Annealing
After metal materials undergo hot working or cold forming, the process of heating to above the critical temperature and controlling the cooling is often adopted to eliminate internal defects. This technology achieves material performance optimization through two-stage temperature control: Firstly, holding above the Ac3 or Ac1 line promotes recrystallization, and then furnace cooling at a rate of ≤50℃/h to below 500℃.
This process can increase the elongation of cold working hardened materials by 15-25%, while reducing the Vickers hardness by about one-third. Especially for low alloy steels containing Cr and Mo, after complete annealing, the grain size can be refined from grade 3 to grade 6-7, and the cutting resistance decreases by approximately 40%.
It is particularly suitable for components that require precise cutting, such as machine tool guide rails (HT300) and hydraulic valve bodies (42CrMo). The surface roughness of the treated workpiece can stably reach Ra1.6, and the subsequent processing deformation is controlled within ±0.05mm/m.
Normalizing
Heat the steel to 30-50℃ above the critical point of Ac3 (for example, heat 45 steel to 850-870℃), hold it at that temperature, and then cool it uniformly in still air. This process refines the grain size to ASTM grade 5-6 by inhibiting the precipitation of secondary cementite and eliminating the network or banded carbide structure formed during forging and rolling.
After treatment, the yield strength of the material increases by 10-15%, the hardness stabilizes within the range of 190-220HB, and the impact energy increases by 20-30J. It is particularly suitable for components that require a balance between machinability and mechanical properties.
Typical applications include the pretreatment of automotive transmission gears (made of 20CrMnTi material), which can eliminate over 90% of free cementite and increase the turning efficiency by 25%. After normalizing, the processing deformation of shaft parts of construction machinery (such as 40Cr) before quenching and tempering can be controlled within 0.1mm/m.
Quenching & Tempering
Heat the steel above the critical temperature ( C45 steel needs to reach 830-850℃), hold it at that temperature, and then rapidly add the cooling medium (water-based solution or rapid quenching oil) to complete the martensitic transformation of the austenite structure within 1.5-3 seconds. Take the automotive transmission gear (20CrMnTi) as an example. After oil quenching, the surface hardness can reach HRC58-62, but there is a residual stress of 800-1000 mpa. Subsequently, low-temperature tempering is carried out at 180-200℃ for 2-4 hours to allow part of the martensite to decompose into tempered martensite. While the hardness stabilizes at HRC56-60, the impact toughness increases by 3-5 times.
For the pins of construction machinery subjected to impact loads (made of 40Cr material), the medium-temperature tempering process at 500-550℃ can adjust the tensile strength to the range of 1100-1300 mpa, while increasing the fracture toughness KIC value to 90MPa·m¹/². The rotor assembly of the hydraulic pump treated in this way has a cycle life of over 500,000 times in the pulsating pressure test, which is 8 to 10 times higher than that of the untreated part. The selection of quenching medium is particularly crucial: For precision die steel (such as SKD11), staged quenching (first staying in a 160℃ nitrate salt bath for 3 minutes, then air cooling) is adopted, which can control the dimensional deformation to be ≤0.02mm/100mm.
Induction Hardening
The surface of the workpiece is selectively heated by a high-frequency electromagnetic field (with a frequency range of 200-300 KHZ), and the surface layer temperature reaches 850-900℃ within 3-5 seconds, followed by immediate water mist quenching. Taking the ductile iron QT600-3 camshaft as an example, a hardened layer of 0.8-1.2mm is formed on the surface, with a Rockwell hardness of HRC55-60, while the core maintains toughness of HB220-250.
After the precision ball screw guide (GCr15 material) is subjected to transverse magnetic field induction hardening, the depth deviation of the hardened layer is controlled within ±0.05mm, and the straightness change is ≤0.01mm/m. The wear resistance of the treated automotive steering rack has been enhanced by three times, and the test life on the bench has exceeded 200,000 reciprocating movements. For thin-walled bearing housing rings (with a wall thickness of 5mm), dual-frequency quenching (preheating at medium frequency of 10kHz first, followed by final heating at high frequency of 200kHz) can prevent deformation, and the ellipticity error is ≤0.03mm.
Stress Relieving
Stress relieving is achieved by precisely controlling the temperature field and aging parameters to conduct continuous heat treatment at medium and low temperatures (typically 200-650℃) on metal components formed through casting, forging, welding or machining.
This process can specifically resolve the residual stress network formed inside the material due to cold and hot processing, thereby reducing the risk of deformation and cracking of the workpiece during subsequent use, while ensuring the stability of dimensional accuracy.
The scientifically designed stress relieving process can make the metal lattice reconstruction tend to a balanced state, significantly improve the fatigue resistance of structural components under complex working conditions, and ultimately achieve the engineering goal of extending the entire life cycle of the product.
carburizing hardening
Carburizing hardening is a surface strengthening process that is widely used in the field of mechanical transmission. This process involves subjzing low-carbon steel components (such as 20CrMnTi, 20CrMo, and other low-carbon alloy steels) to high temperatures (typically 900-950℃) in a specific medium environment, allowing activated carbon atoms to penetrate the metal surface layer and form a carbon-rich area with a depth of 0.3-2mm. After subsequent quenching and low-temperature tempering treatment, the workpiece presents a gradient microstructure: the surface layer forms high-hardness martensite (with a hardness of up to 58-64HRC), while the core retains the original toughness of low-carbon steel (with a hardness of approximately 20-30HRC).
The hardened surface layer effectively resists friction and wear, while the strong and tough core can absorb impact energy. It is particularly suitable for transmission components that bear alternating loads. After this treatment, typical parts such as automotive transmission gears, industrial transmission chains, and bearing rollers can have their service life increased by 3 to 5 times.
Nitriding Hardening
Nitriding hardening is a metal surface modification technology. Its core is to penetrate nitrogen into the metal surface layer to form a high-hardness nitride composite layer. This process is usually carried out within a mild temperature range of 480-580℃. Compared with the traditional quenching process, it reduces the influence of thermal stress and is particularly suitable for easily deformable workpieces such as micro gears and precision shafts. The depth of the nitrided layer is generally within the range of 0.1 to 0.6mm, and the surface hardness can reach HV900 to 1200, which is equivalent to above HRC65.
In the field of medical devices, surgical instruments, after nitriding treatment, not only maintain their sharpness but also enhance their resistance to biological corrosion. In the automotive industry, the engine crankshaft can be enhanced in terms of wear resistance and service life while maintaining dimensional accuracy through ion nitriding. It should be noted that special steels containing chromium and molybdenum are more capable of forming dense nitrided layers, while the effect of ordinary carbon steels is relatively limited.
vacuum heat treatment
Precise temperature control of metal parts is implemented in an oxygen-free negative pressure environment, effectively eliminating surface defect problems caused by traditional heat treatment. This technology, by isolating the air medium, not only prevents the material oxidation reaction under high-temperature conditions but also avoids the degradation of material performance caused by the loss of carbon elements.
Taking the turbine disk of an aero engine as an example, the nickel-based alloy after vacuum heat treatment not only maintains the original surface accuracy, but also presents a uniform and fine grain structure, enabling the component to still maintain excellent creep resistance when subjected to a high temperature of 800℃. This technological characteristic makes it a key technology in the manufacturing of implantable orthopedic devices - the treated titanium alloy joint prosthesis not only ensures biocompatibility but also increases the fatigue life by more than 40%, significantly reducing the risk of fracture during clinical use.
salt bath heat treatment
Salt bath heat treatment uses molten salts as the heat transfer medium, which has significantly improved heat conduction efficiency compared with traditional heating methods. During the operation process, the high thermal conductivity of the molten salt enables the workpiece to heat up rapidly by tens of degrees per minute, and the temperature control accuracy of the system can reach the range of ±3℃.
The core advantage of this heat treatment method lies in the three-dimensional contact characteristics between the medium and the workpiece, which enables parts with complex geometric structures (such as the inner cavity of gears and the gear set of automotive gearboxes) to be heated uniformly. The temperature uniformity of salt bath treatment is improved by more than 40% compared with conventional furnaces, and it is particularly suitable for high-standard processing scenarios such as aerospace precision components.