Electricity: measuring and testing – Magnetic – Susceptibility
Reexamination Certificate
2002-06-13
2003-05-06
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Susceptibility
C324S228000
Reexamination Certificate
active
06559635
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for nondestructively measuring and quantitatively determining deterioration in materials accompanying neutron irradiation, and the like, in a ferromagnetic construction material, or in a structure comprised of such materials.
2. Description of the Related Art
Conventional nondestructive inspection methods for aged material deterioration had generally aimed at investigating of initiation and growth of cracks in the material in almost every case. And thus, the direction of development in present nondestructive inspection methods lies in finding out produced cracks as minute as possible. Accordingly, with such a conventional nondestructive inspection method, it is practically impossible to inspect nondestructively aged deterioration of materials before the initiation of cracks.
By the way, it is generally considered that aged deterioration in a nuclear reactor pressure vessel goes on by combining precipitation of copper atoms, a dislocation loop etc, due to metal fatigue and neutron irradiation.
Another type of previous method is known for nondestructively determining deterioration of material strength due to aging of ferromagnetic construction materials or structures comprised of such construction materials. In this determining method, the coercive force and magnetic susceptibility in the range approaching to saturation of a determining object are measured.
Moreover, Japanese Patent Laid-open No. 2001-021538 discloses about aged deterioration due to metal fatigue of materials before the initiation of cracks. As described in this document, conventionally, the following nondestructive inspection method is known. That is, in the inspection method, the coercive force Hc and susceptibility coefficient c (Hereinafter referred to as a strength parameter c.) are measured. Then, from the strength parameter c, aged deterioration of strength in ferromagnetic construction materials or structures comprised of such the construction materials is determined.
Then, the inventor thought that if a nondestructive inspection for aged deterioration accompanying the change in brittleness of materials could be carried out by combining with the nondestructive inspection for aged deterioration accompanying the change in strength of materials, it would lead to much more improvement in the safety of a nuclear reactor pressure vessel. So the inventor focused attention on nondestructive inspection for determining aged deterioration accompanying the change in brittleness of materials.
However, it was impossible to apply the above-mentioned conventional nondestructive inspection method for aged deterioration of material strength to the nondestructive inspection method for aged deterioration accompanying the change in brittleness of materials due to precipitation of copper atoms and so on.
That is, conventional measuring objects are dislocations produced by metal fatigue. In such dislocations, anisotropic strain fields exist in the interior of materials. Therefore, it was possible to inspect nondestructive aged deterioration of materials by the conventional method measuring the coercive force Hc, because aged deterioration of material strength has much effect on the coercive force Hc.
On the other hand, in aged deterioration accompanying the change in brittleness of materials due to precipitation of copper atoms and so on, measuring objects are defects. The defects are atomic vacancies or interstitial atoms produced by irradiating neutron etc, or precipitation by heat treatment etc., and so on. In such defects, strain fields do not always exist in the interior of materials.
Therefore, aged deterioration accompanying the change in brittleness of materials hardly have much effect on the coercive force Hc. Accordingly, it was impossible to apply the method determining the coercive force Hc among above-mentioned nondestructive inspection methods for aged deterioration of material strength to determining of aged deterioration accompanying the change in brittleness of materials. Also, it was impossible to determine aged deterioration accompanying the change in brittleness of materials even by means of the conventional method obtaining the strength parameter c of the determining objects.
Accordingly, it is difficult to determine quantitatively embrittlement results from increase of precipitation of copper atoms and atomic vacancies.
Therefore, a new determining factor for examining quantitatively such embrittlement was necessary.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide an improved measurement method for nondestructively determining aged deterioration of ferromagnetic construction materials, which advantageously eliminates the above-mentioned problems of the prior art.
One aspect of the present invention resides in the method for nondestructively determining aged deterioration of ferromagnetic construction materials by quantifying the change in brittleness due to aging of the materials. The determining method according to the present invention includes the following steps.
One of the steps is to suppose to acquire an embrittlement coefficient b by measuring a magnetic susceptibility &khgr;
b
of the determining ferromagnetic construction material under a magnetic field having a predetermined magnetic field intensity H over a magnetic coercive force Hc of the determining material, and calculating an embrittlement coefficient b of the determining material by putting the magnetic field intensity H and the measured magnetic susceptibility &khgr;
b
of the determining material into an equation,
b=&khgr;
b
H
2
(1).
Another one of the steps is to obtain a correlation between an embrittlement coefficient b and a referenced embrittlement factor of the same kind of ferromagnetic construction materials as the determining material previously, the value of the referenced embrittlement factor changes corresponding to the change in brittleness of the same kind of ferromagnetic construction materials.
Further one of the steps is to obtain the values of the embrittlement coefficient b of the determining ferromagnetic construction material in the initial state and the deteriorated state by aging.
Further one of the steps is to determine the values of the referenced embrittlement factor corresponding to the values of the embrittlement coefficient b respectively, based on the correlation.
Further one of the steps is to quantify the change in brittleness due to aging of the determining ferromagnetic construction material by comparing the values of the referenced embrittlement factor.
The principle of the present invention will be described below with reference to experimental test data. To clarify the correlation between the mechanical property and the magnetic property of steel materials, test pieces consisting of polycrystalline pure iron (99.992% purity) involving copper atoms (1.5 wt/%) were used. By heat treatment of test pieces in various temperatures, the copper atoms are precipitated in the test pieces.
By above-mentioned treatment of the test pieces, a precipitating quantity of the copper atoms and the size of precipitates can be changed corresponding to the change of temperatures and time in heat treatment.
By the way, it is known that copper atoms are precipitated at the heat treatment temperature, that is, the aging temperature, from 445° C. to 650° C., and such precipitation of cupper atoms in materials is related to hardness of materials.
In this way, precipitation of copper atoms is related to hardness in materials because the hardness of steel materials increases by the precipitation of copper atoms preventing the movement of dislocations.
Then, in this experiment, as a result of test pieces heat-treated at each temperature (aging temperatures: 455° C., 550° C., 650° C.), as shown in
FIG. 4
, the correlation of heat treatment time (minute) and hardness (Vickers hardness Hv) was obtained in each temperature. Here, in
FIG. 4
, it is plotted in solid triangl
Iwate University
Knobbe Martens Olson & Bear LLP
Lefkowitz Edward
Zaveri Subhash
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