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The presence of segregation bands in steel can create hard, brittle regions of martensite or bainite. It is recognised that such bands can adversely influence impact properties, an important matter in those specifications that require minimum properties to be met at the mid-thickness position of plates. The present project had the objective of determining the effect of the segregation intensity and geometry of the segregation bands on the toughness of plate steels. It was also intended to separate the effects of the individual elements within the segregation bands, in particular those of Mn and P. As it is not presently possible to control these factors in commercial material it was decided to manufacture composite specimens containing a controlled segregation zone in the form of an artificial segregation band (ASB). The effects of segregation on toughness were assessed by means of the Charpy impact and crack tip opening displacement (CTOD) tests, results being generated over a range of temperatures to give full transition curves. With inserts of base steel composition, the results obtained were similar to those from slab with no insert, indicating the high quality of the composites. At low segregation intensities the microstructure of the segregation bands remained ferrite and pearlite, and consequently no major effects on toughness were observed. At higher segregation intensities the higher alloy contents produced more martensite in the microstructure and the harder more brittle bands caused an increase in the Charpy impact and CTOD transition temperatures. This increase was least on the low Mn base and low P base steels. With further increases in segregation intensity, fissuring occurred. Although the fissures produced an improvement in toughness, the ASB was still observed to be contributing towards the general brittleness of the specimens.

Additional information

Authors: MORRISON W B, British Steel plc, London (GB);ABERNETHY K, British Steel plc, London (GB)
Bibliographic Reference: EUR 12771 EN (1990) 52 pp., FS, ECU 6.25
Availability: (2)
ISBN: ISBN 92-826-1474-3
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