INFLUENCE OF THE COOLING RATE DURING QUENCHING ON THE TOUGHNESS AT TYPICAL WORKING TEMPERATURES OF DIE-CASTING DIES
The influence of the cooling rate during quenching on the toughness of two hot-work tool steel grades
at ambient temperature and at working temperatures typical for die-casting dies has been compared.
The heat treatments were performed in a vacuum furnace. Different cooling rates were obtained by
varying the nitrogen gas pressure and cooling fan velocity. The impact toughness was researched
by conventional and instrumented Charpy V-notch impact testing at various temperatures. The
fracture toughness was studied by KIc fracture toughness testing at room temperature and JIc fracture
toughness testing at elevated temperatures. The researched grades were Uddeholm Vidar Superior
(X37CrMoV5-1 with reduced silicon content) and Uddeholm QRO 90 Supreme.
The influence of the cooling rate on the toughness differed considerably between ambient and elevated
temperatures. The decrease in toughness with decreasing cooling rate was more gradual at elevated
temperatures. The reason for the difference was that the fracture type at elevated temperature was
fibrous while at room temperature it was more or less completely quasi cleavage.