Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-12-23
2001-11-20
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S620000, C073S629000
Reexamination Certificate
active
06318178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for evaluating the cleanliness of metallic materials. More specifically, the present invention relates to a method for evaluating the cleanliness of a metallic material to be tested by scanning predetermined inspection fields of the metallic material under test by ultrasonic flaw detection method to obtain data on non-metallic inclusions (for example, oxide, nitride, sulfide, etc.) included therein, and calculating estimated maximum non-metallic inclusion diameter in the metallic material to be tested from these data with predetermined equations.
The present invention also relates to a metallic material affixed with the evaluation of cleanliness described above.
2. Description of the Related Art
Recently, with the advancement in the metallurgical technology, cleanliness of metallic materials such as steel has been greatly improved, so that non-metallic inclusions of medium to large sizes beyond 20 &mgr;m are rarely included in metallic materials and sizes of the non-metallic inclusions present have also been decreasing. In this trend, it is becoming very difficult to detect large inclusions that occur accidentally or with an extremely low probability.
There is no technique capable of evaluating and ensuring cleanliness of metallic materials practically to cope with such a situation as described above.
A method for testing cleanliness of metallic materials that is currently a standard practice employs optical microscope observation. However, the area that can be covered with this method is as small as 1000 mm
2
, thus making the method utterly impractical for evaluating the cleanliness of metallic materials of high cleanliness as mentioned above (JIS G0555, ASTM E45, ASTMA 295, DIN 50602, ISO 4967, etc.).
On the other hand, such methods have been proposed that inclusions are extracted from a metallic material by acid dissolution with the particle size of the inclusion being evaluated under a microscope, or a metallic material is dissolved by Electron Beam Melting dissolution with the inclusions that float being observed under a microscope (Japanese Patent Application Laid-open No. Hei 9-125199, Japanese Patent Application Laid-open No. Hei 9-125200). However, in certain cases, as the inclusions dissolve into the acid or the inclusion itself fuses or coagulates, these methods also cannot be applied to the evaluation of cleanliness of metallic materials of high cleanliness.
The methods described above have also such a drawback as the inability to process quickly due to a long time required for the acid dissolution or other cause, and therefore are difficult to adapt to mass production processes.
In an industry where a metallic material of high cleanliness is processed as a raw material, strict machining processes are designed on the basis of assumption that the metallic material has a high cleanliness. When there are variations in the cleanliness of the metallic material, however, such problems as frequent occurrences of defective products result, thus leading to significant decrease in productivity.
In bearing steel, spring steel, steel to make power transmission shaft, gear steel and the like that bear high loads, for example, immature breakage may result from the presence of inclusions of sizes larger than a certain level. In such industries, therefore, there are demands for the supply of metallic materials that bear certification of high cleanliness thereof or that are guaranteed to have a certain level of cleanliness.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for evaluating the cleanliness of metallic materials, which is capable of adapting to the advancements in metallurgical technology that have been achieved recently and the significant improvement in the cleanliness of metallic materials such as steel.
Another object of the present invention is to provide a method for quickly evaluating the cleanliness of metallic materials, which is capable of adapting to the mass production processes of such metallic materials.
Further another object of the present invention is to provide a metallic material affixed with the evaluation of cleanliness thereof in compliance with the significant improvement in the cleanliness of metallic materials such as steel due to the advancements in metallurgical technology achieved recently.
The present inventors started with such an assumption that maximum inclusion diameter in a metallic material determines the basic workability of the metallic material.
However, it is very difficult for the conventional methods employing optical microscopes to determine the maximum inclusion diameter in a metallic material of a lot size of 1 kg to 2 tons or greater lots (for example 2 to 200 tons).
The present inventors have been studying a method for estimating the maximum inclusion diameter in a metallic material to be tested by such a procedure as microscopic observation area is set to standard inspection area of S
0
=100 mm
2
, n=30 to 60 pieces of samples are taken, and extreme value statistics technique is applied to the maximum inclusion diameters determined for the samples. But this method is not sufficiently reliable for estimating such large inclusions as mentioned previously, and is not practical for evaluating the cleanliness of metallic materials.
The present invention provides means for solving the problems described above, and is briefly described as claims. The nature, principle and utility of the invention will become more apparent from the following detailed description with reference to the accompanying drawings.
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patent: 5884685 (1999-03-01), Umezawa et al.
patent: 5887481 (1999-03-01), Leroy et al.
patent: 5955673 (1999-09-01), Leroy et al.
patent: 10002344-A1 (2000-08-01), None
patent: 11271282-A (1999-10-01), None
patent: 2000310620-A (2000-11-01), None
Kato Yoshiyuki
Nuri Yoshio
Takemoto Shoichi
Kanesaka & Takeuchi
Larkin Daniel S.
Miller Rose M.
Sanyo Special Steel Co., Ltd.
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