| The high-density tungsten alloy is a body-centered tungsten matrix phase(content 85%~97%),and the Ni-Fe face-centered cubic structure with a melting point lower than W is used as the main component of the binder phase,and a small amount of Co is added.Two-phase composite alloy composed of strengthening elements such as Mn.Because of its high melting point,high density,low expansion coefficient,high temperature strength and good corrosion resistance,it is widely used in machinery manufacturing and other fields,and is also an ideal material for die-casting molds.Die-casting molds should be serviced under the harsh environment of high-pressure impact of molten metal,repeated extreme heat and cold,and subjected to repeated grinding between mold components,it has high requirements on surface strength,hardness,wear resistance and fit between molds.However,the widely used H11 and H13 series hot working molds have unsatisfactory service life,and it is easy to cause micro-cracks on the surface to affect the product quality or even the mold itself.Therefore,it is necessary to make a reasonable selection of materials for die-casting molds and to carry out surface modification and strengthening research.In this paper,the W-Ni-Fe high-density tungsten alloy with strong R2 M type is selected as the material for die-casting mold,and its surface strengthening and modification process is studied:Firstly,the basic physical and chemical properties of R2 M high-density tungsten alloy were measured,and its microstructure,chemical composition and mechanical properties were characterized.The basic properties of R2 M tungsten alloy for hot working die were preliminarily understood.To study the effect of Surface ultrasonic rolling Extrusion on the microstructure and surface quality of R2 M high-density tungsten alloy,explore reasonable strengthening process parameters,improve the surface mechanics and geometric properties of materials,and achieve the performance requirements of die-casting mold materials.On the basis of surface ultrasonic roller strengthening,Simulated hot work die material service environment R2 M tungsten alloy heat treatment,water quenching at 800°C,1h heat preservation,analysis of the effect of heat treatment on the deformation microstructure and surface hardness of R2 M tungsten alloy after deformation strengthening.Vacuum carburizing test of R2 M high-density tungsten alloy was carried out to study the composition,distribution and microhardness of the carburized layer of R2 M tungsten alloy under different carburizing parameters.Tests on the physical and chemical properties of R2 M tungsten alloy show that R2 M tungsten alloy has high mechanical properties and excellent thermal stability,and can be used as an excellent candidate material for die-casting mold materials.The Surface ultrasonic rolling Extrusion results show that the treatment method can produce a certain thickness of the deformation strengthening layer on the surface of the R2 M tungsten alloy and introduce residual stress,introduce residual stress,and effectively reduce the surface roughness of the material.It is found that the static pressure on the surface properties of R2 M tungsten alloy has the best value in the positive and negative directions.The spindle speed is negatively correlated with its surface properties.Increasing the processing pass within a certain number of times can increase the Surface ultrasonic rolling Extrusion strengthening effect.The surface roughness of the test material R2 M tungsten alloy was the most obvious under the 3 and 4 rolling treatments.The test material was rolled 4 times at 0.10 MPa and 180r/min.The deformation of the surface layer was the highest,the degree of deformation was uniform and there was no obvious microcrack,and the surface hardening effect and calendering effect were the best.The depth of the deformation layer reached 91.39?m.The surface hardness is 523.85 HV,the hardening degree is 85.76%,the surface residual stress is 706 MPa,the surface roughness is Ra0.0863?m,which is 94.80% lower than the initial Ra value of 1.6596?m,and the surface quality is obviously improved.The effect of static pressure on the surface hardness,residual stress and surface roughness of the sample is firstly positively optimized and then negatively weakened.The lower the spindle speed,the better the surface properties of the sample.On the basis of this deformation strengthening,after R2 M tungsten alloy was subjected to heat treatment of simulated hot working die material working environment,the surface deformation structure and surface hardness of the sample remained basically unchanged after quenching at 800 °C for 1 h.Among them,the microhardness of the heat treatment surface after aging of 4 passes,0.10 MPa and 180 r/min was 518.47 HV,which was not significantly lower than the microhardness of 523.85 HV of the same Surface ultrasonic rolling Extrusion unheated sample.Therefore,it is considered that the Surface ultrasonic rolling Extrusion treatment is an effective reinforcement means that can adapt to the general working environment of the hot working mold.The vacuum carburizing heat treatment produces a carburized layer of about 200 ?m on the surface of the R2 M tungsten alloy,and the WC formed by surface chemical reaction causes the surface to harden.The effects of carburizing temperature and swelling time on the carburizing effect of R2 M tungsten alloy are positive,and the carburizing temperature is the dominant factor.With the increase of carburizing temperature and the extension of the percolation time,the outer layer depth,the relative content of WC phase and the grain size of WC of carburized layer increased,and the higher the degree of carburizing reaction,the more obvious the effect of carburizing hardening.The relative content of W phase components of carburized samples at 950 ° C and 180 min was 24.3%.Under this parameter,the surface hardness of the sample is 396.43 HV,and the hardening rate is 40.57%.The hardening effect is the most obvious.The test provides a reliable reference surface strengthening method for the hot work die material R2 M high-density tungsten alloy,which is of great significance for prolonging its service life and improving the working effect of the mold. |
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