Effects Of Prestressing On Bake Hardening Performance Of Ultra-low Carbon Bake Hardening Steel

The effect of prestressing on the baking hardening property for ultra-low bakehardening steel was studied in this paper. The stress-strain state of both standardsample and wide plate sample with uniaxial tension and cross sample with biaxialtension were simulated by the ANSYS software, the baking hardening(BH) value ofthree samples with different prestrain style was determined. The dislocationsmorphology was observed by the transmission electron microscopy. The SKK peakwas obtained through the Internal friction test. The conclusions are as follows：(1)Under the condition of uniaxial tensile deformation that standard specimen wasadopted: The BH value increased with the increase of the pre-strain. The sample was apull-a pressure of plane stress state and a elongation–two shorten of plane strain state.Under different prestrain,the stress and strain distribution was uniform; the strain andthe simulated strain was less than the impressed prestrain, the strain differencebetween the simulated strain and the impressed prestrain increased with the increaseof the prestrain. The dislocation density and SKK peak of10%was significantlylarger than that of2%. With the increase of the pre-strain, the dislocation has tangledgradually to form dislocation cell wall and get fibrous deformation cell of thestructure,the distribution direction is the material’s rheological direction.Cotttel’sreinforcement was increased with the increase of the SKK peak.(2)Under the condition of uniaxial tensile deformation that wide plate sample wasadopted: The BH value also increased with the increase of the pre-strain. But wideplate sample’s BH value was more than standard sample, the BH value’s differencebetween standard sample and wide plate sample increased with the increase of theprestrain.The width variation didn’t effect BH value. The sample was biaxial tensionof plane stress state, Y axial strain was uneven and from edge to center graduallyapproach the plane strain. Under different prestrain, the stress distribution wasuniform but the strain distribution was uneven; the strain difference between thecentral region’s simulated strain and the impressed prestrain increased with theincrease of the prestrain.(3)Under the condition of biaxial tensile deformation that cross sample was adopted:The BH value increased with the increase of the Y axial prestrain. The sample wasbiaxial tension of plane stress state and two elongation–a shorten of plane strain state.The central region’s stress and strain distribution was uniform with concentric circlesdistribution state. But stress and strain value in central region is less than that in crossarm, it show that central region is difficult to reach the plastic deformation.