الفهرس 
dual phase steelsيوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
Although DP steels have promising mechanical properties, there is a
demand to optimize their properties toward a better combination of strength and
ductility to meet automotive industry needs. As a result, a new method was applied
to generate properties similar to those of dual-phase steels by air cooling from
intercritical annealing zone instead of water quenching and subsequent quenching
cracks. The resulting dual-phase steel was subjected to a new technique called
repetitive inter-critically annealing to generate new enhanced grades. The nominal
chemical compositions of steel, in this study, are 0.27C- 0.20Si-1.20Mn wt% in
addition to boron ranging from 0.0020 to 0.0045wt%. Steel grades S355J2 and
27MnCrB5 rolled bars were hot-forged at 1200°C with a reduction in crosssectional
area of about 60%. The hot-forged samples were air-cooled. Dilatation
measurements were carried out to determine the critical transformation
temperatures. The mechanical properties were evaluated using the tensile test.
Microstructure investigation was carried out using an optical microscope and
SEM. Knowing the fraction of each phase present in the steel is a key parameter
in establishing that the material will have the desired properties Thereby, based on
this necessity, the Abbott Firestone curve was adapted to determine the volume
fraction of different phases as a new technique. It depends on surface roughness
deduced from optical or SEM micrographs to construct the Abbott Firestone curve.
Abbott Firestone curve technique results are reliable and very close to that Image
j software results with a percentage of 95%. Repetitive inter-critically annealing
near AC3 formed an enhanced martensitic steel with superior strength–elongation
combination equals to 8855 MPa% which is 1.7 times DOCOL1700 which
possesses 5100 MPa%. The elongation of A31 is 5% without the need for postquench
tempering to improve ductility compared with DOCOL1700 which
possesses 3% elongation with the help of post-quench tempering.