Born at Ilsbo in Sweden, Sefström studied under Jöns Berzelius in Stockholm, graduating in 1813. He taught chemistry at the School of Mines from 1820. While there he was informed that the local steelmakers were able to predict whether iron ore delivered at the foundries would produce steel that was brittle or not. On investigation he found that they tested the ore by dissolving it in hydrochloric acid and if a black powder resulted the steel was likely to be brittle. Sefström investigated and found that what was important in the test was the presence or absence in the ore of a new element. In 1830 he isolated the new element, which he named vanadium after the Norse goddess Vanadis. This proved to be identical to the metal discovered by Andrès Del Rio in 1801 and named erythronium. Del Rio had been dissuaded that this was in fact a new element and had abandoned his claim.