Grain Refinement Of Low Carbon Steel By Ecap Severe Plastic Deformation

The aim of this work is to evaluate the effect of initial structure modification and increased temperature on ultrafine grain structure formation of commercial low carbon steel AISI 1014. Low carbon steel was subjected to a severe plastic deformation technique known as Equal Angular Channel Pressing (ECAP) at different increased temperatures. The steel was subjected to ECAP with channel's angle empty set 90 degrees at different temperature temperatures, in range of 150-400 degrees C. The number of passes at each temperature was N-3 and 4. The impact of different effective strain epsilon(ef) introduced upon microstructure changes was investigated using light, scanning (SEM) and transmission electron microscopy (TEM) methods. The microhardness results (HV) along the deformed bars supported the deformation straining effect. Repeating deformation procedure (Bc) the coarse and modified ferrite grains were refined and resulting structure consisted of the of fine grains having high angle boundaries. The features of grain refinement appeared in structure when effective strain eef reached value of 3 and 4. On the other side the heterogeneity in ultrafine grain structure formation was evident locally. Regardless the initial structure of steel and applied deformation conditions the applied effective strain was insufficient to ensure uniform deformation across and the length of steel bars. The size of newly born polygonal subgrains and new grains was in range of 300 - 600 nm. The tensile tests results confirmed strength increase of the steel. The formation of such predominant submicrocrystalline grain structure resulted in significant increase of the yield and tensile strength of the steel; however the restricted ductility after straining resulted.