Evaluation of microstructure and mechanical properties of 50Cr5NiMoV steel for forged backup roll

The microstructure and mechanical properties of forged 50Cr5NiMoV steel backup roll were evaluated in this study. The microstructure characteristics from surface to center along radial direction of the backup roll were carefully observed by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the chemical composition, hardness, tensile property, impact and fracture toughness in different position of the backup roll were also examined. The results indicate that the finely precipitated carbides at different matrix during heat treatment process strongly influence mechanical properties of the backup roll. Especially, the spheroidized pearlite at the inner regions which consists of large globular or rod-like M7C3 and a little of small globular M23C6 possesses much better toughness and fracture resistance properties than those of the lamellar pearlite with lamellar M23C6 and a little of globular M7C3.