| Austenite-based Fe-Mn-Al-C lightweight steel has become one of the most promising materials in automotive industry owing to its good mechanical properties and low density.However,the austenite-based Fe-Mn-Al-C lightweight steel still has the problem of low strain hardening rate,preventing its tensile strength from being further improved.In this work,V element is added to the austenite-based Fe-Mn-Al-C lightweight steel,and the precipitation of higher hardness V4C3nanoparticles introduces Orowan mechanism during tensile deformation,achieve co-precipitation strengthening of nano-sized V4C3 and?-carbides while increases the strain hardening rate.To avoid element segregation and carbide coarsening,a sub-rapid solidification centrifugal casting method was utilized to prepare the samples considering the its high-content alloying elements.In order to explore the suitable alloy composition,the Fe-20Mn-9Al-1.2C-?0.6,1.0,1.4?V?wt.%?and Fe-20Mn-9Al-?1.0,1.2,1.4,1.6?C-1.0V?wt.%?alloy strip were selected for analysis.The results show that the addition of V has no obvious effect on the contents of austenite and ferrite.With the increase of C content,the ferrite content gradually decrease.Moreover,the plasticity of the sample is significantly affected by the more V and C content.The comprehensive mechanical properties of the alloy strip with 1.2 wt.%C and 1.0 wt.%V is better,the product of tensile strength and elongation is 41.4 GPa·%.Based on the optimized alloy composition above,to further investigated the microstructure evolution of the Fe-20Mn-9Al-1.2C-1.0V alloy strip before and after aging treatment,the?-carbide precipitation during aging treatment at 500-600°C for3 h was studied.The results show that the amount of intragranular?-carbides increase significantly with the increase of aging temperature,and the formation of coarse intergranular?-carbides is detected in the sample being aging at 550°C and600°C.The?-carbides in the aged alloy strip with 20%cold-rolled is easier to precipitate and grow.Regardless of whether it is rolled or not,the mechanical properties of the alloy strip aged at 500°C are better than other aged temperatures,but the strain hardening rate is lower.The precipitation of nano-sized V4C3 particles was studied in the sample performed cold-rolled 20%+high temperature?800-950°C?annealing with 2min+100 K/s rapid cooling process.The results show that a large number of nano-sized V4C3 particles and some intragranular?-carbides are precipitated in the900°C high temperature annealing alloy strip.Meanwhile,the coarse intergranular?-carbides disappeard in this sample.The yield strength and tensile strength of the900°C high temperature annealing alloy strip is 1146 MPa and 1304 MPa respectively,and the elongation is 18.5%,showing better comprehensive mechanical properties.The experimental results of the above showed that both intragranular?-carbides and V4C3 particles effectively increase the yield strength of Fe-20Mn-9Al-1.2C-1.0V alloy strip.However,the tensile strength is not be enhanced accordingly when a large numer of intragranular?-carbides precipitated.Due to the dislocation shearing?-carbides,the strain hardening rate is significantly reduced.The precipitation of nano-sized V4C3 particles has a multiplication effect on the dislocation.The tensile strength is significantly increased simultaneously owing to the unobvious decrease in the strain hardening rate.Therefore,the cold-rolled 20%+high temperature?900°C?annealing+low temperature?450-550°C?aging can achieve the co-precipitation of intragranular?-carbides and V4C3 particles,and the specific strength of the all samples are above 190 MPa·cm3/g. |
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