The Study On Microstructure And Mechanical Properties Of Hypoeutectic Gray Cast Iron Using Thermal Analysis

Gray cast iron as an important casting materials account for 70% of the world's production,with good machinability,wear resistance,shock resistance,low cost and strong casting,long Automotive parts and industrial machines are widely used.In the casting of gray iron pieces,due to composition,pouring temperature and cooling rate change affected the casting solidification and the organization and casting mechanical properties.Therefore,the thermal analysis was used to the study the solidification processes of hypoeutectic gray iron pieces under different cooling conditions,besides,the microstructure and properties of the specimen were studied.After analyzing the regularity and relationship between the mechanical properties and the thermal analysis parameters,thermal analysis of the criteria for strength limit is established;provide the basis for casting production process design and optimization.First,hypoeutectic gray cast iron was used as the research object in this paper,and the different pouring temperature and different cooling rate were controlled to conduct the test.The thermal analysis curves of each specimen were obtained,and he thermal analysis curves were analyzed by differential analysis.The results show that the solidification process provides data reference,and the metallographic observation of casting design under different cooling conditions is carried out.The microstructure characteristics such as eutectic size and austenite dendritic arm spacing are obtained by using the truncation method.The mechanical properties are designed to obtain different stress limit of castings under the cooling conditions.Second,the thermal analysis method was used to analyze the solidification process of the casting under different cooling conditions and the difference of the thermal analysis characteristic,and the influence of different cooling rate on the solidification thermal analysis characteristic of the casting after get rid of the maximum temperature difference is discussed.In addition,in order to make the thermal analysis method better describe the solidification process of the casting,two important parameters are proposed: the eutectic solidification time(35)tES and the actual solidification end temperature difference(35)T2.Third,through the metallographic experiments of the castings under different cooling conditions,it is found that the increase of the cooling rate makes the form of the graphite inside the casting become small,the bending,the austenite dendritic spacing and the austenite dendrite size decrease,The number of eutectic is not only increased,the average size from 489 mm reduced to 192.3 mm.With the increase of pouring temperature,the graphite morphology is coarser,straight,and the austenite dendrites are increased,and the spatial network structure is simplified.The number of eutectic groups decreases and the average size increases from 253.5 mm to 317.8 mm.Finally,from the study of the specimen solidification process of different pouring temperature and different cooling conditions,the relationship between eutectic precipitation undercooling(35)T1 and compressive strength,eutectic recalescence temperature(35)TR and tensile strength are respectively related,therefore,this paper has a nonlinear relationship between compressive strength and(35)T1,tensile strength and(35)TR were established respectively.The results of the study combine the thermal analysis with the prediction of the microstructure and mechanical performance of the castings to provide the basis for the design and optimization of the casting process in the casting production and improve the quality of the castings finally.