| The vibration and noise not only reduce the life and accuracy of equipment,but also have a certain impact on human health.Therefore,it is very urgent to develop and apply structural materials with damping capacity.During plastic deformation,the high-Mn transformation-induced plasticity(TRIP)steel containing ?-martensite has a large work hardening rate due to the multiple TRIP effect.Besides,the high density of partial dislocations in the microstructure also endows the steel with damping capacity.As a structural and functional composite material,the high-Mn TRIP steel with damping capacity has the advantages of low cost,excellent mechanical properties and good damping capacity,compared to other damping alloys.Therefore,it is of great potential to be applicated in the fields of architecture,machinery,and vehicle manufacturing etc.However,there have had few studies on high-Mn TRIP steel with damping capacity in China and abroad now,the effects of compositions and processing technologies on mechanical properties and damping capacity of steel are still needed to be further studied.In this paper,several high-Mn TRIP steels with different compositions were designed,the work hardening behavior and damping mechanism were deeply investigated by thermodynamic calculation and microstructural characterization.The industrial production and practical application of high-Mn TRIP steel with damping capacity were promoted by optimizing the chemical composition and processing technology.The main contents and conclusions are as follows.(1)Four high-Mn TRIP steels with damping capacity(15Mn,17Mn,19Mn and 17Mn0.3Si steel)were designed by varying the amounts of Mn and Si,and the stability of austenite and ?-martensite was studied by thermodynamic calculation.When the amount of Mn was increased,the stacking fault energy(SFE)of austenite was increased,so did the stability of ?-martensite.As Si was added,the SFE of austenite was decreased,but the stability of ?-martensite was increased.In the refined austenite,?-/?'-martensitic transformation should overcome the extra free energy difference.The refinement of austenite had a larger influence on ??? transformation than ???' transformation.(2)The influences of chemical composition on phase transformation behavior and mechanical properties of high-Mn TRIP steel were investigated.During cooling and deformation,???,???',???' and???? transformation occurred in the steels.In the two stages of tensile deformation,the main factor affecting work hardening behavior changed from ??? to ???' transformation when the deformation amount was increased.The microstructural stability was so low in 15Mn steel that ?'-martensitic banded structure formed after solution treatment.The tensile strength of the steel was large,but the ultimate elongation and impact toughness were low.During plastic deformation,the two main phase transformations occurred coordinately in 17Mn steel,resulting in good plasticity and toughness.When the amount of Mn was increased,the mechanical properties of steel were deteriorated because the deformation-induced phase transformation was restricted.Due to the further solution strengthening effect of Si,comprehensive mechanical properties of 17Mn0.3Si steel were the best.(3)By changing the annealing temperature,warm deformation amount and temperature of tensile deformation,the stability of austenite and ?-martensite was varied,then the work hardening behavior of high-Mn TRIP steel was studied.The results showed that the stability of austenite and ?-martensite was increased after low temperature annealing and warm deformation.The strengthening effect of grain refinement and prior work hardening increased the tensile strength of high-Mn TRIP steel,but the ultimate elongation was decreased because deformation-induced ???' transformation was restricted.According to the tensile behavior at elevated temperatures,deformation-induced ?+?' transformation and TWIP effect had more advantages to increasing work hardening exponent than ??? transformation and ???transformation.(4)The effect of chemical composition and working and heat treatment process on damping capacity was studied,and the key factors affecting the damping capacity were revealed.The damping capacity of high-Mn TRIP steel was not only influenced by the number of damping sources,but also closely related to the defects in the microstructure(such as vacancies,interstitials and dislocations,etc.).With increasing the Mn content,damping capacity of high-Mn TRIP steel was decreased,and a small amount of Si addition significantly increased the damping capacities at large amplitudes.When annealing temperature or cooling rate was increased,the damping capacity was increased because a large amount of ?-martensite was thermally induced.After aging for 15 min at 150? or tensile deformation for 5%at room temperature,the amount of ?-martensite was increased,and the pinning effect of vacancies and interstitials to partial dislocations was decreased.However,the segregation of interstitials after long-time aging and the introducing of dislocations and deformation-induced ?'-martensite by tensile deformation deteriorated the damping capacity.(5)By using nanoindentation,the micro damping capacity of high-Mn TRIP steel was investigated to illustrate the damping mechanism,then two new heat treatment processes(solution treatment at high temperature and controlled aging)were designed to enhance damping capacity.The results showed that the partial dislocations formed in both the boundary and internal of ?-martensite plates,the high density of partial dislocations provided many damping sources to high-Mn TRIP steel.After solution treatment at 1200? for 1 min,the original austenitic grain size did not increase obviously,but the amount of thermally?-martensite was significantly increased.The damping capacity of high-Mn TRIP steel was increased without sacrificing mechanical properties.The adverse effects of vacancies and interstitials on damping capacity were decreased by controlled aging at above and below?-martensite start transformation temperature,then the damping capacity of high-Mn TRIP steel was significantly increased after controlled aging. |
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