Titanium tubes are light in quality, high in strength and have excellent mechanical properties. It is widely used in heat exchange equipment, such as tube heat exchanger, coil heat exchanger, serpentine tube heat exchanger, condenser, evaporator and conveying pipeline. Nowadays, many nuclear power industries use titanium tubes as their unit specification tubes. Titanium tube according to the use of the requirements and performance of the implementation of the two countries standards:GB/T3624-1995GB/T3625-1995ASTM33738Supply Trademarks:TA0, TA1, TA2, TA9, TA10, BT1-00, BT1-0, Gr1, Gr2Supply Standards:Diameter φ4~114mm, wall thickness δ0.2~4.5mm, length Within 15m.
Titanium alloy is an alloy composed of titanium as the base and other elements. Titanium has two kinds of homogeneous heterocrystals: α-titanium with dense hexagonal structure below 882℃, and body-centered cubic β-titanium above 882℃.
Alloying elements can be divided into three categories according to their effect on the phase transition temperature:
① The elements that stabilize the α phase and improve the phase transition temperature are α-stabilizing elements, such as aluminum, carbon, oxygen and nitrogen. During this period, aluminum is the main alloying element of titanium alloy, which has obvious effects on improving the strength at room temperature and high temperature, reducing the specific gravity and increasing the elastic modulus.
② stabilize β-phase, reduce the phase transition temperature of the elements for β-stabilizing elements, and can be divided into homocrystalline and eutectic type two. The former has molybdenum, niobium, vanadium, etc.; the latter has chromium, manganese, copper, iron, silicon, etc..
③ The elements that have little effect on the phase transition temperature are neutral elements, such as zirconium and tin.
Oxygen, nitrogen, carbon and hydrogen are impurities in titanium alloys. Oxygen and nitrogen are highly soluble in the α-phase, which has a significant strengthening effect on titanium alloys, but the plasticity is reduced. It is usually stipulated that the content of oxygen and nitrogen in titanium is below 0.15-0.2% and 0.04-0.05% respectively. The solubility of hydrogen in the alpha phase is very small. Excessive dissolved hydrogen in titanium alloys produces hydride, making the alloy brittle. Normally, the hydrogen content in titanium alloys is controlled below 0.015%. The dissolution of hydrogen in titanium is reversible and can be removed by vacuum annealing.
Classification of titanium alloys
Titanium is an allotropic isomer with a melting point of 1720°C. Below 882°C, it has a hexagonal lattice structure called α-titanium; above 882°C, it has a body-centered cubic mass structure called β-titanium. Utilizing the different characteristics of the above two structures of titanium, adding suitable alloying elements, gradually changing the phase transition temperature and phase fraction content, to obtain different titanium alloys. At room temperature, titanium alloy has three kinds of matrix arrangement, titanium alloy is also divided into the following three categories: α alloy, (α + β) alloy and β alloy. Our country to TA, TC, TB, respectively.
α titanium alloy
It is a single-phase alloy composed of α-phase solid solution, which is α-phase no matter at general temperature or higher temperature of practical application, with stable arrangement, higher wear resistance than pure titanium, and strong oxidation resistance. Temperature between 500℃~600℃, still insist on its strength and creep resistance, but can not be strengthened by heat treatment, room temperature strength is not high.
β Titanium Alloy
It is a single-phase alloy composed of β-phase solid solution heat treatment that has high strength, quenching, aging the alloy is further strengthened, room temperature up to 1372 ~ 1666MPa; but poor thermal stability, should not be used at high temperatures.
