98 Prakt. Met. Sonderband 52 (2018) 
the need for detrimental additions of inclusion forming elements. Such potential can be EU 
found for instance in graphite forming steels. 
Steels containing substantial additions of Al, Si and Ni have been known to form certain LARS 
amounts of graphite in addition to cementite upon slow cooling or during tempering. The fos <h 
graphite forming tendency increases with the concentrations of Si and Al, but is he 
counteracted by carbide forming elements such as Mn, Cr, Mo, whereas the role of : 
carbon concentration is thought to be negligible. 
The majority of nanostructured bainitic steels contain rather high concentrations of Si and 
Al often in excess of 1,5% [5]. The high concentration of Si and Al could make such steels 
suitable for graphitization heat treatments, were it not for the usually costly procedures of 
obtaining fully carbide free lower bainitic microstructures. 
MATERIALS AND METHODS 
The alloys studied are 2 experimental KAB steels, which nominal compositions are shown 
in Table 1. The main difference between the 2 alloys is their Mn content, which results in 
different Bs and Ms temperatures. The alloy with a low Mn content is termed HIGH C-Al 
and the higher alloyed variant KAB Hi-Mn. The alloys were vacuum cast under Argon in 
the form of 10kg ingots, homogenized at 1200°C for 2 hours, and forged at 1160°C with 
a deformation ratio of 5. 
Table 1: Nominal steel compositions (in w %) © 
KO 7 (42105700 115775706 0.01 0.02 0.02 oe 
RAB Med C- 04511212 10252 2 106 0.01 0.02 0.02 we 
Tes 
Samples for microstructural observations were cut using a water cooled abrasive disk pe 
and prepared using standard metallographic techniques. The procedure consisted of SE 
planar grinding, to remove about 0.5 mm of material, followed by fine grinding using a ps 
stone with 320-grit, polishing proceeded with 9 um, 3 um and 1 um diamond suspensions aE 
and the final step was polishing with 0.05 um colloidal silica. : nE 
des 
For X-ray diffraction measurements the samples were electrolytically polished to ensure develope 
an undeformed surface and analyzed using a Bruker D8 Advance, the measured peaks Fag ™ 
were interpreted using the Rietveld method. fm resp 
Bee 
fe see 
NdeX afy