Types of tool steel

According to the different chemical composition, tool steel is often divided into carbon tool steel, alloy tool steel, high speed steel (in essence, high alloy tool steel) three categories. According to the use of steel, it can be divided into cutting tool steel, die steel, measuring steel three categories.
Carbon tool steel: Carbon tool steel has a higher carbon mass fraction, between 0.65 and 1.35%, and belongs to hypoeutectoid, eutectoid or hypereutectoid steel according to its organization. After heat treatment, the surface of carbon tool steel has higher hardness and wear resistance, and the core has better toughness. Low annealing hardness (not more than HB207), good processing performance. However, its red hardness is poor, when the working temperature reaches 250 ° C, the hardness and wear resistance of the steel drop sharply, the hardness drops below HRC60, and the hardenability of this kind of steel is low. Larger tools can not be quenched (the diameter of water quench is 15mm), and the hardness of the surface hardened layer and the center part is very different when water is quenched. Make the tool easy to deform during quenching. In addition, the quenching temperature range is narrow, and the temperature should be strictly controlled during quenching. Prevent overheating, decarbonization and deformation.
T7, T7A hypoeutectoid steel: has good plasticity, toughness and strength, as well as a certain hardness, can withstand vibration and impact load, but the cutting ability is poor. It is used to manufacture tools that bear little impact load, and require appropriate hardness and wear resistance, and good toughness, such as forging dies, chisels, hammers, punches, metal shear knives, reaming drills, steel marks, woodworking tools, pneumatic tools, machine tool centers, fitters tools, drilling tools, blunt surgical medical equipment, etc.
T8, T8A eutectoid steel: easy to overheat when quenching heating, deformation is also large, plasticity and strength is relatively low, it is not suitable to manufacture tools to withstand greater impact, but after heat treatment, high hardness and wear resistance. For the manufacture of cutting edge does not heat while working tools, such as woodworking tools, pneumatic tools, bench tools, simple dies, rivet die, center hole and die, cutting steel tools, bearings, knives, aluminum tin alloy die-cast plates and cores, and various types of springs.
T8Mn, T8MnA eutectoid steel: has high hardenability and hardness, but has low plasticity and strength. Used in the manufacture of large section woodworking tools, hand saw blade, marking tools, rivet die, spring, band saw blade, disk saw blade, coal mine chisel, stone chisel and so on.
T9, T9A hypereutectoid steel: has a higher hardness, but lower plasticity and strength. It is used to manufacture various tools requiring higher hardness and certain toughness, such as engraving tools, rivet dies, press dies, punches, woodworking tools, agricultural machinery cutting parts, rock drilling tools and split nails for casting molds.