Effect Of Annealing And Rolling Parameters On Mechanical Properties Of Nano/Micron-crystal Composite Carbon Steel

The nanocrystalline metals have high strength, but low plasticity. In this paper, the1020and1045steel were chosen as the object of this study, and employed the aluminothermic reaction to prepare the large dimensional material with nano/micro-craystalline structure, we studied the thermal stability of the materials by respectively600℃and800℃annealing at different time, and confirmed the optimum heat treatment process for this material. Then according to the results of annealing, the materials were rolled up to different reduction at600℃, and it fully proved the ability of processing about the nano/micro-crystalline carbon steel materials. The comprehensive mechanical properties of the materials were increased significantly by rolling.The large dimensional nano/micro-crystalline1020and1045steel was prepared by aluminothermic reaction which microstructure consisted with nanocrystalline ferrite and pearlite colony with the sub-micrometer structure.The as-cast1020and1045steel had the good mechanical properties. After short-time annealing at600℃, the strength of the materials remained, but the elongation improved, and the elongation was best by annealing6h and4h. But after long-time annealing, the mechanical properties of the materials decreased significantly. And after annealing at800℃, the mechanical properties decreased significantly.After annealing the as-cast nano/micro-crystalline1020and1045steel at600℃by different time, the nano-crystalline ferrite grain size increased, the pearlite interlamellar spacing remained by short time, and increased by long time; After annealing the steels at800℃by different time, the shape of pearlite colony transformed from the chain and strip to globular, and its volume fraction, as the annealing time increased, the pearlite spheroidization was more serious.According to the results of annealing to the nano/micro-crystalline1020and1045steel at600and800℃by different time, the materials were rolled up to different reduction by20%,40%and60%at600℃. After rolling by different deformation, the harder and tensile strength both increased, the elongation rate of1020steel decreased significantly,1045steel decreased slightly. But as the deformation increased, the plasticity of the materials changed little.After rolling the as-cast nano/micro-crystalline1020and1045steel at600℃by different deformation by20%,40%and60%, the microstructure of pearlite lamella was compressed and fragmented along the rolling direction, and the fragmentation become more serious when the deformation increased. After rolling by reduction60%, the lamellar pearlite was disappeared, the microstructure of the materials was the ferrite matrix inlaiding with granular pearlite, and the ferrite grain size remained as cast level after rolling.