Analysis Of The Five Cooling Methods And Process Characteristics Of Titanium Alloy Forging

As the core metal material in the field of high-end manufacturing, titanium alloy is widely used in key fields such as aerospace, precision medical equipment, petrochemical industry, and high-end equipment due to its advantages of low density, high strength, corrosion resistance, and good biocompatibility. Titanium alloy forging is the core process of forming profile and special-shaped forgings, and the cooling process after forging is the key link in determining the metallographic structure, mechanical properties, dimensional accuracy and finished product pass rate of the forgings.

The different cooling rates and cooling media will directly change the hardness, toughness, internal stress and surface state of titanium alloy forgings. According to different material grades, usage scenarios and performance requirements, the industry has formed five mature standardized forging cooling processes. This article disassembles the principles, advantages and disadvantages of various cooling methods and applicable scenarios in detail, and provides a process reference for the production of titanium alloy forging.

1. Natural Air Cooling (Natural Cooling With Temperature)

Natural cooling is the most basic and widely used cooling method in the production of titanium alloy forging. After the forging process is completed, the forgings are placed directly in a room temperature air environment, relying on air convection and thermal radiation to achieve natural cooling, without auxiliary equipment and energy consumption throughout the process.

The process is simple to operate, has zero cost and no operating risks, and is suitable for most ordinary titanium alloy forgings with conventional structures and no strict requirements for high strength. But the shortcomings are also obvious: the cooling speed is slow, the cooling temperature difference of the forgings is small, and the cooling cycle is long. It can easily cause uneven grain tissue thickness inside the workpiece, resulting in residual internal stress, which will affect the overall mechanical stability of the forgings to a certain extent. It is not suitable for the production of high-precision and high-load core components.

2. Forced Air Cooling (Rapid Air Supply And Cooling)

Forced air cooling is an accelerated room temperature cooling process. Continuous forced air supply of high-temperature forgings is carried out through fans and directional blowing equipment to break the static air insulation layer, greatly improving the heat dissipation efficiency, and the cooling speed is far better than natural air cooling.

A reasonable forced air-cooling process can quickly release the waste heat of forging forgings, shorten the production cycle, effectively weaken the thermal accumulation of forgings, balance the internal and external temperature of the workpiece, reduce the residual thermal stress, and improve the stability of the product structure.

In the process control, it is necessary to accurately control the blowing wind speed, blowing distance and cooling time. Excessive cooling strength leads to rapid cooling of the surface of the titanium alloy, causing defects such as surface oxidation, local hardening, and excessive temperature difference between internal and external tissues. Therefore, it is necessary to standardize and regulate the parameters according to the thickness and structural specifications of the forgings to avoid process risks.

3. Water Quenching And Cooling (Extremely Fast Water-Cooled Quenching)

Water quenching is the fastest cooling enhanced process for titanium alloy forging. The high-temperature forgings are completely immersed in a clear water medium, and the high specific heat capacity of water is used to achieve rapid cooling, and the metallographic structure of the forgings after high-temperature molding is quickly fixed.

Titanium alloy forgings that have been water-quenched have a dense grain structure and greatly improved strength and hardness. They are suitable for industrial pressure-bearing parts that require extremely high mechanical strength and compressive properties.

However, the fault tolerance rate of this process is extremely low, and rapid cooling will cause a great temperature gradient inside and outside the forging, which can easily produce cold shrinkage stress, leading to deformation, cracking, brittleness and other quality problems of the workpiece. Therefore, the water quenching process is only suitable for specific high-strength titanium alloy materials, and the inlet water temperature and cooling rate must be strictly controlled. It is only used for customized production of special forgings and cannot be used for general mass production.

4. Oil Quenching Cooling (Constant Temperature Flexible Cooling)

Oil quenching is a medium-speed flexible cooling process between air cooling and water quenching. Special quenching oil is used as the cooling medium to complete the cooling of forgings in a constant oil temperature environment.

Compared with water quenching, the cooling rate of oil quenching is more gentle and uniform, which perfectly solves the cracking, deformation, and embrittlement problems caused by rapid cooling, and preserves the toughness of the titanium alloy substrate to the greatest extent. At the same time, the oil medium can isolate the air, effectively reduce the surface oxidation, peeling, and color difference of the forgings, and greatly improve the surface finish of the forgings and the appearance quality of the finished products.

The core control point of production is constant temperature control of oil temperature. Too high oil temperature will cause cooling failure and tissue softening. Too low oil temperature will cause uneven cooling. Therefore, constant temperature and temperature control equipment is required in production to ensure the unified performance of batch products. It is currently the mainstream cooling process for high-end titanium alloy structural parts.

5. Vacuum Cooling (High-Purity Precision Cooling)

Vacuum cooling is a high-precision process adapted to high-end precision titanium alloy forgings, and the whole process is cooled and dissipated in a closed vacuum equipment.

There is no oxygen and no impurities in the vacuum environment, which completely eliminates the oxidation, impurity, and surface pollution problems of titanium alloy at high temperature, and preserves the purity and original excellent properties of titanium alloy materials to the greatest extent. At the same time, the vacuum heat conduction efficiency is stable, the cooling is uniform, and the tissue consistency is extremely high. The processed forgings have no oxidation layer, high precision and stable performance. It is the core cooling process of titanium forgings in high-end fields such as aerospace and implantable medical devices.

The only limitation of this process is that the equipment input cost is high, the operation process is complex, and the production efficiency is low. It is mostly used for the production of high value-added precision forgings, and it is not suitable for large-scale mass production of ordinary low-end titanium parts.

Summary

In summary, there is no universal “universal cooling process” for titanium alloy forging.

For ordinary civil conventional forgings, natural cooling and forced air cooling are preferred, taking into account cost and efficiency; high-strength industrial accessories, suitable for water quenching and oil quenching, balance hardness and toughness; aviation and medical high-end precision forgings must be vacuum cooled to ensure material purity and high-precision performance.

Precise matching of the cooling process is the core key to avoiding defects such as cracking, deformation, oxidation, and uneven organization of titanium alloy forgings, stabilizing the mechanical properties of the product, and improving the quality of the finished product. It is also the core technological point of titanium alloy refined forging production.