Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2000-12-04
2001-12-25
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S246000, C419S032000, C419S042000, C419S048000
Reexamination Certificate
active
06332905
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high strength metallic solidification body, oxygen steel, and a method for producing the same. In further detail, it relates to an easily producible high strength metallic solidification body of a metallic powder having an extremely high strength and elongation, to oxygen steel as a particular type of the high strength metallic solidification body, which is free of additional elements, and which is a light-weight highly rigid steel, and to a method for producing the same by using plastic working.
BACKGROUND OF THE INVENTION
Conventionally, in case of producing metallic materials by solidification molding of powders, mechanical alloying using ball mills was applied to obtain a powder having a sufficiently finely divided texture to thereby increase the strength of the resulting solidified product, and, furthermore, HIP processing was used to eliminate the pores therefrom. Thus, not only a conventional production method for obtaining a solidified body from a metallic powder required a large production system and a consumption of a vast production time and cost because many process steps were involved, but also it have a great difficulty in supplying a great amount of material at a time to carry out the batch process.
Although mass production is feasible if mechanical alloying and HIP processes are omitted, on the other hand, the resulting material have not only an insufficient strength because of a coarse texture, but also insufficient elongation and rigidity owing to the formation of large amount of coarse pores inside it.
Accordingly, mechanical alloying process and the HIP process subsequent thereto were regarded as indispensable means in the production of a solidification body of metallic powders. Hence, it had been thought difficult to realize a powder solidification body having a higher strength and still yet improved in elongation.
Moreover, in a steel material, regardless of whether it is a solidification body of a metallic powder or not, a high strength material having a TS of 590 MPa or higher had been produced by properly incorporating an additional element such as C, Si, Mn, Nb, Cu, Ni, etc., at a quantity of 0.22 mass % or more in Pcm, and then by applying quenching and tempering, or employing controlled rolling or controlled cooling. However, the steel materials obtained in this manner required the addition of various types of rare elements, and, hence, the resulting materials suffered problems as such that they were not suitable for recycled use, or required preheating in case of applying welding, or caused hardening at the portions which were thermally influenced during welding. Moreover, because it was difficult to obtain a uniform texture for the entire cross section, heterogeneous material distribution was found in the steel material.
SUMMARY OF THE INVENTION
Accordingly, in re-examining the conventional technological knowledge and common beliefs, a first object of the invention according to the present application is to provide a high strength metallic solidification body having, for instance, a strength of 450 MPa or higher and a uniform elongation of 5% or more, which is capable of being produced by mass production but without employing the mechanical alloying process and the subsequent HIP process.
The above object can be accomplished by one aspect of the invention according to the present application, which provides a high strength metallic solidification body which is characterized by being a solidification body of a starting metallic powder containing iron or titanium as the principal component and having a super fine texture comprising a crystalline texture consisting of grains 5 &mgr;m or less in average grain diameter.
In accordance with another aspect of the invention according to the present application, there is provided a high strength metallic solidification body in relation to above, which is solidified by plastic working using hydrostatic pressing, and particularly, by plastic working using at least one selected from flat rolls, grooved rolls, extrusion, and swaging, or a high strength metallic solidification body subjected to plastic working using a sheath material; or a high strength metallic solidification body solidified at a temperature not higher than 800° C.
A second object of the invention according to the present application is to provide a novel steel material almost free of additional elements such as Si, Mn, Nb, Cu, and Ni, and which exhibits, for example, a strength of 590 MPa or higher, a uniform elongation of 5% or more, and superior rigidity, yet having excellent weldability by overcoming the problems of the preheating treatment and the hardening of thermally influenced portions, and also superb properties suitable for recycled use.
As a solution to the object above, the invention according to the present application provides an oxygen steel which is a steel material in which oxide grains 0.2 &mgr;m or less in diameter is dispersed for 0.5 to 60 % by volume.
Furthermore, the invention according to the present application provides the oxygen steel above, wherein the ferritic grains comprising the matrix phase are 5 &mgr;m or less in average diameter; or an oxygen steel according to any of the aforementioned ones, having an oxygen content of 0.05 mass % or more, and furthermore, an oxygen steel according to any of the aforementioned ones, wherein the value of tensile strength (MPa) multiplied by uniform elongation (%) is 4,000 (MPa·%) or greater, and the reduction of area is 50% or higher.
In addition to above, the invention according to the present application provides a method for producing the high strength metallic solidification body and the oxygen steel above.
More specifically, the invention according to the present application provides a method for producing a high strength metallic solidification body which comprises solidifying a starting metallic powder containing iron or titanium as the principal component by means of plastic working using hydrostatic pressing, thereby producing a metallic solidification body having a superfine texture comprising crystalline texture consisting of grains 5 &mgr;m or less in average diameter.
Further, the invention provides a production method in relation to above, wherein the plastic working comprises at least one of those using flat rolls, grooved rolls, extrusion, and swaging, or a production method comprising plastic working using a sheath material; in which the plastic working may be performed at a temperature not higher than 800° C.
Furthermore, the invention provides, in addition to the production method comprising milling a metallic powder and then solidifying the powder by applying plastic working while maintaining it in a sealed state, a method for producing a steel material comprising using a starting powder containing iron as the principal component, wherein the starting powder contains 0.05 mass % or more of oxygen and applying the plastic working in a temperature range of from 500° C. to the transformation temperature of iron, thereby producing a steel material containing dispersed therein oxide grains 0.2 &mgr;m or less in average diameter at a volume ratio of from 0.5 to 60%.
The invention also provides a production method according to those described above, wherein the starting powder containing iron as the principal component comprises from 0.05 to 0.5 mass % of oxygen, 0.01 mass % or less of carbon, 0.1 mass % or less of chromium, 0.1 mass % or less of silicon, and 0.5 mass % or less of manganese.
REFERENCES:
patent: 5006164 (1991-04-01), Kiyota
Hayashi Toru
Muramatsu Yuji
Nagai Kotobu
Ootaguchi Minoru
Tsuzaki Kaneaki
Japan as represented by Director General of National Research In
Mai Ngoclan
Wenderoth , Lind & Ponack, L.L.P.
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