| The critical points and CCT curves of 34MnV steel used for crankshafts were tested byFormastor-F full-automatic transformation testing instrument. The CCT curves and themicrostructures at different cooling rates showed that the transformation products of34MnV were ferrite and pearlite when its cooling rate was lower than 0.1℃/s, while bainiteappeared when the rate was higher than 0.2℃/s. And the microstructure of 34MnV wasahnost martensite at the cooling rate of 20℃/s.The microstructures and the mechanical properties of 34MnV steel after different heattreatments were studied by Olympus-BX60M optical microscopy, Z050 automation tensiletester and JB-30B impact tester. The experimental evidences revealed that the strength andimpact toughness of 34MnV steel held at 900℃for 1 hour and furnace-cooling or held at900℃for 1 hour and air-cooling were enhanced obviously, however, furnace-cooling putemphasis on improving toughness of materials, and air-cooling emphasized theenhancement of strength. After austenitizing for two or three times, the strength of 34MnVwas increased, meanwhile, its impact toughness was improved further and its grain sizewas smaller.The crank austenitized at 900℃was cooled by water mist and the three dimensionaltemperature fields of the cooling process were simulated by means of ABAQUS software.The simulated results indicated that the inner of the crank was transformed into ferrite andpearlite, having better toughness. Furthermore, there existed bainite on the surface layer ofthe crank, whose strength was higher. Therefore this heat treatment process can provide thecrank with the excellent mechanical properties of strengthened surface and toughened inner, which meets working condition of materials well.
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