Hardenable cast iron and the method of making cast iron

Details Hardenable cast iron and the method of making cast iron Hardenable cast iron and the method of making cast iron

1985-09-05

1987-05-19

Rutledge, L. Dewayne

Metal treatment

Compositions

Heat treating

148 3, 148138, 148321, C21D 100

Patent

active

046665331

ABSTRACT:
A method is disclosed for forming a surface hardenable cast iron article by development of metastable retained austenite in the cell boundary of a ductile or semiductile cast iron. The method comprises (a) controlling the solidification of a cast iron melt to extend the eutectic arrest time to 4-12 minutes, the melt having by weight percent a carbon equivalent (carbon plus one-third silicon) equal to 4.3-5.0, manganese 0.55-1.2, nickel 0.5-3.0, and the remainder essentially iron, the melt having been treated to form cell boundaries in the solidified iron with a high proportion of the manganese being segregated in the cell boundaries; (b) subjecting the solidified cast iron to an austempering heat treatment to permit the segregated manganese in the cell boundaries to form metastable retained austenite; and (c) terminating the heat treatment prior to the conversion of the metastable austenite to a stable microstructure. To obtain the benefits of wear resistance, the method further comprises using the heat treated cast iron by stressing a surface region thereof and transforming the microstructure of such surface region to martensite.

REFERENCES:
patent: 2885284 (1957-08-01), Moore
patent: 4096002 (1978-06-01), Ikawa et al.
patent: 4484953 (1984-11-01), Kovacs
"Describing the Eutectoid Transformation and Hyper-Eutectic Ductile Cast Irons", Lalich and Loper, AFS Transactions, 1973, pp. 238-244.
"An Investigation of the Effects of Alloying Elements in White Cast Iron, Frich and Lindsay, AFS Transactions, 1974, pp. 65-70.
"Isothermal Transformation of Cementite in Ductile Iron", Datta and Engel, AFS Transactions, 1974, pp. 267-278.

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