Mechanical, microstructure and texture characterization of API X65 steel

摘要

American Petroleum Institute (API) grade X65 steel plate was characterized for its microstructure, texture and mechanical properties. The microstructure was found to be mainly composed of polygonal ferrite grains coexisting with few quasi polygonal ferrite grains. The average grain size with a critical misorien-tation of 15° was found to be about 3.3 urn. The average misorientation angle was about 36° with a fraction of high angle grain boundaries of 90%. Texture was studied and revealed a high orientation density function values around the γ-fiber. Tensile tests yielded a strength coefficient of 711 MPa, a strain hardening exponent of 0.087 and a tensile yield to ultimate stress ratio of 0.85. Constitutive modeling for the room temperature experimental stress-strain responses in compression was also conducted and the materials constants for the Johnson-Cook model are reported. The correlations from the model were seen to be in close proximity with the observed experimental data. Fracture toughness was measured on a compact tension samples along three directions, as per specifications mentioned in ASTM E399-09 standard. The K_I values were not for the plane strain condition as the thickness requirement was not met.