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.<\/p>\n\n\n\n\n\n
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.<\/p>\n\n\n\n\n\n
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:<\/p>\n\n\n\n\n\n
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.<\/p>\n\n\n\n\n\n
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<\/a> (1.2379 \/ SKD11) and D3<\/a> (1.2080 \/ SKD1), carries around 12 percent chromium for heavy wear resistance. The air hardening A series, led by A2<\/a> (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<\/a> (1.2510) and O2<\/a> (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.<\/p>\n\n\n\n\n\n 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<\/a> (1.2344 \/ SKD61) and H11<\/a> (1.2343 \/ SKD6), uses about 5 percent chromium with molybdenum and vanadium to hold strength while hot. A separate tungsten branch, led by H21<\/a> (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.<\/p>\n\n\n\n\n\n Shock resisting grades put toughness ahead of wear resistance for work that takes repeated impact. The S series, such as S7<\/a> and S1<\/a> (1.2550), is built to absorb shock without cracking. Typical work includes chisels, pneumatic tool bits, impact punches, and shear blades.<\/p>\n\n\n\n\n\n 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<\/a> (1.2311) and the nickel bearing P20+Ni<\/a> (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.<\/p>\n\n\n\n\n\n High speed steels are cutting tool grades that stay sharp even when the cutting edge reaches red heat. The M series, including M2<\/a> (1.3343 \/ SKH51), M35<\/a>, and M42<\/a>, relies on tungsten, molybdenum, vanadium, and cobalt for red hardness. Typical work includes drills, milling cutters, hobs, broaches, and taps<\/a>.<\/p>\n\n\n\n\n\nHot Work Tool Steels<\/h3>\n\n\n\n\n\n
Shock-Resisting Tool Steels<\/h3>\n\n\n\n\n\n
Mold Steels<\/h3>\n\n\n\n\n\n
High-Speed Steels<\/h3>\n\n\n\n\n\n
Alloying Elements and What They Do<\/h2>\n\n\n\n\n\n