A method is disclosed of producing a billet (B14e) which can be heated and rolled or otherwise worked with conventional equipment to form a product with a steel core and a cladding of an alloy comprising stainless steel, nickel-chrome, nickel-copper or copper-nickel. For a product such as corrosion resistant reinforcing bar, the billet (B14e) comprises a solid steel core (C) which is inserted in a tube (J) of the alloy and on which swaging operations are carried out to cause the transverse size of discrete portions of the tube to decrease. The swaging operations may be carried out on the part of the tube that has an interface with the steel body. This can cause the length of the tube to increase and can also cause the transverse size of the steel body at the interface to be decreased. To prevent oxidation of chrome and other metals in the tube, one or more briquettes (Es, Ea, Et) of scavenging metal such as aluminium or titanium are inserted in the parts of the tube that project clear of an end of the core. These parts are then inwardly swaged and sealed by welding or the like before the billet is heated. To produce a tubular product, the core has a bore which houses a second metal tube. In this case, either or both of the tubes can be composed of the alloy.