The microstructure and mechanical properties of forgings are related to many factors, and the forging ratio is one of the most important factors affecting the quality of forgings. Today we will learn about the forging ratio.
The forging ratio is a way of expressing the degree of metal deformation during forging. The larger the forging ratio, the higher the deformation degree of the forging and the deformation degree is directly related to the final inclusion size of the material, the crushing degree of the material eutectic carbide, the fiber flow direction and density after the material is finally formed, etc. greater impact.
At present, there are 3 kinds of process schemes to improve the uniformity of the forging ratio, namely, changing the boundary conditions of the blank and the die, changing the shape of the blank, and changing the upsetting deformation method. And by changing the deformation mode of the flat anvil upsetting, the forging ratio and geometric uniformity of the forging can be effectively improved.
The distribution of the forging ratio (ie the degree of deformation) in the forgings with different forging ratios is uneven, and it is obviously divided into the large forging ratio area, the average forging ratio area and the small forging ratio area. The mechanical properties experiments show that: under the same heat treatment conditions, plastic deformation with a certain forging ratio can significantly improve the strength index and plasticity index of the rolled steel. The best, but the toughness decreased significantly. Under the same strain rate condition, the larger the forging ratio (ie the degree of plastic deformation), the more obvious the dynamic recrystallization in the forging structure. When the forging ratio reaches a certain value, the original grains will be replaced by new recrystallized grains. , a more complete dynamic recrystallization occurs. Therefore, the forging ratio has a great influence on the quality of the forgings.
Forgings are generally used in key parts of machinery. Due to the harsh working environment and complex and changeable forces, the quality of forgings in the production process is very high. Forgings are directly forged from steel ingots. When producing forgings, even if the most advanced metallurgical technology is used, defects such as micro-cracks, porosity, shrinkage holes, and segregation are inevitable inside the steel ingots, which seriously affect the quality of the forgings. In order to eliminate these defects and improve the forgings To improve the quality, the forging process must be improved, and reasonable forging process parameters must be selected. Next, let’s talk about the forging process of three forgings.
The first is the upsetting process. In the free forging production of forgings, upsetting is a very important deformation process. Reasonable selection of upsetting process parameters plays a decisive role in the quality of forgings. Repeated upsetting can not only improve the forging ratio of the billet but also break the carbides in the alloy steel to achieve the purpose of uniform distribution; it can also improve the lateral mechanical properties of the forgings and reduce the anisotropy of the mechanical properties.
Both cake forgings and wide plate forgings are mainly deformed by upsetting, and the deformation amount of upsetting is large, but at present, the rejection rate of ultrasonic flaw detection of such forgings is very high, mainly due to the occurrence of transverse internal crack layer defects. Current technological theory cannot explain this. For this reason, since the 1990s, Chinese scholars have conducted in-depth research on the upsetting theory after a long period of serious research, starting from the theory of the main deformation zone and the passive deformation zone. The tensile stress theory of the rigid-plastic mechanical model and the shear stress theory of the hydrostatic stress mechanical model during plate upsetting are proposed. Solve and analyze the stress state inside the workpiece, a large number of data prove the rationality and correctness of the theory, reveal the distribution law of the internal stress when using the ordinary plate upsetting cylinder, and then put forward a new process of conical plate upsetting, establish A rigid-plastic mechanical model for the upsetting of a square cylinder is presented.
Then there is the tire die forging process. The tire die forging is a forging method that directly uses the blank or pre-forged the blank into the shape and size required for tire forging, and then uses the tire mold on the free forging equipment for final forging. In addition to the upper and lower flat anvils and general forging tools, tire mold forging also requires special tire molds. The tire mold is not fixed on the forging equipment. When it is used, it is placed on the lower flat anvil of the equipment. It can be removed when not in use. It is easy to use, does not require installation, greatly saves the time for mold testing, and the process operation is flexible and diverse; due to metal deformation It is always completed in the die cavity, and the shape and size of the forgings are mainly guaranteed by the tire mold, so forgings with complex shapes and accurate size requirements can be obtained, and the required heating times and deformation processes are also reduced, so not only improves the utilization rate of metal materials, and reduce machining hours, greatly improve labor productivity.
From the aspect of forging quality, the metal deformation is limited due to the action of the die during the forming process. The utilization rate is greatly improved, the production efficiency is relatively high, and forgings with complex shapes can be forged; moreover, forgings can be produced on small equipment, and local forming can also be achieved. Based on the above advantages, tire mold forging has been valued by many manufacturers and favor.
The last is the drawing process. Drawing is a necessary process in the forging process of shaft forgings, and it is also the main process that affects the quality of the forgings. Through the drawing process, the cross-sectional area of the billet is reduced, the length is increased, and the coarse grains are also broken. , Forging internal porosity and holes, refining the as-cast structure, etc., so as to obtain homogeneous and dense high-quality forgings. While studying the flat anvil drawing process, people gradually began to realize the importance of the internal stress and strain state of the forging to the internal defects of the forging. The length and the upper and lower V-shaped anvils are elongated, and then by changing the shape and process conditions of the elongated anvil, WHF forging method, KD forging method, FM forging method, JTS forging method, FML forging method, TER forging method, SUF forging method are proposed. The forging method and new FM forging method, these methods have been applied to the production of large forgings and achieved good results.
