Neutron diffraction texture evaluation of hydrogen charged high strength steel after uniaxial tensile deformation

Xu, P. G.   ; Ishijima, Yasuhiro ; Qiu, H.*; Morooka, Satoshi  ; Gong, W.*; Kawasaki, Takuro   ; Harjo, S.   

High strength steels for pipelines and high-pressure vessels are susceptible to hydrogen embrittlement (HE), which is typically characterized by a loss of tensile ductility. In addition to the conventional factors including microstructure, hydrogen content, strain rate, temperature, and residual stress, the crystallographic texture has recently been reported to affect the HE susceptibility of steel plates. Here, the anisotropic tensile deformation behaviors and the texture evolution were comparably evaluated by using hydrogen-charged and non-charged tensile samples to investigate the mutual effect of texture and hydrogen charging. The changes in normalized diffraction intensities show that 110//RD (RD: rolling direction) preferred orientation becomes stronger during the RD tensile deformation of hydrogen-charged and non-charged samples; the multiaxial stress field during necking deformation induces more evident weakening of final 110//RD preferred orientation in the non-hydrogen steel. It suggests that the in situ neutron diffraction is suitable to monitor the plastic deformation behavior of hydrogen-charged high strength steel. Moreover, during the RD extension, 110//RD texture component becomes strong and the 200//TD200//ND components (TD: transverse direction; ND: normal direction) have a uniform pole density distribution, and the hydrogen charging accelerates the formation of this distribution. During the TD extension, 110//TD component becomes strong, 200//ND component disperses towards the circular direction 60-tilted from ND, and the hydrogen charging accelerates such grain rotations. The appearance of higher maximum pole density of (200) pole figure shows good correspondence to lower uniform ductility of hydrogen-charged TD sample.