Effect Of Modified Nano-powders On The Microstructure And Mechanical Properties Of Ductile Iron

Ductile iron is a kind of casting material which has been developed and widely used in the last century.In recent years,with the rapid development of heavy industry,the demand for ductile iron has been increasing day by day.Besides good mechanical properties,the requirements of wear resistance,heat resistance,fatigue performance and corrosion resistance are also very high.Modified nano-powders with high hardness,high melting point and compatibility in liquid metal have been widely used in the field of strengthening and toughening of ductile iron.According to the QT400-18L,the effects of microstructures and properties were studied.The microstructure,mechanical properties,wear resistance,thermal fatigue resistance and corrosion resistance of the QT400-18L were detected.The mechanism of strengthening and toughening of two kinds of nano-powders A and B after modification treatment was preliminarily analyzed by combining the test results and related detection methods.With the increase of the amount of modified nano-powder A,the nodularity and the total number of graphite in the microstructure increased,and ball diameter reduced slightly,and the spherodization rate,the total number of particles increased,and the ball diameter decreases,and the ferrite content was significantly improved.When the addition content of modified nano-powders A and B was 0.1%-0.15%,their effections were the best.After the samples added modified nano-and B,the law of chang about theirs’tensile strength,elongation,elastic modulus,impact toughness at room temperature and low temperature impact toughness were basically same.that is,showing an increasing trend,the increasing rate was from increasing to reducing.The optimum value basically appeared at the addition content of 0.1-0.15%.The hardness remained unchanged;powder A wear resistance increased significantly,when the adding content of powder A was 0.2%,under 150N and 300N load,the loss rate decreased by 78.1%and 37.3%.Powder B had no significant effect on the wear resistance.Modified nano-powder A had no obvious effect on the thermal fatigue resistance;while adding modified nano-powder B could obviously improve its thermal fatigue resistance,showing that it was more difficult to crack the sample,the crack length was shorter,the degree of surface cracking was reduced.When the addition amount was 0.2%,cracks began to appear in the 70th thermal cycle,and the crack length after 200 thermal cycles was only 295.6μm.The samples added by A and B nano-powders were respectively soaked in 5%H2SO4 and 3.5%NaCl.These samples’ corrosion resistance all were increased remarkably in each concentration.The corrosion rate of 24h of the sample added A nano-powders,in 3.5%NaCl solution,was reduced by 77.8%The corrosion rate of 1h of the sample added B nano-powders,in 5%H2SO4 solution,was decreased by 57.9%...