According to different chemical compositions, tool steels are often divided into three categories: carbon tool steel machining, alloy tool steels, and high-speed steels (essentially high-alloy tool steels). According to the use of steel, it can be divided into three categories: cutting tool steel, die steel and measuring tool steel.
Carbon tool steel: Carbon tool steel has a high carbon mass fraction between 0.65 and 1.35%, which belongs to sub-eutectoid, eutectoid or hypereutectoid steel according to its organization. After heat treatment, the surface of carbon tool steel can obtain higher hardness and wear resistance, the core has better toughness; the annealing hardness is low (not greater than HB207), and the processing performance is good. However, its red hardness is poor. When the working temperature reaches 250 ℃, the hardness and wear resistance of the steel drop sharply, the hardness drops below HRC60, and the hardenability of this type of steel is low. Larger tools cannot be hardened (the diameter of hardened in water is 15mm), and the hardness of the surface hardened layer and the central part are very different during water quenching. Make the tool easy to deform during quenching. Or the formation of cracks. In addition, the quenching temperature range is narrow, and the temperature should be strictly controlled during quenching. Prevent overheating, decarburization and deformation.
T7, T7A hypoeutectoid steel: has good plasticity, toughness and strength, and a certain hardness, can withstand shock and impact loads, but poor cutting ability. Used to manufacture tools that are not subject to impact load, and require appropriate hardness and wear resistance, and good toughness, such as forging dies, chisels, hammers, punches, metal shears, reamers, steel stamps, woodworking Tools, pneumatic tools, machine tool tops, fitter tools, drilling tools, blunt surgical instruments, etc.