4. Mechanical Properties for Ferrite-Pearlite Steels with various Ferrite Grain Sizes

This research aims to clarify the high-speed deformation for an ultrafine-grained steel with impurities as automobile use. Here, I pay attention to stress-strain curve indicating mechanical properties of materials and try to investigate the stress-strain curve with wide range of strain rate.

In 2000

I understood effects of grain, temperature and strain rate on flow stress based on previous reports.

In 2001

Three types of ferrite-pearlite (FP) steels with ferrite grain sizes of 3.6, 9.8, 46.2 mm were prepared by a JIS-SM490 steel (0.15C-0.4Si-1.5Mn (mass%)).
Tensile tests with various strain rates below room temperature were conducted.

Flow stress increases with decreasing of ferrite grain size and temperature, and uniform elongation is almost independent of the ferrite grain size and temperature.




Figure.　Nominal stress-strain curves
for the three ferrite-pearlite steels at 77 and 296 K

The results at 77 K play an important role to understand the high-speed deformation at 296 K because the decreasing of temperature is equivalent to the increasing of strain rate.