Abstract: High-strength bolts are widely used in construction machinery, steel structures, bridges, automobiles, and other industrial sectors owing to their high load-bearing capacity and connection efficiency. With the advancement of modern industry, there is a growing demand to further enhance the strength of high-strength bolt steel without significantly compromising its resistance to hydrogen embrittlement or hydrogen-induced delayed fracture (HIDF). To investigate the potential of microstructural control in improving the HIDF resistance of high-strength bolt steel, a V+Nb-microalloyed Cr–Ni–Mo high-strength bolt steel was subjected to low-temperature ausforming (i.e., controlled forging starting at ～950 ℃ and finishing at ～625 ℃), followed by direct water quenching and tempering at 450 ℃ for 2 h. The HIDF behavior was evaluated using slow strain rate tensile (SSRT) tests on pre-electrochemically hydrogen-charged notched round bar tensile specimens, along with hydrogen thermal analysis. The microstructural features were examined and their influence on HIDF was discussed. For comparison, the same steel was also processed by conventional forging (starting at ～1170 ℃ and finishing above 900 ℃, followed by air cooling), quenching, and tempering (austenitized at 945 ℃, oil-quenched, and tempered at 450 ℃ for 2 h, air-cooled). The results show that low-temperature-controlled forging produced a fine-banded microstructure with pronounced grain elongation along the forging direction and a grain size reduction of ～53%. The prior austenite grain boundaries were serrated and lacked coarse cementite film precipitation, while ～7.7% polygonal ferrite formed along these boundaries. Both the smooth and notched tensile strengths of the low-temperature-controlled forged samples increased by approximately 5.6% and 9.1%, respectively, compared to those of the conventionally forged samples. Notably, despite the increase in strength, the low-temperature ausformed sample exhibited excellent HIDF resistance. The notch tensile strength (indicating HIDF resistance) increased by 62.1%, and the hydrogen embrittlement sensitivity index (measured by the relative notch tensile strength loss rate) decreased by 27.6% after low-temperature-controlled forging. The fracture mechanism transitioned from brittle intergranular fracture along prior austenite grain boundaries (in conventionally forged samples) to transgranular quasi-cleavage fracture in low-temperature ausformed samples. The brittle zone area on the fracture surface was significantly reduced, from ～38% in the former to ～20% in the latter, despite nearly identical diffusible hydrogen content. The enhanced HIDF resistance is mainly attributed to the fine banded structure, formation of polygonal ferrite, and changes in cementite morphology along the prior austenite grain boundaries. Therefore, tailoring the microstructure and grain boundary characteristics through low-temperature deformation is an effective strategy to further improve the HIDF resistance of high-strength bolt steels.