Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
1999-10-28
2001-02-13
Jenkins, Daniel J. (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S572000, C148S567000, C148S639000, C148S600000, C148S662000, C148S621000, C148S622000
Reexamination Certificate
active
06187118
ABSTRACT:
This application is based on and claims priority under 35 U.S.C. § 119 with respect to German Application No. P 198 49 679.6 filed on Oct. 28, 1998, the entire content of which is incorporated herein by reference.
FIELD OF THE INVENTION
This invention generally relates to heat-treating work pieces. More particularly, the present invention pertains to a method for heat-treating by hardening roller bearing steel work pieces to be used in roller bearings.
BACKGROUND OF THE INVENTION
Steel work pieces, such as roller bearing parts, are subject to stringent demands with respect to strength, length of use and microscopic structural stability against aging. These work pieces require a material that in the machined state has a homogeneous microstructure with super finely-distributed globular carbides.
In order for a homogeneous microscopic structure to be achieved after heat treatment, the melting can be controlled in a special way in the manufacture of the material. This necessitates major effort and expense with respect to monitoring and control devices. It is also known to homogenize the microscopic structure after the melting annealing is performed. As a rule, this annealing extends over several hours.
Especially stringent demands are made of roller bearings intended for use in transmissions because the transmission oil that is used to lubricate the roller bearings becomes contaminated by metal abrasion. It has therefore been proposed that these bearings be sealed off or at least provided with an oil filter that is intended to keep the metal particles from reaching the interior of the bearing and in particular the races. It is also known to carbonitride these bearings. All of the provisions at present entail major effort and expense and are thus not particularly advantageous in practice.
A need thus exists for a method which, in a simple and relatively inexpensive way, achieves homogeneity of the material in the microscopic range and realization of a refinement of the globular carbides, thus allowing work pieces having such characteristics to be used in a variety of contexts, particularly under extreme conditions such as in roller bearings.
SUMMARY OF THE INVENTION
In light of the foregoing, one aspect of the invention involves a method of heat-treating a work piece of high-alloy steel by hardening that involves relatively briefly annealing the work piece before hardening, followed by cooling the work piece. The relatively brief annealing can be performed by electromagnetic induction.
By virtue of the relatively brief annealing that is performed before the actual hardening and the ensuing cooling, homogeneity of the material in the microscopic range is attained. Following the annealing, hardening of the work piece can be carried out, for instance by quenching in a salt bath, to achieve a super fine distribution of globular carbides in the microscopic structure with considerably reduced size as compared to the outset state. Also, the microscopic structure created by the method of the invention has improved toughness properties as well as increased microscopic structure stability to aging and leads to a longer service life.
According to another aspect of the invention, a method for heat-treating a roller bearing steel work piece used in a roller bearing involves heating the work piece to a temperature greater than about 1000° C. and less than the melting temperature of the work piece to anneal the work piece, cooling the annealed work piece, heating the work piece after cooling to an austenitizing temperature, and quenching the work piece that has been heated to the austenitizing temperature.
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patent: 4457789 (1984-07-01), Wilks
patent: 4973368 (1990-11-01), Lund
patent: 5861067 (1999-01-01), Hetzner
patent: 5906691 (1999-05-01), Burnett et al.
patent: 2023064 (1970-12-01), None
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Burns Doane Swecker & Mathis L.L.P.
Coy Nicole
Jenkins Daniel J.
SKF GmbH
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