Controlled quenching of hot rolled steel rods - to give fine pearlitic-ferritic, lower bainitic or martensitic structure

摘要

Steel rods are subjected to accelerated cooling from the rolling temp. to a temp. dependent on the compsn. of the steel, the dia. of the rods and the speed at which the rods have the rolling mill. Large dia. microalloyed steel rods are pref. cooled to a temp. at which the major part of the rod section transforms to a fine pearlitic-ferritic structure; medium dia. rods of good bainitic quenchability (pref. contg. boron) are pref. cooled to a temp. at which the cores of the rods transform to a lower bainitic structure, opt. followed by tempering for a few mins. at 500-600 deg.C; and small dia. rods of sufficient quenchability are cooled to a temp. at which practically the whole rod section transforms to a martensitic structure. The accelerated cooling may be preceded by natural cooling to 750-800 deg.C. Steel rods, of up to 80 mm. dia. and having good mechanical properties, are produced in an economical manner using in-line cooling installations of reasonable length (30-50m.).