Pearlite Refining Strategies for Hypoeutectic Gray Cast Iron

Pearlite refining is one of the most used methods to increase the strength of cast irons, and it can be achieved using different strategies. In this work, three strategies to obtain pearlite refining were applied to a given hypoeutectic gray cast iron centrifuged in a coated steel mold: (1) increasing the Cu, Mo and Cr contents; (2) intensifying the cooling rate of the metallic mold; and (3) cooling of the cast iron with forced air. Strategies 2 and 3 aimed to increase the cooling rate during the eutectoid reaction. Then, four experiments were conducted: a reference experiment and other three applying separately the strategies above. Materials samples were characterized by optical metallography, chemical analyses, microhardness, pearlite interlamellar spacing measurements and tensile tests. The metallographic examination did not show any important change in the graphite morphology. The pearlite interlamellar spacing and microhardness were computed as distribution curves from at least thirty measurements in the materials matrices. These curves showed a decrease in pearlite interlamellar spacing and an increase in pearlite microhardness for the three materials in which the pearlite refining strategies were applied as compared to the reference material. The mean pearlite interlamellar spacings were reduced from 0.10 μm for the reference material to 0.07 μm, 0.08 μm and 0.08 μm for the materials in which strategies 1, 2 and 3 were applied, respectively. The UTS increased from 378 MPa for the reference material to 423 MPa, 418 MPa and 390 MPa for the strategies 1, 2 and 3, respectively.