(D) Effect of oxygen on hot workability of steel

Abstract

The detrimental effects of non-metallic inclusions on the ductility of steel at hot-working temperatures are well known. Often, relatively small variations in inclusion contents or distributions may determine whether a steel can be successfully worked without cracking. Although in a recent review it was concluded that sulphides do not lead to problems in hot working the majority of steels, the same cannot be said of oxide-type inclusions, as these have a much greater influence on ductility at hot-working temperatures. There is no absolute measure which can define the level of ductility required in hot working, since different working processes impose different restrains on the steel. Thus, a particular grade of steel may be hot rolled or extruded satisfactorily, since the applied forces are mainly compressive, but may give local fracture in hot-working operations such as rotary piercing and open die forging, where tensile forces are operative. In the latter case, a higher level of ductility would probably be required, and this generally calls for a cleaner steel.