Investigation Of Microstructural Control And Mechanical Behavior For Fe-30Mn-0.14C-7Cr-0.26Ni Steel

In most metal materials,the elongation decreases as the strength increases.The continuous high work hardening rate of high manganese steel in the plastic deformation process enables the material to have a good combination of strength and ductility goal,and has been widely used in the low temperature field.Therefore,the application prospect of high manganese steel in industry is very broad,and it has been widely concerned by materials researchers from all over the world.However,the researchers found that the yield strength of the traditional Fe-Mn binary alloy at room temperature is low,only about 200 MPa,which is difficult to meet industrial needs in practical applications.In this paper,the Fe-Mn-C ternary alloy was added with Cr and Ni alloy elements to improved its strength,anti-corrosion performance and low-temperature performance.The traditional cold rolling and annealing process is used to tailor themicrostructure and adapt strengthening methods such as fine-grained strengthening,precipitation strengthening,solid solution strengthening and dislocation strengthening enhance its yield strength.The premise of microstructure control in this study is to achieve a good combination of strength and ductility.Through the control of microstructure,the martensite is restrained and the yield strength is improved.The layered composite structure further improves the mechanical properties of the test steel.By combining 95%cold rolling with annealing treatments,three kinds of specimens with different microstructures(different grain morphologies and grain size)have been successfully prepared:(1)lamellar structure,where the lamellar boundary spacings vary within the range of 0.03?0.05?m;(2)specimens with a laminated composite structure composited of recovered and recrystallized layers where the grain size is 0.65?m;(3)specimens with a fully recrystallized equiaxed grain structure where the average grain sizes change from 0.80 to 14.05?m.Mechanical performance and deformation mechanism of specimens with different grain sizes were investigate by tensile tests at room temperature and low temperature(-180^oC),respectively.The tensile curves of Fe-30Mn-0.14C-7Cr-0.26Ni specimens with different grain sizes show that:no matter at room temperature or low temperature,the tensile curves of samples with different grain sizes show different flow states:the grain sizes are 0.65,0.80and 1.07?m occurence the yield platform in the tensile curves.There is no yield plateform in the tensile curves of other grain sizes of samples and the curves is continuous flow.The grain size and deformation temperature have significant effect on the deformation mechanism of Fe-30Mn-0.14C-7Cr-0.26Ni steel.Grain refinement inhibits deformation at room temperature.Grain refinement not only inhibits the deformation twins but also inhibits martensite transformation at low temperature.Whether at room temperature or at low temperature,the main deformation mechanism of Fe-30Mn-0.14C-7Cr-0.26Ni steel is occurence of dislocation slip and deformation twins.The Hall-Petch equation was established at room temperature.It was found that the Hall-Petch slope of fine-grained structure is much higher than that of coarse-grained structure,it is 1115 MPa·m^1/2,which indicates that grain refinement can significantly improve the yield strength of test steel.Fe-30Mn-0.14C-7Cr-0.26Ni steel has five strengthening methods,these are fine grain strengthening,precipitation strengthening,solid solution strengthening,dislocation strengthening and lattice friction,respectively.The contribution of five strengthening methods to its yield strength were calculated.The calculation results showed that the contribution of fine grain strengthening,precipitation strengthening and dislocation strengthening to the yield strength is relatively large;the contribution of solid solution strengthening and lattice friction to the yield strength is relatively small.In summary,by adjusted the composition and microstructure of high manganese steel,the mechanical properties of the test steel were optimized on the basis of low cost and simple process.