100 Prakt. Met. Sonderband 52 (2018) 
Detailed analysis of the initial microstructure using FESEM reveals that the bainitic ferrite J 3 
sheaves are lenticular in shape with a width to length ration of between 2 and 5 as can tl 
be seen in Fig. 2-a and 3-a. co 
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Figure 2: FESEM micrographs of steel KAB Med C-Al: a.) initial carbide free 
bainitic/martensitic microstructure (Etched with Vilela) b.)Fully annealed microstructure, 
showing fine newly formed grains and alloy and carbide particles (Etched with Vilela). 
As this steel also contains high concentrations of Al and small additions of Mn, it can be 
expected that the resulting x-carbides (AIMnFe-C), can be expected to exhibit a brittle 
character. 
The graphitization heat treatment is complete after annealing for 6 hours at 953°K (680°C) 
as indicated by the obtainment of a hardness minimum on the graph in Fig. C. The 
tempering decreases hardness, from the initial 58 HRc obtained after forging, down to a 
value of about 290 HBW and 260HBW after 6 hours, for the steels High C-Al and Med C- 
Al respectively. Further annealing doesn’t decrease the hardness to lower levels even 
after as much as 24 hours. It is known that the presence of a high dislocation density 
enables such steels to retain a high hardness after tempering [7], therefore very low foe: 
hardness values are difficult to obtain in such steels. | VE 
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Figure 3: FESEM micrographs od steel KAB1: a.) initial carbide free bainitic/martensitic ae 
microstructure (Etched with Vilela) b.)Fully graphitized microstructure, showinga | ir or 
predominantly uniform grain distribution different morphologies developing from initial Pema 
 bainite and martensite (Etched with Vilela).