2004 Volume 90 Issue 12 Pages 1043-1049
We performed a high-speed tensile test at a strain rate of 103s-1 below room temperature for ultrafine-grained ferrite-cementite (FC) steels with ferrite grain sizes of 0.47, 0.7, 1.1, and 1.5 μm, which were obtained by using a low carbon steel. In the high-speed tensile tests, with decreasing of ferrite grain size, flow stress increased but uniform and total elongations decreased. When the effects of temperature and strain rate on flow stress between the FC steels and the FP steels are compared at the investigated range of temperature and strain rate, thermal stress component of the FC steels is bigger than that of the FP steels. The effect of ferrite grain size on flow stress of the FC steels is almost independent of temperature and strain rate including the high strain rate. That means the ultrafine-grain strengthening depends on the increasing of athermal stress component. The effect of ferrite grain size on absorbed energy obtained by the high-speed test was discussed in various steels.
