About 718H is a plastic mold steel chemical composition elements C Si Mn Cr MO Ni content (%) 0.3 1.4 2.0 0.2 0.9 0.33 factory hardness: Pre-hardened to 35 ~ 39HRC features: 718H for the vacuum melting of chromium - Ni - Mo steel factory former hardened and tempered, has the following advantages: no quenching crack the risk of deformation and heat treatment; without heat treatment costs; shorten molding cycle; reduce tooling costs required (for example, without being deformed overseas); die easy correction; be subjected to nitriding and surface hardening treatment to enhance the mold surface hardness and wear resistance. 718H of the main purposes: large-scale long-life plastic injection mold, such as home appliances, computer shell mold; high surface finish of plastic products die; blow mold; as high hardness, can be used in the plastic mold of the slider; forming tools, compression construction parts and shaft; - Brake mode (Bay board machine model), (depending on production needs may be applied to flame hardening or nitriding). 718H Heat treatment: annealing under protective status, heated to 700 ℃, soaking them in an oven at a rate of 15 ℃ / h of cooling to 600 ℃, then cooled. After the stress relief by roughing, heated to 550 ℃, heat 2 hours, slowly cooled to 500 ℃, then cooled. Conventional quenching - tempering before quenching, it must be fully annealed to eliminate work stress. Preheated at 500 ~ 600 ℃ 2 hours, and incubated for 30 minutes at 850 ℃ quenching temperature; to heat insulation in a protective atmosphere to avoid decarburization and oxidation. Then in oil cooling, or 300 ℃ isothermal four minutes after air cooling. Upon cooling to 50 ~ 70 ℃, should immediately tempered, hardness tempering temperature and time after tempering below. Temperature (℃) Time (h) Hardness 180 2 52HRC 200 2 51HRC 300 2 48HRC 400 2 410HRC 500 2 345 HRC 600 2 280HRC 650 2 270HRC flame hardening - tempering can mold surface hardness, wear resistance is improved. The method of using oxyacetylene flame (wind coal) heating the mold surface, then cooled and solidified, hardness up to 45 ~ 52HRC processing method: Preheat 150 ~ 200 HRC, in order to prevent rupture; mold surface and then continuously heated to 850 to 950. ℃ (surface light red), then air cooling; cooling to 50 ~ 70 ℃, immediately at 180 ~ 200 ℃ tempering, to prevent cracking during the polishing. Carburizing carburizing temperature of 850 ~ 940 ℃, time depends on the depth of demand for our products and OK. If the carburizing temperature exceeds 880 ℃, more than 2 hours, it must be normalized, so as to keep the organization a fine grain size. After completion of carburizing, cooling in the furnace to 830 ℃, soaking after quenching in oil, and then tempering, tempering temperature, such as lists; so that the surface hardness, increased wear resistance. If only high hardness without requiring the organization a fine grain size, can quench the carburizing temperature above 880 ℃. Henry Xin metal plastic mold steel 718H tempering temperature (℃) Time (h) Hardness (HRC) 180 2 60 200 2 59 300 2 55 nitriding harder surface nitriding treatment available, at the same time, there is good resistance wear resistance and corrosion resistance, hardness after nitriding in ammonia up to 650HV. The surface hardness nitriding temperature (℃) Time (h) Depth (mm) 525 20 0.30 525 30 0.35 525 60 0.50 570 ℃ under soft nitriding treatment can be obtained as 700HV, after two hours of treatment, case depth of 0.01mm . Hard chromium layer covering the hard chromium layer through the overlay tool, must be 180 ℃ tempered four hours, in order to avoid hydrogen embrittlement. Grinding proper grinding techniques to avoid cracking, increase die life. After tempering of the material during the grinding, cracking susceptibility strong, then the wheel must be trimmed, soft and open die wheel is suitable, while fully adequate lubricant and the peripheral speed is also important. Polishing 718H good polishing, usually with alumina powder and diamond polishing paste, as follows: 1, then set aside to complete the size 0.05mm. 2, with 45 diamond polishing paste to give a less sharp surface. 3, with 15 diamond polishing paste again. 4, with the 3rd or special high-level diamond paste, the surface-polishing. Each metal has suitable polishing time, determined by the material hardness and polishing technique, long polishing time, it will have bark-like (orange peel-like) surface. The physical properties of 718H: when hardened and tempered to 340HB hardness, physical properties at room temperature and slightly elevated temperature of 20 200 400 Density kg / m3 7800 7750 7700 thermal expansion coefficient of 20 ℃ from 1 / ℃ - 12.7 * 10- 6 13.6 * 10-6 Thermal conductivity W / m ℃ 29.0 29.5 31.0 elasticity N / mm2 205,000 200,000 185,000 Specific heat J / kg ℃ 460 - - 718H tensile strength: approximate value. Test strip drawn by a 25.4 mm diameter round bar. 340HB hardness test temperature 20 ℃ 200 ℃ 400 ℃ Tensile strength Rm N / mm2 1100 1045 870 Yield strength Rp0.2 N / mm2 985 920 775 Reduction of approximately Z Elongation% 505 354% 13 14 16 718H impact strength value. Test strip drawn by a 25.4 mm diameter round bar. 340HB hardness test temperature 20 ℃ 200 ℃ 400 ℃