US2980528A - Process for the manufacture of rustless iron - Google Patents

Description

United States Patent PRocnss non THE MANUFACTURE OF RUSTLESS IRON Sampei Katakura, 60-5 Gotanda, Shinagawa-ku, and Kenkichi Tachiki, 117 Sauyawho Meguro-ku, both of Tokyo, Japan No Drawing. Filed Dec. 24, 1958, Ser. No. 782,621

1 Claim. (CI. 75-28) The present invention relates to a process for producing rust resistant iron by treating iron powder in contact with metallic calcium powder, with its object being to provide a novel method for obtaining stainless iron economically and simply.

Iron, like other metals in general tends to increase in resistance to rusting or corrosion with increase of the purity of the metal. Even though no perfect removal of impurities is attained, a sutficient corrosion resistance may be obtained depending upon the treatment.

We have found, in accordance with the invention, that impurities in iron can be removed therefrom, as shown in Table 1, by bringing pulverized iron into contact with powdered metallic calcium in an atmosphere of argon or other inert gases and that the resistance of the iron to corrosion is thus increased as described hereinafter.

In the above-mentioned test, as shown in Table 1, ferrous substances containing impurities, A, B, C of 250- 300 mesh are brought into contact with metallic calcium powder at 30 C. for 12 to 24 hours, with stirring every two hours, and thereafter the iron ingredient is separated from calcium by elutriation, such iron ingredients being shown in Table 1 as materials after treatment.

The respective results of those materials being either exposed in air or impregnated in 30% (by weight) sulfuric acid solution is as shown in Table 2.

TABLE 2 Rust proof test (a) Rusting in air:

after 1 after 6 month months H0118 u IlOIlG.

110119- X10116. 110116--.. none.

(b) impregnation test (temperature: 20 C.) in sulfuric acid solution (30 by weight percent):

Corrosion loss (g./cm. /hr.)

As shown in the above table, the removal of impurities from iron by calcium treatment is not always perfect, but the corrosion resistance shows a similar result as in a stainless steel. It is presumed that not only the surface but also to a considerable depth the iron particles have been converted into a peculiar state by calcium.

The iron powder used in this invention ranges from common steel, Swedish steel, reduced iron and further to carbonyl iron. Difiiculty or easiness of the reaction is dependent on the respective iron material. For instance, the reaction is easier in common steel than in Swedish steel. As the reaction with calcium is a reaction between solids, the powder is preferable in a fine state. Turnings of the above-mentioned iron material is pulverized in a pulverizing apparatus such as an edge mill to a fine powder of about 250 mesh, which is a suitable size for this purpose. On the hand, as to metallic calcium, those obtained by a reducing process or an electrolytic process are used, which are pulverized in 200 mesh powder in a cyclone crusher for use. In the following is shown an example of analyses of calcium by a reduction method.

Fe Al Mg Si Ga Approx. 20 to 30 parts thereof are added to parts of the above mentioned iron. The contact treatment of the iron powder with the calcium powder is carried out in an atmosphere of inert gas, such as argon, etc. In practice, stirring is made from time to time in order to bring about good contact of both materials.-

This treatment is generally carried out at ordinary temperatures. In particular, heating is effected to some extent, when reaction occurs as in the case of Swedish steel.

The duration of treatment requires ordinarily 24 hours depending upon the grain size and contamination degree, etc. of the raw powdered material. The treatment is continued until the colour of the metal powder mixture under treatment changes to brown colour; In order to separate the iron powder treated, the elutriation method is convenient, since the iron powder is heavier and has become inactive to water'while the calcium used is relatively light. The iron powder thus obtained is extremely strong after being dried by removing water. It is moreover highly durable and lustrous as well as remarkably resistant to corrosion as mentioned above.

The rust resistant iron powder thus obtained is suitable for use in ordinary powder metallurgy. Moreover, when said stainless iron is moulded, sintered in an inert gas atmosphere and forged, it becomes something similar to stainless steel. Besides, a solid stainless iron material can be obtained having under-mentioned characteristic properties and can be fabricated for several purposes.

EXAMPLE 1 from by the elutriation process. The separated iron powderislustrous and will not lose luster even if it is exposed in air for an extended period of time.

If this iron powder is to be used, for example in making lamps, the above-mentioned iron powder is dried and formed in a moulding machine, under'a pressure of 3 ton/cm. The moulded product is sintered in a crucible. The sintering is carried out in an argon atmosphere in a high frequency induction furnace. Sintering is effected in a time ratio of 3 hours to kg. raw material. This sintered material is forged during its course of cooling after sintering. Thus manufactured lamp shaped rust resistant iron is remarkably corrosion resistant and has various mechanical features.

EXALIPLE 2 10 kg. of turnings of Swedish steel containing less than 0.1% carbon are pulverized in an edge mill to 250 to 300 meshes, which are put in an iron receptacle electroplated withplatinum. In argon gas atmosphere, 3 kg. of powdered calcium similar to that described in Example 1 are added to the iron powder and thoroughly mixed and allowed to stand for 24 hours. In this case, the mixture is slightly heated at to 30 C. above room temperature, and mixed again every two hours during reaction. The calcium which absorbed impurities is separated by elutriation after the reaction has been finished. The thus treated material is lustrous as that obtained in the said embodiment 1) and, further, its corrosion resistance is excellent.

EXAMPLE 3 10 kg. reduced iron powder of around 0.05% C are further crushed in an edge mill to 250to 300 meshes, and 25 kg. metallicv calcium similar to that described in Example 1 are added to the material in an argon gas atmosphere. This mixture is allowed to stand at room temperatures for 18 hours, during which time it is stirred again every two hours. The iron particles having completed the reaction are separated perfectly from the cal-. cium having absorbed impurities, by the elutriation proc- 4 ess. The thus treated material is lustrous, similarly as that obtained in the above-mentioned Example 2. Its corrosion resistance, further, is good.

EXAMPLE '4:

2 kg. metallic calcium like that used in Example 3 pulverized to 200 mesh are added to 10 kg. carbonyl iron powder in argon gas atmosphere and mixed thoroughly and let stand for twelve hours at room temperatures, during which time it is stirred again every twohours. The iron particles having completed the reaction are separated perfectly from the calcium having absorbed impurities by the elutriation process. The thus treated material is extremely lustrous, similarly as that obtained in the above-mentioned example, and has high purity. Its corrosion resistance is extremely high.

What we claim:

The process for the production of rust resistant iron which comprises mixing parts finely divided iron containing metallic impurities with 20 to 30 parts powdered metallic calcium in an inert gaseous atmosphere to form amass wherein the calcium and iron particles are in intimate contact, maintaining the particles in intimate contact for from 12 to 24 hours at a temperature in the range of 20 to 3 0'C. above room temperature with stirring every two hours until the mass takes on a brown coloration, and separating the iron particles from the mass.

References Cited in the file of this patent UNITED STATES PATENTS Rostron Mar. 27, 1951 OTHER REFERENCES Jones: Powder Metallurgy, Edward Arnold & Co., London, 1943, page 49.

Goetzel: Treating of Powder Metallurgy, volume II, 1950, Interscience Publishers, Inc., New York, page 627.