POTENTIALS OF USING SOME VEGETABLE OILS AS QUENCHANTS FOR AUSTEMPERING OF STEELS AND CAST IRONS.
POTENTIALS OF USING SOME VEGETABLE OILS AS QUENCHANTS FOR AUSTEMPERING OF STEELS AND CAST IRONS.
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Date
2008-08
Authors
SALIHU, SANI ALHAJI
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Abstract
Austempering heat treatment practice helps in achieving high strength with good
ductility and toughness by evolving a predominantly bainitic or ausferritic
microstructure in steels or cast irons respectively by using salt bath. The
potentials of using fatty-based vegetable oils as quenching media for
austempering of steels, and cast irons have been investigated. Cottonseed,
groundnut and shear butter oils were used as hot quenching bath for
austempering of these materials. The effects of these oils as quenching media
were evaluated in respect of basic mechanical properties and microstructure.
Standard tensile, impact and hardness samples were machined from bar of
0.371%C-steel, low alloyed steel, ductile iron and grey cast iron. The samples
were austenitized at 9500C, quenched at 2500C in hot cottonseed, groundnut and
shear butter oils and austempered for 1to 5hrs. The results of the
microstructures obtained showed that hot shear butter and groundnut oils
formed bainite and ausferrite structures respectively at different austempering
time in carbon steel and ductile cast iron. However, there was partial formation of
bainite in austempered low alloyed steel using shear butter and cottonseed oils.
The results showed clear disparity in mechanical properties between these oils.
The austempered ductile iron and medium carbon steel had the highest tensile
strength values of 1041N/mm2 and 1020N/mm2 using groundnut and shear
butter oils respectively; while austempered grey cast iron had the lowest values of
631N/mm2 and 684N/mm2 in groundnut and shear butter oils respectively.
However, the austempered samples of all the materials investigated gave poor
tensile strength in cotton seed oil. The austempered medium carbon steel and
ductile iron equally showed high impact values of 101J and 68J in shear butter
at 5 and 4hrs respectively while the hardness values of these materials were
353HV and 412HV respectively in hot shear butter oil. Based on the
microstructure developed and mechanical properties results achieved in this
work, hot shear butter and groundnut oils are effective as austempering
quenchants for medium carbon steel and ductile iron up to 4hrs austempering
time.
Description
A Dissertation Submitted to the Postgraduate School, Ahmadu Bello
University, Zaria, for the degree of Doctor of Philosophy (Metallurgical
and Materials engineering).
Department of Metallurgical and Materials Engineering
Faculty of Engineering
Ahmadu Bello University, Zaria.
Nigeria.
August, 2008.
Keywords
POTENTIALS,, USING,, USING,, VEGETABLE,, OILS,, QUENCHANTS,, AUSTEMPERING,, STEELS,, CAST,, IRONS.