Alloy 230, a nickel-based superalloy, is a candidate material for heat exchangers in very high temperature reactors. The heat exchangers are expected to see a wide range of operating conditions, so it is important to understand the effects of both stress and temperature on mechanical behavior and microstructural evolution. We studied crack growth behavior under controlled stress intensity factor near the threshold regime between 650 and 800°C. The tests were performed in using static and cyclic loads with various frequencies and stress ratios. In the different temperature regimes, the damage mechanism is dominated by different phenomena. Electron backscatter diffraction was used to observe the cracking mode and to characterize microstructure and texture at the crack tip. Transgranular cracks were observed from fatigue cracking. In grains near the crack tip, the local orientation spread increased in to as much as 5°, an indication of local deformation.