The influence of the heat treatments on the nitriding of steels

Extensive experiments have allowed to assess the influence of previous treatments upon the hardness characteristics of UNI 41CrAlMo7 and UNI 45CrMo5 steels nitrided using three atmospheres with increasing nitrogen fugacity. Normalizing, normalizing plus quenching and tempering, normalizing plus double quench and tempering were tested. Samples solely normalized exhibited the largest degree of surface hardening, whereas double quench and temper caused the most limited hardening effect more visible in the case of the A1 free steels. The latter steel is more sensible to nitrogen fugacity increases. The interrelation between the degree of carbide formation in the matrix during prior massive heat treating and the consequent matrix depletion of nitride forming elements has been seen as the cause of the different hardnesses determined after various massive and surface heat–treating combination.