The Simulation Studies Of The Influences Of Cooling Rate On The Microstructure And Mechanical Properties Of Heavy Section Ductile Iron

This paper used the method of physical simulation,poured two cubes casts(the side length is 400mm),one of them has a cold iron,the other one don’t have cold iron,and records the solidification curves in different positions of them with a thermocouple.Then sample from different positions of the two casts to study the influence of cooling rate on the microstructure and properties of heavy section ductile iron.From the solidification curves we can see:the solidification time of the center of the cast without cold iron is 270 minute,the solidification time of the center of the cast with cold iron is 90 minute,the temperature gradient is obvious,the chill effect of the cold iron is good.The influence of cooling rate on the graphite morphology has been studied,we can see:At the central axis of the cast 20mm from the surface,the spheroidizing level of the cast without cold iron is level 3,the Spheroidization rate is 80%,while the spheroidizing level of the cast with cold iron is level 1,the spheroidization rate is above 95%,the graphite in the center of the cast without cold iron has recessioned,spheroidal graphite is less than 5%,the cast with cold iron still has about 30%spheroidal graphite.The influence of cooling rate on the mechanical properties has been studied,we can see:at the central axis of the cast 20mm from the surface,the strength of the cast without cold iron is 384MPa,the elongation is 7%,the reduction of area is 11%,the brinell hardness is 144HBW.The strength in the center is 279MPa,the elongation and the reduction of area is nearly zero,the brinell hardness is 135HBW.While at the central axis of the cast 20mm from the surface,the strength of the cast with cold iron is 406MPa,the elongation is 31%,the reduction of area is 24%,the brinell hardness is 147HBW,the strength of the center is 310MPa,the elongation is 1%,the reduction of area is 2%,the brinell hardness is 144HBW.It is visible that cooling speed has a significant effects on the mechanical properties.Cooling speed has a significant effects on the impact toughnesses.The impact toughnesses of the cast with cold iron is bigger than the cast without cold iron,the biggest difference is in the center,at this position the impact toughnesses of the cast without cold iron at-60℃-40℃、-30℃、-20℃、-10℃、0℃ and 25℃ is larger 44J/cm2、52J/cm2、85.3J/cm2、100.1J/cm2、106 J/cm2、101J/cm2 and 97J/cm2。The ductile to brittle transition temperature of positions in cast with cold iron is almost-40℃ to-30℃,while positions in cast without cold iron is almost-10℃ to 0℃.