Evaluation method for cleanliness of metal

Chemistry: analytical and immunological testing – Optical result – With fluorescence or luminescence

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436 73, 436 78, 436127, 436177, 148508, 378 45, G01N 2164

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active

059856742

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

In conjunction with non-metallic inclusions contained in a metal, the present invention relates to an evaluation apparatus for cleanliness of a metal, and a method therefor, which quickly discharges non-metallic inclusions contained in a steel, for example, to the surface portion, detects the non-metallic inclusions accumulating the surface either chemically or physically, and accurately determines the proportion of the non-metallic inclusions in the metal as a total quantity evaluation or as an evaluation of principal components in accordance with a particle size distribution.


BACKGROUND ART

Hereinafter, the explanation will be given using steel as a typical example of a metal. Non-metallic inclusion particles existing in the steel include alumina type inclusions formed as the result of the reaction between oxygen in the steel and aluminum added in the case of an aluminum killed steel, slag type inclusions containing lime/silica, etc., and resulting from a steel making slag, powder type inclusions resulting from a casting mold lubricant in continuous casting, and so forth. Since these inclusions result in defects such as flows and breakage in intermediate products, during rolling of thin sheets, wire materials, etc., or in final products, evaluation of these inclusions by various methods have bean carried out in the past for the purpose of quality control.
If any defects are found in the final product, on the other hand, it is a serious problem to discard the product at the final stage from the aspect of the production cost because the product is produced through various production steps. It is therefore desirable to evaluate quality at an early stage of the production. Particularly because the existence of the inclusions is determined at the stage of refining/solidification of the metal, various evaluation technologies have been conducted in the past.
The evaluation technology of the inclusions of the steel among the metals is described, for example, in "Steel Handbook, 3rd Edition", II Pig Iron & Steel Making (edited by Japan Iron & Steel Institute of Japan, published by Maruzen, Oct. 15, 1979). Examples of the evaluation methods include a total oxygen (T[O]) method based on the oxygen concentration in the steel, a slime method by electrolytic extraction used for evaluating large inclusions, a microscopic method for evaluating the inclusions by magnifying and observing the section of a metal, and so forth. Due to their respective features, these technologies are limited by the kind of inclusions as the investigation object and the sizes of the inclusions as tabulated in Table 1, and they are not free from the problem, either, that a long time is necessary depending on the evaluation method.
It is known that information of intermediate products is not sufficient so as to estimate the product defects. In other words, as shown in Table 1, the conventional means involves the problems that the evaluation sample does not sufficiently represent the quality of the intermediate product and a long time is necessary for the evaluation of the sample, and those methods which invite excessively great super-heat during melting such as an EB (electron beam melting) method involve the problem that the inclusions are denatured during evaluation.
The slime method has been widely employed as a method having relatively high accuracy, but an extremely long time of several days to dozens of days is necessary to electrolyze about 1 kg sample as a whole.
When the evaluation is made by a small amount of metal sample, a metal piece sample of a part of large amounts of metal is evaluated. Therefore, to strictly evaluate the cleanliness of the whole metal, a large number of samples must be collected from the same metal piece, and the problem to be solved is to speed up the evaluation of the cleanliness.


TABLE 1 __________________________________________________________________________ particle diameter evaluation quantity name of inclusions & necessary time others _______________________________________

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