1.7076 | 32CrB4 +QT (12.9)

This chromium and boron-alloyed screw material 32CrMnB4 is available in the following heat treatment conditions and strength classes:

• [491 HV 1] hardened, not tempered (tetragonal martensite)
• 410 HV 1] Strength class 12.9 (lowest tempering temperature)

1st number x 100 = Rm
1st x 2nd number x 10 = Rp0.2.

In the purely hardened state, the microstructure consists of tetragonal martensite. You can see a nice comparison of the needle structure if you compare the tetragonal martensite with the strength class 12.9.
The strength class is set via the height of the tempering temperature. The higher this is, the lower the strength values. The images taken at 1000x optical magnification show the finely precipitated epsilon carbides that form during tempering. The higher the tempering temperature, the more epsilon carbides can precipitate. This in turn leads to greater relaxation of the martensite, accompanied by lower strength and higher elongation coefficients.