Carbide precipitation during tempering of hybrid steel 60

Abstract

The effects of carbide precipitation on mechanical performance of Hybrid Steel 60, known as a novel bearing steel, have not been investigated. In this study, the austenite transformation temperatures of Hybrid Steel 60 during heating were revealed by the thermal expansion curve. The temperature and effective activation energy of the second phase precipitation were determined by the differential scanning calorimetry (DSC) curve. Different solid solution structures after austenitization were detected using various cooling rates. The solubility temperature was determined based on hardness and residual austenite content. The carbides precipitated at the peak temperature were qualitatively identified using XRD. It was discovered that the temperature points Ac1 and Ac3 of the steel were 786 °C and 864 °C, respectively. In addition, the effect of solid solution temperature on quenching hardness is minimal, while the cooling rate has a greater impact on hardness, reaching a peak at 5 °C s ^−1 . The primary carbide phase in Hybrid Steel 60 is the M _7 C _3 and VC. When the temperature ranges from 500 °C to 550 °C, M _23 C _6 begins to precipitate. As a result, after tempering at 525 °C, the hardness peak value reached 566 HV.

Keywords

• bearing steel
• carbide
• DSC
• secondary hardening