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How to determine the hardness of hardened parts?

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Update time : 2020-05-21 07:09:54
The purpose of induction hardening is to use induction hardening equipment for rapid heating and cooling treatment to make the surface hardness of the parts higher, in order to achieve the required physical properties, such as wear resistance.
 
The surface hardness value achieved after induction hardening of steel has the greatest relationship with the carbon content of steel. When the ω (C) of steel is 0.15% -0.75%, the calculation formula of the hardness value is as follows:
HRC=21.5+60×(2C+1.3×C²)
C: ω (C) value of steel.
HRC: average value of the hardness of the martensite hardened layer
 
The hardness of induction hardening of steel is essentially an index that reflects the ability of local areas 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.
 
The hardness range of induction hardened parts is determined according to the performance of the parts. Generally, there are the following types:
  • Used for friction parts, such as crankshaft journal and cam surface. The higher the hardness, the better the wear resistance. The crankshaft journal is usually 55-62HRC, and the camshaft is commonly 56-63HRC.
  • Used in crushing, twisting and shearing parts, the hardness should be high, such as the surface of forged hammer head, automobile half shaft, leaf spring pin, etc. 56-63HRC, 50-55HRC are often used.
  • For parts that are subjected to impact load, or used for gears, splines and other parts that are hardened and require toughness, the hardness should be appropriately reduced. For example, the flywheel ring gear uses 48-56HRC or 40-48HRC.
  • For gray cast iron, ductile iron and malleable cast iron parts, due to the presence of graphite, the hardness measured by Rockwell hardness tester is the average hardness of martensite and graphite. The hardness range of nodular cast iron can reach 45-55HRC, and the hardness of gray cast iron can reach above 38HRC or above 40HRC.
 
In order to ensure that the hardness of the steel after induction hardening reaches the standard, the heating time and temperature should be accurately controlled, so the induction hardening equipment should be equipped with a corresponding temperature control system and heating time timer. Before heating, the temperature control system should be debugged, and the accuracy of the timer should be calibrated.