研究表明，空冷Ｂ／Ｍ组织中，Ｂ下分割γ晶粒，使Ｍ板条束细化，李晶Ｍ减少，具有优于同成份的全Ｍ组织结构。但因空冷过程中在γ晶界上形成部分连续的碳化物薄膜，掩盖其组织的优越性，致使低温回火时韧性低于回火Ｍ。因回火过程中，状碳化物聚集球化，故中温回火时，不仅强度与回火Ｍ相同，而且韧性高于回火Ｍ组织。 The results show that, in air-cooled B / M microstructure, the γ grain is divided under B, the M slab beam is refined and the Li Jing M is reduced, which has the advantage of all M structure with the same composition. However, due to the air-cooled process in the γ grain boundary to form part of the continuous carbide film, cover the superiority of its organization, resulting in low temperature tempering toughness than the tempering M. Due to the tempering process, like carbide aggregation ball, it tempering temperature, not only the same strength and tempered M, and higher toughness than tempering M organization.