In order to produce elements for furnaces, reactors or conduits on the walls of which coke can appear, steels are used with a composition which is adapted to resist coking comprising, by weight, at most 0.25% of C, 1.5% to 5% of Si, 4% to 10% of Cr, 0.5% to 2% of Mo, 0.3% to 1% of Mn, at most 0.030% of S and at most 0.03% of P, the complement to 100% being essentially iron. Novel steel compositions for use in these applications are those which comprise, by weight, at most 0.25% of C, more than 2.5% and up to 5% of Si, 4% to 10% of Cr, 0.5% to 2% of Mo, 0.3% to 1% of Mn, at most 0.03% of S and at most 0.03% of P, the complement to 100% being essentially iron.