A Comprehensive Guide To Plates Of Middle Thickness: Everything You Need to Know About Medium Thickness Plates
What is medium thick plate?
The steel plate is a flat steel which is poured with molten steel and pressed after cooling. Medium-thick plate refers to the steel plate with thickness of 4.5-25.0mm, the thickness of 25.0-100.0mm is called thick plate, and the thickness over 100.0mm is extra thick plate.
Medium thickness plate generally has high comprehensive mechanical properties. Mechanical properties required are: strength, plasticity, hardness, impact toughness, stiffness, etc. Process performance requirements are: welding performance, hardenability, processability, weather resistance, corrosion resistance, wear resistance, fatigue resistance, high temperature characteristics, low temperature characteristics. corrosion resistance, wear resistance, fatigue resistance, high temperature characteristics, low temperature characteristics, etc.
Classification of Medium and Heavy Plates
Plate of middle thickness is a kind of flat steel with large width thickness ratio and surface area. According to different materials, the medium plate can be divided into ordinary carbon medium plate, low alloy medium plate, stainless steel medium plate, etc.
In addition to size, medium thickness plates can also be classified according to strength, chemical composition, usage and delivery status.
- According to the strength classification, the lower limit of tensile strength is classified, and the tensile strength of 50kgf/cm is called high strength steel plate.
- According to the chemical composition, it is classified into ordinary steel plate and special steel plate, the latter including stainless steel plate and composite steel plate.
- It is divided into steel plate, welded structural steel plate, boiler and pressure vessel steel plate, low temperature steel plate, corrosion resistant steel plate, welded steel plate and special purpose steel plate by application.
- According to the delivery status, it is divided into three kinds: rolled steel, heat-treated steel plate and pellet and coated steel plate. Due to the needs of large structures and shipbuilding, the production of pellet and coated steel plates increases year by year.
Ordinary medium and thick plate
1. Plain carbon steel boiling steel plate
Plain carbon steel boiling steel plate as the name implies is a steel plate made of boiling steel hot rolled from ordinary carbon structural steel. Boiling steel is a kind of incomplete deoxidation of steel, high oxygen content of the molten steel, when the steel is injected into the ingot mold, carbon and oxygen reaction produces a large amount of gas, resulting in the steel is boiling state and the name.
2. Plain carbon steel sedimentation steel plate
Plain carbon steel sedimentation steel plate is made of ordinary carbon structural steel sedimentation steel billet hot-rolled steel plate. Sedation steel is completely deoxygenated steel, steel in the injection ingot before the full deoxygenation with ferromanganese, ferrosilicon and aluminum, etc., the steel in the ingot mold is calmer, does not produce a boiling state, so named as sedation steel.
3. Low-alloy structural steel plate
Low-alloy structural steel plate is made of low-alloy structural steel hot-rolled. Low-alloy steel plate are sediment steel and semi-sediment steel plate. Its advantages are higher strength, higher performance, can save a lot of steel, reduce the weight of the structure.
4. Welding structure with weathering steel plate
Weathering steel is atmospheric corrosion resistant steel. Weathering steel for welded structures is a small amount of alloying elements added to the steel, such as steel, chromium, nickel, molybdenum, niobium, titanium, zirconium and vanadium, etc., so that it forms a protective layer on the surface of the metal matrix to improve the weather resistance of steel, as well as good welding performance.
5. High weathering structural steel plate
Weathering steel that is resistant to atmospheric corrosion Ji. Add a small amount of alloying elements in the steel, such as steel, phosphorus, chromium, nickel, molybdenum niobium, titanium, zirconium and vanadium, etc., so that the formation of a protective layer on the surface of the metal matrix to improve the weathering properties of steel.
6. Patterned steel plate
Patterned steel plate is a steel plate with a diamond or lentil shaped protrusion on its surface. Its specifications are expressed in terms of its own thickness (the thickness of the protrusion is not counted).
High-quality Middle Thickness Plates
1. High-quality carbon structural steel hot-rolled medium and mid thickness plate
High-quality carbon structural steel hot-rolled medium and mid thickness plate is referred to as carbon structural steel mid thickness plate, that is, its material is high-quality carbon structural steel, hot-rolled, but also normalized, annealed or tempered state delivery.
2. High carbon hot-rolled mid thickness plate for automobile manufacturing (GB3275-82)
Automotive manufacturing with high-quality carbon structural steel hot-rolled mid thickness plate with high-quality carbon structural steel for the material, hot-rolled. According to the different methods of production and processing and depth, divided into deep drawing (S), ordinary drawing (P) and cold-forming (W) three categories.
3. Carbon tool steel thick plate
Carbon tool steel thick plate for carbon tool steel material, made by hot rolling, this type of steel plate cold, hot processing performance, hardness and high plasticity, low production costs, wide range of uses. The main drawback is the poor thermal hardness, poor hardenability, generally annealed or high-temperature tempered state delivery.
4. Alloy structural steel mid thickness plate
Alloy structural steel mid thickness plate is made of alloy structural steel, hot-rolled.
5. Stainless steel medium thick plate
Stainless steel medium thick plate is mostly silvery white in appearance, and it is extremely difficult to be water soluble, but has good safety. Stainless steel plate is widely used to make various containers (such as furnace shell, furnace plate), bridges, car frames, ships and so on.
Stainless steel plate is divided into austenitic, ferritic, duplex, martensitic, precipitation hardening type, etc.
- Austenitic stainless steel plate is an important class of stainless steel, its production and usage accounts for 70% of the total stainless steel. According to the alloying method, austenitic stainless steel plate can be divided into two categories: chromium-nickel system and iron-chromium-manganese system. The former austenitic nickel as the austenitizing element, is the main structure of the austenitic stainless steel plate; the latter is to manganese, nitrogen instead of the expensive nickel section nickel austenitic stainless steel plate. Overall, austenitic stainless steel plate has good corrosion resistance, good overall mechanical properties and process performance, but the strength and hardness is low.
- Ferritic stainless steel plate contains 11%-30% chromium, basically no nickel, is a section of nickel steel, in the use of the state of the organization structure to ferrite. Ferritic stainless steel plate strength is high, and cold work hardening tendency is low, resistance to chloride stress corrosion, pitting corrosion, crevice corrosion and other local corrosion performance is more excellent, but the intergranular corrosion is very sensitive, low temperature toughness is also poor.
- It is generally believed that the presence of more than 15% ferrite in the austenitic matrix, or more than 15% austenite in the ferritic matrix can be called austenitic + ferrite duplex stainless steel plate. Duplex stainless steel plate is compatible with the advantages of austenitic stainless steel and ferritic stainless steel.
- Martensitic stainless steel plate is a class of steel whose properties can be adjusted by means of heat treatment, and its strength and hardness are higher.
- Precipitation hardening stainless steel plate is a steel grade through heat treatment means to make the carbide precipitation precipitation in the steel, so as to improve the strength of the purpose.
Raw materials of medium and thick plates
The metal materials used for heavy plate rolling mill are blooming slab, continuous casting slab, ingot and forging slab. The blooming width is 2300mm, the thickness is 610mm, and the maximum weight is 45t. In the development of continuous casting technology, it can not only improve the yield of medium and heavy plates, reduce production costs, but also improve the quality of steel plates. Therefore, the proportion of thick plate mills used for continuous casting slabs is increasing to 100%. With the introduction of new technology, the output of plate mill from slab to finished steel plate has reached 94.2%. If there is no blooming slab and continuous casting slab, flat steel ingot can be used as raw material. It is only used as raw materials for the production of special medium plates.
Medium thickness plate production process
Production Process Flow Chart of Medium and Heavy Plate
Selecting raw materials
How to selecting raw materials is one of the important links in the production of thick plate. Whether the choice of raw materials is reasonable, will affect the productivity of the mill, into the rate of steel, steel quality and cost.
Raw material surface defects can generally be used to eliminate the surface cleaning method, and then heating, rolling, otherwise the raw material defects in the rolling process expansion caused by scrap.
Continuous casting billet common defects are: surface cracks, internal cracks, subcutaneous pores and inclusions, non-inclusions, central segregation, central sparse, heavy skin, scratches, pits, etc.. The defects on the surface of the raw material, except for some relatively minor ones that are oxidized during the heating process will not affect the quality of the steel plate, the defects that exceed a certain limit in size need to be removed by some cleaning method to avoid affecting the quality of the steel plate and causing scrap. Surface quality cleaning can not only improve the surface quality of steel plates, but also reduce scrap, save metal and reduce costs. The medium-thick plate branch uses flame cleaning method to carefully inspect and clean the defects of the slab according to Q/WG (LG) 202 standard.
Impact of continuous casting defects on performance:
- (1) Cracks (surface cracks and internal cracks) expand continuously after heating and rolling, even cracking and splitting.
- (2) Steel contains a large number of FeO cast ingot intergranular bonding is extremely weak, rolling is very easy to brittle cracking caused by rolling waste.
- (3) When the steel deviation phenomenon is serious, will lead to uneven performance of various parts of the steel plate, thus affecting the performance of the steel plate.
- (4) When the shrinkage and loosening deep into the ingot does not cut the net, after rolling the formation of internal layering of steel plate, so that the mechanical properties of steel plate significantly reduced.
- (5) Non-metallic inclusions in the steel, after rolling in the formation of laminations or inclusions within the steel plate, destroying the organizational structure of the steel plate, reducing the mechanical properties of steel, easy to form stress concentrations in use.
- (1) In the hot-rolled plate before, the slab must be heated to a certain temperature, so that it has a certain plasticity before rolling.
- (2) The purpose of heating: the purpose of heating steel: to improve the plasticity of steel. Lower deformation resistance for rolling. The following two factors affect the plasticity of metals: (1) plasticity by the intrinsic factors of steel, chemical composition, organizational structure, non-metallic inclusions; (2) Plasticity by the external conditions when rolling steel: deformation temperature; deformation rate; stress state and heating meson.
- (3) Heating, divided into three stages of preheating, heating, even heat. Preheating section is mainly to reduce the thermal stress of the billet and the use of furnace gas temperature to preheat the billet; heating section is the main place to heat the billet, that is, the rapid heating of the billet to the temperature required by the process, the heating section temperature has a great impact on the yield and quality; even heat section has two purposes, one is to make the billet to obtain a smaller section temperature difference, the second is conducive to improving the furnace unit productivity.
- (4) Heating process: the heating process including heating temperature (heating temperature, even heat temperature), heating speed, heating time, furnace temperature system and furnace atmosphere.
Medium-thick plate rolling process is divided into four stages.
- (1) Scale removal stage: to remove the iron oxide on the surface of the rolled parts to ensure excellent surface quality of the steel plate.
- (2) Wide stage: according to the size of the billet and the performance requirements, to determine the rolling method, to solve the difference between the billet and the finished product in the width, to ensure that the steel plate in the width of the specified requirements.
- (3) Rolling length stage: to give the rolled parts a large amount of pressure, so that the rolled parts quickly rolled length, to create conditions for the next stage of rolling.
- (4) Accuracy control stage: according to the product requirements, thickness accuracy control, plate shape control, performance control of the steel plate.
The first and second stages are completed on the vertical roller mill and two-roller mill, and the third and fourth stages are completed on the four-roller mill.
1. The main task of the roughing stage is to stretch the billet to the desired width of the finished product and a large compression extension of the rolled length, as well as the flush edge of the steel plate. Roughing for four-roller finishing rolling to provide the required thickness of semi-finished products, at the same time, the use of high-pressure water, large vertical rolls and “iron oxide” to remove the surface of the rolled parts, as well as the completion of the rolled parts spreading width, to ensure that the finished product width and plate shape. Roughing unit of the main equipment, is a large vertical roll, two-roller pusher and two-roller mill.
2. The choice of rolling method is based on the size of the raw material and the width of the finished product, there are generally the following: full longitudinal rolling method, full cross-rolling method, cross-rolling – longitudinal rolling method, longitudinal rolling – cross-rolling method.
3. Determine the trimming margin: according to the process requirements, correctly determine the trimming margin can obtain the ideal product width, improve the product sizing rate, yield rate, first-class rate, and create favorable production conditions for the next process, therefore, correctly determine the trimming margin, to improve product yield and quality has important significance.
4. Determine the margin of cutting edge: according to the law of constant volume, calculate the reading of the pointer of the completed width of the press. When the thickness of the finished steel rolled below 25mm, the cutting margin is 80 – 100mm; when the thickness is above 25mm, the cutting margin can be 60 – 80mm. the cutting margin of the cross-rolled steel plate is taken as the lower limit, the cutting margin of the longitudinal rolled steel plate Take the upper limit.
5. The impact of the size of the blank.
Rolling according to the task list to calculate the rolling, determine the cutting edge margin for width spreading and thickness gauge calculation. The actual billet deviation is too large, the actual size of the rolled out according to the rolling task list calculation is not enough, the width is not enough, the length can not come out and other dimensional problems.
1. The main task of finishing rolling is to roll the steel plate to the finished size and to control its quality.
2. Finishing mill equipment: 3000mm four-roller reversible mill with automatic position control of the press-down screw (electric APC) and hydraulic AGC combined press-down device to achieve high-speed setting of the roll gap at no load and automatic control of the steel plate thickness during the rolling process.
3. The finishing rolling process requires the production of steel plates with high thickness accuracy, small difference between the same plate, good straightness and good overall performance through thickness control, plate shape control, performance control and surface quality control.
4. Rolling process system including deformation system, speed system and temperature system.
- (1) deformation system: the main content is to determine the total amount of deformation and the amount of sub-pressing, pressing down the gauge is a deformation system.
- (2) speed system: the main content of the speed system is to select the rolling speed, which is to determine the rolling speed of each pass and no different stages of the speed in each pass. Rolling speed is high, the mill output is high. But the rolling speed by the mill and roll strength, motor capacity and other factors. Rolling mill two-roller mill requires slow bite steel low-speed throwing steel, four-roller mill in the rolling stage due to high temperature plasticity, high temperature fast rolling, but the last three passes because of the thickness, performance, plate shape control, rolling speed should not be too fast, otherwise the rolling temperature is low, rolling deformation is fast, resulting in serious uneven deformation, so that the plate shape is bad.
- (3) temperature regime: temperature regime specifies the difference in temperature when rolling, that is, the opening rolling temperature. Temperature system according to the process requirements of the standard implementation, rolling mill two-roller mill open rolling temperature of about 1150 ℃, the final rolling temperature of about 1050 ℃, four-roller mill open rolling temperature of about 1000 ℃, the final rolling temperature of 800-880 ℃ or so.
1. Control rolling is the appropriate control of chemical composition, heating temperature, deformation conditions (including the amount of deformation, total deformation, deformation speed) and cooling rate and other process parameters, so as to significantly improve the overall performance of hot rolling a rolling method, called control rolling, belongs to the category of deformation heat treatment, it is mainly the use of austenite in the organization to influence its phase change, in order to obtain good organizational properties, is deformation and phase change A combination of deformation and phase transformation of a comprehensive strengthening process.
2. Controlled rolling has the following advantages.
- (1) Improve the overall mechanical properties of steel. For example: control rolling can make the ferrite grain refinement, so that the strength of the steel plate is increased, toughness is improved.
- (2) Simplify the production process. Controlled rolling can replace the normalization process.
- (3) Reduce the production cost of steel plate. In the hot-rolled steel plate with the same properties as heat-treated steel, consuming less energy and alloying elements, thus reducing the cost.
- (4) Controlled rolling can be divided into three types: recrystallization controlled rolling, non-recrystallization type controlled rolling, and two-phase zone controlled rolling.
Rapid cooling after controlled rolling, quickly reduce the temperature of the steel plate, so that the time and ability of the steel plate to recrystallize and grow is reduced, refining the grain, increasing the strength of the steel plate without damaging its toughness, thereby improving the mechanical properties of the steel plate; on the other hand, reduce the temperature of the steel plate, after correction will not be scooped due to the action of thermal stress.
The tough-brittle transition temperature depends on the effect of controlled rolling before rapid cooling. Controlled rolling followed by controlled cooling of the steel plate can achieve the requirement of improving the strength without damaging the toughness of the steel plate. Controlled rolling and controlled cooling process system with reasonable, in order to improve the strength of the steel plate at the same time, but also to further improve the toughness of the steel plate.
The post-rolling controlled cooling system of the plate rolling mill is constructed by University of Science and Technology Beijing, the core of which is the establishment and application of the controlled cooling model to realize automatic controlled cooling.
Combination of controlled rolling and controlled cooling process: The reason why the rapid cooling after controlled rolling is valued is because he can produce greater toughness than the accelerated cooling of equiaxed austenite directly after heating, with better production practical results, and can further refine the ferrite at the same time, the pearlite distribution is uniform, the band pearlite can be eliminated, and it is possible to form fine bainite organization. It is generally believed that controlling the rapid cooling after rolling can increase the strength of steel plate without damaging its toughness. The toughness transition temperature depends on the effect of controlled rolling before rapid cooling.
Production practice shows that the control of rolling, after the control of the steel plate for cooling, can be achieved to improve the strength of the steel plate without damaging its toughness. Controlled rolling and cooling process system with reasonable, while improving the strength of the steel plate, but also can further improve the toughness of the steel plate.
Medium thick plate in the production of various processes will produce scoop or wavy defects, the scoop or wavy defects generated in the rolling process can be straightened by a hot straightening machine. Rolling mill has two straightening machines, one is an eleven-roller straightening machine, and the other is a powerful straightening machine.
The process system of the hot straightening machine is mainly based on the requirements of the steel grade, specification, performance and the shape quality of the steel plate to determine the parameters of the straightening process.
Straightening temperature. The general straightening temperature is specified between 600 and 700°C.
The number of straightening passes. The number of straightening passes depends on the straightening effect of each pass, and the operator should determine the number of straightening passes according to the shape of the steel plate, the rolling cycle, the length of the rolled part and the final rolling temperature.
Straightening depression. The amount of straightening depression is also called the overcorrected amount, and its size directly affects the curvature value of the straightened bending deformation of the steel plate.
Steel plate straightening defects and preventive measures.
In the operation of straightening, there are often two deficiencies: one is that the curvature defects of the steel plate can only be effectively controlled within a certain range, or controlled within the range allowed by the product standards, that is, the steel plate more or less still has a certain residual curvature value. Secondly, it may produce indentation, hardness and other defects, the reason is mainly foreign objects pressed into the steel plate and the lower temperature of the head and tail of the steel plate hit the straightening rollers, resulting in bumping, thus making the steel plate surface hardness and bumping defects.
The method of prevention is to strengthen the blowing of iron oxide, reduce the temperature of the straightening roller, improve the hardness of the straightening roller surface, and improve the operation to avoid bumping the straightening roller. If the straightening rollers become bumpy, they can be repaired with special tools and replaced when needed.
The performance of medium thick plate
The main factors affecting the performance of steel plate.
- (1) Chemical composition: the chemical composition of the steel is the internal factors affecting the performance of the steel plate. With the different carbon content in the steel, as well as the type and amount of alloy content is different, the performance of the steel plate is also different. Steel carbon content increases, the alloying elements increase, the strength of steel will also be improved. But the increase in carbon makes the plasticity of the steel plate is reduced, the welding performance becomes bad. And Mn, Ti, Nb, V and other alloying elements can improve and enhance the plasticity and strength of the steel plate.
- (2) The organization of steel: the metallurgical organization of steel has a great impact on the strength index and toughness index of steel. After rolling, if you can get fine, uniform ferrite grains, then the overall performance of the steel plate must be good. From theoretical studies show that: the strength of steel σs with ferrite grain refinement and improve, and with the increase in the amount of pearlite in steel, grain refinement on the impact of σb also increased, the brittle transition temperature of steel FATT with the reduction of ferrite grains and reduce. The lower the brittle transition temperature of the material, the lower the temperature at which it adapts to the environment, indicating that the material is more ductile. Therefore, the performance of steel is closely related to the organization, form, size and distribution of steel.
Chemical composition of the impact on the performance of steel.
1. Carbon, silicon, manganese, phosphorus, sulfur on the properties of steel.
2. Carbon in carbon steel, the higher the carbon content, the worse the plasticity.
3. Most of the silicon in the steel dissolved in the ferrite, so that the ferrite strengthening, especially can significantly improve the elastic limit. In austenitic steel, containing silicon in more than 0.55%, due to the strengthening of the formation of ferrite tendency to produce adverse effects on plasticity, in addition to silicon can promote graphitization, decarburization is more serious when heated.
4. Manganese is added to the steel as a deoxidizer and desulfurizer, can make the steel strength, carbon steel containing no more than 0.6-0.8% of manganese.
5. Phosphorus is a harmful impurity, making steel with cold brittleness, high-quality steel and advanced quality steel containing no more than 0.03-0.04% of manganese.
6. Sulfur is a harmful impurity brought into the steel by the fuel, so that the steel has thermal brittleness, so that the steel plasticity, wear resistance and welding performance is reduced, the content of sulfur in high-quality steel shall not exceed 0.03-0.04%. In ordinary steel shall not exceed 0.05-0.07%.
7. The impact of the alloy on the performance of steel.
The main factors affecting the strength and toughness are the size of the grain, the number, size and distribution of pearlite. As the grain size decreases, the yield limit of the metal rises and the brittle transition temperature decreases. When the percentage of pearlite increases, it hardens the steel and causes the toughness of steel to become bad, the grain beyond fine, the less the amount of pearlite, the lower the brittle transition temperature of steel. Ni, V, Ti and other alloying elements have the effect of refining the grain and improving the strength of metal. Chromium element has a great influence on steel, it can refine the grain of steel, improve the strength limit, yield limit and hardness of steel. In heat treatment, it can improve hardenability without reducing plasticity. The element chromium is the main alloying element of stainless steel. Nickel elements can increase the impact toughness and strength limit of steel, and chromium elements made of nickel-chromium steel, at room temperature can resist chemical corrosion and at high temperatures have corrosion and heat resistance, while the strength and impact toughness is still great.
The effect of heating temperature on the performance of steel plate.
The upper limit of the slab heating temperature, usually take the iron-carbon equilibrium phase diagram in the solid phase line below NJE 100-150 ℃, the lower limit is determined by the final rolling temperature and rolling temperature drop. From the requirements of grain refinement, the heating temperature must be considered not to make the heating austenite grain coarse and uneven. Because, the coarse grain of raw materials will make the deformation after the organization of coarse grains, resulting in phase transformation after the organization of coarse grains, so that the steel plate performance deterioration. Although rolling can refine austenite grains, but can not therefore increase the heating temperature for no reason, because the heating temperature is too high, will inevitably cause the final rolling temperature is also high, and the impact of the finished steel plate grain size coarse, so that the performance decline, but also not conducive to energy saving.
Rolling steel to improve the performance of the steel plate.
Under the same conditions, the various properties of the steel plate is first determined by the chemical composition (i.e., the impact of chemical composition on the organization); under the same chemical composition, its performance is determined by the organization obtained under the production conditions. In the production conditions is to affect the mechanical properties of the metal by changing the structure of the metal organization. Therefore, rolling is through the control, adjust the production conditions, so that the final obtained metal organization is fine, uniform pure ferrite and lamellar dispersion of large pearlite organization, while these organizations are not directional, no stress, organizational stability, so that the metal gets the best mechanical properties, so rolling can improve the performance of steel plates.
Measures to control the performance of steel plate.
In the production of thick plate, the measures to control the performance of the steel plate are.
- 1. Adjust the heating conditions of the slab before rolling (time, temperature, heating speed)
- 2. Determine the deformation conditions of the rolling time (the total press rate, the number of passes, rolling method)
- 3. Good control of the rolling time temperature (opening temperature, final rolling temperature)
- 4. Control the rolling time of the final rolling conditions (the final rolling rate, the final rolling temperature, cooling speed after rolling)
- 5. The essence of these measures is to control the austenite grain size of the rolled parts, the form of carbide present after phase recrystallization, distribution characteristics and the final pure ferrite grain size, so as to achieve the purpose of controlling the performance of the steel plate.
The use of medium thick plate
Medium thick plate can be cut and combined according to the requirements of use, made into various structural parts and mechanical parts, can also be made into welded steel, further expanding the use of steel plate; can be bent and stamping forming, made into boilers, containers, punching car shells, civil utensils, appliances, can also be used as a welded steel pipe, cold-formed steel billet.
Medium thick plate is mainly used in construction engineering, machinery manufacturing, container manufacturing, shipbuilding, bridge construction, etc.. It can also be used to manufacture various containers, furnace shells, furnace plates, bridges and automobile static steel plates, low-alloy steel plates, shipbuilding steel plates, boiler steel plates, pressure vessel steel plates, pattern steel plates, automobile beam steel plates, tractor parts and welded components, etc.
- (A) Bridge steel plate: steel plate used for large railroad bridges, required to withstand dynamic load. Impact. Vibration. Corrosion resistance, such as: Q235q. Q345q, etc.
- (B) Shipbuilding steel plate: used in the manufacture of marine and inland waterway ship hull, requiring high strength. Plasticity. Toughness. Cold bending properties. Welding properties. Corrosion resistance are good. Such as: A32. D32. A36. D36, etc. Boiler steel plate (boiler plate): used in the manufacture of various boilers and important accessories, because the boiler steel plate in the medium temperature (below 350 ° C) under high pressure, in addition to high pressure, but also by the impact. Fatigue load and water and gas corrosion, the requirements to ensure a certain strength, but also good welding and cold bending properties, such as: Q245R, etc.
- (C) Pressure vessel steel plate: mainly used in the manufacture of petroleum, chemical gas separation and gas storage and transportation of pressure vessels and other similar equipment, general working pressure at atmospheric pressure to 320kg/cm2 or even to 630kg/cm2, the temperature in the -20-450°C range, the requirements of the vessel steel plate in addition to a certain strength and good plasticity and toughness, but also must have good cold bending and welding properties Q245R, such as: Q345R. Q345R. 14Cr1MoR. 15CrMoR, etc.
- (D) Automotive beam steel: the manufacture of automotive beam (longitudinal beam, beam), with a thickness of 2.5-12.0mm low-alloy hot-rolled steel plate. Due to the complex shape of the automobile beam, in addition to the requirements of higher strength and cold bending performance, but also requires good stamping performance.
What is the difference between thin plate and thick plate?
Steel plates can be further divided into thin and thick plates. Although the difference between thin and thick plate is not well defined, a ratio of thickness to width or length of less than 10% is usually considered thin plate, while a ratio greater than 10% is considered thick plate.
What is thick plate theory?
Although the thickness is small, but the deformation caused by transverse shear and bending deformation is of the same magnitude, in the analysis of the stress and deformation under static load, still must consider the transverse shear effect, the positive stress perpendicular to the direction of the plate surface can be ignored. In the analysis of stress and deformation under dynamic load, in addition to the consideration of transverse shear effect, but also must consider the micro-segment of inertia and damping moment. Medium thick plate has long been widely used in the machinery industry. In recent years, due to the environmental requirements of high pressure, high temperature and strong radiation, the thickness of the plate in engineering has increased, and many plates have been changed to use the medium-thick plate theory for analysis.
If the medium-thick plate is located in the xy plane, in consideration of the effect of transverse shear and ignore the positive stress perpendicular to the direction of the plate (z direction), the medium-thick plate is subject to z-directional distributed load p the role of the bending differential equation equation is
In the formula:
- ω is the deflection of the plate.
- t is the thickness of the plate.
- v is the Poisson’s ratio.
- are the transverse shear forces in the x and y directions, respectively, and △ is the Laplace operator.
- D is the bending stiffness, where E is the modulus of elasticity.
Theoretically, ω can be obtained from the first equation, then Qx and Qy from the last two equations, and then bending moment and torque can be further obtained. However, this partial differential equation cannot be integrated directly, so it is usually solved by the Navier method, Rayleigh-Ritz method, finite difference method and other methods. In recent years, due to the development of the finite element method, there are many procedures to calculate the medium-thick plate, through which the solution can be easily sought. From the results, after considering the transverse shear effect, the deflection ω increases, the self-oscillation frequency and the critical load of instability decrease, and the variation of the internal force in the plate tends to be flat. The extent of these changes is proportional to the square of the thickness-to-span ratio of the plate.
The transverse shear effect was first considered in the analysis of one-dimensional beams by S.P. Timusinko in the 1920’s. In 1943 E. Risner extended it to two-dimensional problems and derived the differential equations for medium-thick plates. Due to the mathematical difficulties, the theory of medium-thick plates is not widely applied at present.
How to choose the thickness of the steel plate?
The thickness of a steel plate can be calculated as the ratio of the volume of the plate to its surface area. Measure or find the length and width of the board elsewhere. Multiply the length and width (if in inches) by a factor of 2.54 to convert the dimensions to centimeters.
How does the stainless steel plate factory calculate the weight of the steel plate?
304 stainless steel plate is a common material in stainless steel, density of 7.93g/cm^3, the industry is also called 18/8 stainless steel, high temperature resistance 800 ℃, with good processing properties, high toughness, widely used in industry and furniture decoration industry and food medical industry.
About 304 stainless steel plate density weight calculation: To calculate the weight of 304 stainless steel plate, you must first know the density value of 304 stainless steel is 7.93, its calculation formula: weight (kg) = thickness (mm) × width (mm) × length (mm) × density value, want to derive the unit is kg, the length unit all converted into dm. For example, the plate size: 0.41cm × 380mm × 380mm, weight: 0.041dm × 3.8dm × 3.8dm × 7.92kg/dm^3 = 4.69kg.
Standard stainless steel plate theoretical weight calculation formula: weight (kg) = thickness (mm) * width (m) * length (m) * density value
Stainless steel plate weight per square meter (kg) formula: specific gravity × thickness (mm) × width (mm) length (mm)
A, the weight of stainless steel plate with nominal size calculation, such as the thickness of the allowable deviation is specified as positive and negative deviation, when
Take the average of the upper and lower limits of deviation plus the sum of nominal dimensions
Second, the basic weight of the stainless steel plate, refers to the thickness of 1mm, the weight of the area of 1m2
Third, the unit weight (kg/m2) refers to the weight of the steel plate area of 1m2, the basic weight multiplied by the thickness of the steel plate (mm), revised to 4 effective digits
Fourth, the weight of a steel plate is the unit weight multiplied by the area (m2), the area should be about 4 valid numbers, the weight of a steel plate should be about 3 valid numbers, such as a weight of more than 1000kg, should be modified to kg integer.
Laser cut stainless steel medium thick plate
Stainless steel medium thick plate has smooth surface, high plasticity, toughness and mechanical strength, and is resistant to corrosion by acid and alkaline gases and solutions. Nowadays, the laser cutting process of stainless steel medium thick plate is becoming more and more mature and will gradually replace the traditional cutting process. If you want to cut high-quality stainless steel medium-thick plate, you need to fully understand the elements of the cutting process, mainly as follows.
1. Nozzle selection
The diameter of the nozzle determines the shape of the airflow into the kerf, the gas diffusion area and gas flow rate, which will affect the melt removal and cutting stability. The greater the air flow into the kerf, the faster the speed and the more the workpiece is properly positioned in the air flow, the greater the jet capacity to remove molten material. At a fixed flow rate, different nozzle sizes for monitoring air pressure the thicker the stainless steel plate, the greater the choice of nozzle should be, the greater the proportional valve setting, the greater the flow rate, you can ensure that the pressure, the normal slicing effect can be cut.
2. The choice of auxiliary gas and gas purity
Laser cutting stainless steel thick plate often use a variety of auxiliary gases, such as oxygen, nitrogen, air, etc., the use of different types of gas, the effect of cutting cross-section is also different. Oxygen is the black part, air is light yellow, nitrogen can prevent the original color of stainless steel is oxidized.
3. Focus position
In order to ensure the cutting effect of stainless steel thick plate and to protect the nozzle from damage, coaxial test must be conducted before cutting to ensure that the nozzle and the laser output beam coaxial. Test method: stick the transparent tape on the nozzle exit end face, adjust the laser output power of perforation, observe whether the transparent tape has the center hole and the location of the center hole, adjust the adjustment screw on the handle. Lens cavity synchronization until the laser opens the transparent tape hit the hole and the nozzle center overlap.
The focal point is different, the thickness of stainless steel thick plate can be cut, the material and quality is also different. Different materials and thicknesses need to be adjusted to different focal points. Before cutting, the actual zero focus is measured and can be used as a reference for testing and analysis of cutting process parameters. Negative scatter focus is the main process selection direction for stainless steel cutting.
4. Laser frequency adjustment and the impact of duty cycle on the cutting quality
The frequency is reduced from 500-200Hz, the cutting effect is better, and the delamination is gradually improved. When the frequency is set to 100Hz, it will not be cut off and the blue light will be reversed. You can find the right frequency range by frequency change. To ensure the cutting part of the thick stainless steel plate, the number of pulses must match the energy of the individual pulses.
Stainless steel plate transportation and storage requirements
There are many precautions when the manufacturer produces good stainless steel medium thick plate in the loading of. When loading, the first thing should be good bottoming or edging, to avoid deformation of the plate in the process of transportation because of vibration.
Generally speaking, the heavier plates should be placed on the bottom, and the thinner plates should be placed on the top as much as possible to avoid being deformed by the heavy plates. According to the size and quantity of the plate, choose the transportation agency, if the quantity is small, the volume is small, you can choose small and medium-sized express transportation, if the quantity is slightly larger, the plate volume is slightly larger, you can choose small and medium-sized logistics company, if the quantity is larger, the volume is also larger, you can choose large charter logistics.
For precision stainless steel plate loading should be equipped with a special storage rack, the storage rack material used should be wood or carbon steel bracket, carbon steel bracket surface should be painted or padded with rubber pads, so that it can avoid confusion with the plate.
When storing, the storage location should be convenient for lifting, and the storage location should have certain protection measures to avoid moisture, oil and dust from affecting the plates.
In order to avoid the steel in the transport and handling process of scratching the surface, in the lifting, should be to use special lifting tools, such as slings, etc., not to use steel wire rope.
Stainless steel plate is an extremely versatile plate, but if transported and stored improperly, it may lead to plate deformation, rust, surface damage, so both manufacturers and customers need to pay attention to its transport and preservation.
Common defects of medium thick plate
The surface defects of medium thick plate can be divided into two categories according to the source, one is the defects brought by the billet itself, called steel defects; one is the defects caused during the production process from billet to finished product, called operation defects.
I. Steel defects
1. Cracks and cracks
This type of defect in the surface of the steel plate in different shapes, depths, lengths of fissures, generally fish scale or water pattern. Single cracks and cracks can be produced in any part, dense cracks are mostly distributed in the edge of the steel plate parts.
- (1) These defects are generally incomplete cleaning of the cracks present in the continuous casting billet, and the original surface longitudinal cracks, surface transverse cracks and stellate cracks are exposed after rolling.
- (2) Subcutaneous bubbles or subcutaneous inclusions of the slab break or are exposed to form point or stellate cracks during rolling. Slab of subcutaneous bubbles or subcutaneous inclusions are difficult to find before cleaning, the heating process has part of the gas overflow, the rolling process and part of the gas overflow surface, the formation of a breach, after rolling shaped like a crack.
- (3) Uneven heating temperature of the slab, heating speed is too fast, etc. resulting in uneven plasticity of the steel plate, the rolling of the pulling crack.
- (4) Low thermal conductivity of steel, insufficient holding time, or uneven temperature, too much internal stress after deformation, pulling crack during rolling or internal stress release during cooling appears blown crack.
- (1) Strengthen the quality inspection of the billet, the surface of the slab cracks and cracks to clean up.
- (2) Prevent overheating of the billet, control the heating rate and achieve uniform temperature.
- (3) Rolling at high temperatures try to use a large amount of pressure down to make subcutaneous bubbles welded together.
This type of defect in the surface of the steel plate for the irregular distribution, in some localities show a round bump, the outer edge of the bump is more rounded, the bubble is due to the internal gas in the steel plate, the place can not be welded together during rolling and caused, some are torn during rolling.
More gas is gathered inside the slab.
- (1) Steelmaking measures to try to remove the gas in the steel plate.
- (2) Strengthen the quality inspection of the slab, do not use the slab exposed to air bubbles.
3. Surface inclusions
Such defects in the surface of the steel plate with the naked eye visible non-metallic inclusions, is obvious dot, block and long distribution, the color is generally red-brown, yellowish or gray-white. Severe surface inclusions can turn into cracks in the rolling.
- (1) The raw material itself with non-metallic inclusions, after rolling exposed. The crystallizer in the steel surface fluctuations involved in the protection of slag or defective intrusive water spout in the steel broken are caused by billet inclusions.
- (2) Rolling mill spacer brick and heating when the furnace roof or furnace wall refractory materials fall on the surface of the raw material, rolling pressed into the surface of the steel plate to produce non-metallic inclusions.
- (1) Etrengthen the cleaning and acceptance of slabs, do not use slabs with surface inclusions.
- (2) To ensure high-pressure water pressure to remove the iron oxide and debris on the surface of the billet.
II. Operation defects
1. Convex package and indentation
Convex ladle defect is a regular local protrusion on the steel plate, indentation is the surface of the steel plate is pressed out of different shapes and sizes of craters.
- (1) Convex package is the roll or straightening roll surface flesh or surface due to hard objects pressed out of the crater when rolling steel.
- (2) Indentation is in the rolling process or straightening process roll surface sticky steel slag, iron and other hard objects, pressed out of the surface of the steel plate craters of different shapes and sizes.
- (3) Foreign objects fall on the surface of the steel plate, pressed into the surface of the steel plate during straightening, and form indentations after falling off.
- (1) Strengthen the rolling operation, do not roll the “black mark steel”, keep the roll cooling uniform.
- (2) Often check the rolls and straightening rolls, found foreign objects pressed into or off the meat in time to change the rolls.
- (3) Rolling to prevent foreign objects falling on the rolled parts.
In the surface of the steel plate presents a local or continuous crater, the defect can be divided into the following categories according to the formation of causes.
- (1) Raw material heating, fuel spray stains erode the surface of the billet, after rolling the surface of the steel plate is locally black honeycomb rough crater surface, generally more small or dense pockmarked, so called black pockmark.
- (2) Raw materials in the heating due to severe oxidation, rolling iron oxide off the surface of the steel plate to form a block or continuous rough plane or the emergence of gray-white light craters, so called light pockmark.
- (3) Steel plate in the roll bottom heat treatment furnace normalizing, due to the high temperature, the surface of the steel plate is very soft, the furnace bottom rollers bonded with high melting point of gas combustion products, pressed out on the surface of the steel plate with a regular or large area of craters.
- (1) To control the temperature fluctuations of the heating furnace and the amount of oil injection and the temperature, atmosphere and time of the high temperature stage.
- (2) To strengthen the scale-removal during rolling to ensure high-pressure water pressure to remove iron oxide and foreign matter from the surface of the billet.
- (3) To regularly overhaul the bottom rolls of the heat treatment furnace to reduce the bottom rolls of the furnace bonded foreign matter.
3. Iron oxide pressed into
Steel plate pressed into the iron oxide, generally gray-brown or reddish-brown, in the form of lumps or strips of distribution.
- (1) This type of defect is mainly the raw material surface of iron oxide or rolling process produced during the secondary iron oxide scale is not clean, pressed into the surface of the steel plate during rolling. After the slab from the heating furnace, by the point of descaling high-pressure water to remove iron oxide is not exhausted after the rough rolling, rough rolling process is also not exhausted iron oxide, pressed into the called primary iron oxide pressed into.
- (2) In the process of rough rolling and the process of cool steel after rough rolling, the surface of the steel plate produced secondary oxidation, steel plate and secondary iron oxide interface stress is small, so poor peelability, if the finishing rolling jet high-pressure water can not completely remove the secondary iron oxide, pressed in is called secondary iron oxide pressed in.
- (1) Control the heating temperature, furnace atmosphere and time in the furnace to reduce billet oxidation.
- (2) To ensure that the high-pressure water pressure, in rolling to strengthen the descaling, especially the four-roll fine rolling mill high-pressure water phosphorus removal, remove the iron oxide skin on the surface of the billet.
Slight overburning in the corners of the steel plate appears diamond-shaped, chicken claw-shaped or snake-shaped rupture. Severe cases in the fracture of the presence of rough fiber tissue visible to the naked eye, the grain boundaries can be seen under the microscope is oxidized.
- (1) Heating temperature is too high, high temperature zone holding time is too long, resulting in grain growth, intergranular oxidation, causing plasticity reduction.
- (2) Improper adjustment of the heating flame, the flame is sprayed directly onto the surface of the billet, resulting in local overburning.
- (3) Uneven temperature in the furnace, a certain part of the high temperature, the billet in this stay too long, resulting in local overburning.
- (4) High manganese and sulfur content in the steel easily cause overburning.
- (1) According to the steel and furnace conditions to develop a reasonable heating temperature and heating time in the furnace.
- (2) Control the furnace atmosphere, flame length, forbid the flame directly to the surface of the billet.
- (3) To be rolled for a longer period of time, according to the provisions of the cooling.
Stainless steel plate bending process
Stainless steel plate bending process has been applied for many years tends to mature, and according to the development of the industry gradually towards automation, intelligent, digital direction, has emerged a considerable number of bending new-style mold structure, process methods, detection methods.
Stainless steel plate bending process compared with the traditional bending mode, both in terms of efficiency, accuracy, or operational difficulty, labor intensity, manufacturing costs, etc., have made a great breakthrough. Compared with other processing processes, bending process production preparation cycle is short, low cost, because of its flexible processing characteristics favored by various enterprises, it is foreseeable that this flexible processing process will be continuously developed and applied.
Stainless steel plate bending refers to the processing of changing the angle of the plate or plate, such as bending the plate into V-shaped, L-shaped, etc.. At present, our frame type bending products, such as frame connection plate is mainly used for bending machine processing. Our main products are mostly V-shaped, L-shaped thick plate connection plate, the material to 500L is more common, tensile strength is generally between 500 to 750MPa.
Stainless steel plate because of the material and material thickness characteristics, usually the weight of the parts are in 10 – 35kg, the width and length of the parts according to the company’s product design and a lot of changes, which has a great challenge for processing efficiency, cost, including the labor intensity of workers. Many parts are load-bearing parts and connecting parts, there are high requirements for the accuracy of the parts, so in the early bending process layout need to be considered.
First, the quality of bending parts requirements
Bending parts have V-shaped, U-shaped, Z-shaped and other more complex bending shape.
We generally follow the following requirements.
- 1. Bending parts of each part size, angle, straightness accuracy.
- 2. The accuracy of the position of the bent parts hole.
- 3. Bent parts should not be warped or twisted loose tendons phenomenon.
- 4. Bending parts surface should be no obvious scratches, bending indentation phenomenon.
The main factors affecting the quality of bending
- (1) Bending tooling is the main tooling used for bending processing, usually bending the shape and size of the workpiece depends on the accuracy of the mold.
- (2) The higher the accuracy of the mold, the more accurate the assembly, the higher the accuracy of the bent parts.
- (3) In addition, the structure and accuracy of the mold positioning has a greater impact on the accuracy of the size of the workpiece.
2. Plate performance
Bending plate performance on the quality of bent parts is mainly manifested in two areas.
- (1) In actual production we find that even different batches, different manufacturers of materials, there will be performance fluctuations, stress and rebound vary, which directly leads to the bent parts of the precision is not stable.
- (2) The thickness of the material fluctuates within the upper and lower tolerances is also the reason for the impact on accuracy, even if the same bending die is used for bending, the size and shape of the workpiece obtained also varies. Thickness, bending resistance, rebound small; thickness of small rebound is large, affecting the accuracy of the workpiece, and prone to warping and twisting phenomenon.
- (1) Bending process increases, the cumulative error of each process will increase, in addition, the process before and after the order of arrangement will also have a great impact on the accuracy.
- (2) Usually follow the short side after the long side, after the periphery, after the middle, after the local order of the whole.
- (3) Should take into account the mold and workpiece interference, reasonable arrangement of bending order, bending order is not set in stone, according to the shape of bending or workpiece on the obstacles to adjust the processing order.
The shape and size of the workpiece on the impact of accuracy
Asymmetrical shape and shape size of the bent part of the deviation of the springback will significantly increase.
The main factors affecting the rebound
(1) The mechanical properties of the material
Mechanical properties of the material refers to the shear strength, tensile strength and elongation of the yield point of the material. Due to the different types and grades of materials, its mechanical properties are not the same and fluctuate with different batches.
(2) Material surface quality
Plate thickness, surface quality has a greater impact on the rebound. If the surface of the material is not flat, bumpy or foreign objects, in the bending will produce stress concentration, the rebound has a greater impact.
(3) Relative bending radius R / T
R: bending on the radius of the knife; T: material thickness. Relative bending radius R / T value is larger, the greater the rebound value. Because R / T value is larger, the degree of deformation is very small, the center part of the bending section will appear a large elastic zone, accompanied by the rebound value is large. So generally choose a relatively small relative bending radius. But too small bending radius is easy to make the bend rupture, must be balanced consideration.
(4) Bending angle
The larger the bending angle means that the larger the deformation area, the greater the rebound value. But the bending angle and the bending radius of the rebound value is irrelevant.
(5) The impact of equipment accuracy and bending speed
For example, in the U-shaped bending process, due to the size of the bending machine tonnage, working speed and other factors are different, will make the bending size changes.
Source: China Plates Of Middle Thickness Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)