Hvordan svejser man titanium?
Titanium alloy has low density, high specific strength, good corrosion resistance, low thermal conductivity, non-toxic and non-magnetic, and can be welded; it is widely used in aviation, aerospace, chemical industry, petroleum, electricity, medical, construction, sporting goods and other fields.
1. Welding features oftitanium.html> titanium and titanium alloy
(1) Embrittlement caused by impurity contamination
Due to the high chemical activity of titanium, under the action of the welding heat cycle, the welding pool and the weld metal and heat-affected zone above 350°C are easily exposed to hydrogen, oxygen, nitrogen in the air and oil stains on the welding parts and welding wires. , moisture, etc. react. Titanium rapidly absorbs hydrogen above 300℃, oxygen rapidly above 600℃, and nitrogen rapidly above 700℃. When the carbon content is high, a network-like TiC brittle phase will appear. The above conditions drastically reduce the plasticity and toughness of titanium and titanium alloy welded joints, causing the performance of the welded joints to deteriorate.
The color of the oxide film formed on the titanium surface is related to the production temperature. It is silvery white below 200℃, light yellow at 300℃, golden yellow at 400℃, blue and purple at 500℃ and 600℃, and different shades of gray at 700~900℃. The temperature of the unprotected area during the welding process can be judged based on the color of the oxide film formed on the surface.
(2) Performance deterioration caused by welding phase change
There are two allotropic crystal structures. Above 882°C to the melting point, it is a body-centered cubic lattice, called beta titanium. Below 882°C, it is a close-packed hexagonal lattice, called α. Titanium for containers contains very few β-stabilizing elements and is all α-iron alloy. When these titaniums are welded at high temperatures, the weld seam and part of the heat-affected zone have a β lattice, and the grains tend to grow rapidly. Titanium also has the characteristics of high melting point, large specific heat capacity, and low thermal conductivity. Therefore, the high-temperature residence time during welding is about 3 to 4 times longer than that of steel, and the high-temperature heat-affected zone is wider, making the beta of the weld and high-temperature heat-affected zone Significant grain growth will cause a greater decrease in the plasticity of the welded joint. Therefore, when welding titanium, smaller welding heat input and faster cooling rate should usually be used to reduce the high temperature residence time and reduce the degree of grain growth. Reduce the high-temperature heat-affected zone and reduce the impact of plasticity decline.
(3) The welding area needs to be protected by inert gas
The affinity for oxygen in the air is very strong at high temperatures, and in areas above 200°C, inert gas protection must be used to avoid oxidation.
(4) Welding deformation is relatively large
The elastic modulus of titanium is only half that of carbon steel. Under the same welding stress, the welding deformation of titanium will be twice as large as that of carbon steel. Therefore, when welding titanium, backing plates and pressure plates are generally used to compress the workpiece to reduce welding deformation.
(5) Easy to produce pores
Porosity is a common defect in welds. The pores produced during titanium welding are mainly hydrogen pores, and there are also pores formed by CO gas.
(6) Possibility of cracks
Titanium contains very little impurities such as sulfur, phosphorus, and carbon that can form low-melting-point eutectics with titanium at the grain boundaries. The effective crystallization temperature range is narrow, and the shrinkage of the weld is small when it solidifies. Therefore, hot cracks in the weld generally do not occur. Cracks in titanium welds are hydrogen refrigeration cracks.
(7) Cannot be welded to steel
The mass fraction of iron dissolved in titanium at room temperature is only 0.05%~0.10%, so titanium and steel cannot be directly welded.
2. Welding methods of titanium and titanium alloys
The main welding methods used when welding titanium and titanium alloys include tungsten arc welding, melting arc welding, plasma arc welding, etc. For welding of sealed structures that do not bear load, brazing or explosion welding can be used Composite welding of titanium and steel composite panels.
3. Titanium and alloy welding materials
(1) Welding wire: Titanium and titanium alloy welding wires are generally selected according to the welding wire corresponding to the base material, but they should also be qualified by the welding process. When selecting welding wire, there is a problem of matching the appropriate welding wire, because the impurity content of the welding wire is only controlled at the upper limit, and in most cases the lower limit is not controlled. The welding wire produced in each batch only guarantees the chemical composition, and does not guarantee the mechanical properties of the welding wire after welding. . There is a possibility that the impurity content in some production batches of welding wire is particularly low and is a qualified product, but the strength of the weld is low and may not meet the lower limit of the standard tensile strength of the base metal in the annealed state. value requirements. At this time, you should change to a welding wire of the same brand in production batches, or even a welding wire with a higher strength (referring to industrial purity), and re-qualify the process until it is qualified, and then you can select the welding wire.
(2) Protective gas Argon is generally used as the protective gas when welding iron and titanium alloys. The purity of argon (volume fraction should not be less than 99.99%), and the volume fractions of other gas components are oxygen less than 0.002% and nitrogen less than 0.002%. 0.005%, hydrogen less than 0.002%, and moisture less than 0.001mg/L. The gas cylinder pressure shall not be less than 0.5MPa. When using, the air in the protective gas system such as gas hoses, welding torches, and drag hoods must be replaced. The protective gas can also be helium or an argon-helium mixture.
(3) Tungsten electrode: Pure tungsten electrode and cerium tungsten electrode are commonly used. Electrodes containing cerium oxide (impurity mass fraction not greater than 0.1%) in pure tungsten are cerium tungsten electrodes. Cerium tungsten electrode has low electron work function, high chemical stability, high allowable current density, no radioactivity, and has better performance than pure tungsten electrode. It is currently the most commonly used tungsten electrode.
4. Preparation before welding
(1) Cleaning before welding. Before welding titanium and alloy weldments and welding wires, oxides, nitrides, oil stains, moisture, etc. on the surface should be carefully removed. Generally, pickling or polishing with grinding wheels and emery cloths is used. For workpieces that are difficult to pickle, such as the longitudinal circumferential welds of containers, fillet welds, and the welding of tubes and plates of heat exchangers, grind both sides of the groove with a grinding wheel and emery cloth, and pay attention to cleaning up the remaining sand and dust. Welding wires, heads, expansion joints and other parts that are difficult to polish should be pickled before welding and rinsed with clean water after pickling. If the weldment cannot be pickled, it can also be scraped with a carbide scraper. After the weldment has been cleaned as above, the area to be welded should be cleaned with acetone, absolute alcohol and other solvents before welding, and the area to be welded should not be touched or re-contaminated with hands. After re-contamination, it should be cleaned and cleaned again.
(2) Preparation of other protection devices in the welding area. When welding titanium and titanium alloys, the welding gun nozzle protects the molten pool, the drag cover protects the front of the cooling welding joint, and the backing plate protects the back of the welding joint. The welding guns used for welding titanium and titanium alloys are different from those used for welding aluminum and stainless steel. Large-diameter nozzles are commonly used. The nozzle diameter is 14 ~ 20mm for manual welding and 16 ~ 22mm for automatic welding. The drag cover can protect welds and heat-affected zones with temperatures above 400°C. The shape and size of the drag cover should be determined by factors such as the thickness of the weldment, cooling method, welding current, and weld shape. The drag cover should be attached to the welding area and move with the welding gun.
A copper backing plate can be used on the back of the weld to accelerate the cooling of the welding area and isolate the air. Protective gas can also be blown into the copper backing plate, or a drag cover can be attached to the back of the weld area to move along with the welding.
Titanium wire categories
Titanium wire "inherits" the advantages of titanium and titanium alloys, and has a series of excellent properties such as good corrosion resistance, high specific strength, non-magnetic, high biocompatibility, low resistance to ultrasonic waves and good shape memory function. . Therefore, titanium and titanium alloy wires are widely used in many fields such as petrochemical industry, medical and health care, automobiles, construction, and sports and leisure products. And in recent years, due to its continuous development, its varieties have become increasingly diverse, which provides more choices for its application in high-performance industrial supplies and consumer goods.
1. At present, more than 80% of titanium and titanium alloy wires are used as welding wires, such as the welding of various titanium equipment, welding of welded pipes, and the welding of casings, etc.
2. Due to its excellent corrosion resistance, titanium wire has been widely used in chemical, pharmaceutical, papermaking and other industries. It can be made into a mesh and used as a seawater filter, pure water filter, chemical filter, etc.
3. Titanium and titanium alloy wires are also used to manufacture fasteners, load-bearing components, springs, etc. due to their good overall properties.
4. In the medical and health industry, due to its excellent biocompatibility, titanium and titanium alloy wires are used to manufacture medical devices, implanted in the human body for dental crown fixation, skull fixation, etc.
5. Some titanium alloy wires with shape memory function, such as titanium-nickel alloy wire, shoulder pads for clothes, women's bras, glasses frames, etc.
6. In the electroplating and water treatment industries, titanium and titanium alloy wires are used to make various electrodes
