Hot extrusion of compound and clad billets of mild and stainless steel

Abstract

Compound billets of mild steel with either austenitic or ferritic stainless steel have been hot extruded from a reheating temperature of 1170°C with an extrusion ratio of 16:1. Initial extrusion pressures were influenced by the emergence of an unclad length of core material at the front end of the extrusion, which was followed by uniform thickness of the component materials over the remainder of the extrusion. The running pressures are somewhat higher than estimated from solid billets of the component materials. This is attributed to an increase in redundant work due to the presence of the interface between the dissimilar materials and to a change in friction conditions when the same lubricant is used for different outer materials. Extrusion of mild steel billets canned in a thin layer of austenitic stainless steel results in sound cladding for a range of extrusion ratios and shapes of product. The products may be further hot worked and/or given limited cold working without damage to the cladding and with improvement in surface finish. However, the cladding picks up considerable carbon from the core material during extrusion and subsequent reheating.