A comparative study on non-quenched and quenched prehardened steel for large section plastic mould

The non-quenched prehardened (NQP) steel and quenched and tempered prehardened (QP) steel for plastic mould were compared in terms of their microstructures, machinability, hardness and weldability along with their continuous cooling transformation. Results show that the microstructure of the NQP steel bloom consists of bainite through the whole section, while tempered martensite and bainite are found across the whole section of the QP steel. However, hardness fluctuations of two types of steel are not more than 3 HRC, for the former contributed to the high bainitic hardenability, while, for the latter, microstructures were adjusted by heat treatment after forging. Compared with the QP steel, the NQP steel results in better machinability, weldability and requires a simplified process that saves energy.