Steel tube is used as a structural element in buildings, bridges and other structures, and in a wide variety of manufactured products. It's produced in round, square and rectangular shapes in a broad range of sizes and gauges.
Rectangular tubing has many benefits: aesthetic appeal, high strength-to-weight ratios, uniform strength, cost effectiveness and recyclability.
The advantages for designers, specifies, fabricators and end users are outlined on the
Rectangular tubing has greater strength-to-weight ratios. So, with Rectangular tubing you need less steel, by weight, to do the job. And less weight equals less cost
Excellent compression and support characteristics and superior resistance make Rectangular tubes particularly well suited to all types of column applications
Rectangular steel tube is made from steel, one of the world’s most recyclable and recycled materials
Torsional strength makes steel rectangular tube an excellent choice for bear resistant and consistent.
Rectangular tube is fire resistant and does not warp, twist, split, swell or shrink. It resists dry rot and mildew, termites and carpenter ants. For increased fire resistance, the exterior of the product may be sprayed with a fire retardant material. The interior can be filled with concrete. Tube rectangular can be readily bent, formed, punched, and drilled. New and improved methods to fasten Rectangular tubing to itself or to other materials are making its use simpler and fabrication faster.
2019年7月31日星期三
Precision seamless steel tube extrusion process
Precision seamless steel tubes with conventional technology for the furnace + ESR -> forging or forging billet and rolling way. Product shape round bar, square flat and forgings. Then steam turbine plant for further processing, but the processing process more special shape, metal utilization after processing about 30%. To squeeze mode after production, will have the following advantages:
1, Precision seamless steel tubes in the best state of stress in the hot extrusion process, reducing the product of internal defects.
2, Easy to implement diverse cross-sectional shape, adapt more variety, small batch production.
3, In each direction of performance uniformity.
The main way to produce extrusion process: EAF + ESR -> forging or rolling cogging -> induction heating -> Extrusion -> annealing.
Extrusion and forging, rolling approach is the difference between:
1, Precision seamless extrusion heating temperatures than forging, rolling production is higher 30-60 ℃;
2, Deformation, high speed (deformed steel requires only 2-4S).
3, Multi-step, high metal consumption.
1, Precision seamless steel tubes in the best state of stress in the hot extrusion process, reducing the product of internal defects.
2, Easy to implement diverse cross-sectional shape, adapt more variety, small batch production.
3, In each direction of performance uniformity.
The main way to produce extrusion process: EAF + ESR -> forging or rolling cogging -> induction heating -> Extrusion -> annealing.
Extrusion and forging, rolling approach is the difference between:
1, Precision seamless extrusion heating temperatures than forging, rolling production is higher 30-60 ℃;
2, Deformation, high speed (deformed steel requires only 2-4S).
3, Multi-step, high metal consumption.
2019年7月30日星期二
Martensite: Definition, Transformation & Microstructure
Martensite can be divided into lath martensite and lamellar martensite. When the austenite carbon content is less than 0.20%, the quenched martensite is lath-like. When the austenite has a carbon content of more than 1.0%, it is in the form of a sheet.
Bainite has various histological forms and can be roughly classified into granular bainite, upper bainite and lower bainite according to its metallographic structure.
The first stage of tempering (≤250 ° C): decomposition of quenched martensite;
The second stage of tempering (200-300 ° C): the transformation of retained austenite;
The third stage of tempering (250-400 ° C): the transformation of carbide type;
The fourth stage of tempering (≥400 °C): spheroidization, coarsening of ferrite, recovery and recrystallization of ferrite.
According to the tempering temperature and the corresponding tissue change, the microstructure transformation process of the quenched steel during tempering can be divided into four stages:
1. Tempered martensite - The quenched steel is tempered at 150-250 ° C to form a tempered martensite structure.
2. Tempered tortite - After tempering at 350-450 °C, the quenched steel forms a tempered tortite structure.
3. Tempered Sorbite - After quenching at 500-650 °C, the quenched steel forms a tempered sorbite.
4. Tempered pearlite - quenched steel in the temperature range of 650 ° C - A1 after a long time tempering, that is, the formation of tempered pearlite structure.
Bainite has various histological forms and can be roughly classified into granular bainite, upper bainite and lower bainite according to its metallographic structure.
The first stage of tempering (≤250 ° C): decomposition of quenched martensite;
The second stage of tempering (200-300 ° C): the transformation of retained austenite;
The third stage of tempering (250-400 ° C): the transformation of carbide type;
The fourth stage of tempering (≥400 °C): spheroidization, coarsening of ferrite, recovery and recrystallization of ferrite.
According to the tempering temperature and the corresponding tissue change, the microstructure transformation process of the quenched steel during tempering can be divided into four stages:
1. Tempered martensite - The quenched steel is tempered at 150-250 ° C to form a tempered martensite structure.
2. Tempered tortite - After tempering at 350-450 °C, the quenched steel forms a tempered tortite structure.
3. Tempered Sorbite - After quenching at 500-650 °C, the quenched steel forms a tempered sorbite.
4. Tempered pearlite - quenched steel in the temperature range of 650 ° C - A1 after a long time tempering, that is, the formation of tempered pearlite structure.
Welding gap of welded pipe
The strip steel is sent to the welded pipe unit, and the strip is rolled by a plurality of rolls, and the strip is gradually rolled up to form a circular tube blank having an open gap, and the pressing amount of the pressing roll is adjusted to control the weld gap to be 1 to 3 mm. And make the ends of the solder joints flush. If the gap is too large, the proximity effect is reduced, the eddy current is insufficient, and the weld intergranular joint is poor to cause unmelting or cracking. If the gap is too small, the proximity effect is increased, the welding heat is too large, and the weld is burnt; or the weld is pressed and rolled to form a deep pit, which affects the surface quality of the weld.
1, Welding temperature control
The welding temperature is mainly affected by the high-frequency eddy current thermal power. According to the relevant formula, the high-frequency eddy current thermal power is mainly affected by the current frequency. The eddy current thermal power is proportional to the square of the current excitation frequency; and the current excitation frequency is affected by the excitation voltage. Current and capacitance, inductance.
2, The control of the pressing force
After the two edges of the tube are heated to the soldering temperature, under the extrusion of the pressing roller, common metal crystal grains are mutually infiltrated and crystallized, and finally a firm weld seam is formed. If the pressing force is too small, the number of common crystals formed will be small, the strength of the weld metal will decrease, and cracking will occur after the force is applied; if the pressing force is too large, the molten metal will be extruded out of the weld, not only will it be lowered. The weld strength, but also a large number of internal and external burrs, and even caused by welding seams and other defects.
3. Regulation of the position of the high frequency induction coil
The high frequency induction coil should be as close as possible to the position of the squeeze roller. If the induction coil is far away from the squeeze roller, the effective heating time is longer, the heat affected zone is wider, and the weld strength is decreased; otherwise, the weld edge is insufficiently heated, and the extrusion is poorly formed.
4. The resistor is one or a set of special magnetic rods for the welded pipe.
The cross-sectional area of the resistor is usually not less than 70% of the cross-sectional area of the inner diameter of the steel pipe. The function is to form an electromagnetic induction circuit between the induction ring and the edge of the tube blank and the magnetic rod to genera
te a proximity effect. The eddy current is concentrated in the tube blank weld. Near the edge, the edge of the tube blank is heated to the soldering temperature. The resistor is dragged in the tube blank with a wire, and its center position should be relatively fixed near the center of the squeeze roller. When starting up, due to the rapid movement of the tube blank, the resistor is greatly damaged by the friction of the inner wall of the tube blank and needs to be replaced frequently.
5. After the weld is welded and extruded, it will produce a weld bead and need to be removed.
The cleaning method is to fix the tool on the frame and smooth the welding bead by the rapid movement of the welded pipe. The burrs inside the welded pipe are generally not removed.
1, Welding temperature control
The welding temperature is mainly affected by the high-frequency eddy current thermal power. According to the relevant formula, the high-frequency eddy current thermal power is mainly affected by the current frequency. The eddy current thermal power is proportional to the square of the current excitation frequency; and the current excitation frequency is affected by the excitation voltage. Current and capacitance, inductance.
2, The control of the pressing force
After the two edges of the tube are heated to the soldering temperature, under the extrusion of the pressing roller, common metal crystal grains are mutually infiltrated and crystallized, and finally a firm weld seam is formed. If the pressing force is too small, the number of common crystals formed will be small, the strength of the weld metal will decrease, and cracking will occur after the force is applied; if the pressing force is too large, the molten metal will be extruded out of the weld, not only will it be lowered. The weld strength, but also a large number of internal and external burrs, and even caused by welding seams and other defects.
3. Regulation of the position of the high frequency induction coil
The high frequency induction coil should be as close as possible to the position of the squeeze roller. If the induction coil is far away from the squeeze roller, the effective heating time is longer, the heat affected zone is wider, and the weld strength is decreased; otherwise, the weld edge is insufficiently heated, and the extrusion is poorly formed.
4. The resistor is one or a set of special magnetic rods for the welded pipe.
The cross-sectional area of the resistor is usually not less than 70% of the cross-sectional area of the inner diameter of the steel pipe. The function is to form an electromagnetic induction circuit between the induction ring and the edge of the tube blank and the magnetic rod to genera
te a proximity effect. The eddy current is concentrated in the tube blank weld. Near the edge, the edge of the tube blank is heated to the soldering temperature. The resistor is dragged in the tube blank with a wire, and its center position should be relatively fixed near the center of the squeeze roller. When starting up, due to the rapid movement of the tube blank, the resistor is greatly damaged by the friction of the inner wall of the tube blank and needs to be replaced frequently.
5. After the weld is welded and extruded, it will produce a weld bead and need to be removed.
The cleaning method is to fix the tool on the frame and smooth the welding bead by the rapid movement of the welded pipe. The burrs inside the welded pipe are generally not removed.
Factors affecting the transformation rate of austenite
1, The effect of heating temperature
As the heating temperature increases, the nucleation rate, the growth rate, and the atomic diffusion capacity of austenite increase the formation rate of austenite.
2, The impact of heating speed
As the heating rate increases, the various stages of the austenite formation process move to a higher temperature range. The faster the heating rate, the greater the superheat of the pearlite, the shorter the incubation period of the transition, and the longer the time required for the transformation. short.
3. The influence of the chemical composition of steel
The effect of carbon content of steel
When the carbon content in the steel increases, the total interface of the ferrite and the cementite increases, and the carbon diffusion capacity increases. At the same time, the higher the carbon concentration in the austenite, the faster the diffusion rate of the atom, the austenite The greater the probability of nucleation of the body.
Effect of alloying elements in steel
The alloying elements in steel do not change the general course of austenitization during steel heating, but the alloying elements have a great influence on the nucleation, growth, dissolution of carbides, and austenite homogenization of austenite. .
4. The influence of the original structure of steel
The finer the original structure of the steel, the greater the dispersion of carbides, the smaller the interlamellar spacing of ferrite and cementite, and the more the phase interface, the faster the austenite formation.
http://www.xysteelpipe.com/info/Factors-affecting-the-transformation-rate-of-austenite-1470-1.htm
As the heating temperature increases, the nucleation rate, the growth rate, and the atomic diffusion capacity of austenite increase the formation rate of austenite.
2, The impact of heating speed
As the heating rate increases, the various stages of the austenite formation process move to a higher temperature range. The faster the heating rate, the greater the superheat of the pearlite, the shorter the incubation period of the transition, and the longer the time required for the transformation. short.
3. The influence of the chemical composition of steel
The effect of carbon content of steel
When the carbon content in the steel increases, the total interface of the ferrite and the cementite increases, and the carbon diffusion capacity increases. At the same time, the higher the carbon concentration in the austenite, the faster the diffusion rate of the atom, the austenite The greater the probability of nucleation of the body.
Effect of alloying elements in steel
The alloying elements in steel do not change the general course of austenitization during steel heating, but the alloying elements have a great influence on the nucleation, growth, dissolution of carbides, and austenite homogenization of austenite. .
4. The influence of the original structure of steel
The finer the original structure of the steel, the greater the dispersion of carbides, the smaller the interlamellar spacing of ferrite and cementite, and the more the phase interface, the faster the austenite formation.
http://www.xysteelpipe.com/info/Factors-affecting-the-transformation-rate-of-austenite-1470-1.htm
2019年7月22日星期一
Five Different Heat Treatment Technique
Heat treatment is the process of heating and cooling metals to achieve desired physical and mechanical properties through modification of their crystalline structure. The temperature, length of time, and rate of cooling after heat treatment will all impact properties dramatically. The most common reasons to heat treat include increasing strenght or hardness, increasing toughness, improving ductility and maximizing corrosion resistance.
1. Annealing
Annealing is a rather generalized term. Annealing consists of heating a metal to a specific temperature and then cooling at a rate that will produce a refined microstructure. The rate of colling is generally slow. Annealing is most often used to soften a metal for cold working, to improve machinability, or to enhance properties like electrical conductivity.
2. Normalizing
Normalizing is a technique used to provide uniformity in grain size and composition throughout an alloy. The term is often used for ferrous alloys that have been austenitized and then cooled in open air. Normalizing not only produces pearlite, but also bainited sometimes martensite, which gives harder and stronger steel , but with less ductility for the same composition than full annealing.
3. Stress relieving
Stress relieving is a technique to remove or reduce the internal stresses created in a metal. These stresses may be caused in a number of ways, ranging from cold working to non-uniform cooling. Stress relieving is usually accomplished by heating a metal below the lower critical temperature and then cooling uniformly.
4.Quenching
Quenching is a process of cooling a metal at a rapid rate. This is most often done to produce a martensite transformation. In ferrous alloys, this will often produce a harder metal, while non-ferrous alloys will usually become softer than normal.
5. Tempering
Untempered martensitic steel, while very hard, is too brittle to be useful for most applications. A method for alleviation this problem is called tempering. Most applications require that quenched part be tempered. Tempering consists of heating steel below the lower critical temperature, (often from 400 to 1105° F or 205 to 595°C, depending on the desired results), to impart some toughness. Higher tempering temperatures are sometimes used to impart further ductility, although some yield strength is lost.
1. Annealing
Annealing is a rather generalized term. Annealing consists of heating a metal to a specific temperature and then cooling at a rate that will produce a refined microstructure. The rate of colling is generally slow. Annealing is most often used to soften a metal for cold working, to improve machinability, or to enhance properties like electrical conductivity.
2. Normalizing
Normalizing is a technique used to provide uniformity in grain size and composition throughout an alloy. The term is often used for ferrous alloys that have been austenitized and then cooled in open air. Normalizing not only produces pearlite, but also bainited sometimes martensite, which gives harder and stronger steel , but with less ductility for the same composition than full annealing.
3. Stress relieving
Stress relieving is a technique to remove or reduce the internal stresses created in a metal. These stresses may be caused in a number of ways, ranging from cold working to non-uniform cooling. Stress relieving is usually accomplished by heating a metal below the lower critical temperature and then cooling uniformly.
4.Quenching
Quenching is a process of cooling a metal at a rapid rate. This is most often done to produce a martensite transformation. In ferrous alloys, this will often produce a harder metal, while non-ferrous alloys will usually become softer than normal.
5. Tempering
Untempered martensitic steel, while very hard, is too brittle to be useful for most applications. A method for alleviation this problem is called tempering. Most applications require that quenched part be tempered. Tempering consists of heating steel below the lower critical temperature, (often from 400 to 1105° F or 205 to 595°C, depending on the desired results), to impart some toughness. Higher tempering temperatures are sometimes used to impart further ductility, although some yield strength is lost.
Seamless steel tube deformation production process
There are three main deformation processes throughout hot rolled seamless steel pipe production methods.
1. Perforating.
Perforation methods are common rotary piercing and pressure perfortion. In addition, we can use centrifugal casting, continuous casting with electroslag re-melting and other methods to obtain a hollow shell and to eliminate the perforation step.
2. Rolling.
On the extension machine, the pipe billit will roll thin capillary and become close to extending the original pipe wall thickness. The common type of rolling methods including continuous rolling, rolling cycle, automatic rolling tube, top tube, three roll rolllin, two roll rolling etc.
3. Finishing.
The main process for pipe finishing are sizing and reducing. The goal is to achieve improved accuracy of the pipe thickness, improve the surface quality, improve pipe roundness and expand the product specifications.
1. Perforating.
Perforation methods are common rotary piercing and pressure perfortion. In addition, we can use centrifugal casting, continuous casting with electroslag re-melting and other methods to obtain a hollow shell and to eliminate the perforation step.
2. Rolling.
On the extension machine, the pipe billit will roll thin capillary and become close to extending the original pipe wall thickness. The common type of rolling methods including continuous rolling, rolling cycle, automatic rolling tube, top tube, three roll rolllin, two roll rolling etc.
3. Finishing.
The main process for pipe finishing are sizing and reducing. The goal is to achieve improved accuracy of the pipe thickness, improve the surface quality, improve pipe roundness and expand the product specifications.
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