Research On Heat Treatment Process Of Titanium Alloy Plate

Titanium, as a corrosion-resistant structural material, is widely used in aerospace, petrochemical, salt production, printing and dyeing, pharmaceutical, food, seawater desalination, etc. However, in high temperature and high concentration of chloride, crevice corrosion occurs in pure titanium, which affects the service life. In order to solve the problem of crevice corrosion of pure titanium in high temperature and high concentration of chloride, people developed a new type of titanium alloy --- Ti-0.2Pd alloy. The alloy has the ability to resist localized corrosion in reducing media and hot concentrated chlorides, but due to the addition of precious metal palladium, the cost is high, so that its application has been limited. in the mid-1970s, the United States Titanium Metals Corporation developed Ti-0.3Mo-0.8Ni alloy. The alloy is nearly α-type titanium alloy, has good crevice corrosion resistance in high temperature, high concentration of chloride, can partially replace the higher cost of Ti-0.2Pd alloy [3-4], has been included in the United States, the United Kingdom, Russia, Japan, France, Germany, etc. The standard, and put into industrialized production.
In the 1980s, China began to Ti-0.3Mo-0.8Ni alloy material processing and application of research, but also included in our standards (corresponding to China's TA10), and in pure titanium may appear crevice corrosion environment has been applied. For example, in March 1985, it was applied to the heating chamber of the vacuum salt production in Xiangli Salt Mine, and in April 1986, it was applied to the heating chamber of the magnesium chloride evaporation tank in Tanggu Salt Farm. Nanjing Baotai Special Materials Company has undertaken the order of titanium and steel composite materials for a potash fertilizer project production unit abroad. The composite material cladding is 3mm thick TA10 titanium alloy sheet. According to GB/T3621-2007 "titanium and titanium alloy plate" standard, the conventional plate needs to meet the requirements of class A, the elongation at break can reach 18%, while the subsequent plate used for explosion welding needs to meet the requirements of class B, the elongation at break should reach more than 25%. For the explosion composite process of titanium alloy plate plasticity requirements, can be used as raw material production of low hardness 0 titanium sponge plate, in order to achieve the subsequent process on the plasticity index requirements, but this will inevitably increase the cost of raw materials. This experiment uses grade 2 titanium sponge as raw material to prepare TA10 titanium alloy sheet, through the study of different heat treatment systems on the organization and properties of TA10 titanium alloy sheet, to explore the appropriate heat treatment system, with a view to obtaining the plasticity index to meet the requirements of the subsequent explosion composite process TA10 titanium alloy sheet.

1 Experiment

1.1 Experimental materials used 2 sponge titanium, nickel - molybdenum intermediate alloy, after two vacuum self-consumption melting to prepare a diameter of 560mm TA10 titanium alloy ingot, its chemical composition is shown in Table 1. ingot by forging billet, milling, grinding and other processes made of hot-rolled slabs, and then in the 1680 rolling mill by two-fire rolled into a 3.0mm thick plate. Figure 1 for the rolled state TA10 titanium alloy plate metallographic photographs, the organization of its very fine strip rolling state deformation organization. Table 2 shows the room temperature mechanical properties of rolled state TA10 titanium alloy sheet.

1.2 Heat treatment heat treatment test using SX2-2.5-10 resistance furnace, temperature error ± 5 ° C. TA10 titanium alloy is a nearly α-type alloy, the cooling rate has little effect on its organization and properties, the annealing temperature should generally be selected below the α + β / β phase transition point of 120-200 ° C. The temperature of α + β / β phase transition point of α + β / β phase transition point. Therefore, heat treatment specimens were cut on 3.0mm thick hot rolled TA10 titanium alloy plates and annealed at different temperatures, the annealing temperatures were 550, 600, 650, 700, 750 and 800°C, the holding time was 30min, and the cooling method was air cooling. Samples were taken from the annealed plates for microstructure observation and mechanical property testing to explore the appropriate annealing temperature. In the annealing temperature, annealing treatment with different holding time, the holding time were 15, 30, 60, 120, 180min respectively, take samples to observe the microstructure of the plate after annealing for different time and test the mechanical properties, and finally obtain the appropriate heat treatment system.

2 Results and Discussion

2.1 The effect of heat treatment temperature on the organization and mechanical properties of plate TA10 titanium alloy hot rolled sheet by different temperature insulation 30min and air cooling annealing treatment of room temperature mechanical properties and microstructure are shown in Table 3 and Figure 2. as seen in Table 3, TA10 titanium alloy plate by 550 ℃ × 30min/AC annealing treatment, caused by the phenomenon of processing hardening of the strength of the high strength and plasticity of the phenomenon of the poor is not eliminated. Elimination; between 550 ~ 650 ℃, with the increase in heat treatment temperature, the plate processing hardening phenomenon is gradually eliminated, the tensile strength gradually reduced, plasticity slightly improved; between 650 ~ 700 ℃, the strength of hot rolled sheet is almost unchanged, while the plasticity is significantly improved; between 750 ~ 800 ℃, the tensile strength of hot rolled sheet is still unchanged, while the elongation after break is decreasing, plate Plasticity deterioration. As can be seen from Figure 2, TA10 titanium alloy plate at 700 ℃ below the main recovery process, the organization of the rolling deformation of the strip-like organization, when the heat treatment temperature increases to 700 ℃, recrystallization nucleation and grain growth occurs. Heat treatment temperature of 750 ℃, recrystallization is basically complete, the vast majority of the organization for the finer isometric α phase, but there are still a small number of banded deformation organization. When the heat treatment temperature reaches 800 ℃, some of the grains grow abnormally, and the organization is coarse. Therefore, in order to TA10 titanium alloy hot rolled sheet to meet the requirements of the explosion composite process on the plasticity of the plate, the appropriate heat treatment temperature should be selected between 700 ~ 750 ℃.

2.2 The effect of holding time on the organization and mechanical properties of the plate according to the heat treatment temperature experiment selected heat treatment temperature of 750 ℃, the mechanical properties of the plate after heat treatment of different holding time at this temperature is shown in Table 4, microstructure is shown in Figure 3. from Table 4 can be seen, when the heating temperature of 750 ℃, with the prolongation of the holding time, the tensile strength of TA10 titanium alloy plate does not vary much, within 5 ~ 10MPa, the holding time of 5 ~ 10MPa, the tensile strength of TA10 titanium alloy plate is not very large. ~ 10MPa, insulation time in the interval of 15 ~ 60min, plate elongation at break with the extension of insulation time significantly larger, plasticity becomes better; and when the insulation time of more than 60min, the plate elongation at break has a more obvious reduction, plasticity gradually deteriorate. As can be seen from Figure 3, TA10 titanium alloy plate at 750 ℃ after 15, 30, 60, 120, 180min annealing treatment, the organization from the initial strip rolling deformation organization gradually recrystallization nucleation and grain growth, when the holding time of 30min, the recrystallization is basically complete (see Figure 3b), when the holding time reaches 60min, the recrystallization of the whole, the organization is fine and uniform isotropic, and the plasticity is good; when the holding time of more than 60min, the plate has a more obvious reduction in elongation after breakage, plasticity gradually deteriorate. The organization is fine and uniform isometric α phase (see Figure 3c). As the insulation time continues to extend, the deformation structure and other factors hindering grain growth elimination, a few special grain boundaries rapidly migrate [11], some of the recrystallized grains grow abnormally, the organization is gradually coarse.

In summary, TA10 titanium alloy rolled sheet annealing treatment needs to reach a certain temperature in order to effectively respond to obtain a better organization and performance. Such as in 750 ℃ annealing treatment can be obtained when the equiaxial α organization and good plasticity, when the temperature continues to rise when the strength rises, the elongation decreases. TA10 titanium alloy plate annealing treatment should also be controlled when the holding time, otherwise due to the growth of recrystallized grains, will affect the plasticity of the material.

3 Conclusion

(1) When the heat treatment temperature reaches 600 ℃, the organization of TA10 titanium alloy plate can get a good response, but the plasticity is poor. If you need to obtain better plasticity to meet the requirements of the use of titanium plates for explosive composite, you need to carry out a higher temperature (700 ~ 750 ℃) of heat treatment. (2) When the heat treatment temperature is certain, the holding time has little effect on the strength of TA10 titanium alloy plate, but the plasticity has a significant effect. (3) For 3mm thick TA10 titanium alloy hot rolled sheet, after (700 ~ 750) ℃ × (30 ~ 60) min / AC annealing treatment, you can get a more uniform equiaxial α-phase and better comprehensive mechanical properties, to meet the use of titanium plates for explosive composite requirements.