METHOD OF MAKING DUCTILE CAST IRON WITH IMPROVED STRENGTH

摘要

A method of making ductile cast iron with a matrix of acicular ferrite and bainite. A melt by weight of 3.0-3.6% carbon, 3.5-5.0% silicon, .7-5.0% nickel, 0-.3% Mo, > .015% S, > .06% P (remainder Fe) is subjected to a nodularizing agent and solidified. The iron is then heat treated by heating to 1575-1650F for 1-3 hours, quenched to 400-775F at a rate of at least 275F/min., held for .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.