Application of Easy Control Configuration Software in Baosteel’s Flame Cutting Production Line for Wide and Heavy Plate

Steel connectors are used for metal parts connecting steel components, wood components, and steel and wood components. Steel connectors mainly include rivets, bolts, high-strength bolts, welding rods, pivots (pins) and various nails.
Rivet   refers to a cylindrical short rod with a semi-circular nail head at one end. It is inserted into each steel plate or section steel nail hole to be connected, and the protruding end is pressed or hammered into a second nail head. According to the shape of the rivet, it is divided into four types: semi-round head, high head, countersunk head, and half countersunk head. Round head rivets are commonly used in bridges and building structures. The rivets are made of rivets No. 2 steel (ML2) and rivets No. 3 steel (ML3) with better plasticity. The rivet connection has been gradually replaced by welding and high-strength bolts due to the labor-consuming, material-consuming, complicated riveting process, and easy loosening under dynamic loads.

Bolt   is usually a cylindrical metal rod with a square or hexagonal head at one end and a thread at the other end, equipped with nuts and washers, which can fasten steel or steel-wood components together. The material is No. 3 steel or riveted No. 3 steel, which can be divided into two types: rough and refined bolts. The manufacture and installation requirements of refined bolts are relatively high, and they are rarely used at present. The surface of rough bolts does not require special processing, and is mainly used for tension connection and installation connection.

High-strength bolts  Using high-quality carbon structural steel or alloy structural steel, a special bolt with higher strength and a certain degree of plasticity and toughness obtained through heat treatment. A strong pre-tension must be applied during use. At present, there are two types of large hexagon head and torsion shear type in China. The commonly used models in civil engineering are M16, M20, M22, and M24. The maximum specifications can reach M30, and the performance level is divided into 10.9S and 8.8S. The materials are mainly 20MnTiB steel, 40B steel, 35VB steel, 45# steel and 35# steel. High-strength bolts are used for the connection of steel structures in industrial and civil buildings, highway and railway bridges, tower mast structures, pipeline supports, hoisting machinery, etc.

Welding Rod  A rod-shaped metal strip that melts and fills the joints of welded parts during electric welding. It is coated with anti-oxidation (alloying, etc.) flux. According to the mechanical properties and chemical composition of the metal material to be welded, as well as the welding seam requirements and equipment process conditions, choose different types and models of electrodes. Commonly used structural steel electrodes are divided into four categories according to the deposited metal mechanical properties, welding power source, use and welding conditions: T42-0~T42-7; T50-0~T50-7; T55-X; T60-X. Electrode coatings are divided into titanium oxide type, titanium calcium oxide type, ilmenite type, iron oxide type, cellulose type, low hydrogen type and so on. Welding has been widely used in the production and installation of steel structures such as industrial and civil buildings, bridges, tower mast structures, and container equipment.

Pivot  , also known as a pin, is a metal cylindrical connector used to connect two members that can rotate freely at the joint without pretensioning. One joint only needs one pivot, so the diameter is larger. Generally used on steel structures such as crane booms, arch hinges, and disassembly bridges.

Features of heat treatment and surface modification technology

The performance of the material does not depend solely on the type and composition of the material. Changing the internal structure of the material through heat treatment and surface modification will greatly change the material performance. For example, the hardness of high-speed steel in the annealed state is not higher than 280HB and has quite good plasticity and toughness. After quenching and tempering, it has high hardness, red hardness and wear resistance. Since the content of alloying elements dissolved in the matrix and the grain size of austenite are related to the quenching temperature, the trend is that the hardness and red hardness increase with the increase of the quenching temperature, the toughness decreases, and the strength increases first. Descending (Figure 1). Using this rule, the best quenching temperature can be selected according to the use characteristics of different tools and molds (Table 1). The blades and handles of the turning tools are relatively thick, and the strength requirements are not high, and the impact load is lighter. The quenching temperature close to the melting point can be used to dissolve as much alloying elements and carbon as possible into the austenite, thereby improving the red hardness and wear resistance. The cutting edge of the drill bit is not easy to cool when drilling. It is hoped to increase its red hardness as much as possible. However, in order to prevent twisting, the drill bit needs to have higher strength, so its quenching temperature is slightly lower than that of the turning tool. The cutting edges of milling cutters and reamers are relatively thin. In order to avoid chipping, sufficient toughness is required. The quenching temperature should be appropriately lowered. The main damage method of small drills is twisting or breaking. In order to ensure higher strength, the quenching should be further reduced. Heating temperature. The cold extrusion die is subject to high stress, but does not require high red hardness, so select the quenching heating temperature that appears the peak strength, and for some slender or complex shape, subject to greater impact load, you should choose Lower quenching temperature. Table 1 shows that for tools or molds made of the same kind of steel, different quenching temperatures should be selected according to use conditions and failure modes, and the range of changes reaches 150°C. But for a specific workpiece, only ±5°C deviation is allowed.

Structural steel and low-alloy tool steel have a similar situation. The pre-heat treatment structure, quenching heating temperature, cooling method, and tempering temperature all have a significant impact on the performance of the steel. The different combinations between them can make the material obtain different comprehensive properties. . The strength, hardness, toughness, plasticity and elastic limit of structural steel all change with the tempering temperature after quenching. For workpieces that require high plasticity, high toughness, especially low notch sensitivity, high temperature tempering (tempering and tempering) Treatment), and the workpieces that require high strength and higher hardness should be tempered at about 200 ℃, such as 30CrMnSi, 40CrNiMo after quenching at 200 ℃, the tensile strength can be as high as 1600″1800MPa, which is about 1 times higher than quenching and tempering. Springs and other elastic components are usually tempered at medium temperature showing the peak of elastic limit. In addition, processes such as austempering, two-phase zone heating quenching and deformation heat treatment can make structural steel good strength and toughness. As for various chemical heat treatment and surface coating technologies The concentration and depth of the carburized layer surface and the control of the concentration gradient and performance gradient can be adjusted by adjusting the process parameters to adapt to the requirements of different service conditions on the overall performance of the workpiece. For example, the carburizing treatment of different parts should be There are different technical requirements to obtain good performance (Table 2). For oil drilling roller cones, the surface concentration of the carburized layer is reduced from 0.9″1.0%C to 0.7″0.8%C, and the concentration distribution curve is flat. , The service life is increased from 27 hours to 52 hours, and the effect that one drilling team can reach two drilling pairs is received. For example, the surface modification treatment by ion implantation can greatly improve the overall strength and toughness. Improve wear resistance, reduce friction coefficient, improve corrosion resistance, apply to bearings and various friction parts in various transmission mechanisms on spacecraft, wear parts in hydraulic motors on aircraft, and sleeves for mud pumps in the petroleum industry Good results have been achieved in cylinders, etc. In some cases, some seemingly “informal” heat treatment processes are used for the characteristics of the workpiece, and surprising results can be obtained: the quenching temperature range of 3Cr2W8 hot mold steel is generally 1050″1120℃, but The boiler steel pipe hot extrusion die, which is equivalent to the two sides of the steel pipe radiating ribs in the die cavity, bears great stress and is easy to yield in the hot state and cause the die to fail. After the experiment, the quenching temperature is increased to 1170″1180℃, and the water is cooled to “650℃ during quenching cooling, and then transferred to a low-temperature salt bath for cooling. The mold life is increased several times; the blade of the rice harvester is treated with high-concentration carbonitriding; A large amount of carbides and retained austenite appear on the surface layer, which is regarded as unqualified according to conventional inspection standards. However, due to its high wear resistance and good corrosion resistance, the service life of rice harvester blades is longer than that of conventional carburizing Deal with several times higher.

A cursory review of the above-mentioned facts that have long been well-known is just to illustrate an easily overlooked view: the optimal heat treatment process cannot be the same, and the properties of the same material will change due to the heat treatment method and process parameters. , And various performance indicators often fluctuate one after another. Only by selecting appropriate heat treatment process parameters and obtaining the best comprehensive performance compatible with the use status and failure modes of the workpiece can high-quality products be manufactured. This is the characteristic, difficulty and charm of heat treatment and surface modification technology. , Full of space and leeway for people to exert their subjective initiative.

History has proved that improving heat treatment technology and making full use of the potential of materials are often catalysts for product upgrading. After quenching and tempering, the yield strength after high temperature tempering after quenching is about 600” 900 MPa. Both the strength and toughness are significantly better than normalizing treatment, so it became a common heat treatment process for structural steel. Before the Second World War Researchers in the Soviet Union found that after 30CrMnSi quenching and low-temperature tempering, or austempering, the yield strength reaches 1500 MPa and maintains sufficient toughness. It is used to manufacture aircraft landing gear. Medium and low-carbon structural steel quenching and low-temperature tempering treatment is also used Military products such as bullet-proof shields of artillery, and subsequent development of a series of “ultra-high-strength steels” characterized by quenching and low-temperature tempering treatments promoted the upgrading of many important products, such as the rotor of the hydraulic coupler of high-power gas turbines , It transmits tens of thousands to hundreds of thousands of kilowatts of power, and the speed is more than 20,000 revolutions per minute. The original design is SEA4340 steel quenching and tempering treatment, and the yield strength is 800MPa. Later, quenching and low temperature tempering are used to achieve a yield strength of 1800MPa. The weight of the entire coupling is reduced to 1/4 of the original. This is very beneficial for improving the performance of the ship.

Surface modification technology also plays an important role in the development of high-end products. As we all know, the thermal efficiency of gas increases with the increase of gas temperature, but the heat-resistant temperature of superalloys limits the increase in combustion chamber temperature. In foreign countries, due to the successful deposition of a composite coating containing honeycomb ZrO2 on the surface of the heat-resistant alloy, it plays a role of heat insulation, making the temperature of the heat-resistant alloy blades more than 150 ℃ lower than the gas temperature, and developed a higher combustion chamber temperature Gas turbines promote the upgrading of aero engines.

Even in the general machinery manufacturing industry, the technological progress of heat treatment and surface modification is also of great significance to product innovation. For example, the productivity of the cold heading machine for producing standard parts has now reached 600 pieces/min, compared to more than two decades The first 60 pieces/min is increased by 10 times. The outlook of the standard parts industry has been greatly changed. In fact, the cold heading machine is not complicated. It is not difficult to design and manufacture the 600 pieces/min cold heading machine. The problem is that the small hexagonal punch has a lifespan of less than 20,000 pieces. In this case, increase The speed of the cold heading machine is meaningless. Because standard parts are products with extremely large batches, it is usually required that the life of each punch must exceed one shift, otherwise it is difficult to carry out production management. In the early 1980s, through the improvement of the heat treatment process, the life of the punch was increased to more than 50,000 pieces, and the cold heading machine with 100 pieces/min was available. And in the 1990s, the hexagonal punch was made by vapor deposition of titanium nitride. Surface modification treatment has increased its life to more than 350,000 pieces. Become a catalyst for high-speed cold heading machines.

The thin-walled ring gear of a special gearbox is characterized by its ability to significantly reduce the volume and weight of the gearbox, but it is difficult to manufacture with conventional gear heat treatment methods. It is difficult to control carburizing quenching or induction heating quenching. Heat treatment distortion, while the conventional nitriding treatment can not meet the requirements of the contact fatigue strength of the gear, only the application of dynamic controllable nitriding process increases the contact fatigue strength from 1400 MPa to 1700 MPa, and the research has successfully controlled the nitriding distortion of the thin-walled ring gear The method that made the trial production of special gearboxes succeeded.

Only from these examples can be reflected: the technological progress of heat treatment has an important role in promoting product innovation.

In view of the above characteristics, in order to improve the technical level of heat treatment, a systematic study of the influence of heat treatment process parameters on the structure and properties of materials should be carried out first, and secondly, the research work should not only stop at the level of sample research. The heat treatment process research needs to be combined with the product bench test, installation test and failure analysis. After continuous exploration and improvement, the effect of greatly improving the life can be achieved. For example, the cold extrusion punch of truck piston pin shown in Figure 3. To withstand a unit pressure of about 2000MPa, it needs to have a high compressive yield strength, and its shape is slender and easy to break, and it requires sufficient toughness. The extruded metal strongly rubs against the ligament during the extrusion process, so it needs high resistance Abrasion and certain thermal stability. It is made of W6Mo5Cr4V2 high-speed steel. At first, the standard heat treatment specifications given in the manual were used for treatment, and the service life was less than 400 pieces. The failure mode is that the punch breaks during pressing. In order to improve the toughness of the material, the quenching temperature was reduced from 1225°C to 1190°C, which received significant results and the service life was increased to about 2500 pieces. Although the toughness can be further improved by further reducing the quenching temperature, the service life will fall. After careful analysis of the working conditions and failure modes of the punch, it is found that the cutting edge of the punch that is heated and quenched in the low temperature range is gradually drawn, and the resistance during demolding becomes larger and larger. During the demolding process, due to impact tensile stress The effect of causing fracture. For this specific situation, quenching at 1190°C and tempering at 560°C for 4 times, and then gas nitrocarburizing treatment. The hardness of the surface layer (about 0.02mm) is increased to more than 1000HV, while the overall strength and toughness are maintained, and the service life is increased to more than 10,000 pieces.

Furthermore, considering that the heat treatment process parameters are very sensitive to the effect of material properties, in order to ensure the reproducibility and consistency of quality, it is necessary to research and develop advanced heat treatment process equipment, precise and reliable heat treatment process control technology, reasonable design fixtures, and regulations. And strictly implement reasonable furnace installation and operation methods. So improving the quality of heat treatment and its reproducibility is a systematic project. It is not surprising that there are large gaps between different countries and different companies in this field.

Improve the heat treatment process, reduce the heat treatment deformation of the mold

The deformation of the mold after quenching, no matter what method is adopted, the deformation is unavoidable, but the following methods can be used to control the precision and complex molds that must strictly control the deformation amount.

1. Using quenching and tempering heat treatment

For precision and complex molds with low basic hardness requirements but high surface hardness requirements, quenching and tempering heat treatment can be performed after rough machining of the mold, and low temperature nitriding treatment (500″550ºC) after finishing. Due to the low mold nitriding temperature, There is no phase transformation of the matrix structure. In addition, the furnace is cooled to room temperature, and the cooling stress is less, and the mold deformation is small.

2. Using pre-heat treatment

For precision and complex molds, if the hardness requirements are not too high, pre-heated pre-hardened steel can be used, and the die steel (such as 3Cr2Mo, 3CrMnNiMo steel) can be pre-heated to reach the hardness in use (lower hardness is 25″35HRC , The higher hardness is 40″50HRC), and then the mold is processed and formed without heat treatment, so as to ensure the accuracy of the precision and complex mold.

3. Use age hardening die steel

Aging hardening steel can be used for precision and complex molds. For example, PMS (1Ni3Mn2CuA1.Mo) steel is a new type of aging mold steel. The hardness after solution quenching at 870ºC is about 30HRC, which is convenient for machining. After the mold is formed, it can be processed at about 500ºC. The high hardness of 40″45HRC can be obtained by the aging heat treatment, and the mold deformation is small, and only needs to be polished. It is an ideal steel for precision and complex molds.

The influence of heat treatment heating process

1. The influence of heating speed

The deformation of the mold after heat treatment is generally considered to be caused by cooling, which is incorrect. For molds, especially complex molds, the correctness of the processing technology often has a greater impact on the deformation of the mold. A comparison of some mold heating processes can clearly show that the heating speed is faster and often large deformations.

(1) Causes of deformation Any metal will expand when heated. Because steel is heated, the uneven temperature of each part (that is, uneven heating) in the same mold will inevitably cause inconsistent expansion of each part in the mold The formation of internal stress due to uneven heating. At the temperature below the transformation point of steel, uneven heating mainly produces thermal stress. If the heating exceeds the transformation temperature, uneven heating will also produce unequal time of the transformation of the structure, which will result in structure stress. Therefore, the faster the heating rate, the greater the temperature difference between the mold surface and the core, the greater the stress, and the greater the deformation of the mold after heat treatment.

(2) Preventive measures The complicated mold should be heated slowly when heating below the phase transition point. Generally speaking, the deformation of the mold in vacuum heat treatment is much smaller than that in the salt bath furnace. ‚Using preheating, for low-alloy steel molds, one preheating (550-620ºC); for high-alloy steel molds, two preheating (550-620ºC and 800-850ºC).

2. The influence of heating temperature

In order to ensure that the mold reaches a higher hardness, some manufacturers believe that it is necessary to increase the quenching heating temperature. However, production practice shows that this approach is inappropriate. For complex molds, heating and quenching are also performed at the normal heating temperature. The heat treatment deformation after heating at the allowable upper limit temperature is greater than the heat treatment deformation heated at the allowable lower limit temperature. Much larger.

(1) The cause of deformation It is well known that the higher the quenching heating temperature, the more the grains of steel will grow. As larger grains can increase the hardenability, the greater the stress generated during quenching and cooling. Furthermore, since complex molds are mostly made of medium and high alloy steel, if the quenching temperature is high, the amount of retained austenite in the structure will increase due to the low Ms point, which will increase the deformation of the mold after heat treatment.

(2) Preventive measures In the case of ensuring the technical conditions of the mold, the heating temperature should be selected reasonably, and the lower limit quenching heating temperature should be selected as far as possible to reduce the stress during cooling, thereby reducing the complicated heat treatment deformation.

Preventive Measures for Crack Defects of High Speed Tool Steel

High-speed tool steel is a high-end…
High-speed tool steel is a high-end tool steel with good wear resistance and toughness. However, if you do not pay attention to it in production, defects such as cracks will easily occur, resulting in scrap. This is mainly because:

1. Low plasticity. High-speed steel has many alloying elements, especially S, Ph, Sn and other impurity elements, which tend to weaken the inter-grain bonding force and reduce the plasticity.

2. Large deformation resistance. The alloy composition of high-speed steel is complex, the recrystallization speed is slow, the temperature is high, and it has high deformation resistance at the deformation temperature.

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3. Narrow forging temperature range. High-speed steel heating temperature is too high, it is easy to overheat, over-burn, stop forging temperature is too low, it will produce coarse-grain phenomenon, theoretically high-speed steel forging temperature range is very narrow, generally 200-280 ℃.

4. Poor thermal conductivity. The thermal conductivity of high-speed steel is much lower than that of carbon steel. It needs to be heated slowly at 600-900℃, otherwise it will cause temperature stress and cause metal brittleness.

The relevant preventive measures are:

1. Strictly control the metal content of high-speed steel raw materials. For example, the tin content must be strictly controlled below 0.08%.

2. It is stipulated that the ingot must be peeled or cleaned by the grinding wheel before heating forging to improve the performance of high-speed steel processing.

3. Control the heating temperature, holding time and deformation temperature of high-speed steel, and adopt multi-fire forging.

4. When the slab is drawn, lightly tap it at the beginning, and increase the amount of deformation after the as-cast structure is properly broken and the plasticity is improved. When free forging is long, the deformation of each fire is controlled within 2-4 times, and it should be sent from the head to the tail.

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5. When forging high-speed steel, reduce the number of continuous rotation deformations in the same part of the raw material, and specify less than 8 times.

Ultra-pure spring steel wire

Recent studies have shown that the main factors affecting the fatigue life and reliability of oil-quenched-tempered steel wire for valves are the form and content of inclusions in steel: large particles do not deform Type D inclusions and Type B inclusions lead to a sharp decrease in the fatigue life of the spring, while phosphorus, The high content of sulfur, arsenic, lead, tin, and antimony will also increase the temper brittleness of steel. Ultimately reduce the fatigue life. For this reason, ultra-pure oil quenched-tempered steel wire was developed.

The so-called ultra-pure steel is refined outside the furnace, vacuum degassed, electroslag remelting, composite slag system, inclusion deformation treatment, electromagnetic stirring and other technical means to minimize the gas (oxygen, nitrogen, hydrogen) in the steel. The content of non-metallic elements (phosphorus, sulfur, arsenic) and low melting point metals (lead, tin, antimony) can transform large non-deformable inclusions into plastic or semi-plastic fine inclusions. At present, 55CrSiA ultra-pure steel developed in Japan and Europe The 67CrVA. ultra-pure steel developed has made remarkable achievements.

 

The cause of elastic yellow fracture under low stress is non-metallic inclusions, and the cause of fracture under high stress is often surface defects. Therefore, it is necessary to strengthen the grinding and cleaning of the billet used for rolling wire rod, and strengthen the research on the control of cooling and rolling of the wire rod. Or stripping or grinding the wire surface. Clear defects such as surface decarburization, cracks, and folding. At present, among the oil-quenched steel wire production enterprises in China, only Shanghai Steel No. 2 Plant has stripping equipment, while other manufacturers have no secondary equipment. This is also an important factor restricting the improvement of the quality of oil quenched steel wire products in my country. The intermediate annealed structure of the wire rod or semi-finished product should be fine flake pearlite to meet the requirements of rapid heating for oil quenching. Some materials suggest that the intermediate heat treatment of 67CrVA. adopts lead quenching treatment to prepare for oil quenching heating.

What is the method of stainless steel golden process

The method of stainless steel golden process:
Stainless steel products are golden: the surface of stainless steel is treated in chromic acid and sulfate solution to give a golden appearance. The process is as follows:

Chromic anhydride 250g/L

Sulfuric acid 490g/L

Temperature 70℃

Time 18min

The ratio and temperature of chromic acid and sulfuric acid in the above-mentioned solution can be adjusted according to the required color. Generally, 15min can be treated for blue; 18min can be golden; 20min can be purple; 22min can be green. The color brightness of the obtained stainless steel colored film is related to the pretreatment, and the mechanical polishing effect is generally better. The coloring treatment time and temperature can be adjusted according to the specific situation. If the solution temperature cannot be increased, the treatment time can be extended to achieve the same effect.

Shot peening is an ideal process to improve the fatigue strength of compression springs

A spring factory in Beijing is one of the largest manufacturers of cold-coiled springs in China. Its main products are automobile engine valve springs and various clamp, tension, torsion and compression springs. In recent years, the manufacturer has carried out large-scale technological transformations and introduced spring shot peening equipment from Wellbrite Group to improve the fatigue life reliability of valve springs and plunger springs, making its products leading the industry. status.
Compression springs are subjected to high alternating loads and the maximum stress occurs mostly on the surface of the spring material, so shot blasting/shot peening strengthening is also an ideal process to improve the fatigue strength of compression springs. The spring material causes tensile stress during rolling, drawing, coiling and compression. In addition to the high alternating load conditions after service, the coiling process itself will cause destructive tensile stress on the inner ring of the spring.

Shot blasting/shot peening introduces a counteracting compressive stress, which transforms the surface into a residual pressure layer with a strength of about 150 ksi (1035 MPa). This is 60% of the ultimate tensile strength (UTS) of the spring. As a result, the fatigue life of the spring has been extended to 500,000 load cycles without failure.

In addition to compression springs, shot blasting/shot peening is also applicable to the strengthening of other springs such as tension springs, torsion springs, suspension springs, leaf springs, etc. The fatigue failure point usually occurs in the place where the residual tensile stress and the alternating load stress are concentrated, so the strengthening position of different springs is different.

A New Technology and New Process for Modification of Ultra-cold Treatment Materials

The instability of metallic materials and non-metals (deformation of the structure and internal stress caused by processing) has caused instability in production, and over-reliance on workers has always plagued the industry. The company adheres to the spirit of “first-class technology, first-class efficiency, and first-class service” to ensure effective solutions to material deformation, ensure processing dimensional accuracy, increase wear resistance, increase elasticity, eliminate stress, and refine the organization, thereby improving quality. cut costs.
Ultra-cold technology is the only processing technology that can be used on the tools, knives, and parts that have been formed after the material is heat treated. It can stabilize the precise dimensions of the material, improve the wear resistance of the material, and restore the mechanical properties of the material.

The treatment of materials by ultra-cold technology is not limited to the surface treatment of the material, but also penetrates into the internal structure of the material, which reflects the overall effect, especially the regrind of the cutting tool, does not affect the organization structure, can be used repeatedly, and its reusable performance Significantly better than coating technology. The ultra-cold treatment technology can effectively reduce the quenching stress and enhance the dimensional stability of the workpiece.

The competitiveness of traditional industries is facing the transformation and upgrading of the industrial structure, and correct changes must be made. The guarantee of product quality will change from competitive conditions to survival conditions. The improvement of the efficiency of industrial products is a problem faced by industrialists. However, the basic engineering of metal materials is more important. The basic work of heat treatment makes the quality of industrial products not perfect. Although heat treatment gives life to metal materials, it does not give life and efficiency. In addition to the previous heat treatment, the complete basic project also includes the subsequent metal ultra-cold treatment, which is the basic work to ensure product quality. Deep Cryogenic Treatment will be the only choice for the quality of metal products.

Ultra-cold application industries include: precision stamping molds, nano materials, precision plastic molds, cutting tools, hobbing tools, aluminum alloy materials, cemented carbide cutting tools/fixtures, powder metallurgy molds, etc.

Ultra-cold treatment for high-speed steel

In the process of ultra-cold treatment, a large amount of retained austenite in the metal is transformed into martensite, which reduces the saturation of the supersaturated metastable martensite, reduces the microscopic stress, precipitates and disperses, and precipitates dispersed ultrafine carbides When the material is plastically deformed, it effectively hinders the dislocation movement, thereby effectively strengthening the matrix structure.

How to heat treatment of die casting mold parts

Heat treatment of die casting mold parts:
1. The quenching equipment is a vacuum quenching furnace with high pressure and high flow rate.

(1) Before quenching: heat balance method is adopted to improve the overall consistency of mold heating and cooling. All thin-walled holes, grooves, and cavities that affect this point must be filled and blocked, and the mold can be heated and cooled as much as possible; at the same time, pay attention to the furnace installation method to prevent the die-casting mold from being caused by high temperatures. Deformation caused by its own weight.

(2) The heating of the mold: During the heating process, it should be heated slowly (200℃/h heating), and a two-stage preheating method should be adopted to prevent the rapid heating from causing excessive temperature difference between the inside and outside of the mold, causing excessive thermal stress. At the same time, the phase change stress is reduced.

(3) Quenching temperature and holding time: the lower limit of the quenching heating temperature should be used, and the soaking time should not be too short or too long. The soaking time is generally determined by the wall thickness and hardness.

(4) Quenching and cooling: using pre-cooling, and by adjusting the air pressure and wind speed, the cooling rate is effectively controlled to maximize the ideal cooling. Namely: After pre-cooling to 850℃, increase the cooling rate and quickly pass the nose of the “C” curve. When the mold temperature is below 500℃, the cooling rate will gradually decrease. When the temperature is below the Ms point, the cooling method of approximately isothermal transformation is adopted to maximize Minimize quenching deformation. When the mold is cooled to about 150°C, turn off the cooling fan and let the mold cool naturally.

2. Annealing includes two parts: spheroidizing annealing after forging and stress relief annealing during mold making. Its main purpose is to improve the crystalline structure in the raw material stage; facilitate processing and reduce hardness; prevent deformation and quenching cracks after processing to remove internal stress.

(1) Spheroidizing annealing. After the die steel is forged, the internal structure of the steel becomes unstable crystals, and it is difficult to cut with high hardness. The steel in this state has high internal stress, is easily deformed and quenched after processing, and has poor mechanical properties. In order to crystallize carbides To become a spheroidized stable structure, spheroidizing annealing is required.

(2) Stress relief annealing. Machining die steel with residual stress will deform after machining. If there is still stress after machining, great deformation or quenching cracks will occur during quenching. To prevent these problems from occurring, stress relief annealing must be carried out.

Generally, three times of stress relief annealing are carried out during the mold making process:

(1) When cutting away more than 1/3 of the raw material volume or deep processing the raw material thickness 1/2, the machining allowance is left 5-10mm, and the first stress relief annealing is performed.

(2) When there is a margin (2-5mm) for finishing, perform the second stress relief annealing.

(3) After the mold test, the third stress relief annealing is carried out before quenching.

3. When the tempered and quenched mold is cooled to about 100°C, it must be tempered immediately to prevent further deformation or even cracking. The tempering temperature is determined by the working hardness, generally three times of tempering.

4. Nitriding treatment Generally, die-casting molds can be used after quenching and tempering (45~47HRC), but in order to improve the wear resistance, corrosion resistance and oxidation resistance of the mold, prevent mold sticking, and extend the life of the mold, it is necessary Carry out nitriding treatment. The depth of the nitride layer is generally 0.15 to 0.2 mm. After nitriding, it needs to be polished to remove the white layer (thickness about 0.01mm).

5. A few explanations

(1) The heat treatment deformation of the mold is caused by the combined action of phase transformation stress and thermal stress, and is affected by many factors. Therefore, under the premise of correct selection of materials, attention should be paid to the forging of the blank, and the method of six-sided forging should be adopted, and the upsetting should be repeated. At the same time, in the design stage of the mold, it is necessary to pay attention to make the wall thickness as uniform as possible (open process holes when the wall thickness is uneven); for molds with complex shapes, use the mosaic structure instead of the overall structure; for thin-walled molds , Sharp corners of the mold, it is necessary to use fillet transition and increase the fillet radius. During the heat treatment, it is necessary to make a good data record, the amount of deformation in each direction of length, width, and thickness, and the heat treatment conditions (furnace installation method, heating temperature, cooling rate, hardness, etc.), to accumulate experience for the heat treatment of the mold in the future.

(2) There are generally two technological processes for the processing of die-casting molds, both of which are determined according to actual conditions. The first type: general die-casting mold. Forging → spheroidizing annealing → rough machining → first stress relief annealing (leave a margin of 5~10mm) → rough machining → second stress relief annealing (leave a margin of 2~5mm) → finishing → third Secondary stress relief annealing (after mold trial, before quenching) → quenching → tempering → clamp repair → nitriding. The second type: particularly complex and easily deformed molds after quenching. Forging → spheroidizing annealing → rough machining → the first stress relief annealing (leave a margin of 5-10mm) → quenching → tempering → mechanical and electrical machining → the second stress relief annealing (leave a margin of 2-5mm )→Machine and electrical machining→Third stress relief annealing (after mold trial)→Clamping→Nitriding.