Prakt. Met. Sonderband 46 (2014) 129 
ma 
— AF 
vith defined 
sformations 
ite grain is 
contrary to 
controllable 
ooling rate 49 % AF 
Fig. 5: Computer based evaluation of acicular ferrite amount in microstructure 
The sample shown in Fig. 4 is subsequently etched with Nital and analysed by the 
computer based evaluation to an AF amount of 11 % on the total sample area. The 
pretended higher AF amount in the LSCM view field is maybe caused by the large 
austenite grain on which the LSCM focused. This demonstrates the benefit of a 
combination of HT-LSCM and optical microscopy. HT-LSCM can be done with high 
magnification to illustrate the phase transformation and optical microscopy is performed at 
lower magnification to investigate larger areas to obtain statistical results. 
4. SUMMARY 
The present study focuses on the characterization of AF microstructures in HSLA steels by 
a combination of metallographical methods. Heat treatment is done in the high- 
temperature furnace attached to a LSCM. HT-LSCM provides an accurate adjustment of 
temperature, well controllable cooling conditions and the opportunity of an in situ 
observation of phase transformations at high magnification. The austenite grain size is one 
of the major influencing factors for the nucleation of AF. The study of austenite grain size 
by HT-LSCM is difficult due to the high magnification and the low amount of grains visible 
in the microscope view field. The computerized investigation by optical microscopy 
um enables the determination of grain size distribution on the total sample area. The influence 
— of austenitizing temperature, holding time and cooling rate can be analysed systematically. 
or 100 s at The amount of AF after heat treatment can be determined by conventional metallography 
including etching, optical microscopy and a computerized data evaluation. The lower 
magnification of optical microscopy and the computer based evaluation makes it possible 
to analyse larger areas compared to the HT-LSCM to get statistically reliable results. 
Summing up, the combination of HT-LSCM and conventional metallography allows a 
systematic study of the influence of cooling conditions and austenite grain size on the 
ough these amount of AF in microstructure for different steel compositions. 
ymputerized 
lar ferrite in 
the image ACKNOWLEDGEMENTS 
it polygonal SE ; i 
ary etching Financial support by the Federal Ministry for Transport, Innovation and Technology (bmvit) and the 
Austrian Science Fund (FWF): [TRP 266-N19] as well as the Austrian Federal Government and the 
ocess. The Styrian Provincial Government, represented by Osterreichische Forschungsférderungsgesellschaft 
zed method mbH and by Steirische Wirtschaftsférderungs-gesellschaft mbH within the research activities of the 
K2 Competence Centre on “Integrated Research in Materials, Processing and Product 
Engineering”, operated by the Materials Center Leoben Forschung GmbH in the framework of the 
Austrian COMET Competence Centre Programme, is gratefully acknowledged. 
NG