Deformation, fracture, and wear behaviours of C plus N enhancing alloying austenitic steels

The deformation, fracture, and wear behaviours of two new C+N enhancing alloying austenitic steels (CNEASs) for railway crossings under high speeds and heavy loads were investigated by tensile, Charpy impact, and sliding wear tests, in comparison with the traditional Hadfield austenitic steel. The main plastic deformation mechanism of the CNEASs was deformation twinning due to its low stacking fault energy (SFE). The enhanced strength and plasticity resulted from the large amounts of ultra-fine nano-twinning that occurred during plastic deformation, while the oversaturation effect of nitrogen on CNEASs further increased the hardness and work hardening capacity. Contrary to the increased ductile to brittle transition temperature (DBTT) caused by nitrogen in austenitic steel, the new studied steel exhibited a lower DBTT as compared to the Hadfield steel, because the combined alloying with C+N enhanced the metallic character of the interatomic bonds, increasing the fracture-resistance under cryogenic temperatures. Sliding wear tests showed that abrasive wear dominated the wear behaviour of the CNEASs. The remarkable improvement of wear resistance in the steels enhancing alloyed with C+N, particularly at high temperatures, was attributed to the formation of thick tribo-oxides on the worn surface under the effect of Cr and nitrogen. Therefore, the results demonstrated that the experimental steels possessed a higher strength, plasticity, hardness, impact toughness at cryogenic temperatures, work hardening capacity, and wear resistance as compared to the Hadfield steel. This makes the new steel an ideal material for railway crossings under high speeds and heavy loads. (C) 2012 Elsevier B.V. All rights reserved.