JPS6165155A - Instrument and apparatus for testing material - Google Patents

Abstract

PURPOSE:To measure the size of crystal grain non-destructively, easily, accurately and independently of the shape or the like of a member by applying highly intensive magnetic field to a martersitic cast steel material and detecting magnetic flux leaked from a crystal boundary. CONSTITUTION:A fixed electric power per unit volume is supplied from a control box 1 to the martensitic cast steel 6 through an electrode 5 to apply a fixed intense magnetic field. Consequently, magnetic flux is leaked from the crystal grain magnetic powder is attracted to the leaked magnetic flux and a magnetic powder pattern 10 appears. The magnetic powder pattern 10 is detected by an optical detector 8 and displayed on a display device 9. In this case, the peak interval of the reflected light, i.e. the interval of dense parts of the pattern 10, is proprotional to the size of macrostructure. On the other hand, the crystal grain size of the martensitic cast steel has a fixed relation to the size of the macrostructure. Thus, the size of the macrostructure can be found out from the interval of the magnetic powder dense parts of the pattern 10 and the crystal grain size can be calculated from the size of the macrostructure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a test method and apparatus for measuring the grain size of a martensitic cast steel material without destroying or damaging the material.

[Technical backbone of invention]

For materials made of stainless steel, the size of crystal grains directly affects the toughness and ductility of the material, and also serves as a criterion for determining whether sufficient heat treatment has been performed. Therefore, currently the Japanese Industrial Standards (JIs GO5'L1
) etc. also indicate the grain size as a grain size number.

By the way, stainless steel is classified into ferritic, martensitic, and austenitic based on total bending structure. When the material is austenitic or ferritic, the grain boundaries of crystal grains are exposed by etching in the metallurgical microstructure observation test, so the microscopic photograph of hemp is magnified about 100 times and this photograph is used for Japanese industrial purposes. By comparing with a reference photograph such as r6, the size of the crystal grains can be easily measured and evaluated. In addition, even if the material used in the λ1 test is the main body of a component product, it can be accurately measured by the Sumpp method or the like without destroying or damaging the material.

On the other hand, in the case of martensitic materials, grain boundaries do not appear when etching is performed in the dormitory test using a metallurgical microscope 1, so grain boundaries are revealed through heat treatment in a special atmosphere and under special conditions, such as carburizing. The grain boundaries are exposed through etching, which is then taken as a microscopic photograph at a magnification of about 100 times, and compared with a reference photograph to determine the size of the crystal grains.

[Problems with back die technology] As mentioned above, stainless steel is metallographically divided into ferritic, martensitic, and austenitic steels, but martensitic cast steel products are used for hydropower generation. There are products that are large and have complex shapes, such as water wheel liners used in places.

In recent years, as hydroelectric power generation equipment has become higher in head and more efficient, the stress applied to water turbine liners has become extremely high, and cast steel products are now operated under extremely harsh conditions.

High standards are required for materials and quality in order to withstand the conditions of refusal, and testing is required to determine whether they meet these standards. One possible way to do this is to inspect the size of crystal grains as a test to see if sufficient heat treatment has been performed and a predetermined strength is maintained.

However, as mentioned above, in order to determine the grain size of martensitic VJ steel, it is necessary to perform heat treatment in a special atmosphere, and such heat treatment significantly degrades the material (cast steel). become brittle. Therefore, it cannot be applied to the product itself.

Therefore, for martensitic cast steel products such as water turbine liners, metal assembly tests such as the Sumpp method are currently being conducted to evaluate the grain size, etc. of the main parts. However, when conducting metallurgical microstructure tests in the flowing water surface channel of a water turbine liner, etc., if the channel is narrow, grinding, puff polishing, etc. are extremely difficult, and special skills are required, including etching. The work itself is dangerous. Furthermore, even in metallurgical microstructure tests conducted under such conditions, as described above, grain boundaries do not appear, so the size of crystal grains must be estimated from the size of the macrostructure visually observed.

In particular, cast steel products such as water turbine runners have a diameter of several tens of tons, and have complex shapes with large variations in wall thickness, so the solidification cooling effect and heat treatment effect during casting differ depending on each part. Therefore, there are some parts where the crystal grains are coarse and some parts where they are fine. Even if the above-mentioned tests with poor accuracy are applied to each part of such a cast steel product, the expected results will not be obtained.

[Purpose of the invention]

The purpose of the present invention is to easily and accurately measure the crystal grain size of martensitic cast steel products without destroying, damaging, or embrittling the member (material), and without being influenced by the shape of the member. The purpose of the present invention is to provide a material testing method and apparatus for the same.

[Summary of the invention]

In order to achieve the above object, the material testing method according to the present invention includes:
A high-intensity magnetic field is applied to the martensitic viI4 material using half-wave rectified power, the magnetic flux leaking from the grain boundaries of the crystal grains is detected, and the crystal grain size is calculated from the distribution interval of the detected leakage magnetic flux. This is an overview.

Further, the material testing device according to the present invention includes an electrode that applies a constant electric power per unit volume to a martensitic cast steel material to apply a constant magnetic field, a magnetic powder scattering device that scatters magnetic powder on the material, and a magnetic powder pattern. An optical detection device for detecting the number of magnetic particles, or a magnetoelectric transducer that replaces the magnetic particle number [device and the optical detection device, and the optical detection device or! The outline of the device is that it consists of a display device that receives a signal from an electric conversion element and displays the crystal grain size.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a material testing apparatus according to the present invention, in which a control box 1 includes an AC power source 2, a half-wave rectifier 3,
and an ammeter 4 are installed inside. Electrodes 5, 5 led out from the control box 1 are connected to martensitic cast steel 6, which is the material, and this martensitic Vi steel 6
Above is a magnetic powder dispersing device 7, which is a non-destructive inspection device that scatters a fixed amount of magnetic powder per unit time onto the upper surface of the martensitic VI steel 6, and resembles an arc welder. This magnetic powder dispersing device 7 includes a stirring tank 7a that stores magnetic particles of 2μ or less, and a pipe 7b that sends high-pressure air to this tank 7a.
Among the magnetic particles sent from the tank 7a, there is a demagnetizing powder tank 7c for removing heavy particles, and the lighter magnetic particles are stored in the tank 7.
It is sprayed onto the cast steel 6 from the nozzle 7d with the mounting number C. Further, an optical detection device 8 is disposed above the martensitic cast steel 6, and this optical detection device 8
The electrode 5.
5, and the thin light beam emitted from the optical detection device 8 is assumed to be 0.1 mm + 1 degree on the surface of the martensitic cast steel 60.

In the above, a constant electric power per unit volume is applied from the electrodes 5, 5 to the martensitic cast steel 6 via the control box 1, and the DC 250 OA is applied with an electrode spacing of 200 mm.
) give a certain amount of...age. The magnetic field here is set to be extremely strong compared to the magnetic field applied during general non-destructive testing, far exceeding magnetic saturation. This is because the leakage magnetic flux from grain boundaries is significantly weaker than discontinuities detected by non-destructive testing, and becomes increasingly thinner.If this condition is significantly exceeded, when dry magnetic powder is used, This is due to the inability to accurately detect magnetic flux leakage from grain boundaries.

Then, by applying a constant high-intensity magnetic field to the martensitic cast steel 6 as described above, magnetic flux leaks from the grain boundaries, magnetic particles are attracted to this leaked magnetic flux, and the magnetic particle pattern 10 appears. The spacing and density of this magnetic particle pattern 10 are detected as the intensity of reflected light by the optical detection device 8 installed between the electrodes 5, 5, and this detected value is sent as a signal to the display device 9. , displayed graphically or digitally.

Here, the relationship between the peak interval of the reflected light, that is, the interval between the dense parts of the magnetic particle pattern 10, and the size of the macrostructure is proportional as shown in FIG. This relationship can also be understood from the fact that the larger the macrostructure, the rougher, denser, and clearer the magnetic particle pattern is, as shown in reference drawings (A) (large macrostructure) and (B) (small macrostructure), which are micrographs. Approved. In other words, magnetic flux leaks through electromagnetic discontinuities such as grain boundaries,
The degree of this leakage is proportional to the size of the crystal grains.

On the other hand, the grain size of martensitic cast steel is 2 to 3μ on average, although some grain sizes reach 2 to 3M, and the relationship with the size of the macrostructure is as shown in Figure 4. In a relationship.

Therefore, the relationship between the gap between the peaks of the reflected light ξ displayed on the measurement display 9, the tension...the powder dense part spacing (fJ), the size of the macrostructure (S), and the crystal grain size (N>) is 1. Expressed as Q=kNS (k is a constant).

Therefore, the size of the macrostructure is determined from the spacing between the magnetic particle dense areas of the magnetic particle pattern 10, and the crystal grain size can be determined from the size of the macrostructure based on FIG. 4.

It should be noted that the above is an example of the implementation of the present invention, and the present invention is not limited to the above-described example.

For example, in the embodiment, the interval between the electrodes 5.5 is set constant, so it is not necessarily necessary to constantly monitor the current and it is sufficient to keep it constant, but the interval between the electrodes 5.5 can be changed arbitrarily. In this case, it is possible to incorporate a control device that controls the output current according to the spacing between the electrodes.Furthermore, it is possible to install a half-wave rectifier or a magnetic powder dispersion device. good.

In addition, in the embodiment, the magnetic particle pattern 10 is directly analyzed using an optical detection device F (microphotometer), but the magnetic particle pattern 10 is transferred to cellophane tape or the like and analyzed. In this case, if optical means are used, the opposite (
g) It is possible to use not only light but also transmitted light, and it is also possible to know the crystal grain size by directly comparing it with a reference photograph without using optical means. Furthermore, since it is the distribution of iron powder,
It is also possible to use other interview analysis methods.

Furthermore, the crystal grain size can be measured in the same manner as described above by scanning with a flux meter using a Hall element, a magnet diode, etc. as a field detector without attracting magnetic particles to the leakage magnetic flux.

[Effects of the Invention] As explained above, according to the present invention, by applying electricity to martensitic cast steel material, ... The crystal grain size is measured by detecting it with a detection device, etc., and unlike conventional methods, it does not destroy or damage the material.
It is possible to measure the grain size with high accuracy without causing any embrittlement, and is extremely effective in inspecting large and complex martensitic cast steel products such as water wheel runners. In addition, according to the present invention, by installing a separate control device, the monthly crystal grain size can be measured in parallel with the general magnetic particle flaw detection test, thereby achieving many effects such as extremely high efficiency.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a material testing device according to the present invention;
The figure is a lζ graph showing the relationship between the spacing of magnetically dense areas and the size of the macrostructure, and FIG. 3 is a graph showing the relationship between the crystal grain size and the size of the macrostructure. 1...Control box, 2...AC power supply, 3
...Half-wave rectifier, 4...Ammeter, 5...-electrode, 6
... Martensitic cast steel, 7... Magnetic powder scattering device,
8... Optical detection device, 9... Measurement display 10...
・Magnetic powder pattern. Applicant's representative Kiyoshi Inomata Figure 2 +o-2to-'+o'to' Macro structure size Smm2

Claims (1)

[Claims] 1. Applying a high-strength magnetic field to martensitic cast steel material,
A material testing method characterized by detecting magnetic flux leaking from grain boundaries of crystal grains and measuring crystal grain size based on the distribution interval of the detected leakage magnetic flux. 2. An electrode that is connected to a martensitic cast steel material and applies a constant electric power per unit volume to the material to apply a constant magnetic field, and a magnetic powder scattering device that scatters a fixed amount of magnetic powder onto the material per unit time; In order to detect the magnetic particle pattern formed by the magnetic flux leaking from the grain boundaries of the crystal grains of the material, there is an optical detection device that can travel while maintaining a constant distance from the material, and a signal from this optical detection device detects the crystal. A material testing device consisting of a display device that directly or indirectly displays the particle size.