342 Prakt. Met. Sonderband 38 (2006)
be considered, since in this work only one — the direction parallel to the rolling operation - 3.2
is tested. Under the given heat treatment conditions the existing carbides are known to be
alloy carbides of type (Fe,Cr);Cs, which can dissolve large amounts of iron of the steel. The
Electron probe microanalysis revealed that the ratio of iron to chromium in the carbides resi
was 5/4. Stene-Osen [11] recently performed TEM measurements on a similar steel and HR
also identified these carbides as (Fe,Cr);Cs, which show an orthorhombic lattice structure. Fur
Figure 6 shows that carbides mostly appear in rather spherical structures with some was
exception showing elongated geometries. Usually some clusters of carbides were also in t
found. Carbides and carbide clusters were classified according to their sizes by using 11 con
optical micrographs taken at a magnitude of 100x. Corresponding results are presented in obs
Table 2. It is obvious that particles having a diameter larger than 50 um are scarcely iror
found. Most of the carbides or carbide clusters are smaller than 40 ym in diameter. Ret
Furthermore the volume fraction of carbides in the steel was determined using image revi
analyzing software applied on 25 optical micrographs at 500 and 1000 magnification. It son
turned out to be 12 + 1 vol%, which was similar to results found by Fukaura et al [4]. It was
should be noted that non-metallic inclusions have not been detected
1.
Tat
. . 20 um
Figure 3: As-quenched Figure 4: Tempered microstructure revealing fine-
microstructure showing prior structured tempered martensite and excess alloy
austenite grain boundaries. carbides
200 um Sou,
Figure 5: Uniform carbide Figure 6: Carbides mostly appear rather spherical,
distribution in tempered steel except elongated species; carbide clusters can
(cross section). also be found (circled features).
Carbide 20 [40°
cluster) diameters (in um -
Relative frequency (%) | 74 | 21 g Fa
es
Table 2: Classification of carbides according to their sizes as found in metallographic sur‘
sections.
50 60 >60
