The purpose of quenching is to improve hardness, strength and wear resistance to meet the use performance of parts. Quenching technology is widely used, such as tools, measuring tools, molds, bearings, springs, automobiles, tractors, diesel engines, cutting machines, pneumatic tools, drilling machinery, agricultural machinery, petroleum machinery, chemical machinery, textile machinery, aircraft and other parts.
(1) Quenching heating temperature
The quenching heating temperature is determined according to the composition, microstructure and different performance requirements of steel. Underwater steel is AC3+(30 ~ 50℃); * * * and * * steel are AC 1+(30 ~ 50℃).
If the quenching heating temperature of sub-* * steel is lower than AC3, the steel has not been completely austenitized at this time, and there are still some untransformed ferrite, which remains in the quenched structure after quenching. The hardness of ferrite is so low that it can't meet the requirements after quenching, and it will also affect other mechanical properties. If sub * * steel is heated to a temperature much higher than AC3 for quenching, the austenite grains will be obviously coarse and the properties after quenching will be destroyed. Therefore, choosing AC 3+(30 ~ 50℃) as the quenching heating temperature of sub-* * steel can not only ensure full austenite, but also keep austenite grains fine.
In general, the quenching heating temperature of steel after precipitation is recommended as AC 1+(30 ~ 50℃). In actual production, the temperature should be increased by about 20℃ according to the situation. When heated in this temperature range, its structure is austenite with fine grains and some undissolved carbides with fine and uniform distribution. After quenching, except for a small amount of retained austenite, its structure is fine carbide particles evenly distributed on the flaky martensite matrix. This structure has high hardness, high wear resistance and relatively small brittleness.
The quenching heating temperature of steel after precipitation should not be lower than AC 1, because the steel has not been austenitized at this time. When heated to a temperature slightly higher than AC 1, pearlite completely transforms into austenite, and a small amount of cementite dissolves into austenite. At this time, the austenite grain is fine, and its carbon content is slightly higher than * * *. If the temperature continues to rise, the secondary carburizing will continue to dissolve into austenite, which will lead to the continuous growth of austenite grains and the continuous increase of its carbon concentration, which will lead to the increase of quenching deformation tendency and the appearance of microcracks and brittleness in the quenched structure. At the same time, due to the high carbon content of austenite, the number of retained austenite increases after quenching, which reduces the hardness and wear resistance of the workpiece. Therefore, the quenching heating temperature of over-* * steel should not be much higher than AC 1, let alone above ACm.
When selecting the quenching heating temperature of the workpiece in production practice, besides observing the above general principles, we should also consider the influence of chemical composition, technical requirements, size and shape, original structure, heating equipment, cooling medium and other factors, and adjust the heating temperature appropriately. Such as alloy steel parts, usually take the upper limit, and parts with complex shapes take the lower limit.
The quenching heating temperature selected by the new toughening process is different from the ordinary quenching temperature. For example, sub-temperature quenching is to austenitize sub-* * steel at a temperature slightly lower than AC3 and then quench it, which can improve toughness, reduce ductile-brittle transition temperature and eliminate temper brittleness. Such as 45, 40Cr, 60Si2 and other materials, the heating temperature of subcritical quenching is AC3-(5 ~ 10℃).
More lath martensite can be obtained by high temperature quenching, or the strength and toughness of all lath martensite can be improved. For example, 16Mn steel is quenched at 940℃, 5CrMnMo steel at 890℃ and 20CrMnMo steel at 920℃, and the effect is good.
The carbon content in austenite can be reduced and the toughness of steel can be improved by quenching high carbon steel at low temperature, quickly and in a short time, appropriately reducing the quenching temperature of high carbon steel, or adopting the method of rapid heating and shortening the holding time.
(2) heat preservation time
In order to complete the structure transformation, carbide dissolution and austenite composition homogenization inside and outside the workpiece, it is necessary to keep the temperature at quenching heating temperature for a certain time.
(3) Quenching medium
The medium used to quench and cool the workpiece is called quenching cooling medium (or quenching medium). The ideal quenching medium should have such conditions that the workpiece can be quenched into martensite without causing too much quenching stress. This requires slow cooling above the "nose point" of C curve to reduce the thermal stress caused by rapid cooling; The cooling rate at the "nose" is higher than the critical cooling rate to ensure that the undercooled austenite will not undergo non-martensitic transformation; Below the "nose", especially when Ms indicates the temperature, the cooling rate should be as small as possible to reduce the stress of tissue transformation.
Commonly used quenching media are water, aqueous solution, mineral oil, molten salt, molten alkali and so on.
● Water
Water is a quenching medium with strong cooling capacity. Wide source, low price, stable composition and not easy to deteriorate. The disadvantage is that in the "nose" area of C curve (about 500 ~ 600℃), water is in the vapor film stage, and cooling is not fast enough, which will form "soft spots"; However, in the martensite transformation temperature range (300 ~ 100℃), water is in the boiling stage, which is easy to make the martensite transformation speed too fast, produce great internal stress, and lead to deformation and even cracking of the workpiece. When the water temperature rises, the water contains more gas or water is mixed with insoluble impurities (such as oil, soap, mud, etc.). ), which will significantly reduce its cooling capacity. Therefore, water is suitable for quenching and cooling of carbon steel workpieces with small cross-sectional size and simple shape.
● Salt water and alkaline water.
After the high-temperature workpiece is immersed in the cooling medium, a proper amount of salt and alkali are added into the water, and the crystals of salt and alkali are precipitated in the steam film stage and burst immediately, which destroys the steam film and shatters the oxide scale on the surface of the workpiece, thus improving the cooling capacity of the medium in the high-temperature area. Its disadvantage is that the medium is corrosive. Generally, the concentration of brine is 10%, and the concentration of caustic soda solution is 10% ~ 15%. It can be used as quenching medium for carbon steel and low alloy structural steel workpieces, and the service temperature does not exceed 60℃. After quenching, it should be cleaned in time and treated with rust prevention.
● Oil
Mineral oil (mineral oil) is generally used as a cooling medium. Such as engine oil, transformer oil and diesel oil. Engine oil generally adopts 10 #, 20 # and 30 # engine oil. The greater the oil number, the greater the viscosity, the higher the flash point, the lower the cooling capacity and the higher the service temperature.
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At present, there are three new quenching oils: high-speed quenching oil, bright quenching oil and vacuum quenching oil.
High-speed quenching oil is a kind of quenching oil with improved cooling rate in high temperature area. There are two basic ways to obtain high-speed quenching oil. One is to choose different kinds of mineral oils with different viscosities and mix them in a proper proportion, so as to improve the cooling capacity in high-temperature areas by increasing the characteristic temperature. The other is to add additives to ordinary quenching oil to form powdery floaters in the oil. Additives include barium salt, sodium salt, calcium salt, phosphate, stearate, etc. The production practice shows that the cooling rate of high-speed quenching oil is obviously higher than that of ordinary quenching oil in the unstable region of undercooled austenite, but it is close to that of ordinary quenching oil in the low-temperature martensite transformation region. This can obtain higher hardenability and hardening ability, greatly reduce deformation, and is suitable for quenching alloy steel workpieces with complex shapes.
Bright quenching oil can make the workpiece keep a bright surface after quenching. Bright quenching oil with different cooling rates can be obtained by adding polymer additives with different properties to mineral oil. The main component of these additives is brightener, and the function of brightener is to suspend the aging products that are insoluble in oil and prevent deposition on the workpiece. In addition, bright quenching oil additives also contain antioxidants, surfactants and coolants.
Vacuum quenching oil is a cooling medium used for vacuum heat treatment quenching. Vacuum quenching oil must have low saturated vapor pressure, high and stable cooling capacity, good brightness and thermal stability, otherwise it will affect the effect of vacuum heat treatment.
Salt bath and alkali bath quenching media are generally used for step quenching and isothermal quenching.
● New quenchant
There are polyvinyl alcohol aqueous solution and nitrate aqueous solution.
Generally, the mass fraction of polyvinyl alcohol is 0. 1% ~ 0.3%, and its cooling capacity is between water and oil. When the workpiece is quenched in solution, a vapor film and a gel film are formed on the surface of the workpiece, and these two films cool the heated workpiece. After entering the boiling stage, the film breaks and the workpiece cools faster. When it reaches the low temperature, the polyvinyl alcohol gel film is formed again, and the cooling rate of the workpiece is reduced again. Therefore, this solution has low cooling capacity in high and low temperature regions, high cooling capacity in middle temperature regions, and good cooling characteristics.
Nitrate aqueous solution consists of 25% sodium nitrate +20% sodium nitrite +20% potassium nitrate +35% water. At high temperature (650 ~ 500℃), due to the precipitation of salt crystals, a broken steam film is formed, and its cooling capacity is close to that of water. At low temperature (300 ~ 200℃), because of its extremely high concentration, poor fluidity and cooling capacity close to that of oil, it can replace water-oil dual-medium quenching.
(4) cooling method
The most widely used quenching classification in production practice is divided by different cooling methods. There are mainly single liquid quenching, double liquid quenching, graded quenching and isothermal quenching.
● Single liquid quenching
It is a quenching operation method that the austenitic chemical parts are immersed in a certain quenching medium and cooled to room temperature. Single liquid quenching medium includes water, salt water, alkaline water, oil and special quenching agent. Generally speaking, carbon steel is quenched and alloy steel is quenched.
Single liquid quenching operation is simple, which is beneficial to realize mechanization and automation. Its disadvantage is that the cooling speed is limited by the cooling characteristics of the medium, which affects the quenching quality. Single liquid quenching is only suitable for carbon steel with simple shape.
● Double liquid quenching
Austenitic chemical parts are first immersed in a medium with strong cooling capacity, and then taken out before the steel reaches the temperature of quenching medium, and then immediately immersed in another medium with weak cooling capacity for cooling, such as water before oil, water before air, etc. Double liquid quenching reduces the tendency of deformation and cracking, which is difficult to master and has certain limitations in application.
● Martensite graded quenching
The austenitic chemical parts are immersed in a liquid medium (salt bath or alkali bath) with a temperature slightly higher or lower than the martensite point of steel, and the quenching process is kept for a proper time. After the inner and outer layers of the steel parts reach the medium temperature, they are taken out and air-cooled to obtain martensite structure, which is also called graded quenching.
Staged quenching can effectively reduce phase transformation stress and thermal stress, and reduce quenching deformation and cracking tendency because it stays at the staged temperature until the internal and external temperatures of the workpiece are consistent and then air-cooled. Graded quenching is suitable for alloy steel and high alloy steel workpieces with high deformation requirements, and can also be used for carbon steel workpieces with small cross-sectional size and complex shape.
Isothermal quenching of lower bainite
It is a quenching process in which steel parts are austenitized, quickly cooled to the bainite transformation temperature range (260 ~ 400℃), and austenite is transformed into bainite, sometimes called isothermal quenching. The general heat preservation time is 30 ~ 60 min.
● Compound quenching
Quenching the workpiece below Ms to obtain 10% ~ 20% martensite, and then isothermal in the lower bainite temperature zone. This cooling method can make the workpiece with large cross section obtain M+B structure. Martensite formed during pre-quenching can promote bainite transformation and tempered martensite at isothermal temperature. When compound quenching is used for alloy tool steel workpiece, it can avoid the brittleness of the first tempering and reduce the tendency of residual austenite, that is, deformation and cracking.
Special workpieces are also quenched by compressed air, spray quenching and spray quenching.
What are the raw materials, processing technology and detailed heat treatment technology of sprocket?
Reward score: 10- settlement time: 2007- 12-9 00:36.
Question supplement: Thank you very much for your quick and detailed answers. The specific requirements are as follows:
When working, the matrix has certain strength and impact resistance (the number of teeth is 16, which is similar to the size of the matrix compared with the bicycle flywheel, and the strength and impact resistance are smaller), and the tooth surface has good wear resistance.
The material has good processability, good economy and wide sources. (tentatively 15 # steel)
Can you give me an optimal detailed answer? Thank you very much.
Questioner: stdzhou- the best answer during the probation period
Processing technology: Different materials have different processing technologies.
The most common, medium and low speed, low power, can choose A3, A5, cast iron.
When there is impact load, when z is less than or equal to 25, 15# steel or 20# steel can be selected for carburizing, quenching and tempering, with HRC50~60.
When there is impact load, when z is greater than 25, 35# steel can be selected, normalized, 160~200HB.
Wear-resistant, no violent impact, with 45#, 50#, 45Mn, ZG45, quenching and tempering, HRC40~50.
For high power with z less than 30, 15Cr, 20Cr, carburizing \ quenching \ tempering and HRC50~60 are adopted.
Importantly, high strength and wear resistance, quenching and tempering with 40Cr, 35SiMn and 35CrMo, HRC40~50.
What are the similarities and differences between annealing, normalizing, quenching and tempering in heat treatment methods?
Reward score: 0-?
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Why did you run? 007- 1-25 22:39
What are the similarities and differences between annealing, normalizing, quenching and tempering in heat treatment methods?
Questioner: chendan1202-the best answer during the probation period.
Metal heat treatment is a kind of technological method that the metal workpiece is heated to a suitable temperature in a certain medium, kept at this temperature for a certain time, and then cooled at different speeds.
Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing technologies, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but endows or improves the working performance of the workpiece by changing the microstructure inside the workpiece or changing the chemical composition on the surface of the workpiece. Its characteristic is to improve the intrinsic quality of the workpiece, which is generally invisible to the naked eye.
In order to make the metal workpiece have the required mechanical properties, physical properties and chemical properties, in addition to reasonable selection of materials and various forming processes, heat treatment process is often essential. Steel is the most widely used material in machinery industry, and its microstructure is complex and can be controlled by heat treatment, so the heat treatment of steel is the main content of metal heat treatment. In addition, aluminum, copper, magnesium, titanium and their alloys can also change their mechanical, physical and chemical properties through heat treatment, thus obtaining different properties.
In the process from the Stone Age to the Bronze Age and the Iron Age, the role of heat treatment was gradually recognized by people. As early as 770 BC ~ 222 BC, the people of China discovered in production practice that the properties of copper and iron would change due to the influence of temperature and pressure deformation. Softening of white cast iron is an important process for manufacturing farm tools.
In the 6th century BC, steel weapons were gradually adopted. In order to improve the hardness of steel, quenching technology has been developed rapidly. Two swords and a halberd unearthed in Yanxiadu, Yixian County, Hebei Province, China, have martensite in the microstructure, indicating that they have been quenched.
With the development of quenching technology, people gradually discovered the influence of cooling liquid on quenching quality. In the Three Kingdoms period, Shuman Puyuan once made 3,000 knives for Zhuge Liang in this oblique valley in Shaanxi. According to legend, he sent people to Chengdu to get water for quenching. This shows that ancient China paid attention to the cooling capacity of different water quality, as well as the cooling capacity of oil and urine. The sword unearthed in the tomb of Wang Jing in Zhongshan in the Western Han Dynasty (206 BC-24 AD) in China has a carbon content of 0. 15-0.4% and a surface carbon content of more than 0.6%, indicating that carburizing technology has been applied. But at that time, as a personal "craft" secret, it refused to spread, so it developed slowly.
1863, British metallographers and geologists showed six different metallographic structures of steel under a microscope, which proved that the internal structure of steel would change when it was heated and cooled, and the high-temperature phase in steel would change into a harder phase when it was rapidly cooled. The iron isomerism theory established by Frenchman Osmond and the iron-carbon phase diagram first formulated by Englishman Austin laid a theoretical foundation for modern heat treatment technology. At the same time, people have also studied the protection methods of metals during heat treatment to avoid oxidation and decarbonization of metals during heating.
From 1850 to 1880, there are a series of patents on the application of various gases (such as hydrogen, gas, carbon monoxide, etc.). ) for protective heating. From 1889 to 1890, British Lake obtained patents for bright heat treatment of various metals.
Since the 20th century, with the development of metal physics and the transplantation and application of other new technologies, the metal heat treatment technology has been greatly developed. A remarkable progress is 190 1 ~ 1925, which uses rotary hearth furnace for gas carburizing in industrial production; Dew point potentiometer appeared in 1930s, which made the carbon potential in furnace atmosphere controllable. Later, by using carbon dioxide infrared instrument and oxygen probe, a method to further control the carbon potential in the furnace atmosphere was developed. In 1960s, plasma field was used in heat treatment technology, and ion nitriding and carburizing processes were developed. With the application of laser and electron beam technology, new surface heat treatment and chemical heat treatment methods have been obtained for metals.
Bimetallic heat treatment process
The heat treatment process generally includes three processes of heating, heat preservation and cooling, and sometimes there are only two processes of heating and cooling. These processes are interrelated and uninterrupted.
Heating is one of the important steps of heat treatment. There are many heating methods for metal heat treatment. Charcoal and coal were first used as heat sources, and later liquid and gas fuels were used. The application of electricity makes heating easy to control and has no environmental pollution. These heat sources can be used for direct heating or indirect heating through molten salt or metal or even floating particles.
When the metal is heated, the workpiece is exposed to air, which often leads to oxidative decarbonization (that is, the carbon content on the surface of steel parts is reduced), which has a very adverse impact on the surface properties of parts after heat treatment. Therefore, metals should usually be heated in controlled or protective atmosphere, molten salt and vacuum, and can also be protected by coating or packaging.
Heating temperature is one of the important technological parameters in heat treatment process, and the selection and control of heating temperature is the main problem to ensure the quality of heat treatment. The heating temperature varies with the metal material to be treated and the purpose of heat treatment, but it is usually heated above the phase transition temperature to obtain the required structure. In addition, the transformation takes a certain time, so when the surface of the metal workpiece reaches the required heating temperature, it must be kept at this temperature for a certain time, so that the internal and external temperatures are consistent and the microstructure is completely transformed. This time is called holding time. When high energy density heating and surface heat treatment are used, the heating speed is extremely fast, and the heat preservation time is generally short or not, while the heat preservation time of chemical heat treatment is often long.
Cooling is also an essential step in the heat treatment process, and the cooling mode varies from process to process, mainly controlling the cooling speed. Generally, the cooling rate of annealing is the slowest, that of normalizing is faster, and that of quenching is faster. However, due to different steel grades, the requirements are also different. For example, air hardened steel can be hardened at the same cooling rate as normalizing.
Metal heat treatment process can be roughly divided into whole heat treatment, surface heat treatment, local heat treatment and chemical heat treatment. According to the difference of heating medium, heating temperature and cooling mode, each type can be divided into several different heat treatment processes. The same metal can obtain different structures through different heat treatment processes, thus having different properties. Steel is the most widely used metal in industry, and its microstructure is also the most complex, so there are many heat treatment processes for steel.
Integral heat treatment is to heat the workpiece as a whole, and then heat it properly.
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The cooling rate changes the overall mechanical properties of metal heat treatment process. The integral heat treatment of steel has four basic processes: annealing, normalizing, quenching and tempering.
Annealing is to heat the workpiece to a suitable temperature, adopt different holding time according to the material and size of the workpiece, and then slowly cool it, with the purpose of making the internal structure of the metal reach or approach the equilibrium state, obtaining good technological performance and service performance, or preparing the structure for further quenching. Normalization is to heat the workpiece to a suitable temperature and then cool it in the air. The effect of normalizing is similar to annealing, but the obtained microstructure is finer, which is often used to improve the cutting performance of materials and sometimes as the final heat treatment of some parts with low requirements.
Quenching is to heat and insulate the workpiece, and then quickly cool it in quenching media such as water, oil or other inorganic salts, organic water solution, etc. After quenching, steel becomes hard, but at the same time it becomes brittle. In order to reduce the brittleness of steel parts, the quenched steel parts are kept at an appropriate temperature higher than room temperature and lower than 7 10℃ for a long time, and then cooled. This process is called tempering. Annealing, normalizing, quenching and tempering are the "four fires" in the whole heat treatment, among which quenching and tempering are closely related, and they are often used together and are indispensable.
The "Four Fires" evolved heat treatment processes with different heating temperatures and cooling modes. In order to obtain certain strength and toughness, the process of combining quenching with high temperature tempering is called quenching and tempering. Some alloys are quenched to form supersaturated solid solutions and kept at room temperature or slightly higher temperature for a long time to improve the hardness, strength or electromagnetic properties of the alloys. This heat treatment process is called aging treatment. The method of combining pressure working deformation with heat treatment effectively and closely to obtain good strength and toughness of workpiece is called thermomechanical treatment. The heat treatment in negative pressure atmosphere or vacuum is called vacuum heat treatment, which can not only make the workpiece not oxidized and decarbonized, but also keep the surface of the workpiece clean and improve the performance of the workpiece, and can also introduce infiltration agent for chemical heat treatment.
Surface heat treatment is a kind of metal heat treatment process that only heats the surface layer of the workpiece to change its mechanical properties. In order to heat only the surface layer of the workpiece without transferring excessive heat to the interior of the workpiece, the heat source used must have high energy density, that is, the heat energy given to the workpiece per unit area is large, so that the surface layer or part of the workpiece can reach high temperature in a short time or instantly. The main methods of surface heat treatment are laser heat treatment, flame quenching and induction heating heat treatment. The commonly used heat sources are oxyacetylene or oxypropane flame, induced current, laser and electron beam.
Chemical heat treatment is a metal heat treatment process by changing the chemical composition, microstructure and properties of the workpiece surface. The difference between chemical heat treatment and surface heat treatment is that the latter changes the chemical composition of the surface layer of the workpiece. Chemical heat treatment is to heat the workpiece in a medium (gas, liquid and solid) containing carbon, nitrogen or other alloying elements, and keep the temperature for a long time, so that the surface of the workpiece is infiltrated with carbon, nitrogen, boron and chromium. After the elements are infiltrated, sometimes other heat treatment processes such as quenching and tempering are needed. The main methods of chemical heat treatment are carburizing, nitriding, metallization and compound carburizing.
Heat treatment is one of the important processes in the manufacturing process of mechanical parts and molds. Generally speaking, it can guarantee and improve various properties of the workpiece, such as wear resistance and corrosion resistance. It can also improve the microstructure and stress state of the blank, so as to facilitate various cold and hot processing.
For example, white cast iron can be annealed for a long time to obtain malleable cast iron and improve its plasticity; Using the correct heat treatment process, the service life of gears can be doubled or even dozens of times longer than that of gears without heat treatment; In addition, cheap carbon steel has some properties of expensive alloy steel by infiltrating some alloying elements, which can replace some heat-resistant steels and stainless steels; Almost all tools and molds need heat treatment before use.
Classification of three steels
Steel is an alloy with iron and carbon as the main components, and the carbon content is generally less than 2. 1 1%. Steel is an extremely important metal material in economic construction. Steel is divided into carbon steel and alloy steel according to chemical composition. Carbon steel is an alloy obtained by melting pig iron. In addition to iron and carbon, it also contains a small amount of impurities such as manganese, silicon, sulfur and phosphorus. Carbon steel has certain mechanical properties, good process performance and low price. Therefore, carbon steel has been widely used. However, with the rapid development of modern industry and science and technology, the properties of carbon steel can not fully meet the needs, so people have developed various alloy steels. Alloy steel is a multi-element alloy obtained by purposefully adding some elements (called alloying elements) on the basis of carbon steel. Compared with carbon steel, the properties of alloy steel have been significantly improved, so it has been widely used.
Because of the variety of steel products, it is necessary to classify steel products so as to facilitate production, storage, selection and research. According to the use, chemical composition and quality of steel, steel can be divided into many types:
(1). Classification by purpose
According to the use of steel, it can be divided into three categories: structural steel, tool steel and special performance steel.
1. Structural steel:
(1). Steel used as various machine parts. It includes carburized steel, quenched and tempered steel, spring steel and rolling bearing steel.
(2) Steel used as engineering structure. It includes A, B, special steel and common low alloy steel in carbon steel.
2. Tool steel: steel used for manufacturing various tools. According to the different uses of tools, they can be divided into cutting tool steel, die steel and measuring tool steel.
3. Special performance steel: It is a kind of steel with special physical and chemical properties. Can be divided into stainless steel, heat-resistant steel, wear-resistant steel, magnetic steel and so on.
(2) Classification by chemical composition
According to the chemical composition of steel, it can be divided into carbon steel and alloy steel
Carbon steel: according to carbon content, it can be divided into low carbon steel (carbon content ≤ 0.25%); Medium carbon steel (0.25% 10%). In addition, according to the different types of main alloying elements contained in steel, it can also be divided into manganese steel, chromium steel, chromium-nickel steel, chromium-manganese-titanium steel and so on.
(3) Classification by quality
According to the content of harmful impurities phosphorus and sulfur in steel, it can be divided into ordinary steel (phosphorus content ≤0.045%, sulfur content ≤ 0.055%; Or both phosphorus and sulfur content are ≤ 0.050%); High quality steel (phosphorus and sulfur content ≤0.030%).
Besides, according to the smelting furnace?
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When naming steel products, steel mills often combine three classification methods: use, composition and quality. For example, steel is called ordinary carbon structural steel, high-quality carbon structural steel, carbon tool steel, advanced high-quality carbon tool steel, alloy structural steel and alloy tool steel. ≤ 0.040%); High quality steel (phosphorus content ≤0.035%,