Hot Deformation Characteristics of Oxide/Sulphide Inclusions in Low Carbon Steels

Abstract

Studies have been made of the effect of sulphur contents
between 0.02 and 0.2% on the composition of the oxides and
oxy-sulphides produced by deoxidation of a low carbon
(<0.04%) steel with aluminium-manganese-silicon alloys.
The inclusions were analysed by Quantimet for size distribution
and Microscan V for composition. Hot rolling of the
suction cast bars was achieved on a 2 high-rolling mill.
Samples were taken at 50%, 70% and 90% total reductions in
thickness and temperature of rolling was between 800 and
1300°C. Deformation of the inclusions was measured by
optical microscopy.
It was shown that at 0.56% Mn in the steel increasing sulphur
decreased the manganese oxide content of the inclusions but
with higher manganese contents (>1.5% Mn) little or no effect
was observed. The average size of both the oxide and sulphide
inclusions increased with increasing sulphur content in the
Steel.
The relative plasticity indices of inclusions have been
related to inclusion size, matrix strain, composition and the
rolling temperature. It was shown that inclusions less than
about 2 um in diameter did not exhibit any deformation
characteristics under all working conditions. It was also
shown that the relative plasticity index value was lowered as
the matrix strain increased. Spheroidisation of the inclusions
partly contributed towards the decrease in relative plasticity
index with decreasing inclusion size.
Oxide inclusions rolled at the lower temperatures behaved in
a rigid or brittle manner. There was a rapid transition from
non-deformable to deformable behaviour over a narrow range of
temperature. The transition temperatures for the inclusions
were observed to be well below the liquidus temperatures of
any of the oxide compositions. The non-deformable/deformable
transition temperature was decreased with increasing sulphur
content of the steel, reflecting the change in composition
of oxides shown above. A ternary oxide (Al 0.-MnO-SiO )
diagram has been produced to predict the transition temperatures
for the oxide inclusions within the composition range
studied. Deformation of sulphide inclusions decreased with
increasing rolling temperatures.
It was shown that the equations (for estimation of inclusion
strain in a third plane if the inclusion strain in the other
planes are known; width spread, e_z: plane strain plasticity
index, (ν_pξ*)) are valid and can be useful for volume
plasticit?® index determination.
It was found that ductility of the steel decreased with
increasing percentage area of both oxide and sulphide
inclusions. Directionality was found to be pronounced in
steels containing type II MnS inclusions.

Date of Award	1980
Original language	English
Awarding Institution	Aston University