Phase Transformation in Surface Engineering Technologies Applied to A.D.L
= Uti (by S.G. Cast Irons
Wh 2 I. Milesan, R. Dobrota, Transilvania University of Brasov (RO); G. Lupchian, ROMAN S.A.
Ms Truck Company, Brasov (RO)
duly ty
General Remarks
Austempered ductile iron (ADI) has received considerable attention from researchers and
manufactures during the past years for its unique properties (which combines high strength and
good wear resistance) and low cost (1).
This paper studies the influence of some technological factors on the phase transformation in solid
state in surface engineering technologies in A.D.I. S$.G. grade, applied in ,ROMAN” S.A. Truck
Company.
Materials
The studied cast iron has the following chemical composition (% in weight): 3,70% C; 2,46% Si;
0,56 % Mn; 0,038%P; 0,01%S, 0,072%Mg; 0,21% Mo; 0,12% Ni, 0,17%Cu. This cast iron was
made in an induction furnace.
Heat treatments
The parameters of the heat treatment done were the following: the austenizing temperature, Ta =
900 [°C]; the maintained time at austenizing temperature, Ta = 30 [min]; the temperature at
isothermal level, T;;= 300 and 350 [°C]; the maintained time at the isothermal level, tiz = 5, 30 and
60 [min]. All these 2 experimental lots A (Ti; = 300° C) and B (Ti. = 350° C) were performed at
isothermal maintenance in salt-bath, being the cooling after the isothermal maintenance was done in
air.
Transformation kinetics
For the study of the phase transformation kinetics, it was used the first stage of the bainitic reaction:
y>@©+0
where: y - metastable austenite;
(«) - bainitic ferrite;
(y) - austenite enriched in carbon
For obtaining the transformation fraction “f,”, it was utilized the expression:
fi=(%Yyo-Y%yı)/ % Yo
where: “0” and “t” indexes represent the beginning and the reaction at certain time.
In figure 1 is represented the sigmoidal solid curves of the austenitic transformation during the
bainite reaction.
Like the transformation fraction curves have sigmoidal shape , it was used the “Johnson-Mehl-
Avrami” equation:
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