Recherche sur la technologie de forgeage à chaud de barres en alliage de titane
We analyzed the advantages of partial loading hot die forging into shape technology, analyzed the mechanical properties and microstructure of the pièces forgées, and concluded that the partial loading method and hot die forging into shape technology could obtain reliable quality titanium alloy products with mechanical properties far better than the design requirements, and can meet the basic requirements of enterprises for the quality of titanium alloy bars. Our research results can help promote this technology’s use and provide a reference for improving the processus de forgeage.
Titanium alloy bars usually have a high reinforcement structure, complex shape, large parts size, and high bar production accuracy requirements, making titanium alloy bars difficult to process. The traditional method of processing titanium alloy rods is based on forging them into simple-shaped blanks and then combined with modern numerical control machining and other methods to process them one by one, which increases the processing cost and significantly reduces the strength of the obtained product quality.
Therefore, the search for stable processing performance improves the use of material technology when the current urgent need to solve one of the problems. The die forging process is a new titanium alloy bar processing technology that can reduce processing costs and improve material utilization.
1. Hot die local loading forming technology of bars
1.1 Overview of partial loading forming technology
Bar forgings are complex circular forgings made of bars and reinforcement, and the web and reinforcement increase the difficulty of forging. Therefore, in the forging forming design process must be considered the influence of die pressure on the forging. In order to effectively prevent the overall loading in the hot die forging process from causing a large amount of metal flow along the radial direction and then appearing vortex, folding, disorder, and other phenomena, the local loading pad and ring pad are used. The test billet is placed in the middle of the ring mat in the hot die forging deformation test. The partial loading mat is placed between the billet and the upper die, which can effectively ensure that the metal flow deformation is fully filled into the die cavity, effectively avoiding the problems of vortex, turbulence, and so on along the radial flow.
Bar-type hot die forging caused by shaping processing technology is usually used in the overall loading method, the overall loading technology in the forming process. When the reinforcing bar filling to a certain extent, the filling resistance of the bar increased significantly, resulting in a large number of metals along the center of the bar flow around or along the radial flow and causing disorder, folding, vortex, and other phenomena, and finally make the forging filling is not in place, making the forging quality is not up to standard. Suppose the overall loading method is changed to the partial loading step-by-step forming method in the filling process. In that case, the direction of metal flow can be effectively controlled so that the metal can be fully filled to the bottom of the reinforcement, avoiding the problem of metal flowing in the radial direction to the greatest extent. The probability of the above problems can be better avoided.
1.2 Main steps of partial loading forming technology
The hot die forging forming process is broken down into two main steps according to the characteristics of the bar forgings to be tested. The first step is the pre-forming stage of the bar workpiece; the process is to produce axial deformation of the billet under the influence of local loading pad evaluation pressure, fill the lower die rib and other positions with priority, and transport the metal flow along the radial direction until the full filling of the ring pad position; because the relative contact area between the die and the billet in the filling process is small, coupled with the metal flow deformation speed is high-speed, so in the local loading, The heat loss of the billet during the process is small. The pre-formed part of the workpiece can be obtained. Based on the first step, the preformed portion is finally formed, i.e., the ring pad and partial loading pad are removed from the bar forging, and the preformed part is heated up to 950°C and placed in the lower die cavity for the final forming process. The thickness of the billet is gradually thinned during the post-forming process, so the contact area with the die is gradually increased. In addition, the deformation load increases significantly due to the rapid temperature reduction during the final forming process.
1.3 Microstructure characteristics of the hot-die forging of bars after forming
After the two important steps of hot-die forging, the forgings were annealed, and the microstructure of the forgings was observed.
Since the annealing temperature is close to the phase change point of the titanium alloy bar, the incipient α-phase content in the microstructure of the titanium alloy is relatively small. Defect analysis of the forgings showed that no obvious deformation defects were found in the forgings, which indicates that the quality of the bars obtained by this method is reliable.
Compared with the traditional forging process, partial loading hot-die forging technology has significantly improved the utilization rate of raw materials, greatly reduced material waste, and indirectly reduced the forging cost. In summary, the partial loading method and hot die forging into shape technology can obtain reliable quality titanium alloy products with mechanical properties far better than the design requirements and can meet the basic requirements of enterprises for the quality of titanium alloy bars.
2. Common traditional bar hot die forging process introduction
The standard hot die forging technology for bars, in addition to the local loading forming technology, the standard forging process includes:
- ① α + β forging technology, the technology is in the medium strain rate conditions will be α alloy or α + β alloy in the β transition temperature forging process technology, the technology has the advantages of low cost, simple operation, more widely used; the technology in the forging process is prone to local overheating, easy to cause cracks on the surface of the forgings, but with the improvement of the technology forging process, gradually and successfully forged Forgings with high precision and smooth surface finish;
- ② β forging technology, the technology is in the β phase of the high-temperature conditions of the titanium alloy to complete the forging process, with high precision forgings, the advantages of small deformation resistance, significantly improve the life of the forgings; titanium alloy microstructure in the α phase crystal interface significantly increased, mostly in the net basket organization, improve the creep resistance and strength of titanium alloy;
- ③ Sub-beta forging technology is a forging process in which the forgings are heated in the beta-phase region. In contrast, the forging and forming process is completed in the two-phase region. The technology has similar characteristics to beta forging, which mainly breaks the boundary alpha phase first in the forging process. The alpha phase in the boundary region gradually transforms to alpha equiaxialization, thus improving the overall performance of titanium alloy.
In summary, titanium alloy bar has a broad application prospect in modern fields due to their superior performance. The article takes the hot die forging forming technology of titanium alloy bar as the starting point, analyzes the advantages of partial loading hot die forging forming technology from two aspects, analyzes the mechanical properties and microstructure of forgings, and concludes that the loading method and hot die forging forming technology selected in this paper can obtain reliable quality titanium alloy products, whose mechanical properties are far better than the design requirements, and can meet the enterprise’s quality requirements for titanium alloy bar. The mechanical properties are much better than the design requirements and can meet the enterprise’s basic requirements for the quality of titanium alloy bars.
Source: Chine Titanium Alloy Bar: www.titaniuminfogroup.com