Characterization of a New Steel for Class D Forged Railway Wheel

This work aimed to characterize a new class D microalloyed forged wheel (called 7NbMo). For this purpose, the following analyses were carried out: obtaining CCT curves for the steel (cooling rates of 0.5-50 degrees C/s), investigating the microstructure below the rolling track (scanning electron microscopy and hardness), performing mechanical tensile and fracture toughness tests, and verifying the wheel's tribological behavior using twin-disc tests (wear, cracks, and, optical microscopy and scanning electron microscopy analyses of the disc's surface and subsurface). There was an increase in the hardenability of the steel, caused by the addition of microalloying elements, which impacted the microstructure of the wheel up to 15 mm below the rolling track. In this region, tempered bainite and martensite were identified, which provided high values of mechanical resistance. However, the twin-disc tests showed that higher values of hardness and mechanical properties did not suppress the disadvantage of the presence of tempered martensite in the microstructure, since the 7NbMo discs showed the same weight loss of the pearlitic discs and did not achieve better results in the rolling contact fatigue as expected for class D wheel material.