Representation Of The Graphite Morphology Of Cast Iron Alloy And Control Research

Vermicular cast iron was widly used in national defense and civil use, as a very important engineering material, which had excellent properties,such as strength and plasticity, thermal fatigue resistance and thermal conductivity.With the rapid development of engineering equipment technology and high reliability requirement,for instance automobile,engine and turbine blade etc.the hot-end components of the cast iron worked under the higher temperature. So it was very urgent to improve the percentage of vermicular graphite of vermicular cast iron(more than 80%) to derived heat as quick as possible, avoided the influence of high temperature environment on normal operation and service life. The percentage of vermicular graphite of vermicular cast iron uneasy controlled and caused products unqualified in production, it serious affect the credibility of manufacturers and waste of material. A new process was established to forecast the percentage of vermicular graphite, if the percentage of vermicular graphite can not meet requirement with post vermicular graphite before pouring and after creep treatment. It was really effective in science and industrial applications.There were some shortcomings, such as the percentage of vermicular graphite poor, distridution condition badly and the graphite morphology could not be controlled.The differentce of three kinds of cast iron was analyzed by using thermal analysis technique, There was a mew method, which could predict the types of cast iron and establish a model between the percentage of vermicular graphite and the characteristics of thermal analysis curve of characters then verification.Secondly, The influence of fade time on the vermicular ratio, length-diameter ratio and hardness was studied, the technique controlled the percentage of vermicular graphite. Thirdly,the graphite morphology and mechaincal properties of vermicular cast iron were studied. The main results obtained as following:(1) The characteristics of thermal analysis curve of distiguished the characters of vermicular graphite iron were distiguished with that of ductile iron and gray iron. When the different between liquidus temperature and eutectic temperature was equal to or more than 20 ℃, it produced gray cast iron. When the eutectic recalescence was less than 5℃, it produced ductile iron,which could predict the percentage of vermicular graphite,expression of model as follow:Aaccording to experimental verification and enterprise production, the error was less than 10%.(2) Creep recession had a great effect on graphite morphology. The research showed that the number of spheroidal graphite gradually increased and the percentage of vermicular grapgite with the prolonged fading time. There were some synusia graphite, when creep recession occurred,the time was more than 500s before pouring and after creep treatment. The percent of pearlite content decreased and hardness reduced with the prolonged fading time.(3) The post vermicular graphite could improve graphite and block creep recession. When the first and post adding amount of magnesium rare earth were equal to 0.22% and 0.05%-0.20%,the percentage of vermicular graphite increased and then decreased,while aspect ratio reduced.When the second adding amount of magnesium rare earth was 0.10%, the percentage of vermicular graphite was equal to 93.7%,aspect ratio reduced to 7.5. When the first and adding amount of magnesium rare earth was more than 0.30%, the results are reversed.when the first and post adding amount of magnesium rare earth were eaual to 0.30% and 0.05%-0.20%,the percentage of vermicular graphite reduced gradually,spheroidal graphite improved quickly,aspect ratio increased from 8.31 to 10.45.(4)The influence of adding amount of magnesium rare earth on the percentage of vermicular graphite,aspect ratio,distribution condition of graphite particles and shape factor of vermicular graphite. When the adding amount of magnsium rare increased from 0.22% to 0.55%, the percentage of vermicular graphite gradually decreased from 97.76% to 55.21. Distribution condition of graphite particles rapidiy decreased from 83.5% to 32%, almost show a lineariy. The aspect ratio reduced from 8.51 to 4.61. When adding amount of magnesium rare earth improved from 0.22% to 0.32%,the shape factor of graphite slowly decreased from 17.23 to 10.81.Adding amount of magnesium rare earth increased continuousiy to 0.50%,The aspect ratio decreased to 9.11.When adding amount of magnesium rare earth improved 0.55%. The aspect ratio sharply reduced 1.94.(5) The graphite morphology was related to mechanical property in vermicular cast iron. The tensile strength and extensibility increased first and then decreased with the extending percentage of vermicular graphite,tensile strength and extensibility reached the maximum value (365MPa and 3.6%),when the percentage vermicular graphite was equal to 82%. With the distribution condition of graphite particles improved, the tensile strength increased and then decreased.when the percentage of distribution condition of graphite was 54%, the tensile strength and extensibility were equaled to the maximum (365MPa and 3.6%). The tensile strength of vermicular graphite reduced gradually as aspect ratio increased. The tensile strength and extensibility reached the maximum (365MPa and 3.6%).When the aspect ratio of graphite was equal to 6.65, the tensile strength and extensibility of vermicular graphite decreased gradually with shape factor improved,the tensile strength and extensibility were equaled to the maximum (467.5MPa and 7.2%), when the shape factor increased.