The Effect of Vanadium on the Toughness of Welds in Structural and Pipeline Steels
Abstract:
There are few data in the literature on a systematic study of the influence of vanadium on HAZ toughness of structural' and line pipe steels. An extensive programme of work on a series of steels containing up to 0.20% vanadium, with nitrogen in the range 0.005 - 0.018% and niobium additions of up to 0.05% was therefore carried out to evaluate the influence of vanadium additions on HAZ toughness and the results now presented.
Two pass welds, representative of the line pipe seam welds, made at a heat input of 4.9kJ/mm and multipass butt welds, representative of welds in structural steels, made at 2 and 5kJ/mm were made in plate produced from laboratory heats of steel. The HAZ toughness was assessed, in both the as welded and post weld heat treatment conditions, using both Charpy and CTOD transition curves for specimens notched at the fusion boundary. In addition relevant hardness data was produced and accompanying metallographic examination was carried out to observe microstructural changes.
It was found that, particularly in the as-welded condition, substantial additions of vanadium could be tolerated with no adverse effect on the HAZ toughness despite an increase in hardness, indeed, in some instances HAZ toughness was observed to significantly improve with vanadium additions up to 0.15%. It was seen that the vanadium additions promoted the development of a finer transformed microstructure in the HAZ. This beneficial change in the microstructure is believed to be the principal reason for the observed good HAZ toughness behaviour.
Keywords:
vanadium, HAZ toughness, pipeline steel
Author:
P. H. M. Hart (1) and P. S. Mitchell (2)
Affiiation
(1) TWI, Cambridge, UK.
(2), Vanitec, Winterton House, Westerham, Kent, UK.
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Source:
Welding Research Supplement, Vol.74, no. 7, July, 1995, pp.239s-248s (Vanitec Publication - V0294)
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