Delayed hydride cracking (DHC) risk can be minimized by limiting hydrogen concentration, stress intensity factor, K_I, and optimizing temperature maneuvers. Understanding how thermomechanical history affects bulk hydrides and DHC hydrides is critical for predicting DHC and the mechanical properties of zirconium components. On heating from a low temperature, T₁, the DHC crack growth rate reaches a maximum value with temperature, T₂, and then slows with further increase in temperature until cracking effectively stops, T₃. This behavior is observed despite K_I being greater than a threshold value, having hydrides present and a nonzero crack growth rate on cooling to the same temperature. In this study, prior DHC models have been used to predict cracking rates for past and present DHC velocity data, including more than 200 cantilever beam test specimens machined from Zr-2.5Nb plates containing 37 to 108 ppm hydrogen subjected to a variety of thermal histories, including quenching. Differential scanning calorimetry was also performed on quenched material, revealing a shift in heat flow features that contributes to an explanation for higher T₂ and T₃ temperatures after quenching. Examination of DHC fracture surfaces by X-ray diffraction detects the hydrides responsible for cracking; γ hydride is dominant below 125°C and δ hydride is dominant above 225°C, with a smooth transition region between these temperatures. The temperature dependence of the DHC hydride phase is not affected by thermal history. These observations are consistent with γ-phase stability at low temperatures and suggest that inferences about DHC hydrides cannot necessarily be made by observations of bulk hydrides. The results of this study can be used to improve the understanding of the effects of thermal history on DHC and lead to improved temperature maneuvering strategies, increased confidence in the structural integrity of zirconium components, and can be applied to future mechanistic modeling efforts.