Development Of New Age Hardening Plastic Mold Steel

With the application of plastic products more and more widely,the types of plastic products are more and more,the surface quality requirements are getting higher and higher,so it has new requirements to plastic mold steel that the polishing performance requirements is higher and higher,and the corrosion resistance is required.Currently,the widely used high-mirror polishing performance plastic mold steel is NAK80 aging hardening pre-hardened plastic mold steel which developed in Japan.But the domestic NAK80 steel has a series problems that the mechanical properties are poor in the core of the steel,the microstructure is uneven distribution,and the hardenability is poor.At the same time,this steel does not have corrosion resistance,it can not meet the development of plastic products on the corrosion resistance requirements.Research and development with more excellent mechanical properties and corrosion resistance new type age hardening plastic mold steel has great significance.In this paper,based on the NAK80 steel,through the adjustment of alloy composition and optimization of heat treatment process,a new type age hardening plastic mold steel NAK80-M were developed.Compared with NAK80 steel,NAK80-M steel added 2.00%Cr and 0.15%V,Mo content increased to 0.76%,Ni and Cu content decreased to 1.50%,0.49%.By studying the influence of alloying elements on phase composition and phase transformation behavior,microstructure and mechanical properties,and heat treatment process,a new type of age hardening type pre-hardened plastic mold steel with excellent comprehensive performance was developed.Get the following main conclusions:(1)The thermodynamic calculation and isothermal transformation test results show that the NAK80 and NAK80-M have the same balance phases,but the critical temperature points A,3,Ac,of NAK80-M test steel are relatively high,and the dissolution temperature of the carbides is increase.(2)After solution treatment,the microstructure of NAK80 and NAK80-M test steels are mainly contain of lath martensite and residual austenite.Respectively,after 850? and 880? for 2h solution treatment,NAK80 and NAK80-M steel can get the highest hardness.NAK80-M steel has the higher peak hardness.(3)After solid solution aging treatment,the microstructure of NAK80 and NAK80-M test steels are mainly contain of lath martensite,granular bainite,retained austenite,precipitated carbides,the peak mechanical properties of NAK80-M steel is air-cooled at 880? for 2h,aged at 540?.NAK80 steel reaches the peak of mechanical properties at 850?,the peak of mechanical properties ofNAK80-M steel is aged at 540? for 4h.At the same time,the hardness and impact toughness of NAK80-M steel are 2.5HRC and 50J higher than that of NAK80 steel.The best heat treatment process of NAK80-M steel is:880? solution 2h,followed by 540? aging 4h.