The hardness of steel is closely related to its internal structure, especially the dislocation in the structure. Dislocation is a kind of microscopic defects in steel, and their existence and movement play a key role in the deformation behavior of steel.

When the steel deformation occurs, it depends on the dislocation slip in the steel to achieve. Dislocation sliding is the process by which a dislocation moves through the crystal structure, resulting in plastic deformation of the steel. However, when the dislocation density is very high, entanglement can occur between the dislocations, and this entanglement can inhibit the movement of the dislocation, resulting in a higher hardness of the steel at the macro level.

Rolling process is an important part of steel processing, it will produce a lot of dislocation in steel. These dislocations become entangled with each other, making the steel more difficult to deform, which leads to an increase in hardness. However, the dislocation is not static, they can cancel each other in the process of thermal motion, resulting in a reduction in dislocation density, so that the steel softening.

Temperature has a significant effect on the behavior of the dislocation. At high temperatures, the dislocations are more likely to cancel each other out, so the softening effect is more pronounced. This is also why the hardness of hot-rolled steel is generally lower than that of cold-rolled steel. However, if the content of alloying elements in the steel is high, and the hot rolling cooling rate is fast, the cooled steel may be transformed into martensite. Martensite is a structure with high strength and hardness, and there are also a lot of dislocations in it, which will make the overall hardness of the steel higher. However, under normal circumstances, hot-rolled steel will inhibit the production of martensite by controlled cooling, so that it will not show higher hardness.

Compared with hot rolling, cold rolling is carried out at a lower temperature, which allows cold rolled steel to obtain better surface quality and dimensional accuracy. However, lower rolling temperatures also greatly increase the rolling stress required during rolling, so the thickness of cold-rolled steel is usually smaller. Hot rolled steel is more suitable for the production of medium and thick plate products.

At the end of cold rolling, the internal stress and hardness are usually reduced by heat treatment. This heat treatment can adjust the structure and properties of the steel so that it meets the required requirements. Therefore, cold rolled steel does not show high hardness.

As for why the cold-rolled plate will make people feel softer, I think it may be because the cold-rolled plate is thinner than the hot-rolled plate, and the structural stiffness is poor, so it appears softer in the feel. But in fact, the hardness difference between cold-rolled and hot-rolled plates mainly depends on their processing technology and internal organizational structure.

Basic concepts:

Hot rolling raw material continuous casting slab or blooming slab is used as raw material, heated by stepping furnace, dephosphorized by high pressure water into roughing mill, roughing mill through cutting head, tail, and then into finishing mill, implementing computer-controlled rolling, after the final rolling, laminar cooling (computer-controlled cooling rate) and winding machine to become straight coil. The head and tail of the straight hair curl are often tongue and fishtail, the thickness and width accuracy are poor, and the edge often has defects such as wave shape, fold edge and tower shape. The coil weight is heavy, and the inner diameter of the steel coil is 760mm. (The general pipe industry likes to use.) After finishing lines such as cutting the head, cutting the tail, cutting the edge and straightening and leveling for multiple passes, the straight hair coil is then cut or rerolled to become: hot rolled steel plate, flat hot rolled steel coil, longitudinal cutting strip and other products. Hot rolled finishing coil is formed after pickling and oil coating.

Advantages of hot rolling:

It can destroy the casting structure of the ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is dense and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent; Bubbles, cracks and looseness formed during pouring can also be welded under high temperature and pressure.

Cons:

1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into sheets, and the phenomenon of lamination (sandwich) appears. Delamination greatly worsens the tensile properties of steel along the thickness direction, and may cause interlayer tearing when the weld is contracted. The local strain induced by weld contraction often reaches several times of the yield point strain, which is much larger than that caused by load.

2. Residual stress caused by uneven cooling. Residual stress is the internal self-equilibrium stress in the absence of external force. Hot-rolled steel of various sections has such residual stress. The larger the section size of general steel, the greater the residual stress. Although the residual stress is self-equilibrium, it still has a certain effect on the performance of steel members under external forces. Such as deformation, stability, anti-fatigue and other aspects may have adverse effects.

Cold rolling with hot rolled steel coil as raw material, after pickling to remove the oxide, cold continuous rolling, the finished product is rolled hard coil, because of the cold hardening caused by continuous cold deformation, the strength and hardness of the rolled hard coil increase, the toughness and plastic index decline, stamping performance deteriorates, can only be used for simple deformation parts. Rolled hard coil can be used as raw material in hot dip galvanizing plant, because hot dip galvanizing units are equipped with annealing lines. The roll weight is generally 6~13.5 tons, and the inner diameter of the steel coil is 610mm. Generally, the cold continuous rolling plate and coil should be deannealed by continuous annealing (CAPL unit) or cover furnace to eliminate the cold hardening and rolling stress, and achieve the mechanical properties specified in the standard. The surface quality, appearance and dimensional accuracy of cold-rolled steel plate are superior to those of hot-rolled plate.

The advantages of cold rolling: fast forming speed, high yield, and no damage to the coating, can be made into a variety of cross section forms to meet the needs of the conditions of use; Cold rolling can produce great plastic deformation of steel, thus increasing the yield point of steel.

Cons:

1. Although there is no hot plastic compression in the molding process, there is still residual stress in the section, which will inevitably affect the overall and local buckling characteristics of the steel;

2. The cold-rolled steel style is generally an open section, which makes the free torsional stiffness of the section low. It is easy to appear torsion when bending, and easy to appear bending and torsional buckling when pressurized, and the torsional resistance is poor;

3. The wall thickness of cold-rolled steel is small, and it is not thickened at the corner of the connection of the plate parts, and the ability to withstand local concentrated load is weak

The main differences are:

1. Local buckling cold rolling is better than hot rolling. The cold-rolled steel allows local buckling of the section, which can make full use of the bearing capacity of the bar after buckling. Hot rolled steel does not allow local buckling of the section.

2, the type of local residual stress is different. The causes of residual stress in hot-rolled steel and cold-rolled steel are different, so the distribution of residual stress on section is also very different. The residual stress distribution on the section of cold-formed thin-wall steel is curved, while the residual stress distribution on the section of hot-tied or welded steel is thin film.

3, anti-torsion hot rolling is better than cold rolling. The free torsional rigidity of hot-rolled steel is higher than that of cold-rolled steel, so the torsional resistance of hot-rolled steel is better than that of cold-rolled steel. 4. In appearance, hot-rolled black, indentation, irregular surface and uneven edge; Cold rolling is the opposite. From the appearance, the surface of cold-rolled steel is smooth, without indentation and oxidation, the color is usually silver-white, the texture is fine and the edge is neat. The surface of hot-rolled steel is rough, there is an oxide skin, the color is darker, such as brown or black brown, and sometimes there is a pattern. The edges may not be as neat as cold rolled steel, and the shape may not be as regular. During the rolling process, the surface of hot-rolled steel is subjected to extremely high pressure and temperature, so indentation with poor toughness may occur.

Hot rolling is a rolling process that is carried out above the recrystallization temperature. Specifically, when a billet is heated to a high enough temperature, it goes through multiple rolling processes. In this process, the steel plate will be cut and straightened, and finally form our common hot-rolled steel plate.

This hot rolling process has significant advantages. First of all, it can effectively reduce energy consumption. Compared with traditional cold rolling, hot rolling has higher plasticity of the metal and lower deformation resistance, which means that the energy consumption required during the metal deformation process is greatly reduced. This not only helps to improve production efficiency, but also reduces production costs, thus bringing greater economic benefits to enterprises.

Secondly, hot rolling can improve the processing properties of metals and alloys. During the hot rolling process, the coarse grains in the cast state will be broken, which helps to heal significant cracks and reduce or eliminate casting defects. At the same time, the as-cast structure will also be transformed into deformed structure, thus improving the machining performance of the alloy. This makes the hot-rolled steel plate have better performance in the subsequent processing and application.

Hot rolling is an important process of high efficiency, energy saving and improving metal working performance. By rolling at high temperature, it can improve metal plasticity and reduce deformation resistance, thus reducing energy consumption and improving production efficiency. At the same time, hot rolling can also improve the processing properties of metals and alloys, providing a better foundation for subsequent processing and application. Therefore, hot rolling plays an indispensable role in the steel industry.

Ordinary medium and thick steel plate: Advantages: smooth surface, good quality, easy processing, relatively low price. Disadvantages: internal bubbles, impurities, bad welding, poor bearing capacity, not suitable for use as parts that need to withstand gravity. General carbon steel sedative steel plate: Advantages: good surface quality, less impurities, uniform force, good welding performance. Disadvantages: More expensive. Low alloy structure steel plate: Advantages: excellent performance, light weight. Disadvantages: More expensive. The advantages and disadvantages of various steels are as follows: ordinary medium and thick steel plate: Advantages: smooth surface, good quality, easy processing, relatively low price. Disadvantages: internal bubbles, impurities, bad welding, poor bearing capacity, not suitable for use as parts that need to withstand gravity. General carbon steel sedative steel plate: Advantages: good surface quality, less impurities, uniform force, good welding performance. Disadvantages: More expensive. Low alloy structure steel plate: Advantages: excellent performance, light weight. Disadvantages: More expensive. Welding structure with weather-resistant steel plate: Advantages: welding performance and weather resistance are very good, and it is widely used in railway, bridge and other areas that need long-term exposure to the atmosphere. Disadvantages: The production process requirements are very high, and the process is slightly poor can not produce a good weather resistant steel plate. Pattern steel plate: Advantages: good decorative performance, anti-slip effect. Disadvantages: The production process is complex, the price is expensive, and the mechanical properties are not high. Welding structure with weather-resistant steel plate: Advantages: welding performance and weather resistance are very good, and it is widely used in railway, bridge and other areas that need long-term exposure to the atmosphere. Disadvantages: The production process requirements are very high, and the process is slightly poor can not produce a good weather resistant steel plate. Pattern steel plate: Advantages: good decorative performance, anti-slip effect. Disadvantages: The production process is complex, the price is expensive, and the mechanical properties are not high.

The main materials of Marine steel plates are carbon steel and alloy steel.

First, carbon steel ship plate

Carbon steel mainly refers to ordinary steel with carbon content between 0.05-2.0%. Carbon steel ship plate is widely used in various types of ships, which is characterized by high strength, good toughness, good weldability and low cost. In addition, the reliability of carbon steel materials is high and can withstand strong hot and cold deformation, which is necessary for Marine steel plates.

The main disadvantage of carbon steel ship plates is that they are susceptible to corrosion by seawater and air, so special anti-corrosion treatment is required, including painting and the use of anti-rust coatings. At the same time, the service life of the carbon steel ship plate is also relatively short, and it needs to be replaced frequently.

Second, alloy steel ship plate

Compared with carbon steel, alloy steel ship plate has lower carbon content and adds a certain proportion of alloying elements, such as manganese, silicon, chromium, tungsten, molybdenum, etc., to increase the strength and corrosion resistance of steel. Alloy steel ship plates are more resistant to corrosion and last longer than carbon steel ship plates.

Alloy steel ship plate has the following characteristics:

1. High strength: The addition of alloying elements can improve the strength of steel and enhance the carrying capacity.

2. Good corrosion resistance: the alloy elements such as chromium not only increase the strength of the steel, but also form a dense chromium oxide film, which can prevent further corrosion.

3. Good cold working performance: compared with ordinary steel, alloy steel can better withstand strong hot and cold deformation, and it is not easy to produce surface cracking, fracture and other phenomena.

The choice of Marine steel plate material depends on many factors such as the ship's use environment, transportation volume and economic cost. Factors such as physical and chemical properties, corrosion resistance, cost and processing difficulty need to be considered when selecting materials.

Cold rolled steel coil is a kind of steel treated by cold rolling process, which has many excellent properties and wide applications. After the cold rolling process, it not only has a smooth surface, but also has high strength and ductility, which is suitable for various mechanical manufacturing and construction fields. The following will introduce the use of cold rolled steel coil and processing technology.

First, the use of cold rolled steel coil

1. Construction industry: Cold-rolled steel coils are often used in the manufacture of building structures. Such as steel structure buildings, Bridges, highway guardrail and so on. The high strength and excellent ductility of the cold-rolled steel coil make it able to withstand greater pressure and deformation, thus ensuring the structural stability and safety of the building.

2. Automobile manufacturing: Cold-rolled steel coil plays an important role in automobile manufacturing. It is usually used for the production of body, door, roof and other parts. Cold-rolled steel coil has high strength and toughness, which can effectively resist collisions and external shocks, and protect the safety of vehicles and passengers.

3. Electrical industry: Cold-rolled steel coil is widely used in the electrical industry, such as the manufacture of refrigerators, washing machines, air conditioners and other household appliances. Cold rolled steel coil has excellent corrosion resistance and electrical conductivity, making it an ideal material for electrical appliance manufacturing.

4. Furniture manufacturing: Cold-rolled steel coils also have great uses in furniture manufacturing. It is often used to make the skeleton and support structure of furniture. The high strength and durability of the cold-rolled steel coil make it able to withstand large loads and ensure the structural stability and service life of the furniture.

5. Other industries: Cold-rolled steel coil is also widely used in shipbuilding, railway equipment, petrochemical and other fields. Its corrosion resistance, high temperature properties and good machinability make it an indispensable material in these industries.

Second, the processing technology of cold rolled steel coil

1. Cutting: cold-rolled steel coils are often cut as needed during processing. Shearing refers to cutting the edge of a cold-rolled steel coil to the desired size and shape. Cutting can be done by means of mechanical cutting or laser cutting.

2. Crimp: During the processing of cold rolled steel coils, it is often necessary to crimp them into the desired shape. Crimp refers to the cold-rolled steel coil crimp into a cylinder, arc and other shapes. Crimping can be done by rolling or hydraulic pressure.

3. Bending: Cold-rolled steel coils can also be processed by bending. Bending refers to the deformation of the cold-rolled steel coil according to the desired bending Angle and curve. Bending is usually done using a bending machine or roll bending machine.

4. Welding: Cold-rolled steel coil in the process of processing, often need to be welded. Welding refers to joining together two or more parts of a cold-rolled steel coil. Usually using arc welding, gas welding and other methods for welding.

5. Surface treatment: cold rolled steel coils usually need surface treatment after processing. The surface treatment is to improve the durability and aesthetics of cold rolled steel coils. Common surface treatment methods are galvanized, spray, electroplating and so on.

DC01 cold carbon steel coil is a popular choice for a wide range of applications. It is favored for its low cost and excellent molding properties, so it is often used in the automotive industry and consumer goods manufacturing.

The versatility of the DC01 cold-rolled coil makes it suitable for a variety of applications, including but not limited to the following:

First, in the automotive industry, DC01 cold-rolled coil is often used to make automotive body panels. Its good formability makes the manufacture of body panels more efficient and precise, while also providing the required strength and durability.

Secondly, DC01 cold-rolled coil is also widely used in the manufacture of home appliance components. Due to its low cost and easy processing characteristics, it has become one of the preferred materials for many home appliance manufacturers. Whether it is a refrigerator, washing machine or air conditioner and other home appliances, DC01 cold-rolled coil can meet their manufacturing needs.

In addition, furniture components are also one of the important application areas of DC01 cold-rolled coil. Its low carbon steel properties allow furniture components to have sufficient strength and stability, while also providing the desired appearance. Whether it is a furniture component such as a bed frame, chair or table, the DC01 cold-rolled coil provides the ideal solution for manufacturers.

Finally, the DC01 cold-rolled coil is also widely used in the field of consumer electronics. Due to its low cost and ease of processing, it has become one of the preferred materials for many consumer electronics manufacturers. Whether it is a mobile phone, a tablet or a consumer electronics product such as a TV, the DC01 cold-rolled coil can provide the desired structure and appearance.

Overall, the DC01 cold-rolled coil is an excellent choice for many different applications due to its low cost and good formability. Whether in the automotive industry, home appliance manufacturing or furniture and consumer electronics, the DC01 cold rolled coil provides the ideal solution for manufacturers.

The cold-rolled coil is a steel plate with a thickness of less than 4mm, which is rolled at room temperature and below the recrystallization temperature. Because of the rolling at normal temperature, no oxide sheet is produced, so the surface quality of cold-rolled sheet is good, the dimensional precision is high, coupled with annealing treatment, its mechanical properties and technological properties are better than hot-rolled sheet.

Cold-rolled sheet is mainly used in the following fields:

Automobile manufacturing: Used to manufacture automobile body panels, wheel hubs, etc.

Electrical products: Used to manufacture electrical equipment such as motors and transformers.

Rolling stock: used to manufacture structural parts of railway vehicles, car body shells, etc.

Aviation: Used to manufacture aircraft parts, aircraft engines, etc.

Precision instrument: used to manufacture precision instrument structural parts, components, etc.

Food cans: used to manufacture the bottom cover of food cans, side seals, etc.

Construction: Used for the roof, exterior wall, doors and Windows of the building.

What is carbon steel? Is it strong

Carbon steel is a very strong material, its strength and hardness are very high. Carbon steel refers to the steel whose mechanical properties depend on the carbon content in the steel, and generally do not add a large amount of alloying elements, sometimes known as carbon steel or carbon steel. Carbon steel, also known as carbon steel, refers to iron-carbon alloys with carbon content of less than 2% WC. In addition to carbon, carbon steel generally contains a small amount of silicon, manganese, sulfur, phosphorus and other elements.

According to different uses, carbon steel can be divided into carbon structural steel, carbon tool steel and free cutting structural steel three categories. Among them, carbon structural steel is divided into building structural steel and machine manufacturing structural steel two kinds; According to the smelting method can be divided into open hearth steel, converter steel and electric furnace steel; According to the deoxidation method can be divided into boiling steel (F), killed steel (Z), semi-killed steel (b) and special killed steel (TZ); According to carbon content, carbon steel can be divided into low carbon steel (WC ≤ 0.25%), medium carbon steel (WC0.25%-0.6%) and high carbon steel (WC> 0.6%); According to the content of phosphorus and sulfur, carbon steel can be divided into ordinary carbon steel (higher phosphorus and sulfur content), high-quality carbon steel (lower phosphorus and sulfur content) and high-grade high-quality steel (lower phosphorus and sulfur content) and extra high quality steel.

In general, in carbon steel, the higher the carbon content, the greater the hardness, the higher the strength, but the lower the plasticity. Therefore, when using carbon steel, it is necessary to choose the appropriate type and specification according to the specific situation.

What is the material inside the hammer? The inside of the broken hammer is made of high chromium alloy. High chromium alloy is a kind of wear-resistant material with excellent anti-wear properties, but its toughness is low and brittle fracture occurs. In order to make the high chromium alloy hammer work normally, the structure of the hammer is generally adopted.

The first is to use a large area hammer to support the high chromium hammer head, and the toughness of the hammer handle supports the huge impact force during the crushing process.

The second is a dual-hydrothermal composite material, The material uses different optimal combinations of chromium, molybdenum, copper, nickel, vanadium, titanium and other alloys and rigorous unique production process, set high chromium alloy casting excellent wear resistance, high temperature oxygen resistance, thermal fatigue resistance (or corrosion resistance) and cast steel good toughness and machinability and one, with a single metal material is difficult to achieve excellent wear resistance and impact resistance of the overall comprehensive performance.

The high chromium wear-resistant hammer is the raw material of the ordinary crusher hammer, which is loaded with heavy elements of chromium metal. The grain is refined after the metamorphic treatment during melting, and the next pouring molding is carried out in the negative pressure state. The high chromium cast iron material used in the head of the hammer has high density, can withstand the larger impact load, and has sufficient anti-wear performance. The hammer handle is made of low alloy steel with good toughness, good toughness and no fracture to ensure normal operation.

High chromium wear-resistant hammer is mainly used to break some stones with high hardness, such as basalt, granite, river pebbles and so on. With the strengthening of the infrastructure construction project, the development trend of mining machinery industry is becoming more and more prosperous, and the crusher equipment has been a relatively rapid comprehensive development, and the amount of the hammer head of the main parts of the crusher has increased.

1. Classification by thickness: 

(1) thin plate 

(2) medium plate 

(3) thick plate

(4) extra thick plate

2. according to the production method classification:

(1) hot rolled steel plate 

(2) cold rolled steel plate

3. according to the surface characteristics of the classification: 

(1) galvanized sheet (hot galvanized sheet, galvanized sheet) 

(2) tinplate

(3) composite steel plate 

(4) color coated steel plate

4. classified by use: 

(1) bridge steel plate 

(2) boiler steel plate 

(3) shipbuilding steel plate 

(4) armor steel plate 

(5) automobile steel plate

(6) Roof steel plate

(7) Structural steel plate 

(8) electrical steel plate (silicon steel sheet) 

(9) spring steel plate 

(10) other

304 stainless steel plate and Q345 carbon steel plate can be welded. The welding of stainless steel and Q345 belongs to the welding between low carbon steel and austenitic stainless steel in this kind of dissimilar steel welded joint, due to its working conditions have intergranular corrosion and stress corrosion problems, usually choose E309 type welding material, but when the welding joint is in a higher temperature environment (design temperature ≥315℃), In order to prevent the migration of carbon during the working process, welding materials with a high nickel alloy content (such as InCONel 182 electrode, etc.) are usually used.

The difference between carbon steel pipe and seamless steel pipe:

1. Seamless steel pipe is a steel pipe without weld made by perforating hot rolling method.

Sometimes it is necessary to further cold work the pipe after hot working in order to get the corresponding shape and size.

The carbon steel pipe is generally made of round, square, flat and other shapes after multiple rolling.

2. Seamless steel pipe is the most used pipe in petrochemical production equipment today.

Carbon steel pipes are more widely used.

At the same time, carbon steel pipe is the main requirement of its chemical composition is the content of carbon, seamless steel pipe is a large type, referring to seamless steel pipe, a wide range.

Sort

1. according to the use of carbon steel can be divided into carbon structural steel, carbon tool steel and free cutting structural steel three categories, carbon structural steel is divided into engineering construction steel and machine manufacturing structural steel two.

2. according to the smelting method can be divided into open hearth steel, converter steel.

3. according to the deoxidation method can be divided into boiling steel (F), killed steel (Z), semi-killed steel (b) and special killed steel (TZ).

4. according to the carbon content can be divided into low carbon steel (WC≤0.25%), medium carbon steel (WC0.25%-0.6%) and high carbon steel (WC > 0.6%).

5. according to the quality of steel, carbon steel can be divided into ordinary carbon steel (containing phosphorus, sulfur is higher), high-quality carbon steel (containing phosphorus, sulfur is lower) and senior quality steel (containing phosphorus, sulfur is lower) and extra high quality steel.

Carbon steel is a common type of steel whose main components are iron and carbon. The content of carbon is between 0.2% and 2.11%, which makes carbon steel have good hardness and strength, but it also brings some disadvantages, such as easy rust and the need to go through heat treatment to enhance its performance.

The production process of carbon steel is relatively simple and can be obtained through smelting, rolling and other steps. It is widely used in various industrial fields, including construction, automobile manufacturing, machinery manufacturing, etc., because it is strong enough to withstand heavy pressure and has good processability.

However, while carbon steel has many advantages, it also has some limitations. For example, if the carbon content is too high, it may lead to increased brittleness; If the carbon content is too low, it may not provide enough strength. Therefore, choosing the right carbon content is crucial to producing high-quality carbon steel.

In general, carbon steel is an important engineering material, and its existence provides great convenience for our life and industrial production.

No. 35 steel is widely used in the manufacture of various forgings and hot presses, cold drawn and top forged steel, seamless steel pipes, parts in mechanical manufacturing, such as crankshafts, shafts, pins, levers, connecting rods, beams, sleeves, wheels, washers, screws, nuts, motorcycle frames, etc.

Grades and standards

Chinese brand: 35# Standard: GB/T 699-2015

American grade: ASTM1035 Standard: ASTM A29A29M-04

Japanese brand: S35C Standard: JIS G3507
-2005

When the steel or sample is stretched, when the stress exceeds the elastic limit, even if the stress is no longer increased, and the steel or sample continues to have obvious plastic deformation, this phenomenon is called yield, and the minimum stress value when the yield phenomenon is generated is the yield point. With the development of building seismic technology and the in-depth analysis of seismic mechanism, energy dissipation seismic technology has become a developing trend of building seismic technology.

Performance requirement

In addition to the high strength and good plasticity of structural seismic steel, the strain-aging sensitivity, brittle transition temperature, low cycle fatigue resistance and welding properties of steel should also be considered. Low yield point steel is mainly used to make energy dissipation dampers, and its anti-seismic mode determines the performance requirements of steel.

In the earthquake, the energy dissipation damper is required to bear the seismic load before other structural parts, and repeatedly deforms in the plastic zone to absorb seismic energy, so as to achieve the purpose of earthquake resistance. Therefore, the low yield point steel must have a very low yield point and the yield range is controlled in a very narrow range, but also have good processing and welding properties, and have good plasticity, so as to have good deformation ability.

In addition, seismic steel is subjected to repeated alternating loads during an earthquake. The duration of strong earthquakes is generally within 1min, the amplitude frequency is usually 1~3Hz, and the damage of buildings is caused within 100~200 cycles, which belongs to high strain and low cycle fatigue. Therefore, the low yield point steel must have good resistance to low cycle fatigue.

Decarbonization is not only related to temperature, but also depends on the type of metal or alloy, and depends on the heating medium. For example, silicon steel is easy to decarbonize, stainless steel is not easy to decarbonize, heat-resistant steel is not easy to decarbonize, if it is a reducing medium, you heat to the melting state will not decarbonize, if it is an oxidizing medium, it mainly depends on the level of oxidation, if it is heated in the air, the decarbonization situation is more difficult to say, only specific problem specific analysis, general carbon steel about 570 Degree produces strong oxidation decarburization.

Decarbonization or not has a lot to do with chemical composition, heating temperature, holding time, the existence form of carbon in the metallographic organization, and environmental atmosphere. Chemical composition alone cannot determine the heating temperature required to decarbonize the surface of the material.

The surface decarburization of steel materials is related to the carbon content or carbon equivalent. Taking 60Si2Mn as an example, the decarburization sensitive zone is about 1150-1250 degrees.

Decarbonization is also related to the heating atmosphere and heating time.

Another thing to consider is that oxidation and decarbonization generally exist at the same time, if the oxidation rate is greater than decarbonization, then even in the high temperature zone will not cause material decarbonization, but the surface oxide thickness increases. 35CrMo is generally used for the production of high-strength fasteners, which generally requires the spinning temperature not to exceed 880 degrees, the cooling speed in the range of 0.8-0.85 degrees /s, and the decarburization layer can be controlled between (0.2-0.4)D%. This decarbonized layer is tolerable and subsequent cold heading and mechanical properties can be guaranteed.

What is H-shaped steel

H section steel is a new type of economical building steel. It is an economic cross-section steel with good mechanical properties, which is optimized and developed for I-beam steel. It is named because its section is the same as the English letter "H".

The main features are as follows:

1. high structural strength: compared with I-steel section modulus is large, under the same bearing conditions can save metal 10-15%.

2. Flexible and rich design style: in the case of the same beam height, the steel structure can be 50% larger than the concrete structure, so that the building layout is more flexible.

3. high structural stability: the steel structure is dominated by hot rolled H-beam steel, scientific and reasonable structure, good plasticity and flexibility, high structural stability. Especially suitable for some earthquake prone areas of the building structure.

4. increase the effective use area: compared with concrete structure, steel structure column cross-sectional area is small, can increase the effective use area of the building. Depending on the building form, the effective use area can be increased by 4-6%.

5. easy processing: easy structural connection and installation, but also easy to disassemble and reuse.

6. High degree of industrial production: The steel structure based on hot rolled H beam has a high degree of industrial production, which is convenient for mechanical manufacturing, intensive production, high precision, convenient installation and easy quality assurance. You can build real house manufacturing plants, bridge manufacturing plants, industrial plants, manufacturing plants, etc.

7. the construction speed is fast: covers an area of small, suitable for all-weather construction, the influence of climate conditions is small. The construction speed of hot rolled H-beam steel structure is about 2-3 times that of concrete structure, and the capital turnover rate is doubled, which reduces the financial cost and saves investment.