Optics: measuring and testing – By dispersed light spectroscopy – With sample excitation
Patent
1996-10-09
1998-07-21
Nelms, David C.
Optics: measuring and testing
By dispersed light spectroscopy
With sample excitation
356 36, 356316, 356318, G01N 100, G01N 2163, G01N 2172, G01N 2173
Patent
active
057841535
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for rapidly and accurately detecting a cause of an abnormal portion present on a surface of a steel product.
BACKGROUND OF THE INVENTION
In addition to abnormal portions caused by flaws mechanically produced during a rolling process or the like, an abnormal portion may be produced on a surface of a steel product by means of a cause such as non-metallic inclusions in steel, powder added to molten steel in a mold during a continuous casting, brick chips entrapped into steel, or scales not separated. In order to prevent such an abnormal portion from being produced, it is necessary to rapidly and accurately detect a cause of such an abnormal portion and promptly eliminate the cause.
An abnormal portion on a surface of a steel product caused by non-metallic inclusions in steel is produced on the surface of the steel product in such a manner that non-metallic inclusions present in steel reach the surface of the steel product through a rolling, and are linearly rolled in the rolling direction. A cause of the abnormal portion can be clarified on the basis of an investigation of a difference in chemical composition between the abnormal portion and a normal portion in the vicinity of the abnormal portion.
More specifically, a chemical composition of an abnormal portion linearly elongated in the rolling direction, produced on the surface of the steel product, and a chemical composition of a normal portion in the vicinity of the abnormal portion are subjected to a linear analysis across these portions to compare the chemical composition of the abnormal portion with that of the normal portion in the vicinity of the abnormal portion. As a result, for example, when only such elements as Ca and Al which form non-metallic inclusions are detected with high concentrations in the abnormal portion, production of the abnormal portion can be estimated to be due to the presence of an Al.sub.2 O.sub.3 .multidot.CaO composite non-metallic inclusion. In the case where no particular element is detected with a high concentration in the abnormal portion, in contrast, production of the abnormal portion can be estimated to be due to the non-separation of scales or the rolling, whereby it is possible to eliminate the cause of production of the abnormal portion by the separation of scales or by investigating the rolling process or the like.
The foregoing linear analysis has conventionally been carried out by means of an electron beam radiation fluorescent X-ray microanalysis (hereinafter referred to as the "XMA") or an electron microscopic observation. The linear analysis based on such conventional methods requires, however, pretreatments such as a cutting of a sample to incorporate same into an analyzing instrument and a surface preparation of the sample for observing same, thus leading to a problem of requiring a long period of time for obtaining a result of analysis. Since the electron microscopic observation is a micro-observation, a problem is that the observation is one-sided and it is inevitable to overlook non-metallic inclusions or the like (hereinafter referred to as the "origins") present outside the field of view of the electron microscope.
As a means to solve the problems as described above, a method known as the discharge emission spectrochemical analysis is proposed. For example, Japanese Patent Provisional Publication No. 62-162,947 published on Jul. 18, 1987 discloses a method for detecting a cause of an abnormal portion, which comprises the steps of: sheet to continuously discharge-scan the surface of the steel sheet from a normal portion thereof toward an abnormal portion, and comparing intensity of an emission spectrum of the abnormal portion with intensity of an emission spectrum of the normal portion, both of which emission spectra have been obtained by means of the discharge-scanning (hereinafter referred to as the "prior art").
The discharge emission spectrochemical analysis of the prior art, involves the following problems: Electric discharge take
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patent: 3602595 (1971-08-01), Dahlquist et al.
patent: 3791743 (1974-02-01), Cody et al.
patent: 4598577 (1986-07-01), Jowitt et al.
patent: 4615225 (1986-10-01), Sainz
patent: 5537206 (1996-07-01), Akiyoshi et al.
Akiyoshi Takanori
Ishibashi Yohichi
Mochizuki Tadashi
Sakashita Akiko
Sato Shigeomi
Nelms David C.
NKK Corporation
Vierra-Eisenberg Jason D.
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