Production Process And Service Performance Of Non-quenched And Tempered Steel For Plastic Mold

The production of steel for plastic mould is almost the same pattern of ingot - breakdown- rolling - pre-hardening and heat treatment. The disadvantages of this pattern are production link multiple, production cycle long, cost high, and it is a waste of energy when pre-hardening. This paper aims at the using of continuous casting billet to product steel plate which was rolled at heavy plate mill meet the properties of pre-hardened plastic mould steel P20 with the process of controlled rolling and controlled cooling. It has a greater significance to achieve a greater efficiency and production scale.In this paper, the impaction of cooling rates and rolling method on microstructure and properties of tested steel was studied; comparison of polishing performance and abrasion resistance between tested steel and pre-hardened plastic mould steel P20 was made; high-temperature mechanical behavior research of tested steel was done by the use of thermal simulation test machine. Finally, an optimal controlled rolling and controlled cooling process is developed with the consideration of laboratory hot rolling situation.The major achievements of the paper include:1) Chemical composition of the non-quenched-tempered steel for plastic mould is successfully designed (mass %):C:0.09～0.12, Si: 0.32～0.40, Mn: 1.2～1.6, Cr: 1.0～1.4, B: 0.001～0.005, Mo:0.22～0.27, V:0.04%～0.20%, Ti:0.01%～0.04%.2) Through the controlled rolling and controlled cooling experiment, the influence of finished temperature and cooling process on microstructure and mechanical properties of tested non-quenched and tempered steel for plastic mold is studied. The determined optimal controlled rolling and controlled cooling process parameters for the tested steel is shown in as follow: reheating temperature of 1200℃and soaking time of 2 hours. Two-stage rolling process is adopted, rough rolling at 1050℃, finishing rolling at 920℃-860℃and air-cooling after rolling.3) Through the single pass compressing deformation experiment done on the MMS-300 thermal simulation testing machine, the High-temperature mechanical behavior of the tested steel was studied. With the consideration of stress-strain curve got between 800℃and 1050℃, the mathematical model of deformation resistant for tested steel is determined. And then the coefficient of equation was got through the regressing of experiment data. Mathematical model of the deformation resistance for tested steel is as follow:4) Friction and wear test results show that the wear resistance of non-quenched and tempered steel for plastic mold is better than the pre-hardened plastic mold steel P20.5) Mirror polishing performance test result show that the test steel in air-cooling process achieve the fourth level of the standard A4= Ra 0.063μm, and pre-hardened plastic mold steel P20 have a equivalent property with test steel.