Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
1999-03-16
2001-02-20
Jenkins, Daniel J. (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S654000, C148S662000, C148S664000
Reexamination Certificate
active
06190472
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for soft annealing of high carbon steel.
Soft annealing normally takes 12 to 48 hours time and is performed either batchwise or continuously in an oven. The load in the oven is then heated to about 800° C. which takes between 2 and 10 hours, the temperature is maintained for about 2 hours, the temperature is then quickly brought down to about 790° C. and then down to about 690° C. at a rate of about 10° C. per hour.
This procedure is very time consuming, costly and may result in decarburization.
Further, because of different conditions at different locations in the oven, the structure will vary substantially between the objects, and also within one and the same object. A test of a batch of tubes of standard steel, SAE52100, showed that the hardness varied between 170 and 220 HB, depending on where in the oven the respective tube was placed.
When soft annealing a batch of tubes, one tube can be subjected to different conditions over its length, resulting in thermal stresses, and in a considerable distortion at the subsequent hardening.
There is a great need of reducing the costs involved in the soft annealing process for high carbon steel. However, the structure of steel after the soft annealing process is of critical importance for subsequent procedures and for the intended use. Many attempts have been made to develop the soft annealing procedure in different aspects.
According to JP04103715-A (Sumitomo Metals Ind.) high carbon chrornium bearing steel is subjected to spheroidizing treatment; first by heating to 780-820° C. and cooling to below Arlb point at less than 200° C./hr and by heating to Aclb-(Aclb+40)° C., cooling to below Arlb at less than 200° C./hr, heating to Aclb-(Aclb+40)° C. and cooling to below Arlb at less than 75° C./hr. This publication deals mainly with the structure of the steel, and does not teach how to solve the problems discussed above.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of this invention to avoid or alleviate the problems of the prior art.
It is further an object of this invention to provide a method for soft annealing of objects made of a high carbon steel with which the above mentioned drawbacks are eliminated.
More specifically, one object of the invention is to shorten the process time and to make possible an in-line operation, while obtaining a very small decarburization.
Another object is to provide a method for soft annealing high carbon steel which gives little or no pearlite at the surface, and which results in fewer and smaller carbides at the surface, and a smaller structural gradient.
Yet another object is to provide a method of soft annealing which can be performed in-line, and wherein the objects are exposed to identical conditions, and thereby an unitary structure and unitary characteristics are obtained.
It is an aspect of this invention to provide a method for soft annealing high carbon steel articles comprising:
hot forming an article of high carbon steel;
cooling the hot formed article to a temperature at least 20° C. below the Al temperature;
heating the cooled article to a temperature at least 20° C. above the Al temperature;
quickly cooling the heated article below the Al temperature;
heating the cooled article to a temperature at least 20° C. above the Al temperature;
cooling the heated article to about 740° C.;
cooling the said article down to about 690° C. at a cooling rate of a maximum of 3.5° C./min; and
cooling to ambient temperature.
REFERENCES:
patent: Re. 27505 (1972-10-01), Grange et al.
patent: 3178324 (1965-04-01), Grange et al.
patent: 3432368 (1969-03-01), Nakamura
patent: 3762964 (1973-10-01), Kranenberg
patent: 4030944 (1977-06-01), Sommer et al.
patent: 4067756 (1978-01-01), Koo et al.
patent: 4971634 (1990-11-01), Shibata et al.
patent: 5653826 (1997-08-01), Koo et al.
patent: 5827379 (1998-10-01), Okamura et al.
patent: 5830285 (1998-11-01), Katayama et al.
patent: 5900075 (1999-05-01), Koo et al.
patent: 5958158 (1999-09-01), Kron et al.
patent: 0 098 344 (1984-01-01), None
patent: 4103715 (1992-04-01), None
patent: WO83/04267 (1983-12-01), None
Patents Abstracts of Japan, Publication No. 01234519, Sep. 19, 1989.
A.T. Bykadorov, “Spheroidizing of rolled sections of 20G2R steel,” Oct. 1984, pp. 446-448, XP002106012.
E. Doluhnkov et al., “Effect of Preliminary Quenching of Spheroidization of Carbides,”Metal Science and Heat Treatment,vol. 17, No. 3/4, 1975, pp. 211-213, XP002106013.
Larsson Staffan
Lund Thore
Olund Patrik
Burns Doane Swecker & Mathis L.L.P.
Coy Nicole
Jenkins Daniel J.
Ovako Steel AB
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