The key direction to improve metal utilization and reduce product costs is to achieve less or even no oxidation of titanium alloy die forging billets during the heating process. In related studies, BT3-1 titanium alloy extruded bar billets were used for experiments. The billet surface was treated to a smooth state before forging, and then placed in an electric furnace and heated to 950℃-980℃. At the same time, the plate samples of BT20 and OT4-1 alloys and the pipe samples of ПT7M alloy were compared, and the samples were heated synchronously with the die-pressed billets. Elbows, tees, crosses, and other accessories were successfully die-pressed using BT3-1 alloy billets. Titanium forging manufacturers have conducted in-depth studies on the effects of the following factors on the physical and mechanical properties of parts, including pre-low-temperature oxidation treatment, glass enamel protective coating, heating medium and heating method, and surface treatment after die forging.
Effect of pre-oxidation on the surface of the blank
Titanium alloy forging manufacturers found that the surface of the blank without pre-oxidation showed a fish scale texture, while the surface of the pre-oxidation blank was relatively smooth. In addition, the glass enamel coating on the surface of the hot die-pressed blank after pre-oxidation was very easy to remove. This shows that pre-oxidation can not only improve the surface quality of the blank but also has a positive effect on the subsequent coating treatment.
Effect of surface layer state on mechanical properties
The surface layer state (oxidation and air absorption) has a significant effect on the mechanical properties of hot die forging blanks, especially plasticity. Among them, sandblasting is an effective way to improve plasticity. Based on pre-oxidation of the blank, applying a glass enamel coating can also improve the plasticity of the blank surface. This shows that through a reasonable combination of surface treatments, the mechanical properties of titanium alloy forgings can be optimized to meet the needs of different usage scenarios.
Analysis of the effects of different heating methods
Ordinary electric furnace heating
When heating titanium alloy billets in ordinary electric furnaces, if the temperature exceeds the allotropic transformation temperature and the holding time is within 1 hour, it generally does not cause obvious air absorption on the surface. At this time, conventional sandblasting can easily remove the air absorption layer. This provides a certain reference for controlling the surface quality of titanium alloy forgings under ordinary electric furnace heating conditions.
Heating of the loose material pseudo-liquefaction layer
The method of heating the billet before die forging in the pseudo-liquefaction layer of loose materials is a very promising heating method. This heating method can effectively enhance the heat exchange process between particles, gas, and the billet surface. Experiments show that the heat transfer efficiency in the pseudo-liquefaction layer of loose materials is 1.5 orders of magnitude higher than that in a forced convection heating furnace, which is roughly equivalent to the heat transfer efficiency in a molten salt furnace. This means that this heating method can heat the billet more quickly and evenly, reduce the heating time, thereby reducing the risk of surface oxidation, and improving production efficiency and product quality.
In summary, through pre-oxidation treatment, reasonable selection of surface treatment methods and the use of efficient heating methods, the surface oxidation of titanium alloy forgings during the heating process can be effectively reduced, the quality and performance of titanium alloy forgings can be improved, and strong support can be provided for the production and application of titanium alloy forgings.
