JP3447516B2 - Method and apparatus for preparing metal sample for analyzing non-metallic inclusions - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for preparing a metal sample for analyzing non-metallic inclusions.

[0002]

2. Description of the Related Art Turkdogan Symposium Pro is used as a method for evaluating non-metallic inclusions in metals.
Ceedings, p105-112 (1994) discloses a method in which metal fragments are melted by a cold crucible flotation melting method and inclusions discharged on the surface are observed with an electron microscope. Further, Japanese Patent Application Laid-Open No. 7-239327 discloses a method for evaluating the cleanliness of a metal by the area of an inclusion aggregate discharged on the surface of a metal piece melted and solidified by the cold crucible floating melting method. .

[0003]

[Problems to be Solved by the Invention] Turkdogan
Symposium Proceedings, p10
5-112 (1994) only points out a problem as an evaluation method due to the characteristics of the cold crucible itself, and is an industrially inexpensive and rapid method for evaluating a wide range of non-metallic inclusions on a metal surface. Not the one. In addition, as pointed out there, the gathering positions of inclusions may be dispersed on the side surface or the top surface of the sample, and different positions should be used when evaluating the amount of inclusions by observation with an electron microscope or the area of the gathered inclusions. A large number of analyzes and surveys are required, and rapid evaluation is difficult due to repetition of sample set and increase in the number of measurements. On the other hand, as disclosed in Japanese Patent Laid-Open No. 7-239327, when a metal sample for analysis is melted and solidified, non-metal inclusions in the metal are scattered in the circumferential direction of the metal, on the surface of the metal sample such as in the upper part. In this analysis, interspersed inclusions will be analyzed, and there is a problem that the analysis takes a long time. The present invention has been made in order to advantageously solve such a problem, and a method for producing a metal sample and a method for producing the same so as to form an aggregate of inclusions suitable for analysis without scattering inclusions. The purpose is to provide a device.

[0004]

A feature of the present invention is that a metal sample is subjected to cold crucible flotation dissolution in a non-oxidizing atmosphere, and after the melt is held, an inert gas is blown onto the upper surface of the melted metal to dissolve the melted metal. A method for preparing a metal sample for analysis of non-metal inclusions, which comprises solidifying an upper surface and then solidifying the entire molten metal. And a metal for analyzing non-metallic inclusions, characterized by disposing a crucible for cold crucible flotation and melting in a melting device held in a non-oxidizing atmosphere, and disposing an inert gas blowing nozzle on the upper surface of the crucible in an oriented manner. It is a sample preparation device.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION As an apparatus for dissolving a metal sample, for example, a container in which an atmosphere of inert gas or a reduced pressure atmosphere can be controlled as a non-oxidizing atmosphere is composed of circumferentially divided metal segments, and the upper surface is opened. Place a metal crucible (cold crucible) with a water-cooling mechanism whose bottom surface is closed. The crucible has a structure surrounded by a coil 8 through which a high frequency current given by a high frequency oscillator is passed. A target pre-weighed metal sample is placed in the crucible and a current is passed through the coil to melt the metal sample by the electromagnetic force generated and levitate in the crucible. The non-metallic inclusion has a lower specific gravity than the molten metal, and the reaction of the induced electromagnetic force against the force pushing the molten metal inward acts on the non-metallic inclusion and moves to the outer circumference of the float.

A flow which rises in the center and flows downward along the surface is formed in the metal in the levitation and melting by the electromagnetic force by the high frequency current. Due to this flow, the non-metallic inclusions that have moved to the surface of the molten metal move downward and move to the gap of the side wall of the crucible on the side surface of the floating molten metal. When the high-frequency current is cut off in this state, the downward flow of the molten metal surface caused by the electromagnetic force disappears, the buoyancy of the inclusions causes some of the inclusions to move to the upper surface side, and the buoyancy disappears, causing the molten metal to disappear. Are solidified from below by being pressed against the bottom wall of the crucible, and some of the inclusions that have moved to the surface of the molten metal are captured on the side surface and the other part is captured on the upper surface. Therefore, by solidifying while ensuring a downward flow on the surface of the molten metal by the high frequency current, the movement of inclusions to the upper surface is prevented. Alternatively, by solidifying the upper surface to prevent the inclusions from moving to the upper surface side and then cutting the high-frequency current, it is possible to accurately prevent the molten metal from moving to the upper surface and move the molten metal to the side surface. You can

As described above, as a method for cooling the upper surface of the molten metal in the crucible, for example, after the floating and melting of the metal sample is completed, an inert gas is sprayed from above the crucible through a nozzle that is oriented in the crucible and held after melting. , The upper surface of the molten metal is solidified, and then the high frequency current is cut off. Thus, the non-metal inclusions, which are blocked by the solidified metal, do not float on the upper surface, but are trapped on the side surfaces.
In the sample thus produced, inclusions are gathered only on the side surface as shown in FIG. 1. Therefore, when analyzing the amount of inclusions, it suffices to investigate and measure only the strip-shaped inclusion portion on the side surface. . Therefore, the cleanliness of the metal can be evaluated simply and quickly.

As described above, as the gas blown onto the upper surface of the molten metal in the crucible, an inert gas such as helium gas, argon gas or nitrogen gas can be used. In particular, helium gas having high thermal conductivity is preferable. Further, when the inert gas is blown, the high frequency current may be gradually reduced.

[0009]

EXAMPLES Next, examples of the apparatus of the present invention will be described. As shown in FIG. 2, an inert gas as a non-oxidizing atmosphere, or a container 2 in which a reduced pressure atmosphere 1 can be controlled, is composed of metal segments 3 divided in the circumferential direction, the upper surface is open, and the lower surface is closed by internal water cooling. A crucible (cold crucible) 5 having a mechanism 4 is arranged. The crucible 5 constitutes a melting device surrounding a coil 8 through which a high frequency current 7 given by a high frequency oscillator 6 is passed. The pipe 13 is laid from the lid 15 on the upper surface side of the container 2 to above the crucible 5, and the inert gas blowing nozzle 14 is oriented on the upper surface of the crucible 5.

Then, a pre-weighed metal sample 9 of interest is placed in the crucible 5 and a current 7 is applied to the coil 8.
And the metal sample 9 is melted. After holding for a certain period of time to move the non-metallic inclusions to the surface of the molten metal 9 (outer periphery of the float), and after the melting and holding is completed, an inert gas is blown onto the molten metal upper surface 11 from the nozzle 14 arranged above the crucible 5. After solidifying the molten metal 9 on the upper surface 11, the high-frequency current 7 was immediately cut to solidify and cool the entire molten metal 9.

The metal sample 9 after cooling the melted metal 9 is opened from the lid 15 of the container 2 (melting device), taken out from the crucible 5, and conveyed to the scanning electron microscope. The metal sample transferred to the scanning electron microscope is fixed to the sample holding pad of the sample rotating device installed in the scanning electron microscope device so that it can rotate around the central axis of the upper and lower surfaces, and the energy dispersion type is obtained while rotating the metal sample. The analysis device analyzes an aggregated portion of inclusions on the side surface of the metal sample.

[0012]

EXAMPLES Next, examples of the method of the present invention will be described. As a metal sample, width 1400 mm, thickness 2 with continuous casting equipment
A 1/4 width direction of a slab of low carbon aluminum killed steel cast with a 45 mm mold at a casting speed of 1.8 m / min.
Samples of 20 mm in the casting direction, 20 mm in the thickness direction, and 30 mm in the width direction were taken from 1/2 part.

As a melting device, an inner diameter of 40 mm, a depth of 40 mm, and an upper end of 20 mm to 40 mm in a nonoxidizing atmosphere container
A cold crucible with a hemispherical cross section up to mm and consisting of 8 divided metal segments is installed, and an inner diameter for spraying an inert gas onto the molten metal upper surface from a pipe laid from above the crucible from the lid on the container upper surface side. A 4 mm nozzle was placed 30 mm from the top of the crucible.

Then, the above metal sample was set in a crucible, and 30 Kw of electric power was applied to the induction coil under an atmospheric pressure Ar atmosphere to melt it (1550 ° C. or higher), and it was held for 5 minutes to move non-metallic inclusions. Then, when the melting and holding was completed, helium gas (normal temperature) was supplied from the nozzle at 10 Nl / min for 3 times.
After spraying for 0 seconds to solidify the molten metal on the upper surface, the high frequency current was immediately cut to solidify and cool the metal sample.

A pad attached to one end of a rotating shaft of a sample rotating device in which non-metallic inclusions gathered in strips on the side surface of the solidified metal sample are installed in the scanning electron microscope device so as to be rotatable around the sample center axis. Fixed with, rotation speed 0.2
The analysis of the inclusions was completed with the energy dispersive analyzer while rotating at rpm. The time required for analysis was 7 minutes including the sample set.

Next, a comparative example will be described. From the position adjacent to the sample taken in the example, a sample of 20 mm in the casting direction, 20 mm in the thickness direction, and 30 mm in the width direction was taken. The inner diameter is 40 mm, the depth is 40 mm, and the upper end has a hemispherical cross-sectional shape from 20 mm to 40 mm. The metal sample is set in a cold crucible crucible consisting of 8 divided metal segments. Under an atmospheric pressure Ar atmosphere, 30 Kw of electric power was applied to the induction coil to melt it (1550 ° C. or higher), and it was held for 5 minutes to move the non-metallic inclusions. Then, the power was linearly reduced to 0 kW over 10 seconds to solidify and cool the entire molten metal.

Non-metallic inclusions scattered like islands on the surface of the solidified metal sample were analyzed by an energy dispersive measuring device of a scanning electron microscope. In order to measure all the inclusions scattered on the surface of the metal sample, the side surface was changed eight times and the top surface was analyzed once, for a total of nine times. In each analysis, sample setting, analysis, removal and reset were repeated. Each analysis time is 6
It took 0 seconds. The time required for all measurements was 30 minutes.

The time required for the evaluation of the sample manufactured by the method of the present invention was 1/4 of that of the conventional method, which enables quick evaluation. Also,
FIG. 4 shows a comparison of the results of analysis and evaluation of the amount of alumina inclusions according to the method of the present invention and the conventional method.
Accurate analytical values were obtained for the metal sample according to the method of the present invention. In addition, in FIG. 3, the maximum value of the amount of alumina is 1
The relative value when 0 was shown.

[0019]

According to the method of the present invention, since the inclusions in the metal can be analyzed and evaluated quickly, appropriate measures for reducing inclusions can be efficiently performed and the quality can be improved. Further, it is possible to perform quality evaluation / judgment by incorporating it into a production line online, and it is possible to obtain excellent effects such as the efficiency of the product manufacturing process, and the industrial effect is extremely large.

[Brief description of drawings]

FIG. 1 is a plan view (a) and a side view (b) showing an example of a metal sample according to the method of the present invention.

FIG. 2 is a side view showing an embodiment of the device of the present invention.

FIG. 3 is a chart showing a comparison of the amount of alumina inclusions in the metal sample according to the method of the present invention and the metal sample according to the conventional method.

[Explanation of symbols]

1 atmosphere 2 containers (dissolution device) 3 Metal segments divided in the circumferential direction 4 Water cooling mechanism 5 crucibles 6 high frequency oscillator 7 High frequency current 8 induction coil 9 metal samples 10 electromagnetic force 11 Molten metal upper surface 12 Inclusion 13 gas piping 14 Inert gas spray nozzle 15 Container lid

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 33/20 G01N 1/28 G01N 15/00

Claims (3)

(57) [Claims] 1. A metal crucible is subjected to cold crucible flotation melting in a non-oxidizing atmosphere, and after melting and holding, an upper surface of the molten metal is solidified by spraying an inert gas onto the upper surface of the molten metal, and then the entire molten metal is solidified. A method for preparing a metal sample for analysis of non-metallic inclusions, comprising: 2. The method for preparing a metal sample for analyzing non-metallic inclusions according to claim 1, wherein any one of helium gas, argon gas and nitrogen gas is used as the inert gas. 3. A non-metallic inclusion characterized in that a crucible for cold crucible flotation and melting is arranged in a melting device kept in a non-oxidizing atmosphere, and an inert gas blowing nozzle is oriented on the upper surface of the crucible. Metal sample preparation device for analysis.