| The application of tool and die steel is an important basic material for manufacturing and infrastructure construction,and it is an indispensable tool for the country to realize industrialized production of products and economic construction.The gross production value of Chinese tool and die has already ranked third in the world,and the demand for tool and die steel is still increasing.With the continuous upgrading of the manufacturing industry,higher requirements have been placed on the quality of die steel and the development of new products.Modern industry has put forward higher requirements for the properties of tool and die steel,including hardness and red-hardness,room-temperature and high-temperature strength,toughness,and wear resistance.However,the use of traditional methods to improve the properties of steel,such as micro-alloying,ultra-purification,large forging ratio,and heat treatment process optimization,seems to have entered a bottleneck,and it is difficult to greatly improve the mechanical properties of steel by these methods.Adding nano-ceramic particles to steel can keep the original characteristics of steel based on refined microstructure,and improve the strength and elongation of steel due to grain refinement and uniform distribution of carbides,simultaneously,which may become a new method for the study of high-performance steels.However,the high content of nano-ceramic particles will significantly reduce the ductility of steel,thereby reducing the toughness,and there are many problems in the way of adding nano-ceramic particles.In this paper,the Al-Ti-C/B4C system was used to prepare nano-TiC/Al and TiC+TiB2/Al master alloys in situ by SHS reaction.It solves the problems of poor wettability,easy pollution,and difficult dispersion of nano-ceramic particles.The evolution law of microstructure,mechanical properties and wear resistance of forged high Cr tool steel controlled by nanoparticles was studied,and the microstructure,toughening mechanism and wear resistance of nanoparticle controlled high Cr tool steel were deeply analyzed.mechanism.The main innovations are as follows:1.Revealed the microstructure evolution law and action mechanism of 40Cr steel regulated by different contents of nano-TiC particles after as-cast and after heat treatment:It was found that 40Cr steel with different contents of TiC ceramic particles formed finer pearlite,thicker and larger elongated ferrite refined and more complex,a lot of granular ferrite appears,and the ferrite content increases significantly.It was found that the residual ferrite content of 40Cr steel after quenching and tempering treatment decreased,the dislocation density in the martensite decreased,the prior-austenite grains decreased significantly,the martensite laths were significantly refined,and the lamellar spacing between the medium ferrite and cementite is refined.It is revealed that the nano-TiC ceramic particles act as primary austenite nucleation sites during the solidification process,reducing the primary austenite grain size;then act as ferrite nucleation sites,making the elongated ferrite more for small.And refine the prior austenite grains and lath martensite.Due to the change of ferrite morphology,the residual ferrite content after heat treatment is reduced,the carbon element in the prior austenite becomes more uniform and the carbon content decreases,which reduces the dislocation density in the martensite.2.Revealed the effect of trace nano-TiC+TiB2 ceramic particle regulation on the microstructure evolution,mechanical properties and high temperature friction and wear resistance of high Cr die steel(carbon content=0.32 wt.%)and its mechanism of action:found that,the ferrite and granular pearlite grains are significantly refined,the carbide segregation in the forged high Cr steel is significantly improved,and the average size of the ferrite grains is reduced to 7.81?m and 4.92?m,respectively,after adding trace nano-TiC+TiB2 ceramic particles.decreased by 26.5%and 53.6%.The grain boundary carbide segregation of the high Cr die steel after heat treatment is significantly improved,the martensitic lath is refined,the dislocation distribution in the lath is more uniform,and the precipitated carbides become finer and uniform.It was found that the room temperature mechanical properties and impact toughness of the high Cr die steel were significantly improved after adding a small amount of nano-TiC+TiB2 ceramic particles.After adding 0.02 wt.%nano-TiC+TiB2 ceramic particles,the room temperature yield strength,tensile strength,elongation,and impact toughness of the steel were 1694 MPa,2087 MPa,6.64%and 568.79 J/cm~2,which were increased by4.0%and 568.79 J/cm~2,respectively.5.4%,26.7%and 86.3%.The high-temperature mechanical properties are also significantly improved.After adding 0.02 wt.%nanoparticles,the high-temperature yield strength and tensile strength of the steel at600°C are 656.5 MPa and 751.4 MPa,which are increased by 36.5%and 26.5%,respectively.Mechanical properties strengthening mechanism:fine-grain strengthening,high dislocation density strengthening and dispersion strengthening.Dispersion strengthening is the main strengthening method for trace nano-TiC+TiB2 ceramic particles to control steel.It is found that the high Cr hot work die steels have significantly improved high temperature friction and wear resistance after adding nanoparticles.The volume wear rate of high Cr hot work die steel after adding 0.02 wt.%nano-ceramic particles is 5.6×10-13m~3/m,which is 34.9%lower than that of ordinary high Cr hot work die steel.Revealing the mechanism of high temperature mechanical properties enhancement:Under the action of high temperature,many defects are generated near the nanoparticles,which promotes dislocation climbing and is beneficial to the improvement of plasticity.The nanoparticles located at the grain boundary pin the grain boundary at high temperature,which significantly improves the plastic deformation resistance of the steel at high temperature and improves the high temperature strength of the steel.The high temperature yield strength of nano-ceramic particle reinforced steel is significantly improved,the resistance to plastic deformation is improved,and the wear resistance is significantly improved.3.The effect of trace nano-TiC+TiB2 ceramic particle regulation on the microstructure evolution,mechanical properties,and wear resistance of high Cr tool steel(carbon content=0.41 wt.%)and its mechanism of action were revealed.As the fire temperature gradually increased,a small number of carbides were first precipitated at the grain boundaries,and then many C atom segregation areas were formed inside.The temperature further increased,and the C atom segregation areas began to precipitate granular carbides to form tempered troostite.At room temperature,the yield strength,tensile strength,and elongation of HRC steel with a hardness of 58.4 are1923.6 MPa,2415.5 MPa,and 2.88%,respectively.Under the same hardness,the room temperature impact toughness of high Cr tool steel and H13 steel are 39.54 J/cm~2 and12.85 J/cm~2,respectively,which are increased by 207.7%.It is found that the abrasive wear resistance of nano-controlled high Cr tool steel is significantly higher than that of H13 steel under the same hardness.The volume wear rates of the high Cr tool steel with58.4 HRC hardness under the conditions of 25N and 35N are 1.82×10-11m~3/m and3.21×10-11m~3/m,which are reduced by 32.8%and 29.0%,respectively.It is revealed that under the same hardness,the toughness of the steel is the most critical factor affecting the abrasive wear performance,and the toughness of the high Cr tool steel controlled by the trace nano-TiC+TiB2 particles is significantly higher than that of the H13 cutter head steel,and the less likely it is to be peeled off.It is easy to produce micro-cracks,which reduces the micro-crack wear characteristics of high Cr tool steel,thereby improving the wear resistance of the steel. |
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