Complete Annealing Process of Titanium and Titanium Alloys

In the complete annealing process, the purpose of complete annealing of titanium and titanium alloys is to obtain a stable, plastic or microstructure corresponding to certain comprehensive properties. Recrystallization mainly occurs in this process, so it is also called recrystallization annealing. In addition, there are also changes in the composition, morphology, and quantity of a-phase and β-phase. Most a and a+beta titanium alloys are used in fully annealed condition. The two-phase region of all-a-type titanium alloys is very small, and recrystallization occurs mainly during the complete annealing process. The annealing temperature is generally selected to be 120 to 200°C below the a+β/β transformation point. Too high temperature will cause unnecessary oxidation and grain growth, and too low temperature will cause incomplete recrystallization. The cooling rate has little effect on the structure and properties of such alloys, and air cooling is generally used.

In addition to recrystallization during annealing, near-a titanium alloys and a+β titanium alloys also have changes in the composition, quantity and morphology of a-phase and β-phase, and it is also complicated to determine the annealing process. For the delivery state of the metallurgical plant, a stable and plastic structure is mainly required. The annealing temperature is generally selected to be 120-200°C below the a+β/β transformation point, and the cooling method is also air-cooled. However, for the annealing of the product before the final use, it must be determined through experiments according to the influence of the annealing process on the microstructure and mechanical properties.

As for metastable beta titanium alloys, complete annealing is also solution treatment. The annealing temperature of the metallurgical plant before leaving the factory is generally selected to be 80 to 100 °C above the a+β/β transformation point. Within the recommended full annealing process range, the specific process should be determined experimentally based on the processing history of the material, the actual chemical composition, and the equipment used. In order to avoid unnecessary oxidation, the process should be selected with the lowest temperature and shortest time under the premise of meeting the performance requirements.

The beta annealing process has appeared in recent years. The grade 7 titanium alloy plate and a+β titanium alloy are heated in the β phase region and then air-cooled, and a needle (or flake) a is precipitated on the coarse β grains. This structure corresponds to higher fracture toughness, creep resistance and notch sensitivity, but reduces plasticity indicators such as section shrinkage. It can be used as appropriate in situations where this performance is emphasized.

In addition, for some alloys, when it is required to improve the performance stability of long-term operation at the service temperature, a second annealing higher than the service temperature, or isothermal treatment is often used, such as TC9 and tc6 alloys.

Development characteristics of titanium alloy materials and processing technology of titanium products

Due to the high manufacturing cost of titanium alloys, in order to reduce costs, the competitiveness of titanium alloys in the entire metal material market is improved at lower prices. Titanium is widely considered to have unparalleled superior properties compared to other materials, but the price of titanium is often prohibitive for consumers, especially automakers. The emergence of high-quality and low-cost titanium alloys will certainly contribute to the popularization and application of titanium and Ultra-Thin Titanium Alloy Sheet.

From the application status at home and abroad and the development of titanium processing technology, the plastic processing technology of titanium and titanium alloys will develop in the following directions in the future:

1) High performance, that is, to develop alloys with higher service temperature, higher specific strength, higher specific modulus, better corrosion resistance and wear resistance.

2) Multifunctional, that is to develop titanium alloys with various special functions and uses, such as high damping, low expansion, constant resistance, high resistance, anti-electrolytic passivation and hydrogen storage, shape memory, superconductivity, low modulus biomedical and other titanium alloys, and further expand the application of titanium and titanium alloys.

3) Deepen the research on traditional alloys, improve the practical properties of existing alloys, and expand the application scope of traditional alloys through the improvement of equipment and processes.

4) Adopt advanced processing technology and large-scale continuous processing equipment to develop continuous processing technology, direct rolling technology, cold forming technology and near-net forming technology to improve the production efficiency, yield and product performance of ASTM F67 Gr2 Titanium Plate.

5) Reduce costs, develop alloys that contain no or almost no precious metal elements, and add cheap elements such as iron, oxygen and nitrogen, and develop titanium alloys that are easy to process and form, easy to cut, and inexpensive to alloy elements and master alloys. Develop titanium alloys, use prohibited materials, and improve the recovery rate and utilization rate of prohibited titanium. This is particularly important for reducing the cost of civilian titanium alloys.

6) Using advanced computer technology to simulate the deformation and processing process of the workpiece, predict the evolution of the metal microstructure, and even predict the mechanical properties of the product (yield strength, tensile strength, elongation and hardness, etc.). ), and design or improve molds and tooling; analyze and process test results, reduce test volume, improve work efficiency, and reduce development costs.

Russia develops new technology to enhance antibacterial effect of titanium alloy

The Russian State Research University of Technology and other Russian scholars have developed a new technology that enables the antibacterial effect of astm b348 titanium rod, one of the key materials for advanced surgery. Implants processed according to the new method will significantly speed up and facilitate recovery from trauma, the researchers say.

The mechanical properties and resilience of damaged bones decline significantly with age, and such damage requires long-term treatment. The use of implants made of unmodified metals and alloys can lead to complications that may require a second surgical procedure afterward. Materials that can inhibit bacterial activity help in vivo implant surgery to be safer and more reliable. For this reason, Russian scholars have developed a method of spraying antibacterial coatings on Ti-Zr-Nb, one of the Titanium Alloy Rectangular Tube.

Experiments showed that treatment according to the new method completely inhibited the growth of E. coli on the implant surface. At a low dose of silver (about 0.037 mg/L), it is completely safe for the body and achieves a significant antibacterial effect. The "strike" against the bacteria is carried out by silver ions, the researchers said. The scientists chemically synthesized the nanoparticles that released them in a complex alcohol solution, which made them only about 10 nanometers in size. Thanks to this, silver is deposited in the pores of the material to a depth of 60 nanometers, greatly improving the durability and antimicrobial effect of the coating.

Titanium alloy rod hot extrusion forming process!

The thermal conductivity of the titanium alloy billet is low, and the temperature difference between the surface layer and the inner layer will be large during hot extrusion. When the temperature of the extrusion cylinder is 400°C, the temperature difference can reach 200~250°C. Under the combined influence of suction strengthening and the large temperature difference of the billet section, the metal on the surface and the center of the billet has completely different strength and plasticity, which will cause very uneven deformation during the extrusion process, and produce a large additional tensile force on the surface layer. Stress becomes the source of cracks and cracks on the surface of extruded products. The hot extrusion process of titanium rectangular rod and titanium alloy rod products is more complicated than that of aluminum alloy, copper alloy and even steel, which is determined by the special physical and chemical properties of titanium rod and titanium alloy rod.

The research on the metal flow dynamics of industrial titanium alloys shows that there are great differences in the metal flow behaviors of different alloys in different temperature regions. Therefore, one of the main factors affecting the extrusion flow characteristics of titanium rods and titanium alloy rods is the heating temperature of the billet that determines the state of mental transformation. Compared with the temperature extrusion of the P-phase region, the metal flow in the a-phase region or the P-phase region is more uniform. It is difficult to obtain extruded products with high surface quality. Until now, the extrusion of medical titanium rod had to use lubricants. The main reason is that titanium will form eutectic with iron-based or nickel-based alloy mold materials at 980 degrees and 1030 degrees, which will cause strong mold wear.

What are the technical requirements for titanium rods?

Titanium rod has good physical and chemical properties, low density, light weight, non-magnetic, high strength, good corrosion resistance, it has good mechanical properties and welding performance, Baoji titanium rod is widely used in chemical equipment, seawater In desalination, ship parts, electroplating industry, etc., the corrosion resistance of titanium is 10 times that of ordinary stainless steel, and titanium metal is a metal with low human rejection, so the processed parts of medical titanium rods are widely used in human implantation and medical equipment. use. medical titanium bar

skills requirement:

1. The chemical composition of titanium and titanium alloy bars shall comply with the provisions of GB/T 3620.1. When the purchaser re-inspects, the allowable deviation of the chemical composition shall comply with the provisions of GB/T 3620.2.

2. The diameter or side length of the hot-worked bar and its allowable deviation shall comply with the provisions of Table 1.

3. After hot processing, the bar is turned (ground) and cold-rolled. The allowable deviation of the diameter of the cold-drawn bar should meet the requirements of Table 2.

4. The out-of-roundness of the bar that has been turned (ground) after hot processing should not be greater than half of its dimensional tolerance.

5. The indefinite length of the processed bar is 300-6000mm, and the indefinite length of the annealed bar is 300-2000mm, and the fixed or double length should be within the range of the indefinite length.

How to deal with burrs in titanium plate processing

The method of this mechanical treatment is: bury the Grade 1 Pure Titanium Plate in a lot of abrasives, add some grinding and polishing compounds dissolved in water, use the principle of oscillation to mix the abrasives with the material, and continuously ask the workpiece to scour, the surface and edges of the workpiece. Corners, etc. are ground by abrasives and then polished. This technology can be used for deburring, chamfering, rust removal, descaling, flattening and finishing processing for metal parts of various sizes and shapes.

Abrasives can be alumina (including fused, sintered or natural), corundum, plastic, quartz, ceramics, etc., and can be a single species or a mixture of several. The shapes of these abrasives can be made into diagons, cylinders, diamonds, etc. The reason why preformed abrasives are made first is that it is more economical and abrasive than any shape and natural shape materials. According to the shape and size of the workpiece, use abrasives of different shapes and sizes. Rolling abrasives include pumice, quartz, granite leather corners, shells, iron filings and ceramic fragments. The size of the abrasive particles should be larger or smaller than each hole in the part. The amount of content in the drum is also an important factor affecting the quality of the agricultural surface of the parts. The number of people in the drum is usually 70% of the drum volume. The solution in the drum should be added to about 95% of the drum volume (note: when adding acidic solution to the drum, you should add enough water first, and then add acid to avoid corrosion of parts during the rolling process, because the time increases , the concentration of the contained solution gradually decreases, and even loses its effect.

The processing time of Grade 7 Titanium Sheet can range from several minutes to several hours. The key is to choose the abrasive, which is determined by experiment. Only in this way can a uniform, bright appearance be achieved. After processing, the workpiece is unloaded together with the abrasive, which is screened by the separator and taken out, and the recovered abrasive can be continuously returned to the machine for processing. Oscillating finishing machine is divided into two categories: single machine and online, which are selected according to production needs.

Application of Titanium in Onshore Oil and Gas Exploration and Development

Oil and natural gas exploration and development can be divided into land mining and offshore mining. The oil and natural gas stored in the crust accounts for roughly 60% on land and 40% offshore. The oil and gas in the offshore crust such as the Bohai Sea and the South China Sea are also exploited. significant.

Before the industrialization and large-scale application of titanium alloys, the commonly used logging instrument casings were made of 45 steel, 40Cr steel, and 30 MoVNb steel, but none of them could meet the needs of modern technical logging, modern high-tech oil and gas exploration And development requires that the metal casing of the logging tool can not only withstand the pressure of > 98 MPa, but also resist the corrosion of underground crude oil and various media, and in the logging, it must also have a small absorption rate of natural gamma rays. , and should not have a shielding effect on the geomagnetic field. From these performance requirements, Ti 15V-3Cr-3Sn-3Al Titanium Strip is good materials for making logging tool housings.

How to use the mechanical and physical properties of titanium in titanium processing

(1) The elastic modulus of titanium is relatively low relative to its tensile properties, so a larger springback allowance must be considered in the pressing and roller operations. It is precisely because of the lower elastic modulus that in order to achieve the same degree of stability, the cross-section of the titanium part is slightly larger than that of the same steel part.

(2) Titanium is easy to machine, but considering its seizure tendency (larger than stainless steel) and low thermal conductivity, it is necessary to appropriately improve the commonly used machining technology and the design of threads and bearing surfaces. At least a rigid machine tool, a sharp tool, a slow speed, a large amount of cutting, and room for chip removal are also recommended. It is also recommended to use a large amount of cooling lubricant.

(3) The thermal expansion coefficient of titanium is 75% of that of carbon steel. Special attention should be paid to this when combining these two materials in equipment design and manufacture.

(4) Since titanium is an active metal, when heated to above 600 °C, it is easy to combine with oxygen in the air, so it is generally not recommended for long-term use of Titanium Alloy Threaded Rod above this temperature.

(5) When the temperature of industrial pure titanium exceeds 150~200℃, the mechanical strength decreases rapidly.

(6) The diffusion rate of hydrogen in titanium exhaust flange is faster than that of oxygen, so before hot working, the heating furnace used should have a slightly oxidizing atmosphere, so that although a relatively thin oxide film will be produced, it avoids the possible damage caused by hydrogen. Deep pollution.

(7) The softer industrial pure titanium plate is easy to be cold formed after annealing treatment; the harder industrial pure titanium and Ti2.5Cu require medium temperature processing, and the processing temperature for Ti6Al4V is preferably 600~700℃.

(8) Composite plates can be obtained by explosive welding of thin titanium plates and thick steel plates, which can be used to manufacture high-pressure, high-temperature vessels and heat exchangers. But it is not economical to use it to replace the whole titanium or the titanium lining plate of the suit.

Technical extrusion characteristics of titanium screw hydrostatic

Hydrostatic extrusion technology has a history of nearly a hundred years. However, in the process of large-scale and industrialization, the development speed has been slowed down due to the limitation of higher-strength structural materials. The practical application of this technique has been facilitated with advances in materials science. The use of hydrostatic extrusion technology to extrude Titanium Hex Nut has outstanding advantages. In recent years, superconducting materials have developed in the direction of large sections. Due to the increasingly high requirements for continuous steepness, the size and weight of the ingot must be increased. In this way, it is difficult to use ordinary extrusion equipment, and the use of hydrostatic extrusion technology has many advantages.

During metal processing, it is desirable that the workpiece be in a state of triaxial compressive stress, as this facilitates the plastic deformation of the metal and eliminates surface cracks and defects in the product. In addition, it is also required to be in a good lubrication state during processing to reduce the loss of function. If the hydrostatic extrusion technology is used, the above two purposes can be met.

1. The hydrostatic extrusion of Titanium Elbow is in the process of frictionless deformation. The friction between the ingot and the extrusion cylinder is the main obstacle to metal deformation. When hydrostatic extrusion is used, the high-pressure liquid separates the ingot from the wall of the extrusion cylinder, and at the same time, some high-pressure liquid enters the die hole, and the extruded product is also separated from the die wall. Therefore, the friction coefficient can be as low as 0.01 or less, which also greatly reduces the power loss and improves the surface accuracy of the product.

2. Increase the length of the bad ingot of the titanium screw In the traditional extrusion method, 50% of the extrusion force is used to overcome the friction force between the ingot and the extrusion wall. The magnitude of the friction force is proportional to the toughness of the ingot. Therefore, the length of the ingot is limited. If hydrostatic extrusion is used, it is in a frictionless extrusion process, therefore, the length of the ingot can be increased. For example, for the same tonnage extruder, the output of hydrostatic extrusion can be more than three times higher than that of ordinary extrusion.

Application of Titanium in Pharmaceutical Industry

The pharmaceutical industry is an important industry related to people's physical and mental health, including pharmaceuticals, medical machinery, sanitary materials and other fields, and occupies an important position in the national economy. Grade 1 Pure Titanium Plate is widely used in the pharmaceutical industry because it is non-toxic and harmless, and has good compatibility with the human body.

In pharmaceutical production, because the production of drugs is inseparable from acids, alkalis and salts, pharmaceutical equipment is easily damaged by corrosion. The use of steel equipment not only cannot solve the problem of serious equipment corrosion, but also causes a lot of loss of human, material and financial resources, affecting normal production. The use of titanium welding filler wire solves this problem very well.

The processing flow of titanium rod from sponge titanium to rough is as follows:

(1) Compression electrode, the sponge titanium is pressed through a press to form a dense sponge titanium pressed block electrode

(2) Vacuum casting, under the conditions of 1700~1800℃ and -103pa, the above-mentioned sponge titanium pressed block electrode is vacuum casting three times;

(3) Open the billet. Under the condition of 1000 ℃, the billet is opened by the hydraulic press, and the Z is finally pressed into a square billet; when the billet is opened, it should be noted that the life of the titanium rod is reduced due to the high pressure, so when the closed die F9 Titanium Forging method is used. When forging titanium rods, closed die forging must strictly limit the volume of the original blank, which complicates the preparation process. Whether to use closed die forging or not, it must be considered in terms of interest and process feasibility. During open die forging, the loss of burrs accounts for 15%-20% of the weight of the blank. The technological waste of the clamping part (if necessary to keep this part according to the die Titanium Threaded Forged Fitting conditions) accounts for 10% of the weight of the blank. The relative loss of burr metal is usually The weight of the blank has been reduced and increased. Some forgings with asymmetric structures, large cross-sectional area differences, and difficult to fill local forgings. The burr consumption can be as high as 50%. Closed die forging has no burr loss, but the blanking process is complicated and needs to be added. More transitional grooves will undoubtedly increase auxiliary costs.

(4) For the first rolling, under the condition of 970~980℃, the roughness of cylindrical shape is initially rolled by a rolling mill

(5) The second rolling, under the condition of 950 ℃, use a rolling mill to make a blank. There are many rolling methods, which can be classified according to different characteristics. Extrusion is classified according to the characteristics of metal flow and deformation, including forward extrusion, reverse extrusion and special extrusion. Special extrusion includes hydrostatic extrusion, continuous extrusion, lateral extrusion, co-extrusion, compound extrusion, sheath extrusion, peeling extrusion, water-sealed extrusion, bitter die extrusion, powder extrusion, semi-extrusion Melt extrusion, liquid extrusion, etc. Extrusion is classified by temperature, including hot extrusion, warm extrusion and cold extrusion. Hot extrusion and cold extrusion are the two major branches of extrusion. Hot extrusion is mainly used in metallurgical industry systems, which is commonly known as extrusion; cold extrusion is used in mechanical industry systems; the development of warm extrusion is relatively late, and the scope of application is also small.

The influence of laser welding on the surface treatment of titanium rods!

The process parameters of laser welding are difficult to grasp, because the thermal efficiency fluctuates greatly during the welding process, and the surface condition of the welded titanium rod has a great influence on the thermal efficiency: the brighter the surface, the larger the emitted laser light, and most of the laser energy is reflected to other objects , In the form of "heat" to the surrounding materials or media. But the thermal efficiency will suddenly change. Before the titanium metal rod is melted, only about 10%-20% of the light energy is absorbed by the astm b348 titanium rod and heats the titanium metal rod. When the temperature rises to the melting point of the weld metal and starts to melt, the light absorption rate of the titanium metal rod increases sharply . The titanium rod company tells you that at this time, about 60%-80% of the light capacity is absorbed by the metal, and the sudden change in the thermal effect can easily cause the weld to burn through.

In order to avoid or reduce this adverse effect, that you can take corresponding measures, such as welding Grade 1 Titanium Bar; roughening the surface, using pulsed laser beams; adjusting the input energy; adjusting the spot size; changing the attenuation wave Pulse width and steepness.

A natural ruby ​​crystal containing aluminum oxide and dissolved in a low concentration of chromium atoms is used as the working material of the laser generator, which is called a solid-state laser generator. If CO2 is used as the working substance of the laser generator, it is called the force gas laser generator.

At present, the power of the laser welding machine is only kilowatts, and the price is expensive, the welding cost is high, and the application range is not wide. It is only used for the solder joints of some small parts in the manufacture of some instruments and meters, especially when some solder joints are hidden and cannot be welded by ordinary welding methods. Multi-station welding can be realized by using laser beam, optical fiber and deflection prism.

Correction process for internal defects of titanium alloy pipes and titanium pipe welds

The internal shortcomings of Titanium Alloy Seamless Rectangular Tube welds, lack of penetration, refers to a defect in which the workpiece and the weld metal or the part between the weld layers are not fused. Incomplete penetration weakens the welding seam working section, constitutes severe stress concentration, greatly reduces the joint strength, and it often becomes the source of weld cracking. There is non-metallic slag in the slag inclusion weld, which is called slag inclusion. The slag inclusion reduces the working section of the weld, and constitutes a stress concentration, which will reduce the strength and impact toughness of the weld.

When the pore weld metal absorbs too much gas (such as H2) or the gas (such as CO) generated by the internal metallurgical reaction of the molten pool at high temperature, it is too late to be discharged when the molten pool is cooled and condensed and is formed inside or on the outside of the weld Holes are pores. The existence of pores reduces the useful working section of the weld and reduces the mechanical strength of the joint. If there are penetrating or continuous pores, it will severely affect the tightness of the weldment. During or after welding, cracks in the metal part of the welded joint area are called cracks. Cracks can occur in the weld, and can also occur in the heat-affected zone on both sides of the weld. Sometimes it occurs on the outside of the metal, and sometimes inside the metal.

Usually, according to the mechanism of crack occurrence, it can be divided into two types: hot crack and cold crack. Thermal cracks occur during the crystallization process from liquid to solid in the weld metal, and most of them occur in the weld metal. The main reason for its occurrence is the presence of low melting point substances (such as FeS, melting point 1193°C) in the weld, which weakens the contact between the grains. When subjected to greater welding stress effects, it simply causes cracks between the grains. . When the weldment and electrode contain a lot of impurities such as S and Cu, thermal cracking simply occurs. Thermal cracks have the characteristic of spreading along the grain boundary. When the crack penetrates the surface and communicates with the outside, it has a significant hydrogenation tendency. Cold cracks occur during the cooling process after welding, mostly on the base metal or the fusion line between the base metal and the weld. The primary reason for this is that the quenching arrangement is formed in the heat-affected zone of the weld. Under the effect of high stress, it causes cracks in the crystal grains. When welding easy-quenchable ASTM B861 25*1.2mm Titanium Tube For Chemical with high carbon content or more alloying elements, The most prone to cold cracks. Too much hydrogen melted into the weld can also cause cold cracks. Cracks are one of the riskiest shortcomings. In addition to reducing the load-bearing section, severe stress accumulation will occur. During use, the cracks will gradually expand and eventually cause damage to the components. Therefore, such shortcomings are usually not allowed in the welding layout. 

Drilling of titanium alloy

When drilling titanium alloys, it is easy to generate long and thin curled chips. At the same time, the drilling head is large, and it is easy for the chips to accumulate excessively or stick to the drilling edge. This is the main reason for the difficulty in drilling Grade 9 Ti3Al2.5V Titanium Pipe. Use short and sharp drills and low-speed forced feed for drilling. The support brackets must be tightened and adequately cooled repeatedly, especially for deep hole drilling. During the drilling process, the drill bit should be kept in the drilling state and not allowed to run idly in the hole, and the drilling speed should be kept at a low and constant speed. Drill through holes carefully. When it is about to drill through, in order to clean the drill bit and drill hole, and remove drill chips, it is best to return the drill bit, and use forced feed when the hole is finally broken, so that a smooth hole can be obtained.

The occurrence of cracks in the titanium plate and the countermeasures

Titanium weld cracks are cold cracks, mainly caused by hydrogen in the weld. The main sources of hydrogen are moisture and oil in the grade 5 titanium plate and surgical medical titanium wire, and environmental humidity is the main reason for the increase in hydrogen in the weld.

Under the action of high temperature during welding, a large amount of hydrogen is dissolved in the molten pool. During the cooling and solidification process of the weld, due to the rapid decrease in solubility, hydrogen easily escapes. If the welding seam cooling rate is too fast, the hydrogen will not escape and remain in the welding seam, which will make the hydrogen in the welding seam supersaturated, so the hydrogen must be diffused as much as possible and promote the further embrittlement of this area.

If there is a notch effect in this part and the hydrogen concentration is high enough, cracks may occur. Especially in winter construction, the ambient temperature is low, and water vapor adheres to the titanium plate, creating conditions for hydrogenation of the weld. Because the titanium plate is too thin (1.2mm), the steel plate "eats warm" and the temperature rises slowly, and the corresponding titanium composite layer welding seam cools too fast. During the cooling process, the residual hydrogen in the welding seam is too late to escape. It exists in the form of supersaturation in the weld, which eventually leads to the appearance of cracks.

Therefore, during the welding process of the titanium steel clad plate, the surface of the base material and welding wire must be carefully cleaned, and the ambient temperature must not be lower than 5°C. During winter construction, flames are used to preheat the base steel surface, one is to remove the moisture around the weld; the other is to increase the temperature of the weldment and reduce the cooling rate of the weld.

Processing and preservation corrosion problems of titanium alloy fasteners

In the machining and production process of titanium alloy fasteners, because the degree of tightness of the mechanical parts is relatively not so high when the fasteners are installed, it is easy to produce a certain gap, so that there will be a surface between the metal gaps. Paint flows in, which makes the fasteners susceptible to corrosion during the production process. In the subsequent use process, the tightness of the connection will be affected. The high corrosion resistance of titanium alloy materials is due to the presence of oxygen in the air. After the Titanium Wing Nut and oxygen undergo an oxidation reaction, a protective film is formed on the surface. This layer of film can effectively protect the titanium alloy inside the material from being oxidized, thereby improving the corrosion resistance of the titanium alloy material. However, in the actual machining process of titanium alloy fasteners, due to the constant changes in the environment, including the temperature and humidity of the surrounding environment, and the oxidation of equipment during the processing, it will lead to titanium alloy fasteners. Corrosion is easy to occur, which is one of the problems that titanium alloy fasteners are prone to in the production process.

Analysis of Weldability of Titanium

Titanium has the characteristics of corrosion resistance, low thermal conductivity, and good heat resistance. It is a good choice for condenser tubes in power plants. At the same time, titanium has high chemical activity, which makes it suitable for welding seams and welding. The dirt on the surface of the material is very sensitive, and preparations must be made before welding, and strict purity inspection of the welding shielding gas must be carried out to minimize the moisture content in the shielding gas.

Good corrosion resistance

Titanium is a very active metal, its equilibrium potential is very low, and the thermodynamic corrosion tendency in the medium is high. But in fact, titanium is very stable in many media. For example, titanium is corrosion-resistant in oxidizing, neutral and weak reducing media. This is because titanium exhaust flange and oxygen have a great affinity. In the air or in an oxygen-containing medium, a dense, strong adhesion and an inert oxide film are formed on the surface of titanium, which protects the titanium matrix from corrosion. Even due to mechanical wear, it will quickly heal itself or regenerate.

This shows that titanium is a metal with a strong tendency to passivation. The medium temperature of titanium is below 315 ℃, and its oxide film always maintains this characteristic.

Low thermal conductivity

The thermal conductivity of titanium is small, 1/5 of low carbon steel and 1/25 of copper.

Good heat resistance

The new titanium alloy can be used for a long time at a temperature of 600°C or higher.

Welding characteristics of titanium

At room temperature, due to the extremely dense surface passivation layer, titanium is very stable. However, as the temperature rises, its absorption capacity for oxygen, hydrogen and nitrogen continues to increase. In the atmosphere, titanium starts to absorb hydrogen at 250 ℃, oxygen at 400 ℃, and nitrogen at 600 ℃. After these elements are absorbed by titanium, it will obviously increase the hardness of titanium and cause embrittlement, which will affect the performance of titanium metal. Therefore, in the welding process, effective protective measures must be taken to avoid air pollution and the effects of oxygen and nitrogen. Before welding, it must be ensured that there is no grease or other hydrocarbons on the surface of the welded metal.

In addition, iron has a great influence on Grade 5 Ti-6Al-4V Titanium Plate. Iron ions are easy to form titanium-iron compounds in titanium, form galvanic cells in the welding area, corrode the oxide film on the surface of titanium metal, and leave opportunities for hydrogen to enter and cause hydrogen embrittlement.

Due to the high melting point, large heat capacity, and poor thermal conductivity of titanium, the weld and heat-affected zone are easy to grow grains under the action of the welding thermal cycle, which reduces the plasticity and toughness of the welded joint. If larger process parameters are used, the crystal grains will be coarser, so low current process parameters should be used and the interlayer temperature should be controlled.

What are the precautions for titanium tube processing?

1. When installing titanium and titanium alloy pipes, please pay attention not to contact or collide with iron materials when transporting and storing titanium and titanium alloy pipes.

2. The cutting of titanium and titanium alloy pipes should be made by mechanical methods, and the cutting speed should be low; when titanium welded pipes are cut or reground with grinding wheels, special grinding wheels should be used; flame cutting should not be used. The groove should be processed by mechanical methods.

3. Inert gas shielded welding or vacuum welding should be used for welding titanium and titanium alloy pipes. Oxygen-acetylene welding or carbon dioxide gas shielded welding should not be used, and ordinary manual arc welding should not be used.

4. When installing titanium and Grade 9 Ti3Al2.5V Titanium Tubes, it is not allowed to use iron tools and materials to knock and squeeze; rubber or soft plastic plates should be padded between the carbon steel supports and hangers and the titanium and titanium alloy pipes to make them Do not directly contact with titanium and titanium alloy pipelines; when the titanium and titanium alloy pipelines pass through walls and floors, casings should be installed, the gap should not be less than 10mm, and the insulation should be filled. The insulation should not contain iron impurities.

5. Titanium and titanium alloy pipes are not suitable for direct welding connection with other metal pipes. When the connection is required, a loose flange connection can be used. The non-metallic gaskets used are generally rubber gaskets or plastic gaskets, and the chloride ion content should not exceed 25ppm.

Welding conditions of titanium screws

What are the welding conditions for titanium metric screws? Industrial titanium screws can be welded by contact welding without special preparation. When there is a relatively thick oxide film, it needs to be cleaned mechanically or removed in a 5% hydrofluoric acid solution.

Arc welding of titanium screws is carried out in clean gas, and direct current can be used to achieve better results. At this time, the tungsten electrode is the cathode.

The direct welding of titanium screws with nickel, Bromo-chromium alloys, and other nickel-containing alloys is not suitable because of the formation of harmful fusible eutectics. Between materials of different properties, molybdenum, tantalum, or niobium spacers with a thickness of fifteen to twenty microns are required. This method can eliminate the contamination of the connection area by other elements because the dissolution process does not require special solder and pre-metallization. It can obtain a high-quality vacuum dense connection, this method is promising for titanium screws.

Application of titanium alloy materials in the fields of offshore oil drilling and ocean thermal energy conversion

In ocean engineering, titanium and titanium alloy materials are used in seawater desalination, oil and ocean drilling, and ocean thermal energy conversion power stations.

1) Seawater desalination.

There are many methods of seawater desalination. At present, evaporation methods are mostly used in the world. Among them, the multi-stage rapid evaporation method (MSF) used accounts for 67%. Because seawater is very corrosive to the tube material under the conditions of high temperature and high flow rate, many tubes, Especially the tubes of the heating part are mostly made of titanium alloy materials (such as titanium tubes).

2) Offshore oil drilling.

On the ocean platform. Grade 9 Ti3Al2.5V Titanium Pipe is used to make condensing pipes and heat exchange pipes, pumps, valves, pipe fittings, etc. of closed-cycle engines; in deep-sea drilling and production of subsea oil, it is used as riser pipes, pre-stressed pipe joints, fixtures and accessories.

3) Ocean thermal energy conversion project.

In an ocean thermal energy conversion power station, the power system, especially the heat exchanger, is the equipment with the highest metal usage rate. Since the overall cycle efficiency is low, the heat exchanger must be large. The design principle of power station system should be long life (up to 30 years) and low maintenance. Therefore, when selecting materials, materials and manufacturing costs and corrosion properties of materials must be considered comprehensively. titanium heat exchanger tube is undoubtedly the most competitive material. In addition, in terms of geothermal energy, titanium is widely used due to its corrosion resistance to sea water, sulfur-containing gases, chlorides, etc., and the advantages of high specific strength.