Hot-work die steel heat treatment

1. Hot-work die working conditions and performance requirements of mould materials hot-work mold is mainly used for hot pressure processing ( Including hammer forging, hot extrusion, hot upsetting forging, precision forging, high-speed forging, etc. ) And pressure casting, plastic molding. Hot forging die, impact load and working under high pressure, the mould cavity in addition to produce severe friction, often with the blank contact heating to 1050 ~ 1200 ℃ high temperature, usually in the cavity surface temperature of 400 ℃ above, sometimes can reach 600 ~ 700 ℃, then the water, oil or compressed air to forging die for cooling, so hot and cold alternately repeatedly make mold to produce thermal fatigue crack. So the request of hot forging die material with high strength and thermal stability at high temperatures ( The red hardness) As much as possible, the appropriate impact toughness and high thermal conductivity, good wear resistance and thermal fatigue resistance, high hardenability and good performance in the process of cutting processing. In recent years, the promotion of hot extrusion, hot upsetting forging, precision forging, high-speed forging and other advanced technology, as a result of the mold working conditions more severe than general hot forging die, therefore put forward higher request to the mold material. The mould need a long time at work and the contact deformation processing of metal, or withstand larger impact energy, the heat degree of mold cavity often than hammer forging die with high, bear load is larger than the hammer forging die, especially black metal forging, extrusion and high speed mold cavity surface temperature above 700 ℃, usually high speed forging, heating velocity on the surface of the cavity is 2000 ~ 4000 ℃ / s, the temperature can reach 950 ℃ or so, causing a significant reduction in the die life. So special request mold material should have high thermal stability and high temperature strength, good thermal fatigue property and high wear resistance. 2. Hammer forging die of heat treatment used for hammer forging die of the 5 crnimo steel grade 5 crmnmo, 5 crmnsimov, etc. 5 crnimo steel with high hardenability and good comprehensive mechanical properties, mainly used for complex shape, high impact load larger forging die. 5 crmnmo steel does not contain the Ni, Mo in lieu of Ni don't reduce the strength, but the plasticity and toughness, suitable for medium-sized forging die. 5 crnimo steel quenching temperature usually adopt 830 ~ 860 ℃. Due to their high hardenability, austenitic stability, can be used on cooling air cooling, oil cooling, interrupted quenching and isothermal quenching. General is in the air precooling before quenching to 750 ~ 780 ℃, then oil cooled to 150 ~ 180 ℃ or so out of oil, limits the cold again. Die immediately after quenching tempering to prevent deformation and cracking. General hot forging die after tempering hardness need not too high, in order to make sure the toughness. The production requirements for different sizes of hot forging die have different hardness, and tempering temperature should also be different, such as small die 44 ~ 47 HRC hardness requirement, tempering temperature can choose in 190 ~ 510 ℃; 38 to 42 hr of medium-sized mold hardness requirement, tempering temperature is 520 ~ 540; Large mould for 34 ~ 37 HRC, tempering temperature is 560 ~ 580 ℃. Mold internal stress is larger after quenching, tempering should slow heating and heat when heating 350~400℃) Even after the rise to the tempering temperature, holding time not less than 3 h. 3. Hot extrusion and die casting mould hot extrusion and heat treatment of die casting mould for die steel with high temperature performance, such as heat resistance, thermal fatigue, thermal damage, tempering resistance and thermal stability, etc. Therefore, this kind of steel contained more, Si, Cr, W, Mo, V and other elements, to ensure that has more than performance. The application of the most representative brands in China standard has 3 cr2w8v, 4 cr5mosivl, 4 cr5mosiv, 4 cr3mo3siv, 4 cr5w2vsi, etc. Although only 3 cr2w8v steel containing 0. 3% ~ 0. 4% C, but due to the high content of tungsten, chromium, the organization belongs to hypereutectoid steel. The process performance, heat treatment specification and Crl2MoV steel. Annealing process for 830 ~ 850 ℃ heat preservation 3 ~ 4 h, common quenching temperature is 1050 ~ 1150 ℃, in addition to the slow heating, large or complex mould should be in 800 ~ 850 ℃ preheat temperature, also has a secondary hardening tempering phenomenon, tempering choose 550 ~ 620 ℃ high temperature tempering. 3 cr2w8v steel is widely used for ferrous and non-ferrous metal hot extrusion die and Cu, Al alloy die-casting mould. This kind of steel is high, the thermal stability of the temperature of 650 ℃, but tungsten steel is low thermal conductivity, cold and hot fatigue sex differences. In the early 1980 s in China to introduce foreign general chrome hot-work die steel H13 ( 4Cr5MoSiVl) , Hl3 steel alloy content of less than 3 cr2w8v steel, but the hardenability, heat resistance, thermal fatigue, plasticity, toughness is better than the former, while using temperature does not exceed 600 ℃, instead of 3 cr2w8v steel, die life has greatly improved, so the H13 steel is widely used quickly. Heat treatment process of H13 steel are as follows: annealing temperature is 800 ~ 840 ℃, insulation 3 ~ 6 h, to under 500 ℃ to 30 ℃ / h cold air cooling, can also adopt the spheroidizing annealing process. Quenching temperature is 1040 ~ 1080 ℃, oil cooled to 500 ~ 550 ℃ after the air cooling oil. Tempering temperature is 580 ~ 620 ℃, holding 2 ~ 3, temper 2 times. After the above process of H13 steel mold hardness is 44 ~ 51 HRC.