1 Introduction M238 high-quality pre-hardened plastic mold steel, this steel is P20 plus 1.1% nickel, steel surface to the center is consistent uniform hardness, cutting good, excellent sparks and polished performance, suitable for gasification, hard chrome plating and titanium . Uniform hardness and metallurgical structure, special heat treatment has been hardened to 30-34HRC, polishing good performance, easy to reach mirror polished, low distortion after use, and the material may be high, the cost can be reduced, for the size of the high demand plastic mold, especially for electrical erosion operation Factory state: Pre-hardened to 980-1080N / mm2 (30-34HRC) this steel has been heat-treated, uniform hardness, up 278-311HB, 29-33HRC, made mold will never change excellent cutting and polishing performance for electrical erosion operation can be used as flame hardened, chrome plated and nitrided. 2 Supply Status Pre-hardened state, hardness 30 ~ 34HRC [1] 3 Purpose:? For demanding plastic mold, especially over 400MM thick of the mold. 4 Chemical composition Carbon C: 0.95 chromium Cr; 0.5 tungsten w: 0.5 Mn Mn: 1.1 Si Si: 0.3 V V: 0.1 5 Heat Treatment Forged: 1050-850 ℃ furnace cooling. Back to nature: 850-900 ℃ furnace cooling. Stress relief: After the heat evenly, stay 1-2 hours and then cooled in the furnace. Quenching: 840-860 ℃ oil or air: 860-880 ℃. Stay at least 10 minutes, at a thickness of more than 20mm see more 1/2 minutes per 1mm, so the hardness of about 54HRC. Tempering: tempering stay at least 1 hour for each additional 20mm 20mm thick will have more than one hour. Annealing: 720-740 ℃ heat through insulation sufficient time, and then with the furnace cooling to 600 ℃, then cooled in air, the resulting hardness of about 240HB (highest). 6 typical application example (1) for demanding plastic mold. (2) The availability of high hardness steel mold nitriding the surface structure, surface hardness after nitriding can reach 650 ~ 700HV, the service life of up to 100 million times more. (3) suitable for high-precision instruments in plastic mold processing and production.