Investigation of Fracture Process of S355JR Steel in Transition Region Using Metallographic and Fractographic Tests and Numerical Analysis

In the paper are presented test results of fracture process in brittle-to-ductile transition range for two microstructural types of S355JR steel – ferrite-pearlite and ferrite-carbides. For both kinds of S355JR steel obtained in temperature range of transition region the strength and plastic properties are similar, but the fracture toughness characteristics showed significantly are various. To clarify the differences in the course of trends in the mechanical characteristics performed metallographic and fractographic observations using the scanning electronic microscope. The fractographic examination showed that changes in the fracture surface morphology were dependent on the test temperature. It was also found that during the subcritical crack growth the region of ductile fracture extension reduced with decreasing temperature. The results of finite element method (FEM) calculation the stress fields in front of the crack of single edge notch in bending (SENB) specimens in the range of brittle-to-ductile transition are presented also. The FEM calculations were performed on the numerical model of SENB specimen using the ABAQUS program.