形变对奥氏体中温等温转变组织与性能的影响

Effects of Deformation on Structure and Mechanical Properties of Bainitic Ferrite Formed by Isothermal Treatment

报道了对含微量Nb、Ti、B的极低碳Si，Mn高洁净钢和成分相近的工业钢X60及XTE355的研究结果，并讨论了奥氏体形变对γ→α转变、转变组织及力学性能的影响．试样加热到1200℃均匀化处理后，快速冷却到奥氏体的非再结晶温度区变形70％再经500℃中温等温处理，能够获得微米甚至亚微米级的细化组织．纯净钢和工业钢的平均晶粒尺寸都在3μm以下，780℃变形的X60试样得到了最小的平均晶粒尺寸：X方向为0．99μm，Y方向为1．02μm．显著的晶粒细化效果是由于形变奥氏体的晶界面积大幅度增加以及变形带和其他晶体缺陷提供了大量的有利形核地点，使γ→α转变时α相的形核率提高的结果．

The effects of deformation at 900℃ and 780℃ on the microstructure and mechanical properties of the bainitic ferrite formed by isothermal treatment have been studied. The samples include three steels: an ultra-low carbon microalloying clean steel containing Mn, Nb, Ti, B, commercial steels X60 and XTE355. After press 70% at 900℃ or 780℃ followed by isothermal holding at 500℃ for 500 s or 800 s, samples of all three steels showed very fine structure and great improvement in their strength.The smallest overage grain size, which is 0.99μm and 1.02 μm along X and Y direction respectively, is obtained in a X60 specimen pressed 70% at 780℃ before isothermal holding.But the greatest improvement in strength is shown in the clean steel specimen owing to its large fraction of bainite structure. Mechanisms affecting microstructure and strength in the steels,which were deformed at near Ar3 or between Ar3 and Ar1 temperature before isothermal transformation, are discussed.