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电镜观察发现4340加Si钢在320℃及420℃等温形成的贝氏体宽面上均存在巨型台阶,其高度a为320—850(?),宽度b为1500—1800(?),和根据贝氏体增长速率为0.006μm/s计算所得的b=0.5μm在同一数量级,这些台阶位于惯习面上,为贝氏体的长大台阶。无论在320℃或420℃等温形成的贝氏体中均存在ε碳化物,ε和α之间的位向呈Jack关系。因此,Hehemann提出的在350℃附近存在γ→α+ε转变的看法自属疑问。等温较长时出现渗碳体,它位于γ和α之间。Fe_3C和γ之间具有Pitsch关系,Fe_3C和α之间为Isaichev关系,γ和α之间具有K-S关系,由此也可建立γ-α-ε或γ-α-Fe_3C之间的位向关系,但尚不能肯定碳化物系相间沉淀。发现部分γ/α界面呈弯曲状伸展,表示非共格界面。鉴于存在长大台阶以及非共格界面,因此贝氏体的长大机制很难归之于共格切变,而很可能为台阶的伸长。
Electron microscopy showed that there were giant steps on the bainitic surface of 4340 plus Si steel at 320 ℃ and 420 ℃. The height a was 320-850 (?), The width b was 1500-1800 (?), Bainite growth rate of 0.006μm / s The calculated b = 0.5μm in the same order of magnitude, these steps are located in the habitual surface, as bainite growth step. The ε carbides are present in the bainite formed isothermally at 320 ° C or 420 ° C, and the orientation between ε and α shows a Jack relationship. Therefore, Hehemann’s hypothesis of the existence of a transformation of γ → α + ε near 350 ° C is doubtful. Cementite appears when the isotherm is longer, which is between γ and α. There is a Pitsch relationship between Fe_3C and γ, an Isaichev relationship between Fe_3C and α, and a KS relationship between γ and α, and thus a positional relationship between γ-α-ε or γ-α-Fe_3C can also be established. However, it is not yet certain that carbides precipitate in the interphase. It was found that some of the γ / α interfaces were curved and extended, indicating non-coherent interfaces. In view of the existence of growth steps and non-coherent interface, so bainite growth mechanism is difficult to attribute to coherent shear, which is likely to be the extension of the step.