Fracture behavior of bainitic chromium-tungsten and chromium-molybdenum steels

摘要

Bainitic microstructures formed during continuous cooling of low-carbon alloy steels often appear different from classical upper and lower bainite developed by isothermal transformation. The kind of non-classical bainite produced during transformation determines the fracture behavior in a Charpy impact test. Quenching and normalizing treatments of a 3Cr-1.5Mo-0.25V-0.lC steel gave two different bainitic microstructures: a carbide-free acicular structure formed during quenching and a granular bainite formed during normalizing. The superior impact toughness of the quenched steel over the normalized steel was attributed to the difference in microstructure. A similar observation on microstructure was made for a 2.25Cr-2W-0.1C and a 2.25Cr-2W-0.25V-0.lC steel. These observations were used to develop new Cr-W steels with improved strength and impact toughness.