Method of making ductile cast iron with improved strength
AssigneeFord Motor Company
InventorsBela V. Kovacs, Roman M. Nowicki, Charles A. Stickels
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Abstract
A method of making ductile cast iron with a matrix of acicular ferrite and bainite is disclosed. A melt by weight of 3.0-3.6% carbon, 3.5-5.0% silicon, 0.7-5.0% nickel, 0-0.3% Mo, >0.015% S, >0.06% P (remainder Fe) is subjected to a nodularizing agent and solidified. The iron is then heat treated by heating to 1575.degree.-1650.degree. F. for 1-3 hours, quenched to 400.degree.-775.degree. F. at a rate of at least 275.degree. F./min., held for 0.5-4 hours, and cooled to room temperature. The resulting ductile iron exhibits a yield strength of at least 80 ksi, a tensile strength of at least 140 ksi, elongation of at least 6%, and a hardness of at least 270 BHN.
Claims9
A method of making a ductile cast iron having a microstructure with a matrix consisting of ferrite and bainite, said cast iron exhibiting a tensile strength of at least 140 ksi, a yield strength of at least 80 ksi, and an elongation of 6-10%, the method comprising:
- (a) melting a ferrous alloy consisting essentially of by weight 3.0-3.6% carbon, 3.5-5.0% silicon, 0.7-5.0% nickel, 0-0.3% molybdenum, 0.2-0.4% manganese, not greater than 0.06% phosphorus, not greater than 0.015% sulphur, and the remainder essentially iron, said melted ferrous alloy being subjected to a nodularizing agent to form a ductile cast iron upon solidification and cooling;
- (b) heat treating said ductile cast iron by heating to 1575.degree.-1650.degree. F. for a period of 1-3 hours and immediately quenching to 675.degree.-750.degree. F. at a rate of at least 275.degree. F./min.;
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- (c) holding said ductile cast iron in the temperature range of 400.degree.-775.degree. F. for a period of 0.5-4 hours followed by cooling to room temperature.
A ferritic-bainitic ductile cast iron composition, consisting essentially by weight of 3.0-3.6% carbon, 3.5-5.0% silicon, 0.7-5.0% nickel, 0-0.3% molybdenum, 0.2-0.4% manganese, less than 0.06% phosphorus, less than 0.015% sulphur, 0.02-0.06% magnesium, and the remainder essentially iron, said composition being particularly characterized by a microstructure having a matrix with 70-85% bainite, 15-30% acicular ferrite, and 0-2% massive austenite, the graphite nodules being dispersed throughout the matrix.
A method of making a ductile cast iron having a microstructure with a matrix consisting essentially of ferrite and bainite, said cast iron exhibiting a tensile strength of at least 140 ksi, a yield strength of at least 80 ksi, and an elongation of 6-10%, the method comprising:
- (a) melting a ferrous alloy comprising by weight 3.0-3.6% carbon, 3.5-5.0% silicon, 0.2-0.4% manganese, and the remainder essentially iron except for the presence of selected bainite formers and low phosphorus and sulfur, the melted ferrous alloy being subjected to a nodularizing agent to form ductile cast iron upon solidification and cooling;
- (b) heat treating said ductile iron by heating to 1575.degree.-1650.degree. F. for a period of 1-3 hours and immediately quenching to 675.degree.-750.degree. F. at a rate of at least 275.degree. F./min;
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- (c) holding said ductile iron in the temperature range of 400.degree.-775.degree. F. for a period of 0.5-4 hours followed by cooling to room temperature.
Dependencies are inferred from the claim text.