Due to the structural characteristics of the cylindrical spiral spring, within the elastic deformation range of the material, the relationship between the spring load “P” and the deformation amount “F” is not completely linear. As the deformation increases, the helix angle also increases. , The deviation of load and deformation from linearity is also large. However, the relationship between load and deformation is basically linear within the working deformation range of a spring, and the deviation from linearity is generally 1% to 3%.
1. Natural attributes
Copper is one of the earliest ancient metals discovered by mankind. Mankind began to use copper more than 3,000 years ago.
Metal copper, element symbol Cu, atomic weight 63.54, specific gravity 8.92, melting point 1083oC. The pure copper is light rose or light red, and after a copper oxide film is formed on the surface, the appearance is copper-colored. Copper has many valuable physical and chemical properties, such as high thermal and electrical conductivity, strong chemical stability, high tensile strength, easy welding, corrosion resistance, plasticity, and ductility. Pure copper can be drawn into very thin copper wires and made into very thin copper foil. It can form alloys with zinc, tin, lead, manganese, cobalt, nickel, aluminum, iron and other metals.
The development of copper smelting technology has gone through a long process, but so far copper smelting is still dominated by fire smelting, and its output accounts for about 85% of the world’s total copper output. 1) Pyrometallurgy is generally to first increase the raw ore containing a few percent or a few thousandths of copper to 20-30% through beneficiation, and use it as a copper concentrate in a closed blast furnace, reverberatory furnace, electric furnace or flash furnace For matte smelting, the produced matte (copper matte) is then sent to a converter for blowing into blister copper, and then oxidized and refined in another reverberatory furnace to remove impurities, or cast into an anode plate for electrolysis to obtain a high grade 99.9% electrolytic copper. The process is short and adaptable, and the recovery rate of copper can reach 95%. However, because the sulfur in the ore is discharged as sulfur dioxide waste gas in the two stages of matte production and conversion, it is difficult to recover and easy to cause pollution. In recent years, molten pool smelting such as the silver method and the Noranda method, as well as the Mitsubishi method in Japan, has gradually developed towards continuous and automated pyrometallurgy. 2) Modern wet smelting includes sulfuration roasting-leaching-electrodeposition, leaching-extraction-electrodeposition, bacterial leaching, etc., suitable for heap leaching and tank leaching of low-grade complex ore, copper oxide ore, copper-bearing waste ore Or leaching in place. The hydrometallurgical technology is gradually being promoted, and it is expected that it will reach 20% of the total output by the end of this century. The introduction of hydrometallurgy has greatly reduced the cost of copper smelting.
2. Classification of copper and copper products
1. Classification according to the existing forms in nature
Natural copper-the copper content is above 99%, but the reserves are very small;
Copper oxide ore—–not many
Copper sulfide ore-the copper content is extremely low, generally around 2-3%. More than 80% of the world’s copper is refined from copper sulfide ore.
2. Classified by production process
Copper concentrate-ore with higher copper content selected before smelting.
Blister copper-the smelted product of copper concentrate, with a copper content of 95-98%.
Pure copper-copper with a content of more than 99% after smelting or electrolysis. Fire refining can obtain 99-99.9% pure copper, and electrolysis can make the purity of copper reach 99.95-99.99%.
3. Classified by main alloy composition
Bronze—–copper-tin alloy, etc. (except for zinc-nickel, alloys with other elements are called bronze)
4. Classified by product form: copper tube, copper rod, copper wire, copper plate, copper strip, copper strip, copper foil, etc.
3. Copper product number and quality standard
The quality standard for the subject matter of the copper futures contract before September 1997 was the GB466-82 standard, and the delivery product was No. 1 copper. From September 1997 to August 1998, GB466-82 and GB/T-467-1997 were both The standards are implemented at the same time. Since September 1998, all GB/T467-1997 standards have been implemented. Both high-purity copper cathodes and standard copper cathodes can be delivered. There is no quality premium or discount, only brand premiums and discounts.
1. The chemical composition of high-purity cathode copper (Cu-CATH-1): Cu+Ag is not less than 99.95, and the total impurity content does not exceed 0.0065 (the impurity classification content is omitted).
Copper is a widely used metal with unique advantages in terms of conductivity, conductivity, tensile strength, extensibility, corrosion resistance, and fatigue resistance. It is mainly used in industrial equipment manufacturing, electrical Industry, communication industry, construction industry, transportation industry, fastener industry, etc. The numerous uses also make the price of copper very sensitive to changes in supply and demand and fluctuates widely. The close correlation between copper and social life makes copper demand directly related to changes in economic conditions.
In addition to mining, the supply of copper can also be obtained through secondary recovery. The main copper producing countries in the world are Chile, the United States, Canada, Zambia, Zaire and Peru. my country is also a major copper producer, and its output in 1991 ranked seventh in the world. my country’s copper production is mainly concentrated in Jiangxi, Xiangbei, Gansu, Tianjin, Shanghai, Anhui, Liaoning, Shanxi, Hunan, and Yunnan. However, due to the low grade of my country’s copper ore, unsatisfactory resource conditions, and a large demand for copper, copper and copper alloys are imported every year to meet the shortage of supply.
In 2001, the global consumption of copper was about 14.885 million tons, and copper consumption was concentrated in developed industrial countries. The United States is the largest copper consumer. In 2000, it consumed 2.923 million tons, accounting for about one-fifth of the world’s total consumption, followed by China 1.75 million tons, Japan 1.327 million tons, and Europe 4.385 million tons. From an industry perspective, the electrical industry and the construction industry consume the most copper.
In 2002, the world’s refined copper production was 15.02 million tons, consumption was 14.90 million tons, and the supply and demand gap was 120,000 tons. The balance of supply and demand in 2001 was an oversupply of 948,000 tons, and the contradiction between supply and demand has been greatly improved.
As a new term, gas springs have gradually appeared in some Internet newspapers, and its practical range has also developed from some basic car trunk and hood support to the machinery manufacturing industry, which is used for equipment accessory support and equipment shock absorption. As the support of toolbox cover, medical industry, fitness equipment and other fields, as its practicality is further recognized, the scope of use is also becoming wider and wider. Some people in the industry ask: The application range of gas springs is becoming wider and wider. Does it have an impact on the original telescopic spring? I personally think that it will not cause an impact on the original spring. Of course it will have a certain impact, because most of the gas springs are used. It is an innovation in the product design of some companies. For example, the rear box of Sanlun motorcycles was originally supported by iron rods (they are still used). Now the gas springs are very light, convenient and labor-saving. Some units don’t know. His design has certain limitations, but companies must be innovative in order to stay ahead of their peers. I have been making gas springs for many years. Experience tells me that many manufacturers are now trying out our gas springs, and they have all used them formally. The effect is obvious, but some companies don’t know what a gas spring is, let alone its function, so they will In a passive position, I hope that some industries, such as: machinery manufacturing, automobile and motorcycle, transportation equipment, toolbox and other box manufacturing, medical treatment, fitness, kitchen cabinets, etc., if you need to understand the function and use of gas springs, please consult me , I will definitely advise you.
Some experts in the spring industry in my country believe that with the development of the main engine, the spring product market in my country will also grow simultaneously. It is estimated that the sales of the whole industry will exceed 4 billion yuan by 2010, and the proportion of the automobile and motorcycle industries in the spring market will be More than 50%. At the same time, in order to adapt to market changes, the spring industry will show new development trends in the next few years:
-A new combination appears. In the next few years, my country’s spring industry will still be dominated by small companies, but some advantageous companies start from the market and business strategy, use the capital, technology and talent advantages in their hands to merge and acquire some companies to obtain the necessary production factors and market resources , Most of the state-owned and collective enterprises in the spring industry will be transformed into joint-stock or private enterprises.
——Price competition turns to technology and quality competition. With the increasingly fierce market competition, the profit margin of the spring industry has become smaller and smaller. In addition, the main engine manufacturers have higher and higher requirements for the quality of accessories. Enterprises can no longer rely on simple price reductions to win the market. Technology and quality have become the key to competition. From July 1, 2006, my country’s auto parts tariffs will be reduced to 10%, and the final prices of suspension springs, valve springs, stabilizers and other products for the automotive industry will gradually be in line with international prices, and for mini-cars , The products of the van have undergone fierce market competition. The current price has a certain degree of competitiveness compared with the international market, but the quality level cannot compete with similar products. The prices of other products, especially those for motorcycles and some small springs, are already lower than the international market prices. Therefore, similar foreign products pose no threat to us in terms of price, and competition is mainly manifested in quality.
——Products are developing towards lightweight and high reliability. Roughly estimated, in 2010, the annual demand for suspension springs in China’s automobile industry was about 8 million pieces, and the annual demand for valve springs was about 30 million pieces (excluding motorcycles and diesel engines). The technical development trend of these two springs is generally lightweight (high stress) and high reliability. For the currently available special-shaped cross-section suspension springs and valve springs, due to high material prices and complex manufacturing processes, the production cost is higher than that of round-section springs. Therefore, there is no sign that the special-shaped section springs will completely replace the round-section springs.
The working principle of spring-loaded safety valve
The working principle of the spring-loaded safety valve is: when the gas pressure under the safety valve disc exceeds the pressing force of the spring, the disc is pushed open. After the valve flap is opened, the exhaust gas will act on the valve flap clamping ring due to the rebound of the lower adjusting ring, so that the valve will open quickly. As the valve flap moves up, the gas impacts on the upper adjusting ring, causing the exhaust direction to tend to be vertical downward. The reaction force generated by the exhaust pushes the valve flap upwards and keeps the valve flap in a certain pressure range. Sufficient lifting height. With the opening of the safety valve, the gas is continuously discharged, and the gas pressure in the system gradually decreases. At this time, the force of the spring will overcome the gas pressure acting on the valve flap and the reaction force of the exhaust, thereby closing the safety valve. Valve spring
High-speed steel is the main material for manufacturing various cutting tools (or molds) and is currently widely used. When a machined tool is working, due to friction, the temperature of the part where the tool is used will inevitably increase. For example, when the cutting speed of the tool is 10-20M/min, the temperature of the blade is 200-320℃. When the turning speed is 50-80M/min, the blade temperature is 500-600°C. As the processing object changes, in some special cases, the blade will reach 670℃, and even the temperature of some warm extrusion mold parts will reach 700℃. This requires our cutting tools (or tools and moulds) to use corresponding reasonable tool materials, which should have high hardness, high strength, high wear resistance, high red hardness and certain toughness necessary for tool materials. In order to meet the above requirements, the heat treatment of high-speed steel must be strictly controlled from annealing to quenching. According to the service conditions of various tools, the heat treatment process parameters must be reasonably selected to achieve the most ideal performance and minimum deformation. For some tools with special requirements, the surface hardness and wear resistance must be improved by chemical heat treatment.
This standard is re-established on the basis of JB/T 3823-1984 “Technical Conditions for Spiral Springs for Automobiles” and JB/T 3824-1984 “Test Methods for Spiral Springs for Automobiles”. The above two standards were abolished in 1999. Compared with JB/T 3823-1984 “Technical Conditions for Spiral Springs for Automobiles” and JB/T 3824-1984 “Test Methods for Spiral Springs for Automobiles”, the main changes are as follows:
—————Specific regulations on hardness and decarburization:
—————Specific regulations for surface anticorrosion test:
—————Specific regulations are made on the product sampling method:
—————Description of verticality:
—————Specific regulations are made on the pitch uniformity:
—————Tolerance of the outer diameter of the end ring.
This standard was proposed by China Machinery Industry Federation
This standard is under the jurisdiction of the National Spring Standardization Technical Committee (SAC/TC235)
Drafting organizations of this standard: China Spring Factory, Guangzhou Huade Automobile Spring Co., Ltd., Shandong Lianmei Automobile Spring Co., Ltd., Zhuji Jinbao Automobile Spring Factory
The main drafters of this standard: Jiang Ying, Long Aihua, Yang Weiming, Liu Cuiling, Jin Guoxiang.
(7) The key to high strength is the transformation of pearlite
As mentioned above, the pearlite of high-carbon steel has much higher strength than the single ferrite phase of low-carbon ordinary steel. From this, it can be seen that pearlite is easy to obtain high strength under a small amount of drawing deformation, so it becomes an important factor for industrialization. On the contrary, it is difficult to achieve the effect of increasing the strength of pure iron no matter how strong the pressure is applied to cold drawing.
The mechanism by which pearlite can rapidly increase its strength through wire drawing is not yet fully understood. An important reason is that the “fine-grain strengthening” that thins the thickness of the lamellae after the crystallization is refined by wire drawing, and the “dislocation strengthening” that hardens the number of dislocations by processing have played an important role. , This is the same phenomenon that the place becomes hard when the steel wire is continuously bent.
For other organizations, such as cementite without grain boundaries before drawing, the strength of cementite can be improved after drawing to the nanometer level; there is also cementite that stabilizes the metal flower (Fe3C) It is decomposed by wire drawing, and the decomposed carbon adheres to dislocations to make it difficult to move, resulting in “solid solution strengthening” which increases the strength. In the past, it was only known that metal compounds would decompose under the action of a large external force. Recently, it has been discovered that all cementite is decomposed, which has attracted attention from all parties.
As a pioneer in the development of high-carbon steel wires, Nippon Steel takes the strength and elongation changes caused by cementite decomposition as an important research topic, and develops high-strength steel wires by studying its mechanism.
The reason why the decomposition mechanism of cementite is not ascertained is that iron is an excessively fine structure, and the cementite after strong processing is also an excessively fine structure of a few nanometers, which is difficult to observe with ordinary equipment, so its mechanism is difficult to explain. But now, through the “high resolution transparent microscope” that can analyze nanostructures and an atomic observer that can magnify 1 million times, the structure of single iron atoms, ferrite, and cementite can be clearly observed. , The research has made great progress and it is expected to be solved in the near future.
(8) The challenge of strength and extensibility
In order to make high carbon steel wire practical, not only the strength, but also the problem of insufficient elongation caused by breaking must be solved. From the perspective of the relationship between the two, when the strength of the steel wire for bridges exceeds 2000 MPa, its extensibility drops rapidly, that is, the highest practical strength should be balanced with the extensibility. From a technical point of view, the pure pursuit of strength can be further improved, but considering the significant decrease in extensibility, the ultimate strength of the radial steel wire is now only specified below 4000MPa.
A steel wire with high extensibility is subjected to a thermal break test by applying uniform pressure on the cross section of the steel wire. After dozens of twists, the vertical direction of the drawn wire breaks (normal breaking), but the steel wire with low extensibility deforms under torsion In the early stage, cracks (twisting) occurred along the vertical direction of the wire drawing. The occurrence of this phenomenon is known as an important reason for high strength. In addition, when the wire diameter is large, twisting occurs at about 2000 MPa, and when the wire diameter is small, it does not occur until 4000 MPa. This is called the “wire diameter effect”. There are many opinions on the causes of twisting cracks. According to research, the decomposition of cementite is the main cause.
(9) Minimize the high-strength steel processed by wire drawing
Use a processing process that takes into account both the strength and elongation of the steel. When strengthening the steel wire, first increase the strength by toughening treatment, and then increase the increase in strength per deformation (work hardening rate) by increasing the wire drawing (processing deformation) , As well as steel wire for bridges, some measures should be taken to suppress the strength drop caused by heating such as galvanizing (450℃) and bluing treatment.
While adopting the above methods to maintain high strength, it should also prevent the decrease in extensibility, that is, starting from the causal relationship that maintaining extensibility can avoid twisting, the test results prove that the toughened material is used to increase the strength and reduce the amount of wire drawing. The method of increasing the work hardening rate is more effective than increasing the amount of wire drawing to maintain the elongation. For example, when the final strength target is 2000 MPa, for low toughness treated materials (1000-1300 MPa level), twisting will easily occur when the target is reached by increasing the amount of drawing processing; if the 1400 MPa toughness treatment material is appropriately reduced It does not happen when measuring. It can be seen that the latter is more effective for maintaining the necessary extensibility under high strength. Precision spring
There are also many strengthening methods for toughening materials, and the representative method is alloying. That is, increasing the content of carbon, vanadium, chromium, silicon and other elements in the steel can increase the strength. Among them, the general basic method is to increase the carbon content; silicon can play a positive role in the solid solution strengthening of ferrite; chromium can make the thickness of the lamellae finer during the toughening treatment, so that the effect of increasing the strength is obvious. In addition, adding 0.2 to 0.5% of chromium to high carbon steel (containing C0.82%) can significantly increase the work hardening rate during wire drawing, so it is very helpful to increase the strength of high carbon steel wire. The application of meridian steel wire and bridge steel wire has been introduced in the previous article.
At present, in order to reduce CO2 emissions, automobile manufacturers are generally adopting measures to reduce fuel consumption by lightening the car body. Recently, high-strength aluminum alloy materials composed of aluminum with a small specific gravity are used, and the simple evaluation of the materials used uses the specific strength per unit weight. (Tensile strength/specific gravity).
Steels of 800 to 1200 MPa, which are generally called high-strength steels, have less specific strength than aluminum alloys, but steel materials have various structures. As methods to increase the strength of steels, there are “fine grain strengthening”, “solid solution strengthening”, and Organizational control techniques such as precipitation strengthening” and “dislocation strengthening”. Taking fine grain strengthening as an example, the following is an explanation. The method of refining the crystals of usually 20-30um ferrite to increase its strength, especially the effect of increasing the strength when the grain diameter is refined below 1um (see Table 2). The combination of microstructure technology and processing and heat treatment may achieve ultimate strength. Based on this, “ultra-high-strength steel” that rivals aluminum alloys has been developed.
Table 2 The relationship between ferrite grain refinement and strength
Grain diameter (um) 1251020304050
0.2C% strength (MPa) 920 700 400 325 280 240 230 220
Solid solution strengthening refers to the hardening phenomenon caused by the increase of a large amount of intrusive atoms such as C and N and substitution elements such as Si and Mn. Precipitation strengthening is due to the increase of compounds, and dislocation strengthening is due to the increase in the number of dislocations in the steel produced by processing. The hardening phenomenon caused.
(5) High carbon steel wire pursuing the ultimate strength
In rod and wire products, the material that pursues ultimate strength is high-carbon steel wire. The process technology of steel wire for bridge is described as follows.
Secondary processing companies require toughening treatment for hot-rolled semi-finished products to improve their strength while requiring good workability. This technology obtained a British patent in the 19th century. This kind of heat treatment adopts isothermal and homogenized heat treatment in a metal bath with good thermal conductivity to transform the ferrite and cementite structure existing in the steel into austenite at room temperature, and then transform it into austenite by rapid cooling Pearlite (Layered structure composed of cementite and ferrite). In the pearlite structure produced by this method, the strength of the wire is determined by the spacing between cementites (that is, the thickness of the lamellae). The smaller the thickness, the higher the strength. If it is cooled to room temperature without toughening treatment, the thickness of the lamellae is not uniform and the drawing processability is reduced, and the final strength is also reduced. For this reason, toughening treatment is an indispensable process for the production of steel that requires high strength.
In the process of the steel structure from high temperature to low temperature, austenite forms pearlite and grows up; but when it is rapidly cooled from 950°C to a low temperature of 550°C, it becomes uniform pearlite, which changes from hard and brittle cementite phase. It is formed side by side with the soft and good extensibility ferrite phase in the same direction; while for automotive plates and other materials with good workability, a softer single ferrite phase is formed.
If the toughening treatment can be omitted, it will bring great benefits to the user to simplify the processing. The above-mentioned “DLP” equipment can play this role, that is, uniformly adjust the cooling in a salt bath at 550°C to make it a semi-finished product When it turns into pearlite. For the production of high-strength steel wire for concrete shrinkage, Nippon Steel also uses “DLP” equipment processing to create conditions for users to eliminate toughening processing. In the production of steel wire for bridges, after toughening treatment, it is first subjected to pickling and zinc phosphate film treatment for “lubrication” treatment after being toughened, and then drawing is performed in multiple stages at room temperature. The hot-rolled Φ13mm semi-finished wire rod is cold drawn to Φ7mm, and finally galvanized to improve the corrosion resistance. However, the radial steel wire for tire reinforcement has many processing steps, that is, it uses Φ5.5mm wire, which is drawn into a Φ3mm steel wire. After intermediate toughening treatment, it is then drawn to a Φ1.5mm steel wire, and then finally toughened. Treatment and brass plating (which can improve the adhesion to rubber) treatment, and finally wire drawing to Φ0.3mm and composed of 5 pieces. The reason for the intermediate toughening treatment is to prevent wire breakage due to poor toughness when the wire is drawn from Φ5.5mm to Φ1.5mm at a time. In short, when all steels become higher in strength, their extensibility decreases as their strength increases. Therefore, the key to practical high-strength limit is extensibility. The key technology of high-strength high-carbon steel wire is also how to maintain extensibility.
(6) High carbon steel wire with finer diameter and higher strength
The strength of the steel wire has an obvious relationship with the wire diameter. For example, the wire diameter of the steel wire for bridges is Φ5～7mm, and its strength is below 2000MPa, while the radial steel wire for tires with a wire diameter of Φ0.2～0.4mm has a strength of about 4000MPa. . By increasing the strength of the steel wire, it is helpful to reduce the construction cost and reduce the weight of the tire.
When the diameter of the steel wire is reduced, due to the pressure applied during the wire drawing process, the strength will increase correspondingly as the degree of thinning (deformation processing amount) increases, which is the fundamental principle. Although there are certain differences between different steel grades, the strength of the steel wire with a strength of 1200～1500MPa after toughening treatment continues to increase when it continues to be drawn. The deformation of steel wire for bridges is about 1.5, and the deformation of meridian steel wire is as high as 3.5 to 4. The relationship between the deformation and strength of the processing is shown in Table 3.
Table 30. Relationship between processing deformation and strength of 82%C steel
Machining deformation (%) 012345
Tensile strength (MPa) 120017002000280035004300
This principle can be explained by the changes in the structure of steel. The smaller the width of the ferrite interval (that is, the thickness of the lamella), the higher the strength. Because the steel wire that has just been toughened, the crystal directions of ferrite and cementite are random and irregular. The crystals of high-strength cementite and good elongation ferrite are processed by wire drawing. The direction becomes uniform, so the thinner the steel wire, the smaller the thickness of the sheet and the higher the strength. For example, the grain size of ferrite in steel is Φ10～30um, which is only 0.5～0.8um as the “super metal (high-strength steel)” in national project development; while the thickness of steel wire after toughening is only It is about 0.1um (1200～1500MPa). The most advanced radial steel wire becomes 0.01um after about 20 times of drawing, and the corresponding strength also rises to 4500MPa.
It is a common phenomenon of steel materials to increase the strength if the crystallographic direction after rolling is the same, but the crystals only extend in the rolling direction and not in the width direction during rolling of products such as thin plates. Therefore, the crystal grain size varies with the direction. Also different. The cold drawing die used in the wire drawing process uses a strong pressure different from the rolling method to uniformly squeeze the wire from all around, so the crystallization can only develop in the drawing direction. As a result, the lamellae are uniform and the thickness is reduced, which makes the strength Improve quickly. In order to apply strong pressure to ultra-high-strength steel wire, ultra-high hardness diamond molds are often used when drawing. Stainless steel spring
Introduction of Japanese high-strength rods and wires
(1) Rods and wires can be processed into a variety of products
In addition to being directly used in construction, rods and wires can also be processed into various parts for other purposes. Taking a common car as an example, each car uses about 150Kg of rods and wires, which is about 10% of the car’s weight. Among them, the materials used for engine components (crankshafts, camshafts, valve springs, etc.) and drive system components (various gears, screw shafts, etc.) are inseparable from rods and wires. “Driving, turning and stopping” are the basic actions of a car. If a component supporting these actions is damaged, the car will stop running. This shows their importance.
In addition, as a reinforcing material for automobile tires, some organic fibers were used in the past. Later, the rigidity of automobile tires has been significantly improved after the use of radial steel wires. Therefore, in recent years, the tire damage and deflation accidents during automobile driving have been greatly reduced; now as a standard The Φ0.3mm radial steel wire used in the product has made a significant contribution to saving resources and improving tire performance through high-strength (an annual output of 300,000 tons). According to statistics, the amount of meridian steel wire in 1975 was ~ 20,000 tons, which increased sharply to 100,000 tons in 1985, 200,000 tons in 1995, and 300,000 tons in 2005, showing its rapid development.
In buildings and steel structures, high-strength rods and wires have also begun to be widely used. Among them, such as telegraph poles and concrete reinforcement materials, suspension bridges, cable-stayed bridges, etc., their strength is generally reinforced 3 to 4 times, which also brings many benefits.
In addition, various bolts, nuts and springs made of rods and wires are also widely used in various aspects, led by the machinery industry; even our common daily necessities such as piano wires, guitar strings and fishing wires are processed by wires. Become. Although their final products have different shapes and properties, they have in common that they are all processed from steel rods and wires. Nippon Steel produces rods and wires, including Muroran Steel Plant, Kamaishi Steel Plant, and Junjin Steel Plant. The classification and use of wire products are shown in Table 1.
Table 1 Classification and use of rods and wires
Classification specification name JIS symbol main purpose
Ordinary wire, mild steel wire SW(-)RM nail, steel wire, traveller, etc.
Special wire rod hard steel wire rod
Spring steel wire
Very low carbon steel wire SW(-)RH
Steel rope, tire wire, spoke wire
Meridian steel wire, steel wire for bridge, steel wire for compaction of concrete
Suspension spring, valve spring
Steel wire for glass enclosure
Wire rod for cold working Wire rod for cold rolling
Low alloy steel spring wire
Wire rod for polished steel
Wire for reinforced concrete SW(-)RH
SD various steel bolts, nuts, mechanical parts
Various steel bolts, nuts, mechanical parts
Polished rod, wire
(2) Bars and wires supplied as semi-finished products
The difference between bars, wire rods and other hot-rolled steels is that they are supplied as semi-finished products in a hot-rolled state, which are then processed and heat-treated by users such as automobile manufacturers and component manufacturers to become final products; and medium-thick plates and thin plates Steels such as steel pipes, steel pipes and H-beams are supplied by steel mills rolled into finished steel products of a certain shape and strength.
Take the processing process of a pinball as an example. The brief introduction is as follows: the wire produced by the steel plant is sent to the secondary processing factory, and is cold drawn -> molded into a ball -> rough polishing -> surface marking -> heat treatment -> grinding -> mirror Polished -> After chrome plating, the product is formed. The small pinball section has three different structures: the surface layer is 3um chromium-plated, the lower 1mm thickness is the martensite structure with 0.8% carbon after carburizing treatment, and the inside is iron with only 0.2% carbon. The soft structure of body + martensite. The above structure makes the surface of the pachinko ball have high hardness and strong impact resistance, and the interior of the pachinko ball can absorb the impact and make the ball difficult to break. This carburizing treatment is also applied when using rods and wires to produce gears and other parts.
In addition, the size, weight, and processing accuracy of the pinball depend on the molding process. The general size tolerance is controlled within 0.01mm and the weight error is within 0.01g. For this reason, the requirements for the workability of the wires used are very strict. This shows the difference between bars, wires and other steels.
(3) Consider the adjustment and cooling of the processing procedure
Generally, the cost of materials made of rods and wires only accounts for 20% of the production cost of the parts (the remaining 80% is forging 20%, cutting 40%, heat treatment 10% and other 10%). Due to the high cost of secondary processing, the development of steel should focus on favoring secondary processing. Even if the final product requires high strength, the rods and wires supplied by steel mills are also required to be “easy to process in order to simplify the processing procedures.” In other words, the rods and wires provided should be the opposite of the high strength required by the final product, that is, they should be softer, thus creating a contradiction. In order to meet this requirement, “adjusted cooling” technology has been adopted. Generally, the strength of the hot-rolled steel material is increased after rapid cooling, and the strength is decreased after slow cooling. “Slow cooling” equipment is to keep the rolled wire coils warm and slowly cool them to reduce their strength. For example, bolts are cold forged with wires at room temperature. The processed steel must be soft to make it easy to form. For this reason, the above-mentioned slow cooling measures are taken for the hot-rolled material to improve its cold forgeability, and the strength is increased by heat treatment after processing to reach the required level.
Due to the different strength requirements of various products, there are also many cooling methods. In addition to the above-mentioned “slow cooling” equipment, there are also cooling methods such as “air cooling” where air is fed for faster cooling, “DLP” through 550°C salt bath cooling, and “EDC” through hot water cooling. Among them, the “DLP” equipment has obvious adjustment effects on the strength and extensibility of high-carbon steels that require high strength, which is beneficial to users to simplify the process in the subsequent toughening treatment, especially the use of salt baths that do not contain metals such as lead, not only thermal conductivity Good, and the salt adhering to the wire can also be simply washed with hot water to remove it and recycled and reused, and it has less pollution than the lead bath treatment.
(4) Master the strength of steel through organizational control
As mentioned above, adapting the properties of rods and wires to the user’s processability is the first condition. However, due to the wide range of purposes and applications, the required strength level of the final product is in the range of 300-5000 MPa. For example, ordinary wires for steel wire and wire mesh are only 300 MPa, while the aforementioned radial steel wires for automobile tires and wire saws for cutting silicon wafers require high-strength wires up to 4000 MPa. For this reason, the chemical composition and crystalline structure of rods and wires are also diversified, because the strength of steel increases with the increase in carbon content, but the corresponding extensibility needs to be considered in thin and medium plate products, so carbon is contained The amount is generally kept below 0.2%. However, in order to meet the requirements of various strengths for rods and wires, the range of carbon content has been expanded to between 0.01 and 1.1%; with such a wide range of carbon content, the organizational forms that affect strength, elongation and toughness are also diverse.