In order to meet the high temperature performance requirements of high power density diesel engine block and cylinder head materials,changes of mechanical properties and microstructure of high strength vermicular graphite cast iron for diesel engine cylinder head after different thermal exposure temperatures of 350,500℃and different holding time of 0-1000h were studied.The results show that after thermal exposure,the tensile strength Rm of the compacted graphite cast iron test piece decreases with the increase of holding time,and the elongation A increases with the increase of holding time.The tensile strength Rm(25℃)and elongation A25℃of the specimens at room temperature decreased by 20.0%and increased by 41.7%,respectively after thermal exposure at 350℃for 1000h.The high temperature tensile strength Rm(200℃)and elongation A200℃decreased by 20.2%and increased by 125%respectively compared with those without heat preservation.The room temperature tensile strength Rm(25℃)and elongation A25℃of the specimens exposed at 500℃for 1000h decreased by 46.7%and increased by 36.1%,respectively,compared with those without heat preservation.The high temperature tensile strength Rm(200℃)and elongation A(200℃)decreased by 14.6%and increased by 50%,respectively,compared with those without heat preservation.With the increase of thermal exposure time,the amount of pearlite in the matrix of compacted graphite cast iron gradually decreases,and the amount of ferrite gradually increases,which is the main reason for the change of microstructure and mechanical properties.
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