CRACKING OF FERRITIC STAINLESS STEEL TUBES DURING PRODUCTION PROCESS

1 MAJTÁS Dušan
Co-authors:
2 KREISLOVÁ Kateřina 1 VIANI Alberto 1 PÉREZ-ESTÉBANEZ Marta 2 GEIPLOVÁ Hana
Institutions:
1 Centre of Excellence Telč, ITAM AS CR v.v.i., Telc, Czech Republic, EU
2 SVÚOM s.r.o., Prague, Czech republic, EU
Conference:
24th International Conference on Metallurgy and Materials, Hotel Voronez I, Brno, Czech Republic, EU, June 3rd - 5th 2015
Proceedings:
Proceedings 24th International Conference on Metallurgy and Materials
Pages:
768-772
ISBN:
978-80-87294-58-1
ISSN:
2694-9296
Published:
12th January 2015
Proceedings of the conference were published in Web of Science and Scopus.
Metrics:
147 views / 36 downloads
Abstract

From the economic reasons many products originally made from austenite stainless steel are nowadays made from ferritic stainless steel. Ferritic steels have relatively low yield strength and the work hardening is limited. They cannot be hardened by heat treatment and only moderately hardened by cold working. Commercially made stainless steel tubes from ferritic steel, used for industrial plumbing was examined on presence of cracks. The cracking was present on the inner side of the convoluted tube shape. The tube manufacturing process consisted of continual bending of the sheet to tube shape, weld the tube, then of cold shaping by pulling through rib-forming frames, which is done in several steps. Then thermal treatment applies to the nearly finished product to remove stress remaining in the structure. Prime suspect was deformation beyond the ductility of used material. However the stress-strain tensile testing does not approved this hypothesis. Several samples of failed material were taken together with reference, and were examined by optical microscopy, and X-Ray Diffraction structure analysis. The structure of the cracked tubes does not show the signs of deformation over the limit, except the location near to the crack itself. Interestingly enough the failed material showed more homogenous structure than the original one. Needle like structures were found when the material is “over-etched”, on these structures concentration of stress under bending occur. This structure was identified as δ-ferrite however its presence in α-ferrite matrix is unclear.

Keywords: Delta ferrite, metallography, mechanical failure, crystallographic defects

© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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