CONTROL OF DUPLEX GRAIN-STRUCTURE AT EDGE OF HOT-ROLLED STEEL SHEETS

The conditions which prevent the occurrence of duplex grain structure of hot rolled steel sheets have been studied by using a model which can predict the strain induced transformation of ferrite from hot worked austenite. The obtained results are the following. The occurrence oi duplex grain structure depends upon the temperature schedule during finish rolling and it occurs in case that the sum of the consumption oi fractional incubation time becomes 1.0 before the last reduction of finish rolling. The critical temperature for preventing the duplex grain structure reduces with increasing C and Mn, reducing the strip thickness and decreasing the rolling speed. The close agreement between these tendencies and the values calculated by a newly developed model to prevent the duplex grain structure has been obtained. On the basis of these results, a control technique of edge heating machine for preventing the duplex grain structure has been developed.