How to choose the hardness of quenched parts?

The surface hardness value reached after quenching in the induction heating furnace of steel has the greatest relationship with the carbon content of the steel. When the w(C) of steel is 0.15% -0.75%, the test data can be summarized as the following formula:

HRC =21. 5 +60 (2C -1. 3C2)

In the formula, C——w(C) value of steel, such as 0.35 when w(C) is 0.35%;

HRC——The average value of the hardness of the martensite hardened layer.

Table 4-10 shows the average hardness of several steels after quenching in induction heating furnaces.

The hardness of steel induction heating furnace quenching is essentially an indicator reflecting the ability of a local area on the surface of a metal material to resist plastic deformation. Under certain material and heat treatment specifications, it has a corresponding relationship with the material’s tensile, bending and other performance indicators.

The hardness range of induction heating furnace quenched parts is determined according to the performance of the parts. Generally, there are the following types:

1) For friction parts, such as crankshaft journals and cam surfaces, the higher the hardness, the better the wear resistance. Crankshaft journals are commonly used at 55-62HRC, and camshafts are commonly used at 56-63HRC.

2) Used in crushing, torsion and shearing parts, the hardness should be high, such as forging hammer head surface, automobile axle shaft, leaf spring pin, etc., usually 56~63HRC, 50~55HRC, etc.

3) For parts subjected to impact load, or used for partial hardening of gears, splines, etc. and toughness is required, the hardness should be appropriately reduced. For example, the flywheel ring gear adopts 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 the Rockwell hardness tester is the average hardness of martensite and graphite. The hardness range of ductile iron can reach 45~55HRC, and the hardness of gray cast iron can reach above 38HRC or above 40HRC.