Prakt. Met. Sonderband 50 (2016) 63 
surements. 
g raphically | 
pears darker Sia _ 
Li, 20 20 
sitation of Hn pn 
ing carbide Figure 3: Microstructure of the steel KAB 1 after air cooling from the forging temperature of 1150°C, determination of 
chi martensite phase fraction based on color contrast and indicated as red (etched with 7% Na28:05). 
yr etching, 
wed in dark 
hen . . ot . . 
Ss vary The steel KAB 1 with a lower Mn content, predominantly forms bainite upon cooling with 
dots could some martensite observed metallographically adjacent to comparably coarse regions of 
ne fractions retained austenite as can be seen in Fig. 3. The occurrence of coarse retained austenite 
ly tint suggests a positive segregation, which has been previously connected to the formation of 
martensite 1°, whereby the effect is similar to the one observed in KAB Hi-Mn. It is 
interesting that martensite is observed metallographically, but not confirmed by XRD 
measurements. As the observed volume fraction of martensite is very small this would 
suggest that the detection threshold of the metallographic method is lower compared to XRD. 
Martensite is a coarse, comparably brittle phase, and therefore not desired in the final 
microstructure of such steels. After heat treatment it is almost entirely removed as shown in 
Fig 4-a and Fig 4-b for the steels KAB 1 and KAB Hi-Mn respectively. 
100 um 
lla (micrograph 
sd strain 20 pm 20 pm 
This narrows Figure 4: a.) Microstructure of the steel KAB 1 afer heat treatment, b.) Microstructure of the steel KAB Hi-Mn after heat 
action of treatment. Determination air of martensite phase fraction based on color contrast, and indicated as red (etched with 7% 
here a fine Na25:0s)