Metal Casting Technologies : Whos who September 2012
42 www.metals.rala.com.au TEcHNicAL fEATURE Substitution for ferrite-pearlite Grade ISO 1083/500-7 In the 500/7 (FCD 50) intermediate grade the matrix structure can vary from near fully ferritic to near fully pearlite in different sections of the same casting, and there is also similar variation between castings situated at different positions in multi-cavity moulds. This variation not only gives rise to variations in mechanical properties within and between castings but also causes considerable difficulties in machining. Detailed studies in Sweden have shown that conventional 500/7 can be safely replaced by an as-cast fully ferritic iron with %Si levels of 3.6- 3.85% for components such as front axle housings for load dumpers and front wheel hubs for trucks [5, 6]. Mechanical testing  has revealed that the Si strengthened fully ferritic material is slightly tougher that ferritic-pearlitic iron having the same tensile strength (Figure 4) and that fatigue properties are equivalent. The 3.7%Si grade is now standardized as ISO 1083/ JS/500/10; one example of its use is in hydraulic rotators where it has given 75% reduction in hardness variation within castings resulting in a 30% increase in cutting tool life . Heavy castings for wind power The demand for alternative green sources of energy has lead to the rapid development of the wind power industry, notably in Europe, together with a demand for reliable and safe performance from cast components in Grade 400/18LT ferritic DI [7, 8, 24-26]. The LT denotes the requirement for the iron to satisfy an average V-notched Charpy value of 12J when tested at -20oC . Low temperature toughness is critical in wind turbines located in N. Europe, China, N. America, etc and offshore to cope with exposure to severe weather. Large Fig 4. Charpy V notch impact properties for higher Si ferritic ductile irons compared with conventional grades 400/15 (ferritic) and 500/7 (ferrite +pearlite) [6, 22]. Fig 5. Form of “chunky” graphite in heavy section ductile iron  THE DEMAND fOR ALTERNATiVE GREEN sOURcEs Of ENERGY HAs LEAD TO THE RAPiD DEVELOPMENT Of THE WiND POWER iNDUsTRY, NOTABLY iN EUROPE, TOGETHER WiTH A DEMAND fOR RELiABLE AND sAfE PERfORMANcE fROM cAsT cOMPONENTs iN GRADE 400/18LT fERRiTic Di.
Whos who September 2011