JP2508631B2 - Metal chrome processing method - Google Patents

Description

The present invention relates to a method for processing high-purity metallic chromium,
More specifically, the temperature at which oxidization or nitridation does not matter in a metal chromium molded body having a purity of 99% or more, that is, 750
By giving a pre-deformation of 1 to 5% at a deformation rate of 0.1 to 50 mm / min. At a temperature of ℃ or less, plastic deformability (ductility) is imparted (that is, brittleness-ductility transition temperature is lowered), The present invention relates to a method of performing plastic working at a relatively low temperature.

Metallic chromium has excellent chemical resistance such as acid resistance and alkali resistance even at high temperatures, and also has excellent weather resistance, and is one of the extremely useful metals. However, despite such excellent properties, pure chromium or a chromium-based alloy has not been put into practical use due to its low ductility at low temperature and difficulty in processing.

The present invention provides a processing method for obtaining a plastically worked product of metal chromium that takes advantage of the original properties of metal chromium.

[Prior Art] The following methods have been known so far as methods for forming metallic chromium.

1) A method of forming a metal powder into a plate shape through steps of powder rolling (cold), sintering, re-rolling, and annealing (JP-A-58-55502).
2) Alloy material powder containing 70% by weight or more of chromium is vacuum-sealed in a metal container under reduced pressure of 10 ^-2 torr or less at a temperature in the range of 150 to 800 ° C, and then 200 kg / cm ² Under the above inert gas pressure, a method of heating and holding at 1000 to 1400 ℃, pressure sintering, and rolling in the temperature range of 800 to 1350 ℃ (Japanese Patent Publication No. 60
-58289).

[Problems of Prior Art] Each of the above conventional technologies has the following problems.

That is, the method of 1) requires many steps and the operation is complicated. In cold rolling, the gap between the powder particles is reduced to some extent, but the deformation of the powder particles themselves is difficult to proceed, and There are problems such as low phase density.

In the method 2), since the metal is rolled at a high temperature of 800 to 1350 ° C, the metallic chromium itself reacts with oxygen and nitrogen in the air,
High-purity rolled metal chrome cannot be obtained.

A method of processing in a sealed container to control the atmosphere in order to suppress these reactions can be considered, but it is difficult to completely suppress these reactions, and it is practically impossible to process into any shape. It is impossible.

[Means for Solving Problems] In the present invention, metal chromium powder having a purity of 99% or more or a molded product is sealed in a sealed container and closed while heating to 200 ° C. or more under reduced pressure of 10 ⁻⁴ torr or less. The temperature at which oxidation or nitridation is not a problem for a molded body obtained by hot isostatic pressing at 1000 bar or more with an inert gas within a temperature range of 1000 to 1400 ° C, that is,
Deformation rate of 100 to 500 mm / min. At a temperature above and below the temperature at which prestraining is applied, after prestraining 1 to 5% at a deformation rate of 0.1 to 50 mm / min. The present invention provides a method for processing metallic chrome, which is characterized by performing the plastic working.

The purity of metallic chromium, which is the starting material in the present invention, is 99.
% Or more, and the inclusion of impurities such as carbon and nitrogen should be avoided as much as possible. This is because low temperature plastic working can be more easily performed by removing these impurities.

Such high-purity metal chromium powder is obtained by electrolyzing a chromium salt solution, or by purifying a chromium salt solution by a solvent extraction method, and oxidizing the obtained chromium salt solution or the chromium salt obtained from this solution. It can be obtained by pulverizing metal chromium obtained by reducing the obtained chromic acid by a hydrogen reduction method or the like. The particle size of the metallic chromium powder in the present invention may be small, but is generally 100 μm or less.

In the present invention, it is preferable to use the metallic chromium powder as a compact in advance. This molded product is usually obtained by encapsulating the powder in a rubber packaging bag such as latex, and then isostatically pressing (CIP) at room temperature under a pressure of 2000 kgf / cm ² . The packing density in this packaging bag is 4.0 g / cm ² or more, and the density is 5.5 g / cm ² or more by the isotropic pressure treatment at room temperature. At this time, the volumetric shrinkage is about 24% and the linear shrinkage is about 10%.

Next, the molded body thus obtained is stainless steel,
It is placed in a pressure-tight sealed container made of mild steel or the like. After charging, evacuate under reduced pressure of 10 ^-4 torr or less while closing the container while heating it to about 200 ° C or more. Subsequently, hot isostatic pressing is performed with an inert gas such as argon. The temperature at this time is
The temperature is 1000 to 1400 ° C, preferably 1100 to 1350 ° C. Pressure is
It may be 1000 bar or more, but it is preferably 2000 to 5000 bar. This heating / pressurizing process is preferably performed gradually, and is maintained at a predetermined temperature and pressure for about 30 minutes to 2 hours.
Then, the system is gradually cooled and reduced in pressure, returned to normal pressure and room temperature, and the metallic chrome compact is taken out from the sealed container. The volumetric shrinkage due to this hot isostatic pressing is about 21%, the linear shrinkage is about 7%, and the density of the obtained metallic chrome compact is 7 g.
/ cm ³ or more.

The metal chromium molded body obtained by the above operation is cut as it is or cut into an arbitrary size and subjected to prestrain treatment.

The pre-strain treatment is performed at a temperature at which oxidation or nitridation does not become a problem, that is, a pre-strain of 1 to 5% is 0.1 to 50 at 750 ° C or lower.
It is performed by giving a deformation speed of mm / min. This prestraining is a "ductility treatment". In principle, the pre-deformation may be applied in any stress state of tension, compression, and torsion, but from a practical point of view, it is preferable to employ a method of uniaxial compression (sliding) or rolling.
Rolling is generally performed by rolls.

The pre-strained compact is continuously heated to a temperature above or below the pre-strained temperature (350 to 750 ° C), and at a higher speed than when pre-strained, 100 to 500 mm / mi.
A plate material can be obtained by subjecting it to flat rolling, for example, at a deformation rate of n. If other plastic working is adopted instead of flat rolling, it is possible to obtain a product (for example, a deep-drawn product) having a shape peculiar to the plastic working.

[Effects of the Invention] According to the present invention, by giving a prestrain of 1 to 5%, metallic chromium becomes sufficiently ductile at 350 to 750 ° C. Therefore, secondary processing such as rolling can be performed in air within this temperature range, and deterioration of the material due to oxidation or nitriding of the obtained rolled body is not recognized. Further, since the secondary working can be performed in the air in this way, a conventional plastic working machine can be adopted, and the sheathing work which has been conventionally required when rolling the metal chrome becomes unnecessary, which is extremely economically excellent. Will be things.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is in no way limited by these examples.

Example 1 300 kg of metal chromium powder having a purity of 99.9% was packed at a density of 4.2 g / cm.
^{In 3} , a columnar bag made of latex was charged and wasotropically pressurized at room temperature under a pressure of 3000 kgf / cm ² to obtain a molded body, and then the bag was removed. The density of the obtained molded product was 5.7 g / cm ³ and the volume shrinkage ratio was
The linear shrinkage was 24% and the linear shrinkage was 10%. The resulting upper side of the columnar molded product was cut to a plane of the lower side, evacuating the vessel with a vacuum pump while heating gradually to about 700 ° C. packed this pressurizing stainless steel container, and finally 10 ^{- It} was sucked up to ⁴ torr and sealed. Then, gradually raise the temperature and raise the pressure to 1350 ° C. and 2000 bar for 5 hours, hold at the same temperature and pressure for 40 minutes, and then gradually cool and lower the pressure to normal temperature and normal pressure, and form a metal chrome compact. Was taken out of the stainless steel container. At this time, pressurization was performed using purified argon. The metal chrome compact thus obtained weighs 290 kg and has a density of 7.2 g /
It was cm ^3. Also, the volume shrinkage ratio in this treatment is 20
%, And the linear shrinkage rate was 7%.

Next, a metal chrome molded body is 200 mm in length, 100 mm in width, and 10 in thickness.
A sample was prepared by cutting it into a tanzaku-shaped piece of mm, pre-strained by low-speed rolling using a roll, and subsequently rolled to obtain a rolled body. The conditions for these pre-straining and rolling processes are shown in the following table.

In the present invention, a rolling compact having an arbitrary thickness can be obtained by repeating the above rolling process several times.

Claims (4)

(57) [Claims] 1. A metal chromium powder having a purity of 99% or more or a molded product is sealed in a hermetically sealed container, and the temperature is 200 ° C. under a reduced pressure of 10 ⁻⁴ torr or less.
The molded body obtained by performing hot isostatic pressing (HIP) at 1000 bar or more with an inert gas in the temperature range of 1000 to 1400 ° C while heating is closed above 1 to 5% at 750 ° C or less. Pre-strain
After applying at a deformation rate of 0.1 to 50 mm / min., The temperature is higher or lower than the prestrained temperature and 350 to 750.
A method for processing metallic chromium, which comprises performing plastic working at a deformation rate of 100 to 500 mm / min. At a temperature of ℃. 2. The method for processing metallic chromium according to claim 1, wherein hot isostatic pressing is carried out at 1100-1350 ° C. under an inert gas pressure. 3. The method for processing metallic chromium according to claim (1) or (2), wherein hot isostatic pressing is performed at 1500 to 2000 bar. 4. The method for processing metallic chromium according to any one of claims (1) to (3), wherein a prestrain of 1 to 5% is applied at 300 to 750 ° C.