Experimental Apa 
The AFM studies were performed with a Dimension 3000 AFM from Digital Instruments in tapping After ei 
mode. Different microalloyed steels were investigated in this study, where small amounts of a lines 
carbides distributed in ferrite should have an influence on the mechanical properties. The shows $ 
nanoindentation measurements shown in this paper were performed with an add-on force transducer Both 
from Hysitron Inc. A three sided Berkovich indenter was used for imaging and indenting. may 
Evaluations of the load-displacement curves was done with the method developed by Oliver and a 
Pharr [3], where the hardness and modulus are determined based on a previously calibrated tip has 40/1 
shape. Loads of 200 uN and 100 uN were used for the nanoindentation measurements in pearlite HE 
lamella. More experimental details on the nanoindentation measurements can be found in [4]. 
Microstructure of microalloyed steels in an AFM 
AFM images from microalloyed steels (Fig. 1) show ferrite and pearlite after the electropolishing 
procedure. Since the AFM shows the surface topography of the specimens, surface preparation has 
to be done carefully to produce smooth surfaces with a very low surface roughness. The 
microstructure of these alloys is then visualized by a small height contrast between different phases. 
The lower image in Fig. 1 shows an overview of the microstructure with different grains. Small 
carbides are visible in ferritic grains. The upper image shows an enlarged view from a pearlite area, 
where a linescan through that image gives the height profile. The linescan shows a height contrast 
of 24 nm between cementite and ferrite lamella. From the linescan the lamella distance in pearlite 
was determined. In the example shown in Fig. 1 a lamella distance of 98 nm was obtained from the 
AFM image. 
nM . vr 
o 
8 i 
gv Y canbe 
[EM 
2 A aan 
4 > 
"o 200 400 600 800 oe 
nM 
Mech 
carbides LC 
Fig. 1: Microstructure of the investigated steels in an AFM. A large scan from the surface is shown a 
in the lower image where a pearlite area is marked. The enlarged image (above) is shown with a 
linescan through the pearlite microstructure. 
97