What is the heat treatment of 40Cr tool steel?

40Cr material is a GB standard steel grade, and 40Cr steel is one of the most widely used steels in the machinery manufacturing industry. After quenching and tempering, it has good comprehensive mechanical properties, good low temperature impact toughness and low notch sensitivity. The hardenability of steel is good. It can be hardened to Ф28～60mm in water quenching and Ф15～40mm in oil quenching. In addition to quenching and tempering, this steel is also suitable for cyanidation and induction hardening. The cutting performance is better. When the hardness is 174～229HB, the relative machinability is 60%. The steel is suitable for making medium-sized plastic molds.
 
Mechanical properties of 40Cr tool steel
Tensile strength (σb/MPa): ≥810 (when actual hardness is 25HRC)
Yield point (σs/MPa): ≥785
Elongation after breaking (δ5/%): ≥9
Reduction of area (ψ/%): ≥45
Impact absorption (Aku2/J): ≥47
Brinell hardness (100/3000HBW) (annealed or high temperature tempered state): ≤207
 
Heat treatment of 40Cr tool steel
The first quenching heating temperature (℃): 850; coolant: oil
The second quenching heating temperature (℃):-
Tempering heating temperature (℃): 520;
 
40Cr tool steel use
After quenching and tempering, this kind of steel is used to manufacture mechanical parts under medium load and medium speed, such as car steering knuckles, rear half shafts and gears, shafts, worms, spline shafts, and top sleeves on machine tools.
After quenching and tempering at medium temperature, 40Cr tool steel is used to manufacture parts that are subjected to high load, impact and medium speed work, such as gears, spindles, oil pump rotors, sliders, collars, etc.
After quenching and low-temperature tempering, it is used to manufacture parts with heavy load, low impact and wear resistance, and the solid thickness on the section is below 25mm, such as worms, spindles, shafts, collars, etc.