Intoduce Tool steel Grade Group
Tool steel refers to a spread of steel and steel that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion and deformation, and their ability to carry a leading edge at elevated temperatures. As a result, tool steels are fitted to use within the shaping of other materials. With a carbon content between 0.5% and 1.5%, tool steels are manufactured under carefully controlled conditions to supply the specified quality. The presence of carbides within the ir matrix plays the dominant role in the qualities of alloy steel . The four major alloying elements that form carbides in alloy steel are: tungsten, chromium, vanadium and molybdenum. the speed of dissolution of the various carbides into the austenite sort of the iron determines the high-temperature performance of steel (slower is best , making for a heat-resistant steel). Proper heat treatment of those steels is vital for adequate performance.The manganese content is usually kept low to attenuate the likelihood of cracking during water quenching.
There are six groups of tool steels: water-hardening, cold-work, shock-resistant, high-speed, hot-work, and special purpose. the selection of group to pick depends on cost, working temperature, required surface hardness, strength, shock resistance, and toughness requirements.The more severe the service condition (higher temperature, abrasiveness, corrosiveness, loading), the upper the alloy content and consequent amount of carbides required for the alloy steel .
Tool steels are used for cutting, pressing, extruding, and coining of metals and other materials. Their use, like the assembly of injection molds, is important , thanks to their resistance to abrasion, which is a crucial criterion for a mold which will be wont to produce many thousands of moldings of a product or part.
The AISI-SAE grades of alloy steel is that the commonest scale wont to identify various grades of alloy steel . Individual alloys within a grade are given a number; for example: A2, O1, etc.
1 Water-hardening group
W-group alloy steel gets its name from its defining property of getting to be water quenched. W-grade steel is actually high carbon plain-carbon steel. This group of alloy steel is that the most ordinarily used alloy steel due to its low cost compared to others. They work well for parts and applications where high temperatures aren’t encountered; above 150 °C (302 °F) it begins to melt to a clear degree. Its hardenability is low, so W-group tool steels must be subjected to a rapid quenching, requiring the utilization of water. These steels can attain high hardness (above HRC 66) and are rather brittle compared to other tool steels. W-steels are still sold, especially for springs, but are much less widely used than they were within the 19th and early 20th centuries. this is often partly because W-steels warp and crack far more during quench than oil-quenched or air hardening steels.
The toughness of W-group tool steels is increased by alloying with manganese, silicon and molybdenum. Up to 0.20% of vanadium is employed to retain fine grain sizes during heat treating.
Typical applications for various carbon compositions are for W-steels:
0.60–0.75% carbon: machine parts, chisels, setscrews; properties include medium hardness with good toughness and shock resistance.
0.76–0.90% carbon: forging dies, hammers, and sledges.
0.91–1.10% carbon: general purpose tooling applications that need an honest balance of wear and tear resistance and toughness, like rasps, drills, cutters, and shear blades.
1.11–1.30% carbon: files, small drills, lathe tools, razor blades, and other light-duty applications where more wear resistance is required without great toughness. Steel of about 0.8% C gets as hard as steel with more carbon, but the free cementite particles in 1% or 1.25% steel make it hold a foothold better. However, the fine edge probably rusts off faster than it wears off, if it’s wont to cut acidic or salty materials.
2 Cold-work group
The cold-work tool steels include the O series (oil-hardening), the A series (air-hardening), and therefore the D series (high carbon-chromium). These are steels wont to cut or form materials that are at low temperatures. This group possesses high hardenability and wear resistance, and average toughness and warmth softening resistance. they’re utilized in production of larger parts or parts that need minimal distortion during hardening. the utilization of oil quenching and air-hardening helps reduce distortion, avoiding the upper stresses caused by the quicker water quenching. More alloying elements are utilized in these steels, as compared to the water-hardening class. These alloys increase the steels’ hardenability, and thus require a less severe quenching process and as a result are less likely to crack. they need high surface hardness and are often wont to make knife blades. The machinability of the oil hardening grades is high except for the high carbon-chromium types is low.
Oil-hardening: the O series
This series includes an O1 type, an O2 type, an O6 type and an O7 type. All steels during this group are typically hardened at 800 °C, oil quenched, then tempered at < 200 °C
Air-hardening: the A series
The first air-hardening-grade alloy steel was mushet steel, which was referred to as air-hardening steel at the time.
Modern air-hardening steels are characterized by low distortion during heat treatment due to their high-chromium content. Their machinability is sweet and that they have a balance of wear and tear resistance and toughness (i.e. between the D and shock-resistant grades)
High carbon-chromium: the D series
The D series of the cold-work class of tool steels, which originally included types D2, D3, D6, and D7, contains between 10% and 13% chromium (which is unusually high). These steels retain their hardness up to a temperature of 425 °C (797 °F). Common applications for these tool steels include forging dies, die-casting die blocks, and drawing dies. thanks to their high chromium content, certain D-type tool steels are often considered stainless or semi-stainless, however their corrosion resistance is extremely limited thanks to the precipitation of the bulk of their chromium and carbon constituents as carbides.
3 Shock-resisting group
Main article: Shock resisting steel
The high shock resistance and good hardenability are provided by chromium-tungsten, silicon-molybdenum, silicon-manganese alloying. Shock-resisting group tool steels (S) are designed to resist shock at both low and high temperatures. a coffee carbon content is required for the required toughness (approximately 0.5% carbon). Carbide-forming alloys provide the required abrasion resistance, hardenability, and hot-work characteristics. This family of steels displays very high impact toughness and comparatively low abrasion resistance and may attain relatively high hardness (HRC 58/60). In the US, toughness usually derives from 1 to twenty silicon and 0.5–1% molybdenum content. In Europe, shock steels often contain 0.5–0.6% carbon and around 3% nickel. a variety of 1.75% to 2.75% nickel remains utilized in some shock resisting and high strength low alloy steels (HSLA), like L6, 4340, and Swedish saw steel, but it’s relatively expensive. An example of its use is within the production of jackhammer bits.
4 High-speed group
Main article: hot-work steel
Hot-working group
Hot-working steels are a gaggle of steel wont to cut or shape material at high temperatures. H-group tool steels were developed for strength and hardness during prolonged exposure to elevated temperatures. These tool steels are low carbon and moderate to high alloy that provide good hot hardness and toughness and fair wear resistance thanks to a considerable amount of carbide.H1 to H19 are supported a chromium content of 5%; H20 to H39 are supported a tungsten content of 9-18% and a chromium content of 3–4%; H40 to H59 are molybdenum based.
Examples include DIN 1.2344 alloy steel (H13).
5 Special-purpose group
P-type alloy steel is brief for plastic mold steels. they’re designed to satisfy the wants of zinc die casting and plastic injection molding dies.
L-type alloy steel is brief for low alloy special purpose alloy steel . L6 is extremely tough.
F-type alloy steel is water hardened and substantially more wear resistant than W-type alloy steel .
