Effect of hydrogen on the microstructural evolution and local mechanical properties of 430 ferritic stainless steel at high-temperature conditions

The present study investigated the impact of hydrogen on the microstructural evolution and mechanical properties of 430 ferritic stainless steel at high-temperature conditions. Hydrogen trap sites were analyzed at high temperatures using thermal desorption spectrometry through high-temperature hydrogen atmosphere charging and electrolytic hydrogen charging. The microstructural evolution was characterized using scanning electron microscopy and electron backscatter diffraction. The nanoindentation technique was employed to analyze the local mechanical properties of ferrite matrix, grain boundaries, and M23C6/matrix interfaces. Hydrogen trap sites in 430 ferritic stainless steel included ferrite crystal lattice, grain boundaries, intragranular dislocations, and M23C6/matrix interfaces where hydrogen could not intrude at room temperature. At high temperatures, hydrogen caused a decrease in grain size. Furthermore, at high temperatures, hydrogen altered the crystal orientation and texture of the ferrite matrix. There was an increase in the number of ferrite grains with (001) and (101) orientation increase and the formation of a new α-fiber texture. Hydrogen inhibited the triggering of the slip system in body centered cubic crystal lattice and induced an increase in dislocation density and internal stress. While hydrogen at high temperatures had a minimal impact on the matrix strength limit, it reduced the strength limit of the near grain boundaries and (Fe, Cr)23C6 precipitates. The influence of hydrogen on the microstructural evolution and mechanical properties of 430 ferritic stainless steel could be elucidated by the mechanisms of hydrogen enhanced decohesion, hydrogen-enhanced localized plasticity, and hydrogen enhanced specific crystal plane rotation suggested in the present study.