US3334999A

US3334999A - Method of manufacturing semi-fabricated products of chrome-nickel steels

Info

Publication number: US3334999A
Application number: US347127A
Authority: US
Inventors: Naeser Gerhard
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1964-02-25
Filing date: 1964-02-25
Publication date: 1967-08-08
Anticipated expiration: 1984-08-08

Description

United I StatesPatent O 3,334,999 METHOD OF MANUFACTURING SEMI-FABRI- CATED PRODUCTS OF CHROME-NICKEL STEELS Gerhard Naeser, Duisburg, Germany, assignor to Mannesmann Aktiengesellschaft, Dusseldorf, Germany, a corporation of Germany N Drawing. Filed Feb. 25, 1964, Ser. No. 347,12 Claims. (Cl. 75-201) The invention relates to the manufacture by press-ureforming of sheet metal, wires or tubes, or the like, from chrome-nickel steel powder; and relates more particularly to such manufacture from powder obtained by the atomization with pressure water from a chrome-nickel steel melt.

It is known that the manufacture of semi-fabricated products of sheet metal, metal bands, wires, or tubes in accordance with existing powder metallurgical methods, can be economical only if it results in a raised output and quality as compared to the normal manufacture methods for such products from starting materials obtained by melting techniques.

It had been proposed to manufacture semi-fabricated products from powdered steel alloys with a high chrome content or chrome-nickel content, the powder being obtained by atomization of a melt with pressure water. It was found, however, that the oxygen absorption of the steel powder upon its atomization is very high, in fact so high that it requires a reduction annealing with pure hydrogen. This treatment, however, is so expensive as to render this method uneconomical.

Another proposal, namely to carry out the atomization under the protective shield of inert gases has, for the same reason, proved to be uneconomical.

It is accordingly among the principal objects of the invention to avoid the drawbacks of the prior art, and to provide for the economical manufacture of semi-fabricated quality products from chrome-nickel steel powder.

It is a further object of the invention to preoompress the powder that has predetermined carbon and oxygencontents, and to anneal or sinter the precompressed articles subsequently in a vacuum while simultaneously-decarbonizing and tie-oxidizing the articles, and thereafter to subject them to pressure forming.

Further objects and advantages of the invention will be set forth in part in the following specification and in part will be obvious therefrom without being specifically referred to, the same being realized and attained as pointed out in the claims hereof.

The foregoing aims, and particularly the aim of improved quality, and still more particularly of high economy, for manufacturing semi-fabricated products powdermetallurgically broadly may be realized in accordance with the instant invention as follows: The chrome-nickel steel powder may be obtained by atomization from a melt, and may contain equivalent amounts of carbon and oxygen; the powder is first pre-compressed into porous pressed articles such as bands, and these articles thereafter are annealed or sintered in a vacuum while simultaneously being decarbonized and de-oxidized, and subsequently these articles are rolled or pressed.

In order to adjust the stoichiometrical relation of the carbon and oxygen contents of the steel powder, the invention provides for adding to the chrome-nickel-steel melt before the atomization an amount of from about .3 to about 1.0 percent carbon. The addition of the carbon effects a decrease in the oxygen absorption while the metal is in the melt stage, as well as during atomization. This addition of carbon in accordance with the invention must be sufficiently large, so that during the subsequent vacuum annealing of the pre-compressed articles carbon and oxy- 3,334,990 Patented Aug. 8, 1967 ICC gen are removed entirely in the form of carbon oxide.

The stoichiometrical relation between the carbon and the oxygen may also be adjusted by mixing various types of steel powders having diiferent carbon contents and oxygen contents and, if desired, admixing thereto graphite powder and/ or powdered oxides such as chromic oxide.

The chrome-nickel steel powder which has thus been obtained, by atomization with pressure water, in spite of its high carbon content and oxygen content lends itself surprisingly well to the formation into pressed articles, such as by rolling into porous bands or, by pressing, into blooms for the subsequent manufacture of tubes.

After the annealing of the aforesaid pressed articles in a vacuum, which is a good deal less expensive than the annealing in pure hydrogen of the prior art as mentioned, there are obtained carbon contents of below .002 percent, which heretofore had been unattainable for objects made of chrome-nickel steel.

The further working of the annealed or sintered pressed articles into finished articles, may subsequently be carried out in accordance with well-known methods, such as rolling or pressing, either hot or cold.

Example A melt on one metric ton of a steel alloy having 18 percent chrome and 8 percent nickel, the carbon content of which had been increased by the addition of graphite to .6 percent, was atomized with pressure water having a pressure of 60 atmospheres excess pressure (atii), in 3 minutes, into a steel powder having a particle size of less than .5 mm. The oxygen content of the steel .powder amounted to .9 percent. The stoichiometrical relation between the carbon content and the oxygen content was adjusted by mixing the powder obtained with a different steel powder that had a higher oxygen content. The resultant mixture was formed into a porous band of a thickness of 4 mm., which was then rolled up on a reel and annealed for two hours in a vacuum of .3 mm. mercury at a temperature of 1170 C. This caused the carbon content to be lowered from .6 percent to .002 percent, and the oxygen content to be lowered to .06 percent. The annealed and sintered band subsequently was subjected to hot rolling. It showed thereafter excellent strength properties which were equivalent to those of steel bands made in accordance with the usual normal rolling process.

I wish it to be understood that I do not desire to be limited to'the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

Having thus described the invention, what I claim as new and desire to be secured by Letters Patent, is as follows:

1. In a method of manufacturing semi-fabricated products, such as sheet metal, wires or tubes, the steps comprising, preparing a chrome-nickel steel melt, atomizing said melt with pressure water thereby obtaining a chrome-nickel steel powder, pre-compressing said powder into porous pressed articles, subsequently sintering said articles in a vacuum at a temperature above 1000 C. for a period in excess of one hour, while simultaneously decarbonizing and deoxidizing said articles and thereafter subjecting them to pressure forming of the rolling and, respectively, pressing type.

2. In a method of manufacturing semi-fabricated products, as claimed in claim 1, and adjusting the stoichiometrical relation between the carbon content and the oxygen content of the powder by the mixing, into a mixture, of various types of chrome-nickel steel powders having different carbon contents and oxygen contents.

3. In a method of manufacturing semi-fabricated products, as claimed in claim 2, and admixing to said mixture at least one powder taken from a group of powders, consisting of graphite powder and oxide powder.

4. In a method of manufacturing semi-fabricated products, as claimed in claim 3, said oxide powder being chromic oxide powder.

5. In a method of manufacturing semi-fabricated products, such as sheet metal, wires, or tubes, of chromenickel steel, the steps comprising, preparing a chromenickel steel melt, atomizing said melt with pressure Water thereby obtaining a chrome-nickel steel powder, adjusting the stoichiometrical relation between the carbon content and the oxygen content of said powder by adding to the melt, prior to the atomization, of from about .3 to about 1.0 percent carbon, pro-compressing said powder into porous pressed articles, subsequently sintering said articles in a vacuum at a temperature above 1000 C. for a period in excess of one hour while simultaneously decarbonizing and deoxidizing said articles and thereafter subjecting them to pressure forming of the rolling and, respectively, pressing type.

References Cited UNITED STATES PATENTS OTHER REFERENCES Cox, Vacuum sintering, Metal Industry, Sept. 16, 1960.

'CARL D. QUARFORTH, Primary Examiner.

BENJAMIN R. PADGETT, Examiner. A. J. STEINER, Assistant Examiner.

Claims

1. IN A METHOD OF MANUFACTURING SEMI-FABRICATE PRODUCTS, SUCH AS SHEET METAL, WIRES OR TUBES, THE STEPS COMPRISING, PREPARING A CHROME-NICKEL STEEL MELT, ATOMIZING SAID MELT WITH PRESSURE WATER THEREBY OBTAINING A CHROME-NICKEL STEEL POWER, PRE-COMPRESSING SAID POWDER INTO POROUS PRESSED ARTICLES, SUBSEQUENTLY SINTERING SAID ARTICLES IN A VACUUM AT A TEMPERATURE ABOVE 1000* C. FOR A PERIOD IN EXCESS OF ONE HOUR, WHILE SILULTANEOUSLY DECARBONIZING AND DEOXIDIZING SAID ARTICLES AND THEREAFTER SUBJECTING THEM TO PRESSURE FORMING OF THE ROLLING AND, RESPECTIVELY, PRESSING TYPE.