128 Prakt. Met. Sonderband 46 (2014)
3.2 IN SITU OBSERVATION OF THE ACICULAR FERRITE FORMATION DURING
COOLING WITH DEFINED RATES
After setting of the defined initial austenite grain size the sample is cooled with defined
rates. Fig. 4 shows an image sequence of the in situ observation of phase transformations
during heat treatment by HT-LSCM. The formation of AF inside the austenite grain is
clearly observable. It is apparent that AF nucleates on non-metallic inclusions, contrary to
perlite and bainite which nucleate at grain boundaries. Due to the well controllable
temperature cycles the effect of austenitizing temperature, holding time and cooling rate
can be investigated in situ in a systematic way. Fig
The samp
computer
pretended
austenite
combinatio
magnificati
lower mag
4, SUMM
The preser
a combing
temperatur
temperatur
observatiol
of the majc
by HT-LSC
in the mic
100 um enables the
. mn of austeniti
Fig. 4: In situ observation of AF-formation by HT-LSCM (sample austenitized for 100 s at The amour
1400 °C and cooled with about -7 °C/s between 800 and 600 °C) including €
magnificati
to analyse
3.2 ANALYSIS OF ACICULAR FERRITE AMOUNT Summing
systematic
A standardized method for the determination of the AF amount [15] exists. Although these amount of
method offer a valuable basis for manual analysis, within this study a computerized
method is developed and used in order reduce time effort. The amount of acicular ferrite in
microstructure is determined computer based using an evaluation routine of the image ACKNOW!
analysis software Clemex: selection of ferrite by color thresholds — sorting out polygonai
ferrite and Widmannstatten ferrite by grain size — correction of grain boundary etching Financial Su
. . : . . Austrian Sci
effects — calculation of selected acicular ferrite area. Fig. 5 illustrates this process. The Styrian Pros
comparison of the computerized method using Nital etching with the standardized method mbH and by
[15] shows a good agreement. K2 Compete
Engineering
Austrian CC
