The effect of thickness reduction on microstructure and mechanical propertiesof cold rolled and cryorolled low carbon steel
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Date
2018-06
Authors
Mohammed Zul Azeem Mohammed Kassim
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Abstract
The low carbon steel has very extensive application in the industrial field. Its limited strength
becomes the obstacle to develop its potential applications. In recent years, ultrafine grained
(UFG) structural materials have been studied aggressively, because they are expected to
provide superior mechanical properties. The present work investigated the microstructure and
mechanical properties of cold rolled and cryorolled low carbon steel at different thickness
reduction. Firstly, low carbon steel was heat treated at 550 ºC for 60 minutes. For cryorolling,
sample was dipped in the liquid nitrogen for 10 minutes before rolled. Then both cold rolled
and cryrolled samples were rolled at different thickness reduction; 50%, 70%, 80% and 90%.
Microstructure, crystallite size, strain, dislocation density and mechanical properties for both
cold rolled and cryorolled low carbon steel at different thickness reduction were investigated
using scanning electron microscope (SEM), X-ray Diffraction (XRD), Vickermicrohardness
and tensile test. All the samples showed severely deformed grains which were elongated
along the rolling direction. Cryorolled low carbon steel showed the finest grain size compared
to the cold rolled low carbon steel with average grain size of 8.06 µm at 90% reduction. The
pearlite started to break at 70% thickness reduction for both cold and cryorolled low carbon
steel. Amount of cementite increases with increasing thickness reduction. Cryorolled low
carbon steel have finer crystallite size, higher micro strain and higher dislocation density for
all reduction compared to cold rolled low carbon steel. Tensile strength, yield strength and
hardness shows increasing trend while ductility decrease with increasing thickness reduction
and cryorolled at 90% thickness reduction showed the highest tensile strength, yield strength
and hardness with value of 828.35 MPa, 810 MPa and 208.5 Hv.