WHAT IS TOOL STEEL?
Tool steel encompasses a wide variety of carbon and alloy steels that have particular mechanical or physical properties, such as strength, hardness, workability, abrasion, corrosion and heat resistance.
This makes them well suited to be made into tools, essentially used in the shaping of other materials, and especially for drilling and cutting as they are able to hold a cutting edge at elevated temperatures.
Tool steels contain differing amounts and combinations of tungsten, molybdenum, cobalt and vanadium.
WHAT’S THE DIFFERENCE BETWEEN TOOL STEEL AND HIGH SPEED STEEL?
High-speed steel (HSS or HS) is a sub-group of tool steel with high carbon & high alloy content that is hardenable and can withstand the sort of high temperatures (400-600 degrees celsius) you get when turning, milling and drilling.
As a result they are commonly used in tool bits and cutting tools, such as power-saw blades and drill bits, where they can cut faster than high carbon steels which would lose their hardness (temper) if used in such temperatures.
WHAT IS TOOL STEEL USED FOR?
Tool steel is used to make other products, for cutting, stamping, punching and machining other metals, plastics and wood. They are usually supplied in a soft annealed condition, machined into the tools required, then heat-treated to improve their hardness.
TOOL STEEL GRADES
There are several types of tool steel grades:
Cold Work Tool Steel Grades
Cold work tool steels are high carbon steels containing smaller amounts of manganese, tungsten, molybdenum, and chromium. These are steels used to cut or form materials that are at low temperatures. They have good dimensional stability, hardenability & wear resistance, and average toughness and heat softening resistance. They are further divided into 3 subgroups: Air Hardening (A series); High Carbon, high Chromium steels (D series) and Oil hardening steels (O Series). Some of the oldest and most commonly used tool steels sit within this subgroup: D2, D6, O2, D3, A2.
Hot Work Tool Steel Grades
Hot work tool steels are a group of low carbon steels, known as “H-steels”, used to mainly shape and form materials in manufacturing units that perform at high temperatures of 480 to 760°C (900 to 1400°F), including punching, forging and shearing. They have high wear resistance at high temperatures, high thermal conductivity and maintain their mechanical properties up to 540 degrees celsius. These properties are achieved by the addition of alloy elements such as chromium, molybdenum, tungsten, vanadium, nickel and cobalt in varying amounts. The commonly used hot work tool steel is H13.
High Speed Tool Steel Grades
High–speed steel (HSS or HS) are tool steels, commonly used for high-speed cutting applications, for example in power-saw blades and drill bits. They are superior to the older high-carbon steel tools in that they can withstand higher temperatures without losing their temper (hardness). This property allows HSS to cut faster than high carbon steel, hence the name high-speed steel. High speed steels gain their properties from a variety of alloying metals added to carbon steel, typically including tungsten (T series) and molybdenum (M series), or a combination of the two, often with other alloys as well. Perhaps the most commonly used high speed steel is M2.
Plastic Mould Tool Steel Grades
Plastic mould steels will ensure companies involved with injection moulding and extrusion tools, a long production tool life and tool reliability, with a mix of good corrosion resistance, hardness, toughness and resistance properties. They have good dimensional stability during heating, is easy to polish and has high impact strength. Different plastic mould steels will deliver better on each of these properties. Some also offer improved corrosion resistance so are best suited to moulding chemically aggressive plastics, sometimes in the food industry e.g. 1.2083, 1.2316 & 1.2085. Other commonly used plastic mould steels are P20, P20N & P20S.
Powder Metallurgy Tool Steel Grades
Powder metallurgy tool steels are very high alloy steels (HATS) that use metal powders and high temperature isostatic pressing (HIP) to make higher performance materials, where a long tool life is critical for machining metals. The products have a fine, uniform structure and provide the greatest possible combination of hardness, toughness and wear resistance. Powder metallurgy uses “gas atomization” where a stream of liquid steel is passed through nitrogen sprays that instantly solidify the steel into a fine powder. That powder is then pressed into a canister at high pressure and temperature to create a solid ingot that can then be processed normally.
Next Generation Tool Steel Grades
Finally our main supplier Dorrenberg has invested research time and resources into developing a group of innovative new special steels and alloys, many of which improve upon the more traditional cold work steels and perform under the toughest of conditions. For example, during hot stamping of high-strength sheet metals, the forming tools are exposed to high wear. More common steels such as 1.2367 or 1.2344 (H13) are often not sufficient in terms of wear resistance. Therefore, many operators use our special next generation tools steels WP7V & CP2M®. WP7V is characterised by an excellent ratio of hardness and toughness and has a high wear resistance even at elevated temperatures. CP2M® is a newly developed special material, which achieves excellent wear resistance due to high hardness and high thermal conductivity.
TOOL STEEL PROPERTIES
The tool steel that is most appropriate for an application will depend on the combination of properties required.
The primary tool steel properties are:
HIGH SPEED TOOL STEEL PROPERTIES
- High strength at high temperatures
- Good toughness
- High compressive strength
- Good wear resistance
COMPARING TOOL STEEL GRADES
01 vs 02 tool steel
The two steels are very close in properties, both cold-work steels used for cutting tools like knives and blades. O2 has a slightly higher level of manganese (Mn) giving slightly better hardening properties. O1 tool steel is a bit more corrosion resistant and can keep a slightly better edge.
01 tool steel vs D2
O1 & D2 tool steel are both cold work steels, used for cutting tools. D2 can be sharpened to a greater degree. O1 is the strongest and the easiest to sharpen, but less rust resistant. D2 with its high chromium content is semi-stainless.
M2 tool steel vs D2
M2 is a popular high speed steel, whereas D2 is a cold work steel. M2 & D2 are about the same toughness, but M2 tool steel will hold a better edge as the grain structure is finer, but it is not very corrosion resistant & can rust, whereas D2 is semi-stainless.
A2 tool steel v D2
Both are cold work steels, with very high hardness after heat treatment. A2 tool steel is a multipurpose tool steel, offering a combination of good wear resistance and high toughness. D2 tool steel is harder and more wear-resistant, but less tough and a little more brittle.
TOOL STEEL FAQS
How do you drill tool steel?
You can drill into hardened tool steel with either a carbide bit or a diamond bit but it will most likely need cooling. A commercial metal working shop would do this with either a plasma cutter or a water jet cutter.
How do you soften tool steel?
To soften tool steel, and make it easier to work with, heat it up to 100 degrees F above its critical temperature in a heat treat oven or forge (this will be different for each grade of steel), soak it at that temperature for one hour for every inch of thickness and let it cool in a slow controlled way at a maximum rate of 70 F per hour.
How do you machine tool steel?
Tool steel is usually supplied in the soft annealed condition, so it can be machined into the required tool shape, then hardened.
What is the hardest tool steel?
Hardness in tool steel is measured by the Rockwell C test, whereby a standardised load is used to make an indentation. A small indentation indicates high hardness. Hardened cold work tool steels are generally about 58/64 HRC (hardness Rockwell C). Most are circa 60/62 HRC, although some can go up to 66 HRC.
The hardest tool steels are the ones with the highest content of vanadium carbides, for example A7 & D7 are high vanadium versions of A2 & D2