Metal treatment – Process of modifying or maintaining internal physical... – Producing or treating layered – bonded – welded – or...
Reexamination Certificate
1999-05-25
2001-07-10
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Producing or treating layered, bonded, welded, or...
C148S529000, C148S561000
Reexamination Certificate
active
06258185
ABSTRACT:
TECHNICAL FIELD
The invention pertains to methods of forming steel.
BACKGROUND OF THE INVENTION
Steel is a metallic alloy which can have exceptional strength characteristics, and which, accordingly, is commonly utilized in structures where strength is required or advantageous. Steel can be utilized in, for example, the skeletal supports of building structures, tools, engine components, and protective shielding of modern armaments.
The composition of steel varies depending on the application of the alloy. For purposes of interpreting this disclosure and the claims that follow, “steel” is defined as any iron-based alloy in which no other single element (besides iron) is present in excess of 30 weight percent, and for which the iron content amounts to, at least, 55 weight percent, and carbon is limited to a maximum of 2 weight percent. In addition to iron, steel alloys can incorporate, for example, manganese, nickel, chromium, molybdenum, and/or vanadium. Steel alloys can also incorporate carbon, silicon, phosphorus and/or sulfur. However, phosphorus, carbon, sulfur and silicon can be detrimental to overall steel quality if present in quantities greater than a few percent. Accordingly, steel typically contains small amounts of phosphorus, carbon, sulfur and silicon.
Steel comprises regular arrangements of atoms, with the periodic stacking arrangements forming 3-dimensional lattices which define the internal structure of the steel. The internal structure (sometimes called “microstructure”) of conventional steel alloys is always metallic and polycrystalline (consisting of many crystalline grains).
Steel is typically formed by cooling a molten alloy. The rate of cooling will determine whether the alloy cools to form an internal structure that predominately comprises crystalline grains, or, in rare cases, a structure which is predominately amorphous (a so-called metallic glass). Generally, it is found that if the cooling proceeds slowly (i.e., at a rate less than about 10
4
K/s), large grain sizes occur, while if the cooling proceeds rapidly (i.e., at a rate greater than or equal to about 10
4
K/s) microcrystalline internal grain structures are formed, or, in specific rare cases amorphous metallic glasses are formed. The particular composition of the molten alloy generally determines whether the alloy solidifies to form microcrystalline grain structures or an amorphous glass when the alloy is cooled rapidly. Also, it is noted that particular alloy compositions have recently been discovered which can lead to microscopic grain formation, or metallic glass formation, at relatively low cooling rates (cooling rates on the order of 10 K/s), but such alloy compositions are, to date, bulk metallic glasses that are not steels.
Both microcrystalline grain internal structures and metallic glass internal structures can have properties which are desirable in particular applications for steel. In some applications, the amorphous character of metallic glass can provide desired properties. For instance, some glasses can have exceptionally high strength and hardness. In other applications, the particular properties of microcrystalline grain structures are preferred. Frequently, if the properties of a grain structure are preferred, such properties will be improved by decreasing the grain size. For instance, desired properties of microcrystalline grains (i.e, grains having a size on the order of 10
−6
meters) can frequently be improved by reducing the grain size to that of nanocrystalline grains (i.e., grains having a size on the order of 10
−9
meters). It is generally more problematic to form grains of nanocrystalline grain size than it is to form grains of microcrystalline grain size. Accordingly, it is desirable to develop improved methods for forming nanocrystalline grain size steel materials. Further, as it is frequently desired to have metallic glass structures, it is desirable to develop methods of forming metallic glasses.
SUMMARY OF THE INVENTION
In one aspect, the invention encompasses a method of forming a steel. A metallic glass is formed and at least a portion of the glass is converted to a crystalline steel material having a nanocrystalline scale grain size.
In another aspect, the invention encompasses another method of forming a steel. A molten alloy is formed and cooled at a rate which forms a metallic glass. The metallic glass is devitrified to convert the glass to a crystalline steel material having a nanocrystalline scale grain size.
In yet another aspect, the invention encompasses another method of forming a steel. A metallic glass steel substrate is provided, and a molten alloy is formed over the metallic glass steel substrate to heat and devitrify at least some of the underlying metallic glass of the substrate.
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J.V. Armstrong, et al.; “Enhanced Corrosion Resistance in Nd15Fe77B8by Laser Surface Amorphization”; Hyperfine Interactions vol. 46, 1989; pp. 467-471.
W.L. Johnson; “Metallic Glasses”; Keck Laboratory of Engineering, California Institute of Technology; pp. 804-821.
A. Peker et al.; “Time-temperature-transformation diagram of a highly processable metallic glass”; Materials Science and Engineering A179/A180, 1994; pp. 173-175.
Branagan Daniel J.
Burch Joseph V.
Bechtel BWXT Idaho LLC
Combs-Marillo Janelle
Wells St John Roberts Gregory and Matkin
Wyszomierski George
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