What Is Tool Steel?
Tool steel is a high carbon, high alloy steel made for cutting, forming, and shaping other materials. It is what tools, dies, and molds are built from, and it is engineered for hardness, wear resistance, and toughness instead of the strength and weldability that structural steel is built around.
What sets it apart is its chemistry. Carbon content varies with the job: cold work and high speed grades run high, from about 0.8 to 2.5 percent, while hot work and plastic mold grades run lower, around 0.3 to 0.4 percent, to keep toughness. On top of carbon, tool steels carry chromium, molybdenum, tungsten, vanadium, and cobalt. Part of this alloy dissolves into the matrix and slows the steel down during quenching, which is what gives deep hardenability from surface to core. The rest combines with carbon to form hard carbides, and those carbides are what resist wear.
What Makes Tool Steel Different
A tool has to cut, form, or hold shape under heavy load without cracking, wearing out, or losing its edge. That working demand is what tool steel is engineered around, and it is why these grades are judged on a specific set of properties:
- Alta dureza, which lets a tool cut and form harder materials. Cold work and high speed grades typically reach 55 to 65 HRC, while hot work dies and pre hardened mold steel are run softer on purpose to keep toughness.
- Resistência ao desgaste, supplied by hard chromium, vanadium, and tungsten carbides held in a martensitic matrix.
- Robustez, the resistance to cracking and chipping under impact loads.
- Dureza quente, the ability to stay hard at elevated temperature, which decides whether a grade can be used for hot work at all.
- Estabilidade dimensional, low distortion during hardening so finished tools stay on size.
- Temperabilidade, full hardness from surface to core in heavy sections, not just a hard skin over a soft center.
Types of Tool Steel
Tool steels are grouped by how they are used and the temperature they see in service. The AISI system gives each group a letter prefix, and choosing the right group is the first step in matching a grade to a job.
Aços para ferramentas de trabalho a frio
Cold work grades run below about 200 C at the tool surface, so they are built for wear resistance and compressive strength rather than heat resistance. The high carbon, high chromium D series, such as D2 (1.2379 / SKD11) and D3 (1.2080 / SKD1), carries around 12 percent chromium for heavy wear resistance. The air hardening A series, led by A2 (1.2363 / SKD12) at 5 percent chromium, gives up some wear resistance in exchange for better toughness and stability. The oil hardening O series, including O1 (1.2510) and O2 (1.2842), runs leaner on alloy and machines easily. Typical work includes blanking dies, punches, shear blades, cold extrusion and forming dies, thread rolling dies, gauges, and cutting tools.
Need cold work grades like D2, A2, or O1 in bulk for dies and punches?
Aços para ferramentas de trabalho a quente
Hot work grades operate from roughly 300 to 700 C and have to resist softening, thermal fatigue, and heat checking. The chromium based H series, such as H13 (1.2344 / SKD61) and H11 (1.2343 / SKD6), uses about 5 percent chromium with molybdenum and vanadium to hold strength while hot. A separate tungsten branch, led by H21 (1.2581) with around 9 percent tungsten, trades some toughness for higher hot strength in heavier hot work tooling. Typical work includes die casting dies, aluminum extrusion dies, hot forging and hot stamping dies, and hot shear blades.
Sourcing hot work grades like H13 or H11 for die casting or extrusion?
Aços para ferramentas resistentes a choques
Shock resisting grades put toughness ahead of wear resistance for work that takes repeated impact. The S series, such as S7 e S1 (1.2550), is built to absorb shock without cracking. Typical work includes chisels, pneumatic tool bits, impact punches, and shear blades.
Looking for S7 or S1 in bulk for chisels, punches, and impact tooling?
Mold Steels
Mold steels are made for plastic injection molds and similar tooling, where machinability, polishability, and dimensional stability matter most. The P series, such as P20 (1.2311) and the nickel bearing P20+Ni (1.2738), is usually supplied pre hardened so it can be machined and put straight to work without further heat treatment. Typical work includes plastic injection molds, blow molds, and compression molds.
Aços de alta velocidade
High speed steels are cutting tool grades that stay sharp even when the cutting edge reaches red heat. The M series, including M2 (1.3343 / SKH51), M35, e M42, relies on tungsten, molybdenum, vanadium, and cobalt for red hardness. Typical work includes drills, milling cutters, hobs, broaches, and taps.
Alloying Elements and What They Do
| Elemento | Faixa típica | Primary Function |
|---|---|---|
| Carbono (C) | 0.5 to 2.5% | Forms martensite for hardness and carbides for wear resistance. |
| Cromo (Cr) | 0.5 to 12% | Carbide formation and deep hardenability; gives corrosion resistance only in stainless grades such as 440 °C, not in high chromium cold work steel like D2. |
| Molibdênio (Mo) | 0.2 to 10% | Hot hardness, secondary hardening, and carbide formation. |
| Tungstênio (W) | 0.5 to 18% | Hot hardness and wear resistance. |
| Vanádio (V) | 0.1 to 5% | Fine grain size and wear resistance through hard VC carbides. |
| Cobalto (Co) | 5 to 12% | Red hardness in high speed steel grades. |
| Manganês (Mn) | 0.2 to 2% | Hardenability and deoxidation. |
| Silício (Si) | 0.2 to 2% | Strengthening and deoxidation. |
Tool Steel Compared With Other Steels
Buyers often have to decide whether a job really needs tool steel or whether a cheaper, more common steel will do. The difference comes down to carbon and alloy content, and what they let the steel do.
Tool Steel vs Structural Steel
Structural steels such as A36 and S355 are made for load bearing, weldability, and ductility. They carry under about 0.3 percent carbon and little alloy, and they are not meant to harden to tool levels. Tool steel carries far more carbon and alloy, which is exactly what lets it reach and hold high hardness.
Tool Steel vs Alloy Engineering Steel
Alloy engineering steels such as 4140 and 4340 harden to moderate levels, usually 30 to 50 HRC, and 4140 can reach about 55 HRC in thin sections. What they lack is the carbide volume to match the wear resistance of D2 or the hot hardness of H13, so they suit shafts and gears more than dies and cutting tools.
Tool Steel vs Stainless Steel
Most stainless steels put corrosion resistance ahead of hardness. The martensitic grades bridge the two worlds. Steels like 420 and 440C are stainless by composition but work as tool steels in knives and bearings, with 440C reaching 58 to 60 HRC while staying corrosion resistant.
Tool steel selection is always a balance. Higher wear resistance often reduces toughness, while higher toughness can reduce edge retention or abrasive wear life. The best grade is the one that matches the actual failure mode of the tool.
Supply Forms
Aobo Steel supplies tool steel as forged or hot rolled round bar, flat bar and plate, and forged block for large die applications. Surfaces are available black as forged or as rolled, peeled, turned, or milled. Material ships in the annealed, machinable condition, with hardened and tempered supply available on request for selected grades. Contact us for current sizes and stock, including large forged sections.
Need Tool Steel for Dies, Molds, or Cutting Tools?
Send your grade, size, condition, and quantity requirements to Aobo Steel. We can quote available forged or hot rolled tool steel in bulk supply forms.