Browsing by Author "Ashok Kumar Panda"

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Effect of thermomechanical treatment on structure and mechanical properties of Mo-bearing dual phase steel
(Verlag Stahleisen mbH, 1995) Ashok Kumar Panda; Ratan Indu Ganguly; Dharba Subramanya Sarma; Ramesh Chandra Gupta; Somnath Misra
The effects of hot rolling of a dual phase steel in the (α+γ) range on microstructure and mechanical properties was investigated by using two thermomechanical (TMT) routes. The first consisted of heating Ac(3), soaking, cooling to deformation temperature in the (α+γ) range. The second comprises heating to deformation temperature in the (α+γ) range, followed by rolling and quenching. Parameters varied were temperature (with the first route) and extent of deformation (with the second). The microstructures were characterized by optical and transmission electron microscopy. The results indicate a distinct difference in the final structure and properties due to the two different TMT routes. The first TMT route resulted in a greater amount of ferrite, finer lath width of martensite, finer ferrite grain size and increased density of dislocations. The strength properties decreased, the YS/UTS ratio decreased and ductility increased with the increase in the extent and temperature of deformation. However, TMT route 2 resulted in an increase in the amount of martensite, finer ferrite grain size, decrease in the martensite lath width and increased dislocation density. The strength properties increased, YS/UTS ratio increased and ductility decreased with increase in the extent and temperature of deformation.
Tempering behaviour of a dual-phase low-alloy steel
(1993) Ashok Kumar Panda; Dharba Subhramanya Sarma; Ratan Indu Ganguly; Somnath Misra
The tempering behaviour of a dual phase steel of 0.08% C, 1.21% Mn, 1.00% Si, 0.42% Cr, and 0.41% Mo composition with two different martensite contents of 30 and 52%. (obtained by intercritical treatments at 820 and 860 °C, respectively) has been studied. The ultimate tensile strength decreased and percentage elongation increased continuously with increasing tempering temperature up to 600 °C for both intercritical treatments. The yield strength has, however, increased up to 300 °C, beyond which it decreased for the steel with 30% martensite. In contrast it remained almost constant for 52% martensite up to 300 °C, beyond which it decreased. The martensite of dual-phase steel for both the intercritical treatments has undergone microstructural changes on tempering that are akin to those of fully martensitic low carbon steels. The SEM fractographs from the as-quenched specimens indicate that the tensile specimens failed by microvoid coalescence with the martensite areas appearing facetted and featureless while those for 600 °C tempered condition by the formation of equiaxed dimples.