Composition: 0.70-0.80 C; 0.25-0.50 Mn; <0.25 Si; <0.03 P; <0.03 S.

Processing: Annealing (950ºC – 20 min), Water quenching, Impacto, Annealing (960ºC – 20 min) and Furnace cooling.

Etching: 15-30 s immerison in 2% nital.

This specimen shows a combination of the defects that were present in the AC4 and AC5 specimens. At low magnification, surface decarburization and cracking are readily visible. Cracking was due to impact after quenching, whereas decarburization was produced during subsequent annealing in an oxidizing atmosphere. The most interesting feature of this specimen is the decarburization surrounding the cracks. This confirms that crack nucleation and growth happened prior to the final heat treatment.

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