Effect of Hot Rolling Process on Microstructure
and Properties of Low-Carbon Al-Killed Steels
Produced Through TSCR Technology
S.K. Paul, U. Ahmed, and G.M. Megahed
(Submitted October 29, 2009; in revised form April 27, 2010)
Low-carbon Al-killed hot rolled strips for direct forming, cold rolling, and galvanizing applications are
produced from the similar chemistry at Ezz Flat Steel (EFS) through thin slab casting and rolling (TSCR)
technology. The desired mechanical and microstructural properties in hot bands for different applications
are achieved through control of hot rolling parameters, which in turn control the precipitation and growth
of AlN. Nitrogen in solid solution strongly influences the yield strength (YS), ductility, strain aging index
(SAI), and other formability properties of steel. The equilibrium solubility of AlN in austenite at different
temperatures and its isothermal precipitation have been studied. To achieve the formability properties for
direct forming, soluble nitrogen is fixed as AlN by coiling the strip at higher temperatures. For stringent
cold forming, boron was added below the stoichiometric ratio with nitrogen, which improved the formability
properties dramatically. The requirements of hot band for processing into cold rolled and annealed
deep drawing sheets are high SAI and fine-grain microstructure. Higher finish rolling and low coiling
temperatures are used to achieve these. Fully processed cold rolled sheets from these hot strips at customers
end have shown good formability properties. Coil break marks observed in some coils during uncoiling
were found to be associated with yielding phenomenon. The spike height (difference between upper and
lower yield stresses) and yield point elongation (YPE) were found to be the key material parameters for the
break marks. Factors affecting these parameters have been studied and the coiling temperature optimized
to overcome the problem.
原来要1500，现在就这么点啦，估计500不到！
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