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1. (WO2019043369) IRON BASED ALLOY
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IRON BASED ALLOY

The present invention relates to iron based alloy compositions which have a number of industrial applications. The alloys may be used in a variety of welding applications on account of their superior galling resistance, low coefficient of friction and shrinkage. The alloys may also be used for protecting or re-finishing industrial tools which will be or have been exposed to wear during use. Wear arises as a result of the normal cutting or drilling or similar operations of the tool. Large industrial tools which suffer wear include drill strings used in the oil and gas industry. The ability to form reliable welded joints between materials is important in a variety of civil engineering applications. Similarly, in industrial manufacture and processing, the issue of wear at contacting surfaces in production engineering applications or mineral extraction is a widespread problem. The present invention is concerned with providing alloys which can be used in welding fabrication applications and also in tool production and maintenance applications in order to overcome or reduce such issues. The alloy is also intended to show superior galling and wear resistance.

In welding fabrication applications, distortion of the welded piece is an important consideration. Welding involves highly localised heating of joint edges to fuse the material with the result that non-uniform stresses are set up in the component because of expansion and contraction of the heated material. Initially, compressive stresses are created in the surrounding cold parent metal when the weld pool is formed due to the thermal expansion of the hot metal (heat affected zone) adjacent to the weld pool. However, tensile stresses occur on cooling when the contraction of the weld metal and the immediate heat affected zone is resisted by the bulk of the cold parent metal. The magnitude of thermal stresses induced into the material can be seen by the volume change in the weld area on solidification and subsequent cooling to room temperature.

It is almost impossible to predict accurately the amount of shrinking. Various procedures have been suggested in order to minimise distortion due to welding including the recommendation not to overweld, the use of intermittent welding and planning the sequence of welding. Nevertheless, the issue of distortion remains a technical problem during the weld fabrication process. There are a number of inherent material properties which influence distortion. These include the coefficient of thermal expansion and the specific heat per unit volume. Distortion is determined by expansion and contraction of the material so the coefficient of thermal expansion of the material plays a significant role in determining the stresses generated during welding. This in turn affects the amount of distortion. Different materials therefore suffer differing degrees of distortion and, by way of example, a material such as stainless steel which has a higher coefficient of expansion than normal low carbon steel is more likely to suffer from distortion during welding.

Alloys which has a low coefficient of shrinkage and which can be used to form welded joints are therefore highly desirable

In the field of engineering tools, surfaces which are prone to wear are normally protected by the application of hard surfacing alloys. These hard surfacing alloys are sometimes known as hard-banding alloys, particularly in the oil and gas drilling industry. The tools are expensive and worn or part-worn tools may be re-finished to extend their useful working life by the application of a hard surfacing alloy to the used tool. The hard surfacing alloys perform the function of improving the wear resistance of tools and provide a region of increased wear resistance and hardness relative to the rest of the tool.

In certain cases, the hard-banding alloy is applied to a new surface to provide an initial protective layer. When the surface has been worn it can be reapplied over existing hard-banding. Normally the surfaces are inspected to ensure that any subsequent hard-banding layer is compatible with the underlying existing hard-banding layer from a metallurgical point of view. However, different layers may be the same or different composition.

A drill string is used to access underground or undersea reserves of hydrocarbon deposits in the form of oil and gas. The drill string has a drill bit at its remote end for drilling through earth and rock in the ground or seabed which is joined to a series of pipe sections which extend the length of the drill. This is done incrementally as the drill string is gradually formed from multiple sections of pipe which are screwed together as the drill bit penetrates the ground or seabed. The individual sections are usually connected together by tool joints

The drill string is rotated inside a casing which prevents collapse of the hole that is formed by the drill as it progresses. The casing is designed so that the drill bit, joints and individual pipe sections forming the drill sting as a whole can pass through the inside of the casing. As drilling progresses, some of the earth and rock which is being drilled inevitably ends up inside the drill casing and contributes to wear of the drill string as it rotates within the casing hence the casing is also prone to wear. This is of particular concern at the joints between sections of the drill string because these are of slightly larger diameter than the pipe sections forming the drill string itself. In addition, the joints may also directly contact the casing providing another source of wear at the joints. Casing is particularly prone to wear in directional wells where the well path is highly deviated.

Conventionally, this problem has been addressed by providing a surface treatment on the joints. This type of surface treatment is known as hard-facing. Hard-facing refers to the application of a wear-resistant alloy to that part of the surface of a tool which is prone to wear. The hard-facing alloy is normally applied by welding to the surface.

There is a need for an alloy which can be used in welding fabrications and other similar applications. There is also a need for a hard-facing alloy which can be used to protect or extend the life of machine tools and the like. Ideally, the alloy produced for either application should be relatively economical to manufacture.

It is therefore an aim of the present invention to provide alloys which are designed so that they provide a relatively low degree of thermal shrinkage for welding applications. Another aim is that the alloy should contribute to the structural integrity of the welded ensemble as a whole. A further aim is that the composition of the alloy of the present invention is compatible with forming welded joints in a range of steel, stainless steel and other alloys. The alloy should desirably have good flow ability and / or wettability. A further aim is to provide an alloy that is resistant to corrosion. Yet another aim is to produce an alloy which can be welded without the need for special atmospheric shielding. The alloys should ideally have good durability and resistance to cracking.

A separate ambition of the invention is to provide alloys having a protective function to surfaces prone to wear, such as the tool joints of drill strings. Ideally such alloys should provide wear resistance whilst at the same time not suffering the disadvantages of known materials such as tungsten carbide. Ideally, the alloy is at least as hard or is harder than the rock or earth which is being drilled. Thus, one aim of the present invention is to provide a hard-facing alloy which is sufficiently hard to provide the protective function whilst at the same time not causing excessive wear in any surface that it might contact when in use (for example, the inside of a well casing).

One aim is to provide a hard-facing alloy which has a relatively low coefficient of friction. Another aim of the present invention is to provide a hard-facing alloy which is strong and does not degrade the structural integrity of the substrate i.e. tool surface to which it is being applied. It is also an aim that the hard-facing alloy contributes to the integrity of the ensemble as a whole i.e. in the case of a drill string to the strength of the joint between successive sections of the drill string. Another aim is to provide a hard-facing alloy which has good resistance to the formation of cracks.

It is also an aim that the alloy will have good longevity in use. A further aim is to provide steel alloys that have good corrosion resistance, including at elevated temperatures. A further aim is to provide a hard-facing alloy which is economical to manufacture. Another aim is to provide a hard-facing alloy which is presented in a convenient form and which is convenient to apply to a variety of industrial tools. It is also an aim of the present invention to prepare an alloy which can be produced in a process which is convenient to run so that the manufacturing process is relatively straight forward. It is also an aim to provide a process which is applicable to the large scale production of hard-banding alloy.

The present invention satisfies some or all of the above aims. It is the interplay between the various elemental components that gives rise to the superior properties of the iron based alloys both as welding alloys and as hard-banding alloys when compared with conventional alloys.

According to a first aspect of the present invention, there is provided an alloy having the following composition:

manganese in an amount of 8 to 12% by weight,

nickel in an amount of 8 to 12% by weight,

carbon in an amount of 2 to 4% by weight,

silicon in an amount of 2% to 6% by weight.and

cerium in an amount of 0.01 % to 0.15% by weight, wherein the alloy optionally further comprises one or more of the following elements:calcium in an amount of up to 1.0% by weight,

magnesium in an amount of up to 0.15%by weight,

titanium in an amount of up to 9% by weight,

molybdenum in an amount of up to 4% by weight,

vanadium in an amount of up to 4% by weight,

phosphorus in an amount of up to 0.05% by weight, and

sulphur in an amount of up to 0.05% by weight,

and wherein the balance is Fe and incidental impurities.

These figures represent the results which can be obtained using Leco for C, S and XRF for the remainder of the elements.

This is the composition of a iron based alloy that has been applied to a substrate as discussed below. Methods of preparing such alloys are also discussed later below in more detail.

The iron based alloy composition has been carefully chosen and is advantageous in hardbanding applications for example for a number of reasons. These include the fact that there is a low coefficient of friction behaviour and an excellent galling resistance (Galling is the form of adhesive wear between sliding surfaces)- which is beneficial for the casing friendliness. There is also a low coefficient of thermal expansion - which is beneficial for the non-cracking behaviour during hardbanding and while in use. This is beneficial in the formation of welded pieces also.

The alloys of the present invention are based on high manganese steel and as such manganese is an important component of the alloys. Manganese steels, and in particular high manganese steels, have been known for about 200 years and are known as "Hadfield steels" after their inventor. These steels provide a combination of high wear resistance with high toughness.

The steels generally include a significant amount of manganese in order to obtain the wear resistance, toughness and work hardening that is required. In the case of the alloys of the present invention, we have determined that an amount of 8 to 12wt% by weight of manganese is necessary in order to obtain the optimum work hardening behaviour in the hardbanding alloy. If there is less than 8wt% manganese there is insufficient work hardening. Similarly, beyond the content of about 12wt%, an increasing content of manganese does not lead to any improvement and may even cause deterioration of the alloy's properties. Furthermore, since manganese is a more expensive element than iron the addition of unnecessary quantities of manganese is not desirable for economic reasons.

In an embodiment, the amount of manganese is preferably 1 1 to 12% by weight. This amount of manganese results in better work hardening behaviour in the hardbandings. More preferably, the amount of manganese is 11.5 to 12% by weight since this gives the best work hardening behaviour. Alternative, in some embodiments, it is preferable that the amount of manganese is in the range of 9 to 11 % by weight since this leads to the optimum level of work hardening in the alloys of the invention; this is particularly the case where there is also a relatively low content of nickel. By the same token, alloys containing 1 1-12% by weight of manganese may be preferred when there is a relatively high nickel content.

Nickel is an essential component of the alloy and provides both strength and corrosion resistance to the alloy. The amount of nickel should be in the range of 8-12wt%. In an embodiment, the amount of nickel is preferably 11 to 12% by weight. This amount of nickel results in better work hardening. More preferably, the amount of nickel is 11.5 to 12% by weight since this gives the best work hardening behaviour. Alternative, in some embodiments, it is preferable that the amount of nickel is in the range of 9 to 11 % by weight since this leads to the optimum level of work hardening in the alloys of the invention; this is particularly the case where there is also a relatively low content of manganese. By the same token, alloys containing 10.5-12% by weight of nickel may be preferred when there is a relatively high manganese content, with a nickel content in the range of 11-12wt% being more preferable. If there is less than 8wt% nickel then insufficient work hardening results. Similarly, increasing the nickel content beyond 12wt% does not confer any advantage on the alloy and may even cause a deterioration of the alloy's properties. Furthermore, since nickel is a more expensive element than iron the addition of unnecessary quantities of nickel is not desirable for economic reasons

The relative contents of manganese and nickel are important and preferably lie within the range of from a ratio of 1.2:1.0 manganese to nickel content by wt% to a ratio of 1.0: 1.2 manganese to nickel content by wt%. More preferably, the relative contents of manganese and nickel lie within the range of from a ratio of 1.1 : 1.0 to a ratio of 1.0: 1.1. In some embodiments the ratio is about 1 : 1 manganese to nickel by wt%.

We have also found that it is possible to increase the wear resistance of iron based alloy by addition of manganese and nickel as elemental components. The manganese

and nickel are incorporated into the iron matrix leading to the beneficial properties of the alloys of the invention.

Some of the important features of a suitable hardbanding material include casing friendliness and wear resistance. We have added relatively high amounts of manganese and relatively high amounts of nickel in order to improve the wear resistance of iron based weld. At the same time, it is important that the amounts of manganese and nickel are not to excessive or these beneficial properties deteriorate and the alloy becomes unworkable. In this respect, it is important to recognise that the alloy represents a careful balance between the various elemental components and that all of the essential elements contribute to the properties of the iron based alloy. In the present case, the manganese and nickel are added principally to obtain an austenitic Hadfield work hardening behaviour in the alloy.

We have found that carbides that have been used in other hardbanding alloys (specifically carbides of titanium, molybdenum and vanadium) can be added to improve the wear resistance. In the iron based alloys of the present invention, titanium can be added in an amount of up to 9%wt. Molybdenum can be added in an amount up to 4%wt. Vanadium can be added in an amount up to 4 wt%. The addition of each of titanium, molybdenum and vanadium may occur independently of each other.

The titanium, molybdenum and vanadium are important carbide forming elements in hardbanding alloys and find utility in the alloys of the present invention. The presence of these elements in the hardbanding alloys of the invention is found to impart exceptional resistance to the formation of cracks, improved wear resistance, and improved hardness to the surface of the underlying joint or tool. The weld deposit characteristics in the hardbanding include a matrix having a fine grain size and small, evenly dispersed carbides within the matrix. A small amount of carbon is present in the matrix. Various other alloying elements may optionally be included in the hardbanding alloys to further enhance various properties exhibited by the weld deposit as described in greater detail below.

Titanium can be added to the alloy because it readily forms a carbide. The titanium in the composition reacts fastest and preferentially to form titanium carbide in the presence of other elements. This material has a very high melting point, is stable at high temperature and has a low chemical reactivity. It is also extremely hard. It can be added independently of the other carbide forming elements molybdenum and vanadium.

Molybdenum can be added to the alloy because molybdenum is able to penetrate into the unit cell of titanium carbide (forming a so called solid solution) when titanium is present and makes the whole unit cell denser. This results in the titanium carbide being sufficiently dense that it does not float to the top of the alloy. In other words it imparts neutral buoyancy to the alloy. Molybdenum thus functions as a bimetallic carbide forming element together with titanium. Molybdenum is an element that also provides improved tensile strength of the weld and is a solid-solution strengthener. Thus molybdenum can also be added in the absence of titanium and / or vanadium i.e. independently of titanium and/or vanadium.

Vanadium can be added in order to produce a ternary carbide. The ternary carbide has a low coefficient of friction and this contributes to one of the beneficial properties of the hard-banding alloys of the present invention. Vanadium is a secondary carbide former and a grain refiner. Vanadium also increases the toughness of the weld deposit. Thus vanadium can be added independently of molybdenum and/or titanium.

In certain applications, it is preferable that each of molybdenum, titanium and vanadium are all present in the alloy. In such circumstances, it is preferable that the minimum content of each of these elements is at least 0.1 %wt, and more preferably at least 0.5%wt.

It is important to achieve the correct balance between the amounts of manganese and nickel, as well as between the amounts of titanium, molybdenum, vanadium and carbon so that an alloy of the correct hardness, coefficient of friction and density is produced. It is the interplay between these various factors that gives the alloy of the present invention it superior properties relative to conventional alloys. Furthermore, the relative amounts of manganese and nickel together on the one hand, and one or more of titanium, molybdenum and vanadium on the other hand is also very important in the alloys of the present invention. In other words, the relativity between the manganese and nickel as compared to titanium, molybdenum and vanadium (when these elements are present) also requires careful control. This is the reason for the limitations on the maximum amounts of titanium, molybdenum and vanadium.

Carbon is an essential component of iron based alloys. Carbon should be present in an amount of 2 to 4%wt. In some preferred embodiments, carbon is present in an amount of 2 to 2.5%wt. In alternative embodiments for high carbon iron based alloy applications, the preferred amount of carbon is 3 to 4%wt.

When carbide forming elements are present it is also possible to form primary, secondary or ternary carbides with carbon. The extent to which this is desirable depends on the exact application of the alloy. Thus, when titanium, molybdenum and vanadium are present, carbides may be formed including a ternary carbide of these elements. In certain cases, it is desirable for there to be sufficient quantity of available carbon to form the mixed solid solution of TiMo(V)C .

Titanium is added in an amount of up to 9wt% in the alloys of the invention. Higher levels create a very viscous weld bead, lower levels can be used but wear resistance is reduced. In an embodiment the titanium is present in a first subrange in an amount of from 2 to 4.5 wt%, and more preferably the amount of titanium is from 3wt% to 4.5 wt%.This first subrange provides an optimum combination of wear resistance and low coefficient of friction. In another embodiment, the amount of titanium in a second subrange is from 4.0 to 9 wt%. This second subrange provides an alloy with more wear resistance than the first subrange with a balanced low coefficient of friction.

In an embodiment, the amount of molybdenum in the alloy is preferably up to 4.0% Molybdenum content in this range is related to the titanium content and leads to optimum buoyancy i.e. a buoyancy approaching neutral buoyancy for the mixed carbide in the weld bead. In another embodiment the molybdenum is present in a first subrange in an amount of from 0.5% to 2.5 wt%. This first subrange provides an optimum combination of wear resistance and low coefficient of friction. In another embodiment, the amount of molybdenum in a second subrange is from 2% to 4wt%. This second subrange provides an alloy with more wear resistance than the first subrange with a balanced low coefficient of friction.

The amount of vanadium in the alloy is preferably up to 2.5% by weight. In some cases, vanadium can be omitted from the alloys since the relative amounts of titanium, molybdenum and manganese provide the necessary balance of wear resistance and low coefficient of friction. When present, an amount of vanadium within the range up to 2.5wt% provides an alloy having the correct viscosity in order to be able to disperse

properly around the joint and to form an effective hardbanding. If the viscosity is too low the hardbanding will spread too widely when being applied. Equally, if the viscosity is too large it becomes difficult to work and thus to form a suitable hardbanding around the joint. In an embodiment the vanadium is present in a first subrange in an amount of from 1 to 2.5wt%. This first subrange provides an optimum combination of wear resistance and low coefficient of friction. In another embodiment, the amount of vanadium in a second subrange is from 2 to 4 wt%. This second subrange provides an alloy with more wear resistance than the first subrange with a balanced low coefficient of friction.

Where first and second subranges have been defined for each of titanium, molybdenum, vanadium and carbon, these different sub ranges apply independently to those elements. In other words, it is possible to use an amount within the first subrange in relation to say titanium and yet use an amount within the second sub range in relation to one or more of the remaining elements molybdenum, vanadium and carbon. The extent to which this is done will depend on the requirement in any particular case to optimise the combination of wear resistance and low coefficient of friction in the final alloy based on operating wholly or largely within the first subrange or the requirement of achieving an overall higher level of wear resistance based on operating wholly or largely within the second subrange.

Calcium is added as an agent to improve the weldability of the hardbanding around the joint. Calcium is important because it also improves the welding finish. It can be added in an amount of up to 1 % by weight. A minimum amount of calcium of 0.1 wt% provides a good technical benefit. An amount of 0.5 to 1 % by weight provides a good welding finish and thus represents the optimum amount of calcium.

Silicon may also be independently added as an agent to improve the weldability of the hardbanding around the joint and increases strength and hardness but to a lesser extent than manganese. Silicon is also not an essential component of the alloy but, when added, it also improves the welding finish. Silicon can be added in an amount of 2-6wt% by weight. When present, a minimum amount of silicon of 2wt% provides a beneficial effect. The optimum amount of silicon, when present, lies in the range 2-3wt% by weight since this gives the best improvement in strength and weldability. Silicon also provides the function of a deoxidiser to improve the soundness of the weld and to be free from defects such as porosity and other discontinuities and is often an important component in stainless steel. Silicon may also contribute to increasing the stability of any surface oxide film. On the other hand, if the content of silicon is too high the workability of the steel is reduced.

Although calcium and silicon may independently perform the same function in improving the weld finish, in certain cases it is desirable to both of those elements in combination. Thus, the inclusion of both of those elements can in certain cases provide an improved weld in the hardbanding applied to a joint.

Cerium is mainly added to reduce the susceptibility of the alloys to cracking. Furthermore the addition of cerium to the alloy not only improves the quality of the alloy but also makes it easier to handle. A further benefit of cerium addition is that it contributes to the strength of the iron based alloy. Cerium may be present in an amount of up to 0.15%wt. A minimum amount of 0.01wt% of cerium may lead to a beneficial effect, though the lower limit of cerium, when present, is normally 0.05wt%. Preferably, cerium is present in an amount of from 0.05 wt% to 0.15 wt%, and more preferably is present in an amount of from 0.05 wt% to 0.10 wt%.

Magnesium may also be added to the iron based alloys of the invention. When present, magnesium acts as a scavenger. It also improves wettability in welded joints. Magnesium may be present in an amount of up to 0.15wt% or even up to 0.25wt%. A minimum amount of 0.01wt% may lead to a beneficial effect, though the lower limit of magnesium, when present, is normally 0.05wt%. Preferably, magnesium, when present is present in an amount of 0.12wt% to 0.25wt% in order to provide the strongest scavenging effects. However, in certain cases, it is preferable that there is no magnesium in the iron based alloys at all because the presence of magnesium may reduce the effectiveness of the manganese and nickel at work hardening.

Phosphorus, when present, is generally present as a trace element in the alloy.

Sulphur, when present, is generally present as a trace element in the alloy.

A number of elements will be present in the alloy as inevitable impurities. Such incidental elements will not have any discernible technical benefit or adverse effect on the alloys of the present invention. In some cases, the presence of such elements can be tolerated in relatively large amounts provided that they do not affect the desired

properties of the alloy. For example, although not specifically envisaged in the alloys of the present invention, it is conceivable that an element such as aluminium may arise as an incidental impurity as a consequence of its occurrence as an impurity in one of the deliberately added elemental components. This is acceptable provided that the presence of such an element, for example aluminium, does not have any deleterious effects on the alloy. In certain cases, elemental components such as titanium may bring with them other incidental elements. These can be generally tolerated as incidental impurities at low levels. Where analysis reveals that such impurities are unacceptable, an alternative source of the desired elemental component (free of damaging impurities) is used.

Titanium that is frequently used in alloy manufacture is introduced into the alloy in the form of a titanium addition agent. Titanium addition agents generally fall into three general categories: metal scrap, ferroalloys and master alloys. The source of the titanium may therefore give rise to one or more incidental impurities which may be present in trace amounts or may be present in more substantial quantities while still not impacting on the performance of the iron based alloy.

Addition of the other essential components of the alloys to a melt may similarly give rise to the presence of incidental impurities depending on the source of the element concerned. In each case, such impurities are deemed incidental if they have no technical effect on the resulting alloy. This may be the case even if an incidental impurity is present in an amount of say 1wt% or 2wt%. The skilled person will immediately recognise which elemental components may be regarded as incidental impurities and which are essential to the working of the invention.

In circumstances in which the addition of a particular essential element in the alloy composition of the invention also results in the addition of another essential element (because the other essential element is perhaps present as an impurity in the addition agent for the first essential element) then the overall composition must be carefully monitored to ensure that all of the essential components remain within the desired parameters. If necessary, this can be compensated for by adjusting the relative proportions of additional materials used for each of the essential components in the alloys of the invention. The skilled person will be able to analyse and compensate as necessary for variations in the essential elemental components due to the presence of incidental impurities using known analytical techniques and by varying the amounts of the usual addition agents for each essential component.

The alloys of the invention can be used in a wide range of applications such as in drill strings, piping systems for oil transportation, chemical engineering plant applications, heavy industry and mining applications, material conveying systems, and fluids and solids transport systems where abrasive wear is a particular issue.

The alloys of the invention are frequently used in the form of a wire. The wire is effectively a precursor to the hardbanding alloy composition which is applied to the target surface by welding.

The hardbanding alloys of the present invention are used to produce a weld deposit. The alloys are formed into wires which are then applied to the tool or joint. The weld deposit is thus produced by melting the welding wire onto the surface to be treated. The wire may be a solid wire, a metal-cored wire or a flux-cored wire.

A metal-cored wire is in the form of a metal sheath which is then filled with a powdered metal alloy. Similarly, a flux-cored wire may is in the form of a mixture of powdered metal and fluxing ingredients.

One benefit of both the metal-cored and flux-cored wires of the invention is that they allow a wide variety of alloy components and alloys to be included within the powdered metal core in addition to the alloy content provided by the sheath. This allows the overall composition of the hardbanding alloy to be fine-tuned.

Normally, for example, a hardbanding alloy precursor in the form of a wire or a strip is made from U-shaped, or similar, length of metal or alloy to which further components are added in powder form. Thus, in a first step the U-shaped length of metal has the powdered components necessary to achieve the overall alloy composition added to it, and in a further step the U-shaped tube then has its two longitudinal open edges folded together to form a tube which encapsulates the powder. This traps the powder within the void to form a powder-filled tube. The composition of the metal casing and powder thus corresponds with the composition of the ultimate hardbanding alloy and represents the composition referred to above. The precursor wire, which can be referred to as the hardbanding wire or strip, can be thought of as a blend of alloys since the metal casing may either be a single metal or an alloy and one or more of the powder components may be a single element (metallic or non-metallic) or an alloy. Conveniently, some of the alloy metals are included in the composition in the form of powdered carbides which are added to the wire.

In certain embodiments, the alloy is in the form of a tubular wire formed from a steel sheath with alloying elements contained to form the desired alloy when deposited. This is in contrast with the conventional situation of a solid wire made from the alloy. The alloy is in the form of a tubular wire formed from a steel sheath with alloying elements contained within the sheath so that an alloy of the invention having the composition described above in the various embodiments is formed in use i.e. when the tubular wire is used in a welding or hardbanding application. Thus the melted sheath and components merge to form an alloy of the ultimate composition during use.

Two different sets of iron based alloy compositions according to the invention were prepared and tested for microstructure, casing friendliness and wear resistance.

The first set, designated Composition 1 , contained the following components: 2.22 wt% carbon, 2.38 wt% silicon, 10.54 wt% manganese, 9.34 wt% nickel, 0.04 -0.08 wt% cerium, with the balance being iron and incidental impurities

The second set, designated Composition 2, contained the following components: 3.5 wt% carbon, 5 wt% Silicon, 10 - 11 wt% manganese, 9 wt% nickel, 0.1 - 0.15 wt% cerium, with the balance being iron and incidental impurities

The Figures show the results obtained with alloys according to the invention in comparison with known alloys.

The difference between composition 1 & 2, is the difference in increased level of carbon, cerium & silicon in 2 as compared to 1.

Figure 1 shows the microstructure of composition 1. This shows the unetched micrograph of composition 1 from the surface of the hardbanding down to the weld interface. The micrograph was obtained using Scanning Electron Microscope. The micrograph shows that there is no precipitation of any Intermetallic/ graphite throughout the weld.

Figure 2 shows the microstructure of composition 2. This shows the unetched micrograph of composition 2 from the surface of the hardbanding down to the weld interface. The micrograph was obtained using Scanning Electron Microscope. The micrograph shows that there is uniform graphite distribution throughout the weld.

The composition mentioned above are the composition of a 1.6mm diameter flux cored wire, the composition is analysed by XRF - fusion bead and Leco method for carbon. The weld bead composition deposited using this flux cored wire will be varying by 15-40wt% due to the difference in the dilution of iron from the base material.

Figure 3 shows a comparison between alloys of the invention and conventional alloys. Both compositions, Composition 1 designated as C&W CASTHAD in Figure 3 and composition 2 designated as CastHad 2.4 in Figure 3, have the best casing friendliness compared to all other hardbanding materials in the market. The figure shows the relative performance of the alloys of the invention in terms of their casing friendliness as compared with known alloys. In the figure, the lesser the casing wear factor the better the casing friendliness.

Figure 4 shows the casing wear scar for different hardbandings.

The invention also relates to a process for forming a wire having a composition as defined above (and also including the preferred ranges of components discussed in relation to the alloy and the wire).

The present invention relates to improved iron based alloys based on high manganese steel. The experimental results presented above demonstrate that the iron based alloy of the invention have improved wear and galling resistance relative to conventional steels and other hardbanding alloys. Furthermore, the alloys of the invention can be conveniently and relatively economically prepared.

It is important to recognise, as discussed below in relation to the methods of producing the alloys, that the above composition represents the composition of the hardbanding wire. The composition of the welded deposit will be different due to factors inherent in the welding process. In particular the weld deposit will be lower in alloy levels compared to the wire due to dilution with the base materials. The degree of dilution could be reduced drastically by following a different welding technique such as Cold Metal Transfer (CMT), Laser Deposition & Plasma Transfer Arc (PTA) Welding Technique.

Most of the conventional hardbanding materials currently used in the market are laid down by a MIG welding setup. In the MIG welding setup there is high amount of dilution in the weld. In contrast in Cold Metal Transfer (CMT), Laser deposition & Plasma Transfer Arc (PTA) welding techniques as used in the case of the materials of the invention there will be a reduced amount of dilution. This leads to improved properties in hardbanding. The alloys of the present invention can be deposited using the above said welding techniques (CMT, Laser & PTA) and consequently exhibit improved properties relative to conventional hardbandings.

The term dilution refers to the Fe (iron) from the base material to the weld bead during welding process. As the dilution of iron increases, the composition of weld bead changes as well. A discussion concerning the influence of the welding process and parameters on dilution can be found in the following technical paper: http://www.twi-qlobal.com/technical-knowledge/published-papers/cra-weld-overlay-influence-of-welding-process-and-parameters-on-dilution-and-corrosion-resistance/. Figure 7 in that paper shows the relationship between dilution and heat input for the first weld-bead for different welding processes. It can be seen for example that the degree of iron dilution in MIG welding is 20 -40% which changes the composition of weld bead by 20-40% (since more iron goes into the weld bead, other ingredients in the weld bead decreases by 20 - 40wt%). It can also be seen from the same graph that there is a low iron dilution value of 0-20% for short circuit transfer technique (STT) and this is similar to that obtained in the Cold Metal Transfer Technique. Similar issues of dilution occur in relation to other base metals when forming welds. Thus the dilution of elements other than iron can also have a negative effect on the properties of the weld bead.

The composition quoted represents the average composition of the precursor material as a whole across the bulk material which is used to form the hardbanding layer. This point is important because the composition of the precursor wire or strip etc. that is used to form the hardbanding layer may not be uniform prior to being welded. This is because the contents of the hardbanding wire or strip are a physical mix of different elements and compounds.

According to a second aspect of the invention, there is provided a wire having the following average composition:

manganese in an amount of 8 to 12% by weight,

nickel in an amount of 8 to 12% by weight,

carbon in an amount of 2 to 4% by weight,

silicon in an amount of 2% to 6% by weight, and

cerium in an amount of 0.01 % to 0.15% by weight, and

wherein the alloy optionally further comprises one or more of the following elements: calcium in an amount of up to 1.0% by weight, magnesium in an amount of up to 0.15% by weight,

titanium in an amount of up to 9% by weight,

molybdenum in an amount of up to 4% by weight,

vanadium in an amount of up to 4% by weight,

phosphorus in an amount of up to 0.05% by weight, and

sulphur in an amount of up to 0.05% by weight,

and wherein the balance is Fe and incidental impurities.

The wire described above is a precursor to the hardbanding alloy composition which is applied to the target surface by welding. The wire can also be used for welding to metal components together to form welded joint or piece.

The alloys of the invention in a wide range of applications such as in drill strings, piping systems for oil transportation, chemical engineering plant applications, heavy industry and mining applications, material conveying systems, and fluids and solids transport systems where abrasive wear is a particular issue.

The hardbanding alloys of the present invention can be used to produce a weld deposit. The alloys are formed into wires which are then applied to the tool or joint. The weld deposit is thus produced by melting the welding wire onto the surface to be treated. The wire may be a solid wire, a metal-cored wire or a flux-cored wire.

A metal-cored wire is in the form of a metal sheath which is then filled with a powdered metal alloy. Similarly, a flux-cored wire may is in the form of a mixture of powdered metal and fluxing ingredients.

One benefit of both the metal-cored and flux-cored wires of the invention is that they allow a wide variety of alloy components and alloys to be included within the powdered metal core in addition to the alloy content provided by the sheath. This allows the overall composition of the hardbanding alloy to be fine-tuned.

Normally, for example, a hardbanding alloy precursor in the form of a wire or a strip is made from U-shaped, or similar, length of metal or alloy to which further components are added in powder form. Thus, in a first step the U-shaped length of metal has the powdered components necessary to achieve the overall alloy composition added to it, and in a further step the U-shaped tube then has its two longitudinal open edges folded together to form a tube which encapsulates the powder. This traps the powder within the void to form a powder-filled tube. The composition of the metal casing and powder thus corresponds with the composition of the ultimate hardbanding alloy and represents the composition referred to above. The precursor wire, which can be referred to as the hardbanding wire or strip, can be thought of as a blend of alloys since the metal casing may either be a single metal or an alloy and one or more of the powder components may be a single element (metallic or non-metallic) or an alloy. Conveniently, some of the alloy metals may be included in the composition in the form of powdered carbides where appropriate which are added to the wire.

One important feature of the present invention is that the resulting hardbanding alloys that are ultimately applied to the target substrate are produced from the blend of powdered materials in the precursor wire. Adding all of the necessary elemental components and melting them together to form a uniform composition which is then used as the welding composition is not practicable. Conversion of a cast ingot to a wire would be very difficult and expensive if not impossible as would conversion of the ingot to powder.

The hard-facing material of the present disclosure may be applied onto the surface of new tools or tools having a surface comprising another worn hard-face material. The tools to which the hard-face material is applied are typically metallic in nature with steels having less than about 1 percent carbon. Examples of base metals to which the hard-face materials of the present disclosure may be applied include, but are not limited to, stainless steels, manganese steels, cast iron and iron steels, nickel-based alloys, and copper-based alloys. Examples of several hard-face materials over which

the hard-face materials of the present disclosure may be applied include, but are not limited to, tungsten carbide, martensitic, and chromium carbide deposits.

According to a third aspect of the invention, there is provided a process for hardbanding a tool joint, the process comprising welding a precursor material having the composition of the alloy or wire as discussed above to a target substrate.

The ranges and preferred ranges stated for the individual elemental components in the first, second and third aspects apply equally to each of the aspects. However, the preferred ranges may in some circumstances be independent of one another.

The invention thus provides a process for preparing a hardbanding at a joint. This process comprises welding a precursor material having the composition described above to a target substrate. In other words, the process involves welding wire of the second aspect of the invention to a target surface to achieve a hardbanding alloy composition on the target surface. The hardbanding alloy which results effectively has a uniform composition which is the same as the average composition in the precursor wire. It is possible to compensate for loss of certain elemental components during the welding process by varying slightly the composition of the wire. Such variation is entirely within the capabilities of the skilled person.

The invention also relates to a tool which includes the hardbanding alloy of the present invention.

The wear resistant properties of the alloys of the present invention can be assessed in a variety of ways. One method of measuring where involves following the Casing Wear Tests described in the American Petroleum Institute (API) Standard 7CW, the first edition was published in June 2015. The content of that document and the testing procedure are not reproduced here in the interest of brevity. However, it is specifically intended that the details of that testing protocol, which are readily available to the skilled person, are specifically incorporated into the present disclosure. Thus, it is intended that this document forms part of the disclosure of the present invention in so far as it relates to the wear properties of the alloys of the present invention and means for measuring the wear.

This document describes a test method to create a measurable wear groove and classify the wear by determining the amount of material worn away from a casing specimen by means of abrasion and most importantly galling. Briefly, the abrasion and galling is created by rotating and reciprocating a hardbanded drill stem element test specimen against a stationary casing specimen at a prescribed side-load. Additional abrasion is supplied by materials in the drilling fluid continuously circulated during the test procedure. The chief abrasive component within that drilling fluid is 100 mesh sand.

The iron based alloys of the invention are strengthened by manganese and nickel and exhibit work hardening behaviour with the defined carbon and manganese and nickel ratios. Hardbanding materials formed from the alloys of the invention demonstrate a good combination of wear resistance and being casing-friendly.