Prakt. Met. Sonderband 38 (2006) 105
QUANTIFICATION OF POROSITY OF A POWDER
METALLURGICAL STEEL BY IMAGE ANALYSIS
n martensiti- G. Kalss*, H. Danninger*, C. Gierl*, G. Stetina**, P. Orth**
Auswertung
0 und 550°C * Vienna University of Technology, Institute of Chemical Technologies and Analytics.
5) entstehen, Getreidemarkt 9/164, 1060 Vienna, Austria
f diese Weise ** MIBA Sinter Austria GmbH, Dr. Mitterbauer-Str. 1, 4655 Vorchdorf, Austria
bnissen.
onen im Ein-
1 Lattengren-
treubeitrige. ABSTRACT
werden. Dies
es Zementits In this work the suitability of image analysis for porosity quantification in powder
>nen ist groB metallurgical steels was examined. A material with known theoretical density was pressed
to different density levels and sintered. Metallographic samples were prepared and the
planar porosity visible under a light microscope captured digitally. The digital images were
prepared by several digital filters to facilitate the quantification of porosity by the difference
in brightness of pores and matrix. The results for porosity obtained after using different
| . combinations of digital filters at several magnifications were compared with the true
in porosity calculated from theoretical density and sintered density. By comparing the
deviation of measured porosity from true porosity the most accurate method used for
fe precipitation porosity quantification on the examined material was determined. Reliability of the
examined methods was evaluated by calculating statistical intervals of confidence from
; standard deviation and the number of images used. For a demanded interval of confidence
analysis of the .
the necessary number of images can thus be calculated.
7, A. Bodin and
LA steel. Met.
1055. 1. INTRODUCTION
ring. Plenum, . . . . . . :
The porosity of a powder metallurgical, i.e. pressed and sintered, steel after sintering is of
“th Main Grou high importance for material performance. Quantification of porosity by oil impregnation is
erg, New a method widely used in powder metallurgy [1]. However, only interconnected pores can
; ' be impregnated, in case of materials with at least partially closed porosity impregnation
jth Main Group yields too low results for the pore volume. Porosity can also be calculated from the
lin, Heidelberg, theoretical density and sintered density. Sintered density can be measured by the
Archimedes (water displacement) method, but the theoretical density is frequently not
nenforschungs- precisely known in case of sintered steels because of desired chemical inhomogeneity.
Image analysis is a method for porosity quantification which avoids the described
Determination problems of impregnation and calculation, since both interconnected and closed pores are
Surements. In quantified and the theoretical density has not to be known for correct quantification.
‘Belgum), June
Butterworth-
mbrittlement in
and tempering.
