When the carbon content of steel is 0.15% ~ 0.75%, the test data can be summarized as the following formula:
HRC = 20+60[2 w (C) -1.3 W (C) 2]
Where w (C) — carbon content of steel, if W (C) is 0.35%, 0.35 is substituted into the above equation;
HRC — Average martensitic hardening layer hardness.
Table 1 shows the hardness values of several common steels after induction hardening.
Table 1 Average hardness of several kinds of steel after induction hardening
|
Steel No. |
Chemical composition (mass fraction, %) |
Heating temperature /℃ |
Mean hardness HRC |
|
|
C |
Mn |
|||
|
20 |
0.15 |
0.63 |
1030～1050 |
36.5 |
|
20Mn |
0.21 |
0.87 |
1010～1030 |
43.5 |
|
25 |
0.28 |
0.45 |
990～1020 |
47 |
|
35 |
0.35 |
0.57 |
940～960 |
52 |
|
40 |
0.38 |
0.50 |
940～960 |
55.5 |
|
45 |
0.46 |
0.48 |
910～940 |
58.5 |
|
50Mn |
0.51 |
0.75 |
900～930 |
61.5 |
|
T7 |
0.74 |
0.25 |
880～900 |
66.0 |
The hardness of steel-induced quenching is essentially an index reflecting the plastic deformation resistance of the local area on the surface of metal materials. Under certain conditions of materials and heat treatment specifications, it has a corresponding relationship with the tensile, bending, and other performance indexes of materials.
The hardness range of induction hardening parts is determined according to the performance of the parts. It is generally divided into the following types:
1) For wear resistance such as crankshaft journal, CAM, raceway, support wheel, chain rail surface, the higher the hardness, the better wear resistance, crankshaft journal commonly used 55 ~ 62HRC, CAM surface commonly used 56 ~ 64HRC, the tool file surface is 64 ~ 67HRC and so on.
2) Used in crushing, torsion, and shear parts of the workpiece, the hardness should be high, such as forging hammer surface, car half shaft, leaf spring pin, torsion bar, and so on, commonly used 56 ~ 64HRC, 50 ~ 55HRC and so on.
3) For the parts bearing impact load, or because the gear teeth, splines, and other parts are hardened and require toughness. At this time, the hardness should be appropriately reduced, such as engine flywheel tooth ring hardness 48-56HRC, or 40-48HRC, and so on. For gray cast iron, ductile cast iron, and malleable cast iron parts, due to the presence of flake and spherical graphite, the hardness measured by the Rockwell hardness tester is the combined hardness of martensite and graphite. The hardness range of ductile iron can reach 45 ~ 55HRC, and the hardness of gray iron can reach 38HRC or 40HRC.