Ferritic ductile iron (DI). grade 400-15 with a tensile strength R_m 400 MPa. and ferritic/pearlitie ductile iron. grade 500-7 with R_m 500 MPa, are widely used in the vehicle industry. To bring the hardness of conventional ductile iron to a certain level, and within narrow limits, makes considerable demands on the foundry's process control. The chemical composition, cool- ing rate and nucleation state of the melt require careful atten- tion. For given construction, with large variations in material thickness, a spectrum of different cooling rates is obtained that cannot be influenced by the foundry. These variations can only be prevented at the design stage.
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