The Structure Stability of Carbide-Free Bainite Wheel Steel

Abstract

Metallographic structures of carbide-free bainite steel wheel rim are mainly composed of supersaturated lath ferrite and retained austenite film among bainitic ferrite laths. It is suspected that supersaturated ferrite and retained austenite are likely to decompose under the influence of temperature change and mechanical stress. Stability of wheel rim structure is studied by means of x-ray diffraction, dye microscopy, and micro-hardness test. When the samples are tempered in the range of 150-350°C, the retained austenite films are at the state of relative stability. Fifty percent of retained austenite is decomposed when the sample is tempered at 400°C. Microhardness increases when the sample is tempered at 150°C. The decrease in hardness is mild when the samples are tempered from 200 to 500°C. The mechanical stability of retained austenite film is studied with tensile sample under the effect of tensile stress. The retained austenite appears to be stable in low and middle degree of deformation, and decomposition occurs at great amount of deformation. Diffraction peak of carbide is not found in all above experiments. The steel enriched silicon prevents the carbide precipitation during the transformation. It indicates the carbide-free bainite wheel steels have an excellent thermal and mechanical stability.

The role of microstructure and its stability in performance of wheels in heavy haul service

“…Alternative microstructures have been considered in the literature (e.g. bainitic wheels including recent development of carbide free super-bainitic wheel steels) [19][20][21], but pearlitic steels still offer the best combination of stable performance, better wear rate predictability and lower cost. All of these advantages are supported by providing homogeneous pearlitic microstructure throughout the whole wheel.…”

Effect of Multi-Step Austempering Treatment on the Microstructure and Mechanical Properties of a High Silicon Carbide-Free Bainitic Steel with Bimodal Bainite Distribution

“…Blocks of austenite, due to the lower carbon content in comparison with films [16,25], have poor stability and a high tendency to undergo martensitic transformation during applied stress, leading to large brittle martensitic islands, thus decreasing material toughness [26]. On the contrary, the presence of austenitic films generally leads to an enhancement in material properties [27][28][29][30][31].…”

Effect of original microstructure on wear property of ER9 wheel steel

“…The results of Gao et al [20] and Li et al [21] showed that the non-uniform microstructure caused the formation of rolling contact fatigue cracks. In recent years, the bainite wheel steel is also used [22]. Therefore, the microstructure uniformity is the key to improve the fatigue life of the wheel material.…”