Method for preparing high silicon, low carbon austempered cast iron

A method of preparing an austempered cast iron, comprising:

• (a) melting a cast iron mixture containing
• (i) from about 1.6 to about 2.4 weight percent silicon, and
• (ii) from about 1.6 to about 2.2 weight percent carbon to form a homogeneous melt, said melt having a carbon equivalent from about 2.1 to about 3.0 weight percent;
• (b) pouring the melt into a mold to form a casting having eutectic carbide particles;
• (c) shaking out the casting to remove any residual mold sand;
• (d) altering the temperature of the casting to about 1650.degree.-1900.degree. F. and maintaining the temperature of the casting at about 1650.degree.-1900.degree. F. until substantially all of the eutectic carbide particles convert to temper graphite nodules to form a temper graphite-containing casting;
• (e) cooling the temper graphite-containing casting to about 1500.degree.-1750.degree. F. for about 1 to about 4 hours and maintaining the temperature of the temper graphite-containing casting at about 1500.degree.-1750.degree. F. until a fully austenitic matrix is achieved, and the matrix is saturated with carbon;
• (f) quenching the austenitic matrix casting to a temperature of about 460.degree. to about 750.degree. F. and maintaining that temperature until the casting is substantially transformed to an ausferritic matrix;
• and
• (g) cooling the ausferritic matrix casting to room temperature before a significant amount of bainite is formed.

A method of preparing an austempered cast iron, comprising:

• (a) melting a cast iron mixture containing
• (i) about 1.8 weight percent silicon,
• (ii) about 2.0 weight percent carbon, and
• (iii) 0.2-0.35 weight percent manganese to form a homogeneous melt;
• (b) pouring the melt into a mold to form a casting;
• (c) cooling the casting to a temperature below solidification;
• (d) shaking out the solidified castings to remove the mold and any residual mold sand;
• (e) heating the casting to about 1650.degree.-1900.degree. F. at a rate of about 500.degree. to 2000.degree. F. per hour and maintaining the temperature of the casting at about 1650.degree.-1900.degree. F. for about 2 to 8 hours until substantially all of the eutectic carbide particles convert to temper graphite nodules to form a temper graphite-containing casting;
• (f) cooling the temper graphite-containing casting to about 1500.degree.-1750.degree. F. at a rate of about 50.degree. to 500.degree. F. per hour and maintaining the temperature of the temper graphite-containing casting at about 1500.degree.-1750.degree. F. for about 1 to about 4 hours until a fully austenitic matrix is achieved, and the matrix is saturated with carbon;
• (g) quenching the austenitic matrix casting to a temperature between about 460.degree. to about 750.degree. F. at a rate of about 100.degree. to about 1000.degree. F. per minute by immersing the casting in a medium for about 0.25 to about 8 hours until the casting is substantially transformed to an ausferritic matrix;
• and
• (h) then cooling the casting to room temperature before a significant amount of bainite is formed.