What is High Speed Steel?

what is high speed steelFor decades, Griggs Steel has provided quality high speed tool steel to many clients for all of their machining and fabrication needs. Our standards for both our products and service keep us moving forward to satisfy customers and build lasting relationships with them. What is high speed steel? What makes it stand out in industry, and what can we make for you?

Defining High Speed Steel

High speed tool steel comprises a set of tool steel alloys named for their capacity to cut materials faster than traditional high-carbon steels previously used in cutting tools. This is on account of exceptional hardness, abrasion resistance and resistance against softening at high temperatures, owing to the alloying metals and heat treatment used. We follow the American Society for Testing and Materials in its definition of high speed steel as given in Specification A600-79—a high-carbon steel containing tungsten and/or molybdenum, along with chromium, vanadium and sometimes cobalt.

The heat treatment used is also a major component of what defines high speed steel, as its martensitic structure contributes to its high hardness. This is achieved by austenizing to nearly the steel’s melting temperature, then quenching in a salt bath or by air cooling and multiple tempering cycles to convert any remaining austenite to martensite.

Though the term “high speed tool steel” describes multiple alloys, these traits are common to all of them:

  • High alloy content, primarily tungsten or molybdenum, with lesser amounts of chromium, vanadium and cobalt;
  • High carbon content—a minimum of 0.65% by weight, but commonly anywhere from 0.8% to 1.5% carbon content;
  • Rockwell hardness of at least 64 HRC at room temperature;
  • A heat treatment process that produces a high quantity of complex metallic carbides—chiefly tungsten, molybdenum and vanadium carbides—suspended in a steel substrate, which results in hardness and wear resistance.

Common Grades and Properties of High Speed Steel

high speed tool steelOver forty classifications of high speed steel are recognized by the American Iron and Steel Institute (AISI), and more still are also produced by manufacturers. Two general categories comprise these various classifications: those primarily alloyed by tungsten and those alloyed by molybdenum.

Each grade is designated with T or M, respectively, as well as a unique number distinguishing it from other grades. Despite this naming, all but two M-type steels also contain some tungsten, and all T-types but one contain some amount of molybdenum; both of these form the metal carbides essential to achieving the desired properties. ASTM specifications exist for 7 T-types and 17 M-types.

The chief alloying elements have a strong influence on the properties of high speed steel, and the various grades were developed through extensive experimentation.

  • Tungsten and molybdenum form the carbides that define the structure of high speed steel. Generally, molybdenum steels have higher toughness, while tungsten steels display higher hot hardness—the hardness retained at very high temperatures.
  • Vanadium improves wear resistance and hot hardness in tool steels by the formation of stable vanadium carbides. A higher proportion of vanadium requires an increase in carbon content to counteract the loss of toughness, though. High vanadium steels are used for specialty cutting tools where wear resistance and heat tolerance are paramount.
  • Chromium is included mainly to enhance hardenability and reduce oxidation damage during heat treatment.
  • The inclusion of cobalt improves hot hardness in high speed steels, though brittleness increases as well.
  • Trace inclusions of silicon and sulfur have some niche applications, but generally do not significantly impact the steel’s properties.
  • Manganese and phosphorus should be kept to a minimum, as these elements significantly increase the brittleness of steels and can induce cracking during quenching.

Surface Treatments

High speed steel tools often receive a bright or black oxide finish for use with non-ferrous or ferrous metals, respectively. Other coatings and treatments are possible, as well. Nitriding diffuses nitrogen into the surface of the steel during heat treatment, producing a case-hardened surface that shows higher wear resistance at the expense of notch hardness.

Another common treatment is titanium nitride (TiN) via physical vapor deposition, which enhances edge retention significantly. This, combined with a lower coefficient of friction, means an extended lifespan and improved machining, though TiN-coated tools react adversely with titanium or nickel alloys.

Our HSS Products

We produce and ship HSS stock in the form of block sheets, plates and hardened round bars of various sizes. Our regular inventory includes the M2, M3, M4, M7 and M42 grades of high speed steel. M2 is widely considered the industry standard for high speed steels, well-balanced in toughness, abrasion resistance and hot hardness for general purpose, replacing the original T1 grade in most uses due to the molybdenum inclusion improving most properties and being more economic.

Other HSS grades are used instead for more specific applications, typically for better wear resistance or hot hardness. M3, M4 and M7 feature increased carbon and vanadium for higher abrasion resistance and grindability, and M42 possesses a high cobalt content that gives it exceptional hot hardness.

Additionally, we manufacture several grades using the proprietary Crucible Particle Metallurgy process, a form of powder metallurgy. This involves pouring the molten alloy through a spray nozzle and atomizing it to produce tiny droplets of steel that quickly cool into a fine powder, stored in sealed and decontaminated capsules.

The powder is then subject to hot isostatic pressing—a combination of high pressure and near-melting point temperature—to compact it. This produces a fine-grained, homogeneous bulk structure with a uniform distribution of carbides and little to no precipitation of alloying elements. We refer to the resulting alloys as particle metals, designated with PM.

Our particle metals include the standard grades M4, T15, M48 and A11 (a primarily vanadium-based steel), as well as PM 23, 30 and 60; these are also included in the regular inventory. The fine-grained and uniform structure of these particle metals grants them high impact toughness and makes them exceptional for cold working.

Applications of High Speed Steel

Broadly, high speed steel excels in hardness and abrasion resistance, with different grades trading for toughness, hot hardness or reduced brittleness. As a result, these alloys see the most use in industrial cutting tools—tool bits, milling cutters, saw blades, drills, taps, broaches and more.

Tools made of high speed steel frequently keep a sharp edge for longer than other carbon steels, and the variety of grades and surface treatments available provide options for specialized applications. These products see use anywhere from woodworking to machining high-grade alloys.

Though not traditionally considered to be cutting tools, punches, dies and other components in progressive stamping can also be made from high speed steel. Additionally, the properties of high speed steels, particularly hardness and wear resistance, are desirable for hand tools such as chisels, files, blades for hand planes and kitchen and pocket knives.

Turn to Griggs Steel

Griggs leads the industry in high speed tool steels, not only for the quality of our steels but also for affordability, rapid response and delivery, ISO-9001 expertise and dedicated customer service. Every order includes a certificate of quality, and we’re ready to back that by refunding you if our high speed steel fails due to defects. Contact us today to request a quote and learn more about our options and how they can benefit you.

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