Basic concepts: tool steels are used in the manufacture of cutting tools, measuring tools, moulds and high-temperature softening spring, all kinds of bearing and wear-resistant parts such as steel. Usually divided into carbon tool steel, alloy tool steel and high-speed tool steel.
Characteristics of tool steel The good performance of strength, toughness, hardness, wear resistance and tempering stability with tool steel. Mainly used for the forming of tools and measuring tools, all kinds of cutting tools manufacturing.
(1) hardness Tool steel tool after heat treatment has high hardness, such as for metal cutting tools is generally more than HRC60, the heating conditions of high temperature and tool generated at high cutting speed and machining of hard materials, can still keep high hardness and good red hardness. Carbon tool steel, alloy tool steel in general working temperature 180 ℃ -250 ℃, high speed tool steel at 600 ℃, still can maintain high hardness. Red hardness on the thermal deformation of die and the high speed cutting tool steel is very important for performance. (2) wear resistance Tool steel with good resistance to wear, or abrasion resisting ability. Tool in under a lot of pressure and friction condition, still can maintain its shape and size invariant. (3) the strength and toughness A certain strength and toughness steel tool having, the tool can bear load, impact, vibration and bending stress complex in the work, to ensure normal use of tools. (4) other properties Because of the variety of tools to work under different conditions, tool steel also has a number of other properties, such as mold steel also has a certain degree of high temperature mechanical properties, thermal fatigue, thermal conductivity and corrosion resistance etc..
Tool steel has the performance, but also has good technological properties. (1) processing Tool steel with heat pressure and good processability and mechanical properties, in order to ensure the manufacture and use of tools. Steel processing depends on the chemical composition, microstructure and quality. (2) the quenching temperature range The range of quenching temperature of tool steel should be wide enough, in order to reduce the possibility of overheating. (3) hardenability and hardenability Hardenability is the performance of the steel can achieve the highest hardness after quenching. Hardenability and the chemical composition of the steel is carbon content, carbon content is higher, is the higher the hardenability of steel. Hardenability said steel after quenching hardness distribution from surface to inside. High hardenability and the chemical composition of the steel, purity, grain size of. According to the different tools for manufacturing, have different requirements for the two performance.
(4) decarburization sensitivity The tool surface decarburization, will make the surface layer hardness decreases, so the requirements of decarburization sensitivity of tool steel low. At the same heating condition, steel decarburization sensitivity depends on its chemical composition. (5) heat treatment deformation Tool during the heat treatment, the size and shape stability. 6) grinding The manufacturing tool and gauge steel. Must have good grinding. Steel grinding and chemical composition of vanadium content, especially, if the vanadium content of not less than 0.50% grinding deterioration. Classification of tool steel A, carbon tool steel Carbon mass fraction of high carbon tool steel, in between 0.65-1.35%, according to which belongs to the hypo eutectoid, eutectoid or hypereutectoid steel microstructure. Carbon tool steel after heat treatment, surface can obtain higher hardness and wear resistance, the heart has good toughness; annealing hardness is low (less than HB207), good processing performance. But the red hardness difference, when the temperature reached 250 ℃, hardness and wear resistance of the steel fell sharply, the hardness decreases to less than HRC60, this kind of steel hardenability is low. Great tool does not harden (water quenching diameter is 15mm), water quenching hardness of surface hardened layer and center difference. The tool is easy to produce deformation in quenching. Or the formation of crack in addition, the quenching temperature range is narrow, should strictly control the temperature in the quenching. To prevent overheating, decarburization and deformation.
Carbon content and hardness of carbon tool steel and steel in size, its hardness and mechanical properties are not only related to the carbon content, but also with the quenching and tempering temperature. The quenching temperature is too high or too low as the mechanical properties and wear resistance of carbon tool steel is disadvantageous, carbon tool steel after quenching and low temperature tempering to must be carried out, the residual stress after quenching are partially eliminated, avoid excessive stress cracking or deformation, and not reduce or slightly lower hardness the case, increase the strength and plasticity. Influence of carbon content in carbon tool steel after quenching and low temperature tempering water on the strength and plasticity. Hypoeutectoid steel strength increases with the increasing of carbon content, to the 0.60-0.70% reaches the maximum value when the strength, with the increase of carbon content decreases, then close to eutectoid steel components, the lowest strength, strength and with carbon content increasing, when the carbon content is higher than 0.15%, strength and with the increasing of carbon content and decline.
As can be seen, hypo eutectoid composition of steel, such as T7, T7A, with plastic and good strength, suitable for the manufacture of impact load tools and cutting of soft material tool; eutectoid steel, such as T8, T8A, T9, T9A, its strength and low plasticity, heated easily overheat, deformation a large, not suitable for manufacturing by the impact of large tools, hardness and wear resistance after heat treatment, but has higher; the eutectoid composition of steel, such as T10, T10A, T11, T11A, has good mechanical properties, such as hardness, wear resistance and toughness, mainly used in the manufacture of not subject to sudden shock tool; such as T12, T12A, with high hardness and wear resistance, but low toughness, for free vibration and impact tool. Used in the manufacture of carbon tool steel tool, its working conditions and the different requirements are also different. Cutting tool steel high hardness, wear resistance and red hardness; measuring steel except hardness, wear resistance and high dimensional stability outside, also requires high and enough toughness; cold working die steel except hardness, wear resistance and high, also require high strength, enough toughness and good processing properties.
Two, alloy tool steel Alloy tool steel, hardenability hardenability and toughness, wear resistance than carbon tool steel high, according to use can be divided into cutting tools, tooling and gage steel 3. The high carbon content steel (carbon mass fraction is greater than 0.80%) used for the manufacture of cutting tools, measuring tool and die, this kind of steel after quenching hardness above HRC60, and have sufficient wear resistance; carbon content medium steel (mass fraction of carbon 0.35%-0.70%) used for the manufacture of hot work die, this kind of steel after quenching the hardness slightly lower, to HRC50-55, but a good toughness. (a) cutting tool steel cutting tool in working conditions, strong wear and heat, and the vibration and shock loading certain. Cutting tool steel has high hardness, wear resistance and good toughness, red hardness. In order to ensure its high hardness, meet the needs of the formation of carbides, mass fraction of carbon steel in general 0.80%-1.45%, Cr is the main alloy elements of this kind of steel, the mass fraction of 0.50%-1.70% in general, some steel containing tungsten, in order to improve the performance of metal cutting. This kind of tool steel with alloying elements, so the hardenability than carbon tool steel, small deformation resulting from heat treatment, with high hardness and wear resistance. Steel commonly used are steel, silicon steel and chromium tungsten steel etc..
(two) die steels The mold can be broadly classified as mould, cold hot mold and plastic mold 3, used for forging, stamping, cutting, die, die casting, because of various kinds of mold for different purposes, the work condition is complex, so the die steel performance requirements are also different. Cold working die includes a die, drawing die, drawing die, stamping die, rubbing plate, thread rolling plate, Leng Dunmo and cold extrusion die. Cold work die steel, according to the mold working conditions, should have the strength, hardness, wear resistance and high uplift, enough toughness, and high hardenability, hardenability and other process performance. For alloy tool steel such use is usually belong to the high carbon alloy steel, carbon content was above 0.80%, chromium is an important alloying element of this kind of steel, the mass fraction is usually not more than 5%. But for some wear resistance requirement is very high, after quenching deformation of small steel, high chromium content, reached 13%, and in order to form a large number of carbide, carbon content in steel is also very high, up to 2.0%-2.3%. Cold working die steel with high carbon content, the organization mostly hypereutectoid steel or ledeburite steel. Steel used in high carbon low alloy steel, high carbon chromium steel, chrome molybdenum steel, medium carbon chromium tungsten Bracelet steel etc.. Hot work die for hammer forging, forging, extrusion and die-casting of several main types, including hot forging die, press forging die, stamping die, hot extrusion die and metal die casting die. Hot die for hot metal or molten metal to obtain the required shape, made of needed products. The mould in the work in addition to bear great mechanical stress, but also bear the repeated heat and cooling effect, caused by thermal stress. Hot work die steel should have high hardness, strength, toughness, red hardness wear resistance, but also should have the high temperature strength, good thermal fatigue, thermal stability and corrosion resistance, also has high hardenability, to ensure that the whole section is consistent to mechanics.
For die casting die steel, also has a surface layer after repeated heating and cooling does not crack, and to the liquid metal flow impact and erosion performance. This kind of steel is usually belongs to the medium carbon alloy steel, carbon content in the 0.30%-0.60%, which belongs to the sub eutectoid steel, there is also a part of steel as the alloy adding more (such as tungsten, molybdenum, vanadium) and become the eutectoid and hypereutectoid steel. Steel used in chromium manganese steel, nickel chromium steel, chrome steel etc.. Plastic mould comprises a mould for thermoplastics and thermosets mould. Plastic mould steel with strength, hardness, wear resistance, thermal stability and corrosion resistance properties of certain. In addition, but also has good processing properties, such as heat treatment deformation small, good processing performance, good corrosion resistance, grinding and polishing good performance, welding performance is good, high roughness, good thermal conductivity and working condition stable size and shape, etc.. In general, injection molding or extrusion die can be used for hot work die steel; thermal forming and die high wear resistance, high strength can be used for cold working die steel. (three) for measuring tool steel Gage should has good dimensional stability, high wear resistance, high hardness and certain toughness. Therefore, gage steel has high hardness, organizational stability, good wear resistance, and the grinding and processing properties, good heat treatment deformation small, small expansion coefficient and good corrosion resistance. This kind of steel in general are the eutectoid steel. The addition of the alloying element chromium, manganese, molybdenum, tungsten. Steel commonly used with chromium, chromium tungsten steel, manganese steel etc..
Three, high speed tool steel High speed tool steel is mainly used for cutting tool manufacturing efficiency, because of its high red hardness, good wear resistance, high strength characteristics, also used in the manufacture of high performance requirements of the mold, high temperature and high temperature, roll shaft spring etc.. High speed tool steel by heat treated using hardness up to HRC63, can still keep high hardness in 600 ℃ temperature, but its toughness, wear resistance and heat resistance are good. High speed tool steel annealing state also has good mechanical properties, precision tool manufacturing complex shapes. The main alloy elements of high speed tool steel, chromium, molybdenum tungsten, vanadium, and some high speed tool steel with cobalt, aluminum etc.. This kind of steel is a high carbon high alloy ledeburite steel, one of the main characteristics of the organizations contain a large amount of carbides. The as cast high speed tool steel carbide is eutectic carbide, the thermal pressure processing and then crushed into granular distribution in steel, known as a secondary carbide precipitation; from austenite and martensite carbide known as the two. Great influence on the performance of these carbides in high speed tool steel, especially the two carbide, has great influence on the austenite grain size and two hardening properties. Chemical composition of carbide quantity, type and steel, and the deformation of particle size and distribution of carbides and steel related. Tungsten, molybdenum is the main alloy element in high speed tool steel, plays an important role in the two hardened steel and other properties. Chromium on the hardenability of the steel, oxidation resistance and wear resistance plays an important role, also has a certain effect on the two secondary hardening. Vanadium steel two hardening and wear resistance plays an important role, but decreased grindability. Cobalt is non carbide forming elements, the two hardened steel can be improved and heat resistance, aluminum can improve the cutting performance of steel.
High speed tool steel quenching temperature is very high, close to the melting point, its purpose is to make the alloy carbide more into the matrix, the two hardening ability makes the steel has better. High speed tool steel after quenching temperature rise, this is the first time hardening, but the higher the quenching temperature, tempering and has lower strength and toughness. After quenching and low temperature below 350 ℃ tempering hardness decrease, in more than 350 ℃ temperature tempering hardness increases gradually, to the range of 520-580 ℃ tempering (chemical composition is different, the tempering temperature of different hardness peak) occurred second times, and more than quenching hardness, this is the two time hardening. This is an important characteristic of high speed tool steel. High speed tool steel has the red hardness, wear resistance, high hardness and other performance, but also has some thermoplastic, grinding process performance. The main alloying element tungsten series high speed tool steel tungsten, molybdenum containing or not containing a small amount of molybdenum. Its main characteristic is overheating sensitivity, decarburization sensitivity of small, heat treatment and thermal processing temperature range is wide, but coarse carbide particles, distribution uniformity, impact toughness and plasticity. The main alloy elements of W-Mo high-speed tool steel tungsten and molybdenum. Its main characteristic is the particle size and distribution of carbides are better than that of tungsten series high speed tool steel, decarbonization and overheating sensitivity than molybdenum high speed tool steel, high-speed tool steel main alloy elements using properties and process performance are good molybdenum molybdenum, tungsten containing or not containing a small amount of tungsten. Its main characteristic is fine carbide particles, uniform distribution, good toughness, but the decarbonization and overheating sensitivity high, narrow range of thermal processing and heat treatment. Cobalt high speed tool steel is added with a certain volume based on universal high-speed tool steel on the cobalt, can significantly increase the hardness, wear resistance and toughness. Powder high-speed tool steel is produced by powder metallurgy method. Firstly, the oxygen atomization in high speed tool steel pre alloyed powder, and then use the cold, hot static press billets will powder compaction into dense, after forging, rolling material. The distribution of carbide particles, powder high-speed tool steel of uniform, toughness, grindability and dimensional stability are very good, super hard high speed tool steel can be produced by casting method may produce higher content of alloy element.
Powder high-speed tool steel can be divided into 3 categories, the first category is cobalt high speed tool steel, its characteristics are close to the hardness of the hard alloy, but also has good ductility, workability, grindability and toughness. The second category is tungsten, molybdenum, cobalt free high vanadium high speed tool steel. The third category is the super wear-resistant high speed tool steel. Its hardness is not too high, but the excellent wear resistance, mainly for high wear resistance and withstand the impact load working conditions.