Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1997-12-11
1999-05-04
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148662, 148332, 148320, C21D 600, C22C 3842, C22C 3844
Patent
active
059000821
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION OF INVENTION
This invention relates to a method of making a heat treated steel casting and to a heat treated steel casting.
It is known to make steel castings of a low alloy steel by casting in air followed by a solution heat treatment, then quenching and finally tempering the casting. Whilst such castings may have relatively good toughness, as obtained by Charpy impact test, a relatively high hardness is not achieved. For example, whilst toughness may lie in the range 10-40 (V-notch Charpy), a hardness of only about 300-350 Brinell may be obtained.
The above mentioned properties may be improved to a limited extent by utilising techniques such as vacuum induction melting but high hardness with high toughness is not achieved. However, this form of bulk casting production is not practical.
Objects of the invention are to provide a method of making a heat treated steel casting and a heat treated steel casting which overcomes or reduces the above mentioned disadvantages.
According to one aspect of the invention we provide a method of making a heat treated steel casting comprising the steps of taking an "as-cast" steel casting comprising not more than 0.2% carbon, a total alloy content of less than about 4%, a carbon equivalent, as herein defined, lying in the range 0.45-0.7 after cooling subsequent to and performing a heat treatment operation by re-heating the casting to a temperature above the AC.sub.3 temperature to homogenise the casting, then cooling the casting to an inter-critical temperature lying between the AC.sub.3 and AC.sub.1 temperature and then quenching to room temperature.
The method of making a heat treated steel casting, may comprise the step of performing a castings operation to make said "as-cast" steel casting and then performing said heat treatment operation.
Preferably the heat treatment operation is performed without any intervening step between said casting operation and said heat treatment operation other than said step of cooling subsequent to casting.
The casting may be re-heated, after said cooling after casting, to a temperature lying in the range of room temperature to about 350.degree. C.
The casting may be heated to a temperature lying in the range 900.degree. C. to 1100.degree. C. and preferably about 1050.degree. C. to homogenise the casting.
The thus homogenised casting may then be cooled to a temperature lying in the range 700.degree. C. to 800.degree. C. at a rate lying in the range 2.degree. C. per minute to 10.degree. C. per minute, or 2.degree. C. per minute to 6.degree. C. per minute or about 5.degree. C. per minute.
The homogenised casting may be furnace cooled to said temperature lying in the range 700.degree. C. to 800.degree. C.
The casting may be quenched to about room temperature by quenching at a water quenching rate and preferably by quenching the casting to about room temperature in water.
The casting may comprise 0.10%-0.20% carbon or 0.15% to 0.2%, carbon.
The casting may comprise a steel and including Mn, Cu, Ti, W
The casting may comprise a steel comprising:
The steel of which the casting is made may be conventionally melted and cast, for example, in air.
According to a second aspect of the invention we provide a casting when made by the method of the first aspect of the invention.
According to a third aspect of the invention we provide a heat treated steel casting comprising not more than 0.2% carbon, a total alloy content of less than about 4%, a carbon equivalent, as herein defined, lying in the range 0.45 to 0.7 and which has been heat treated, after casting and then cooling, by re-heating the casting to a temperature above the AC.sub.3 temperature to homogenise the casting, then cooling the casting to a inter-critical temperature lying between the AC.sub.3 and AC.sub.1 temperature and then quenching to room temperature.
The casting after said heat treatment, may comprise a two-phase structure comprising retained austenite and ferrite and at least one of an acicular bainite, acicular ferrite, bainitic ferrite and optionally martensite.
The
REFERENCES:
patent: 4398970 (1983-08-01), Marder et al.
Analysis of Intercritical Heat Treatment of Cast Steels, Journal of Heat Treating, vol. 1, No. 2, 1989, Robert C. Voight.
Mechanical Properties of Ferritic--Martensitic Structures of a 0.2% C Steel with Different Distribution of the Phases, Zeitschrift Fur Metallkunde, Jun. 1988, Karl Heinz Zum Gahr and Michael Rosenheinrich.
Patent Abstracts of Japan No. 04160111, Jun. 3, 1992, Heat Treatment for Cast Steel Product, Kubota Corp.
Patent Abstracts of Japan No. 07102316, Apr. 18, 1995, Heat Treatment for Steel Casting, Kubuto Corp.
NACO, Inc.
Yee Deborah
LandOfFree
Method of making a heat treated steel casting and a heat treated does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of making a heat treated steel casting and a heat treated, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of making a heat treated steel casting and a heat treated will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1867768