GB1025230A - Improvements in the production of alloy steel - Google Patents

Abstract

A process for making an alloy steel having an alloying content of over 5% comprises oxygen top blowing of the liquid crude iron, which comprises 20-75% of the total charge, in a crucible under a highly basic slag rich in ferric oxide to give an intermediate product having a phosphorus content of less than 0.025%, the slag is then removed and the non-oxidizing solid alloy carriers are added, blowing is continued to cause liquefaction finally the oxidizing alloy carriers (containing carbon and silicon) are added and the blowing is completed, under a basic slag having a Ca O/SiO2 ratio of at least 2. 5 or a CaO + MgO/SiO2 ratio of at least 1.5, until the carbon and silicon introduced with the alloy carriers have been removed. The slag is then treated with a reducing agent to remove the slagged alloy constituents and, after removal of the reduced slag, any remaining alloying elements of high quality are added to the crucible. The non-oxidizing alloy carriers may consist of Ni or Mo alloys and chemical heat carriers, such as FeSi, may be added therewith. The second blowing stage is preferably stopped when an appropriate carbon content has been achieved. The oxidizing alloy carriers disclosed are Cr and Mn alloys and the reducing agent for the slag may be Al, Si, or Ca-Si. After addition of the high quality alloy carriers slag formers, e.g. lime and ingot iron, can be added to make a fining slag.