中文摘要：

研究了激光修复300M超高强度钢冲击韧性及断裂机理。结果表明,激光修复300M超高强度钢沉积态的显微组织从修复区顶部到基材区发生了显著变化,经过热处理后显微组织发生明显均匀化,修复试样沉积态的冲击韧性为14.3J/cm2,远低于300M超高强度钢锻件。经过热处理后,冲击韧性有了显著地提高,达到28.3J/cm2。沉积态试样的断裂方式为准解理断裂,主裂纹在扩展的过程中横穿马氏体领域,且在遇到下一个领域时会发生偏转。热处理态试样的断裂方式为韧性断裂。

英文摘要：

The microstructure and impact toughness of laser repaired 300M ultra-high strength steel has been studied. The re- suits showed that the microstructure of the as-deposited laser repaired 300M ultra-high strength steel changed significantly from the top of the repaired zone to the substrate zone. After heat treatment, the microstructure became uniform. The impact tough hess of the as-deposited samples was 14.3 J/cm2 , and much lower than that of the 300M forgings. Results also showed that the impact toughness was improved significantly to 28.3 J/cm^2 after heat treatment. The fracture mode of the as-deposited sample was quasi cleavage fracture. The main cracks would across the martensite packet during the process of extending and deflected in the next packet. The fracture of the sample was change to ductile mode after heat treatment.