Temperature and structural changes during hot rolling.

The 'published literature on strength, structural and
thermal aspects of hot working has been reviewed with particular
reference to their application to the hot rolling of stainless steel.
Mild and stainless steel slabs. have been hot rolled on a
mill instrumentated to measure load, torque and speed. Internal
temperatures have been measured during rolling using embedded
thermocouples whose outputs have been recorded on a U.V. recorder
coupled with an automatic back-off system.
As-rolled stainless steel slabs recrystallised very
~ slowly relative to the rate found by previous workers for simpler
austenitic stainless steels. Additionally, slabs exhibited
retarded recrystallisation at the surface compared with the centre
whereas theoretical analysis predicts the reverse. These
phenomena have been explained by rapid precipitation at temperatures
~950oC and limited electron microscopical evidence has been
obtained to support this. Precipitation also increased the flow
stresses at lower rolling temperatures and masked any effects that
different substructures were expected to have on the hot strength.
A finite difference computer programme has been developed
to predict the temperature changes that occur through a two
dimensional transverse section of a slab during a hot rolling
SChedule. The air cooling and roll contact heat transfer coefficients
have been derived by comparison of measured and computed
temperature-time curves. This programme enabled a mean pass
temperature to be derived from measured temperatures which then
resulted in good agreement between hot strengths derived from
rolling and torsion tests on stainless steel.
The programme has been simplified to a one dimensional model for simulating temperature changes over central regions of
wide sections during industrial hot rolling. Data have been
presented to enable mean temperatures to be derived from measured
surface temperatures and to illustrate the effects of various
parameters on the heat loss during a pass.