Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reissue Patent
1998-08-19
2001-04-10
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S240000, C075S242000
Reissue Patent
active
RE037127
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the composition of hardfacing materials applied to surfaces subjected to abrasive wear to increase their wear resistance. More particularly, the present invention relates to hardfacing compositions applied to one or more surfaces of an earth-boring bit of the rolling cutter variety.
2. Background Information
It is a long-standing practice in the design and manufacture of earth-boring bits to apply wear-resistant hardfacing materials to the surfaces of such bits that are subjected to abrasive wear during drilling operations. In earth-boring bits of the rolling cutter variety, these surfaces include the teeth of bits of the milled or steel tooth variety, the gage surfaces of the rolling cutters, and the shirttails of the bit legs comprising the bit body.
In the past, these hardfacing compositions generally comprise carbides of the elements of Groups IVB, VB, and VIB in a matrix metal of iron, cobalt, or nickel and alloys and mixtures thereof. The hardfacing is applied by melting the matrix and a portion of the surface to which the hardfacing is applied with an oxyacetylene or atomic hydrogen torch. The carbide particles give the hardfacing material hardness and wear resistance, while the matrix metal lends the hardfacing fracture toughness. A hardfacing composition must strike an adequate balance between wear resistance (hardness) and fracture toughness. A hardfacing composition that is extremely hard and wear-resistant may lack fracture toughness, causing the hardfacing to crack and flake prematurely. Conversely, a hardfacing with adequate fracture toughness, but inadequate hardness and wear resistance, is eroded prematurely and fails to serve its purpose.
Many factors affect the suitability of a hardfacing composition for a particular application. These factors include the chemical composition and physical structure of the carbides employed in the composition, the chemical composition and microstructure of the matrix metal or alloy, and the relative proportions of the carbide materials to one another and to the matrix metal or alloy.
One early advance in hardfacing compositions for use in earth-boring bits is disclosed in commonly assigned U.S. Pat. No. 3,800,891, Apr. 2, 1974 to White et al. This patent discloses a hardfacing composition comprising sintered tungsten carbide in an alloy steel matrix. Sintered tungsten carbide comprises grains or particles of tungsten carbide sintered with and held together by a binder of non-carbide material, such as cobalt. The sintered tungsten carbide possesses greater fracture toughness than the more conventional cast tungsten carbide, such that the resulting hardfacing composition possesses good fracture toughness without sacrificing hardness and wear resistance.
U.S. Pat. No. 4,836,307, Jun. 6, 1989 to Keshavan et al., discloses a hardfacing composition employing particles of cemented or sintered tungsten carbide and relatively small particles of single crystal monotungsten carbide, sometimes referred to as “macrocrystalline ” tungsten carbide, in a mild steel matrix. This composition purports to possess the advantages of sintered tungsten carbide, as disclosed in U.S. Pat. No. 3,800,891, with the advantages of single crystal monotungsten carbide, which is harder than the cemented or sintered tungsten carbide, yet is less brittle than the alternative cast carbide.
U.S. Pat. No. 5,089,182, Feb. 18, 1992, to Findeisen, et al. discloses a method of manufacturing cast carbide pellets that are generally spherical in shape and have improved mechanical and metallurgical properties over prior-art carbide pellets. These cast pellets are not truly spherical, but are sufficiently symmetrical that residual stresses in the pellets are minimized. Also, the generally spherical shape of these pellets eliminates corners, sharp edges, and angular projections, which are present in conventional crushed particles, that increase residual stresses in the particles and tend to melt as the hardfacing composition is applied to the surface.
A need exists, therefore, for a hardfacing composition having a near-optimal balance between wear-resistance and toughness and that incorporates the properties of several types of carbide materials.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide an improved hardfacing for use in earth-boring bits and other applications having a need for good wear resistance in combination with good fracture toughness.
This and other objects of the present invention are accomplished by providing a hardfacing composition comprising at least 60% by weight of hard metal granules including a quantity of sintered carbide pellets and a quantity of cast carbide pellets. The cast and sintered carbides are selected from the group of carbides consisting of chromium, molybdenum, niobium, tantalum, titanium, tungsten, and vanadium carbides and alloys and mixtures thereof. The balance of the hardfacing composition is matrix metal with traces of flux or deoxidizer, and alloying elements. All percentages given are pre-application ratios.
According to the preferred embodiment of the present invention, the carbide materials are provided in granular form with the balance of the material being matrix metal. The granules comprise about 67-71% by weight of the composition. The sintered carbide pellets comprise about 62.5 to 68.5% by weight of the granules and the cast carbide pellets comprise 12-18% by weight of the granules. Crushed sintered carbide particles comprise about 12-18% by weight of the granules. The sintered carbide pellets range in size between about 16 mesh and 30 mesh and the cast carbide pellets range in size between about 40 mesh and about 80 mesh. The crushed sintered carbide particles range in size between about 20 mesh and about 30 mesh.
According to the preferred embodiment of the present invention, the matrix metal is low-carbon steel alloyed with niobium and is present in the form of a tube containing the granules.
Other objects, features and advantages of the present invention will become apparent with reference to the detailed description, which follows.
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British Search Report dated Jan. 24, 1996.
Jones Ronald L.
Massey Alan J.
Overstreet James L.
Schader Kevin W.
Scott Danny E.
Baker Hughes Incorporated
Bradley James E.
Felsman, Bradley, Vaden, Gunter & Dillon L.L.P.
Mai Ngoclan
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