| In recent years quantity demand for plastic mold steel billets is increasing,and a higherdemand is put forward in its quality and specification．At present,the main requirements ofplastic mold steel billet production are pre-hardening,large-scale and high purity,steelbillets are deliveried after heat treatment frequently．Curving deforming and crack occurfrequently on billets thickness of which is less than 200mm when quenched in oil orwater,while hardness of billet can't match requirements when air quenching．A new Heattreating system by using which billets are free of curving deforming,crack,pollution andnon-homogeneous of hardness distribution must be developed and researched immdiately．In this thesis,a swing water-jet quenching system is concepted and designed basedon the requirements of mold steel billet quenching．The performance of this system isobserved approximately when water-jet quenching test of plastic mold steel 718 billetthickness of which is 90mm is tried out by this system．At the same time,water quenchingis effectuated on a plastic mold steel 718 billet thickness of which is 200mm as acontrastive technology,and billets quenched using this system have a more uniformhardness distribution is approved by this test．Temperature field calculation model of alloyed steel is estiblished in this thesis,and coefficientof heat transfer of water-jet quenching is estimated through finite element methodusing data of water-jet quenching on mold steel billet for 718．Then a water-jet quenchingexperiment is carried out on a plastic mold steel billet for NAK80 with thickness of 200mm to examine and amend the coefficient of heat transfer of water-jet quenching,which isabout 0.6 times of that of water quenching．Before water-jet quenching of high-alloy plastic mold steel 3Cr17NiMo billet,coolingcurve of billet should be figured out using temperature field calculation model to determinethe optimal time of water-jet quenching of billets with different thickness；In considerationof high hardenability of 3Cr17NiMo Water-jet quenching with a 15 seconds imtermittentbetween every 30 seconds injection is performed until spraying time aggrigat the optimaltime．Plastic mold steel billets for 3Cr17NiMo with thickness less than 100mm quenched according to this technology have a uniform hardness distribution and little curvingdeformation．Air quenching,oil quenching,water quenching are substituded by water-jet quenchingwith excellence of little deformtion,cooling speed controllable and environmentalfriendly,and many disadvantage of mold steel billets are completely avoided,such ashardness defect(billets air quenched),deformation and crack(billets oil or waterquenched)．This system is suitable for low and high alloy mold steel,such as P20,718,NAK80 and 3Cr17NiMo,and this system deserve to be promoted．...
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