DE2426920

1471740 Heat-treating steel rod HOOGOVENS IJMUIDEN BV 3 June 1974 [4 June 1973] 24410/74 Headings C7A and C7N Low carbon steel bar or rod leaving the final stand of a hot-rolling mill is drastically waterquenched to produce a surface zone at least 0À2 mm. deep consisting of fine martensite, which is immediately allowed to temper by temperature equalization as the bar passes through a still air cooling stage. The cooling may be such that a ring of bainite is formed within the martensite zone . Following the tempering, and possibly after shearing, the rod may be subjected to further water cooling, as a result of which a further bainite zone is formed within which is a ferrite-bainite region containing very fine ferrite and then a pearlitetroostite-bainite structure. Following cooling the rod may be cold drawn with 20-40% reduction and/or may be aged at 200-500‹C. The steel may contain, in percentage by wt:- with optionally up to 0À1 % of Nb, V, Ti or B and/ or up to 0À5 % each of Cr, Mo. Suitable apparatus may include a rapid cooling and temperature equalization unit 40 followed by shears 77 and further cooling installations 1, 3.