High-chromium creep-resistant welding metal for arc welding of thin steel materials

Abstract

To provide a high chromium creep resistant weld metal for arc welding of thin walled steel members.SOLUTION: Steel weld metal compositions can include 9.00 to 12.00 wt.% chromium, from 0.02 to 0.06 wt.% carbon, from 0.3 to 0.7 wt.% manganese, from 0.1 to 0.3 wt.% silicon, from 0.5 to 1.2 wt.% nickel, from 0.1 to 0.5 wt.% molybdenum, from 1.0 to 1.5 wt.% cobalt, from 0.03 to 0.08 wt.% niobium, from 0.2 to 0.8 wt.% tungsten, from 0.3 to 0.8 wt.% copper, from 0.005 to 0.010 wt.% boron, and from 0.005 to 0.025 wt.% nitrogen; wherein the balance of the steel weld metal composition is iron and unavoidable impurities. Methods of depositing the steel weld metal compositions on a workpiece by an electric arc welding process without the use of a post weld heat treatment are also described. Consumable electric arc welding electrodes producing high chromium creep resistant steel weld metal compositions are also described.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] A high-chromium creep-resistant steel weld metal composition is provided. A method of depositing a high-chromium creep-resistant steel weld metal composition onto a workpiece by an arc discharge welding process without using post-weld heat treatment (PWHT) is also provided. A consumable arc discharge welding electrode for manufacturing a high-chromium creep-resistant steel weld metal composition is also provided.

Background Art

[0002] Martensitic high-chromium steel materials are widely used in the power generation industry or the chemical and petrochemical industries. In particular, bainite and martensitic Cr steels are used in thin boiler membrane walls. These components are subjected to high operating temperatures and the stresses that occur simultaneously. The construction and repair of high-chromium steels widely use arc welding, and subsequently, post-weld heat treatment (PWHT) is carried out to restore sufficient ductility and impact strength in the weld joints. The weld joints must conform to the oxidation / corrosion resistance and creep strength of the base metal steel. Furthermore, PWHT of large welded structures such as boiler membrane walls is highly impractical, costly, and time-consuming.

[0003] For high-temperature applications, steel compositions having a chromium content of about 9 wt% have been widely used. However, in these compositions, insufficient oxidation resistance occurs in a steam atmosphere at temperatures higher than 620°C, thereby significantly limiting their applicable temperature range. In particular, in boiler components involving heat transfer, the oxide scale acts as an insulator, thereby increasing the metal temperature and thus reducing the life of the corresponding component. Furthermore, the oxide scale, when peeled off during operation, will cause erosion damage on the components that subsequently carry the steam. The peeled oxide scale can cause blockages, often obstructing the steam flow and resulting in local heating and catastrophic failure.

[0004] A high chromium content, i.e., more than 9 wt% chromium, is indispensable for good steam oxidation resistance. A chromium content of about 11 - 12% is currently considered to enable working temperatures up to 650 °C, thereby significantly increasing power plant efficiency. However, such a chromium content increases the driving force for Z-phase formation. The Z-phase is a complex nitride that rapidly coarsens and thereby consumes the surrounding strengthening MX precipitates, and mainly contributes to the creep strength of 9 - 12% Cr steels (M is niobium or vanadium, and X is carbon or nitrogen). The high chromium content also increases the coarsening rate of chromium carbide precipitates. The loss of the microstructure stabilizing effect of both MX and chromium carbide precipitates causes a decrease in the long-term creep rupture strength of martensitic (Cr > 11%) high chromium heat-resistant steel grades.

[0005] The creep behavior and the degradation of creep properties of high-temperature materials limit the service life of components and structures designed to operate under high-temperature stress for a long time. Creep is a time-dependent deformation of materials under load, which most often occurs at high temperatures. The structural changes of materials usually promote creep and subsequently accelerate the rate of appearance of intergranular creep damage. Creep, if not weakened, leads to rupture and significantly affects the life of components. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] From the viewpoint of limiting the chromium content in martensitic steel compositions that can be used for welding steel members requiring high working temperatures, oxidation and corrosion resistance, and creep strength, there is a need for high chromium steels used for thin-walled welded configurations in power engineering applications. Furthermore, such high Cr steels should be suitable for use in the as-welded state (without performing PWHT). MEANS FOR SOLVING THE PROBLEMS

[0007] A high-chromium creep-resistant steel weld metal composition is provided without using post-weld heat treatment (PWHT). A method of depositing a high-chromium creep-resistant steel weld metal composition onto a workpiece by an arc discharge welding process is also provided.

[0008] In one embodiment, a steel weld metal composition comprising 9.00 to 12.00 wt% chromium (Cr), 0.02 to 0.06 wt% carbon (C), 0.3 to 0.7 wt% manganese (Mn), 0.1 to 0.3 wt% silicon (Si), 0.5 to 1.2 wt% nickel (Ni), 0.1 to 0.5 wt% molybdenum (Mo), 1.0 to 1.5 wt% cobalt (Co), 0.03 to 0.08 wt% niobium (Nb), 0.2 to 0.8 wt% tungsten (W), 0.3 to 0.8 wt% copper (Cu), 0.005 to 0.010 wt% boron (B) and 0.005 to 0.025 wt% nitrogen (N); the balance of the steel weld metal composition being iron (Fe) and unavoidable impurities, the steel weld metal composition.

[0009] In another embodiment, a method of depositing a steel weld metal composition onto a workpiece by an arc discharge welding process, comprising: a) at least partially melting a consumable electrode by an arc discharge and depositing the molten steel weld metal composition onto the workpiece; and b) cooling and solidifying the molten steel weld metal composition to form a deposited steel weld metal composition on the workpiece, the steel weld metal composition comprising 9.00 to 12.00 wt% Cr, 0.02 to 0.06 wt% C, 0.3 to 0.7 wt% Mn, 0.1 to 0.3 wt% Si, 0.5 to 1.2 wt% Ni, 0.1 to 0.5 wt% Mo, 1.0 to 1.5 wt% Co, 0.03 to 0.08 wt% Nb, 0.2 to 0.8 wt% W, 0.3 to 0.8 wt% Cu, 0.005 to 0.010 wt% B and 0.005 to 0.025 wt% N; the balance of the steel weld metal composition being Fe and unavoidable impurities, and the steel weld metal composition not undergoing PWHT, the method.

[0010] Certain embodiments of the present invention may be the physical form and arrangement of certain components, the preferred embodiments of which are described herein and illustrated in the accompanying drawings which form a part thereof.

Brief Description of the Drawings

[0011]

Figure 1

Embodiments for Carrying Out the Invention

[0012] One embodiment of the present invention may include a steel weld metal composition deposited by various consumables. To deposit the consumables, various welding processes such as shielded metal arc welding (SMAW), submerged arc welding (SAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), flux cored arc welding (FCAW) processes and combinations thereof may be used. The steel weld metal composition comprises iron (Fe), chromium (Cr), carbon (C), manganese (Mn), silicon (Si), nickel (Ni), molybdenum (Mo), cobalt (Co), niobium (Nb), tungsten (W), copper (Cu), boron (B), nitrogen (N) and potential additional elements.

[0013] Another embodiment of the present invention may include a steel weld metal composition intended for high use temperatures and thin materials that exhibits good creep characteristics over extremely long periods. In one embodiment, this composition further exhibits excellent oxidation and corrosion resistance, including strength, toughness, etc. In one embodiment, it is intended that post-weld heat treatment (PWHT) is not used. The present steel weld metal composition may be included in a welded structure having a high chromium content that is creep resistant and can be used in the power generation industry or the chemical and petrochemical industries where the structure is subjected to continuous use at high temperatures, for example, in thin-walled members.

[0014] The definitions and methods described in this specification are provided to better define embodiments of the present invention and to guide those skilled in the art in the practice of the embodiments. Unless otherwise noted, the terms will be understood by those skilled in the relevant art according to their conventional usage.

[0015] Unless otherwise indicated, all numerical values representing amounts of ingredients, reaction conditions, etc. used in this specification and the appended claims should be understood to be modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations, which may vary depending upon the desired properties sought to be obtained by the embodiments of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the claims, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0016] In some embodiments, the use of the particular terms "a", "an", and "the" and similar uses in connection with the description of particular embodiments (especially in relation to particular following claims) can be construed to include both the singular and the plural unless specifically noted otherwise. In some embodiments, the term "or" as used in this specification, including in the claims, is used to mean "and / or" unless expressly stated otherwise, referring only to alternatives or where the alternatives are mutually exclusive.

[0017] The terms "comprise", "have", and "include" are non - limiting conjunctive verbs. Any form or tense of one or more of these verbs, such as "comprises", "comprising", "has", "having", "includes", and "including", is non - limiting. For example, any method that "comprises", "has", or "includes" one or more steps is not limited to having only those one or more steps, and may include other steps not described. Similarly, any composition or device that "comprises", "has", or "includes" one or more features is not limited to having only those one or more embodiments, and may include other embodiments not described.

[0018] All methods described herein are executable in any suitable order, unless otherwise expressly stated herein or clearly precluded by context. The use of any and all examples, or exemplary terms (e.g., "such as") provided with respect to specific embodiments herein is intended only to better illustrate the invention and is not intended to limit the scope of the invention as otherwise claimed. Terms in the specification should not be construed to indicate that any non - claimed element is essential to the practice of the invention.

[0019] The grouping of other elements or embodiments disclosed herein is not to be construed as limiting. Each group member can be described and claimed individually or in any combination with any other member of the group or other elements found herein. One or more members of a group can be included in or deleted from the group for convenience or for reasons of patentability. If any such inclusion or deletion occurs, the specification is considered to contain the group as modified and thus fully achieves all the Markush group recitations used in the appended claims.

[0020] Although the embodiments have been described in detail, it will be apparent that modifications, variations, and equivalent embodiments are possible without departing from the scope of the embodiments defined in the appended claims. Furthermore, it should be understood that all examples of the embodiments are provided as non-limiting examples.

[0021] Additional features and elements of the embodiments will be better understood by reference to the appended description and claims.

[0022] Steel weld metal composition Chromium: Chromium is an essential element for improving the creep rupture strength of steel by stabilizing martensite and is also added to give the steel a satisfactory level of hot corrosion (oxidation) resistance. Chromium is an essential element in the formation of a stable oxide scale with respect to sustained high-temperature oxidation resistance, so chromium is also a major component of carbide formation and is dissolved in the matrix. In certain embodiments, the chromium content of the steel weld metal composition can be from 9.00 to 12.00 wt%. Such a content results in a martensitic structure of the steel upon cooling from the molten state at any cooling rate that is of practical interest in arc welding.

[0023] Carbon: Carbon is an essential strengthening element and can form carbide / carbonitride phases in combination with Cr, Mo, V, Ta, N, and Nb. With an increase in carbon content, the applicability for high-temperature use decreases. Furthermore, a high amount of carbon increases the volume fraction of carbide / carbonitride, decreases the ductility of the steel, and increases the hardness to an undesirable level, thereby reducing formability and weldability. If the carbon concentration is too low, low-strength soft as-quenched martensite is induced. In certain embodiments, the carbon content of the steel weld metal composition may be from 0.02 to 0.06 wt%.

[0024] Manganese: Manganese is an effective deoxidizing element. Thereby, hot formability is improved during melting and the removal of impurities such as phosphorus and sulfur becomes easier. Manganese combines with sulfur and reduces ferrite formation. In certain embodiments, the manganese content of the steel weld metal composition may be from 0.3 to 0.7 wt%.

[0025] Silicon: Silicon is a deoxidizer, improves weldability, and increases resistance to steam oxidation. High concentrations of silicon decrease high-temperature strength and especially creep rupture strength. Also, silicon preferentially segregates at grain boundaries and reduces toughness. In certain embodiments, the silicon content of the steel weld metal composition may be from 0.1 to 0.3 wt%.

[0026] Nickel: Nickel stabilizes the martensite structure and suppresses the formation of ferrite. However, it improves toughness and the creep resistance decreases with increasing nickel content. Furthermore, an increase in nickel content has a significant impact in terms of cost. In certain embodiments, the nickel content of the steel weld metal composition may be from 0.5 to 1.2 wt%.

[0027] Molybdenum: Molybdenum is a factor for solid solution strengthening and also improves creep rupture strength. Molybdenum is also a ferrite stabilizing element. The addition of molybdenum must be carefully controlled. High contents of molybdenum can deteriorate toughness and cause an increase in ferrite content during the service life in high-temperature environments. Furthermore, high concentrations of molybdenum may be difficult to effectively homogenize, which inhibits the ability to obtain control over the location of chemical properties. In certain embodiments, the molybdenum content of the steel weld metal composition may be from 0.1 to 0.5 wt%.

[0028] Cobalt: Cobalt is an austenite stabilizing element in steel and is useful in limiting the retention of harmful delta ferrite at low temperatures. It increases the creep rupture strength by solid solution strengthening. Low concentrations of cobalt have the effect of strengthening the resistance to temper softening. Conversely, high amounts of cobalt can induce embrittlement due to the enhanced precipitation of intermetallic phases during high-temperature operation. High concentrations of Co may be difficult to homogenize, which inhibits the ability to obtain control over the location of chemical properties. In certain embodiments, the cobalt content of the steel weld metal composition may be from 1.0 to 1.5 wt%.

[0029] Niobium: Niobium combines with carbon (and nitrogen) to form fine precipitates such as NbC. This is effective for improving creep rupture strength. Furthermore, niobium-rich precipitates improve the steel particle structure and assist in preventing the excessive coarsening of austenite particles during austenitizing heat treatment. If the amount of niobium added is too low, the volume fraction of the precipitate is low and the effect noticed is minimal. However, by increasing the niobium content, the precipitation of other nitrides can be suppressed, the efficient vanadium precipitates for creep rupture resistance decrease, and the carbon in the matrix is consumed, thereby, the martensite lath number density, and M 23The number density of other carbide precipitates such as C6 decreases, and the long-term creep rupture resistance may decrease. Furthermore, a high niobium content may promote primary carbide formation, and its diameter may be overly large, thereby promoting damage to the microstructure during use. High concentrations of niobium may be difficult to homogenize, which inhibits the ability to obtain control over the location of chemical properties. Niobium added in small amounts can dissolve in vanadium nitride and thus can improve the stability of vanadium nitride. In certain embodiments, the niobium content of the steel weld metal composition may be from 0.03 to 0.08 wt%.

[0030] Tungsten: Tungsten is a solution strengthener. Tungsten is incorporated into carbides and contributes to creep strength enhancement and long-term stability. However, this element is expensive, and high amounts can lead to strong segregation during steelmaking and casting processes and can result in the formation of intermetallic layers that cause significant embrittlement. In certain embodiments, the tungsten content of the steel weld metal composition may be from 0.2 to 0.8 wt%.

[0031] Copper: Copper is an austenite stabilizer and may be added to effectively stabilize the martensite structure after quenching. Copper suppresses harmful delta ferrite and can be advantageous in providing substitutional matrix strengthening and precipitate strengthening in the form of copper-rich FCC phases. In certain embodiments, the copper content of the steel weld metal composition may be from 0.3 to 0.8 wt%.

[0032] Boron: Boron stabilizes carbide precipitates by suppressing the coarsening of carbides. Boron also segregates at grain boundaries, strengthening the boundaries and enhancing the creep resistance at high temperatures. A high amount of boron requires the use of a higher austenitizing temperature for proper dispersion of boron in steel, which in turn leads to an increase in grain size and thus a decrease in mechanical properties such as ductility and toughness due to the formation of a coarsened boron nitride phase. Furthermore, a high amount of boron has an adverse effect on hot workability. In certain embodiments, the boron content of the steel weld metal composition may be from 0.005 to 0.010 wt%.

[0033] The components of the steel weld metal composition are as described above, and the balance or remainder includes iron and unavoidable impurities. The unavoidable impurities may include elements (such as P, S, etc.) that can be trapped in the weld metal depending on the conditions, including raw materials, recycled materials, and manufacturing equipment.

[0034] In one embodiment, the steel weld metal composition may comprise about 11 wt% Cr and has excellent oxidation and corrosion properties at temperatures above 620°C and up to 650°C, which exceeds steels for membrane wall tubes having nominally 2.25 wt% Cr (ASME T23, T24) and 9 wt% type (ASME T91) that are limited in use up to 580 - 620°C. Furthermore, in certain embodiments, the steel weld metal composition has short-term static tensile properties that exceed existing chromium-containing martensitic steels. Additionally, in another embodiment, the steel weld metal composition is designed to be used without PWHT on thin-walled tubes (such as small-diameter hollow tubes) and has a creep strength and oxidation and corrosion resistance similar to or comparable to that of the welded thin-walled tubes. The steel weld metal composition has a high hardenability and as such, the response to differences in welding parameters is minimal, thus providing improved weldability compared to T23 and T24 grades.

[0035] In another embodiment, the steel weld metal composition may comprise from about 10.50 to about 11.50 wt% Cr, from about 0.03 to about 0.05 wt% C, from about 0.4 to about 0.6 wt% Mn, from about 0.15 to about 0.25 wt% Si, from about 0.8 to about 1.0 wt% Ni, from about 0.2 to about 0.4 wt% Mo, from about 1.1 to about 1.4 wt% Co, from about 0.04 to about 0.07 wt% Nb, from about 0.3 to 0.7 wt% W, from about 0.4 to about 0.7 wt% Cu, from about 0.006 to about 0.009 wt% B and from about 0.005 to 0.025 wt% N; the balance of the steel weld metal composition being iron and unavoidable impurities.

[0036] In another embodiment, the steel weld metal composition may comprise from about 10.75 to about 11.25 wt% Cr, from about 0.035 to about 0.045 wt% C, from about 0.45 to about 0.55 wt% Mn, from about 0.15 to about 0.25 wt% Si, from about 0.85 to about 0.95 wt% Ni, from about 0.25 to about 0.35 wt% Mo, from about 1.2 to about 1.35 wt% Co, from about 0.04 to about 0.06 wt% Nb, from about 0.4 to about 0.6 wt% W, from about 0.5 to about 0.65 wt% Cu, from about 0.007 to about 0.009 wt% B and from about 0.005 to 0.025 wt% N; the balance of the steel weld metal composition being iron and unavoidable impurities.

[0037] In another embodiment, the steel weld metal composition may comprise 11.0 wt% chromium, 0.04 wt% carbon, 0.5 wt% manganese, 0.2 wt% silicon, 0.9 wt% nickel, 0.3 wt% molybdenum, 1.3 wt% cobalt, 0.05 wt% niobium, 0.5 wt% tungsten, 0.6 wt% copper, 0.008 wt% boron and 0.0230 wt% nitrogen; the balance of the steel weld metal composition being iron and unavoidable impurities.

[0038] In another embodiment, the steel weld metal composition has a low-carbon, untempered martensitic microstructure.

[0039] In addition, in another embodiment, the steel weld metal composition is creep resistant at high temperatures. In particular, in one embodiment, the steel weld metal composition has a uniaxial creep strength at a temperature of 650 °C of at least 300 hours at 100 MPa, at least 600 hours at 90 MPa, at least 1500 hours at 70 MPa and at least 2500 hours at 55 MPa.

[0040] More particularly, in certain embodiments, the steel weld metal composition has a uniaxial creep strength at a temperature of 650 °C of at least 330 hours at 100 MPa, at least 610 hours at 90 MPa, at least 1600 hours at 70 MPa and at least 2800 hours at 55 MPa.

[0041] More particularly, in certain embodiments, the steel weld metal composition has a uniaxial creep strength at a temperature of 650 °C of 336 hours at 100 MPa, 619 hours at 90 MPa, 1609 hours at 70 MPa and at least 2879 hours at 55 MPa. As such, in certain embodiments, the creep resistance of the weld metal composition is equal to or exceeds that of existing compositions containing only 2.25 wt% Cr.

[0042] In one embodiment, the deposited steel weld metal composition can have a uniaxial creep resistance at a temperature of 620 °C for at least 5000 hours. More particularly, the deposited steel weld metal composition can have a uniaxial creep resistance at a temperature of 620 °C for at least 10000 hours.

[0043] In one embodiment, the steel weld metal composition has an impact toughness of at least 27 J at 20 °C. As such, in one embodiment, the impact toughness of the steel weld metal composition exceeds the applicable requirements set by ANSI, ASME, EPRI, EN, TUV codes, standards and recommended practices.

[0044] In another embodiment, the steel weld metal composition has a Vickers hardness of 360 VHN or less.

[0045] Method for depositing a steel weld metal composition In one embodiment, as shown in FIG. 1, a method 100 for depositing a steel weld metal composition on a workpiece by an arc discharge welding process is provided. In one embodiment, the method includes step 102 of at least partially melting a consumable electrode by an arc discharge and depositing the molten steel weld metal composition on the workpiece; and step 104 of cooling and solidifying the molten steel weld metal composition to form the deposited steel weld metal composition on the workpiece, wherein the steel weld metal composition comprises about 10.50 to about 11.50 wt% Cr, about 0.03 to about 0.05 wt% C, about 0.4 to about 0.6 wt% Mn, about 0.15 to about 0.25 wt% Si, about 0.8 to about 1.0 wt% Ni, about 0.2 to about 0.4 wt% Mo, about 1.1 to about 1.3 wt% Co, about 0.04 to about 0.07 wt% Nb, about 0.3 to 0.7 wt% W, about 0.4 to about 0.7 wt% Cu, about 0.006 to about 0.009 wt% B and about 0.005 to 0.025 wt% N; the balance of the steel weld metal composition is iron and unavoidable impurities, and the steel weld metal composition does not undergo post-weld heat treatment (PWHT) 106.

[0046] In another embodiment, a method is provided for depositing a steel weld metal composition on a workpiece by an arc welding process. In one embodiment, the method includes at least partially melting a consumable electrode by an arc discharge and depositing the molten steel weld metal composition on the workpiece; and cooling and solidifying the molten steel weld metal composition to form a deposited steel weld metal composition on the workpiece, wherein the steel weld metal composition comprises from about 10.75 to about 11.25 wt% Cr, from about 0.035 to about 0.045 wt% C, from about 0.45 to about 0.55 wt% Mn, from about 0.15 to about 0.25 wt% Si, from about 0.85 to about 0.95 wt% Ni, from about 0.25 to about 0.35 wt% Mo, from about 1.2 to about 1.35 wt% Co, from about 0.04 to about 0.06 wt% Nb, from about 0.4 to about 0.6 wt% W, from about 0.5 to about 0.65 wt% Cu, from about 0.007 to about 0.009 wt% B and from about 0.005 to 0.025 wt% N; the balance of the steel weld metal composition is iron and unavoidable impurities, and the steel weld metal composition does not undergo PWHT.

[0047] In one embodiment, a method is provided for depositing a steel weld metal composition on a workpiece by an arc welding process. In one embodiment, the method includes at least partially melting a consumable electrode by an arc discharge and depositing the molten steel weld metal composition on the workpiece; and cooling and solidifying the molten steel weld metal composition to form a deposited steel weld metal composition on the workpiece, wherein the steel weld metal composition comprises 11.0 wt% chromium, 0.04 wt% carbon, 0.5 wt% manganese, 0.2 wt% silicon, 0.9 wt% nickel, 0.3 wt% molybdenum, 1.3 wt% cobalt, 0.05 wt% niobium, 0.5 wt% tungsten, 0.6 wt% copper, 0.008 wt% boron and 0.0230 wt% nitrogen; the balance of the steel weld metal composition is iron and unavoidable impurities, and the steel weld metal composition does not undergo PWHT.

[0048] In certain embodiments, the method of the present disclosure may also include selecting a workpiece. In the method according to certain embodiments, the deposited steel weld metal composition has a martensitic microstructure.

[0049] In addition, in the method according to certain embodiments, the steel weld metal composition has a uniaxial creep strength at a temperature of 650 °C of at least 300 hours at 100 MPa, at least 600 hours at 90 MPa, at least 1500 hours at 70 MPa, and at least 2500 hours at 55 MPa.

[0050] More particularly, in the method according to certain embodiments, the steel weld metal composition has a uniaxial creep strength at a temperature of 650 °C of at least 330 hours at 100 MPa, at least 610 hours at 90 MPa, at least 1600 hours at 70 MPa, and at least 2800 hours at 55 MPa.

[0051] More particularly, in the method according to certain embodiments, the steel weld metal composition has a uniaxial creep strength at a temperature of 650 °C of 336 hours at 100 MPa, 619 hours at 90 MPa, 1609 hours at 70 MPa, and at least 2879 hours at 55 MPa.

[0052] In the method according to certain embodiments, the deposited steel weld metal composition may have a uniaxial creep resistance at a temperature of 620 °C of at least 5000 hours. More particularly, in the method according to one embodiment, the deposited steel weld metal composition may have a uniaxial creep resistance at a temperature of 620 °C of at least 10000 hours.

[0053] In the method according to certain embodiments, the steel weld metal composition has an impact toughness of at least 27 J at 20 °C.

[0054] In the method according to certain embodiments, the steel weld metal composition has a Vickers hardness of 360 VHN or less.

[0055] The method of depositing the steel welding metal composition may include any arc welding method. For example, shielded metal arc welding (SMAW), submerged arc welding (SAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), flux cored arc welding (FCAW) method, and combinations thereof may be used.

[0056] The welding conditions and the welding material components can be appropriately controlled according to methods known in the art.

[0057] In one embodiment, the steel welding metal composition deposited under the above conditions exhibits advantageous creep characteristics at extremely long periods and high service temperatures, as well as other advantageous characteristics including impact toughness, oxidation resistance, corrosion resistance, strength, and hardness. Further, a welded structure containing such a welding metal can be obtained without using PWHT.

[0058] Consumable arc discharge welding electrode In one embodiment, a consumable arc discharge welding coated electrode for the SMAW (MMA) method is provided. The consumable arc discharge welding coated electrode comprises a steel metal core and an external coating containing metal powder, ferroalloy, oxide, slag former, binder, extrusion aid, fluxing component, gas generator, and deoxidizer, which are present in amounts such that the electrode comprises from about 10.75 to about 11.25 wt% Cr, from about 0.035 to about 0.045 wt% C, from about 0.45 to about 0.55 wt% Mn, from about 0.15 to about 0.25 wt% Si, from about 0.85 to about 0.95 wt% Ni, from about 0.25 to about 0.35 wt% Mo, from about 1.2 to about 1.35 wt% Co, from about 0.04 to about 0.06 wt% Nb, from about 0.4 to about 0.6 wt% W, from about 0.5 to about 0.65 wt% Cu, from about 0.007 to about 0.009 wt% B, and from about 0.005 to 0.025 wt% N, and the balance of the steel welding metal composition is iron and unavoidable impurities.

[0059] In another embodiment, a consumable arc discharge welding wire electrode for the FCAW process is provided. The consumable arc discharge welding wire electrode comprises an outer steel metal sheath and a core surrounded by a sheath comprising metal powder, ferroalloy, oxide, slag former, binder, fluxing component, gas generator, and deoxidizer, which are present in amounts such that the wire electrode produces a steel weld metal composition comprising about 10.75 to about 11.25 wt% Cr, about 0.035 to about 0.045 wt% C, about 0.45 to about 0.55 wt% Mn, about 0.15 to about 0.25 wt% Si, about 0.85 to about 0.95 wt% Ni, about 0.25 to about 0.35 wt% Mo, about 1.2 to about 1.35 wt% Co, about 0.04 to about 0.06 wt% Nb, about 0.4 to about 0.6 wt% W, about 0.5 to about 0.65 wt% Cu, about 0.007 to about 0.009 wt% B, and about 0.005 to 0.025 wt% N, with the balance of the steel weld metal composition being iron and unavoidable impurities.

[0060] In another embodiment, a consumable arc discharge welding wire electrode for the GMAW process is provided, which is made from a steel having a composition comprising about 10.75 to about 11.25 wt% Cr, about 0.035 to about 0.045 wt% C, about 0.45 to about 0.55 wt% Mn, about 0.15 to about 0.25 wt% Si, about 0.85 to about 0.95 wt% Ni, about 0.25 to about 0.35 wt% Mo, about 1.2 to about 1.35 wt% Co, about 0.04 to about 0.06 wt% Nb, about 0.4 to about 0.6 wt% W, about 0.5 to about 0.65 wt% Cu, about 0.007 to about 0.009 wt% B, and about 0.005 to 0.025 wt% N, with the balance of the steel weld metal composition being iron and unavoidable impurities.

[0061] In another embodiment, there is provided a consumable arc discharge welding wire or rod for the GTAW process, made from a steel having a composition comprising from about 10.75 to about 11.25 wt% Cr, from about 0.035 to about 0.045 wt% C, from about 0.45 to about 0.55 wt% Mn, from about 0.15 to about 0.25 wt% Si, from about 0.85 to about 0.95 wt% Ni, from about 0.25 to about 0.35 wt% Mo, from about 1.2 to about 1.35 wt% Co, from about 0.04 to about 0.06 wt% Nb, from about 0.4 to about 0.6 wt% W, from about 0.5 to about 0.65 wt% Cu, from about 0.007 to about 0.009 wt% B and from about 0.005 to 0.025 wt% N, the balance of the steel weld metal composition being iron and unavoidable impurities.

[0062] In another embodiment, there is provided a consumable arc discharge welding wire electrode for use in combination with a agglomerated flux for the SAW process. The combination of the consumable arc discharge welding wire electrode and the flux comprises a solid or flux cored steel metal wire and an agglomerated flux containing silicate, oxide, carbonate, fluorite, metal powder, ferroalloy, these being present in amounts such that the combination of the wire electrode and the flux produces a steel weld metal composition comprising from about 10.75 to about 11.25 wt% Cr, from about 0.035 to about 0.045 wt% C, from about 0.45 to about 0.55 wt% Mn, from about 0.15 to about 0.25 wt% Si, from about 0.85 to about 0.95 wt% Ni, from about 0.25 to about 0.35 wt% Mo, from about 1.2 to about 1.35 wt% Co, from about 0.04 to about 0.06 wt% Nb, from about 0.4 to about 0.6 wt% W, from about 0.5 to about 0.65 wt% Cu, from about 0.007 to about 0.009 wt% B and from about 0.005 to 0.025 wt% N, the balance of the steel weld metal composition being iron and unavoidable impurities.

[0063] One or more exemplary embodiments are presented herein. For clarity, not all features of a physical implementation are described or shown in this application. In developing a physical implementation that incorporates the features of the present invention, it will be understood that numerous implementation-specific decisions must be made in order to achieve the developer's objectives, such as compliance with system-related, business-related, government-related, and other constraints, which vary by implementation or over time. The developer's efforts are time-consuming, but such efforts would nevertheless be routine work for those of ordinary skill in the art.

[0064] The method is described herein with respect to "comprising" various components or steps, but the method is also capable of "consisting essentially of" or "consisting of" various components or steps.

[0065] To facilitate a better understanding of embodiments of the present invention, the following examples of preferred or representative features are provided. The following examples should not be understood as limiting or defining the scope of the embodiments.

Example

[0066] The following non-limiting examples are provided to further illustrate embodiments of the present invention. It should be recognized by those of ordinary skill in the art that the techniques disclosed in the following examples are approaches that the inventor has found to work well in implementing embodiments of the present invention, and thus can be considered as constituting examples of modes for its implementation. However, those of ordinary skill in the art should recognize that many changes can be made to the specific embodiments disclosed with respect to embodiments of the present invention without departing from the spirit and scope of the embodiments, and still obtain the same or similar results.

[0067] Example 1 The chemical composition of the weld metal is shown in Table 1 (amounts are shown in wt%).

[0068]

Table 1

[0069] Using a 4 mm diameter low-hydrogen covered electrode and a preheat / interpass temperature of 250 °C, the composition was welded by the SMAW process and deposited onto a workpiece conforming to the AWS 5.5 standard geometry.

[0070] The deposited molten composition was cooled and solidified on the workpiece. PWHT was not performed.

[0071] The weld metal composition had the following properties: (Without PWHT) Structure of the composition: Low-carbon, non-tempered martensite. Uniaxial creep strength under various stress conditions

[0072]

Table 2

[0073] The impact toughness of the steel weld metal composition was measured to be >27 J at 20 °C (exceeding the applicable requirements set by ANSI, ASME, EPRI, EN, TUV codes, standards and recommended methods).

[0074] The Vickers hardness of the steel weld metal composition was <360 VHN.

[0075] The specific embodiments disclosed above are for illustrative purposes only, as they may be modified and implemented in different but equivalent manners that will be apparent to those skilled in the art and that have the advantages of the teachings herein. Further, no limitation is intended with respect to the details of construction or design shown herein other than as described in the claims below. Accordingly, it is evident that the specific exemplary embodiments disclosed above may be varied, combined, or modified, and all such variations are considered to be within the scope and spirit of the invention. The embodiments disclosed herein as examples may be suitably practiced in the absence of any element not specifically disclosed herein and / or in the absence of any optional element disclosed herein. Also, unless otherwise expressly or clearly defined by the patentee, the terms in the claims have their plain and ordinary meaning.

[0076] The research leading to this invention has received funding from the European Union’s Research Fund for Coal and Steel (RFCS) research program under grant agreement RFSR-CT-2014-00032.

Explanation of Signs

[0077] 100 Method for depositing a steel weld metal composition on a workpiece by an arc welding process 102 Step of at least partially melting a consumable electrode by an arc discharge and depositing the molten steel weld metal composition on the workpiece 104 Step of cooling and solidifying the molten steel weld metal composition to form the deposited steel weld metal composition on the workpiece 106 The steel weld metal composition does not undergo post-weld heat treatment (PWHT)

Claims

Claim 1. A deposited steel weld metal composition comprising: 9.00 to 12.00 wt% Cr, 0.02 to 0.06 wt% C, 0.3 to 0.7 wt% Mn, 0.1 to 0.3 wt% Si, 0.5 to 1.2 wt% Ni, 0.1 to 0.5 wt% Mo, 1.0 to 1.5 wt% Co, 0.03 to 0.08 wt% Nb, 0.2 to 0.8 wt% W, 0.3 to 0.8 wt% Cu, 0.005 to 0.010 wt% B, and 0.005 to 0.025 wt% N wherein the balance of the deposited steel weld metal composition is iron and unavoidable impurities, the deposited steel weld metal composition. Claim 2 The deposited steel weld metal composition according to claim 1, wherein the Cr content is 11 wt%. Claim 3 The deposited steel weld metal composition according to claim 1, wherein the Mn content is 0.4 to 0.6 wt%. Claim 4 The deposited steel weld metal composition according to claim 1, wherein the Ni content is 0.8 to 1.0 wt%. Claim 5 The deposited steel weld metal composition according to claim 1, wherein the Mo content is 0.2 to 0.4 wt%. Claim 6 The deposited steel weld metal composition according to claim 1, wherein the Co content is 1.1 to 1.3 wt%. Claim 7 The deposited steel weld metal composition according to claim 1, wherein the Nb content is 0.04 to 0.07 wt%. Claim 8 The deposited steel weld metal composition according to claim 1, wherein the W content is 0.3 to 0.7 wt%. Claim 9 The deposited steel weld metal composition according to claim 1, wherein the Cu content is 0.4 to 0.7 wt%. Claim 10 The deposited steel weld metal composition according to claim 1, wherein the B content is 0.006 to 0.009 wt%. Claim 11 The deposited steel weld metal composition according to claim 1, wherein the steel weld metal composition has a low-carbon, non-tempered martensite microstructure. Claim 12 The deposited steel weld metal composition according to claim 1, wherein the steel weld metal composition has a uniaxial creep resistance of at least 2500 hours at a temperature of 55 MPa and 650 °C. Claim 13 The deposited steel weld metal composition according to claim 1, wherein the steel weld metal composition has an impact toughness of at least 27 J at 20 °C and / or a Vickers hardness of 360 or less. Claim 14. A consumable arc discharge welding electrode for shielded metal arc welding (manual metal arc welding), comprising: a steel metal core, ​ An external coating containing metal powder, ferroalloy, oxide, slag former, binder, extrusion aid, fluxing component, gas generator, and deoxidizer, having, A consumable arc discharge welding covered electrode on which the deposited steel weld metal composition according to claim 1 is formed.

15. A consumable arc discharge welding wire electrode for the flux cored arc welding method, an external steel metal sheath, a core surrounded by the sheath, comprising metal powder, ferroalloy, oxide, slag former, binder, fluxing component, gas generator, and deoxidizer, having, A consumable arc discharge welding wire electrode on which the deposited steel weld metal composition according to claim 1 is formed.

16. A consumable arc discharge welding wire or rod for gas metal arc welding or gas tungsten arc welding method, composed of the deposited steel weld metal composition according to claim 1.

17. A consumable arc discharge welding wire electrode used in combination with the agglomerated flux of the submerged arc welding method, a solid or flux cored steel metal wire, an agglomerated flux containing silicate, oxide, carbonate, fluorite, metal powder, ferroalloy, having, A consumable arc discharge welding wire electrode on which the deposited steel weld metal composition according to claim 1 is formed.

18. A method of depositing a steel weld metal composition on a workpiece by an arc discharge welding process, a) melting at least a part of the consumable electrode by an arc discharge and depositing the melted steel weld metal composition on the workpiece; b) cooling and solidifying the melted steel weld metal composition to form the deposited steel weld metal composition on the workpiece, having, The deposited steel weld metal composition, contains 9.00 - 12.00 wt% Cr, 0.02 - 0.06 wt% C, 0.3 - 0.7 wt% Mn, 0.1 - 0.3 wt% Si, 0.5 - 1.2 wt% Ni, 0.1 - 0.5 wt% Mo, 1.0 - 1.5 wt% Co, 0.03 - 0.08 wt% Nb, 0.2 - 0.8 wt% W, 0.3 - 0.8 wt% Cu, 0.005 - 0.010 wt% B, and 0.005 - 0.025 wt% N, and, the balance of the deposited steel weld metal composition is iron and unavoidable impurities, The deposited steel weld metal composition is not subjected to post-weld heat treatment.

19. The method according to claim 18, wherein the deposited steel weld metal composition has a martensitic microstructure. **Claim 20** The method according to claim 18, wherein the deposited composition has a uniaxial creep resistance of at least 2500 hours at a temperature of 650 ° C and 55 MPa.

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