Skip directly to search Skip directly to A to Z list Skip directly to page options Skip directly to site content

NIOSHTIC-2 Publications Search

Search Results

Metallographic etching for carbide volume fraction of high-chromium white cast irons.

Authors
Collins-WK; Watson-JC
Source
Mater Charact 1990 Jun; 24(4):379-386
NIOSHTIC No.
10008240
Abstract
This paper describes the preparation of samples for the rapid determination of carbide volume fraction in high-chromium white cast irons by the use of the zeiss/kontron scanning electron microscope- image processing system (sem-ips). Sample composition ranges were, in percent: 17.7-28.8 Cr, 2.0-3.15 C, 0.02-1.10 Mo, and 0.5-6.3 Mn; balance fe. It was discovered that the normal metallographic etches used to enhance the carbide phase did not provide uniform contrast over the 6 by 3 mm area required for image analysis measurements, thus preventing accurate analysis. This nonuniformity of contrast prevented the ips from forming the required black and white binary image that distinguishes the carbide from the matrix, allowing the carbide area to be measured. The images observed by the human eye differ from those formed by the high-resolution analytical tv camera because the camera sees light in a linear range of brightness, while the eye responds logarithmically. The eye also is sensitive to edges---in this case carbide boundaries. Nonuniform areas of brightness and/or contrast are compensated by the eye and the metallographic image that is observed has the carbide well defined. In fact, the image has nonuniform contrast (nonuniform etch) in the region of interest, a feature quite readily apparent to the camera or image analyzer. A search is underway to find an etch that uniformly attacks the carbide phase or the matrix, thus allowing the operator of the ips to set the threshold levels to separate carbide from matrix and measure carbide volume fraction.
CODEN
MACHEX
Publication Date
19900601
Document Type
OP; Journal Article
Fiscal Year
1990
NTIS Accession No.
NTIS Price
Identifying No.
OP 174-90
Issue of Publication
4
ISSN
1044-5803
NIOSH Division
ALRC
Source Name
Materials Characterization
State
OR
TOP