Selected Metals - 9: Tool Steels
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.

The term "tool steel" can be applied logically to any steel that is used as a tool. However tool steel is generally considered to be those steels that can be machined in an annealed condition, heat treated to a very high hardness, and then ground to size and finish. In the common machine shop vernacular different types of tool steel are often differentiated by AISI single letter that identifies the kind of quenching used in heat treat, the application of the tool steel, or its main alloy. The most common quenching techniques being air-hardening (A), oil-hardening (O), and water-hardening (W). Other steels are chromium tool steel (H), die steel (D), high speed steel (M), cobalt tool steel (T), and shock-resistant tool steel (S). Listed below are the properties of one each of these groups.

The following examples would be familiar to most machinist. Especially those machinist involved in tool and die work.

T3102 (AISI A2)

  • Hardness 56 - 62 RC Air quenching
  • Machinability 85% of W steels (baseline)
  • Applications die shapes, slitters and similar where wear resistance is important.
  • Comments This alloy is one of the Cold Work, Medium Air Hardening type tool steels. It contains chromium and molybdenum with a relatively high (1%) carbon content and is capable of deep hardening from air quench so as to minimize distortion.

T31501 (AISI O1)

  • Hardness 57 - 62 RC oil quenching
  • Machinability 90% of W steels (baseline)
  • Applications short run tooling for blanking dies, cold forming dies and cutting tools
  • Comments This alloy is one of the Cold Work, oil hardening type tool steels. It is relatively inexpensive containing small amounts of manganese, tungsten and chromium. Hardening by oil quench minimizes distortion and cracking.

T72301 (AISI W1)

  • Hardness 50 - 64 RC water quenching
  • Machinability this steel is the most machinable tool steel and serves as a baseline
  • Applications hand operated metal* cutting tools, cold heading, embossing taps and reamers as well as cutlery.
  • Comments This alloy is one of the common Water Hardening tool steel grades available. W1 is basically a simple high carbon steel and is easily hardened by heating and quenching in water, just as with plain carbon steel alloys.

T20811 (AISI H11)

  • Hardness 38 - 54 RC air quenching
  • Machinability 75% of W steels (baseline)
  • Applications often used for highly stressed structural parts such as aircraft landing gear.
  • Comments This alloy is one of the Hot Work, Chromium type tool steels. It is relatively low in carbon content and has good toughness and deep hardens by air quench from heat treatment

T30402 (AISI D2)

  • Hardness 54-61 RC air quenching
  • Machinability poor- 50% of W steels (baseline)
  • Applications Used for long run tooling applications where wear resistance is important, such as blanking or forming dies and thread rolling dies.
  • Comments This alloy is one of the Cold Work, high carbon, high chromium type tool steels. D2 is a deep hardening, highly wear resistant alloy. It hardens upon air cooling so as to have minimum distortion after heat treatment.

T11301 (AISI M1)

  • Hardness 63 RC oil quenching
  • Machinability poor- 50% of W steels (baseline)
  • Applications Used for long run tooling applications where wear resistance is important, such as blanking or forming dies and thread rolling dies.
  • Comments M1 is a molybdenum, chromium, vanadium alloy tool steel generally known as a Molybdenum High Speed Tool Steel. It is on of the most widely available tool steels in use today. It is similar in properties to the tungsten cobalt tool steels (T series) at a lower cost.

T12004 (AISI T4)

  • Hardness 62 - 66 RC oil quenching
  • Machinability 55% of W steels (baseline)
  • Applications Generally used as cutting tools, broaches and cold extrusion punches. .
  • Comments This alloy is a High Speed, tungsten type tool steel. It is a deep hardening alloy capable of Rockwell C 64 hardness.

T41902 (AISI S2)

  • Hardness 50-60 RC water quenching
  • Machinability 85% of W steels (baseline)
  • Applications Used for chisels, hammers and similar repetitive, hard impact, applications.
  • Comments This alloy is one of the Shock Resisting tool steel types. It retains reasonable ductility even in the hardened condition which enables it to perform in applications where shock impact is imparted to the alloy.

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label: stainless steel, aisa, sae, aluminum, copper, tool steel, history of metal