FIELD

[0001] The present disclosure relates to methods of increasing the durability of machinery

BACKGROUND

[0002] Certain machinery, such as that which is used in the hydraulic fracturing industry are subject to heavy wear due to pressure, friction, temperature, duration of use, the chemical environment, exposure to particulates and the like.

[0003] Various methods of increasing durability of a machine piece or tool may be employed. For example the selection of proper metals, such as steel alloys, with which to form such tools can increase durability.

[0004] There are different types of stainless steels: when nickel is added, for instance, the austenite structure of iron is stabilized. This crystal structure makes such steels virtually nonmagnetic and less brittle at low temperatures. For greater hardness and strength, more carbon is added. With proper heat treatment, these steels are used for such products as razor blades, cutlery, and tools.

[0005] Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low-alloy steels and high-alloy steels.

[0006] Carbon steel is steel in which the main interstitial alloying constituent is carbon in the range of 0.12-2.0%. Steel is generally considered to be carbon steel when no minimum content is specified or required for chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect; when the specified minimum for copper does not exceed 0.40 percent; or when the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60. [0007] Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion, their ability to hold a cutting edge, and/or their resistance to deformation at elevated temperatures (red-hardness). Tool steel is generally used in a heat-treated state. Many high carbon tool steels are also more resistant to corrosion due to their higher ratios of elements such as vanadium and niobium.

[0008] With carbon content between 0.7% and 1.5%, tool steels are manufactured under carefully controlled conditions to produce the required quality. The manganese content is often kept low to minimize the possibility of cracking during water quenching. However, proper heat treating of these steels is important for adequate performance, and there are many suppliers who provide tooling blanks intended for oil quenching.

[0009] Tool steels are made to a number of grades for different applications. Choice of grade depends on, among other things, whether a keen cutting edge is necessary, as in stamping dies, or whether the tool has to withstand impact loading and service conditions encountered with such hand tools as axes, pickaxes, and quarrying implements. In general, the edge temperature under expected use is an important determinant of both composition and required heat treatment. The higher carbon grades are typically used for such applications as stamping dies, metal cutting tools, etc.

[0010] Tool steels are generally grouped into six types: 1) high speed, 2) hot work, 3) cold work, 4) shock resisting, 5) special purpose and 6) water hardening. Grades of tool steels include, but are not limited to the following: Wl, W2, W3, W4, W5, W6 and W7 (which are high carbon water hardening tool steels); A2, A3, A4, A5, A6, A7, A8, A9 and A10 (which are air hardening tool steels); D2, D3, D4, D5, D6 and D7 ( which are high carbon, high chromium steels); 01, 02, 03, 04, 05, 06 and 07 (which are low carbon, oil hardening steels); H10, Hl l, H12 and H13 (which are hot work tool steels comprising chromium and molybdenum); HI 4, HI 6, H19 and H23 (which are hot work tool steels comprising chromium and tungsten); H20, H21, H22, H23, H24, H25 and H26 (which are hot work tool steels comprising tungsten); HI 5, H41, H42 and H43 (which are hot work tool steels comprising molybdenum); Ml through M47 (which are high speed molybdenum alloy tool steels); and Tl through T15 (which are high speed tungsten alloy tool steels); and P2, P3, P4, P5 and P6 (which are low carbon mold steels). Others include special purpose types such as LI through L6 (which are tough, low carbon steels); and F2 and F3 (which are special purpose carbon tungsten steels).

[0011] Other steel grades which are contemplated in the methods herein include, but are not limited to: 1018, 1045, 1140, 1215, 12L14, 4130, 4140, 4340, 8620, 301, 301LN, 303, 304, 304L, 304LN, 304H, 305, 316, 316L, 316LN, 316ΤΪ, 317L, 321, 321H, 409, 410, 430, 440A, 440B, 440C, 430F, and 904L.

[0012] Another method of increasing the durability of a machine part or a tool is the use of a chemical surface treatment.

[0013] Surface treatment by thermochemical diffusion processes are known to impart abrasion resistance to the surface of steels, for example, plain carbon or medium alloy steels, without affecting the tougher, impact-resistant underlying material. In particular, nitrocarburizing processes, such as disclosed in U.S. Pat. No. 5,102,476, are known to provide increased wear and corrosion resistance to steel surfaces. The disclosed nitrocarburizing process introduces nitrogen and carbon into the surface of steels to produce a "white" or "compound" layer. The compound layer, depending on the steel alloy and the diffusion atmosphere, contains varying amounts of cementite, carbides, and nitrides. Similarly, nitriding introduces nitrogen into the surface of steel to form a hardened, abrasion resistant layer.

[0014] In the case of ferritic carburizing, briefly carbon is added to the surface of a ferrous metal such as a steel alloy. The metal is subsequently heated such that the surface portion carburizes. In early applications, carburizing, such as box carburizing, involved the use of wood fires to carburize carbon coated metal. In such applications, carbon forms on the surface of the ferrous metal by the decomposition of carbon monoxide into carbon and carbon dioxide. The carbon dioxide reacts with uncondensed carbon in an applied carburizing compound until the metal is saturated. Other types of carburizing include gas carburizing and liquid carburizing.

[0015] Ferritic nitrocarburizing is a range of case hardening processes that diffuse nitrogen and carbon into ferrous metals at sub-critical temperatures. The processing temperature ranges from 525 °C to 625 °C, but usually occurs at 565 °C. At this temperature steels and other ferrous alloys are still in a ferritic phase, which is advantageous compared to other case hardening processes that occur in the austentic phase. There are four main classes of ferritic nitrocarburizing: gaseous, salt bath, ion or plasma, and fluidized-bed.

[0016] It is known that ferritic nitrocarburizing enhances the corrosion resistance of carbon steels and low alloy steels, particularly if a post nitrocarburizing treatment, such as a quench- polish-quench, is employed.

[0017] Ferritic nitrocarburizing diffuses mostly nitrogen and some carbon into the case of a machine part below the critical temperature, approximately 650 °C. Under the critical temperature the metal micro structure does not convert to an austenitic phase, but stays in the ferritic phase. The process is used to improve three main surface integrity aspects: scuffing resistance, fatigue properties, and corrosion resistance. It has the added advantage of inducing little shape distortion to the metal during the hardening process. This is because of the low processing temperature, which reduces thermal shocks and avoids phase transitions in steel. It is to be appreciated that the metal's underlying hardness (i.e. 20 C to 30 C Rockwell) remains relatively unchanged while the nitriding process adds an exterior comprising an increased surface hardness in the range of 60 C to 75 C Rockwell. In addition, the other core properties of the parts undergoing the ferritic nitrocarburizing process remain relatively unchanged.

[0018] Regarding liquid carburizing, salt bath ferritic nitrocarburizing is a thermo-chemical diffusion process, whereby a ferrous metal is submerged in an elevated temperature nitrocarburizing salt. This temperature is kept below the critical temperature, which is the temperature at which a phase transition in the material of the metal may occur. The resulting chemical reactions produce free nitrogen and carbon species which in turn diffuse into the surface of the metal and combine with the iron therein. This provides a hard case composed of a shallow compound zone, as for example of about less than a millimeter deep, and a subjacent diffusion zone of approximately less than one millimeter deep. Thus, salt bath nitrocarburizing improves wear resistance, lubricity, fatigue strength, and corrosion resistance as a result of the presence of an iron nitride compound(s) formed at the surface, in addition to a zone of diffused nitrogen in solid solution with the base material, subjacent to the compound layer. Both of these zones are metallurgically discernible, each providing specific engineering properties. [0019] Nitrocarburizing by means of molten cyanide and/or cyanate bath treatments results in formation of an epsilon iron carbonitride phase on the surface which improves the fatigue resistance, and wear and anti-scuffing properties. Typically, during ferritic nitrocarburizing only nitrogen diffuses inwardly from the carbonitride compound surface layer as the ferrite is already at its equilibrium concentration with respect to carbon.

[0020] Other forms of surface treatment are also used in the process of protecting tools and machine equipment from damage due to heavy wear. These include treating the surfaces of metallic articles with such processes as hardening, bluing, blackening, controlled oxidizing and/or controlled reducing.

[0021] One oxidative treatment used in the process of protecting tools and machine equipment is the use of black oxide, an oxidation process used in steel to protect from rust. Bluing is a passivation process in which steel is partially protected against rust, and is named after the blue- black appearance of the resulting protective finish. It is an electrochemical conversion coating resulting from an oxidizing chemical reaction with iron on the surface selectively forming magnetite (Fe304), the black oxide of iron.

[0022] Bluing may be applied, for example, by immersing the steel to be blued in a solution of potassium nitrate, sodium hydroxide, and water heated to the boiling point, 135 °C to 155 °C depending on the recipe. Similarly, steel to be blued may be immersed in a mixture of nitrates and chromates, similarly heated. Either of these two methods is called hot bluing.

[0023] Other types of black oxide coatings to protect steel include methods using a hot bath of sodium hydroxide, nitrates, and nitrites, at 141 °C to convert the surface of the steel into magnetite (Fe304). Hot blackening typically involves dipping the steel into various tanks. The steel is usually immersed by automated part carriers for transportation between tanks. These tanks contain, in order, alkaline cleaner, water, caustic soda at 140.5 °C (the blackening compound), and finally the sealant, which is usually oil. The caustic soda bonds chemically to the surface of the metal, creating a porous base layer on the surface.

[0024] Another form of treatment of protecting tools and machinery includes shot peening. Shot peening is a cold working process used to produce a compressive residual stress layer and modify mechanical properties of metals. It entails impacting a surface with shot (round metallic, glass, or ceramic particles) with force sufficient to create plastic deformation. In some ways, it is similar to sandblasting, except that it operates by the mechanism of plasticity rather than abrasion: each particle functions as a ball-peen hammer.

[0025] Peening a surface spreads it plastically, causing changes in the mechanical properties of the surface. Shot peening is often called for in aircraft repairs to relieve tensile stresses built up in the grinding process and replace them with beneficial compressive stresses. Depending on the part geometry, part material, shot material, shot quality, shot intensity, shot coverage, shot peening can increase fatigue life up to 1000%.

[0026] Plastic deformation induces a residual compressive stress in a peened surface, along with tensile stress in the interior. Surface compressive stresses confer resistance to metal fatigue and to some forms of stress corrosion. The tensile stresses deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start in the interior.

[0027] Although simple in concept, shot peening has become quite technical in recent years. Different shot types (grade, type, hardness, and shape), varying impact angles, intensities, velocities, nozzle-diameters, peening-times, the type of material and the surface coverage can all affect the end-physical properties of the peened metal.

[0028] It would therefore be useful to combine strategies in a new manner which would confer increased durability and corrosion resistance to machine parts and tools used in highly stressed environments.

SUMMARY

[0029] Certain embodiments of the invention pertain to method for improving the durability of iron alloy steel machine parts comprising: a) selecting a steel alloy; b) forming a tool out of the steel alloy; c) subjecting the tool to ferritic nitrocarburizing; and d) subjecting the tool to shot peening.

[0030] In certain embodiments concerning the iron alloy steel, the steel is a tool steel. In such embodiments concerning the iron alloy steel, forming the machine part comprises machining the part out of a block of the steel. In other embodiments, the machine part comprises casting the steel into a machine part.

[0031] Further, in embodiments of the invention concerning forming the machine part out of the steel, the machine part is subjected to oxidation. In such embodiments, the oxidation is a hot bluing oxidation or a black oxide oxidation. In such embodiments the oxidation forms Fe304 on a surface of the machine part.

[0032] Further embodiments concern the ferritic nitrocarburizing of the steel. The process may be any type of ferritic nitrocarburizing. In particular embodiments the ferritic nitrocarburizing is a fluidized bed ferritic nitrocarburizing

[0033] Still further, in certain embodiments wherein shot peening is concerned, the shot peening comprises a plurality of rounds of shot peening. In such embodiments, the rounds of shot peening comprise bombarding the tool with carbon steel shot. Still further the shot peening comprises bombarding the machine part with a plurality of rounds of steel shot. In such embodiments, each round has a smaller shot size.

[0034] In embodiments of the invention concerning the improvement, after the methods described herein, the machine part has a hardness of between 60 and 75 Rockwell where the shot bombarded the machine part.

[0035] Other embodiments herein concern a machine part produced by any of the aforementioned processes. Still other embodiments concern a machine part with properties conferred by any of the aforementioned processes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0001] In order that the manner in which the above-recited and other enhancements and objects of the invention are obtained, we briefly describe a more particular description of the invention briefly rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope, we herein describe the invention with additional specificity and detail through the use of the accompanying drawings in which:

[0002] Fig. 1 is flowchart schematic of the tool and machine part improving process; and

[0003] Fig. 2 is a figure of a fluid end illustrating the location of shot peening to harden the machine part.

List of Reference Numerals

[0004] 10 fluid end

[0005] 20 machining process

[0006] 30 oxidation process

[0007] 40 ferritic nitrocarburizing

[0008] 50 internal surfaces

[0009] 60 large diameter shot peening process

[0010] 70 smaller diameter shot peening process

DETAILED DESCRIPTION

[0011] The embodiments of the invention relate to methods of increasing the durability of machinery. The particulars shown herein are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of various embodiments of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for the fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention are embodied in practice. [0012] Certain embodiments of the invention comprise a method of increasing the durability of machine parts by choosing a grade of steel, machining the part desired, subjecting the part to a passivation process such as oxidation, subjecting the part to a carburizing treatment and subjecting the part to bombardment with shot to increase hardness and durability.

[0013] While the invention contemplates the improved durability of tools and machine parts, persons of ordinary skill in the art should understand that the methods disclosed herein can be used to increase the durability of other steel objects as well, such as gun parts, utensils, steel plates, steel bolts, steel structural supports, steel vehicles, steel construction equipment, steel medical devices, steel sporting goods, steel plumbing equipment, steel valves, steel pipes used in chemical and petroleum industries and the like. In the foregoing, a tool and a machine part are interchangeable terminology.

[0014] Certain embodiments of the invention concern choosing the correct metal out of which to fabricate the machine part. In specific embodiments the metal is a steel. The steel may be any steel capable of undergoing a carburization process or a passivation process such as oxidation, or both. Examples of steel contemplated for use in the invention include the following: 1018, 1045, 1140, 1215, 12L14, 4130, 4140, 4340, 8620, 301, 301LN, 303, 304, 304L, 304LN, 304H, 305, 316, 316L, 316LN, 316Ti, 317L, 321, 321H, 409, 410, 430, 440A, 440B, 440C, 430F, and 904L. However, in certain embodiments, any iron alloy steel can be used.

[0015] In particular embodiments, the steel used is a harder alloy such as tool steel. In certain embodiments the tool steel is a high carbon water hardening tool steel such as Wl, W2, W3, W4, W5, W6, or W7. In other embodiments the tool steel is air hardening tool steels such as A2, A3, A4, A5, A6, A7, A8, A9 or A10. In still further embodiments, the tool steel is air hardening high chromium steel such as D2, D3, D4, D5, D6 or D7. In some embodiments, the tool steel is low carbon oil hardening steel 01, 02, 03, 04, 05, 06 or 07. In further embodiments, the tool steel is a hot work tool steel comprising chromium and molybdenum such as H10, Hl l, H12 or H13. Alternatively, the tool steel is a high speed molybdenum alloy steel such as M- through M 47. In other embodiments the tool steel is a low carbon mold steel alloy such as P2, P3, P4, P5 or P6. Still further, the tool steel can be a high speed tungsten alloy tool steel such as Tl, T2, T3 or T4 or T5. In other embodiments, the tool steel is a special purpose steel such as a tough low carbon steel of LI, L2, L3, L4, L5 or L6. Alternatively, the tool steel is a special purpose carbon tungsten steel such as F2 or F3.

[0016] Other embodiments of the invention concern the use of a passivation process for treating the machine part or tool part after selection of the desired steel and part machining.

[0017] In certain embodiments, bluing is applied as a passivation process for preventing red oxidation, rust, from damaging the durability of the machine part. In such embodiments, the bluing a hot bluing. In further embodiments, the bluing is accomplished by immersing the steel to be blued in a solution of potassium nitrate, sodium hydroxide at a temperature of approximately 500 °C. In other embodiments, the machine to be blued is immersed in a mixture of nitrates and chromates.

[0018] In further embodiments concerning a passivation process, the process is a black oxide passivation. In such embodiments, the machine part is immersed into a plurality of tanks. These tanks contain, in order, alkaline cleaner, water, caustic soda at 140.5°C (the blackening compound), and finally the sealant, which is usually oil. The caustic soda bonds chemically to the surface of the metal, creating a porous base layer on the machine part. Oil is then applied to the heated part, which seals it by sinking into the applied porous layer. It is the oil that prevents the corrosion of the machine part.

[0019] Additional embodiments of the invention concern ferritic carburization of the tool or machine part. In certain embodiments of the invention, the carburization is box carburization. In other embodiments of the invention, the carburization is gas carburization. In still further embodiments, the carburization is liquid carburization.

[0020] In particular embodiments of the invention, the carburization is ferritic nitrocarburizing.

[0021] In certain embodiments, the ferritic nitrocarburizing is a salt bath nitriding. Salt bath ferritic nitrocarburizing is a thermo-chemical diffusion process, whereby a ferrous metal is submerged in an elevated temperature nitrocarburizing salt. This temperature is kept below the critical temperature, which is the temperature at which a phase transition in the material of the metal may occur. The resulting chemical reactions produce free nitrogen and carbon species which in turn diffuse into the surface of the metal and combine with the iron therein. This provides a hard case composed of a shallow compound zone, as for example of about less than a millimeter deep, and a subjacent diffusion zone of approximately less than one millimeter deep. Thus, salt bath nitrocarbunzing improves wear resistance, lubricity, fatigue strength, and corrosion resistance as a result of the presence of an iron nitride compound(s) formed at the surface, in addition to a zone of diffused nitrogen in solid solution with the base material, subjacent to the compound layer. Both of these zones are metallurgically discernible, each providing specific engineering properties.

[0022] In embodiments concerning salt bath nitriding, the nitriding is performed at a high temperature of around 580.5°C. Such salt bath nitriding enhances the corrosion resistance of carbon steels and low alloy steels, particularly if a post nitrocarbunzing treatment, such as a quench-polish-quench, is employed.

[0023] In further embodiments, the ferritic nitrocarburizing is gas nitrocarburizing.

[0024] In further embodiments, the ferritic nitrocarburizing is a fluidized bed nitrocarburizing.

[0025] In certain embodiments, the oxidation step takes place at the same time as the ferritic nitrocarburizing step. In other embodiments, the oxidation step takes place before the ferritic nitrocarburizing step. In embodiments wherein the ferritic nitrocarburizing step is a fluidized bed ferritic nitrocarburizing step, the oxidation process is contemplated to take place at the same time.

[0026] Upon completion of ferritic nitrocarburizing, the machine part or tool is subjected to shot peening. In certain embodiments, the shot peening is done with spherical shot having about the same diameter. In other embodiments, the shot peening is done with a mixture of different spherical shot having different diameters. In other embodiments, the shot peening is completed in a plurality of rounds with one size particle in one round and another size particle in another round. In other embodiments, the shot particle is cut shot.

[0027] In certain instances, the shot peening lasts for 1 minute to one hour during a single round or some time in between. [0028] In embodiments of the invention concerning the composition of the particles, the particles may be comprised of alumnosilicate, cast aluminum oxide, cast carbon steel, cast zinc, cast ferrite steel shot, cast iron, a ceramic, aluminum cut wire, carbon steel cut wire, stainless steel cut wire, zinc cut wire, copper cut wire, nickel cut wire, titanium cut wire, silicon carbide or garnet. In specific embodiments, the particles comprise cast carbon steel.

[0029] In embodiments wherein the particles comprise cast carbon steel, the shot size may be any size typically used in the industry. Examples of shot size used in the industry include diameters of .070 mm, .125 mm, .180 mm, .300 mm, .355 mm, .425 mm, .500 mm, .600 mm, .710 mm, .850 mm, 1.00 mm, 1.18 mm, 1.40 mm, 1.70 mm, 2.00 mm, 2.36 mm and 2.80 mm. These correspond to a mesh numbering of 200, 120, 80, 50, 45, 40, 35, 30, 25, 20, 18, 16, 14, 12, 10, 8 and 7 respectively.

[0030] In further embodiments concerning the shot peening, the shot peening is delivered at a pressure ranging from 20 psi, 30, psi, 40 psi, 50 psi, 60 psi, 70 psi, 80 psi, 90 psi 100 psi or some pressure therein. In other embodiments concerning the shot peening, the shot peening is delivered by a nozzle. Standard nozzle sizes include 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm and the like.

[0031] In a specific operation, a fluid end 10, as seen in Fig. 1, which is used in the fracking industry, is subjected to a machining process 20 out of a solid block of tool steel as charted in Fig. 2. Upon machining the part, it is subjected to an oxidation process 30. In this process, the fluid end is subjected to a hot bluing process. In order to blue the fluid end, bluing is an electrochemical conversion coating resulting from an oxidizing chemical reaction with iron on the surface selectively forming magnetite (Fe304), the black oxide of iron.

[0032] Following the oxidation process, or at the same time as the oxidation process, the fluid end is subjected to ferritic nitrocarburizing 40 wherein the fluid end is subjected to a fludized bed nitrocarburizing to enhance the corrosion resistance of the machine part. This process adds an exterior comprising an increased surface hardness in the range of 60 C to 75 C Rockwell.

[0033] Following nitrocarburizing, the fluid end is subjected to shot peening on its internal surfaces 50 as depicted in Fig. 2. Herein two rounds of shot peening are employed, each with different size carbon steel shot. The dual shot starts with using a large diameter shot peening process of 2 mm in size, 60 as depicted in Fig. 1 on the first round, and then it is followed up with a second smaller diameter shot peening process 70 of 1 mm in size. The small diameter shot increases the depth and consistency of the compressive stress and further reduces surface imperfections. Upon completion of the shot peening, the fluid end is considered to have increased durability over fluid ends which do not undergo this process. The resultant fluid end is capable of operation for an increased length of time. In the aforementioned example, a fluid end without the improved process will typically last for approximately 300 to 600 hours of use. Following the improved process, a fluid end produced by this process will typically last for between 600 and 1500 hours of use.

[0034] From the foregoing description, one of ordinary skill in the art can easily ascertain the essential characteristics of this disclosure, and without departing from the spirit and scope thereof, can make various changes and modifications to adapt the disclosure to various usages and conditions. For example, we do not mean for references such as above, below, left, right, and the like to be limiting but rather as a guide for orientation of the referenced element to another element. A person of skill in the art should understand that certain of the above-described structures, functions, and operations of the above-described embodiments are not necessary to practice the present disclosure and are included in the description simply for completeness of an exemplary embodiment or embodiments. In addition, a person of skill in the art should understand that specific structures, functions, and operations set forth in the above-described referenced patents and publications can be practiced in conjunction with the present disclosure, but they are not essential to its practice.

[0035] The invention can be embodied in other specific forms without departing from its spirit or essential characteristics. A person of skill in the art should consider the described embodiments in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. A person of skill in the art should embrace, within their scope, all changes to the claims which come within the meaning and range of equivalency of the claims. Further, we hereby incorporate by reference, as if presented in their entirety, all published documents, patents, and applications mentioned herein.