Research On Microstructure And Properties Of Compacted Graphite Iron

There is an increasing demand on the transportation industry for environment sustainable transports. The development is forced by governmental decrees as well as customer requirements. The increasing of engine specific power resulting in higher and higher engine operating temperature, which puts higher demands on engine material performance. As to engine, a material with good thermal conductivity results in a lower and more even temperarure distribution in the engine and reduces thermal stresses. Consequently the combination of strength and thermal transport properties of the engine material has to be optimised. Compacted graphite iron (CGI) has high strength as well as nodular cast iron, and at the same time, its vibration, thermal capacity and casting performance are similar to gray cast iron. CGI can obtain high-strength at high carbon equivalent, thus it’s easier to produce lightweight thin-walled castings. So, CGI has been grown to be a research hotspot.The production process of CGI is very complicated, many factors can effect it. In this stuy, steel scrap, carbon agent and75FeSi were used under laboratory condition, and by means of controlling the amounts of vermiculizer and inoculation to produce CGI without carbides. The effects of time of compacted reaction and incubution, temperture, cooling rate to the graphite morphology were also discussed. Vermicularity is not the only factor to the degree of graphitization of CGI. The number and area of graphite, number of vermicular graphite are as important as vermicularity to the degree of graphitization.During the production, SG were used as to modify the CGI. The Optical Microscopy, FESEM were used to observe the microstructure, matrix structure of CGI. Tensile test measured the mechanical properties, FL4010measured thermal conductivity to analyse thermal properties. It is found that, after the addition of SG to the CGI, the degree of graphitization is improved, vermicularizing range is also broadened. And at the same time, SG modification can reduce the lamellar spacing of pearlite, increase the strength of cast iron, it can also greatly increase the thermal conductivity of CGI. Compared the performance of these properties with factory production, which is15.9L six-cylinder in-line diesel engine cylinder material, the CGI, modified by SG, has higher comprehensive performance.CGI was deep-etched with hydrochloric acid alcohol solution, after extraction, using FESEM to observe the three-dimensional morphology of vermicular graphite. The result shows that, as similar to ductile iron and gray cast iron, CGI is also composed of eutectic cell. In each eutectic cell, graphite is connected to each other and generates new branches, it surrounded around by metal. Vermicular graphite is not exist in isolation, it’s connected to each other with graphite surrounding branches that cross each other, forming as similar as coral formation, the structure is extremely complex branched polymers. It is this cluster of interconnected graphite-like structure, giving higher thermal conductivity of compacted graphite iron. Vermicular graphite has rug side, significantly layered structure, and the growth of blunt front end. CGI has complex structure, the presence are vermicular graphite, spherical graphite," spheroidal graphite with foot" and even blossom-shaped graphite.