Effect Of Processing Technologies On Microstructure And Mechanical Properties Of Powder Forged Low Alloy Steel

Powder forging is a new technology that is green,efficient,energy-saving and environmentally friendly.It combines powder metallurgy technology with precision forging technology.It not only has the advantages of powder metallurgy without cutting or less cutting processing,high material utilization,but also has the advantages of high precision forging precision,fewer pores,and good mechanical properties.In recent years,the world's powder forging industry has developed rapidly.China's powder forging industry also relies on independent research and development,combined with the introduction of foreign advanced technology,presenting a new trend of rapid development.However,at present,the research focus of powder forging technology in China is still focused on the optimization of powder forged parts,material design,and numerical simulation.The influence of processing technology parameters on the microstructure and properties of powder forged alloy is a lack of systematic research.Therefore,this dissertation uses different process parameters to prepare powder forged low alloy steel,and explores the effects of three processing technologies such as forging temperature,preforming density and sintering temperature on the microstructure and properties of Fe-x C-2Cu-y Mo-z La₂O₃powder forged alloy.First,the effect of forging temperature(900?,950?,1000?,1050?)on the microstructure and mechanical properties of powder forged Fe-1C-2Cu-y Mo(y=0.5,0.85,1.46 wt.%)alloys show that:the forged microstructure of Fe-1C-2Cu-y Mo(y=0.5,0.85,1.46wt.%)alloy is mainly acicular martensite,bainite,and retained austenite.When forging at950?,the alloy structure is uniform and no obvious defects,which is suitable for the forging temperature of Fe-1C-2Cu-x Mo(y=0.5,0.85,1.46 wt.%)alloy.Forging can greatly increase the density of the alloy.Among them,the density increases the most when the forging temperature is 950?,and the relative density of the alloy can reach 0.985.The effect of forging temperature on the apparent hardness of Fe-1C-2Cu-x Mo(y=0.5,0.85,1.46 wt.%)alloy is more significant.The hardness of the three component alloys reaches the highest after forging at 1050?.The transverse fracture strength of Fe-1C-2Cu-x Mo(y=0.5,0.85,1.46wt.%)alloy after forging at 950?and 1000?is generally good,and the fracture modes of the alloy are all tough-brittle mixed fractures;When forged at 950?,the Fe-1C-2Cu-x Mo(y=0.5,0.85,1.46 wt.%)alloy with Mo content of 1.46 wt.%has the lowest friction coefficient under oil lubrication conditions.Then,the effect of the green density(6.2 g/cm³,6.6 g/cm³,7.0 g/cm³)on the microstructure and mechanical properties of powder forged Fe-x C-2Cu(x=0.2,0.5,0.8 wt.%)alloys show that:the forged microstructure of the Fe-x C-2Cu(x=0.2,0.5,0.8 wt.%)alloys is mainly pearlite,ferrite and a small amount of cementite.The alloy with the green density of6.6 g/cm³has the highest pearlite content and the most uniform and fine structure.After forging,the densities of the alloys have been greatly improved.Due to the restriction of the macroscopic flow of the metal by the hot recompression forging die,the density after forging is the smallest when the green density is 6.2 g/cm³.Fe-x C-2Cu(x=0.2,0.5,0.8 wt.%)with a green density of 6.6 g/cm³has the best apparent hardness after forging,and the highest apparent hardness reaches HRA65.0.The green density has a greater influence on the transverse fracture strength of the alloy.The influence of the density and microstructure makes the maximum fracture strength of the Fe-0.8C-2Cu alloy with a green density of 7.0g/cm³.The impact toughness of Fe-x C-2Cu(x=0.2,0.5,0.8 wt.%)increases with the increase of the green density.The fracture modes of alloys are tough-brittle hybrid fracture.For Fe-0.5C-2Cu alloy,the friction coefficient changes with the preform density.The friction coefficient reaches the lowest and the fluctuation is small when the green density is 6.6 g/cm³under oil lubrication conditions.The wear form of the alloy is abrasive wear.The effect of sintering temperature(1120?,1200?,1280?)on the microstructure and mechanical properties of powder forged Fe-0.8C-2Cu-0.2La₂O₃alloys show that:the microstructure of the forged Fe-0.8C-2Cu-0.2La₂O₃alloy is mainly pearlite,ferrite,cementite,and a small amount of La₂O₃particles which exists as grains at the grain boundaries.Increasing the sintering temperature results in the coarsening of the grains of the forged alloy,the increase of pearlite content in the structure,and the intensification of the La₂O₃particles at the grain boundaries.The main factor affecting the forged density of Fe-0.8C-2Cu-0.2La₂O₃alloy is the hindrance of La₂O₃on the grain boundary migration.As the sintering temperature increases,the density decreases first and then increases,and sintered at 1280?the relative density of Fe-0.8C-2Cu-0.2La₂O₃alloy can reach 0.992 after forging.The Fe-0.8C-2Cu-0.2La₂O₃alloy sintered at 1280?has sufficient diffusion,the alloy structure is uniform,the apparent hardness of the forged alloy reaches the highest HRA64.5.With the increase of the sintering temperature,the transverse fracture strength of the forged Fe-0.8C-2Cu-0.2La₂O₃alloy decreases first and then increases.The fracture mechanism of forged alloys sintered at 1120?and 1200?is crystalline fracture,and the forged alloys sintered at 1280?are cleavage fracture.For the forged Fe-0.8C-2Cu-0.2La₂O₃alloy,the higher the sintering temperature,the better the impact toughness of the alloy after forging.When the sintering temperature is 1120?,the minimum average friction coefficient of the forged Fe-0.8C-2Cu-0.2La₂O₃alloy is only 0.027 under oil lubrication conditions.