High Temperature Tribological Behavior of Borocarburized Layer on Q235 Steel

Abstract

A borocarburized layer was successfully fabricated on the surface of Q235 low-carbon steel via double glow treatment to improve the wear resistance at elevated temperature. The phase composition and microstructure of borocarburized layer were investigated by XRD and SEM. The microhardness of borocarburized layer from the surface to the substrate were detected. And the tribological behaviors of borocarburized layer and substrate were investigated under the dry-sliding against ZrO2 ball at three temperatures. The results indicate that the borocarburized layer consists of an outermost boride layer and a transition layer of carburized layer. The boride layer with main phase of Fe2B has a high hardness around 1700 HV, and the hardness of transition layer with main phase of Fe5C3 is around 600 HV. The novel gradient structure of an outermost boride layer and inner carburized layer is design in this research decreases the hardness mismatch of coating to prevent the boride layer peeling off. The friction coefficient and specific wear rate of borocarburized layer are much lower than that of substrate at the same temperature. In addition, the wear mechanism of substrate is mainly fatigue wear and slightly adhesive wear at 20℃. When the wear test performs at 200℃, the substrate wear mechanism is adhesive wear and fatigue wear. The wear mechanism of borocarburized layer is main abrasive wear at 20℃ and 200℃. And the wear mechanism of both substrate and borocarburized layer are main oxidation wear and adhesive wear at 500℃. The borocarburized layer effectively improves the wear resistance of low carbon steel due to the higher hardness and great thermal stability at high temperature.

Keywords

• borocarburizing
• double glow
• surface hardness
• tribological behaviour
• surface modification