| Gray cast iron is the most widely used casting alloy,and research on particle reinforced casting alloy has become a hotspot in recent decades.Although there are many reports on the properties of particle reinforced gray cast iron,the studies on behavior and distribution of additional particles added from outside the furnace in the matrix of the gray cast iron before casting;the effect of additional particles on the hypoeutectic transformation,especially the effect on the subcooling degree and latent heat of crystallization during solidification;the effect of additional particles on the high-temperature mechanical properties of gray cast iron and the application of strengthening effect of additional particle under production conditions have not been systematically reported.In this study,a small amount of high-energy activated SiC particles were added to the melt of Hypoeutectic gray cast iron by adding outside the furnace under production conditions.The effects of high-energy activation treatment on SiC particles,the behavior and distribution of high-energy activated SiC particles in Hypoeutectic gray cast iron and their effects on the solidification process of Hypoeutectic gray cast iron,especially the undercooling and crystallization latent heat,were systematically studied The key problems such as the influence of mechanical properties and service properties,especially high-temperature properties,were studied,and the production and application of Hypoeutectic gray cast iron strengthened with high-energy activated SiC particles were studied.The mechanism of strengthening hypoeutectic gray cast iron with high energy activated SiC particles is discussed,and the method of dispersing SiC particles in the matrix and improving the strengthening effect is put forward.It provides necessary experimental data and theoretical reference for the industrial application of particle reinforced cast iron alloy.By studying the effect of high-energy activation treatment on SiC particles,it can be found that high-energy activation treatment leads to an increase in lattice defects that occurred in the SiC particles at a high-energy state,makes the particles more round and smaller in size,and causes great improvements in the specific surface area and the surface activity,which has an important influence on the behavior of SiC particles in cast iron melt.The absorption rate of high-energy activated SiC particles obtained by tracer elements in cast iron melt is 68-72%.It is observed that SiC particles are dispersed and evenly distributed in the matrix without agglomeration.The distribution in pearlite crystal accounts for 78.12% and the distribution at grain boundary accounts for 21.88%.It is worth noting that the SiC particle size observed in the matrix is significantly smaller than that before adding to the cast iron melt,of which the proportion of particles below 1μm increased by 345.09%;1-2 μm particles increased by306.88%;2-5 μm particles increased by 28.63%;5 μm decreased from 61.44% to 0.The study on the effect of adding trace high-energy activated SiC particles on the hypoeutectic transformation of gray cast iron shows that with the increase of the addition of trace activated SiCp,the microstructure of Hypoeutectic gray cast iron is improved,the undercooling degree is increased and the crystallization latent heat is reduced.Wherein,the addition amount is 0.15 wt.%,the dendrite content of primary austenite increased by 35.4% and the morphology improved by 57.98%.The size decreases of graphite and eutectic cluster were56.52% and 64% respectively.The undercooling increased by 27.27% and the latent heat of crystallization decreased by 38.52%.The effect of adding trace amount of high-energy activated SiC particles on the properties of Hypoeutectic gray cast iron,especially high temperature,is studied.The results show that the tensile strength increases with the addition of trace amount of high-energy activated SiC particles.In particular,the high temperature strength achieves maximum increment of 21.62%and 18.67% at 450 ℃ and at 700 ℃,respectively.The type of SiC particles,addition amount,addition method,holding time,and composition of cast iron have significant effects on the strengthening effect.By studying the influence of particle preparation method,it is found that the strengthening effect of SiC particles treated with high-energy activation is the best,whose tensile strength at room temperature and 450 ℃ are increased by 11.19% and 22.53%,respectively.The tensile and compressive high cycle fatigue strength at room temperature,450 ℃,and 650 ℃ increases with the increase of the amount of activated SiCp.The fatigue strength at room temperature is increased by 28.24% and 16.47% at 450 ℃ and 650 ℃,respectively,,and the number of tests at the same strength is increased by 566%.It also finds that the addition of trace activated SiCp can significantly improve the heat fatigue,wear resistance,and corrosion resistance of Hypoeutectic gray cast iron with different alloy components.The above results are of great significance for the application of gray iron castings under high temperature conditions.The application of high energy activated SiC particles for strengthening hypoeutectic gray cast iron is studied in thin-walled cylinder block without cylinder liner and four valve cylinder head of diesel engine.The results show that after adding high-energy activated SiC particles,the key items of thin-walled cylinder block material,such as wear resistance,room temperature tensile strength,and cavitation resistance,are significantly improved,the cylinder block has passed the bench reliability test,the oil consumption is 39% lower than that of thin-walled cylinder block,and the air leakage of piston is 38%.Besides,the temperature and high temperature tensile strength of the four valve cylinder head chamber are increased by 11.63%and 20.77%,respectively.The thermal fatigue performance is improved by 48.55%,and the cylinder head has also passed the bench reliability test.More than 12000 cylinder linerless cylinders with trace activated SiCp have been put on the market,with a maximum mileage of more than 320000 kilometers,stable quality and no problem feedback.The results of the research on the strengthening mechanism of hypoeutectic gray cast iron by using high-energy activated SiC particles can be summarized as follows: the reactions involving high-energy activated SiC particles happen in the molten cast iron lead to a smaller size of particles.The products including C and SiC can be used as the core of primary austenite and graphite to increase the number of dendrites,graphite,and eutectic clusters.The "microchill" effect of SiC in cast iron melt and endothermic reaction cause an increase in the subcooling degree and reduction in the latent heat of crystallization,thus affecting the nucleation and growth of austenite,graphite and eutectic.The small particle SiC is mainly dispersed in the crystal after reaction and plays the dislocation strengthening effect as well as the Orowan strengthening effect.Compared with the direct addition of nanoparticles into the molten iron,the SiC becomes smaller in the reactions happen in the molten iron,which can not only play a strengthening effect,but also avoid agglomeration.High energy activation treatment improves both the surface activity of SiC and the reaction speed,and it also can meet the time requirements of production and application.According to the derivation formula,the particle size distribution with best strengthening effect can be deduced inversely by combining the reaction speed with the time of SiC in molten iron,which provides a new idea for solving the problem of agglomeration of cast alloy strengthened by adding particles. |
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