Method of producing spheroidal graphite cast iron article

Details Method of producing spheroidal graphite cast iron article Method of producing spheroidal graphite cast iron article

1997-04-28

1999-03-02

Yee, Deborah

Metal treatment

Process of modifying or maintaining internal physical...

Heating or cooling of solid metal

148618, 148902, C21D 500

Patent

active

058765239

ABSTRACT:
A method of producing a spheroidal graphite cast iron article containing at least one pearlite stabilizing element selected from the group consisting of Mn, Cu, Sn, Sb and Pb and having a double layer structure which comprises a surface layer portion and an inner portion. The surface layer portion has a matrix 60% or more of which is ferrite phase and a thickness of at least 0.5 mm. The inner portion has a matrix substantially comprising pearlite phase. The method comprises: (1) heat-treating a starting spheroidal graphite cast iron at a temperature which transforms a whole part of a matrix of the starting spheroidal graphite cast iron substantially to austenite phase; (2) slowly cooling the austenitized spheroidal graphite cast iron at a cooling rate (5.degree. to 20.degree. C./min) which allows in a subsequent step the surface layer portion to be ferritized before the inner portion starts to be pearlitized; (3) holding the cooled spheroidal graphite cast iron at a temperature (710.degree. to 770.degree. C.) which allows the surface layer portion to be first ferritized and subsequently allows the inner portion to be pearlitized while preventing the ferrite phase of the surface layer portion from being transformed to another; and (4) cooling the spheroidal graphite cast iron thus transformed immediately after completion of the pearlitization of the inner portion.

REFERENCES:
patent: 4990194 (1991-02-01), Obata et al.
patent: 5346561 (1994-09-01), Obata et al.

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