Microstructure And Mechanical Properties Of H13 Steel Manipulated By Trace TiC/?TiC+TiB₂? Nanoparticles

As a kind of structural material,steel materials are widely used in long-span bridges,long-distance oil,gas pipelines,aerospace equipment,large capacity storage containers,weapons equipment,precision instruments,super large ships and offshore drilling platforms,etc.The performance requirements of steel materials are also increasing,which requires the development of new steel materials with longer service life and higher mechanical properties.In this case,it is very important to develop new high-performance steel and new methods of strengthening steel.Nanoparticles can be added to metal materials as reinforcing phases to improve the mechanical properties of metal materials,which is an innovative way to strengthen metal materials.However,it is very difficult to add nanoparticles into steel due to the large difference in the specific gravity between nanoparticles and steel,which makes nanoparticles easy to agglomerate,uneven dispersion in steel,and large specific gravity difference,which leads to the problems such as agglomeration and floatation of nanoparticles.It is of great practical significance and application value to solve a series of problems in the preparation process of nanoparticles reinforced steel,such as realizing the control of nanoparticles on the structure and properties of steel,effectively strengthening the mechanical properties of steel,and providing a new method for strengthening steel.In this paper,H13 steel reinforced by nanoparticles was prepared by using master alloy as the carrier of nanoparticles.The microstructure evolution of H13 steel reinforced by single-phase TiC and dual-phase TiC+TiB₂ nanoparticles with different contents was studied,and the mechanism of nanoparticles controlling the microstructure of H13 steel was revealed.The tensile and impact properties of H13 steel reinforced by different contents of single-phase TiC and dual-phase TiC+TiB₂ nanoparticles were studied,and the mechanism of strengthening H13 steel by nanoparticles was revealed.The effect of nanoparticles on the high temperature wear resistance of H13 steel was studied.The difference of the effect of different kinds and contents of nanoparticles on the high temperature wear resistance of H13steel was analyzed.The mechanism of improving the high temperature wear resistance of H13 steel by nanoparticles was revealed.The effect of nanoparticles on the room temperature wear resistance of H13 steel was studied.The effect of different kinds and contents of nanoparticles on the room temperature wear resistance of H13 steel was analyzed.The mechanism of improving the room temperature wear resistance of H13 steel by nanoparticles was revealed.This paper has four innovations as follows:1.The effect of nanoparticles on the structure of H13 steel and the corresponding control mechanism were revealed:?1?The effect of nanoparticles on the structure of H13 steel was revealed.The microstructure of H13 steel without nanoparticles is mainly coarse tempered martensite with uneven distribution,accompanied by a lot of tempered sorbite and a small amount of point like residual carbide.The structure of H13 steel with 0.01 wt.%TiC is mainly tempered sorbite,accompanied by many fine tempered martensite and a small amount of carbide.The microstructure of H13 steel with 0.02 wt.%TiC is more fine tempered martensite,which is evenly distributed.The microstructure of H13 steel with 0.01wt.%TiC+TiB₂ is mainly fine tempered martensite,which is distributed evenly and its directionality disappear.The structure of H13 steel with 0.02 wt.%TiC+TiB₂ is mainly tempered martensite,and the tempered sorbite in the composition is greatly reduced.The proportion of martensite in H13 steel with 0.03 wt.%TiC+TiB₂ is further increased.Some tempered martensites are more slender,uniformly distributed and highly directional.?2?The mechanism of adjusting the structure of H13 steel by adding nanoparticles was revealed.Nanoparticles can effectively improve the nucleation efficiency of austenite and increase the number of nucleation cores,while nanoparticles not act as nucleation site can inhibit the growth of dendrites,and control the austenite grains in the process of nucleation and growth.More refined austenite grains are beneficial to the microstructure refinement after heat treatment,and can effectively refine the martensite structure.2.The effect of nanoparticles on mechanical properties of H13 and the strengthening and toughening mechanism were revealed:?1?The strengthening mechanism of nanoparticles in H13 steel was revealed.The yield strength,tensile strength,fracture strain and strength-ductility of H13 steel reinforced by single-phase TiC nanoparticles increase with the increase of nanoparticles content,and the uniform elongation increases first and then decreases with the increase of nanoparticles content.The yield strength,tensile strength and strength-ductility of H13 steel reinforced by dual-phase TiC+TiB₂ nanoparticles increase with the increase of nanoparticles content,while the fracture strain and uniform elongation decrease with the increase of nanoparticles content.The results show that the tensile properties of H13 steel are improved more obviously by adding dual-phase TiC+TiB₂nanoparticles,but when the content of dual-phase TiC+TiB₂ nanoparticles reaches more than0.02 wt.%,the improvement effect of properties is not stable and the dispersion degree of properties is large.?2?The mechanism of strengthening and toughening of H13 steel by nanoparticles was revealed.It is mainly grain-refinement strengthening,dislocation strengthening and second phase strengthening.Grain-refinement strengthening:after adding nanoparticles,the structure is refined and more uniform and dense,thus improving the plasticity of the material.Dislocation strengthening:high thermal mismatch results in many dislocations in the matrix after heat treatment.After dislocation movement,the interaction between dislocations and grain boundaries and between dislocations and dislocations improves the strength of materials.Second phase strengthening:nanoparticles hinder dislocation slip and enhance the strength of steel by the effect of dislocation pinning.3.The effects of nanoparticles on the high temperature wear resistance of H13 steel and the mechanism to improve the wear resistance are revealed:?1?the effects of different wear parameters on the high temperature wear resistance of H13 Steel reinforced by nanoparticles are revealed.When the temperature is 573K,the material surface wear form is ploughing wear,and when the temperature is 723K,the wear form of material surface is adhesive wear.Compared with 573K,the wear resistance of H13 steel increased more obviously at 723K.When the load is high,the main wear form is adhesion wear.While when the load is low,the main wear form is ploughing wear.The wear resistance of H13 steel with the addition of dual-phase nanoparticles increased more obviously and the increase of nanoparticles content results in the increase of wear resistance of composite.Compared with the rotation speed of150 r/min,the adhesive wear on the surface of the composite increases when the rotation speed is 300 r/min.The wear form of the material can be changed from adhesive wear to plough wear by adding dual-phase nanoparticles,and the wear degree of the material surface can also be reduced.?2?The mechanism of improving high temperature wear resistance of nanoparticles reinforced steel is revealed.At 573K,the material is mainly ploughed wear.Nanoparticles,especially dual-phase nanoparticles,can resist the pressure of abrasive particles,and the ploughing degree is reduced.The increase of nanoparticles content enhances the ability of load transfer,and the depth of abrasive particles into the matrix and ploughing degree are both reduced.At 723K,the existence of nanoparticles hinders the plastic deformation of the material surface,and the effect of adding dual-phase nanoparticles to resist the plastic deformation is more significant.Therefore,the addition of nanoparticles reduces the degree of peeling off and adhesive wear of the material surface.4.The effect of nanoparticles on the wear resistance of H13 steel at room temperature and the mechanism of improvement are revealed:?1?the effect of different wear parameters on the wear resistance of H13 steel at room temperature is revealed.Compared with the single-phase nanoparticles,the dual-phase nanoparticles have better effect on the improvement of the wear resistance of the material,and the increase of the content of nanoparticles can enhance the wear resistance of the material.Compared with 360 mesh of sandpaper,the furrow depth of the material is shallower and the wear resistance is improved more obviously under 600 mesh of sandpaper.?2?The mechanism of improving the wear resistance of nanoparticles reinforced steel at room temperature is revealed.Because the microstructure of nanoparticles reinforced steel is finer and denser,the steel matrix can resist the pressure of abrasive particles and reduce the pressure depth of abrasive particles.Compared with the single-phase nanoparticles,the dual-phase nanoparticles have a better resistance to abrasive pressure,making the matrix not easy to be ploughed out,so it can effectively reduce the depth and width of the furrow,at the same time,the increase of the nanoparticles content can also improve the load transfer ability,resulting in the improvement of the wear resistance of materials.