FIELD OF THE INVENTION
The present invention is directed to coated grinding articles and methods for forming coated grinding articles. More particularly, the present invention is directed to coated grinding articles and methods for forming coated grinding articles having a plurality of particles dispersed in a matrix in the coating.
BACKGROUND OF THE INVENTION
Coal crusher rolls are used to crush coal which is fed to a boiler for producing steam, reducing the size of the coal units from about 20 mm to about 200 mesh size. During the crushing process, the grinding surfaces of the coal crusher rolls become worn due to the inherent abrasive nature of the coal which is being crushed. Coals which have elevated ash content are typically more abrasive than coals with lower ash content, and may cause faster erosion of the grinding surfaces of the coal crusher roles, both by attrition and wear from the crushing loads applied on the coal crusher rolls. Further degradation of the coal crusher rolls may be caused by contaminants in the coal supply such as iron and stone, which may cause sudden impacts when introduced into the coal crusher.
Coal crusher rolls may be encased in sinter-cast materials to extend the useful life, but such solutions are expensive and are limited in the increase in useful life they provide.
BRIEF DESCRIPTION OF THE INVENTION
In an exemplary embodiment, a treated grinding article includes an untreated portion, a treated portion disposed on the untreated portion, and a grinding surface. The untreated portion includes an iron alloy and an untreated hardness. The treated portion includes a treated iron alloy and a treated hardness. The treated iron alloy includes a material composition essentially identical to the iron alloy except that

the treated iron alloy includes elevated carbon content relative to the iron alloy. The treated hardness is greater than the untreated hardness.
In another exemplary embodiment, a method for forming a treated grinding article includes applying a carburizing composition to an article. The article includes an iron alloy and an untreated hardness. The iron alloy is carburized at a carburization temperature below about 550 °C, diffusing carbon atoms into the iron alloy and forming a carburized portion on an untreated portion. The carburized portion includes a partially-treated iron alloy and a partially-treated hardness greater than the untreated hardness. The partially-treated iron alloy is annealed at a temperature of at least about 100 °C for a duration of at least about 5 hours, forming a treated portion disposed on the untreated portion. The treated portion includes a treated iron alloy and a treated hardness greater than the partially-treated hardness. A grinding surface of the treated grinding article is formed.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an assembly, according to an embodiment of the present disclosure.
FIG. 2 is a sectional view of an article, according to an embodiment of the present disclosure.
FIG. 3 is a sectional view of the article of FIG. 2 following carburization, according to an embodiment of the present disclosure.

FIG. 4 is a sectional view of the article of FIG. 3 following annealing, corresponding to the treated article of FIG. 1 taken along lines 4-4, according to an embodiment of the present disclosure.
FIG. 5 is a sectional view of the article of FIG. 4 following application of a grinding coating, according to an embodiment of the present disclosure.
Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts.
DETAILED DESCRIPTION
Provided are exemplary treated grinding articles, and methods for forming the treated grinding articles. Embodiments of the present disclosure, in comparison to articles and methods not utilizing one or more features disclosed herein, decrease costs, increase process efficiency, increase durability, increase reliability, increase service lifetime, decrease erosion, decrease wear, or a combination thereof.
Referring to FIGS. 1 and 2, in one embodiment, a method for forming a treated grinding article 100 includes applying a carburizing composition to an article 200. The article 200 includes an iron alloy 202 and an untreated hardness. Referring to FIGS. 2 and 3, the iron alloy 202 is carburized at a carburization temperature below about 550 °C, diffusing carbon atoms into the iron alloy 202 and forming a carburized portion 304 on an untreated portion 300. The carburized portion 304 includes a partially-treated iron alloy 302 and a partially-treated hardness greater than the untreated hardness. Referring to FIGS. 3 and 4, the partially-treated iron alloy 302 is annealed at a temperature of at least about 100 °C for a duration of at least about 5 hours, forming a treated portion 400 disposed on the untreated portion 300. The treated portion 400 includes a treated iron alloy 402 and a treated hardness greater than the partially-treated hardness. A grinding surface 404 of the treated grinding article 100 is formed.

Referring to FIG. 4, in one embodiment the treated grinding article 100 includes the untreated portion 300, the treated portion 400 disposed on the untreated portion 300, and the grinding surface 404. The untreated portion 300 includes the iron alloy 202 and the untreated hardness. The treated portion 400 includes the treated iron alloy 402 and the treated hardness. The treated iron alloy 402 includes a material composition essentially identical to the iron alloy 202 except that the treated iron alloy 402 includes elevated carbon content relative to the iron alloy 202. The treated hardness is greater than the untreated hardness. The material composition of the treated iron alloy 402 being essentially identical to the untreated iron alloy 202 save for the increased carbon content allows for some minimal additional differences in composition arising from chemical and structural changes caused by carburization and annealing as well as introduction of impurities during processing. In one embodiment any such additional differences in composition are de minimus, such that no material affect arises from the additional differences to the material properties of the alloys. In a further embodiment, the treated iron alloy 402 includes a material composition identical to the iron alloy 202 except that the treated iron alloy 402 includes elevated carbon content relative to the iron alloy 202. The treated iron alloy 402 may include a carburized and annealed structure.
The iron alloy 202 may be any suitable alloy, including, but not limited to chrome-iron alloys, chrome-iron alloys including at least about 30 wt% chrome, steel alloys, 4340 alloy steels, 4140 alloy steels, stainless steel alloys, austenitic stainless steel alloys, duplex stainless steel alloys 304, 316, 310, NITRONIC® 60, NITRONIC® 30, or NITRONIC® 50, Hadfield steels 2205 or 2507, or combinations thereof.
The treated portion 400 may include any suitable hardness, including, but not limited to a treated hardness of at least about 900 VPN, alternatively at least about 950 VPN, alternatively at least about 1,000 VPN, alternatively at least about 1,050 VPN, alternatively at least about 1,100 VPN, alternatively at least about 1,150

VPN, alternatively between about at least about 800 VPN and about 1,500 VPN, alternatively between about at least about 900 VPN and about 1,400 VPN, alternatively between about at least about 950 VPN and about 1,300 VPN, alternatively between about at least about 1,000 VPN and about 1,200 VPN.
Referring to FIG. 1, the treated grinding article 100 may be any suitable article. In one embodiment, the treated grinding article 100 is a grinding roll 102 such as, but not limited to, a coal grinding roll. The grinding roll 102 may be an independent component or the grinding roll 102 may be a component of a grinding apparatus 104, such as, but not limited to, a bowl mill, a ball and race mill, a drum and ball mill, a coal crusher, or combinations thereof.
In one embodiment, the treated iron alloy 402 is essentially free of chromium carbides at grain boundaries of the treated iron alloy 402. As used herein, "essentially free of chromium carbides" indicates that less than about 3% of the grain boundaries includes chromium carbides, alternatively less than about 2%, alternatively less than about 1%, alternatively less than about 0.5%, alternatively less than about 0.1%, alternatively less than about 0.05%, by weight. In a further embodiment, the treated iron alloy 402 is free of chromium carbides at grain boundaries of the treated iron alloy 402.
Referring to FIG. 2, in one embodiment the method for forming the treated grinding article includes activating a surface 204 of the article 200 prior to diffusing the carbon atoms into the iron alloy 202. Activating the surface 204 may include removing surface oxides from the surface 204 by any suitable technique, including, but not limited to, pickling with HC1, abrasive shot blasting, electrolysis, or combinations thereof.
Referring to FIGS. 2 and 3, carburizing the iron alloy 202 may include any suitable carburization technique, including, but not limited to, exposing the iron alloy 202

to a gas. Suitable gasses may include, but are not limited to, acetylene, carbon monoxide, or combinations thereof. In one embodiment, carburizing the iron alloy 202 occurs at a carburization temperature below about 550 °C, alternatively below about 525 °C, alternatively below about 500 °C, alternatively below about 475 °C, alternatively below about 450 °C, alternatively below about 425 °C, alternatively below about 400 °C, alternatively below about 375 °C. Carburizing the iron alloy 202 may be essentially free from forming chromium carbides at grain boundaries of the iron alloy 202, alternatively free from forming chromium carbides at grain boundaries of the iron alloy 202.
In one embodiment, diffusing carbon atoms into the iron alloy 202 includes essentially uniformly diffusing the carbon atoms into austenite and ferrite regions of the iron alloy 202, alternatively uniformly diffusing carbon atoms into austenite and ferrite regions of the iron alloy 202. "Essentially uniformly diffusing carbon atoms" indicates less than about a 10% variance in distribution, alternatively less than about a 5% variance in distribution, alternatively less than about a 1% variance in distribution, alternatively less than about a 0.1% variance in distribution. In another embodiment, diffusing carbon atoms into the iron alloy 202 includes non-uniformly diffusing the carbon atoms into austenite and ferrite regions of the iron alloy 202.
Diffusing carbon atoms into the iron alloy 202 may include increasing carbon content in the carburized portion 304 by any suitable amount, including but not limited to, up to about 10 wt%, alternatively up to about 7 wt%, alternatively up to about 6 wt%, alternatively between about 1 wt% and about 10 wt%, alternatively between about 1 wt% and about 7 wt%, alternatively between about 2 wt% and about 8 wt%, alternatively between about 3 wt% and about 7 wt%, alternatively between about 5 wt% and about 7 wt%, alternatively between about 6 wt% and about 7 wt%.

Referring to FIGS. 3 and 4, the partially-treated iron alloy 302 may be annealed at any suitable temperature and for any suitable duration. In one embodiment, the temperature of annealing the partially treated iron alloy 302 is at least about 100 °C, alternatively at least about 125 °C, alternatively at least about 150 °C, alternatively at least about 175 °C, alternatively at least about 200 °C, alternatively between about 100 °C and about 250 °C, alternatively between about 125 °C and about 225 °C, alternatively between about 150 °C and about 200 °C. The duration of annealing the partially-treated iron alloy 302 is at least about 5 hours, alternatively at least about 7.5 hours, alternatively at least about 10 hours, alternatively at least about 15 hours, alternatively at least about 20 hours, alternatively between about 5 hours and about 50 hours, alternatively between about 10 hours and about 25 hours.
Referring to FIGS. 4 and 5, in one embodiment, the method for forming the treated grinding article 100 further includes applying a grinding coating 500 to the treated portion 400, wherein applying the grinding coating 500 forms the grinding surface 404. Applying the grinding coating 500 may include any suitable technique selected, including, but not limited to, thermal spraying, cored wire arc spraying, wire arc spraying, high velocity air fuel spraying, cold spraying, welding, cladding, composite coating by plating, composite coating by electro-less plating, and combinations thereof.
The grinding coating 500 may be disposed directly on the treated portion 400 or may be disposed on an intermediate layer (not shown) such as a bond coat. Any suitable bond coat may be disposed between the grinding coating 500 and the treated portion 400, including, but not limited to, molybdenum, M-5A1, M-20A1, Ni-20Cr, MCrAlY (where M is nickel, cobalt, or iron), or combinations thereof.
The grinding coating 500 may include any suitable thickness, including, but not limited to, a grinding coating thickness 502 of between about 0.1 mm and about 10

mm, alternatively between about 0.25 mm and about 5 mm, alternatively between about 0.5 mm and about 3 mm.
In one embodiment, the applying the grinding coating 500 includes forming a matrix 504 having a matrix hardness on the treated portion 400, and dispersing a plurality of particles 506 having a particle hardness in the matrix 504, wherein the particle hardness is greater than the matrix hardness and greater than the treated hardness. The matrix hardness may be less than the treated hardness, about equal to the treated hardness, or greater than the treated portion hardness.
The plurality of particles 506 may include any suitable particles. In one embodiment, the plurality of particles 506 includes a plurality of ceramic particles. Suitable ceramic particles may include, but are not limited to, particles formed from a material including metal carbides, metal borides, metal oxides, boron nitrides, boron carbides, boron carbon nitrides, zirconia toughened aluminas, silicon carbides, silicon nitrides, silicon oxy-nitrides, silicon aluminum oxy-nitrides, or combinations thereof.
The plurality of particles 506 may include any suitable particle size distribution, including, but not limited to, a particle size distribution of up to about 10 nm, alternatively up to about 20 nm, alternatively up to about 25 nm, alternatively up to about 10 mm, alternatively up to about 20 mm, alternatively up to about 25 mm, alternatively from about 1 nm to about 25 mm, alternatively from about 1 nm to about 25 nm, alternatively from about 1 mm to about 25 mm. In one embodiment, the plurality of particles 506 includes a plurality of fine particles having a fine particle size distribution up to about 25 nm, and a plurality of coarse particles having a coarse particle size distribution from about 1 mm to about 25 mm, the plurality of fine particles and the plurality of coarse particles being intermixed. The intermixed plurality of fine particles and plurality of coarse particles may be distributed to optimize protection against erodent abrasive particles having

different sizes. The plurality of fine particles in the plurality of particles 506 may also fill in gaps which may be present between the plurality of coarse particles in the plurality of particles 506, thereby enhancing the resistance of the plurality of particles 506 to erosion and abrasion.
The matrix 504 may include any suitable material, including, but not limited to, cobalt-chromium alloys, nickel-chromium alloys, nickel aluminum alloys, iron-chromium alloys, iron-chromium-aluminum alloys, nickel-aluminum-chromium alloys, or combinations thereof.
In one embodiment, the plurality of particles 506 in the grinding coating 500 is essentially free of oxidation and decarburization chemical structure modifications. As used in this context, "essentially free" indicates that less than about 20%, by weight, of the plurality of particles 506 are oxidized or decarburized, alternatively less than about 15%, by weight, alternatively less than about 10%, by weight, alternatively less than about 5%, by weight, alternatively less than about 1%, by weight, alternatively less than about 0.5%, by weight.
The plurality of particles 506 may be randomly dispersed in the matrix 504 multi-modally dispersed in the matrix 504, essentially uniformly dispersed in the matrix 504, uniformly dispersed in the matrix 504, dispersed in the matrix 504 per a predetermined pattern, or combinations thereof. As used herein, "multi-modally dispersed" indicates a region having a greater concentration and a region having a lesser concentration, and "essentially uniformly dispersed" indicates a variance in concentration throughout the matrix 504 of less than about 20%, alternatively, less than about 15%, alternatively less than about 10%, alternatively less than about 5%,

alternatively less than about 1%. "Multi-modally dispersed" further may refer to the distribution of different sizes within the plurality of particles 506.
In one embodiment, the plurality of particles 506 is dispersed in the matrix 504 at a density (average, by weight) of at least about 50%, alternatively at least about 55%, alternatively at least about 60%, alternatively at least about 65%, alternatively at least about 75%, alternatively at least about 80%, alternatively at least about 85%), alternatively at least about 90%, alternatively between about 50% to about 99%), alternatively between about 60% to about 95%, alternatively between about 75%) to about 94%, alternatively between about 85% to about 93%, alternatively between about 90% to about 95%, alternatively about 93%.
In another embodiment, applying the grinding coating 500 includes ULTRAFLEX cladding the treated portion 400 with a cobalt-chromium alloy such as, but not limited to, the commercially available STELLITE® alloys. Suitable commercially available STELLITE® alloys include, but are not limited to, STELLITE® 20, STELLITE® 720, or combinations thereof. As used herein, "ULTRAFLEX" refers to a two-layer brazed clad process including a binder layer and a top layer. The binder layer is an organic coating including chromium carbide as hard particles, and the top layer is a STELLITE® composition. These combined layers are vacuum heat treated at about 1,000 °C to form the ULTRAFLEX cladding.
As used herein "STELLITE® 20" refers to an alloy including about 33 wt% chromium, about 17.5 wt% tungsten, about 2.45 wt% carbon, less than about 3 wt% nickel, less than about 1 wt% molybdenum, less than about 3 wt% iron, less than about 1 wt% silicon, less than about 1 wt% additional inclusions, and a balance of cobalt.
As used herein "STELLITE® 720" refers to an alloy including about 33 wt% chromium, about 2.45 wt%> carbon, less than about 3 wt% nickel, about 18 wt%

molybdenum, less than about 3 wt% iron, about 0.5 wt% silicon, less than about 1 wt% additional inclusions, and a balance of cobalt.
In yet another embodiment, applying the grinding coating 500 includes ULTRAFLEX cladding the treated portion 400 with a cobalt-chromium alloy and forming a matrix 504 having a matrix hardness on the treated portion 400, and dispersing a plurality of particles 506 having a particle hardness in the matrix 504, wherein the particles hardness is greater than the matrix hardness and greater than the treated hardness. The cladding may precede or follow
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

WE CLAIM:
1. A method for forming a treated grinding article, comprising:
applying a carburizing composition to an article, the article including an iron alloy and an untreated hardness;
carburizing the iron alloy at a carburization temperature below about 550 °C, diffusing carbon atoms into the iron alloy and forming a carburized portion on an untreated portion, the carburized portion having a partially-treated iron alloy and a partially-treated hardness greater than the untreated hardness;
annealing the partially-treated iron alloy at a temperature of at least about 100 °C for a duration of at least about 5 hours, forming a treated portion disposed on the untreated portion, the treated portion having a treated iron alloy and a treated hardness greater than the partially-treated hardness; and
forming a grinding surface of the treated grinding article.
2. The method as claimed in claim 1, including activating a surface of the article prior to diffusing the carbon atoms into the iron alloy, activating the surface including removing surface oxides from the surface.
3. The method as claimed in claim 1, wherein carburizing the iron alloy includes exposing the iron alloy to a gas selected from the group consisting of acetylene, carbon monoxide, and combinations thereof.
4. The method as claimed in claim 1, wherein the temperature of annealing the partially-treated iron alloy is at least about 150 °C.
5. The method as claimed in claim 1, wherein the duration of annealing the partially-treated iron alloy is at least about 10 hours.

6. The method as claimed in claim 1, wherein diffusing carbon atoms into the iron alloy includes increasing carbon content in the carburized portion by up to about 10wt%.
7. The method as claimed in claim 1, wherein carburizing the iron alloy is essentially free from forming chromium carbides at grain boundaries of the iron alloy.
8. The method as claimed in claim 1, including applying a grinding coating to the treated portion, wherein applying the grinding coating forms the grinding surface.
9. The method as claimed in claim 8, wherein applying the grinding coating includes:
forming a matrix having a matrix hardness on the treated portion; and dispersing a plurality of particles having a particle hardness in the
matrix, the particle hardness being greater than the matrix hardness and
greater than the treated hardness.
10. The method as claimed in claim 9, wherein applying the grinding coating
includes forming the matrix including a material selected from the group
consisting of cobalt-chromium alloys, nickel-chromium alloys, nickel
aluminum alloys, iron-chromium alloys, iron-chromium-aluminum alloys,
nickel-aluminum-chromium alloys, and combinations thereof, and dispersing
the plurality of particles in the matrix, the plurality of particles including a
ceramic material selected from the group consisting of metal carbides, metal
borides, metal oxides, boron nitrides, boron carbides, boron carbon nitrides,
zirconia toughened aluminas, silicon carbides, silicon nitrides, silicon oxy-
nitrides, silicon aluminum oxy-nitrides, and combinations thereof.

11. The method as claimed in claim 8, wherein applying the grinding coating includes ULTRAFLEX cladding the treated portion with at least one of STELLITE® 20 and STELLITE® 720.
12. The method as claimed in claim 8, wherein applying the grinding coating includes a technique selected from the group consisting of thermal spraying, cored wire arc spraying, wire arc spraying, high velocity air fuel spraying, cold spraying, welding, cladding, composite coating by plating, composite coating by electro-less plating, and combinations thereof.
13. The method as claimed in claim 1, wherein diffusing carbon atoms into the iron alloy includes essentially uniformly diffusing carbon atoms into austenite and ferrite regions of the iron alloy.
14. A treated grinding article, comprising:
an untreated portion including an iron alloy and an untreated hardness;
a treated portion disposed on the untreated portion, the treated portion including a treated iron alloy and a treated hardness, the treated iron alloy including a material composition essentially identical to the iron alloy except that the treated iron alloy includes elevated carbon content relative to the iron alloy, and the treated hardness being greater than the untreated hardness; and
a grinding surface.
15. The treated grinding article as claimed in claim 14, wherein the treated iron alloy includes a carburized and annealed structure.
16. The treated grinding article as claimed in claim 14, wherein the iron alloy is selected from the group consisting of chrome-iron alloys, chrome-iron alloys including at least about 30 wt% chrome, steel alloys, 4340 alloy steels, 4140 alloy steels, stainless steel alloys, austenitic stainless steel alloys, duplex

stainless steel alloys 304, 316, 310, NITRONIC® 60, NITRONIC® 30, and NITRONIC® 50, Hadfield steels 2205 and 2507, and combinations thereof.
17. The treated grinding article as claimed in claim 14, wherein the treated portion includes a treated hardness of at least about 900 VPN.
18. The treated grinding article as claimed in claim 14, wherein the treated grinding article is a coal grinding roll.
19. The treated grinding article as claimed in claim 14, wherein the treated iron alloy is essentially free of chromium carbides at grain boundaries of the treated iron alloy.
20. The treated grinding article as claimed in claim 14, including a grinding coating disposed on the treated portion, the grinding coating forming the grinding surface, wherein the grinding coating includes a least one of:
a plurality of particles having a particle hardness dispersed in a matrix having a matrix hardness:
the particle hardness being greater than the matrix hardness and greater than the treated hardness;
the plurality of particles including a plurality of ceramic particles selected from the group consisting of ceramics, metal carbides, metal borides, metal oxides, boron nitrides, boron carbides, boron carbon nitrides, zirconia toughened aluminas, silicon carbides, silicon nitrides, silicon oxy-nitrides, silicon aluminum oxy-nitrides, and combinations thereof; and
the matrix including a material selected from the group consisting of cobalt-chromium alloys, nickel-chromium alloys, nickel aluminum alloys, iron-chromium alloys, iron-chromium-aluminum alloys, nickel-aluminum-chromium alloys, and combinations thereof; and

ULTRAFLEX cladding including at least one of STELLITE® 20 and STELLITE® 720.