NDTnet 1998 Aug, Vol.3 No.8

Abstract

The tasks set by the automotive industry for cast iron manufacturers are increasing steadily. This is one of the reasons for cast iron manufacturers not only to reduce production costs but also to take measures in order to reduce rejectable parts and improve the quality of their products. However, these aims - the delivery of faultless products fulfilling high reliability requirements - claim a permanent process control.

Chilled areas - that means ledeburitic and cementite phases - in cast iron components cause the embrittlement of the material resulting in an adverse effect on component readability and the ductility of nodular cast iron. This leads to high reject rates for critical components. The microstructure states of chilled areas are significantly harder than graphitic areas leading to a reduction in service life and higher costs for machining.Up to now, quality assurance of such components was carried out only on a random sampling basis, using destructive methods. This expensive and time-consuming inspection of microstructure states is carried out by means of mechanical hardness testing and metallographic polished section imaging.

The micromagnetic testing method described here can be used for a nondestructive detection of chilled areas. It also provides the possibility to detect high ferrite contents indicating a lower mechanical hardness of the material.
After having carried out a positive test series on step wedges a prototype testing device was developed which has already been used for field inspections in several foundries. Here, vast charges of different types of caliper holders were inspected. The micromagnetic results were confirmed by me/allographic polished section imaging results. By means of a calibrationusing acceptable and rejectable parts it is possible to obtain a threshold evaluation and thus an in-line control of the production.

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Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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