مطالعه تاثير نرخ كرنش بر استحاله ديناميكي تحت كرنش القاء شده آستنيت به فريت در فولاد كم كربن ميكروآلياژي

Study on the Effect of Strain Rate on the Dynamic Strain-Induced Transformation in a Low Carbon Microalloyed Steel

In the present research, the microstructural evolution and ferrite grain refinement at the deformation temperature of 845 C (i.e. between Ae3-Ar3) with different strain rates were investigated usingvsingle pass isothermal hot compression experiments for a low carbon Nb-Ti microalloyed steel. The physical processes that occurred during deformation were discussed by observing the optical microstructure and analyzing the true stress-true strain responses. At strain rates of 0.001 and 0.01s"1, there is no evidence of work hardening behavior during hot deformation and strain-induced dynamic transformation (SIDT) leads to dynamic flow softening in flow curves. Optical microscopy observation shows that ultrafine and equiaxed ferrite with grain sizes of 2//mean be obtained by applying deformation with strain rate of 0.1s"1 due to SIDT just after deformation. Furthermore, increasing the strain rate from 0.001 to 0.1s"1 reduces both the grain size of the equiaxed ferrite and the amount of deformed ferrite. As high strain rates reduce the extent of dynamic softening events, DRC/DRX, occurring during deformation and in turn increases the driving force for SIDT just at the end of deformation. It was realized that high strain rates is considered to be favorable conditions to produce ultrafine ferrite.