Microstructural Refinement and Precipitation Behavior of Low Carbon Steel Produced by Compact Strip Production

Abstract

3(a), in addition, a low internal dislocation density was revealed, which resulted from the great reduction of single rolling pass during continuous rolling, these internal dislocation and deformation band provide nucleation site, and result in the high nucleation rate of ferrite crystal. Moreover, the dislocation/precipitation interaction in ferrite matrix would be one of the dominant reasons of strengthening.8) It was observed that the precipitates are mostly spherical in appearance, and the TEM microstructure of extraction replica also reveal the existence of precipitates clearly in Fig. 3(b). Large precipitates have been identified as carbide particles through electron dispersive analysis as shown in Fig. 3(c), but the size distribution of other shapes could not be estimated because the number was so small, which indicates that they are present in the austenite prior to precipitate from the austenite during cooling.Selective area electron diffraction study was carried out with TEM to clarify the orientation relationship between the tiny precipitates and the a-Fe matrix. beam parallel to [100] direction. A lot of diffraction spots are seen in addition to the matrix spots. It is difficult to determine the relationship between the particles and the matrix from this pattern. If we assume that the particles have a cube relationship with the matrix, the spots that do not belong to the matrix correspond very well to those of ferrite phase with the zone axis being parallel to [001]. Thus, the assumption that the tiny have cube-cube relationship with the matrix is reasonable. The dark field image in Fig. 3(e) is taken using the super lattice spots shown in the inset diffraction pattern of Fig. 3(d) and reveals that the precipitates (bright) are very small and coherent with the matrix; it would show a very effective pinning in ferrite matrix.9) The coherent orientation relationship between the tiny precipitates and the a-Fe suggests that these tiny particles may precipitate from the a-Fe instead of the g-Fe. Furthermore, the coherent orientation relationship may influence the interfacial energy between the particle and the matrix as well as the nucleation process of the particles. 10)As shown in Fig. 4(a), a small cluster of particles were observed at junctions of a curved grain boundary. The recrystallization nuclei in these alloys would form primarily adjacent to nanometer-sized particles that are produced during casting and the movement of the boundary need overcoming the pinning force of particle, which will result in a local increase in the driving force due to changes in boundary curvature and thermal activation.11) In conclusion, small particles can restrict subsequent grain boundary movement and promote a fine-grained microstructure through Zener drag. Smith 12) attributes to Zener the analysis of the pinning force exerted by particles on grain boundary, and Azmir Har et al. had also simulated particle pinning force acting on the grain boundary.13) The geometry of such an interaction is shown in Fig. 4(b).C...

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Study on Corrosion Behavior and Mechanism of Ultrahigh-Strength Hot-Stamping Steel Based on Traditional and Compact Strip-Production Processes

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