EVALUATION OF HOT- BITUMEN BATH AS A QUENCHING MEDIUM FOR AUSTEMPERING OF STEEL AND DUCTILE CAST IRON
EVALUATION OF HOT- BITUMEN BATH AS A QUENCHING MEDIUM FOR AUSTEMPERING OF STEEL AND DUCTILE CAST IRON
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Date
2008-04
Authors
TERVER, AUSE
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Abstract
In this research work, the possibility of using hot bitumen as quenching medium
for austempering of steel and ductile cast iron was investigated. Standard izod
Impact, hardness and tensile samples were machined from 0.55%C-steel,
0.75%C-steel and ductile cast iron bars. The samples were austenitized at
800,850, 900 and 950oC, quenched in hot bitumen at 350oC and austempered for
5minutes, 30minutes, 1, 2, 3, 4 and 5hours respectively. The samples were tested
for hardness, impact and tensile strength, microstructures were also examined.
The result of the microstructures obtained showed that hot bitumen was able to
cause formation of bainite structure in the samples. Austempering in hot bitumen
resulted to increase in hardness. The as-received hardness value of 0.55%C-steel
increased from 200 to 430HV after austempering, while 0.75%C-steel with asreceived
hardness value of 260HV increased to 548HV and the as cast hardness
value of ductile cast iron increased from 148 to 410HV. Austempering of ductile
cast iron in hot bitumen resulted to improved impact strength which increased
from 17J (as-cast) to 29J (austempered). Austenitization temperature was found
to have influence on the impact strength of ductile cast iron.
The highest impact strength of 29J was obtained at 850oC while the lowest
impact energy was 4J at 950oC. At all the austempering times, the impact energy
of 0.55%C-steel (21, 22, 37, 33, 29J at 1, 2, 3, 4, 5hrs respectively) was found to
be higher than that of 0.75%C-steel (18, 17, 17, 16, 24J at 1, 2, 3, 4, 5hrs
respectively). Results of tensile test showed that austempering in hot bitumen
resulted to increase in tensile strength, percent elongation and percent reduction
in area of ductile cast iron. The investigation carried out showed that hot bitumen
can be used as quenching medium in austempering process.
Description
A DISSERTATION SUBMITTED TO THE
POSTGRADUATE
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE AWARD OF DOCTOR OF PHILOSOPHY IN
METALLURGICAL ENGINEERING
DEPARTMENT OF METALLURGICAL ENGINEERING
FACULTY OF ENGINEERING
AHMADU BELLO UNIVERSITY
ZARIA
NIGERIA.APRIL, 2008
Keywords
EVALUATION,, HOT- BITUMEN BATH,, QUENCHING MEDIUM,, AUSTEMPERING,, STEEL,, DUCTILE CAST IRON.