Forming and Microstructure Development of AHS Steels by Temperatures under A_(C3)

摘要

With the prices of raw materials as well as final products growing a significant tendency to search for weight reduction of the machine components through improving their quality can be observed at present. To achieve as good mechanical properties as possible, efforts are made to reach the finest microstructure possible in steels. Besides the fine grain microstructure the required phase volume fraction must also be obtained in the case of AHS steels to ensure the possibility of utilizing the TRIP effect during the final cold deformation. Their structure usually consists of ferrite, bainite and retained austenite, which transforms to deformation induced martensite during final cold deformation. With an appropriate volume fraction of these phases, the materials show good combination of strength and ductility. In the experiment eight and twenty step incremental deformation was applied within identical thermomechanical sequences in the deformation temperature range of 900 - 720°C. At the same time, the influence of twenty step incremental deformation on the development of microstructure was examined down to 600°C. Comparison of the results was carried out by means of light and electron microscopy. The volume fraction of structural phases including the fraction of retained austenite was determined by image analysis.