The Rearch Of Low Cycle Fatigue Properties 、 Dislocation And Texture Of Q225

Using all Q225 steel samples which have and do no have the heat treatment to do the high strain and low cycle fatigue experiment under 1 Hz, 2Hz and 3 Hz frequency. Then methods of using metallographic microscope and TEM are observed microstr ucture and distribution of dislocation.It turned out that, before the heat treatment, with the increase of the fatigue frequ ency, dislocation tangles after polymerization and rearrangement cancellation, it has t he biggest cycle under 2 Hz frequency for the macro performance. With the continues increase of the strain rate, when the frequency increased to 3Hz, high strain rate dislo cation sharpening and increase the number of the slip system, then it produce the cryst al. It has the indirect effect of refining grain. It is difficult for the steel to plastic defor mation and strength under high strain rate. The cycle decline and the grain size increa se after the first down under 3Hz in the macroscopic. After heat treatment, with the in crease of frequency, dislocation tangles from grain boundary begin to form dislocatio n cells and dislocation cell extends to the interior of the grain. Finally, the plastic toug hness enhanced, dislocation wall thinning, and grain size increase through the rearran gement cancellation. The plastic deformation is easier to occur before heat treatment. It is more likely to rely on its own deformation to absorb energy, and effectively prote ct the stability of the building when an earthquake occurs. After the heat treatment, reduce of dislocation source eventually lead to form the dislocation.Before heat treatment, the internal friction increase successively after different frequency,and after heat treatment there is an increasing tendency to reduce after the first heat treatment. By comparing the peak frequency of the same before and after heat treatment, when 1Hz, as a result of dislocation cells did not form clearly, the peaks of after treatment is taller then the peaks before treatment. When 2Hz, the height of peak is almost no difference between the two. 3Hz, due to both of them form the clear crystal, and after heating, the dislocations are reduced, Therefore, the peak after the treatment is much smaller than the peak before treatment.Because of the(115) [ 011-texture basically eliminated, the sample after the heat treatment will produce more gauss texture in subsequent simulation deformation. It means that when the crystal is out of shape, it slides more along the row of plane. Lattice distortion and dislocation tangles will be less accordingly, it will lead to a drop of crystal. While the decline of the crystal will cause yield strength decrease, thus making Q225 steel has lower yield ratio and has better seismic performance.