High-strength bolt steel with excellent delayed fracture resistance and preparation method thereof

The invention provides high-strength bolt steel with excellent delayed fracture resistance and a preparation method thereof. The high-strength bolt steel comprises the following components in percentage by weight: 0.35-0.50% of carbon, 0.20-0.70% of manganese, 0.75-1.35% of chromium, 0.55-1.45% of molybdenum, 0.10-0.50% of vanadium, 0.005-0.10% of aluminum, 0-0.005% of sulfur, 0.02-0.05% of silicon, 0.005-0.15% of titanium, 0.0005-0.003% of oxygen, 0.001-0.007% of nitrogen, and the balance iron and other inevitable impurities; the content of titanium is not less than 3.5 times of the content of nitrogen; the sum of the contents of chromium, molybdenum and vanadium is not lower than 1.75%; and the sum of the contents of sulfur, oxygen and nitrogen is not higher than 0.01%. The high-strength bolt steel is high in purity and refined in grains, can be used for manufacturing high-strength bolts with tensile strength not lower than 1400MPa, has a section shrinkage rate not lower than 50%, is excellent in delayed fr