Real-time characterization of non-metallic inclusions by optical scanning and milling of steel samples

Johannes Herwig; Christoph Buck; Matthias Thurau; Josef Pauli; Wolfram Luther

doi:10.1117/12.924059

4 May 2012 Real-time characterization of non-metallic inclusions by optical scanning and milling of steel samples

Johannes Herwig, Christoph Buck, Matthias Thurau, Josef Pauli, Wolfram Luther

Proceedings Volume 8430, Optical Micro- and Nanometrology IV; 843010 (2012) https://doi.org/10.1117/12.924059
Event: SPIE Photonics Europe, 2012, Brussels, Belgium

Abstract

The cleanliness of steel is described by the amount, size, composition, morphology, and distribution of nonmetallic inclusions (NMIs). These nonmetals are present because of natural physical-chemical effects, and because during continuous casting steel is accidentally contaminated with slag, refractories, and materials from casting moulds. NMIs influence the properties of steel. Therefore, in this paper, a combined milling and image processing system is proposed that mills and scans slices of steel samples to retrieve volumetric information about NMIs. The system is capable of scanning steel samples of 300 × 100 × 90mm³ in size at spatial resolutions of either 3, 5, 10, or 20μm and a volumetric resolution of 10μm within a few hours. After each milling operation the steel surface is captured by a moving large-area CCD image sensor. The optical system further consists of a distortion-free macro lens and diffuse coaxial lighting for brightfield illumination. Additional results using dome lighting are also presented. The interaction of an NMI with the milling cutter results in non-homogeneous NMI reflectances which carry information about the NMI's mass density and chemical compound. Although the steel surface is highly reflective, the milling cutter creates a periodic pattern of moldings which is accentuated by patterns of shadow and light. An adaptive wedge filter in the Fourier space dampens those artifacts. NMIs are binarized separately in every image by local thresholding. In order to reduce segmentation artifacts neighboring slices in the volumetric stack of images are filtered using morphological operators. A statistical analysis of the segmentation results estimates the macro cleanliness. Furthermore an interactive 3D visualization enables the exploration of NMIs and their distribution within the sample. Different viewing, filtering and sorting capabilities are implemented, like ordering NMIs with regard to their shape factor. It is expected that the study of these attributes will lead to information about the composition and formation of NMIs.

Citation Download Citation

Johannes Herwig, Christoph Buck, Matthias Thurau, Josef Pauli, and Wolfram Luther "Real-time characterization of non-metallic inclusions by optical scanning and milling of steel samples", Proc. SPIE 8430, Optical Micro- and Nanometrology IV, 843010 (4 May 2012); https://doi.org/10.1117/12.924059

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