Protection against corrosion

Rust is the most important degradation phenomenon of metal substances. At the beginning of the degradation process, the beauty of the metal fastener may be lost, and then the function of the parts may be lost, and the fastening coupling must be replaced. In fact, the appearance and functionality of bolts are very important, because in addition to the mechanical properties required by the application, general bolts must also have good corrosion resistance, and must be beautiful in most mechanical components. Appearance.
1. The rust phenomenon appears in different forms.
The corrosion of fasteners in general is the same degree of damage to the metal surface. Other cases may be local rusting. In this case, we observe that the metal is oxidized in the small anode area, but there is no change in the metal surface in the large cathode area.
2. Types of corrosion
The first is uniform rust. This kind of rust phenomenon spreads over the entire fastener tissue surface and continues to produce metal reduction. This is the most common corrosion process. This corrosion does not cause too much danger and is easy to detect in advance.
Secondly, it is the phenomenon of local corrosion that is dangerous. Pinhole corrosion. In this case, it can be observed that local erosion will lead to material perforation. The anode area is very small, and the cathode area without any changes on the surface is rather large. This phenomenon often occurs in stainless steel, nickel steel and aluminum fasteners. Electric rotary rust. As far as fasteners are used, the damage caused by electro-rotating corrosion is very serious. Electro-rotation corrosion may occur in the joining of any two types of fasteners of different metal materials; the reason is that one of the metals has high activity and is easier to cause chemical reactions, so the corrosion rate increases, while the other metal has low activity and it is difficult to cause reactions. While the corrosion rate is reduced, the connection structure causes a reaction in the cathode direction. This phenomenon is even more pronounced when the electrochemical reactions of the two metals are quite different. If carbon steel is matched with stainless steel fasteners, the corrosion rate of steel parts will increase. When screws are connected, they are actually used to join two or more components. In order to avoid electro-rotating corrosion, when joining parts, the same joining materials or materials with similar electrochemical reactions should be specified.
Electro-rotation corrosion form or reaction of various metals in seawater
Form Metal Material
Inert or reactive toward the cathode
Stainless steel 18-8 type grades
Stainless steel (including 11%-30% chromium) series
nickel
Bronze (copper tin alloy)
Brass (copper-zinc alloy)
cast iron
steel
Active or react towards the anode
cadmium
aluminum
Zinc
Magnesium or magnesium alloy
Generally, fastener coatings are divided into two types. With the phosphate layer as the base, painting can increase the corrosion resistance of the fastener surface. The electrolytic galvanized layer is used as a barrier protection, and when the paint is bad and the electro-rotating rust phenomenon starts, the zinc material is used as the anode material, and the steel is used as the cathode material, which can avoid the danger of rust. Type of protection a. Electro-galvanized layer
The electro-galvanized layer is a typical anode plating layer. When corrosion occurs, the anode is preferentially dissolved to protect the base material. Limited by the thickness of its coating of 8-15μm, after chromate passivation treatment, its anti-corrosion performance is greatly improved, can withstand the 48-96h neutral salt spray test, and can be used for neutral outdoor protection. Zn-Ni, Zn-Fe, Zn-Co electroplated layers developed in recent years, especially Zn-Ni, Zn-Co electroplated layers, when the Ni content in the coating is 6%-10% or the Co content is 0.4%-1.0 %, after passivation of the 5-8μm coating, excellent anti-corrosion effect can be obtained, and it can resist the neutral salt spray test for more than 720h.
b. Non-electroplated zinc layer
The non-electrogalvanized layer mainly includes hot-dip galvanized layer, mechanical galvanized layer and Dacromet coating.
Hot-dip plating is formed by the natural adhesion of molten metal on the surface of metal fasteners to form a thin film, which is characterized by a thick coating. Mechanical plating uses the mechanical action of the small spherical object and the coating metal powder to rotate and collide in the aqueous solution to make the coating metal form a thin film. Its characteristic is that the coating is generally a composite film with good corrosion resistance. Dacromet coating is formed by sintering flake metal powder, organic matter and additives at about 300℃ to form a film. Its characteristic is that the film has good corrosion resistance.

Comparison of Fastener Pre-heat Treatment Normalizing and Annealing Process

Green manufacturing is an important strategy for the sustainable development of the machinery manufacturing industry. Normalizing and annealing in the pre-heat treatment of fasteners are the two most commonly used processes, accounting for about 30% of the heat treatment of fasteners. Although these two process methods have their own different characteristics in process, they can achieve the same (or similar) process goals when dealing with low carbon steel or medium carbon steel materials.
According to GB/T16923-1997 “Normalizing and Annealing of Steel Parts”, it can be seen that the normalizing and annealing process methods are divided into a variety of sub-categories. Among them, normalizing and incomplete annealing, isothermal annealing process processing objects, technical requirements Most identical (or similar).
1. Function
According to the low-carbon steel or medium-carbon steel used in the fasteners, normalizing is to heat the steel to 30~70℃ above Ac3, and then air-cooled or air-cooled to room temperature; incomplete annealing or isothermal annealing is to heat the steel to Ac1 is above 30~50℃, after holding for a certain period of time, it is cooled to a certain temperature with the furnace and then air cooled to room temperature. They are similar or similar in that they can treat medium carbon steel and low carbon steel, and the metallographic structure obtained by the treatment is ferrite + pearlite, which can be used as a preliminary heat treatment or final heat treatment under certain circumstances. So as to achieve the purpose of refining the structure, improving the mechanical properties and cutting performance, and eliminating internal stress.
2. Comparison of process characteristics
a. The grains after normalizing are smaller than the annealed ones, and more pearlite is obtained, and the mechanical properties are slightly higher than that of annealing;
b. Normalizing parts are often charged into the furnace, the heating temperature is generally slightly higher than that of annealing, and the holding time is shorter than that of annealing;
c. Normalizing can eliminate the network structure of carbides, but annealing cannot;
d. Normalizing treatment of carbon steel with lower carbon content is better than annealing, on the contrary, annealing is better than normalizing.
3. Process cost
The comparison between normalizing and annealing mainly exists in the power consumption of resources, the difference in heat preservation and cooling in time, and the corresponding cost difference.
The energy cost is 0.542Kw.h.Kg for normalizing and 0.580Kw.h.Kg for the domestic heat treatment industry evaluation unit consumption value, and the industrial electricity cost is calculated at 0.70 yuan/Kw.h. The average cost of annealing power is 0.03 yuan. /Kg.
The labor cost is about 1 yuan/Kg according to the lowest price of normalizing processing in various places in China. The labor cost of the normalizing process is about 0.32 yuan/Kg, and the labor cost of the annealing process is about 0.35 yuan/Kg, and the difference is 0.03 yuan. /Kg or so.
The price difference between normalizing and annealing heat treatment in the same area in China is about 0.2 yuan/Kg. In fact, after a specific analysis of the price difference, it can be known that the price difference is still based on the traditional heating method and the larger production batches.
4. Process evaluation
When the requirements of manufacturing fasteners and processing technology are basically the same, the normalizing process is more green than the annealing process, which is mainly reflected in the energy consumption and processing man-hours.
Low temperature annealing (stress relief annealing): heating temperature Ac1 carbon steel 550~650℃, eliminate the internal stress in the upsetting and cutting process, and make it reach a stable state.
Recrystallization annealing: heating temperature TR+150~250℃, holding time 0.5~1h, air cooling, recovering recrystallization process occurs, making deformed grains into small equiaxed grains, eliminating cold work hardening effect and internal stress. The annealing temperature for recrystallization of low carbon steel is 600~650℃ and the hardness is in the range of 75~90HRB.
Incomplete annealing: heating temperature Ac1+30~50℃, carbon steel is generally between 700~750℃, to refine grain, reduce hardness, improve plasticity and remove internal stress.
Spheroidizing annealing: The heating temperature is slightly higher than Ac1, and then slowly cooled to less than 500℃ air cooling after long-term heat preservation to spheroidize the carbides and reduce the hardness to improve the cold upsetting performance.
Normalizing: Low-carbon and medium-carbon steel heating temperature Ac3+ (50~70℃), low-carbon steel improves hardness, which is good for cutting, medium-carbon steel refines grains, and uniformly organizes stress relief.
Applications:
For example: 20# steel three-point welded gasket, using 850℃×0.5h normalizing and 720℃×3h incomplete annealing, the hardness is basically similar to 125~165HBW, normalizing saves production cycle and high efficiency than incomplete annealing.
SWRM15 steel single-sided rivets are normalized at 840℃×0.5h and recrystallized and annealed at 600℃×4h. The hardness of the former is greater than 95HRB, and the hardness of the latter is 78~88HRB which meets the requirements of riveting performance.
For 45 steel large washers, when the hardness requirement is greater than 200HV, normalizing at 870℃×1h is better than incomplete annealing at 760℃×2.5h. The hardness can reach more than 200HV, and the productivity is significantly higher than annealing.
According to statistics, the cost difference between normalizing and annealing processes is 0.2 yuan/Kg~0.45 yuan/Kg. If the normalizing process is properly selected to replace the annealing process, it can bring considerable benefits to fastener companies while achieving green manufacturing. Economic benefits.
In short, with the development of the fastener industry and the promotion of advanced technology, energy saving and consumption reduction will be in the first place, and the green characteristics of the normalizing process will be more obvious and prominent than the annealing process.

The main purpose and scope of application of electronic tensile testing machine

The main purpose and scope of application of the electronic tensile testing machine: this series of material testing machines are widely used in various small cross-section metal wires, dry mortar, waterproof materials, rubber and plastics, insulation materials, textiles, wires and cables, coatings, non-woven fabrics, and paper Test various physical properties such as stretching, tearing, peeling, elongation, etc. for various materials, as well as mechanical properties of other parts. Comply with GB2611-81 “General Standard for Testing Machines”, “Test Methods for Asphalt Waterproof Rolls” GB/T328-89, “Determination of Tensile Properties of Vulcanized Rubber and Mat Plastic Rubber” GB/T528-1998, “Polyvinyl Chloride Waterproof Rolls” “GB12952-2003, “Petroleum Asphalt Fiberglass Tire Felt” GB/T14686-93 and other national standards.

Utilize the function of spring

Spring measurement function
We know that within the limits of elasticity, the extension (or contraction) of extension springs, compression springs, torsion springs, bending springs, springs, and coil springs is proportional to the external force. Use the nature of the spring to make a spring balance.
Spring compression function
Observing various electrical switches, you will find that one of the two contacts of the switch must be equipped with a spring to ensure that the two contacts are in close contact and are in good conduction. If the contact is poor, the resistance at the contact will increase, and the heat generated when the current passes will increase. In severe cases, the metal at the contact will melt. The two metal posts of the bayonet base are equipped with springs for good contact; as for the central metal piece of the screw base and the plug-in metal pieces of all sockets are reeds, their function is to make the two sides in close contact to maintain Same good. In a magnetic tape, there is a piece of phosphor bronze reed, which uses the elastic force generated when it is bent and deformed to make the magnetic head closely contact the tape. There is a long coil spring in the stapler. On the one hand, it is used to tighten the staples. On the other hand, when the front staple is pushed out, the back staples can be sent to the front to prepare the staples to be pushed out comfortably. In this way, the nails can be pushed to the front automatically one by one until all the nails are pushed out. Many machines feed automatically, and the automatic loading of bullets in automatic rifles relies on this function of springs. In addition, clips like clothes clips, ball-point pens, and pen holders are clamped on clothes by the pressing function of springs.
Spring return function
The spring is deformed under the action of external force, and after the external force is removed, the spring can be restored to its state. Many tools and equipment use springs to reset. For example, many building door hinges are equipped with return springs. After people enter and exit, the door will automatically reset. People also use this function to make automatic umbrellas, automatic pencils and other supplies, which is very convenient. In addition, various buttons and keys are also indispensable for return springs.
Spring drive function
Mechanical clocks and clockwork toys are driven by winding up the clockwork. When the mainspring is tightened, the mainspring is bent and deformed, storing a certain amount of elastic potential energy. After release, the elastic potential energy is transformed into kinetic energy, which is driven to rotate by the transmission device. In toy guns, starting guns and military guns, they also work with springs.
Spring buffer function
A spring is installed between the vehicle frame and the wheel, and the elasticity of the spring is used to slow down the bumps of the vehicle.
Spring vibration sound function
When air flows from the reed hole in the harmonica or accordion, it impacts the reed and the reed vibrates to make a sound.

The name and size relationship of each part of the spring

Spring is an elastic element widely used in the mechanical and electronic industries. The spring can produce greater elastic deformation when loaded, converting mechanical work or kinetic energy into deformation energy, and the deformation of the spring disappears and returns to its original shape after unloading. Deformation energy is converted into mechanical work or kinetic energy.
1. The main functions of the spring are:

① Force measurement, such as spring scales and gauge springs;

②Control movement, such as clutch, brake and valve control spring;

③Vibration reduction and buffering, such as buffers, springs of shock absorbers, etc.;

④ Energy storage or energy transmission, such as springs on clocks, meters and automatic control mechanisms.

2. Type of spring:

There are many types of springs, such as compression springs, extension springs, torsion springs and metal wire forming.

3. The name and size relationship of each part of the spring:

(1) Talk about spring wire diameter d: the diameter of the steel wire used to make the spring.

(2) Spring outer diameter D: the maximum outer diameter of the spring.

(3) Spring inner diameter D1: the minimum outer diameter of the spring.

(4) Spring diameter D2: the average diameter of the spring. Their calculation formula is: D2=(D+D1)÷2=D1+d=D-d

(5) t: Except for the support ring, the axial distance between the corresponding points of two adjacent coils of the spring on the pitch diameter becomes the pitch, which is represented by t.

(6) Effective number of turns n: the number of turns that the spring can maintain the same pitch.

(7) Number of support turns n2: In order to make the spring work evenly, to ensure that the end of the axis is vertical, the two ends of the spring are often tightened during manufacturing. The number of tight turns only serves as a support and is called a support ring. Generally there are 1.5T, 2T, 2.5T, and 2T is commonly used.

(8) Total number of turns n1: the sum of effective number of turns and support ring. That is, n1=n+n2.

(9) Free height H0: the height of the spring without external force. Calculated by the following formula: H0=nt+(n2-0.5)d=nt+1.5d (when n2=2)

(10) Spring unfolding length L: The length of steel wire required to wind the spring. L≈n1(ЛD2)2+n2 (compression spring) L=ЛD2n+ hook extension length (tension spring)

(11) Spiral direction: there are left and right rotations. Right-handed is commonly used, and right-handed is generally used if it is not indicated in the drawing.

4. The prescribed drawing method of the spring:

(1) On the view of parallel coil spring lines, the contour lines of each circle are drawn as straight lines.

(2) If the effective number of turns is more than 4 turns, you can only draw 1 to 2 turns at both ends (not including support ring). The middle is connected by a dotted line through the center of the spring wire.

(3) On the drawing, when the direction of rotation of the spring is not specified, the coil spring is drawn as right-handed, and the left-handed spring is also drawn as right-handed, but the word “left” should be marked.

Titanium alloy cutting performance

Cutting characteristics
When the hardness of titanium alloy is greater than HB350, cutting is particularly difficult, and when the hardness is less than HB300, it is prone to sticking and cutting is difficult. But the hardness of titanium alloy is only one aspect that is difficult to cut. The key lies in the influence of the combination of chemical, physical and mechanical properties of titanium alloy on its machinability. Titanium alloy has the following cutting characteristics:

(1) Small deformation coefficient: This is a significant feature of titanium alloy cutting processing, and the deformation coefficient is less than or close to 1. The sliding friction distance of chips on the rake face is greatly increased, which accelerates tool wear.

(2) High cutting temperature: Because the thermal conductivity of titanium alloy is very small (only equivalent to 1/5 ~ 1/7 of 45 steel), the contact length between the chip and the rake face is extremely short, and the heat generated during cutting is not easy to transfer It is concentrated in a small area near the cutting area and the cutting edge, and the cutting temperature is very high. Under the same cutting conditions, the cutting temperature can be more than twice as high as when cutting 45 steel.

(3) The cutting force per unit area is large: the main cutting force is about 20% smaller than that during steel cutting. Because the contact length between the chip and the rake face is extremely short, the cutting force per unit contact area is greatly increased, which is likely to cause chipping. At the same time, due to the small modulus of elasticity of titanium alloy, it is prone to bending deformation under the action of radial force during processing, causing vibration, increasing tool wear and affecting the accuracy of parts. Therefore, the process system is required to have better rigidity. Supreme enterprise

(4) Chilling phenomenon is serious: due to the high chemical activity of titanium, it is easy to absorb oxygen and nitrogen in the air to form a hard and brittle skin at high cutting temperature; at the same time, plastic deformation during cutting will also cause surface hardening . Chilling phenomenon not only reduces the fatigue strength of parts, but also aggravates tool wear, which is a very important feature when cutting titanium alloys.

(5) The tool is easy to wear: After the blank is processed by stamping, forging, hot rolling and other methods, a hard and brittle uneven skin is formed, which can easily cause chipping, making the removal of the hard skin the most difficult process in titanium alloy processing. In addition, due to the strong chemical affinity of titanium alloy to tool materials, the tool is prone to bond wear under the conditions of high cutting temperature and high cutting force per unit area. When turning titanium alloy, sometimes the wear of the rake face is even more serious than that of the flank; when the feed rate f<0.1 mm/r, the wear mainly occurs on the flank; when f>0.2 mm/r, the front The blade face will be worn; when using carbide tools for fine turning and semi-finishing turning, the wear of the flank face is more suitable for VBmax<0.4 mm.

Tool material

Cutting titanium alloy should start from the two aspects of lowering cutting temperature and reducing adhesion. It is suitable to choose tool materials with good red hardness, high bending strength, good thermal conductivity, and poor affinity with titanium alloys. YG cemented carbide is more suitable. Due to the poor heat resistance of high-speed steel, tools made of cemented carbide should be used as much as possible. Commonly used cemented carbide tool materials include YG8, YG3, YG6X, YG6A, 813, 643, YS2T and YD15.

Coated inserts and YT cemented carbide will have a violent affinity with titanium alloys, which will aggravate the bonding and wear of the tool, and are not suitable for cutting titanium alloys; for complex and multi-edge tools, high-vanadium high-speed steel (such as W12Cr4V4Mo ), high-cobalt high-speed steel (such as W2Mo9Cr4VCo8) or aluminum high-speed steel (such as W6Mo5Cr4V2Al, M10Mo4Cr4V3Al) and other tool materials, suitable for making drills, reamers, end mills, broaches, taps and other tools for cutting titanium alloys.

Using diamond and cubic boron nitride as tools for cutting titanium alloys can achieve significant results. For example, the cutting speed can reach 200 m/min under the condition of emulsion cooling with natural diamond tools; if the cutting fluid is not used, the allowable cutting speed is only 100 m/min at the same amount of wear.

Precautions

In the process of cutting titanium alloy, the matters that should be paid attention to are:

(1) Due to the small modulus of elasticity of titanium alloy, the clamping deformation and force deformation of the workpiece during processing will reduce the processing accuracy of the workpiece; the clamping force should not be too large when the workpiece is installed, and auxiliary support can be added when necessary.

(2) If a cutting fluid containing chlorine is used, it will decompose and release hydrogen at high temperatures during the cutting process, which will be absorbed by titanium and cause hydrogen embrittlement; it may also cause high-temperature stress corrosion cracking of titanium alloys.

(3) The chloride in the cutting fluid may also decompose or volatilize toxic gas during use. Safety protection measures should be taken during use, otherwise it should not be used; after cutting, the parts should be thoroughly cleaned with a chlorine-free cleaning agent in time to remove chlorine residues Things.

(4) It is forbidden to use lead or zinc-based alloy tools and fixtures to contact titanium alloys, and copper, tin, cadmium and their alloys are also prohibited.

(5) All tools, fixtures or other devices in contact with the titanium alloy must be clean; the cleaned titanium alloy parts must be protected from grease or fingerprint contamination, otherwise it may cause salt (sodium chloride) stress corrosion in the future.

(6) Under normal circumstances, there is no risk of ignition when cutting titanium alloys. Only in micro-cutting, the small chips cut off will ignite and burn. In order to avoid fire, in addition to pouring a large amount of cutting fluid, it is also necessary to prevent the accumulation of chips on the machine tool. The tool should be replaced immediately after being blunt, or the cutting speed should be reduced, and the feed rate should be increased to increase the chip thickness. In case of fire, fire extinguishing equipment such as talcum powder, limestone powder, dry sand should be used to extinguish the fire. Carbon tetrachloride and carbon dioxide fire extinguishers are strictly prohibited, and watering is prohibited, because water can accelerate the combustion and even cause hydrogen explosion.

Titanium alloy features:

Titanium has a relatively low density of 4.5g/cm3, which is only 60% of iron. It is usually called light metal with aluminum and magnesium, and its corresponding titanium alloys, aluminum alloys, and magnesium alloys are called light alloys. Many countries in the world have recognized the importance of titanium alloy materials, and have successively conducted research and development on titanium alloy materials, and have been practically applied. Titanium is an important structural metal developed in the 1950s. Titanium alloys are widely used in various fields because of their high specific strength, good corrosion resistance, high heat resistance, and easy welding. High strength and easy welding are beneficial to the manufacture of golf club heads.

The first practical titanium alloy was Ti-6Al (aluminum)-4V (alum) alloy successfully developed by the United States in 1954. Ti-6Al-4V alloy has reached a good level in terms of heat resistance, strength, plasticity, toughness, formability, weldability, corrosion resistance and biocompatibility. The amount of Ti-6Al-4V alloy used has accounted for 75-85% of all titanium alloys. Many other alloys can be regarded as modifications of Ti-6Al-4V alloy. At present, there are hundreds of titanium alloys developed in the world, and there are 20 to 30 kinds of the most famous alloys, for example, Ti-6Al-4V, Ti-5Al-2.5Sn, Ti-2Al-2.5Zr, Ti -32Mo, Ti-Mo-Ni, Ti-Pd, Ti-811, Ti-6242, Ti-1023, Ti-10-5-3, Ti-1100, BT9, BT20, IMI829, IMI834, etc.; for ball The rods are 10-2-3, SP700, 15-3-3-3 (commonly referred to as β titanium), 22-4, DAT51.

Introduction of cryogenic treatment technology

The improvement effect of cryogenic treatment technology is to penetrate the inside of the treated part (the overall effect), which is not limited to the surface, so when the cutting tool is re-grinded and reused, the modification effect of the workpiece will not be invalid; it will not cause the shape and size of the workpiece. Change, and have the effect of enhancing the size stability and reducing the quenching stress; the process system is simple, the power consumption is low, and the shape and size of the workpiece are not limited, and the operation is simple; there is no environmental pollution, and it is a completely environmentally friendly technology
The application of cryogenic modification technology is gradually being recognized and developed by the business community. The experimental results and results obtained so far show that cryogenic modification technology can be applied in the following aspects: 1. High-speed steel cutting tools and cutting tools , The improvement of the life of measuring tools; 2. The improvement of the life of cemented carbide cutting tools and cutting tools; 3. The improvement of the life of carbide drills and drilling tools; 4. The improvement of the performance of diamond products, such as the thermal stability of synthetic diamonds Progress, the performance of artificial diamond mining drill bits, diamond Φ105mm saw blades, etc.; 5. The top hammer function of the diamond hot press is improved; 6. The size of the assembly parts of precision machinery is not disordered; 7. The function of carbon fiber yarn is improved; 8 , The service life of oil nozzles, springs, gears and bearings is improved; 9. The service life of hot work molds and cold work molds in the machinery manufacturing industry is improved. Cryogenic treatment technology is a new technology that has emerged in recent years to improve the performance of metal workpieces. The so-called cryogenic treatment is to use liquid nitrogen (-196℃) as the cooling medium to inherit the cooling process of the quenched metal material, reaching a temperature far below room temperature, and promoting the retained austenite present after conventional heat treatment Further transformation, thereby improving the performance of metal materials.

. Cryogenic treatment can significantly improve the wear resistance, toughness and size stability of metal workpieces, and double the service life of the workpieces.

The emergence of cryogenic treatment technology has aroused a high degree of attention from the scientific research community and the industry. It has been used in cutting tools, measuring tools, molds and precision parts abroad, such as oil pump nozzles, turbine shafts, rollers, valves, and gears. , Modification of springs and other workpieces.

Ball mill steel balls are classified according to the manufacturing process: casting and forging

The ball mill steel balls on the market can be divided into two types according to the manufacturing process: casting and forging, but their wear resistance is different. Because of the crushed material, the steel ball needs good wear resistance and sufficient toughness. Usually, alloy steel, high manganese steel, cast iron and ferrochrome are used for forging or casting, and it is more economical to equip with the corresponding heat treatment process. , Ball mill steel balls can be divided into:
1. Forged steel balls: low carbon alloy steel balls, medium carbon alloy steel balls, high manganese steel balls, rare earth chromium molybdenum alloy steel balls;

2. Cast steel ball: low chromium cast ball, medium chromium cast ball, high chromium cast ball.

Which steel ball is the best on the market now? Let us analyze it now:

1. Forged steel balls:

Good surface quality, good impact resistance, strong toughness, good wear resistance, not easy to break and lose round. That is, the metal is heated to a temperature of 700-1300°C, and the forging machine is used to apply pressure to the metal blank to cause plastic deformation to obtain a processing method for forgings with certain mechanical properties, certain shapes and sizes. One of the two major components of forging (forging and stamping). Forging can eliminate defects such as loose as-cast during the smelting process and optimize the microstructure. At the same time, due to the preservation of complete metal flow lines, the mechanical properties of forgings are generally better than castings of the same material. For the important parts of related machinery with high load and severe working conditions, forgings are mostly used except for simpler shapes that can be rolled, profiles or welded parts. In addition, for forging steel balls to be wear-resistant, the most wear-resistant materials must be selected, such as national standard 60Mn, 65Mn, or high-efficiency wear-resistant alloy steel materials independently developed by some companies, and it is recommended to use steel produced by national super large steel plants. The quality of the materials produced in different steel plants is also different, and the quality of forgings is 80% dependent on the quality of the material. For example, the use of high manganese steel has good impact resistance, strong toughness and good wear resistance. , Not easy to break. Forged steel balls are favored by users because of their low price, economy and durability. For example, international mining giants Rio Tinto, BHP Billiton, and Anglo Gold all use forged steel balls.

Features of forging production:

(1) Forging the heated metal material into various shapes of tools, mechanical parts or blanks is called forging. Forging can change the internal structure of metal materials, refine crystals, and improve their mechanical properties.

(2) Forging production must use heating equipment, forging equipment and many auxiliary tools.

(3) Forging equipment mainly includes steam hammer, air hammer, die forging hammer, mechanical hammer, splint hammer, spring hammer, belt hammer, crank press, friction press, press, reaming machine, roll forging machine, etc.

2. Cast steel balls:

Low and medium chromium cast balls have poor wear resistance and high crushing rate. Although they are cheap, the overall cost performance is not high, so they are not recommended here. High chromium cast ball has excellent hardness and is a high-quality wear-resistant material. It has been widely used in dry ball mills in the cement industry. However, high chromium cast balls have poor toughness and are prone to breakage in ball mills with a diameter of more than 3 meters. The price is higher.

Influence of cast steel ball material: Generally speaking, the harder the steel ball, the greater the wear resistance. To improve the wear resistance of the steel ball, it is necessary to increase its hardness, but as the hardness increases, the impact toughness of the steel ball will decrease. At the same time, the hardness of the steel ball must also take into account the material and hardness of the liner, not too high (Damage the liner), and should not be too low (not wear-resistant). Therefore, how to balance the suitable hardness and good impact toughness of steel balls is the key to improving the wear resistance of steel balls.

The commonly used materials for steel balls are: low carbon alloy, high manganese steel, high chromium cast iron, high carbon and high manganese alloy steel.

Low-carbon alloy steel balls have good toughness and low price. Under the same working conditions, their service life is more than twice that of low-chromium cast balls;

High manganese steel has good toughness, good manufacturability and low price. Its main feature is that under the action of greater impact or contact stress, the surface layer will quickly produce work hardening, and its work hardening index is 5-7 times higher than other materials. The wear resistance has been greatly improved;

High chromium cast iron is a kind of wear-resistant material with excellent abrasion resistance, but its toughness is low, brittle and broken easily and expensive.

High-carbon and high-manganese alloy steel is mainly alloy structural steel containing chromium, molybdenum and other elements, with high hardness and good toughness. Its matrix structure has martensite, bainite or bainite + martensite composite structure. The hardness of the steel ball is about HRC60, and the impact toughness is ≥15J/CM2. Under the same working conditions, its service life is at least one time longer than that of the high manganese steel ball.

But the quenching and tempering heat treatment of the steel ball is the key. After the quenching and tempering heat treatment, not only the overall toughness is required to reach 12 joules/CM2, but also considerable plasticity and wear resistance are required. However, the general casting process can only reach 3-5 joules, resulting in breakage The rate is higher, even for high chromium cast balls, so forgings are recommended when the working conditions are strong. The manufacturing process of the steel ball is also a key factor in determining its service life. If there are defects in the surface or internal manufacturing of the steel ball, such as shrinkage holes, cracks, transcrystallization, etc., it will not only reduce the performance of the steel ball, but even cause the steel ball to break. Therefore, reasonable forging, casting and heat treatment processes must be formulated in the production of steel balls. For example, for high chromium cast iron balls, vertical pouring and reasonable use of external cooling iron should be adopted, and the casting temperature should be strictly controlled. This can make the steel balls have a good solidification sequence and feeding conditions in the casting, and then obtain a dense internal structure. And weaken the phenomenon of coarse grains. The heat treatment process of the steel ball determines the realization of its mechanical properties and the distribution of carbides. Since the composition of the steel ball contains a certain amount of chromium and other alloying elements, how to make these alloying elements form hard point carbides is also a factor considered when formulating the heat treatment process. In short, formulating a reasonable production process and strict quality inspection methods are the prerequisites for ensuring the performance of steel balls.

Investigate and analyze the gap between domestic and foreign spring steel wires

Spring steel wire is the main raw material of spring, and its quality mainly determines the quality of the final product. The unconventional development of China’s automobile industry not only provides rare development opportunities for the spring manufacturing industry, but also creates a market pull for spring raw materials. The development of spring technology will inevitably raise higher and higher requirements for their raw materials. The spring industry hopes that the domestic metal product industry will keep pace with the times and propose more high-quality and low-cost materials for spring production.
From the perspective of users of spring steel wires, there is still a big gap between domestic spring steel wires and similar foreign products.

A. Steel wire raw material quality Baosteel is a leading domestic enterprise, but compared with the famous Kobe Steel, there is still a gap in bloom technology, harmless treatment of inclusions, and uniformity of overall materials.

B. Production of variable cross-section materials for suspension springs and oval-shaped cross-section materials for valve springs. Domestic companies have no ability to produce them and can only give up the market.

C. In terms of mechanical properties, the strength range of the same batch of domestic steel wire materials, even the same disk material, fluctuates greatly, which makes it difficult to control the outer diameter, free length and shrinkage of the spring during production. The stability of mechanical properties of imported steel wire is obviously better than that of domestic steel wire.

D. Steel wire products foreign companies have used peeling and eddy current flaw detection technology, most domestic steel wire manufacturers do not have the corresponding equipment, or the testing technology is not enough.

E. The two indexes of surface defects and decarburization, which have the greatest impact on the fatigue life of the spring, cannot reach the level of similar foreign products.

F. The development of new steel grades is the weakest link for domestic enterprises. So far, the development of new suspension spring materials and ultra-pure valve spring materials is still blank, and there is no development plan in the near future.

Talking about high-strength spring steel with plasticity and corrosion resistance

Spring steel mainly has good elasticity, and because it works under dynamic load environmental conditions, the most important material for manufacturing springs should have high yield strength; it should not cause plastic deformation when subjected to heavy loads; should be High fatigue strength, long service life under repeated loads; and sufficient toughness and plasticity to prevent sudden brittle fracture under impact force.
As economic and environmental pressures continue to grow, the automotive industry continues to improve to reduce weight. For example, the weight of the coil spring has been reduced from 4kg in 1975 to 2kg today, a half reduction. This is mainly due to improved design and increased hardness (the current hardness is 52~56HRC). The higher strength can not only reduce weight but also improve the resistance to bending deformation, but also provide the possibility for the new design of the suspension system. However, higher hardness means increased sensitivity to surface defects during fatigue and corrosion fatigue. Indeed, the fracture of high-strength suspension springs is mainly caused by corrosion pits. Therefore, in order to ensure reliability, in addition to improving strength, it should also have good plasticity (impact toughness) and corrosion resistance.

Studies have found that reducing the carbon content can improve corrosion resistance, impact toughness and plasticity. However, in order to obtain the same strength when the carbon content is reduced, the tempering temperature must be lowered, and the carbon content should be controlled as far as possible to 0.45 ~ 0.55wt%; silicon can improve the yield strength and toughness, but in the process of heat treatment Silicon is also easy to cause decarburization. Therefore, the content of silicon should be controlled at 1.6~2.1wt%; the addition of Cr, Ni, Cu can be adjusted to control the morphology of corrosion pits to improve corrosion resistance and corrosion fatigue resistance, and obtain the required hardenability And keep enough low cost to ensure the economy of new steel grades; the microalloying elements Ti, V, Nb can make the steel have finely dispersed carbonitride precipitates. These precipitates, especially those containing V, are beneficial Obtain higher hardness and yield strength. Nb, Ti and a small amount of V help control the grain size during the austenitization process and obtain a fine structure, thereby improving toughness, corrosion resistance and bending resistance.

The biggest challenge in designing high-strength steel for spiral springs is to ensure that they have high hardness, while having good plasticity and corrosion fatigue resistance and reasonable cost. Kobe Steel and ASCOM Metal jointly developed a new type of high-strength spring steel (HRC>55). The design idea of ​​this kind of steel is: adding controllable alloying elements and microalloying elements to improve the fatigue, corrosion fatigue and bending deformation resistance of steel. Combining the effects of these elements on hardness, corrosion resistance, corrosion pit morphology, hydrogen embrittlement resistance, toughness and cost, the content of alloying elements can be precisely controlled.

Compared with SiCr steel, this type of steel has excellent hydrogen embrittlement resistance, toughness and corrosion resistance, and can meet the needs of higher quality springs that can improve corrosion fatigue resistance under high stress (1300MPa). The difference in the chemical composition of these steels allows users to choose the best composition combination by adjusting cost, corrosion fatigue and toughness according to their needs.

Spring steel definition

Spring steel refers to steel specially used for manufacturing springs and elastic elements due to its elasticity in the quenched and tempered state. The elasticity of steel depends on its elastic deformation ability, that is, within the specified range, the elastic deformation ability makes it bear a certain load, and no permanent deformation occurs after the load is removed.

Spring steel should have excellent comprehensive properties, such as mechanical properties (especially elastic limit, strength limit, yield ratio), elastic reduction properties (that is, elastic reduction resistance, also called relaxation resistance), fatigue properties, hardenability , Physical and chemical properties (heat resistance, low temperature resistance, oxidation resistance, corrosion resistance, etc.). In order to meet the above performance requirements, spring steel has excellent metallurgical quality (high purity and uniformity), good surface quality (strict control of surface defects and decarburization), precise shape and size.

According to the GB/T 13304 “Steel Classification” standard, according to basic performance and service characteristics 1, spring steel belongs to mechanical structural steel; according to the quality grade, it belongs to special quality steel, that is, the steel that requires strict quality and performance control during the production process . According to our country’s custom, spring steel belongs to special steel. When making spring steel, the technical requirements are relatively high, and the technical excellence directly determines the quality.