heat treatment

Metal heat treatment processes can generally be divided into overall heat treatment, surface heat treatment, local heat treatment, and chemical heat treatment. Depending on the heating medium, heating temperature, and cooling method, each major category can be divided into several different heat treatment processes. Different heat treatment processes can be used for the same metal to obtain different microstructures and thus exhibit different properties. Steel is the most widely used metal in industry, and its microstructure is also the most complex, resulting in a wide variety of steel heat treatment processes.

Overall heat treatment is a metal heat treatment process that heats the workpiece as a whole and then cools it at an appropriate rate to change its overall mechanical properties.

Heat

Heating is one of the important steps in heat treatment. There are many heating methods for metal heat treatment, initially using charcoal and coal as heat sources, and then applying liquid and gas fuels. The application of electricity makes heating easy to control and has no environmental pollution. These heat sources can be used for direct heating, as well as indirect heating through molten salts or metals, as well as floating particles.

When metal is heated, the workpiece is exposed to air and often undergoes oxidation and decarburization (i.e., the carbon content on the surface of steel parts decreases), which has a very adverse impact on the surface performance of the parts after heat treatment. Therefore, metals should usually be heated in a controlled or protective atmosphere, molten salt, and vacuum, and can also be protected and heated using coatings or packaging methods.

Heating temperature is one of the important process parameters in heat treatment process, and selecting and controlling the heating temperature is the main issue to ensure the quality of heat treatment. The heating temperature varies depending on the metal material being treated and the purpose of the heat treatment, but generally it is heated above the phase transition temperature to obtain the required structure. In addition, the transformation requires a certain amount of time. Therefore, when the surface of the metal workpiece reaches the required heating temperature, it is necessary to maintain this temperature for a certain period of time, so that the internal and external temperatures are consistent and the microstructure transformation is complete. This period of time is called insulation time. When using high-energy density heating and surface heat treatment, the heating speed is extremely fast, and generally there is no insulation time or the insulation time is very short, while the insulation time of chemical heat treatment is often longer.

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It is also an indispensable step in the heat treatment process, and the cooling method varies depending on the process, mainly controlling the cooling speed. Generally, annealing has the slowest cooling rate, normalizing has a faster cooling rate, and quenching has a faster cooling rate. But there are also different requirements for different types of steel, such as air hardened steel, which can be quenched at the same cooling rate as normalizing.

Heat treatment technology

Heat treatment technology is a treatment technology adopted by metal materials to improve their mechanical properties during the processing process. In order to ensure that metal workpieces have the required mechanical, physical, and chemical properties, in addition to the reasonable selection of materials and various forming processes, heat treatment processes are often essential. An improper surface treatment will make the previous processing of the product become a bubble in the manufacturing process, invisibly reducing the productivity and quality of the product, increasing manufacturing costs, and relatively reducing the competitiveness of the industry. Based on this, we introduce several modern heat treatment technologies for your reference and application.

1. Vacuum heat treatment technology method: Vacuum heat treatment is a technology that places metal workpieces in evacuated containers and then performs various repeated heating and cooling operations according to the desired purpose. Usage or advantages: The surface of the workpiece is a shiny surface, the deformation of the workpiece is small, the workpiece will not be oxidized, decarburized or carburized, there are no corrosion and environmental issues, and the quality is stable. It is suitable for heat treatment of tools or molds, and will be the mainstream of future heat treatment technology.

2. Zero temperature treatment technology method: Zero temperature treatment is a heat treatment method that places metal workpieces in a zero temperature environment, forcing them to change material properties. Traditional zero temperature treatment is usually carried out after quenching steel materials to effectively reduce residual Austen iron content, which can improve the dimensional stability and wear resistance of steel materials, especially for tool steel with high carbon content. Usage or advantages: The application of sub zero processing will be applied to non ferrous metals such as superhard alloys and copper alloys to improve the residual problem of internal application of workpieces and increase the lifespan of workpieces by more than twice the original.

3. Ion nitriding technology method: First, the metal workpiece is placed in a vacuum container, and then nitrogen gas is introduced. The container itself is used as an anode and the workpiece is used as a cathode. Then, high voltage direct current is applied to force the nitrogen gas to dissociate into positively charged nitrogen ions, which rush towards the cathode metal workpiece at a very high speed, allowing the surface of the metal workpiece to be instantly nitrided. This is a surface heat treatment technology. Usage or advantages: Effectively improving the wear resistance, fatigue resistance, corrosion resistance and other properties of metal materials. In addition, it also has the characteristics of small workpiece deformation, pollution-free, and energy-saving. Widely used for nitriding treatment of various steel and non-ferrous metal workpieces.

4. Low pressure nitriding technology method: Low pressure nitriding technology is a gas nitriding process where NH3, N2O, N2, etc. are injected under a pressure of approximately 300mba, and CH4 can also be added for gas nitriding and carbonization. The processing temperature is about 400-600 ℃. Low pressure nitriding and nitriding carbonization can obtain a higher hardness nitriding layer on the surface of the workpiece, increase the compressive stress on the surface of the workpiece, and improve its wear resistance and fatigue resistance; The nitriding speed is fast, and the nitriding layer structure can be selected as a pure diffusion layer or a dense white layer. It can nitride deep holes and narrow gaps, and the surface of the workpiece is clean, with good mass production performance, saving labor and gas energy. The working environment is excellent, and the application is becoming increasingly widespread. Usage or advantage: Because low-pressure nitriding can obtain a uniform hardening layer for complex shaped and deep hole workpieces, it is very suitable for wear and fatigue resistant workpieces such as die-casting molds, forging molds, aluminum extrusion molds, and rollers, tooth plates, nozzles, engine cylinders, etc.

5. Salt bath carbonitriding technology method: Salt bath carbonitriding technology is to place the workpiece in a soft nitriding salt bath for treatment, form a wear-resistant diffusion nitriding layer on the surface of the workpiece, and then quickly move the workpiece into an oxide salt for oxidation treatment, allowing the outer surface of the workpiece to form another wear-resistant oxidation layer. Usage or advantages: The use of salt baths is simple and easy to operate, with small deformation of the workpiece, and can effectively improve the mechanical properties of the workpiece, such as wear resistance, fatigue resistance, corrosion resistance, etc. It can be applied to cutting tools and various mechanical components.

6. Physical evaporation plating technology method: The physical evaporation plating technology is to coat a layer of ceramic film on the surface of the substrate in high vacuum, which is harder than tungsten carbide alloy and has advantages such as high corrosion resistance, wear resistance, adhesion, and low friction coefficient. At present, there are two physical evaporation systems: cathode arc plasma and unbalanced Magnetron sputtering. The developed and applied systems include TiN, TiCN, CrN, CrCN, TiAIN and amorphous carbon films. Usage or advantages: The physical evaporation temperature is approximately 100-500 ℃, which is lower than the tempering temperature of high-speed steel and mold steel. Therefore, the workpiece will not soften or deform, and can be applied to products such as superhard alloys, high-speed steel, mold steel, stainless steel, titanium alloys, and aluminum alloys. When the tool is evaporated with Ceramic membrane, the phenomenon of edge melting can be reduced, the wear rate of the edge can be slowed down, and the service life of the tool can be increased by 2~7 times; The steam plating treatment of the mold can increase its release performance, wear resistance, reduce adhesive wear and burning phenomena, effectively improve the mold life several times, not only reduce production costs, but also increase the competitiveness of the product.

7. Plasma chemical evaporation plating technology method: Using plasma CVD to evaporate hard films such as TiN, TiCN, and TiC, it has the advantages of high adhesion of CVD and low temperature treatment characteristics of PVD. It can reduce the treatment temperature (about 500 ℃), effectively prevent workpiece deformation, and achieve uniform adhesion of the coating. The coating effect is the best for complex shaped tools and molds. Purpose or advantage: It can apply hard film on the surface of metal workpieces, such as forming tools, cutting tools, and molds, as well as workpieces that need to improve the wear resistance/adhesion resistance of materials. It can increase the lifespan of workpieces, improve processing speed, increase production, and save costs

8. TD carbide coating technology method: TD treatment (Toyota Diffusion Process) is a coating method that adds alloy elements in a molten borax bath to generate carbides on the surface of the impregnated steel material. Its main feature is the extremely high hardness of the coating layer, excellent wear resistance, and the same level of hardness as PVD or CVD treatment, but the equipment is simple and easy to operate. Usage or advantages: The hardness of vanadium carbide (VC) obtained by TD treatment reaches HV2200 or above, and it has strong adhesion with the base material and is not easy to peel off. Therefore, it can be applied to die-casting molds, cutting and cutting tools, molds, cutting tools, or other mechanical parts that require wear resistance, such as sheet metal stamping dies, cold forging dies, hot forging dies, pipe forming tools, plastic molds, rollers, mechanical parts, etc.

Water soluble oil quenching liquid can be used for quenching forged steel, cast steel, cast iron, and stamped parts. Suitable for open-end quenching tanks, continuous furnaces, multi-purpose furnaces with quenching tank peripherals, and induction quenching furnaces.

1. Forged steel: Low hardenability forged steel or high hardenability alloy forged steel, ranging from one kilogram to several tons, can be quenched using Haiyi water-based quenching agent, and the concentration used varies with the alloy composition, ranging from 10% to 30%.

2. Cast steel: Just like forged steel, cast steel and alloy cast steel with varying single weight and hardenability can also be quenched using Haiyi water-based quenching agent. The concentration used varies with the alloy composition and casting shape, ranging from 10% to 30%.

3. Cast iron: Ductile iron and malleable iron are usually quenched with a 20% -30% concentration of Haiyi water-based quenching agent.

4. Induction quenching: Flame or induction quenching is often used for gears, mandrels, camshafts, bearing journals, etc. Haiyi water-based quenching agent is the most ideal substitute for quenching oil, which can completely eliminate oil fumes and fire hazards.

The above is only the applicable range of water-soluble oil quenching fluid. On site, comprehensive consideration can be given based on the steel type, complexity of shape, size, heat treatment requirements of the workpiece, and the cooling equipment in the workshop. Finally, the selected concentration is best determined through experiments.