With the development of science and technology, the progress of society, and the persecution of various industrialized productions to the environment are also growing. However, the superior performance of titanium alloys is increasingly reflected in the production of chemical industry.
Like isothermal forging, hot forging is also a promising precision forging process. The difference is that the mold temperature of hot forging is higher than that of ordinary forging, but lower than the temperature of isothermal forging. Typical hot forging die temperatures are 110 to 225 ° C lower than the billet temperature. Compared with isothermal forging, the mold temperature can be widely used to reduce the mold temperature, but the ability to form very thin and complex shape forgings is slightly worse.
Compared with conventional forging, hot die forging has the following advantages:
(1) Reducing the consumption of forging materials Due to hot die forging, the chilling of the mold contact blank and the work hardening of the material are alleviated, and the forgeability of the material is improved, thereby allowing the forging to have a smaller fillet radius and a smaller draft. The slope and the small forging allowance greatly reduce the quality of the forging. For example, a Ti-6Al-4V alloy structural part has a mass of 28 kg, a forging piece produced by a conventional forging process has a mass of 154 kg, and a forging piece produced by a hot die forging process has a mass of 109 kg, and the difference between the two methods is 45 kg.
(2) Reduce the number of forging operations and improve the working capacity of the press. Due to the hot die forging, the mold temperature is higher, the temperature drop of the blank is less, and the conventional forging requires two fires, three fires or more fires to form the forgings, hot forging Just one time, up to two fires can be done. Because of the hot die forging, the deformation resistance of the metal is relatively low, which relatively increases the working capacity of the device.
(3) Reducing the machining amount of forgings Since the forgings produced are close to the weight and contour size of the parts, the amount of material removed in machining is reduced as compared with the forgings produced by conventional forging.
(4) The uniformity of the product is better. Because the temperature gradient is greatly reduced during the forging process, the uneven deformation caused by the temperature gradient is easy to be alleviated, so the uniformity and consistency of the structure and performance of the product are superior to the conventional forging production forgings. , but not as forgings produced by isothermal forging.
In hot forging, although the billet has a temperature drop, it is still in the forging temperature range, and the deformation resistance is not as sharp as that in conventional forging. The strain rate used in hot forging varies from 0.05 to 0.2 s-1, and if the strain rate is too low, the billet temperature may decrease.
In hot forging of titanium alloys, forging heating temperature, strain rate, microstructure of the preform and holding time are extremely important factors, which play a decisive role in the dimensional accuracy and microstructure of the formed part. Generally lower strain rates and longer dwell times increase the likelihood of precision forming. The microstructure of the preform has a direct influence on the flow stress and superplasticity of the material, especially for the microstructure after forging, and it cannot be attempted to completely eliminate defects and grain unevenness in the raw material by isothermal forging or hot forging.