Z.N. Yang

Effect of Annealing on Microstructure and Hardness of Hot and Cold Rolled Zr705

Abstract The annealing behaviors of hot and cold rolled Zr705 were investigated in a wide temperature range of 200∼850 °C. Compared to the cold rolled specimens, the hot rolled specimens exhibited lower hardness at temperatures

Sliding wear and low cycle fatigue properties of new carbide free bainitic rail steel

Abstract A new carbide free bainitic rail steel was prepared, whose comprehensive mechanical properties are equal or superior to current premium pearlitic and bainitic rail steels. The new bainitic rail steel possesses better low cycle fatigue properties and approximate resistance to wear compared with current pearlitic rail steel. The carbon enriched film-like austenite between the ferrite of the new bainitic rail steel can delay crack initiation and propagation in fatigue processes, resulting in a relatively high low cycle fatigue life (about two times) compared to the pearlitic rail steel. Finally, a wear model during sliding wear and deformation model during the low cycle fatigue of pearlitic and bainitic rail steels were established. As a result, the bainitic rail steel with a relatively reasonable combination of wear and fatigue properties compared to pearlitic rail steel is obtained, in which the initiation and propagation of cracks may be partially or entirely removed during the wear process.

Wear resistance of bainite steels that contain aluminium

Four steels containing Si + Al = 2 wt-% were investigated in this study. Three mixed microstructures, namely, bainite + martensite + retained austenite (MB+Ar), martensite + retained austenite (M+Ar) and low-temperature bainite + retained austenite (LB+Ar) were obtained. Wear resistance was determined by dry sliding friction testing under different conditions. Results showed that Al promoted the formation of oxide films during wear process, resulting in the improvement of wear resistance, especially under a high-load condition. Under the same hardness, the wear resistance of MB+Ar was improved by 65 and 100% compared with that of LB+Ar and M+Ar microstructures, respectively. At high temperature, the worn surface was covered by oxide films and the samples exhibited abrasive and adhesive wear mechanisms. However, at low temperature, the oxide films were difficult to generate on the worn surface; the adhesive wear mode was dominant and resulted in severe wear.

Study on carbide-bearing and carbide-free bainitic steels and their wear resistance

Carbide-free and carbide-bearing bainitic steels have been obtained. The relationship between the bainitic microstructure and wear resistance has been studied. Results show that carbide-free upper and lower bainitic microstructures obtained in the steel with Si + Al mainly consist of bainitic ferrite and retained austenite. Carbide-bearing upper and lower bainitic microstructures obtained in the steel without Si + Al consist of bainitic ferrite, carbide and trace amounts of retained austenite. The carbide-free bainite exhibits higher strength and toughness than carbide-bearing bainite, especially the toughness. Under lower wear loading, carbide-bearing lower bainite (LB) exhibits higher wear resistance. Under higher wear loading, carbide-free LB exhibits higher wear resistance, which results from the improved surface hardness due to strain-induced martensitic transformation from the retained austenite.