Transmission Electron Microscope Observation of the Process of Bainite Reaction in an Fe-Ni-C Alloy (The Study on the Mechanism of Bainite Reaction II)

Abstract

In order to clarify the processes of bainite reaction, an Fe-6%Ni-0.6% carbon alloy, transformed for a short time at 300°C and 450°C isothermally and then quenched into water, was examined by transmission electron microscopy. The results are as follows: (1) The growing edge of the bainite plate is low carbon ferrite with lower dislocation density and with no precipitation in it. This fact supports the conclusion obtained by the same anthors in the preceding paper. (2) At 300°C plane faults parallel to {123}_α were observed at the growing edge. These faults are considered to be formed due to the sidewise growth of bainite in the form of thin ferrite plates. Ribbon-shaped cementites nucleate at the ends of these faults, with the habit plane of {112}_α. (3) At 450°C, cementites first precipitate at the sides of ferrite plate directly from austenite. These cementite plates, parallel to {112}_α, are then converted into rod-shaped cementites with a long axis parallel to the ⟨111⟩_α direction. (4) Selected area diffraction patterns show the same orientation relationship between ferrite and cementite as Pitsch-Schrader’s at 300° and 450°C.