EFFECT OF INTERCRITICAL HEAT TREATMENT ON THE MICROSTRUCTURES AND MECHANICAL PROPERTIES OF MARTENSITIC DUAL PHASE STEEL
EFFECT OF INTERCRITICAL HEAT TREATMENT ON THE MICROSTRUCTURES AND MECHANICAL PROPERTIES OF MARTENSITIC DUAL PHASE STEEL
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Date
2007-03
Authors
BELLO, KAMILU ADEYEMI
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Abstract
The effects of variation of the intercritical annealing (ICA) temperature and time on the
microstructural and mechanical property behaviours of high martensite dual phase (HMDP)
steel have been investigated by intermediate quenching of microalloyed steel. The
treatment consisted of initial austenitization and rapid quenching of the steel samples to
achieve a fully martensitic state followed by annealing in ferrite and austenite (+) region
between 730oC and 810oC and subsequent quenching to produce dual phase microstructure
containing varying proportion of ferrite and martensite constituents. The annealed samples
were further subjected to tempering treatment at different tempering temperatures.
Microstructural characterization and mechanical properties of these steel samples were
studied and compared to those of conventionally quenched and tempered steel specimens.
The results show that HMDP steel specimens annealed in the intercritical temperature range
of 770oC to 790oC revealed finer martensite and precipitate-free ferrite microstructure. The
tensile, hardness and impact properties of the developed HMDP steels increase with
increasing intercritical annealing temperatures, with optimum properties obtained at 790oC.
At all the ICA temperatures, an increase in the intercritical annealing time from 30 to 90
minutes was found to enhance the tensile, hardness as well as impact properties of the
HMDP steels. The tempering of HMDP steel samples significantly increases their ductility
and toughness with only slight loss to strength as compared to the normal quenched and
tempered steel specimens. Hence, the developed HMDP and tempered HMDP steel
samples exhibited enhanced mechanical properties as compared to the conventional
quenched and tempered heat-treated ones.
Description
A THESIS SUBMITTED TO THE POSTGRADUATE SCHOOL
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
AWARD OF THE DEGREE OF MASTER OF ENGINEERING IN
METALLUGICAL ENGINEERING
DEPARTMENT OF METALLURGICAL ENGINEERING
FACULTY OF ENGINEERING
AHMADU BELLO UNIVERSITY
ZARIA
NIGERIA
MARCH, 2007
Keywords
EFFECT,, INTERCRITICAL HEAT TREATMENT,, MICROSTRUCTURES,, MECHANICAL, PROPERTIES,, MARTENSITIC DUAL PHASE STEEL