Insufficient through-hardening - 1.8519
At the bad sample, only the area near the surface is quenched and tempered faultlessly. The core- and transition zone is converted predominantly by formation of bainite. Cause is a too low quenching effect. The cooling has been carried out by quenching into oil. For comparison purposes a well hardened sample is represented.
Steel bar 27,00 mm round - quenched and tempered