How Does Alloying Affect Microscopic Structure and Properties?
SILICON: Promotes ferrite. High silicon ductile irons (Si>4.0%) are resistant to oxidation but are increasingly more brittle with increased silicon content. Within 1 to 4 percent range silicon markedly increases the strength of ferrite. For this reason ferritic ductile irons – annealed or as-cast – should, normally contain at least 2.75 percent of this element. Exceeding the 2.75 percent limit is not desired in cases where the need for a high impact resistance is clearly indicated. MANGANESE: Promotes pearlite, harden-ability, and carbides. Because of the last, it is seldom desired for alloying. NICKEL: Promotes pearlite, bainite and harden-ability without the disadvantages of manganese. Promotes austenite at high concentrations. CHROMIUM: Promotes harden-ability and carbides. Use is limited to carbide containing grades (such as austenitic grades). COPPER: Promotes pearlite and harden-ability. Its use is controlled for developing high strength pearlitic grades. TIN: Acts similarly to c
