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The heterogeneous mixed-grain microstructure is a common defect for the heavy forging of 316 LN austenitic stainless steel. Isothermal compression experiments were performed on a Gleeble-3500 thermo-mechanical simulator to investigate the effect of process parameters on the fragment and refinement of millimeter-grade coarse grains( MCGs) during hot cogging. The experimental results indicate that the stress of MCG specimens is much larger than that of fine grain( FG) ones at 1 150 °C,while the stress difference between MCG and FG samples became smaller at 1 200 °C. Moreover,the MCGs can be well fragmented and refined under the condition of temperature of 1 200 °C,strain rate of 0. 01 s~(-1),and reduction rate of 50%. Meanwhile,numerical simulations were conducted to study the influences of temperature,strain and strain rate on microstructure evolution. The results of experiments and simulations comprehensively demonstrate that the MCG results in the increase of deformation resistance and incompatibility of deformation,and it can be fragmented and refined at 1 200 °C so that the plastic deformation energy decreases remarkably with the increase of temperature from 1 150 to 1 200 °C.
The heterogeneous mixed-grain microstructure is a common defect for the heavy forging of 316 LN austenitic stainless steel. Isothermal compression experiments were performed on a Gleeble-3500 thermo-mechanical simulator to investigate the effect of process parameters on the fragment and refinement of a millimeter- The experimental results indicate that the stress of MCG specimens is much larger than that of fine grain (FG) ones at 1 150 ° C, while the stress difference between MCG and FG samples becomes smaller at 1 200 ° C. Moreover, the MCGs can be well fragmented and refined under the condition of temperature of 1 200 ° C, strain rate of 0.01 s ~ (-1), and reduction rate of 50%. Meanwhile, numerical simulations were conducted to study the influences of temperature, strain and strain rate on microstructure evolution. The results of experiments and simulations comprehensively demonstrate that the the MCG results in the increase of deformation resistance and incompatibility of deformation, and it can be fragmented and refined at 1 200 ° C so that the plastic deformation energy decreased remarkably with the increase of temperature from 1 150 to 1 200 ° C.