Why do we need to carburize the surface of titanium alloy wire?

The excellent characteristics of titanium make its use continue to expand, and the demand for high-quality titanium pipes is also increasing. In the past, the thin titanium pipe processing methods mostly used the die drawing method, and there was fierce friction between the titanium pipe and the mold. The surface of the titanium tube is ablated and bonded, and the dimensional tolerances are difficult to control. In order to prevent these ills, it is usually necessary to perform oxidation treatment on the titanium material to form an oxide film on the surface for lubrication, and the amount of processing after each oxidation treatment It should not be too large, the oxide film is very hard, it is easy to cause mold wear, and there are problems in product size and surface quality. Therefore, it is eager to develop low-cost and high-quality titanium thin titanium tube processing methods.

According to the rolling theory of titanium tubes, the Q value (the ratio of the relative wall reduction to the relative reduction in diameter) has a great influence on the inner surface quality of the tube during the rolling process. In the three-roll rolling process, for a certain pass, after flaw detection and sampling to observe the cross-section, to ensure that there are no cracks on the inner surface, different Q values ​​(0.87, 1.00, 1.26) are selected for rolling. In the middle pass, ultrasonic flaw detection is performed on the pipe, and the cross section is sampled and observed to ensure that there are no cracks on the inner surface before proceeding to the next rolling. Results When the Q value was 0.87, the inner surface micro-cracks were very shallow, with a depth of about 5 μm, and there were fewer cracks; when the Q value increased to 1.26, the inner surface micro-cracks depth reached 50 μm. The micro-cracks appearing on the inner surface of the pipe are mainly due to the three-roll rolling that reduces the diameter first and then reduces the wall. The reduction is large and the reduction is too small, which causes the accumulation of materials during the reduction process and the formation of longitudinal micro-cracks on the inner surface. Therefore, when rolling titanium alloy pipes with a three-high rolling mill, the Q value should not exceed 0.87, otherwise cracks are prone to appear on the inner surface of the pipe.

During the cold-rolling process of small-size thick-walled titanium alloy pipes, micro-cracks are prone to occur on the inner and outer surfaces. The microcracks on the outer surface are usually removed by grinding and scraping, and the effect is very good; for the microcracks on the inner surface, in the industrial production process, the main method of boring is used to remove the inner hole larger than 13mm, and the inner hole smaller than 13mm Generally, no treatment is required, so the internal surface quality control is difficult.

(1) When rolling small-size thick-walled titanium alloy pipes, the deformation of the two-roll billet rolling is selected at 39%, and the inner and outer surfaces of the pipe are of better quality.

(2) When three-roll cold-rolling small-size thick-walled titanium alloy pipes, the Q value should not exceed 0.87, which can ensure that the inner surface of the pipe has a good quality and no cracks. Considering the good match of strength and plasticity, the deformation of three-roll rolling is selected at 30%, which can obtain better mechanical properties and microstructure.

(3) In the rolling process of titanium alloy pipes, for every 1 to 2 passes of rolling, degreasing, pickling, annealing, and straightening are performed, and then sandblasting + pickling is used to remove internal surface cracks. . Taking this measure can increase the flaw detection qualification rate of finished pipes to 35%-40%.

The microstructure of the finished pipe after being vacuum annealed at 750℃ under the conditions of 25%, 30%, 36% rolling deformation. It can be seen that the microstructure of the annealed titanium alloy tube is an equiaxed structure. As the amount of deformation increases, the degree of recrystallization becomes more complete and the crystal grains become finer. The room temperature mechanical properties of the finished pipe after vacuum annealing at 750℃ under the conditions of rolling deformation of 25%, 30%, and 36%. It can be seen that when the deformation is 25%, the yield strength of the finished pipe is 550MPa, the tensile strength is 675MPa, the elongation is 15.5%, and the elongation is slightly higher than the standard required value of 15%; when the deformation is 30%, the resistance The tensile strength is 670MPa, the yield strength is 535MPa, and the elongation is 17%; when the deformation is 36%, the tensile strength is 640MPa, and the yield strength is 517MPa, which is slightly higher than the standard required value of 515MPa, and the elongation reaches 19%. Considering the good match of strength and plasticity, comparing the mechanical properties and microstructure under different deformation conditions, it is reasonable to select 30% for the rolling deformation of the finished pipe.
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Treatment method of titanium tube surface

Titanium alloy screws are prone to rust when exposed in the air, so titanium alloy screws need to be moisture-proof and moisture-proof:

1. The choice of component insulation impregnating varnish, such as epoxy resin or polyurethane impregnating varnish. Choose paint that does not contain volatile acids. The vibration machinery uses solvent-free paint.

2. For the use of titanium alloy screw melamine alkyd paint, the curing temperature and curing time should be adjusted. The curing temperature is slightly higher than 130 degrees Celsius and the curing time is greater than 180 minutes. It is appropriate to implement the process strictly, especially in the hot and humid seasons. Because of the concept of rust and rust, the conventional drying time of the sample paint factory is not necessarily abundant, and cars have a specific internal shape.

3. Surface corrosion treatment of titanium alloy screws refers to the use of various methods to maintain the metal surface. The role is to isolate the metal from the corrosive environment to inhibit the corrosion process, reduce the contact between corrosive media and the metal surface, and achieve the purpose of preventing or slowing down corrosion.

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Do you know what factors are related to the quality of titanium plate?

The unique properties of titanium make it an excellent material for making bicycle frames. Its high strength, low density, and low modulus of elasticity (the modulus of elasticity can be regarded as an index to measure the degree of ease of elastic deformation of the material), excellent Fatigue resistance and corrosion resistance make the titanium alloy frame not only very strong and durable, but also very light.

Titanium materials will not break, will not rust, and will not corrode in any atmospheric environment. Titanium is so resistant to corrosion that it doesn't even need any paint treatment. We just lightly rub its surface to brighten its natural color, and the titanium color can better reflect the low-key and luxurious texture of this metal.

Titanium has an inherent flexibility like steel, but this characteristic of titanium is more obvious. Therefore, it has a very slight elasticity, which means that it can absorb vibrations from the road surface. Before it is transmitted to the rider, (the titanium seatpost can also eliminate some vibrations) will have a very smooth riding feeling.

Unlike aluminum or carbon bicycle frames, titanium bicycle frames will not break suddenly in an accident. This is because, like steel, it has a certain degree of flexibility. (In fact, titanium is more flexible than steel, which is why its riding quality is so famous.) It is more like steel because it has incredible strength; but it is much lighter than steel, and less rust.

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The difference between manual and machine polished titanium rods

Titanium is a very corrosion-resistant metal. The thermodynamic data of titanium shows that titanium is a very thermodynamically unstable metal. If titanium can be dissolved to generate Ti2+, its standard electrode potential is very negative (-1.63V), and its surface is always covered with a passive oxide film. In this way, the stable potential of titanium is stably biased to a positive value. For example, the stable potential of titanium in seawater at 25°C is about +0.09V. In chemistry manuals and textbooks, standard electrode potentials corresponding to a series of titanium electrode reactions can be obtained. It is worth pointing out that, in fact, these data are not directly measured, but often can only be calculated from thermodynamic data, and due to different data sources, several different electrode reactions may be displayed at the same time, and different data may not appear. Strange.

The electrode potential data of the electrode reaction of titanium shows that its surface is very active, and is usually always covered with an oxide film that is naturally formed in the air. Therefore, the excellent corrosion resistance of titanium stems from the existence of a stable, adherent, and particularly protective oxide film on the surface of the titanium. In fact, it is the stability of this natural oxide film that determines the titanium surface. Corrosion resistance, including titanium and titanium alloy titanium rods, titanium wires, titanium plates, etc., have strong corrosion resistance. Of course, the corrosion resistance of various grades is different. We talked about it in the previous content of the website I won’t say much today. In theory, the P/B ratio of a protective oxide film must be greater than 1. If it is less than 1, the oxide film cannot completely cover the metal surface, so it is impossible to protect it. If this ratio is too large, the compressive stress in the oxide film will increase correspondingly, which will easily cause the oxide film to rupture, and it will not provide protection. The P/B ratio of titanium is between 1 and 2.5 depending on the composition and structure of the oxide film. From this basic point of analysis, the titanium oxide film can have better protective properties.

When the surface of titanium is exposed to the atmosphere or aqueous solution, a new oxide film will be automatically formed immediately. For example, the thickness of the oxide film in the atmosphere at room temperature is 1.2~1.6nm, and it will thicken with time, and it will naturally increase to 5nm after 70 days. Gradually increase to 8-9nm after 545 days. Artificially intensified oxidation conditions (such as heating, using oxidants or anodic oxidation, etc.) can accelerate the growth of the surface oxide film and obtain a thicker oxide film, thereby improving the corrosion resistance of titanium. Therefore, the oxide film formed by anodic oxidation and thermal oxidation will significantly improve the corrosion resistance of titanium. Now our customers have made many similar products with our titanium rods and wires, which shows that this is a feasible way.

Titanium oxide film (including thermal oxide film or anodic oxide film) is usually not a single structure, and its oxide composition and structure vary with the production conditions. Under normal circumstances, the interface between the oxide film and the environment may be TiO2, but the interface between the oxide film and the metal may be dominated by TiO. In other words, the surface of the titanium rod we produce is TiO2 under normal conditions, and the interface between the metal and the oxide film is TiO. Of course, the titanium wire, titanium plate, and titanium forgings are the same here, and the surface of the titanium alloy rod is more complicated. However, whether it is a pure titanium rod, a titanium alloy rod, or a titanium alloy wire, there are transition layers with different valence states in the middle, and even non-chemically equivalent oxides, which means that the oxide film of titanium materials has a multilayer structure. As for the formation of this oxide film, it cannot be simply understood as a direct reaction between titanium and oxygen (or oxygen in the air).

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What are the defects that occur when producing titanium plates?

At present, the smelting method widely used in my country's industry is the vacuum consumable electrode arc smelting method. Although it can effectively ensure that the alloy liquid has a certain degree of superheat and a more accurate alloy melt composition, this method has extremely high requirements for the quality of the raw electrode, and the surface area of ​​the molten pool is large and the depth is small, resulting in high vapor pressure elements (such as A1 The volatilization loss of the element) is very large, which is unfavorable for controlling the alloy composition.

The water-cooled copper crucible induction smelting method is to place a copper crucible that is split and cooled by water under an induction electromagnetic field for smelting, which can maximize the advantages of the induction smelting method. Between the water-cooled copper crucible and the metal melt, there is a solid shell layer produced by the solidification of the Gr5 Ti-6Al-4V Titanium Foil melt, the so-called condensed shell. At this time, the crucible lining is equivalent to being made of molten metal, that is, the inner surface of the crucible has the same composition as the molten metal, which prevents the crucible from contaminating the molten metal. With the increase in the number of cold crucible combinations and the input power of the power supply, the strong magnetic field promotes the rapid melting of the charge and produces a strong stirring effect, so that the temperature and composition of the metal melt are uniform, and a consistent degree of superheat can be obtained. Due to the complex composition of the new  Grade 7 Titanium Rod alloy and TiAl compound alloy, the allowable deviation of the alloy element content is small, it is difficult to meet the requirements of the alloy composition by the common arc melting method of ASTM F136 6Al-4V ELI Titanium Bar alloy. Water-cooled crucible induction condensed shell melting is particularly suitable for this work. The molten alloy composition is uniform, and the superheat of the alloy liquid with the interstitial element content is appropriate, which meets the requirements of static and centrifugal casting.

What should be paid attention to when processing titanium rods

With the change in people's understanding of bicycle functions, especially the increasingly fierce international bicycle competition, bicycle manufacturers continue to seek new materials with lightweight and high strength, so titanium has become their target of attention.

At that time, the processing and welding technology for the production of bicycle titanium parts had not been up to date, and mass production capacity could not be formed. After entering the 1980s, with the continuous advancement of science and technology, various bicycle iron parts came out one after another, which promoted the use of titanium for bicycles.

The application status of titanium in the bicycle industry

According to the functions of each part of the bicycle, the bicycle can be divided into 13 parts, namely, the body part, the control part, the drive part, the walking part, and the transmission part. Braking part, seat part, loading part, parking part, alarm part, lighting part, accessories, and connecting parts. The car body includes the frame, the front car, the front, the suspension, the valve seat, and the mudguard. This part accounts for about 27% of the car's weight in terms of its weight. The driving part includes a sprocket, a crankshaft, a pedal, a chain, a flywheel, and a chain box. This part accounts for about 22% of the car's weight. The walking part includes tires, inner tubes, rims, spokes, and wheels, which account for about 24% of the total weight of the bicycle. It can be seen that the total weight of the three parts of the car body, the driving part, and the walking part account for more than 70% of the total weight of the bicycle.

Therefore, the issue of titanium materialization aimed at reducing the weight of bicycles first started here, and after more than 10 years of development and research, some of the human components have been made of titanium material.
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Method for using titanium plate in power industry

In the welding of titanium alloy pipes, the welding depth is determined by the thickness of the titanium alloy pipe. The production goal is to improve the formability of the titanium alloy tube by reducing the welding width, while achieving a higher speed. Therefore, when choosing the most suitable laser, we must not only consider the quality of the beam, but also the accuracy of the tube mill. Because the dimensional error of the pipe rolling mill takes effect, it is necessary to consider the limitation of reducing the light spot.

There are many unique dimensional problems in the welding of titanium alloy pipes. However, the main factor that most affects the welding is the seam on the welding box, because once the titanium plate is formed and prepared for welding, the characteristics of the weld include: Titanium plate gap, severe/minor welding dislocation, change of weld centerline. To a certain extent, the gap determines how much material is used to form the weld pool. Too much pressure is likely to cause excess material on the top or inner diameter of the titanium alloy welded pipe. , Or serious slight welding misalignment will lead to beautiful welding appearance.

In both cases, after the titanium plate is cut and cleaned, it is rolled up and sent to the welding point. Coolant is used to cool the induction coil used in the heating process. Some coolant will be used in the extrusion process. A lot of force is exerted on the squeeze pulley to prevent us from creating porosity in the welding area; however, using a larger squeeze force will result in a sharp increase in burrs (or weld beads). Therefore, a specially designed cutter is used to remove some burrs inside and outside the pipe.

One of the main advantages of the high-frequency welding process is that it can process titanium tubes at high speed. However, a typical situation in most solid phase forging joints is that it is not easy to perform reliable tests on high-frequency welded joints if traditional non-destructive techniques are used. Welding cracks are likely to appear in the flat and thin areas of the low-strength joints. The cracks cannot be detected using traditional methods. They may lack reliability in some demanding automotive applications.

In all titanium pipe welding applications, the edges of the titanium plate are melted, and when the edges of the titanium alloy pipe are squeezed together with the clamping bracket, solidification occurs at the edges. However, titanium alloy tube has high energy beam density for laser welding. The laser beam not only melts the surface of the material, but also creates a keyhole, which makes the weld seam very narrow. The welded titanium alloy tube first forms a flat titanium plate, and then makes its shape into the shape of a round tube. Once formed, the seams of the titanium alloy tube must be welded together. This weld affects the formability of the part. Therefore, in order to meet the strict test requirements and welding profile in the manufacturing industry, it is extremely important to select the appropriate welding technology. Gas tungsten arc welding (GTAW), high frequency (HF) welding, and laser welding have been applied in the manufacture of titanium alloy tubes.
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