Brittle Fracture Stress of Ultrafine-Grained Low-Carbon Steel

Abstract

The variation of brittle fracture stress on grain size in a wide range of 138 μm to 1 μm was studied in low-carbon steel. The steel bars with an ultrafine elongated grain structure and equiaxed grain structure were fabricated by caliber rolling. The brittle fracture stress was quantitatively estimated through a three-point bending test at 77 K with a notch sample and finite element analysis. A reduction in grain size leads to higher fracture stress, compared with yield strength, and steel with a grain size of 1 μm was estimated to have a very high fracture stress of 6.8 GPa. It has been shown that significant improvement of brittle fracture stress is one of the advantages of grain refinement.

Fig. 4 Fracture stress as a function of the inverse square root of effective grain size in all samples.