Effect Of Heat-Treatment On Precipitation And Properties Of Cast Ti-V-Nb Alloyed High-manganese Steel

Precipitation strengthening is a kind of strengthening method with the minimum brittleness vector except fine-grained strengthening,which can enhance the yield strength and tensile strength of steel at the same time,and will not significantl y deteriorate the processabilit y of the steel.For the past few years,Ti,V and Nb are widel y used in the investigation of precipitation strengthening of steel because of their easy combination with C and N.Through Ti-V-Nb alloying and heat treatment,the precipitates with different size can be precipit ated in the austenitic matrix,which can significantl y enhance the mechanical properties and wear resistance of high-Mn steel.Heat treatment is an effective technology to control the precipitation and improve the microstructure and mechanical properties o f the as-cast Ti-V-Nb alloyed high-Mn steel.Therefore,the effect of heat treatment process es on the precipitates and mechanical properties of Ti-V-Nb alloyed high-Mn steel is investigated,which has important theoretical significance and industrial application value for research,development and industrialization of high wear resistant austenitic steel with excellent comprehensive performance and low production cost.Based on the optimized compos ition,Fe-0.88C-17Mn-2Cr-0.81Si-0.73Mo-0.29Ni-0.49Cu-0.09Ti-0.43V-0.25Nb high manganese steel was selected as the research object.The precipitation process of Ti,V and Nb carbide s in austenite was controlled by solid-solution and aging treatment respect ivel y,in order to prepare cast alloyed high-Mn steel with excellent mechanical properties and wear resistance.The main research contents and results are as follows:(1)The microstructure transformation of experimental steel during solidification was studied by theoretical calculation and as-cast microstructure anal ysis,the(Ti,V,Nb)C particles with large-sized and cladding structure had been precipitated in situ during the solidification process of the experimental steel.The effect of continuous heating process(CHP)and segmented heat preservation process(SHPP)on the precipitates and mechanical properties of experimental steel were studied.SHPP could not onl y refine grain,but also improve the distribution and refine the size of the precipitates,the impact toughness and yield strength of the SHPP increased b y28.3 J and 68 MPa,respectivel y.Finall y,the strengthening mechanism of the two samples was discussed according to the experimental results.In both SHPP and CHP samples,solid-solution strengthening was the main strengthening mechan ism,and the increment of solid-solution strengthening of SHPP samples was larger.(2)The calculation results of MC binary phase equilibrium solid solubilit y product and thermodynamic phase diagram declared that the decreased of the average size and quantit y of precipitates in the experimental steel after solid-solution was mainl y related to the dissolution of V carbides.The effect of solid-solution temperatures on microstructure of experimental steel was studied,1100?was an appropriate solid-solution temperature for balancing the size of austenite grains and precipitates in Ti-V-Nb alloyed high-Mn austenitic steel.Finall y,the sub-micron precipitates in the 4 50A and 500A samples were mostl y composed of V₂C particles,and the volume percentage of sub-micron precipitates in experimental steel was increased with the aging temperatures.The nano hardness of the austenitic matrix in 450A and 500A samples was about 0.39 GPa and 0.94 GPa higher than that of the 1100S respectivel y,the Young's modulus was about 5 GPa and 19 GPa higher than 1100S,and the Brinell hardness was higher than 8 HBW and 15 HBW,respectively.(3)The effects of aging temperatures on yield strength,hardness,Young's modulus,strain hardening capacit y and wear resistance of experimental steel were studied.The yield strength of the 400 A,450A and 500A steels increased by 38 MPa,61 MPa,and 82 MPa compared to 1100S,respectivel y.The hardnesses of the 400 A,450A and 500A increased by 0.521 GPa,0.921 GPa,and 1.427 GPa compar ed with1100S,respectivel y,and the modulus increased by 6.1 GPa,11.2 GPa,and 23.7 GPa,respectively.The higher hardness and modulus enhanced the wear resistance of the steel during the initial stage of wear.With the extension of sliding distance,its wear resistance was mainly related to the yield strength of experimental steel,the increased yield strength enhanc ed the resistance of the matrix to deformation and thus improved the supporting effect of the austenitic matrix on the micron-sized particles.The wear mechanism of the tested steel was transformed from deep grooves to microploughing,pits,and fa tigues with increased tempering temperature,the higher strain hardening rate of matrix increase d the critical stress threshold for micro-cutting.