Nitriding tailored to your needs
1: A most serious factor causing deterioration of the nitrided surface is prolonged preheating in air. If the time of preheating is limited to approximately 4 hours, or at least not more than 5 hours, this initial deterioration is not significant.
2: A better method of limiting the destructive effect of air oxygen would be to preheat dies in a protective gas atmosphere, for example in nitrogen. Protective atmospheres prolong the allowable pre-heating time and protect the nitrided surface against oxidation.