Study On Strengthening Mechanism And Solid State Welding Process Of Ultra-high Vanadium And Niobium Powder Metallurgy High Speed Steel

Powder metallurgy high-speed steel(referred to as powder high-speed steel)has a history of more than 50 years as the main material for cutting tools in machining.From the first generation of powder high-speed steel adopting electro slag remelting and hot isostatic pressing to the third generation of powder high-speed steel with diversified production processes and matrix components,powder high-speed steel has gradually completed the optimization control of liquid steel composition,the improvement of the properties of the powder and the improvement and upgrading of the production equipment in each stage;In response to the needs of industrialization,scientific research workers have extended to the exploration of high-alloy and even super-alloyed materials,focusing on better organization and performance;so far,more excellent alloying schemes and high-performance powder high-speed steel have emerged endlessly,and gradually It has developed into a cutting tool material with great potential and development in the 21 st century.In this study,the limitations of alloying elements added by traditional smelting and atomization processes were broken,and ultra-high content of vanadium and niobium was introduced through DFT direct preparation process for composite strengthening,and the two key processes of material preparation and strengthening were studied,including ultra-high alloy Solidification sintering and densification technology,Vanadium-Niobium composite strengthening mechanism,and composition optimization,ultra-high alloy powder high-speed steel toughening behavior,etc.Gradually establish and perfect the densification mechanism of ultra-high alloy powder high-speed steel,the action mechanism and limits of ultra-high vanadium niobium,and the toughening process of ultra-high alloy powder high-speed steel.Secondly,to reduce the use cost of high alloy powder high-speed steel and improve the utilization rate of materials,the research attempts to use hot-press assisted diffusion welding to conduct the docking experiment of ASP 60 and W18Cr4 V.In sum:1.The ultra-high vanadium niobium powder high-speed steel with different compositions was prepared by DFT.By studying its densification behavior,microstructure,and phase evolution,the effect of different vanadium and niobium addition on the density,structure,and mechanical properties of the material is established.The results indicate that:(1)The material obtained a higher density(?99.13%)after sintering at 1165?;(2)With the increase of Nb content,a large number of fine bright white WC particles,bridging and bonding massive M6 C carbides and strip M2 C carbides appear in the material;(3)The material obtains the best comprehensive mechanical properties and microstructure when the Nb content is3%;(4)when Nb content is more than 5%,the material shows the strong secondary hardening effect.After three times of tempering,the hardness increases rapidly from58 hrc as-quenched to 72.6HRC;(5)High V/Nb powder high-speed steels with different compositions all have good tempering resistance.2.Secondly,the method of hot deformation was used to carry out rotary forging of 0%,10%,20%,30% and 40% of the powder high-speed steel with excellent comprehensive properties,and the microstructure,fracture and mechanical properties(including hardness,bending strength and impact toughness)of different rotary forging deformation were characterized.It was found that hot deformation can effectively improve the strength and toughness of the material When the deformation reaches 40%,the impact toughness and bending strength of the material are increased by 43.86% and 20.74% respectively compared with the material without forging,reaching 10.43J/cm2 and 3731.9 MPa.At the same time,the microstructure and fracture analysis show that the material properties are mainly strengthened by high-density dislocation and grain refinement.3.The hot press assisted diffusion welding is utilized to bond the high-performance powder high-speed steel ASP60 and W18Cr4 V,and the three parameters of welding temperature,welding pressure and welding holding time are tested through the principle of a single variable and the best welding parameters are found,Combined with the macro-morphology of the butt welding material(post-weld morphology,fracture morphology,etc.),mechanical property test and microstructure(SEM)analysis under each group of parameters,we can conclude that when the welding temperature is 1000?,the welding pressure is 25 MPa and the welding holding time is 30 min,the best welding performance is obtained?At this time,the tensile strength of the material is 1157 MPa,and the fracture is broken along the W18Cr4 V side.