Effect Of Modified Ultra-fine Ceramic Powders On The Properties Of HT250

Gray cast iron is one of the most widely used cast metal materials in modern industrial production.Due to the good casting performance,excellent cost performance and many other advantages,gray cast iron has been widely used in various fields.With the development of industrial technology,the performance requirements of gray cast iron are also getting higher and higher,not only need to have a good wear resistance property,but also need a good thermal fatigue resistance.Therefore,it is urgent to improve the performance of gray cast iron by continuous research and improvement.As the high melting point,high hardness and good compatibility with liquid metal and many other advantages,modified ultra-fine ceramic powders have been used into the strengthening and toughing field of gray cast iron.In this paper,the HT250 gray cast iron is taken as the object of study.The influence on microstructures,mechanical properties,wear resistance and thermal fatigue resistance of HT250 by different amounts and kinds of modified ultra-fine ceramic powders is under discussed.Comparing with the test results of original sample and powder-modified sample,the strengthening and toughening mechanism of HT250 by ceramic powders is preliminary analysis.The results show that the comprehensive performance of powder-modified HT250 gray cast iron has been effectively improvedFor the HT250 with A,B and C three different kinds of modified ultra-fine ceramic powders:The microstructures of HT250 have been significantly refined with powder addition.The length and the head of graphite are shorter and smoother respectively,the majority of the graphite is A-type.The number of eutectic cells increase obviously and little change in the matrix.Powder A is the most effective among these three powders.The hardness of HT250 gray cast iron with powder addition is improved slightly;however,the tensile strength is improved obviously.The strengthening effect of powder A is the most significant,the hardness and tensile strength compared with the original sample are increased by 8.1%and 36.9%respectively.The wear resistance of powder-modified HT250 gray cast iron is improved,which powder A is the most effective.The wear loss at load 300N and 150N is reduced by 47.2%and 45.5%compared to the original sample.The average wear surface scratch depth is reduced by 47.9%.The thermal fatigue cracks of sample with powder C is the shortest,which has the best thermal fatigue resistance.Sample with powder C shows the worst thermal fatigue resistance.For the HT250 with 0.2%,0.4%and 1%three different amounts of modified ultra-fine ceramic powders:With the increase of powder amounts in HT250 gray cast iron,the graphite is shorter and shorter and a lot of needle graphiteappears in the matrix.There is a certain amount of ferrite appears in the matrix,the pearlite interlamellar spacing becomes smaller;the number of eutectic cells gradually increased and the grain size becomes more and more small.The hardness and the tensile strength of HT250 gray cast iron with powder addition is improved obviously.The mechanical properties improve significant when the powder mass fraction is 1%which the hardness and the tensile strength compared to the original sample are increased by 10.8%and 16.2%.The wear resistance of powder-modified HT250 gray cast iron is improved with the increase of powder mass faction,which the 1%powder content is the most effective.The wear loss at load 300N and 150N is reduced by 55.4%and 60.9%compared to the original sample.The average wear surface scratch depth is reduced by 72.9%.When the mass fraction of the powder is 1%,the thermal fatigue resistance of HT250 gray cast iron is the best.In this condition,the length of thermal fatigue crack is the shortest,crack is fine and the surface crack is not clear.