EFFECT OF STRAIN RATE ON, THE MECHANICAL BEHAVIOUR OF PLAIN CARBON DUAL-PHASE STEELS

Abstract

Dual-phase steels are characterised by a microstructure consisting of a dispersion of about 20% martensite in a ductile, ferrite matrix. Dual - phase steels have good combination of strength and ductility like composites and formability approaching that of plain carbon steels. As a result these steels are an attractive, material for weight saving in automotive applications. The aim of the present investigation is to analyzed the effect of strain rate on the, mechanical behaviour of dual phase steel. In view of above, dual-phase steels are developed by intercritical annealing treatment of plain carbon steels at 740°C for holding time 10 min. Strain rate behaviour of plain carbon dual-phase steels have been investigated-at the strain rate of 0.04 mm/mm., 0.10 mm/min., 1 mm/min., 5. mm/mm., 10 mm/mm., 50 mm/mm., 100 mm/mm., 200 mm/min., and 300 mm/min. The tensile properties reported at above mentioned strain rates are yield strength, tensile strength, uniform and. 'total elongation. INSTRON, Universal testing machine is used in this investigation. The experiment has been done on the as-received plain carbon steel also on the same strain rates. In general, the yield and tensile strength of dual-phase steels and as-received plain carbon steels increase with increasing strain rate. The uniform and total elongation of dual-phase steel increase with increasing strain rate, while the uniform and total elongation of as-received plain carbon steel went through minimum in the strain rate range of 1-10 mm/min. To understand the type of fracture, fractured surfaces have been studied under SEM. It is observed that dual-phase steel exhibited ductile fracture at all strain rates. And at low strain rates as-received plain carbon steel exhibited ductile fracture whereas at medium and high strain rates ductile fracture alongwith some amount of cleavage fracture is observed in as-received plain carbon steel. It is observed that dual-phase steels have continuous yielding behaviour at all strain rates.