The heat treatment processing of die parts refers to the processing of forming and blanking tools, shearing die and die-cutting die. The mould consists of two parts: the upper die and the lower die. The steel plate will be placed between the upper and lower die, in the role of the press to achieve the molding of the material, when the press open, will be determined by the shape of the mold to obtain the workpiece or to remove the corresponding waste. The heat treatment processing technology of die parts mainly includes: cutting die, blanking die, compound die, extrusion die, four-rail die, progressive die, stamping die, die-cutting die and so on. Heat treatment process of die parts:
1. Heat treatment furnace annealing heat treatment of die parts: the steel parts are heated to the critical temperature above the critical temperature for a certain time, and then cooled slowly with the furnace temperature or in the dust and quartz sand. Objective: to eliminate the internal stress, improve the structure, reduce the hardness and increase the plasticity of the casting, forging or cold pressing parts of the mould, so as to facilitate the cutting process.Classification: diffusion annealing, complete annealing, spheroidizing annealing, etc.
(1) Diffusion annealing purpose: it is suitable for alloy steel ingot to eliminate the inhomogeneity of composition in alloy steel ingot, so it is also called homogenization annealing.
(2) purpose of complete annealing: it is mainly used in hypoeutectoid steel with carbon content less than 0.77% to reduce hardness, refine grain and eliminate cold and hot working stress.
Spheroidizing annealing purpose: mainly used for steel with carbon content ≥ 0.77%, making iron carbide spherical, reducing hardness, improving cutting performance and preparing for quenching.
(3) the purpose of incomplete annealing: it is mainly used for high carbon steel with carbon content higher than 0.77%, reducing hardness and relieving internal stress. The purpose of isothermal annealing is to improve the metallographic structure, reduce the hardness and improve the machinability.
(4) the purpose of recrystallization annealing is to eliminate the deformation of microstructure after cold working and to eliminate the work hardening.
2. Normalizing: the process of heating the steel parts above the critical temperature, holding them for a certain time, taking them out, and cooling them naturally in the air. Objective: to eliminate the residual stress, reduce the hardness, refine the grain size and improve the microstructure of steel parts. Applications:
(1) Elimination of reticulated carbides in high carbon steel;
(2) replacing the complete annealing of low carbon steel to improve its toughness and machinability;
(3) replacing the complete annealing of some medium carbon steel, cast steel and cast iron castings to shorten the machining cycle.
(IV) as a pre-heat treatment and subsequent heat treatment, in preparation for other heat treatments.
3. Quenching: the process of heating steel parts above the critical temperature, holding them for a certain period of time, and then placing them into a quenching medium (water, oil, salt or alkali aqueous solution) for rapid cooling. Methods:
(1) single liquid quenching: a quenching of hot steel pieces into a quenchant until it is cooled to room temperature. For example, carbon steel is generally quenched in water or aqueous solution, and alloy steel is quenched in oil.
(2) Dual-solution quenching method: firstly, the heated steel parts are put into a medium with stronger cooling capacity, so that the austenite is rapidly undercooled to close to the martensite transformation area, and then the austenite is immediately transferred to another medium with weaker ability and cooled to room temperature. Thus the operation of martensitic transformation is obtained. Benefits: compared with the single solution quenching method reduces the quenching of the internal stress, reduce the workpiece cracking and deformation.
(3) Pre-cooling quenching method: after the heated steel parts are removed from the heating furnace, the air is now cooled to a certain temperature, and then put into the quenching cooling medium for cooling.
(4) step quenching method: the heated steel parts are first put into the martensite transformation point, in the cooling medium near Ms for a period of time (2-5Min), when the surface temperature of the workpiece is basically the same as the center temperature. The martensite is then cooled in air to obtain quenching of the martensite structure. For example: carbon tool steel, alloy tool steel, high-speed tool steel, alloy structure steel and steel structure of cemented carbide quenching, and workpiece size is small.
(5) Isothermal quenching method: put the heated steel into the salt bath or alkali bath with the temperature slightly higher than Ms point, keep the temperature for long enough (generally more than half an hour), make the undercooled austenite transform into the lower bainite structure; The process of removing air cooling after the completion of the basic transformation. Features: after quenching, the internal stress of the workpiece decreases, and the workpiece is not easy to deform and crack. The obtained lower bainite structure has good comprehensive mechanical properties, and its strength, hardness, toughness and wear resistance are relatively high.Applicable to medium carbon steel, alloy tool steel and workpiece size is not too large.
(6) Flame heating surface quenching method: it uses combustible gases (such as acetylene, methane, propane, gas, natural gas) as fuel, oxygen as fuel, gas welding or air gun; Heats the parts of the mold that need to be hardened to the quenching temperature, The process of obtaining the required surface hardness and hardened depth after rapid cooling with water or air. Features: the main is surface quenching and the matrix structure has not changed, the use of cold working die steel flame quenching must be used to reduce the original flame to avoid oxidation. So-called reductive flame is to point to welding torch place to supply oxygen must be appropriate, cannot overmuch. In general, the flame length is controlled at 10-15mm, the oxygen pressure is 4.9-6.9MPa and the acetylene pressure is 4.9-6.9MPa. When the flame is heated, the distance between the flame end and the edge of the heating surface is 2-3mm and the 4-6mm heating zone is controlled at 8-12mm.
(7) vacuum quenching: the method of heating the workpiece in an airtight vacuum furnace to a certain temperature and then cooling it in the furnace. Features: the workpiece is heated and cooled in the furnace, the oxide layer on the surface of the part is controlled, and a bright surface layer is obtained. The vacuum was 10 1-10 2 torr. 1 trot = 133.32MPa.
Tempering: the process of reheating a steel piece to a temperature below the critical temperature, holding it for a certain time, and then cooling it in air or oil to room temperature.
(1) low temperature tempering: (150-250 ℃) reduces the brittleness of quenched steel without decreasing the hardness. Mainly used for high carbon stamping die, tempering hardness for 58-64HRC.
(2) Intermediate tempering: (300-500 ℃) to improve the toughness and elasticity of the quenched steel. It is mainly used in the treatment of springs and moulds.
After tempering, the hardness is generally 35-50HRC.
(4) quenching and tempering: the combination of quenching and high temperature tempering heat treatment. The yield limit and impact toughness are much higher than those of annealing and normalizing. It can be used as pre-heat treatment before quenching and soft nitriding.
5. Cold treatment is also called cold treatment, cryogenic treatment or ultralow temperature treatment (cryogenic treatment): the retained austenite of the steel is completely transformed into stable martensite, and the strength, toughness and wear resistance of the steel are improved. At the same time, it can also achieve the purpose of dimensional stability. The temperature of cold treatment is -80 -50 ℃. Matters needing attention in cold treatment:
(1) after the workpiece has been heated, it must be boiled for 1 hour. The purpose is to partially eliminate the quenching stress before cold treatment and prevent deformation and cracking of the workpiece during cold treatment.
(2) after cold treatment, the workpiece should be put into water at room temperature (20 ℃) instead of directly tempering. Reduce the new residual stress, avoid quenching and breaking edge.
(3) the size of the die after cold treatment is slightly enlarged.
6. Carburizing: the process by which steel parts are heated to a certain temperature (850-900 ℃) in a carbon-containing medium (gas, liquid, solid) to allow carbon atoms to infiltrate into the surface layer of the steel piece. The surface hardness of the carburized workpiece can reach 56-65HRC after quenching. Benefits: the surface of the part has high hardness and wear resistance, while the center still retains the original good toughness and strength, suitable for low carbon steel. Carburizing methods: solid Carburizing, Salt Bath Carburizing and Gas Carburizing. The salts carburized in the salt bath are Na2 CO3, SiC, etc., and the catalyst salts are melted in the salt bath furnace. The infiltration depth of solid Carburizing method is 0.1-0.15mm for every hour of heat preservation.