Effect Of Heat Treatment On Damping Properties Of Ductile Iron

Ductile iron is an important casting metal material.It has good mechanical properties and has been widely used in industry.Its mechanical properties mainly depend on matrix structure.Heat treatment can change the matrix structure and significantly improve the mechanical properties of ductile iron.For the mechanical properties of ductile iron,the scholars have already had a very deep research,However,the damping capacity of ductile iron is rarely studied.Therefore,this paper mainly deals with the different heat treatment processes on ductile iron,and explores the influence of heat treatment process on damping capacity of ductile iron.Three main heat treatment processes of ductile iron are used in this paper,the incomplete austenitisation normalizing process,isothermal quenching process and quenching and tempering process with low temperature,according to the characteristics of each process with different heat treatment conditions such as heating temperature,holding time and quenching medium,using dynamic mechanical analyzer(DMA)test for the measurement of damping performance,and by means of metallographic microscope,image J software,XRD(X ray diffraction)the structure analysis of the heat treatment test.The strain internal friction curves of the samples under different heat treatment processes show that when the strain amplitude is very low,the internal friction values of each sample are not very different under the same heat treatment process,and the internal friction values of each specimen increase monotonously with the increase of strain.Under the incomplete austenitization normalizing process,when the normalizing temperature is 825 ℃,the ductile iron has the best damping performance.Combined with the microstructure,the more pearlite content,the damping property of ductile iron under the incomplete austenitizing normalizing process is better.Under the isothermal quenching process,when the isothermal temperature is 240 degrees,the ductile iron has the best performance.Combining with the microstructure and XRD analysis,we know that the damping capacity is good when the number of ferrite is large,the grain size is small,the retained austenite content is small.Under quenching and low temperature tempering process,the damping capacity of ductile iron is different when quenching medium is different.When quenching medium is tap water,the damping capacity is relatively high,which the retained austenite of the specimen is the least.Compared with the cast microstructure,the morphology of heat treatment microstructure of ductile cast iron has changed a lot,comparing the strain internal friction curves of as cast ductile iron,it is known that the damping capacity of ductile iron is higher than that of other heat-treated ductile iron,which can further study whether the ductile iron can obtain higher damping capacity under other heat treatment conditions.