The conditions which prevent the occurrence of duplex grain structure
of hot rolled steel sheets have been studied by using a model which ca
n 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 fi
nish rolling and it occurs in case that the sum of the consumption oi
fractional incubation time becomes 1.0 before the last reduction of fi
nish rolling. The critical temperature for preventing the duplex grain
structure reduces with increasing C and Mn, reducing the strip thickn
ess and decreasing the rolling speed. The close agreement between thes
e tendencies and the values calculated by a newly developed model to p
revent the duplex grain structure has been obtained. On the basis of t
hese results, a control technique of edge heating machine for preventi
ng the duplex grain structure has been developed.