What are the chemical element classifications of titanium tubes

Titanium tube is an allotrope with a melting point of 1720°C. When it is lower than 882°C, it has a close-packed hexagonal lattice structure, called α titanium; above 882°C, it has a body-centred cubic lattice structure, called β titanium. Using the different characteristics of the above two structures of the titanium tube, adding appropriate alloying elements to gradually change the phase transformation temperature and phase content to obtain titanium alloys with different structures. At room temperature, titanium alloys have three matrix structures, and titanium alloys are divided into the following three categories: α alloys, (α+β) alloys and β alloys.

Titanium tube is a single-phase alloy composed of α-phase solid solution. It is α-phase no matter at normal temperature or at higher practical application temperature, with stable structure, higher wear resistance than pure titanium, and strong oxidation resistance. At a temperature of 500°C to 600°C, it still maintains its strength and creep resistance, but cannot be strengthened by heat treatment, and its room temperature strength is not high. It is a single-phase alloy composed of β-phase solid solution. It has a high strength without heat treatment. After quenching and aging, the alloy is further strengthened. The room temperature strength can reach 1372 ~ 1666 MPa, but the thermal stability is poor and it is not suitable for use at high temperatures.
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The influence of alloy elements in titanium plate and tube on welding performance

The welding seam and heat-affected zone have a high temperature after welding, and the cooling rate is very fast under the influence of the surrounding base material. Therefore, after fusion welding of titanium plate and titanium tube, it is easy to produce metastable structures such as martensite a', a", quenched ω phase and metastable β. In alloys with a small content of β stable elements, thick needles Martensitic structure will reduce plasticity. Quenching omega phases in alloys with more β-stabilizing elements will cause weld embrittlement. These meta-stable structures also have an adverse effect on welding performance. Use reasonable welding specifications and welding The post-heat treatment system can reduce or even eliminate this effect.

The composition of the alloy has a great influence on the welding performance. When welding with a welding wire with a high content of β-stabilizing elements, compared with the base metal, the plasticity reduction of the weld is generally more severe than that of the less β-stabilizing element. As their strengthening ability increases, the more serious the reduction in plasticity, the lower the welding performance. Generally speaking, the weldability of a-type titanium plate is better, but the tendency to generate pores and cold cracks is greater; the weldability of a+β-type titanium plate is slightly worse, and it becomes better with the decrease of β-stabilizing element content; The thermally stable β-type titanium tube has better overall performance without heat treatment after welding. Heat-treatable beta alloys tend to have a sharp decline in plasticity after aging of the weld, and it is difficult to obtain good comprehensive properties.

In summary, in order to obtain high-quality welded joints in titanium plates and tubes, the following points must be paid attention to:

(1) Strictly control the harmful impurities in the base metal and welding materials (including filler materials and oxygen-free flux), especially the content of interstitial elements such as hydrogen, oxygen, nitrogen, and carbon. Strictly clean the workpiece, welding materials and equipment before welding;

(2) Use high-purity inert gas, oxygen-free flux or vacuum conditions to protect the weld and heat-affected zone so that it will not be contaminated by gas during welding and cooling;

(3) Use welding specifications with low heat input as much as possible to reduce the tendency of a metal to overheat; for different alloys, choose a suitable post-weld heat treatment system to adjust the structure and mechanical properties of the weld and heat-affected zone.
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Main features of titanium rod and titanium alloy material processing

Titanium rods and titanium alloys have high chemical activity. Titanium rods and titanium alloys easily react violently with oxygen, nitrogen and other oxygen-containing gases at high temperatures. When heated in air, the surface of the blank forms an oxide scale and a surface getter layer. Titanium rods and titanium alloys are easy to absorb hydrogen when heated, which causes difficulties in the processing of certain types of titanium alloy materials.

Titanium rods and titanium alloys have poor thermal conductivity. The thermal conductivity of titanium rods and titanium alloys is usually only 1/15 of that of alloys and 1/5 of that of steel. The lower thermal conductivity results in a large temperature difference between the ingot and billet section in the hot B inch, which produces a large thermal response, and cracks will form in severe cases. Therefore, the heating speed must be limited, and the temperature change, deformation speed, Deformation rate, deformation equipment.

Polycrystalline transformation of titanium rods and titanium alloys. Titanium has a-β phase transition. Heating top temperature can significantly increase plasticity and reduce deformation resistance, but the deformation of the β zone is not good enough to obtain a structure with good performance.

The cold deformability of titanium alloy is low. Cold working deformation of most titanium alloys is difficult. A little preheating (to 200~300T) can significantly reduce the deformation resistance and improve plasticity.

Titanium is easy to bond and deform tools. This tendency tends to deteriorate the surface quality of the processed material and puts forward more stringent requirements on the deformed tools and molds and process lubrication.

High yield ratio and low elastic modulus. Straightening in a cold state is very difficult.
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The titanium tube is heat-treated to remove residues

When the hydrogen content in the titanium tube is too much, the impact toughness and notched tensile strength will drop sharply due to brittleness. Therefore, it is generally stipulated that the hydrogen content in the titanium tube should not exceed 0.015%. In order to reduce the amount of hydrogen absorption, fingerprints, rolling mill marks, grease and other residues should be removed before heat treatment. There is no moisture in the atmosphere of the heat treatment furnace. If the hydrogen content of the titanium tube exceeds the allowable value, it must be removed by vacuum annealing. Vacuum annealing for dehydrogenation is generally held at 538-760°C and pressure lower than 0.066Pa for 2-4 hours.

When the temperature does not exceed 540°C, the oxide film on the surface of the titanium tube will not be significantly thickened. At higher heat treatment temperatures (above 760°C), the oxidation rate will increase rapidly, and oxygen can expand into the material to form a diffusion layer— Pollution layer. The high brittleness ratio of the oxygen contamination layer causes cracks and damage on the surface of the part. There are mechanical processing methods (such as sandblasting, house cutting, etc.) or chemical methods such as pickling and chemical milling to remove the oxygen pollution layer. During the heat treatment, the heating time should be as short as possible while ensuring the heat treatment of the meteorite. It is carried out in a vacuum furnace or an inert gas (argon, nitrogen, etc.) heating furnace. The appropriate application can also avoid or reduce the pollution caused by the titanium tube parts being heated in the air furnace.

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Application of titanium alloy forgings such as titanium ring and titanium cake in aviation manufacturing

In the chemical industry and other application fields, high requirements are placed on semi-finished products and processed parts of titanium or titanium alloys. Therefore, in the fields of aviation and aerospace, the cost of developing inspection instruments and monitoring devices is particularly high. The price of the parts has a big impact. Titanium alloy has the highest tensile plasticity and can be welded in various ways. It can be used for a long time at a temperature of up to 250 degrees Celsius. It is mainly used to make various structural parts of aircraft and engines that are not stressed. Industrial pure titanium has good plasticity, can form various sheet metal stamping parts in a cold state, and has relatively high corrosion resistance. Ti5Al2.5Sn titanium alloy has a moderate room temperature tensile strength (800 degrees Celsius 1000MPa and good welding performance. Compared with industrial pure titanium, the new titanium alloy mainly includes various levels of industrial pure titanium and widely used Ti5Al2.5Sn For titanium alloys, the room temperature tensile strength of industrial pure titanium fluctuates within the range of 350 degrees Celsius and 700 MPa. Ti5Al2.5Sn alloy has slightly lower plasticity and higher thermal strength, and the long-term working temperature can reach 450 degrees Celsius.

With the rapid development of cutting-edge science and technology such as aviation, aerospace, and nuclear energy, the requirements for materials are becoming more and more stringent. Not only are the materials used for manufacturing these equipment parts to be corrosion-resistant, wear-resistant, and anti-fretting, but also require high resistance. temperature. It is necessary to pay attention to the long-term test, in many places, before the large-scale application of titanium to the chemical industry. Under the test conditions, cooperate to test its service life and material structure. If the lack of safety (immature) due to the use of conventional structural data is mostly indicated and the economic benefits are not great, then the first step is to gradually develop titanium and titanium alloys, and in recent decades, the development of high-level technology in the field of structural data Various other mature new materials. Therefore, the military sector has developed faster in the application field of titanium and its alloys than in the civilian field.

In many industrial media, rare earth metals and precious metals are mainly used for stability, or materials such as stainless steel can only reach a certain limit in corrosion resistance. Most application fields use titanium to obtain benefits due to its low density, corrosion resistance and high strength. So far. Moreover, the consumption cost is relatively high, so the application of titanium or titanium alloy can obtain relatively high corrosion resistance strength. The creep characteristics of hard titanium at temperatures exceeding 150T surpass that of aluminum and its alloys. Considering that compared with other materials, titanium alloys have the advantages of unique creep characteristics under the condition of low density. It is found that hard titanium is used in aircraft manufacturing and missile manufacturing. The importance of the application. The earliest application of titanium and titanium alloys is the aviation industry. Recently, the aviation industry has become increasingly urgent for high-strength and low-density materials, which has greatly promoted the development of titanium manufacturing. At present, titanium alloys are widely used as structural materials in many high-speed aircraft in the world.
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Difficulties in grinding and polishing titanium alloys

The preparation of metallographic samples of titanium and titanium alloys is more difficult than that of steel. The polishing and polishing efficiency is low. Excessive cutting and polishing will produce deformation twins in the α phase. After the deformation twins are generated, the microstructure of titanium The analysis will be disturbed.

Pure titanium is more suitable for cold mounting than hot pressure mounting, which may change the content and distribution of hydrogen in pure titanium. It is very difficult for pure titanium to remove scratches and plastic rheology during sample preparation.
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How to improve the yield rate of mechanical equipment titanium plate?

During the production and processing of titanium plates, many processes are involved, and each link is very important, which affects the quality and appearance of the titanium plates. If you are not careful, it will deviate from the ideal product specifications. So, what are the countermeasures?

Compared with other pipe materials, mechanical equipment titanium plate has a higher resistance to internal force and external pressure, better corrosion resistance and wear resistance. At the same time, it has the advantages of convenient construction, good interface sealing performance, and large operating safety factor. In recent years, there has been a rapid development momentum in the cast titanium material market. So how to improve the yield rate of mechanical equipment titanium plate?

In the production of this material, three quality problems, cracks, heavy leather, and slag inclusion, are more likely to occur. Cracks occur with the centrifugal pouring process, and the pouring criteria are unreasonable; heavy skin is related to pouring temperature and pouring speed; slag inclusion is related to metal chemical element content and slag removal.

The avoidance and control methods are 1. Improve the centrifugal equipment to effectively avoid cracks. Reduce the residence time of the titanium solution at high temperature, and strengthen the inoculation, especially the inoculation with the flow. The amount of inoculant used to control the flow is 0.1-0.25% of the amount of titanium liquid; to ensure that the pipe mold powder is evenly distributed, the amount of control inside and outside of the pipe mold is 20-30g/m2. Control the technical parameters of the water-cooled metal centrifuge.

2. Optimize technical parameters to reduce the weight of the tube body. Reasonably control the pouring temperature and the temperature of the cooling water inlet and outlet of the fuselage to shorten the interval between two castings. The temperature of the cooling water inlet of the control fuselage is 28-36℃, and the temperature of the outlet is 50-57℃. In the water-cooled metal centrifugal casting technology, avoid excessively high casting speed, adjust the suitable turning speed and host speed; ensure that the depth of the pipe mold is 0.25-0.3mm, the diameter is 4-5mm, point and point The marginal distance is 0.5-0.7mm.

3. Control the participation of materials to reduce the disadvantages of slag inclusion. In order to reduce the sulfur content in the titanium solution and reduce the occurrence of sulfides, W(S)<0.02% should be controlled; appropriately increasing the casting temperature is conducive to the floating of slag inclusions; the rare earth content in the nodulizer is not easy to be too high, and the rare earth content It is advisable to control 1-2%; strengthen the slag removal and slag blocking effect of the titanium liquid; the residual magnesium flow in the titanium liquid is not easy to be too high (control at 0.035-0.045%) to reduce the surface oxidation of the titanium liquid.

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