The processing characteristics of hardened steel

(1) High hardness, high strength, and almost no plasticity: This is the main cutting characteristic of hardened steel. When the hardness of hardened steel reaches HRC50-60, its strength can reach σb=2100～2600MPa. According to the grading rules of the processing property of processed materials, the hardness and strength of hardened steel are all grade 9a, and it belongs to the most difficult cutting material. 

(2) High cutting force and high cutting temperature: To cut chips from high hardness and high strength workpieces, the unit cutting force can reach 4500 MPa. In order to improve the cutting conditions and increase the heat dissipation area, the tool selects the smaller main and auxiliary angles. This will cause vibration and require a good process system rigidity. 

(3) It is difficult to generate a built-up edge. Hardened steel has high hardness and brittleness. It is not easy to generate built-up edge when cutting, and the surface to be machined can obtain a low surface roughness.

 (4) The blade is easy to disintegrate and wear: Due to the brittleness of the hardened steel, the chip and blade contact with each other during cutting is short. The cutting force and cutting heat are concentrated near the cutting edge of the tool, and the blade is easily disintegrated and worn. 

(5) Low thermal conductivity: The general thermal conductivity of hardened steel is 7.12W/(m·K), which is about 1/7 of that of No. 45 steel. The machinability rating of the material is 9a grade and it is a hard-to-cut material. Due to the low thermal conductivity of the hardened steel, the cutting heat is difficult to carry away through the chips, the cutting temperature is high, and tool wear is accelerated.