitic steel

The microstructure, hardness and wear resistance of bainitic steel containing 1.0%–2.8% Mn were investigated by means of optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, x-ray diffractometer, hardness tester and M-200 wear tester. The results show that the as-cast structure is mainly composed of pearlite and a small amount of bainite when the Mn content is less than 1.6%. When the Mn content reaches 2.2%, the as-cast steel is mainly composed of acicular lower bainite and retained austenite. With the increase in Mn content, the amount of retained austenite decreases, the acicular lower bainite content increases, and the hardness tends to increase. After normalizing at 900 °C, the microstructure of the steel is mainly acicular lower bainite and film-like retained austenite. As the Mn content increases, the bainitic transformation curve moves to the right and down, the bainitic transformation start temperature (Bs) decreases, the bainitic laths are more refined, the retained austenite content is reduced, and the hardness is increased. The wear resistance of normalized bainitic steel increases obviously with the increase in Mn content. (paper)