There are six different categories of tooling steel including; cold-work, water-hardened, hot-work, high-speed, shock-resisting, and special purpose tool steels. Below are the classifications of tool steel and their application.
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This is one of the major types of tool steel. It is tough, hard, and wear-resistant in cold environments with temperatures below 200ºC. However, cold-work tool steel does not perform well when exposed to hot environments.
Besides, cold-work steel has high machinability. This is due to the presence of graphite and the lubrication it provides. What&#;s more, the most commonly used tool steel grades in this category include; D2, O2, A2, D3, and D6.
These are the different subcategories of cold work tool steel.
This cold-working tool steel is also known as stainless due to its high chromium content and contains 11-13% chromium. Although they have limited corrosion resistance, their 1.4-2.5% carbon content gives them a high abrasion resistance. It also enables them to function at temperatures as high as 425ºC.
Besides, their ability to undergo oil or air quenching with minimal distortion gives this tool steel application in making cutters. It also makes the D series tool steel ideal for making seaming and forming rolls, plastic injection molds, lathe centers, and woodworking knives. Its other applications include making burnishing tools, lamination dies, draw punches, as well as cold extrusion, dies.
These types of tool steel have a carbon content of 0.05-2.85% and up to 5% chromium content. Furthermore, this grade of tool steel is very tough with high wear resistance. Common applications include coining, embossing, blanking, and blending dies.
Quenched by oil during production, this series of tool steel has a carbon content ranging between 0.85-2.00%. They are also tough with have high abrasion resistance. The applications of Oil hardening tool steels include making bushings, collets, gauges, master engraving rolls, punches, and chasers for thread cutting.
This category of tool steel contains heat-treated carbon steel. Produced at low-cost and water-quenched, water-hardened tool steel has a carbon content ranging between 0.5-1-5%. The high carbon content of water-hardened steel makes them brittle and hard. However, it is low on other alloying metals like tungsten, nickel, or molybdenum, usually less than 0.5%.
The types of tool steel in this category usually have a carbon content of less than 0.6%. However, they contain a greater percentage of other alloying elements. This enables them to keep their characteristics and work optimally even at extreme temperatures up to 540ºC due to the creation of more carbides.
The high-temperature resistance of hot work tool steel makes it ideal for use in manufacturing materials like metal and glass that require high temperatures for optimal malleability.
Additionally, one benefit engineers derive from using tool steel under this category is their continued functionality, even after exposure to extended heat. The most commonly used tool steel in this category is the H13.
Based on the percentage of alloying elements used, there are three main alloy elements in this category: molybdenum, and chromium.
This is a hot work tool steel that has a high molybdenum content. Furthermore, this type of tool steel has high wear resistance and heat stability, especially in situations of extreme temperature. What&#;s more, their ability to handle force and heat gives Molybdenum-type tool steel applications in metal mills as cutters or dies.
This type of tool steel contains 9-18% tungsten and 2-4% chromium. Tungsten hot work tool steel although brittle, it has excellent heat resistance. Furthermore, one way to circumvent the brittleness of this tool steel is preheating it to operating temperature before use.
The Chromium type is the most used hot work tool, containing 3-5% chromium. They could also contain below 5% of other alloying elements like molybdenum, tungsten, or vanadium. Common applications of chromium-type tool steel, include hot forging, hot working punches, and plastic injection mold.
High-Speed tool steel contains many elements, including 0.6% carbon, 3-5% chromium, and 14-18% tungsten. Furthermore, the invention of this category of tool steel is partly responsible for ushering in the era of modern production. Before the invention of high-speed tool steels, when cutting tools and machines worked for long periods, their efficiency decreased due to friction. However, with this tool steel, cutting tools and edges keep working efficiently, performing at optimal speeds.
Common applications of high-speed tool steel include the production of power-saw blades, milling cutters, router bits, gear cutters, and drill bits. The M2 high-speed tool steel is the most common in this category.
Developed to have high-level impact resistance, shock-resisting tool steels are remarkably strong. Furthermore, this tool steel&#;s strength is due to its high toughness value and low carbon content. This tool steel category contains alloying elements found in other categories, as well as 0.15-3% silicon.
Although this steel does not have optimal abrasion resistance, it has excellent resistance to shock regardless of temperature. Besides, these properties make S-grade tool steels ideal for producing jackhammer parts, blacksmith chisels, and clutch parts.
In addition, its other applications include hot stamps, pneumatic tools, chipper knives, cold and hot working chisels, hot forming dies, and cold gripper dies. The S7 tool steel is the most popular in this category.
These are tool steels like an excellent mix of toughness, corrosion, hardness, and resistance to wear and tear. Furthermore, tool steel under this category also has high impact strength and is easy to polish.
Besides, plastic mold tool steels are ideal for companies that use the processes of extrusion and injection molding to produce plastic. Using this tool steel for making molds ensures tool durability and reliability.
Also, they are tool steels created for special purposes. Like the water-hardened tool steel, these ones are water-quenched. Tool steels in this category contain high-iron steels, while other alloying elements are either absent or present in minute quantities. Adding other alloying elements sparingly helps improve the mechanical properties of this tool steel while ensuring it is not as expensive as other tool steels.
An instance of special-purpose tool steels is the low-carbon mold steels used in thermoplastic molding. This specially crafted mold steel does not require high impact resistance but excellent wear resistance and heat tolerance. In common, the P20 is the most popular used tool steel in this category.
You have designed your tooling or forming die based on the finished part you need, and you know how you will manufacture the tool or die. Perhaps you plan on utilizing MetalTek&#;s sand or centrifugal casting processes. However, you need to determine the best alloy for your tooling or forming die. Since every application is different, there is no magical &#;one size fits all&#; alloy for tooling but this article will provide tips for choosing the best alloy based on your application, requirements, and potential challenges you currently face.
If, after reading this article, you need additional assistance, MetalTek is here to help and we would love to hear from you.
When selecting an alloy, there are two primary factors to consider &#; physical and mechanical properties.
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Typically, an alloy&#;s mechanical properties are used for selection but there are physical properties to keep in mind as well. So, let&#;s dive a little deeper and look at which specific properties should be considered when selecting the right alloy for your tooling application.
Yield Strength describes the point after which the material under load will no longer return to its original position or shape after the stress no longer exists. Deformation moves from elastic to plastic. Design calculations include the Yield Point to understand the limits of dimensional integrity under load. Yield strength is measured in Newtons per square millimeter (Mega Pascals or MPa) or pounds per square inch (PSI).
Permanent deformation in tooling is typically unacceptable because it leads to inconsistent parts and premature replacement. To help prevent this from happening, make sure you select an alloy with a yield strength higher than the forces put on the tooling.
Fatigue can lead to fracture under repeated or fluctuating stresses (for example loading or unloading) that have a maximum value less than the tensile strength of the material. Higher stresses will accelerate the time to failure, and vice versa, so there is a relationship between the stress and cycles to failure.
Fatigue limit, then, refers to the maximum stress the metal can withstand (the variable) in a given number of cycles. Conversely, the fatigue life measure holds the load fixed and measures how many cycles the material can withstand before failure. Fatigue strength is an important consideration when designing components subjected to repetitive load conditions.
Does your tool need to make 5 parts before being replaced or does it need to make 5,000? Depending on how many parts your tooling needs to produce (cycles), this is a critical factor in selecting the right alloy.
Hardness is defined as a material&#;s ability to resist permanent indentation (that is plastic deformation). Typically, the harder the material, the better it resists wear or deformation. The term hardness, thus, also refers to local surface stiffness of a material or its resistance to scratching, abrasion, or cutting. Hardness is measured by employing such methods as Brinell, Rockwell, and Vickers, which measure the depth and area of a depression by a harder material, including a steel ball, diamond, or other indenter.
Coefficient of thermal expansion measures how much a material expands when heated. Since many forming processes involve elevated temperatures, along with heat/cool cycles, alloys with low coefficients of thermal expansion will help maintain dimensional accuracy.
Shear occurs when directional forces cause the internal structure of the metal to slide against itself, at the granular level. Shear strength should be considered in applications where the direction as well as the magnitude of the stress is important because of extensive shear or torsion loads.
While some tooling is made of non-ferrous metal or even a non-metallic material altogether, ferrous alloys are the most common. More specifically, popular groups of alloys (alloy families) are specialty alloys, stainless steels, tool steels, and carbon steels.
Heat-resistant alloys are those capable of being used at temperatures above ºF / 670ºC under load in particular gas environments and are indicated by acceptable levels of stress rupture and creep strengths that correspond to the required time of service. Main groups of heat-resistant alloys are high chrome nickel austenitic alloys a.k.a. heat resistant stainless, nickel-based alloys, and cobalt chrome nickel-based alloys. Common heat resistant stainless steels used for tooling applications are: MTEK 20-25, MTEK 20-25MA, MTEK 25-12.
MTEK 625 (Inconel 625®) is designed for some of the toughest applications in manufacturing. It works extremely well in high heat applications and doesn&#;t lose much tensile strength at elevated temperatures like other steels. As a result, it resists deformation at hot-working temperatures. Inconel 625® is not only stronger than stainless steel at elevated temperatures, but it also offers better resistance to corrosion, oxidation, and scaling. Because of its properties, it works well in extreme pressure and heat environments as well as being corrosion resistant.
MTEK Invar (K, FeNi36) is an alloy with 36% nickel and is strong, ductile, and fairly corrosion resistant. What makes Invar a great alloy is that the coefficient of thermal expansion is nearly zero. As a result, it offers dimensional stability across a range of temperatures &#; cryogenic temperatures to 500°F.
Invar&#;s coefficient of thermal expansion properties makes it a good candidate for the manufacturing of precision instrumentation and equipment like tooling for aerospace components, electronic devices, and lasers.
MTEK X is a nickel-based alloy with outstanding high temperature strength at °F and oxidation resistance up to °F. It&#;s also resistant to stress-corrosion cracking in high temperature applications and has good ductility when exposed to high temperatures for extended periods of time. While nearly half of the alloy is made from nickel, it contains roughly 22% chromium and 18% iron.
A common type of alloy used is stainless steel because of its temperature and corrosion resistant properties. Stainless steels owe their ability to resist corrosion primarily to the presence of a passive film on their surface.
Chromium is chiefly responsible for the formation of the passive film. Iron ceases to rust at approximately 12% chromium content and resistance to oxidizing corrosives increases rapidly with chromium content up to approximately 20%. Beyond that level, resistance is increased at a more gradual and declining rate. Consequently, few stainless alloys contain more than 27% chromium.
Within the stainless-steel family, there are four main categories-austenitic, duplex, precipitation hardening, and martensitic. Common stainless steels used for tooling applications are: MTEK 304, MTEK 304L, MTEK 309, and MTEK 310.
Tool steel alloys are high carbon chrome steels containing various amounts of molybdenum, cobalt, vanadium, and other elements. Some tool steels are designed to handle repeated loads and impacts at ambient temperature with exceptional wear resistance. Other tool steel alloys will exhibit stability at elevated temperatures and repeated loads.
Tool steels are typically provided in an annealed condition which softens the very hard material so that it may be machined or formed for use. After machining, the material is heat treated again to increase toughness and strength.
There are several classes of tools steels available which can be selected based on the specific environment, particularly allowing for temperature. Among those are Cold-work, Hot-work, and High-speed.
Carbon steels are primarily made from iron and carbon and are the cheapest alloy for tool applications. As a result, it&#;s one of the most common alloys used for tools. Carbon steels are categorized by their amount of carbon-low, medium, and high.
When selecting a specific carbon steel alloy, it&#;s critical to find the right balance between performance and labor costs for machining and/or welding.
There is no &#;one size fits all&#; when it comes to picking the best alloy for every tooling application. However, if you are looking to make your products better or solve a current problem you are having, the below are MetalTek&#;s top three alloys to consider. See charts for typical chemistry and mechanical property ranges.
To learn more about what alloy might be the best fit for your application, please contact us.
Disclaimer: The information in this publication is for informational purposes and does not replace good engineering practices. MetalTek International does not give any warranty or assumes any legal liability for its accuracy or completeness. In addition, the company makes no warranty of results obtained for any specific use of the information given in this publication.
#1) MTEK Invar: Great strength and toughness and a superior coefficient of thermal expansion.
#2) MTEK 625: Can withstand some of the toughest applications in manufacturing. It works extremely well in high heat applications and doesn&#;t lose much tensile strength at elevated temperatures like other steels.
#3) MTEK 20-25: All around good alloy for strength and toughness over a range of temperatures. If you are looking for something better than a typical stainless steel like 309 or 310, this might be a good place to start.
METALTEK GRADECASTWhile selecting the best alloy based on the application should be the top priority, other factors to consider is cost, both upfront and long term.
If a specific alloy causes the total cost of the forming die to be twice as much, can you manufacture at least twice as many parts? If paying twice as much yields four or five times as many parts versus using a standard type of alloy, higher upfront tooling costs may be the best long-term decision.
On several occasions, MetalTek has worked with a customer to fully understand their application to recommend the best alloy for the job to make their products better and last longer. In turn, saving money in the long run.
Disclaimer: The information in this publication is for informational purposes and does not replace good engineering practices. MetalTek International does not give any warranty or assumes any legal liability for its accuracy or completeness. In addition, the company makes no warranty of results obtained for any specific use of the information given in this publication.
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