Why don't carbon tools steel be used to make Broaches and gear cutters?
Because of its hardness is too high, easy to crack, and if you do gear cutters and broaches, not only a few times will collapse.Therefore, Broaches and gear cutters must be cemented carbide.The carbon content of carbon tool steel is high, between 0.65-1.35%, and belongs to sub eutectoid, eutectoid or eutectoid steel. The carbon tool steel can get higher hardness and wear resistance after heat treatment, and the core has good toughness. The annealing hardness is low (not more than HB207), and the processing performance is good. However, when the working temperature reached 250 DEG C, the hardness and wear resistance of steel decreased rapidly, the hardness decreased to below HRC60, and the hardenability of this kind of steel was low. Larger tools can not be quenched (water quenched by 15mm), and when water is quenched, the hardness of the surface hardened layer differs greatly from that of the central part. Cause the tool to deform easily when it is quenched. In addition, the range of the quenching temperature is narrow and the temperature should be strictly controlled during quenching. Prevent overheating, decarburization and deformation.
Carbon steel is of high hardness, wear-resistant and difficult to heat deformation
Carbon tool steel is cheap and easy to forge, and its machinability is better. The main disadvantage of carbon tool steel is its poor hardenability. It needs water, brine or alkaline water quenching. The tendency of distortion and cracking is great, and its abrasion resistance and thermal strength are very low. Therefore, carbon tool steel can only be used to make some small hand tools or woodworking tools, and the accuracy requirements of the small cold is not high, simple shape, small size, light load of mold, such as used in the manufacture of small punch, scissors, die, cold die etc..Broaches and gear cutters are usually made of high speed steel
