Abstract: To investigate the low temperature brittleness of high-strength gapless atomic steel, secondary processing embrittlement tests were conducted on different batches of 450 MPa high-strength gapless atomic steel. The results show that the larger the roughness of the sample cup edge, the higher the secondary processing embrittlement temperature of the material. Appropriately increasing the content of B element could effectively improve the low temperature impact resistance of materials. When the mass fraction of B element was 0.001 2% and the roughness of the sample cup edge was 0.3 μm, the secondary processing embrittlement temperature was less than －60 ℃.