Ferrite Zone Deformation On Microstructure And Hardness Of Steel

With the development of technology and society, The requirements for the using property become more and more higher. So, To improve the smelting and rolling processing, and then to enhance the using performance of steels, lower production costs and energy saving has become the goals and directions of development of steels in modern iron and steel materials sector. The reality of the production process, The final rolling process is processing near high temperature in the traditional rolling process. But in the production practices, we found, with the decreases of the final rolling temperature, the property of the steel and iron will have a certain level of upgrade. When the final deformation is in the ferrite region, a large number of crystal defects and deformation energy will be introduced. Then, the nucleation rate of the second phase will be improved, promoting the precipitation of micro-allying elements. Furthermore, when deformation in ferrite region, we can obtain the precipitates which smaller than10nm. According to Orawan strengthening mechanisms, with the decrement of the size of precipitates, precipitation strengthening will increase significantly.Accordingly, the effects of deformation in ferrite region for the micro-structure and micro-hardness of tested steels was study in this paper. Gleeble thermal simulation machine was used for the deformation thermal simulation of different tested steels, to study the influence of the deformation in ferrite region for the microstructure and micro hardness of tested steels. The metallographic electron microscope (OM), scanning electron microscope (SEM), transmission election microscope (TEM) were used to observe the microstructure and precipitates of samples processed by Gleeble thermo simulation machine; using Vickers hardness tester measure the micro hardness. The result of experiments was showed as follows:In the study of changing final deformation from high temperature to ferrite region, for different kinds of tested steels, we found a similar mechanism for the microstructure and microhardness for different tested steels. When reduced the final deformation to ferrite region, the main influences performance is:refine the ferrite grain and the pearlite colony size, increase the percentage of pearlite and dislocation density. The impact of these aspects will be inhancing the hardness of structure.In the study of deformation+isothermal processing on the influence of precipitetes, we found, deformation+isothermal processing will refine the size of precipitates significantly. By deformation+isothermal processing at600℃, we can obtain the precipitates which average size is2.8nm. In addition, calculated the volume fraction of (Nb1-xMox)C under equilibrium conditions at600℃and700℃Then, combination with the experimental statistics of the average size of precipitates, derived the relationship between precipitation strengthening and volume fraction of precipitates in different of processing. It was found, in the same isothermal time, deformation+isothermal processing could gain finer precipitation particles at600℃, while the volume fraction of precipitation (Nb1-xMox)C is not very high, finer precipitation particles can contribute considerable precipitation strengthening.