Abstract
Vanadium has been used for several decades in many pipeline and other structural steels to provide a high strength by its effect of refining ferrite grain size and causing precipitation of carbonitrides in the polygonal ferrite grains. It has also been reported to have a strong-hardenability effect on steel, but this property of vanadium has not previously been used in structural or engineering steels. In this paper experiments are described in which sufficient vanadium is added to a low-carbon-manganese steel to enable the vanadium in solid solution to delay the completion of the transformation of austenite. This delay produces a martensite-ferrite structure which gives a continuous stress-strain curve in the tensile test and a UTS of over 620 MNm−2 in 20 mm plate and a 0·2% PS/UTS ratio of less than 0·65, together with good notch toughness as measured by the Charpy and BDWT tests. The steel is weldable by normal procedures for X70 pipelines.
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