Hollomon i Jaffe [1],[2] su dali funkcionalnu ovisnost parametra popuštanja (temperature i trajanja) P=f(T, t). Drugim riječima ako se koriste kombinacije temperature i trajanja popuštanja, koje rezultiraju jednakom vrijednošću parametra, tvrdoća će ostati nepromijenjena. Ova funkcija se odnosi samo na čelike. Za određivanje parametara popuštanja uz postizanje željene mikrostrukture i tvrdoće nakon obrade, potrebno je poznavati dijagram popuštanja promatranog čelika. U ovom radu je istražena mogućnost dobivanja izraza gdje je tvrdoća u funkciji temperature i vremena popuštanja (H=f(T, t)). Plan pokusa i statistička analiza rezultata su obavljeni korištenjem programa „Design expert 6.0“[3]. Izrađeni su cilindrični uzorci duljine 10 mm i promjera 25 mm. Pokus je obavljen u dva dijela. Prvi dio se odnosio na visokotemperaturno popuštanje, a drugi dio na niskotemperaturno. Ovakav pristup ispitivanju je odabran zbog bitno različitih struktura koje se pojavljuju na niskim i visokim temperaturama popuštanja.Hollomon and Jaffe [1], [2] have given the functional dependence of the annealing parameters (temperature and time) P = f (T, t). In other words, if using a combination of temperature and annealing time, resulting in equal parameters value, hardness will remain unchanged. This function refers only on steels. To determine the parameters of annealing for desired hardness after treatment, it is necessary to know the annealing diagram (H=f(T)) of the observed steel. This paper investigates the possibility of obtaining a mathematical model where the hardness is function of annealing temperature and time (H=f(T, t)). Design of experiments and statistical analysis were performed using the program "Design Expert 6.0" [3]. The cylindrical specimens were 10 mm length and 25 mm in diameter. The experiment was conducted in two levels. The first level was related to high temperature annealing, while the second level was related to the low temperature annealing. The reason for this approach was based on significantly different microstructure that appears at low and high annealing temperatures
