Tempering Process to Improve Hardness Uniformity of Plastic Mould Steel

A new design of copper-bearing non-quenched plastic mold steel is presented and explained. Two kinds of microstructure can be obtained from this new type copper-bearing steel via cooling with different cooling rates, bainite and a mixed microstructure consisting of ferrite and bainite. It is found that, after proper tempering process, the hardness will be increased. Moreover, the hardness difference between different microstructures will be reduced. For further investigation, the samples tempered at different temperatures were examined by XRD and 3DAP (three dimensional atom probe) analysis. Results show that the improvement is contributed mainly by the precipitation of Cu phase and transformation of residual austenite.