The hardness value of steel is an important criterion for judging the effect of induction hardening. Induction hardening is the use of induction hardening equipment to rapidly heat and then cool the surface of a metal workpiece. Its purpose is to make the surface hardness of the parts higher to achieve the required physical properties, such as high wear resistance. Before beginning induction hardening, we need to determine the target hardness for the heat treatment of the workpiece.

The following is the calculation method for the hardness value of the workpiece to be quenched and the commonly used hardness value range of some metal workpieces.

Calculation of hardness value of steel in the induction hardening process

The surface hardness value achieved after the induction hardening of steel is closely related to the carbon content of the steel.
When the ω(C) of steel is 0.15%-0.75%, the formula for calculating the hardness value is as follows:
C: ω(C) value of steel.
HRC: The average value of the hardness of the martensitic hardened layer
The hardness of steel after induction hardening is essentially an index reflecting the ability of the local area on the surface of the metal material to resist plastic deformation. Under certain material and heat treatment specification conditions, it has a corresponding relationship with the material’s tensile, bending, and other performance indicators.

Common hardness values of steel parts after induction hardening

The hardness value range of the workpiece after induction hardening needs to be determined according to the performance of the parts. The hardness value ranges are generally as follows:
1. Workpieces used for friction, such as crankshaft journals and cam surfaces: the higher the hardness, the better the wear resistance. The common hardness value range of a crankshaft journal is 55-62HRC, and the common hardness value of a camshaft is 56-63HRC.
2. The parts used in crushing, twisting, and shearing parts should have high hardness. The commonly used hardness values are 56-63HRC and 50-55HRC for the surface of the forge hammer, automobile axle shafts, leaf spring pins, etc.
3. For parts subject to impact load, or for gears, splines, etc., when they are partially quenched and require toughness, the hardness should be appropriately reduced. The flywheel ring gear adopts 48-56HRC or 40-48HRC.
4. For gray cast iron, ductile iron, and malleable cast iron parts, due to the presence of graphite, the hardness measured by the Rockwell hardness tester is the average hardness of martensite and graphite. The hardness of ductile iron can reach 45-55HRC, and the hardness of gray cast iron can reach above 38HRC or above 40HRC.

Hardness value control

In order to ensure that the hardness of the steel after induction hardening reaches the standard, the heating time and temperature should be precisely controlled. Therefore, the induction heating equipment should be equipped with a corresponding temperature control system and a heating time timer. Also, the temperature control system should be debugged before heating, and the accuracy of the timer should be calibrated.

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