T8A钢混合马氏体的形成规律

The Formation Processes and the Transition Morphology of Martensites in T8a Steel

采用马氏体等温淬火法，对Ｔ８Ａ钢马氏体进行了光镜及屯镜观察．发现Ｔ８Ａ钢中可以出现晶界片状马氏体、｛２２５｝＿ｒ蝶状马氏体、｛２２５｝＿ｒ片状马氏体、｛１１１｝＿ｒ片状马氏体、｛１１１｝＿ｒ蝶状马氏体以及｛１１１｝＿ｒ条状马氏体．随着形成温度的降低，所形成的马氏体的形态发生由蝶状或片状到条状的变化，亚结构由部分孪晶到位错的变化，惯习面由｛２２５｝＿ｒ到｛１１１｝＿ｒ的变化．这些变化受控于母相奥氏体弹性应变能的释放．在一个条状马氏体的微区内，马氏体是沿着二个｛１１１｝＿ｒ面各自单独生核，为填空式形成．本文所发现的｛１１１｝＿ｒ片状马氏体，其形貌类似于薄片状马氏体，但多半呈平行排列，其亚结构为部分孪晶．

The martensitic morphology and habit plane in T8A steel have been investigated by opticalmicroscope and Transmission Electron Microsco pe(TEM).Various martensites are identified by martempering.It is revealed that there are plate martensite with habit plane {225}r,and{111}r,butter-fly martensite with {225}r, and{111}r, lath martensite with{111}r. With the decrease of formation temperature of martensites ,the morphology of martensites is changed from butterfly or platemartensite with partial twinning substructure to lath martensite with dislocation substructure,thehabit plane from {225}r, to{111}r.The changes in morphology and substructure depend on releasingof plastic strain energy in austensite.Within one small region of lath martensites, nucleation andgrowth of martenstites are along two{111}r plane, as.it is filled in the blanks. The morphology of{111}r plate martensite in present paper is similar to the thin plate martensite,arranged paralleleach other,and substructure are partical transformation twins.