7 Tool Steels
Tool steel is any of various carbon steels and alloy steels that are particularly well-suited to be made into tools and tooling, including cutting tools, dies, hand tools, knives, and others. Their suitability comes from their distinctive hardness, resistance to abrasion and deformation, and their ability to hold a cutting edge at elevated temperatures. As a result, tool steels are suited for use in the shaping of other materials, as for example in cutting, machining, stamping, or forging.
Tool steels have a carbon content between 0.5% and 1.5%. The presence of carbides in their matrix plays the dominant role in the qualities of tool steel. The four major alloying elements that form carbides in tool steel are: tungsten, chromium, vanadium and molybdenum. The rate of dissolution of the different carbides into the austenite form of the iron determines the high-temperature performance of steel (slower is better, making for a heat-resistant steel). Proper heat treatment of these steels is important for adequate performance. The manganese content is often kept low to minimize the possibility 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 choice of group to select depends on cost, working temperature, required surface hardness, strength, shock resistance, and toughness requirements.[2] The more severe the service condition (higher temperature, abrasiveness, corrosiveness, loading), the higher the alloy content and consequent amount of carbides required for the tool steel.
Tool steels are used for cutting, pressing, extruding, and coining of metals and other materials. Their use in tooling is essential; injection molds for example require tool steels for their resistance to abrasion- an important criterion for mold durability which enables hundreds of thousands of moldings operations over its lifetime.
Tool Steel Codes
Tool Steels depart somewhat from the AISI to UNS conversion scheme. AISI designates many tool steels with a combination of letters and numbers and UNS allows only one letter… the first one. For example, oil hardened tool steel is designated O1 or O2 and so on. Water hardened is W1, W2 and so on. High Speed Steel can be T10 and T15 and so forth. The UNS scheme has no letter system easily correlating and identifying all of these as tool steels. So the basic UNS system for some of the tool steel types is:
- High Speed Tool Steels
- UNS T11301 through T12015
- Oil Hardening Tool Steels
- UNS T31501-S31507
- Mold Tool Steels
- USN T51602-T51621
- Water Hardening Tool Steels
- UNS T72301-T72305
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 are:
- 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 machinists. Especially those machinists 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.
Video
Watch this :18 video of a Design of Press Tool for Process Improvement.avi
The above animation by Sridharan P on Youtube demonstrates how tool steel punches and knives are used in a punch and die set to pierce, form or cut softer materials. However, “soft” is always relative to the hardness of the tools used.
Tool steels are steels used to make tooling.
Tooling can be a punch for a punch and die set, a knife blade roller for a shear press, or a mold cavity for a plastic injection mold. There are hundreds of applications for tool steels.
The most common heat treatable tool steels are “W” type which is quenched in water, “A” type which is quenched in air, and “O” type which is quenched in oil.
Derived from Wikipedia (Tool steel – Wikipedia) accessed and available online 18 January 2024 and The Virtual Machine Shop:
- http://www.jjjtrain.com/vms/eng_heat_treat/eng_heat_treat_06.html.
- http://www.jjjtrain.com/vms/eng_metal_stds/eng_metal_stds_05.html.
- http://jjjtrain.com/3engineering/7eng_metalsl_hist/eng_metal_hist_09.html
retrieved from Wayback Machine 13 January 2024.
