Quality control in metal making

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November 2003 Analytical Instrumentation & Environmental Monitoring

Many microscope users do not know that microscopes can be applied not only in medicine and biology, but also in the materials sector in the steel, automotive and mechanical engineering sectors. Swiss Steel, based in Germany, produces more than 400 000 tons of steel every year; about 200 types for more than 250 international customers, mostly car manufacturers and their suppliers and the manufacturers of plants and machines.

Quality control at Swiss Steel is monitored by a staff of more than two dozen and the spectroscopy laboratory monitors the precise dosage of alloying materials in various molten steels. The biggest laboratory, however, deals with metallography. Here production samples (~20 mm diameter) are ground, finely polished using a diamond suspension and then examined under the microscope. Due to their great influence on steel properties, the determination of non-metallic inclusions (NMI) - oxides, sulphides and silicates which can make steel brittle and result in failure of the finished steel components in the case of high strain - is a major routine check in steel laboratories.

Ever since the laboratory has used Axioplan 2 microscopes from Carl Zeiss, metallurgists need do no more than look into the eyepieces for control purposes. As soon as the samples are placed under the objective, the relevant software does everything else: it controls the microscope, creates the image on the monitor and archives the image data.

The software specifically detects the data about NMIs, including the distribution, size and type. Although the KS 400 software from Carl Zeiss was designed for image analysis and not the requirements of a steel laboratory, an integrated macro editor enables the users to program their own routine procedures.

Digital image recording not only offers the benefit of automatic evaluation, but also facilitates archiving of the images needed for documentation purposes. In the past a member of staff was constantly taking photos - this was before 1999, when Carl Zeiss microscopes and digital processing techniques were used for the first time.

Carl Zeiss launched a new range of materials microscopes last year with a number of new techniques providing options for more efficient and more precise analysis in the steel industry. These include the existing software for NMI examinations as well as special grain boundary programme, which eliminates the need to create a special macro under KS 400. There are now special prefabricated application solutions for measurement of the graphite portion, determination of grain sizes and particle analysis support evaluation in compliance with international (ASTM) and DIN standards.

For more information contact Gail Giordani, Carl Zeiss, 011 886 9510, [email protected], www.zeiss.co.za

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