Low-angle boundary engineering for improving high-cycle fatigue property of 430 ferritic stainless steel

Grain boundary engineering (GBE) based on the control of a low-angle grain boundary (LAGB) network was investigated to improve the fatigue property in 430 ferritic stainless steel. The development of a subboundary structure during annealing in a specimen that was cold rolled at a high reduction ratio was evaluated quantitatively by electron backscatter diffraction measurements. The fine subgrain structure with a high fraction of LAGBs ( F L = 54%) was produced with the formation of a sharp {100} and {111} texture by cold rolling to 95% with subsequent annealing at 973 K for 600 s. The LAGBs interconnected to form networks in the GBEed specimen. The kernel average misorientation maps suggest that the dislocation density within the LAGB network was higher than that in the recrystallized grains, particularly near the LAGBs. The high-cycle fatigue property in specimens with different magnitudes of LAGB networks was compared with that in the annealed commercial 430 stainless steel. The kernel average misorientation maps for the post-fatigued GBEed specimen reveal that the dislocation density decreased during cyclic deformation, whereas the fine-grained structure and high fraction of LAGBs were maintained. It was concluded that the grain refinement and introduction of a high fraction of LAGBs can achieve a higher fatigue strength and longer fatigue life for 430 stainless steel.