Systems, methods, and compositions for corrosion resistant stainless steel coatings

Abstract

In an exemplary embodiment, a coating is disclosed that can be applied to steel reinforcing bars (e.g., steel rebar) to significantly extend the life of concrete structures by reducing steel reinforcing bar corrosion. The coating includes a thin passivated steel (e.g., stainless steel) layer applied to the outside of conventional steel reinforcing bars. The coating can be applied in-line by metal cold spray manufacturing, a high-throughput coating technology that can be integrated into existing steel manufacturing plants. Additionally, a novel high-performance ferritic steel with tailored resistance to chloride corrosion is described. This new ferritic steel is distinct from other commercial and experimental steels and is more suitable for coating low-cost steel structures such as reinforcing bars. Multiple alloying elements, including Cr, Al, and Si, each independently form protective oxides, increasing the total amount of protection and extending protection over a much wider range of pH and potential.

Description

[Technical field]

[0001] Priority This patent application claims priority from U.S. Provisional Patent Application No. 63 / 255,520, filed October 14, 2021, entitled “INTEGRATED HIGH THROUGHPUT COLD SPRAY COATING MANUFACTURING SYSTEM,” and listing Samuel McAlpine and Steven Jepeal as inventors, the disclosure of which is incorporated herein by reference in its entirety.

[0002] This patent application also claims priority from U.S. Provisional Patent Application No. 63 / 219,436, filed July 8, 2021, entitled “CORROSION-RESISTANT FERRITIC STAINLESS STEEL,” and listing Samuel McAlpine and Steven Jepeal as inventors, the disclosure of which is incorporated herein by reference in its entirety.

[0003] This patent application also claims priority from U.S. Provisional Patent Application No. 63 / 219,434, filed July 8, 2021, entitled “STAINLESS-COATED STEEL REINFORCEMENT BAR,” and listing Samuel McAlpine and Steven Jepeal as inventors, the disclosure of which is incorporated herein by reference in its entirety.

[0004] background Steel reinforcement bars (rebars) are used to increase the strength of concrete under tension and shear, but uncoated bars offer little corrosion resistance. As steel reinforcement corrodes, it expands in volume, eventually pushing the surrounding concrete apart and causing cracks. If corrosion progresses sufficiently, it can cause major structural problems, such as concrete spalling, where blocks of concrete fall away, or delamination, where layers of cracks spread and the reinforcement separates from the surrounding concrete. In either case, this corrosion can cause significant structural damage to the concrete, putting it at risk for catastrophic failure and requiring major repairs or replacement.

[0005] With regard to steel reinforcing bars, after fabrication, the bars can corrode in the presence of atmospheric moisture or rain, forming undesirable iron oxides on the outer surface, which reduces the marketability of the bars. After the bars are impregnated into concrete, corrosion can cause significant structural deterioration, often by pitting corrosion due to the presence of chloride ions. This subsequent form of corrosion can severely limit the life of concrete structures using steel reinforcing bars.

[0006] There are several methods to improve the corrosion resistance of steel reinforcing bars. Many of these options add a high cost to the steel reinforcing bars and have inherent limitations in their effectiveness. For example, epoxy coatings are known to delaminate from the reinforcing bars during use, thus providing very limited corrosion resistance. The zinc layer produced during galvanization is susceptible to attack by the liquid concrete mix during concrete solidification, reducing its effectiveness and requiring thicker applied layers, which makes them more costly. In addition, to further illustrate, both galvanization by hot dip application and epoxy coatings present additional manufacturing steps that cannot be easily integrated into modern high throughput manufacturing methods for steel reinforcing bars.

[0007] Pure stainless steel rebar and stainless clad steel rebar exist, but are cost prohibitive for most applications.

[0008] Overview of Various Embodiments According to an embodiment of the present invention, a steel component includes a carbon steel reinforcing bar and an outer coating metallurgically bonded to the steel component and including a ferritic stainless steel. The outer coating forms a corrosion resistant coating on the steel component. The average thickness of the outer coating is between 10 μm and 300 μm.

[0009] There may be an interdiffusion zone between the carbon steel reinforcing bar and the outer coating, where the composition of the interdiffusion zone changes continuously from the composition of the coating to the composition of the carbon steel reinforcing bar. The width of the interdiffusion zone may be 10 nm to 10 μm.

[0010] The stainless steel coating may include cold spray coating, thermal spray coating, plasma spray coating, laser deposition coating, twin wire arc spray coating, or arc weld overlay coating. The stainless steel coating may have an average thickness of 20 μm to 100 μm. The stainless steel coating may include at least one of 316 stainless steel, 2205 stainless steel, or 304 stainless steel. At least one of 316 stainless steel, 2205 stainless steel, or 304 stainless steel may be mixed with a metal carbide or metal oxide. The metal carbide may include at least one of chromium carbide, molybdenum carbide, silicon carbide, or manganese carbide.

[0011] In some embodiments, the stainless steel coating comprises: 12 to 25 weight percent chromium (Cr); 2 to 10 weight percent molybdenum (Mo) and the following: 0-10 weight percent aluminum (Al); 0-5 weight percent silicon (Si); 0-5 weight percent nickel (Ni); 0 to 1.0 weight percent manganese (Mn); 0.0-0.1 weight percent carbon (C); 0.0 to 0.1 weight percent nitrogen (N); or At least one of 0.0 to 0.05 weight percent sulfur (S); The remaining iron (Fe) Includes.

[0012] In some embodiments, the stainless steel coating comprises: 16 to 20 weight percent chromium (Cr); 3 to 6 weight percent molybdenum (Mo) and the following: 0-4 weight percent aluminum (Al); 0-2 weight percent silicon (Si); 0-0.1 weight percent nickel (Ni); 0.1 to 0.5 weight percent manganese (Mn); 0.0-0.1 weight percent carbon (C); 0.0 to 0.1 weight percent nitrogen (N): or At least one of 0.0 to 0.05 weight percent sulfur (S); The remaining iron (Fe) Includes.

[0013] The stainless steel coating may include a face-centered cubic crystal structure. The stainless steel coating may include a ferritic / austenitic dual-phase microstructure. The stainless steel coating may be a ferritic stainless steel. The stainless steel coating may have sufficient ductility to bend a reinforcing bar up to 180 degrees around an object 3.5 times the diameter of the reinforcing bar without visible cracking of the stainless steel coating. The stainless steel coating may have sufficient ductility to have an inherent ductility to allow at least 5% elongation before failure.

[0014] According to another embodiment of the invention, the stainless steel coated steel component comprises a steel component and a corrosion resistant ferritic stainless steel coating metallurgically bonded to the steel component. The stainless steel coating may passivate the steel component against corrosion. The stainless steel coating may be a cold spray coating. The stainless steel coating may be a weld overlay coating. The stainless steel coating may be a twin wire arc spray coating. The stainless steel coating may be a laser cladding. The stainless steel coating may be a thermal spray coating. The stainless steel coating may have an average grain size of 500 nm to 10 μm.

[0015] In some embodiments, the stainless steel coating comprises: 16 to 20 weight percent chromium (Cr); 3 to 6 weight percent molybdenum (Mo) and the following: 0-4 weight percent aluminum (Al); 0-2 weight percent silicon (Si); 0-0.1 weight percent nickel (Ni); 0.1 to 0.5 weight percent manganese (Mn); 0.0-0.1 weight percent carbon (C); 0.0 to 0.1 weight percent nitrogen (N): or At least one of 0.0 to 0.05 weight percent sulfur (S); The remaining iron (Fe) Includes.

[0016] According to another embodiment of the invention, a method of forming a steel component includes providing a steel component having an exterior surface and coating at least a portion of the exterior surface with an exterior layer including a layer of ferritic stainless steel that forms a metallurgically bond to the exterior surface, the metallurgically bonded exterior layer coating forming a corrosion resistant coating on the steel component.

[0017] In some embodiments, the coating step may include providing a carrier gas at high pressure in a first gas flow path to a gas heater to heat the carrier gas to an elevated temperature along the first gas flow path. The coating step may include providing a carrier gas at high pressure in a second gas flow path to a particle feeder for stainless steel particles carried by the carrier gas along the second gas flow path. The coating step may include mixing the heated carrier gas in the first flow path with the stainless steel particles carried in the second flow path in an array of spray nozzles in fluid communication with the first and second flow paths. The coating step may include ejecting a plume of gas and stainless steel particles from the array of nozzles and coating the exterior surface of the steel component with a coating of stainless steel as the steel component is carried through the plume. The ejected stainless steel particles may impact the surface of the steel component at high velocity and form a metallurgical bond to the surface of the steel component to form an outer coating of ferritic stainless steel. The high velocity may be supersonic.

[0018] In some embodiments, the array of nozzles surrounds the steel component to provide coverage of the steel component with the plume. The high pressure may be from about 700 psi to about 800 psi. The high temperature of the heated gas is from about 900° C. to about 1100° C.

[0019] In some embodiments, the stainless steel particles may have an average particle size of 5 μm to 25 μm. The stainless steel coating may have an average thickness of 10 μm to 300 μm. Additionally, the stainless steel coating may have an average thickness of 20 μm to 100 μm.

[0020] In some embodiments, the component may be a steel rail, a steel beam, a steel girder, a steel rod, a steel bar, or a steel tube. In some embodiments, the component may be a steel billet.

[0021] In some embodiments, the method of forming the steel component may further include heating the coated steel billet material to a temperature of 1000°C to 1300°C. The method of forming the steel component may further include sequentially rolling the coated stainless steel billet material into a profiled reinforcing bar. The method of forming the steel component may further include coating the profiled reinforcing bar with an outer layer comprising a layer of ferritic stainless steel that forms a metallurgical bond to an outer surface of the profiled reinforcing bar. The method of forming the steel component may further include heat treating the coated profiled reinforcing bar. The heat treating may include laser heating.

[0022] In some embodiments, the steel component comprises a steel billet material. The steel billet material may have a rectilinear cross-section. The array of spray nozzles may surround the steel billet material in a rectilinear configuration to ensure that there is an unobstructed line of sight between each area of ​​the surface of the billet material and at least one of the nozzles in the array of nozzles. The stainless steel coating may cover an outer surface of the steel billet material.

[0023] According to an embodiment of the invention, a coating deposition system for applying a coating of stainless steel to a surface of a steel component includes a gas inlet for fluid connection to a high pressure gas supply configured to supply gas at high pressure to one or more flow paths. The coating deposition system also includes a heated gas flow path in thermal communication with the gas heater, the heated gas flow path in fluid communication with the high pressure gas supply. The gas heater is configured to heat the high pressure flowing gas in the heated gas flow path. The system also includes a stainless steel particle feeder flow path in particulate communication with the feeder inlet for receiving a source of stainless steel particles. The stainless steel particle feeder flow path is in fluid communication with the high pressure gas supply. The stainless steel particle feeder is configured to supply stainless steel particles to the high pressure flowing gas in the stainless steel particle feeder flow path.

[0024] The system also includes an array of spray nozzles in fluid communication with the heated gas flow path and the stainless steel particle feeder flow path. The array of spray nozzles is in particulate communication with the stainless steel particle feeder flow path. The array of spray nozzles is configured to surround the steel component such that there is an unobstructed straight line between each area of ​​the surface of the steel component and at least one of the nozzles in the array of nozzles. The array of spray nozzles is also configured to accelerate the stainless steel particles in the heated gas and the plume of stainless steel particles by a force provided by the high velocity of the heated gas exiting each of the nozzles in the array of nozzles. The array of spray nozzles is further configured such that the stainless steel particles impact the surface of the component at high velocity and metallurgically bond to the surface of the component to form a stainless steel coating. The stainless steel coating is ferritic, austenitic, or duplex. At least one of the spray nozzles generates a stream of stainless steel particles at least partially longitudinally and at least partially radially.

[0025] In some embodiments, an array of spray nozzles may be in particulate communication with the stainless steel particle feeder flow path. The array of spray nozzles may be configured such that for each nozzle in the array of nozzles, heated gas and particles can enter the nozzle. The heated gas may be compressed through a converging section of the nozzle. The heated gas may then expand through a diverging section of the nozzle. After passing through the converging and diverging sections of the nozzle, the heated gas and stainless steel particles may exit the nozzle as a plume and impact the surface of the steel component at supersonic speeds.

[0026] In some embodiments, the system may further include a conveyor configured to transport the component through the plume of hot gas and stainless steel particles. The component may have a linear cross-section. The array of spray nozzles may be configured to circumscribe the linear cross-section with the heads of each of the nozzles in the array of spray nozzles being linearly disposed.

[0027] Further, the components may have a circular, oval, or modified circular cross-section. The array of spray nozzles may be configured to enclose a circular, oval, or modified circular cross-section, with the heads of each of the nozzles in the array of spray nozzles being disposed in the respective circular, oval, or modified circular cross-section.

[0028] In some embodiments, the gas may include at least one of nitrogen (N2), helium (He), air, argon (Ar), xenon (Xe), or forming gas (5% H2 in N2). The high pressure may be about 700 psi to about 800 psi. The temperature of the heated gas may be about 900°C to about 1100°C. The high velocity may be supersonic. The stainless steel particles may have an average particle size of 5 μm to 20 μm. The stainless steel coating may have an average thickness of 0.5 mm to 5 mm. The stainless steel coating may have an average thickness of 35 μm to 350 μm. The stainless steel coating may have an average thickness of 25 μm to 300 μm. The stainless steel coating may have an average thickness of 10 μm to 100 μm. The stainless steel coating may have a BCC ferritic matrix.

[0029] In some embodiments, the stainless steel particles include 16 to 20 weight percent chromium (Cr); 3 to 6 weight percent molybdenum (Mo) and the following: 0-4 weight percent aluminum (Al); 0-2 weight percent silicon (Si); 0-0.1 weight percent nickel (Ni); 0.1 to 0.5 weight percent manganese (Mn); 0.0-0.1 weight percent carbon (C); 0.0 to 0.1 weight percent nitrogen (N): or At least one of 0.0 to 0.05 weight percent sulfur (S); The remaining iron (Fe) may include:

[0030] According to another embodiment of the invention, a method of applying a stainless steel coating to a steel component includes providing a carrier gas at high pressure in a first gas flow path to a gas heater to heat the carrier gas to an elevated temperature along the first gas flow path. A method of applying a stainless steel coating to a steel component includes providing a carrier gas at high pressure in a second gas flow path to a particle feeder for stainless steel particles carried by the carrier gas along the second gas flow path. The method includes mixing the heated carrier gas in the first flow path with the stainless steel particles carried in the second flow path in an array of spray nozzles in fluid communication with the first and second flow paths. The method also includes ejecting a plume of gas and stainless steel particles from the array of nozzles and coating an exterior surface of the steel component with a coating of ferritic stainless steel as the steel component is carried through the plume. The ejected stainless steel particles impact the surface of the steel component at high velocity and form a metallurgical bond to the surface of the steel component to form an exterior coating comprising ferritic stainless steel.

[0031] Each nozzle in the array of nozzles can compress the mixed heated carrier gas and particles through the converging section of each nozzle. Each nozzle in the array of nozzles can expand the mixed heated carrier gas and particles through the diverging section of each nozzle. Each nozzle in the array of nozzles can accelerate the mixed heated carrier gas and particles to supersonic speeds.

[0032] In some embodiments, the stainless steel particles include at least one of 316 stainless steel, 2205 stainless steel, or 304 stainless steel.

[0033] The steel component may be a steel billet material. The steel billet material may have a linear cross-section. The array of spray nozzles may surround the steel billet material in a linear configuration to ensure that there is an unobstructed straight line between each area of ​​the surface of the billet material and at least one of the nozzles in the array of spray nozzles. The stainless steel coating may cover the entire outer surface of the steel billet material, and the stainless steel coating may be between 150 μm and 500 μm thick. The stainless steel coating may be between 150 μm and 2000 μm thick.

[0034] The method may further include heating the stainless steel coating on the steel billet material at 1200° C. for a period of about 3 hours to about 9 hours. The method may further include hot rolling the stainless steel coating on the steel billet material to form a reinforcing component having a stainless steel coating. In some embodiments, the stainless steel coating may have a ceramic material alloyed with the stainless steel to improve bonding of the stainless steel coating to the steel component. The ceramic material includes at least one of a metal carbide or a metal oxide.

[0035] In some embodiments, the stainless steel particles may include at least one of spherical particles produced by gas atomization, approximately spherical particles produced by high pressure water atomization, or irregularly shaped particles produced by mechanical crushing.

[0036] The method may further include heat treating the stainless steel coating on the steel component. The step of heat treating the stainless steel coating on the steel component may include laser heat treating.

[0037] Heat treating the stainless steel coating on the steel component may include heating the stainless steel coating on the steel component to about 1100°C for a period of 1 hour. Heat treating the stainless steel coating on the steel component may include quenching the stainless steel coating on the steel component to room temperature. Heat treating the stainless steel coating on the steel component may include tempering the stainless steel coating on the steel component at about 600°C for a period of 1 hour.

[0038] According to an embodiment of the present invention, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 12 to 25 weight percent chromium (Cr); 2 to 10 weight percent molybdenum (Mo) and the following: 0-10 weight percent aluminum (Al); 0-5 weight percent silicon (Si); 0-5 weight percent nickel (Ni); 0 to 1.0 weight percent manganese (Mn); 0.0-0.1 weight percent carbon (C); 0.0 to 0.1 weight percent nitrogen (N); and At least one of 0.0 to 0.05 weight percent sulfur (S); The remaining iron (Fe) Includes.

[0039] In some embodiments, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 16 to 20 weight percent chromium (Cr); 3 to 6 weight percent molybdenum (Mo) and the following: 0-4 weight percent aluminum (Al); 0-2 weight percent silicon (Si); 0-0.1 weight percent nickel (Ni); 0.1 to 0.5 weight percent manganese (Mn); 0.0-0.1 weight percent carbon (C); 0.0 to 0.1 weight percent Nitrogen (N): At least one of 0.0 to 0.05 weight percent sulfur (S); The remaining iron (Fe) may include.

[0040] In some embodiments, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 18% by weight of chromium (Cr); 6 weight percent molybdenum (Mo); 4 weight percent aluminum (Al); 2 weight percent silicon (Si); The remaining iron (Fe) may include.

[0041] In some embodiments, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 18% by weight of chromium (Cr); 3 weight percent molybdenum (Mo); 4 weight percent aluminum (Al); 2 weight percent silicon (Si); The remaining iron (Fe) may include.

[0042] In some embodiments, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 18% by weight of chromium (Cr); 8 weight percent molybdenum (Mo); 5 weight percent aluminum (Al); The remaining iron (Fe) may include.

[0043] In some embodiments, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 18% by weight of chromium (Cr); 8 weight percent molybdenum (Mo); 2 weight percent silicon (Si); The remaining iron (Fe) may include.

[0044] In some embodiments, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 18% by weight of chromium (Cr); 4% by weight of molybdenum (Mo); The remaining iron (Fe) may include.

[0045] According to another embodiment of the present invention, a method of making a corrosion resistant ferritic BCC stainless steel alloy includes: 12 to 25 weight percent chromium (Cr); 2 to 10 weight percent molybdenum (Mo) and the following: 0-10 weight percent aluminum (Al); 0-5 weight percent silicon (Si); 0-5 weight percent nickel (Ni); 0 to 1.0 weight percent manganese (Mn); 0.0-0.1 weight percent carbon (C); 0.0 to 0.1 weight percent nitrogen (N); or At least one of 0.0 to 0.05 weight percent sulfur (S); The remaining iron (Fe) The method includes providing a metal mixture comprising:

[0046] The method of making the corrosion resistant ferritic BCC stainless steel alloy also includes providing a furnace for melting the metal mixture, heating the metal mixture in the furnace to form a liquid metal mixture molten, and cooling the liquid metal mixture molten to form a solid metal mixture. The solid metal mixture includes the corrosion resistant ferritic stainless steel alloy. The furnace may be a vacuum induction melting furnace. The furnace may be a vacuum arc melting furnace. Cooling the liquid metal mixture molten may include quenching the liquid metal mixture molten.

[0047] The method of making a corrosion-resistant ferritic BCC stainless steel alloy may further include atomizing the corrosion-resistant ferritic stainless steel alloy to produce corrosion-resistant stainless steel alloy particles. The method may include providing the corrosion-resistant stainless steel alloy particles to a cold spray system. The method may include coating a steel component with the corrosion-resistant stainless steel alloy particles ejected from the cold spray system. The ejected corrosion-resistant stainless steel alloy particles may metallurgically bond to an outer surface of the steel component to form a corrosion-resistant stainless steel coating having a BCC ferritic matrix on the steel component.

[0048] The method of making a corrosion resistant ferritic BCC stainless steel alloy may further include heat treating the corrosion resistant stainless steel coating having a BCC ferritic matrix on the steel component. The step of heat treating the corrosion resistant stainless steel coating having a BCC ferritic matrix may include laser heat treatment.

[0049] The step of heat treating the corrosion resistant stainless steel coating having a BCC ferritic matrix may include heating the corrosion resistant coating on the component to a temperature of about 1000°C to about 1300°C for a period of 1 hour to 24 hours. The step of heat treating may include quenching the corrosion resistant coating on the steel component. The step of heat treating may include tempering the corrosion resistant coating on the steel component at a temperature of 400°C to 700°C for a period of 10 minutes to 4 hours.

[0050] The step of atomizing the corrosion-resistant stainless steel alloy may include at least one of the steps of gas atomizing the corrosion-resistant ferritic stainless steel alloy to produce spherical particles of the corrosion-resistant stainless steel alloy, atomizing the corrosion-resistant ferritic stainless steel alloy to produce approximately spherical particles of the corrosion-resistant stainless steel alloy, or mechanically crushing the corrosion-resistant ferritic stainless steel alloy to produce irregularly shaped particles of the corrosion-resistant stainless steel alloy.

[0051] The corrosion resistant stainless steel alloy particles may have an average particle size of 5 μm to 20 μm. The average thickness of the stainless steel coating may be 10 μm to 500 μm.

[0052] The component may be a steel billet. The component may be a steel reinforcing bar, a steel beam, a steel track, or a steel tubular material.

[0053] According to another embodiment of the present invention, a method of making a ferritic stainless steel alloy includes: 12 to 25 weight percent chromium (Cr); 2 to 10 weight percent molybdenum (Mo) and the following: 0-10 weight percent aluminum (Al); 0-5 weight percent silicon (Si); 0-5 weight percent nickel (Ni); 0 to 1.0 weight percent manganese (Mn); 0.0-0.1 weight percent carbon (C); 0.0 to 0.1 weight percent nitrogen (N); or At least one of 0.0 to 0.05 weight percent sulfur (S); The remaining iron (Fe) The method includes providing a metal mixture comprising:

[0054] The method of making a ferritic stainless steel alloy also includes providing a furnace for melting the metal mixture. The metal mixture is heated in the furnace to a temperature of about 1600°C to about 2000°C to form a liquid metal mixture melt. The liquid metal mixture melt is cooled to an intermediate temperature of about 1000°C to about 1300°C for a first period of time to initiate a solidification process. The liquid metal mixture melt is held at the intermediate temperature of about 1000°C to about 1300°C for a second period of time. The liquid metal mixture melt is quenched to a temperature of about 400°C to about 600°C for a third period of time. The first period of time may be 5 minutes to 100 minutes. The second period of time may be 0.5 seconds to 10.0 seconds.

[0055] The quenching step limits the formation of carbide precipitates. The metal mixture is tempered at a temperature of about 450° C. to about 600° C. for a period of about 10 minutes to about 60 minutes. The metal mixture is cooled in the absence of active heating. The metal mixture includes a ferritic stainless steel alloy. The ferritic stainless steel alloy may be corrosion resistant. The ferritic stainless steel alloy may have a body-centered cubic crystal structure.

[0056] The furnace may include a cold sprayer. The method may further include atomizing the ferritic stainless steel alloy. The method may further include depositing the atomized ferritic stainless steel alloy as a coating on the steel component. The ferritic stainless steel alloy coating may be metallurgically bonded to a surface of the steel component. The ferritic stainless steel alloy coating on the steel component may resist corrosion of the steel component. The ferritic stainless steel alloy may be a bulk material. [Brief description of the drawings]

[0057] Those skilled in the art will more fully appreciate the advantages of various embodiments of the present invention from the following Description of Exemplary Embodiments, discussed with reference to the drawings summarized immediately below. [Figure 1] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of steel reinforcing bars having a stainless steel coating according to exemplary embodiments. [Diagram 2] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of an interface region between a protective coating and concrete, according to exemplary embodiments. [Diagram 3] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of an interface region between a protective coating and concrete, according to exemplary embodiments. [Figure 4] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of an interface region between a protective coating and concrete, according to exemplary embodiments. [Diagram 5] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of an interface region between a protective coating and concrete, according to exemplary embodiments. [Figure 6] FIG. 1 is a schematic diagram showing corrosion through and pitting corrosion. [Figure 7] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of a coating interface for cold spray application, according to exemplary embodiments. [Figure 8] FIG. 1 is a schematic diagram of a poorly bonded and porous coating. [Figure 9] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of a cold spray deposition system according to exemplary embodiments. [Figure 10A] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of a cold spray deposition system according to exemplary embodiments. [Figure 10B] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of a cold spray deposition system according to exemplary embodiments. [Figure 11] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of nozzle designs according to exemplary embodiments. [Figure 12A] 1A-1C are schematic diagrams illustrating various embodiments of the present disclosure of a nozzle array, according to exemplary embodiments. [Figure 12B] 1A-1C are schematic diagrams illustrating various embodiments of the present disclosure of a nozzle array, according to exemplary embodiments. [Figure 13] The left side of FIG. 13 is a schematic diagram of various embodiments of the present disclosure of a nozzle array according to an exemplary embodiment, and the right side of FIG. 13 is a schematic diagram of various embodiments of the present disclosure of a nozzle array according to an exemplary embodiment. [Figure 14] The left side of FIG. 14 is a schematic diagram of various embodiments of the present disclosure of a nozzle array according to an exemplary embodiment, and the right side of FIG. 14 is a schematic diagram of various embodiments of the present disclosure of a nozzle array according to an exemplary embodiment. [Figure 15] 1A-1C are schematic diagrams illustrating various embodiments of the present disclosure of a nozzle array, according to exemplary embodiments. [Figure 16] 1A-1C are schematic diagrams illustrating various embodiments of the present disclosure of a nozzle array, according to exemplary embodiments. [Figure 17A] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of the integration of a spray system into a manufacturing line according to exemplary embodiments. [Figure 17B] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of the integration of a spray system into a manufacturing line according to exemplary embodiments. [Figure 18] 1A-1D are schematic diagrams illustrating various embodiments of the present disclosure of corrosion resistant stainless steel alloys according to exemplary embodiments. [Figure 19] FIG. 2 shows an Ellingham diagram presenting the relative driving forces for oxide formation between the constituent elements in the present invention. [Figure 20] FIG. 1 illustrates the equilibrium phase composition for a range of Cr and Mo contents in iron, chromium, and molybdenum stainless steel alloys. [Figure 21]FIG. 1 shows an equilibrium phase fraction plot of an example Fe—Cr—Mo—Al—Si composition, highlighting secondary phases that should be limited or avoided entirely. [Figure 22] FIG. 2 is a diagram showing time-temperature-transformation curves for an example of an Fe—Cr—Mo—Al—Si composition. [Diagram 23] FIG. 1 shows a phase composition map of Fe-18Cr-3Mo-4Al-2Si illustrating the presence of deleterious secondary phases at low temperatures. [Figure 24] FIG. 2 shows the time-temperature-transformation diagram of Fe-18Cr-3Mo-4Al-2Si. [Diagram 25] FIG. 1 shows an equilibrium phase fraction plot of an example Fe—Cr—Mo—Al composition, highlighting secondary phases that should be limited or avoided entirely. [Figure 26] FIG. 1 shows a time-temperature-transformation diagram of Fe-18Cr-8Mo-5Al. [Figure 27] FIG. 1 shows an equilibrium phase fraction plot for an Fe—Cr—Mo—Si alloy, highlighting secondary phases that should be limited or avoided entirely. [Figure 28] FIG. 2 shows the time-temperature-transformation diagram of Fe-18Cr-8Mo-2Si. [Figure 29] FIG. 1 shows an equilibrium phase fraction plot for an Fe—Cr—Mo alloy, highlighting secondary phases that should be limited or avoided entirely. [Diagram 30] FIG. 2 shows the time-temperature-transformation diagram of Fe-18Cr-4Mo.

[0058] Description of exemplary embodiments In an exemplary embodiment, a coating is applied to steel reinforcing bars (e.g., steel rebar) that can significantly extend the life of concrete structures by reducing steel reinforcing bar corrosion. The coating includes a thin passivated steel (e.g., stainless steel) layer applied to the outside of conventional steel reinforcing bars. The coating can be applied in-line by metal cold spray manufacturing, a high-throughput coating technology that can be integrated into existing steel manufacturing plants. This technology solves the challenge of reinforcing bar corrosion in the presence of water and chlorides (salt), which limits the service life of many concrete structures, including bridges, roads, and marine structures. The coated reinforcing bars have a longer life and are less expensive than traditional coatings such as epoxy coatings. The in-line coating application method can be integrated directly into steel manufacturing plants.

[0059] In an exemplary embodiment, a high performance ferritic steel with tailored resistance to chloride corrosion is described. This new ferritic steel is distinct from other commercial and experimental steels and is more suitable for coating low-cost steel structures such as reinforcing bars. This new steel completely prevents corrosion in the presence of chlorides. This new ferritic steel coating is distinct from conventional steels because it is formulated to act as a thin coating designed to produce multiple protective oxide layers to give a broader range of corrosion protection than existing stainless steels. Multiple alloying elements, including Cr, Al, and Si, each independently form protective oxides, increasing the total amount of protection and extending protection over a much wider range of pH and potential. A high concentration of Mo is included to reverse any pitting caused by chlorides by repassivating newly formed pits. The resulting steel is more corrosion resistant than conventional stainless steels or galvanized steels, especially to high concentrations of chloride ions. This new high performance ferritic steel can also be applied in-line through metal cold spray manufacturing to resist corrosion to reinforcing bars.

[0060] However, while steel reinforcing bars have been described, it should be noted that the various embodiments also apply to other types of steel products, such as I-beams, strips, pipes, billets, tubes, etc. Thus, the description of steel reinforcing bars is for illustrative purposes and is not intended to apply to all embodiments.

[0061] Corrosion resistance Corrosion of reinforcing bars occurs by at least two pathways. One pathway is oxidation of the steel surface caused by exposure to water. The other pathway is pitting, where chloride ions attack the steel surface in pits formed on the surface of the reinforcing bars. Corrosion caused by pitting is caused by chloride ions (e.g., Cl - ) corrosion caused by exposure to salts such as sodium chloride (e.g., NaCl). Chloride ions have access to the surface iron of steel.

[0062] Oxidation pathways can be blocked by forming an oxidation barrier on the surface of the steel forming a passivation layer (e.g., a passivation coating). Passivation layers of certain metal oxides, such as chromium oxide Cr2O3 (e.g., chromia), silicon dioxide SiO2 (e.g., silica), aluminum oxide Al2O3 (e.g., alumina) on the surface of the steel can protect the steel from oxidative corrosion. Pitting corrosion in particular can be blocked by certain metal oxides, such as molybdenum oxide MoO3, which are resistant to chloride ion attack (e.g., corrosion).

[0063] For passivation layers to be effective in preventing corrosion, they must be strongly bonded to the steel surface, completely cover the surface, and be of sufficient thickness to provide a robust coating. To create a passivation layer, the application of a metal coating naturally creates the desired oxide layer. A strong bond between the metal coating and the underlying component can be obtained by a metallurgical bond (e.g., metallurgically bonded). Certain techniques, such as cold spray and weld overlay, allow the application of metal coatings to metallurgically bonded (e.g., metallurgically bonded) steel. Furthermore, these techniques also allow the deposition of coatings over the entire surface of steel components, such as reinforcing bars or billet material. Furthermore, these techniques (cold spray and weld overlay) allow the application of metal coatings to steels that are thick enough to provide robust corrosion resistance, often 50-300 μm.

[0064] In an embodiment, a metal coating, such as stainless steel, is applied to a steel component, which forms a native oxide coating that acts as a passivation layer. A native oxide coating is a layer of one or more metal oxides that form spontaneously on a metal surface in water or air due to an exothermic driving force of metal oxide formation. Oxygen from the water or air oxidizes the metal's surface atoms to form a thermodynamically stable oxide coating. This surface oxide forms whenever exposed metal atoms are exposed by fresh deposition, scratching, or otherwise penetrating a protective oxide layer.

[0065] One example of this process is the deposition of a chromium-containing stainless steel onto a steel component. In this example, the deposited stainless steel coating contains chromium metal, some of which is at the coating surface. Oxygen in the water or air spontaneously forms a surface oxide of chromium (e.g., chromium oxide, Cr2O3), and the spontaneously formed surface layer of chromium oxide reacts with the oxygen in the water or air to provide protection from oxidation and pitting corrosion.

[0066] This process of surface oxide formation from atoms at the surface of stainless steel occurs spontaneously. Additionally, the thermodynamic strength of the metal-oxygen bond may cause rearrangement of surface atoms to form a layer of a particular metal oxide. In the above example describing the formation of chromium oxide, the thermodynamic driving force for the formation of Cr2O3 may cause the metal atoms at the surface of the stainless steel coating to rearrange (e.g., diffuse) to allow the formation of a chromia layer. That is, metal atoms close to the surface of the alloy may diffuse from their positions below the surface of the alloy to the surface under the thermodynamic potential to form a native metal oxide on the surface of the alloy.

[0067] The thermodynamic driving force for oxide formation of each atom that composes the stainless steel coating can cause metal oxide layers to separate and stack on top of each other in a predictable order, spontaneously forming a multilayer structure. The stacking order of the metal oxide layers in the multilayer structure is determined by the free energy of formation (ΔG) of each of the metal oxides. Metal oxides with the highest ΔG (in absolute value) tend to form closest to the steel component, while metal oxides with the lowest absolute value of ΔG form at the surface of the coating. That is, metal atoms diffuse from their location in the alloy structure through the metal alloy to the surface to form each metal oxide layer, and the location of a particular metal oxide in the multilayer structure is determined by the ΔG of each metal oxide.

[0068] In some embodiments, the incorporation of certain metals such as chromium and molybdenum as primary alloys into iron-based stainless steel coatings may provide structural benefits as well as corrosion resistance. Disclosed herein are various stainless steel coatings with different alloy compositions using different elements as primary alloying elements (e.g., chromium (Cr), molybdenum (Mo), nickel (Ni), and / or manganese (Mn)), secondary alloying elements, and tertiary alloying elements (e.g., aluminum (Al), silicon (Si), carbon (C), nitrogen (N), and / or sulfur (S)). In some embodiments, the primary alloying elements may be primary oxide formers, and the secondary alloying elements may be secondary oxide formers.

[0069] Bimetallic Steel Composite To provide robust corrosion resistance to steel components (e.g., steel reinforcing bars) at a low cost, an exemplary embodiment utilizes a thin outer coating of stainless steel on conventional carbon steel reinforcing bars. This thin coating can passivate the steel reinforcing bars in the same manner as pure stainless steel reinforcing bars, providing corrosion resistance before and after consumption in concrete structures. As a result, the concrete structures are more resistant to corrosion and therefore have an extended service life.

[0070] FIG. 1 shows a schematic representation of a steel reinforcing bar with a stainless steel coating 100. FIG. 1 (left) shows a schematic cross-section of a bar coated with a corrosion-resistant stainless steel, and FIG. 1 (right) shows a schematic plan view of a portion of a bar coated with a surface corrosion-resistant stainless steel. The steel reinforcing bar 110 has ribs 120, the reinforcing bar being shown with a stainless steel coating 130. The stainless steel coating 130 completely covers the steel reinforcing bar 110 including the ribs 120. Complete coverage of the reinforcing bar 110 with the ribs 120 with the stainless steel coating 130 is necessary for comprehensive corrosion resistance.

[0071] In some embodiments, the use of a molybdenum-containing coating (e.g., outer layer) provides resistance to chloride attack, providing resistance to salt-containing environments such as marine applications and locations where deicing salts are used. In some embodiments, the use of secondary oxide formers including aluminum and silicon enhances corrosion resistance in a wider range of environments.

[0072] FIG. 2 shows a schematic of an embodiment of an interface region between a protective coating and concrete, according to an exemplary embodiment. FIG. 2 (left) shows a schematic of an interface 210 between a coating 220 on a coated steel reinforcing bar and concrete 230. The interface region 210 is clearly defined, indicating that the formation of a passivation layer has not yet begun. FIG. 2 (right) shows a schematic of an interface 240 between a coating 220 on a coated steel reinforcing bar 250 and concrete 230. As a result of oxidizing components in the concrete, a native protective oxide layer 260 (e.g., a passivation layer) has grown on the surface of the coated reinforcing bar 220. The protective oxide layer 260 provides resistance to corrosion of the underlying reinforcing bar 250. The outer oxide layer 260 contains passivating compounds (e.g., Cr2O3 and MoO3) that protect against corrosion and prevent potentially corrosive species from coming into contact with the reinforcing bar. These compounds form a native protective oxide layer on the outside of the coating at the interface between the coating 220 and the concrete 230, thereby preventing corrosion of the underlying carbon steel reinforcing bars.

[0073] FIG. 3 illustrates a schematic of an embodiment of an interface region between a protective coating and concrete, according to an exemplary embodiment. 300 in FIG. 3 illustrates a schematic of a protective oxide layer 360 of Cr2O3 formed on an Fe-Cr alloy. A native protective oxide layer 360 of Cr2O3 is formed on the surface of the Fe-Cr alloy due to thermodynamic forces that form oxide compounds when an oxidizing element (e.g., oxygen) comes into contact with a metallic element (e.g., chromium, molybdenum, etc.). The protective oxide layer 360 of Cr2O3 is a passivating layer that provides a barrier that limits the diffusion of oxygen from the concrete 330 to the metal surface of the steel component (e.g., reinforcing bars, steel billet material, etc.). The passivating Cr2O3 layer thus limits the corrosion rate. FIG. 3 illustrates a schematic of how the chromium in the outer coating 320 forms a chromia (Cr2O3) 360 outer layer to prevent and / or substantially mitigate the corrosion of the iron in the steel component core.

[0074] In some embodiments, secondary oxide formers, such as silicon and aluminum, can be added to the stainless steel alloy to reinforce the chromium oxide and / or molybdenum oxide layers with additional protective oxides. The function of these secondary oxide formers is shown diagrammatically in FIG.

[0075] FIG. 4 shows a schematic of an embodiment of an interface region between a protective coating and concrete, according to an exemplary embodiment. 400 in FIG. 4 shows a schematic of a protective oxide 460 of Cr2O3 / Al2O3 / SiO2 formed on an Fe-Cr-Si-Al alloy. The protective oxide 460 of Cr2O3 / Al2O3 / SiO2 forms a passivating multilayer (multilayer structure not shown in FIG. 4) that provides a barrier to limit oxygen diffusion from the concrete 430 to the iron core metal surface. The passivating Cr2O3 / Al2O3 / SiO2 multilayer limits the corrosion rate. FIG. 4 shows a schematic of how chromium, silicon, and aluminum in the outer coating 420 form a Cr2O3 / Al2O3 / SiO2 360 multi-oxide layer barrier to prevent and / or substantially mitigate corrosion of the iron in the coating or reinforcing core.

[0076] In addition to oxygen in the air and concrete, chloride ions present in many salts (e.g., Cl - ) leads to corrosion of steel components. Chloride ions can not only form metal chlorides that corrode steel components, but can also form metal oxychlorides with oxygen that are very effective in corroding and weakening structural steel, such as reinforcing bars.

[0077] Molybdenum oxide (e.g., MoO3) is an effective barrier oxide that prevents chloride ions from corroding steel. Metallic molybdenum forms a native oxide barrier layer, molybdenum oxide (e.g., MoO3), on stainless steel alloys containing molybdenum. In some embodiments, the molybdenum in the coating can disulfidize to pits in the coating to form molybdenum oxide. This MoO3 repassivates the formed pits and prevents the progression of pitting-type corrosion. This is particularly important in chloride environments where pitting-type corrosion can breach the protective oxide layer and damage the underlying steel components (e.g., reinforcing bars, etc.). Repassivation of pitting corrosion by molybdenum is shown in Figure 5-1.

[0078] FIG. 5 shows a schematic of an embodiment of an interface region between a protective coating and concrete according to an exemplary embodiment. 500 in FIG. 5 shows a schematic of a protective oxide layer 560 of Cr2O3 formed on an Fe-Cr-Mo alloy. The native protective oxide layer 560 of Cr2O3 is formed on the surface of the Fe-Cr-Mo alloy due to thermodynamic forces that form chromium oxide compounds when an oxidizing element (e.g., oxygen) comes into contact with a metallic element (e.g., chromium). The protective oxide layer 560 of Cr2O3 is a passivating layer that provides a barrier that limits the diffusion of oxygen from the concrete 530 to the metal surface of the steel component (e.g., reinforcing bars, steel billet material, etc.). Thus, the passivating Cr2O3 layer at least limits the corrosion rate by oxygen.

[0079] FIG. 5 also illustrates, in a schematic manner, how forming an oxide on the surface of an Fe-Cr-Mo alloy can reduce corrosion due to pit / crevice formation in the alloy coating. Crevice / pits 570 can form in the Fe-Cr-Mo alloy coating 520 through the oxide passivation coating Cr2O3 560. As shown in the schematic, molybdenum oxide (e.g., MoO3) in the stainless steel alloy is converted to Cl - A repassivation layer 580 can be formed that prevents and / or substantially reduces corrosion of the underlying steel components from chloride ions. That is, the presence of Mo in the stainless steel alloy provides metal (Mo) that can diffuse to the surfaces of the pits / crevices to form an effective oxide layer of MoO3 that can enhance corrosion resistance in the presence of chloride ions.

[0080] Thus, the formation of pits and / or crevices in a steel component can significantly increase corrosion of the steel component, but the application of a stainless steel barrier to the steel component, as disclosed herein in multiple embodiments, can significantly reduce or even prevent corrosion of the steel component in the presence of pits / crevices. If the metallurgical bond is successful, the stainless steel coating will remain attached to the bar through deformation of the bar, such as bending. The complete coating is expected to perform equivalently (or similarly) to a bar made entirely of stainless steel, albeit with a significantly lower percentage of stainless steel (e.g., 5% or less). If the metallurgical bond is successful, the coating is expected to perform much better than state-of-the-art epoxy-coated reinforcement bars due to the tough, robust nature and inherent corrosion resistance of the stainless steel coating.

[0081] General manufacturing method At least two common approaches for producing coated steel components disclosed herein in exemplary embodiments include spray deposition and weld overlay deposition techniques. In the first approach, a spray technique, such as cold spray, is used on a finished or nearly finished steel component, such as a reinforcing bar. In the second approach, a weld overlay deposition technique is used to deposit a corrosion resistant coating at a thickness greater than the thickness of the finished product. The following discussion of these two techniques is in no way limiting, and one of ordinary skill in the art may use other approaches to form the stainless steel coatings disclosed herein. These two approaches are discussed for illustrative purposes only.

[0082] The first approach, which uses cold spray to deposit the coating on finished bar stock, is the best choice when the high throughput required to manufacture components is required.

[0083] The second approach, using weld overlay, or some other coating deposition method / technique followed by sequential rolling, is appropriate when coating quality is important but lower throughput is acceptable. In general, weld overlay processes take significantly longer to deposit the coating than cold spray.

[0084] Using the first approach of cold spray deposition, the deposited particles are propelled upon impact with sufficient velocity to achieve adiabatic shear instability, thereby causing plastic deformation, thus creating a cold weld (e.g., metallurgical bond) between the metallic coating and the underlying steel component.

[0085] When the second approach of overlay welding is adopted, special attention is paid to the heat affected zone of the corrosion resistant coating and the possibility of carbide formation, which can lead to cracking of the coating during the subsequent rolling process. If carbide formation occurs, heat treatment of the overlaid billet material (e.g., 1200 degrees Celsius for 1 hour) can be employed. After heat treatment, the total thickness of the bar and the thickness of the coating can be reduced through several sequential rolling steps.

[0086] Coating Requirements The corrosion resistant metal coating must completely cover the surface of the bar. If the coating is not complete, small openings or "holidays" can be the source of pitting attack. Pits (e.g., crevices) can be formed by the ingress of metals, particularly chlorides (e.g., chloride ions, Cl). - ), this can lead to significant corrosion. An example of this pitting process due to coating loss is shown in Figure 6.

[0087] 6 shows a schematic of a coating gap 600, which indicates that pitting may result from a coating defect. When a corrosion resistant stainless steel coating 620 on a steel component 650 has a coating gap 690, pitting may result. Attack of the structural integrity of the steel component by chloride ions and / or oxygen may proceed to cause pitting 695. Such coating gaps may occur when the coating coverage is incomplete and / or when the coating is poorly bonded or when the coating is porous.

[0088] 7 illustrates various embodiments of the present disclosure of a coating interface for cold spray application, according to an exemplary embodiment. A schematic cross-sectional view 700 of a coating interface 715 for cold spray application is shown. In cold spray deposition, a full contact surface interface 715 is formed between a particle 705 and the surface of a substrate (e.g., a steel component) 750. The coated particle 705 is flattened, which indicates plastic deformation and cold welding of the impacted particle 705 to the substrate 750, resulting in a well-bonded coating 720.

[0089] In some embodiments, the average particle size of the particles 705 may be between 5 μm and 20 μm. The corrosion resistant stainless steel coating 720 may have an average thickness between 10 μm and 100 μm. The corrosion resistant stainless steel coating 720 is fully adhered to the underlying steel bar (e.g., component) 750 by a metallurgical bond at the interface between the coating 720 and the bar 750.

[0090] FIG. 8 800 shows a schematic of a poorly bonded porous coating 820. A poorly bonded porous coating 820 is undesirable and can lead to spalling of the coating 820 or penetration of the coating 820 by liquids in a corrosive environment. If the bond fails, the coating will not cover the surface 850 of the steel component and / or will not adhere to the underlying substrate at the interface 815. There can be pores 825 that allow corrosive liquids and / or gases to penetrate the poorly bonded coating 820 and corrode the underlying steel component 850.

[0091] Coating Materials In some embodiments, various coating metals can provide corrosion resistance. For example, ferritic stainless steels, including grade 430 steel, iron-chromium-aluminum alloys, iron-chromium-molybdenum-aluminum alloys, iron-chromium-molybdenum-aluminum-silicon alloys, etc., provide effective corrosion resistance to steel components as described herein. Furthermore, ferroalloys (e.g., containing at least 14 wt. % Cr) significantly improve the corrosion resistance of reinforcing bars. In high chloride environments, such as seawater environments or roads, chloride-resistant coating alloys containing at least 2 wt. % Mo can be used to resist chloride attack.

[0092] Additionally, new ferritic stainless steel alloys having a body-centered cubic (e.g., BCC) structure are disclosed below. Other embodiments utilize martensitic steels, such as grade 4130 steel. Still other embodiments utilize austenitic stainless steels, such as grade 304 and grade 316 steel. Still other embodiments utilize non-ferrous metals and alloys, such as aluminum, titanium, and chromium-based metals. The coating metals listed above and those described in the examples below are for illustrative purposes only. Those skilled in the art may use other coating materials not listed herein.

[0093] Cold Spray System Exemplary embodiments relate to a process for high throughput metal coating of metal components by continuous cold spray additive manufacturing. Exemplary embodiments also relate to components associated with this process.

[0094] Many low-cost steel structures suffer from reduced operational life due to the effects of corrosion on structural integrity. In many cases, it would be beneficial to apply a corrosion-resistant outer layer to extend performance life. Existing methods such as epoxy coatings, painting, and galvanization offer limited corrosion resistance, are not easily integrated into modern high-throughput steel manufacturing methods, and are costly.

[0095] Cold spray additive manufacturing is a relatively high-throughput method of applying metal coatings to the surface of components. In cold spray, metal particles are sprayed from the nozzle of a spray coater at high velocity onto a substrate at a temperature significantly lower than the melting point of the metal. These particles are accelerated to high speed by a supersonic carrier gas before impacting the substrate. The coating particles then bond to the substrate upon impact when their kinetic energy causes severe plastic deformation and cold welding. The coating particles form metallurgical bonds (e.g., metallurgical bonds) with the substrate.

[0096] FIG. 9 illustrates various embodiments of the present disclosure of a cold spray deposition system 900, according to an exemplary embodiment. In some embodiments, the cold spray deposition system 900 includes a spray gun 910. The spray gun 910 includes a gas inlet 912 that allows for connection of a gas source to the spray gun 910. The gas may include at least one of nitrogen (N2), helium (He), air, argon (Ar), xenon (Xe), or forming gas (5% H2 in N2). The gas may be at high pressure, between about 700 psi and about 800 psi. The gas may be heated by an energy source 914 to a temperature of between about 900° C. and about 1100° C.

[0097] The spray gun 910 includes a feeder inlet 918 for receiving a supply of stainless steel particles from a particle feeder. The particle feeder may be a hopper for feeding the stainless steel particles to the spray gun 910. The stainless steel particles may have an average particle size of 5 μm to 20 μm. The feeder feeds the stainless steel particles into a flow line with high pressure gas, which is a carrier gas for the particles.

[0098] The spray gun 910 includes an array of spray nozzles (not shown) configured to surround the steel component such that there is an unobstructed straight line between each area of ​​the surface of the steel component and at least one of the nozzles in the array of nozzles.

[0099] The high pressure heated gas carrying the particles is supplied to an array of nozzles. The array of spray nozzles is configured to accelerate the stainless steel particles by a force imparted by the high velocity of the heated gas exiting each nozzle within a plume of the heated gas and stainless steel particles 920. The stainless steel particles impact the surface of the component 930 at high velocity and metallurgically bond to the surface of the component 930 to form a stainless steel coating 940. In some embodiments, the high velocity is supersonic.

[0100] Components 930 move within spray plume 920 with component motion 950. Component motion 950 may be provided by a conveyor or other mechanism that moves metal components 930 through spray plume 920.

[0101] A close-up view 960 of an embodiment of a spray deposition system 900 shows a particle 925 moving towards the component 930, as indicated by the arrow. The corrosion resistant coating 940 is shown deposited on the component 930 as an accretion of the particle 925 onto the component. The particle 925 has a flattened appearance due to arriving at the component 930 at supersonic speed. The flattened appearance indicates plastic deformation and cold welding of the impacted particle 925 to the component (e.g., substrate) 930, resulting in a well-bonded coating 940.

[0102] Sprayer Components 10A and 10B show various embodiments of the present disclosure of a cold spray deposition system according to an exemplary embodiment. As shown in FIG. 10A and 10B, the spray systems of 1000 and 1010, respectively, include multiple components including a gas supply 1012, a particle (e.g., powder) feeder 1018, a gas heater 1014, and an array of spray nozzles 1024. The spray system 1000 of 10A is configured in a parallel arrangement. The spray system 1010 of 10B is configured in an in-line arrangement. In some embodiments, the spray system can utilize a parallel arrangement or an in-line arrangement. In some embodiments, only one of each of the aforementioned components is utilized. In other embodiments, multiple of one or more of the aforementioned components are utilized, such as multiple arrays of nozzles connected to one system, or multiple separate systems of gas heaters and nozzle arrays sharing one central gas supply.

[0103] metal particles An exemplary embodiment utilizes metal particles (e.g., powder) as the consumable input. These particles are fed into a carrier gas and carried to the substrate at high velocity. The particles then impact the substrate (e.g., a metal component) and form a metallurgical bond to the substrate surface, thereby forming a coating. The particles can be produced in several ways, including gas atomization, water atomization, and mechanical crushing.

[0104] In some embodiments, the applied particles are spherical particles created by gas atomization. In some embodiments, the applied particles are approximately spherical particles created by high pressure water atomization. In some embodiments, the applied particles are irregularly shaped particles created through mechanical crushing.

[0105] In some embodiments, the particles have an average particle size in the range of 5 to 20 μm, hi some embodiments, the applied coating has an average thickness in the range of 10 to 100 μm.

[0106] In some embodiments, the applied particles are stainless steel, such as 300 or 400 series steel, to impart corrosion resistance to steel components. In other embodiments, other corrosion resistant materials, such as aluminum, are used for the coating. In other embodiments, sacrificial metals, such as zinc, are used to provide cathodic protection against corrosion.

[0107] In some embodiments, ceramic particles or other non-metallic materials are incorporated into the metal coating to increase hardness or modify other surface properties.

[0108] Carrier Gas In exemplary embodiments, a high pressure carrier gas is utilized to transport and impart kinetic energy to the coating particles. In some embodiments, the carrier gas is provided by a pressurized gas tank that is periodically filled or replaced. In some embodiments, the carrier gas is provided by a gas compressor. In some embodiments, the pressure of the carrier gas may be between 500 pounds per square inch (e.g., psi) and 1000 psi, or the pressure may be between 600 psi and 900 psi, or the pressure may be between 700 psi and 800 psi, or the pressure may be about 725 psi.

[0109] The carrier gas (e.g., gas) can be preheated with a gas heater integrated into the cold sprayer. The carrier gas can also be heated before being delivered to the cold sprayer. In some embodiments, the temperature of the gas can be between 700°C and 1300°C, or the temperature of the gas can be between 850°C and 1150°C, or the temperature of the gas can be between 900°C and 1100°C, or the temperature of the gas can be about 1000°C.

[0110] In some embodiments, a variety of carrier gases may be used, including nitrogen (N2), helium (He), a mixture of nitrogen (N2) and helium (He), air, and argon (Ar). In some embodiments, a reactive gas such as forming gas (e.g., 5% H2 in N2) may be used. In other embodiments, other carrier gases or gas mixtures are utilized.

[0111] nozzle FIG. 11 shows a schematic of various embodiments of the present disclosure of nozzle designs according to an exemplary embodiment. In an exemplary embodiment, a converging-diverging nozzle design 1100 is utilized to accelerate carrier gas and coating particles to supersonic speeds. A high pressure, high temperature carrier gas is mixed with the coating powder and fed into the nozzle 1110. As the gas and particles enter the nozzle, the gas becomes high pressure, high temperature, and subsonic 1110. The gas is compressed through the converging section 1120 of the nozzle, reducing the pressure and temperature of the gas while simultaneously reaching sonic speed at the throat 1125 of the nozzle. The gas then expands through the diverging section of the nozzle 1130, further reducing the pressure and temperature and increasing the gas velocity beyond sonic speed. The coating particles are carried by the gas through both the converging and diverging sections of the nozzle and are accelerated by the force imparted by the high velocity of the gas. The carrier gas and powder exit the nozzle forming a spray plume. The spray plume is directed onto a substrate where the coating particles collide at high velocity and bond to the surface. In some embodiments, a converging-diverging nozzle design is utilized with multiple such nozzles surrounding the component of interest to achieve a complete coating.

[0112] Exemplary embodiments utilize the adaptation of a cold spray deposition process as a high throughput, low cost method for applying corrosion resistant coatings in a manner that is integrated into existing manufacturing processes for steel and other metals. In some embodiments disclosed herein, multiple stationary converging-diverging spray nozzles are oriented to completely coat the manufactured steel material as it passes through an automated manufacturing line. Additionally, other embodiments disclosed herein utilize multiple movable converging-diverging spray nozzles that move to completely coat the manufactured steel material as it passes through an automated manufacturing line.

[0113] Although steel components have been described, it should be noted that the various embodiments apply to other metals, including aluminum, copper, and / or nickel-based alloys. Additionally, the various embodiments apply to other shapes, including pipes, tubes, beams, and girders. While corrosion protection has been discussed, the various embodiments modify other surface properties, including hardness, roughness, wear resistance, and appearance. Thus, the discussion of steel bars and corrosion is for illustrative purposes and is not intended to apply to all embodiments.

[0114] Some embodiments apply corrosion resistant coatings to existing steel and / or other metal products without significant changes to the manufacturing process. Such coatings impart corrosion resistance to the products, extend their shelf life and operational life, and increase the value of the products to users.

[0115] Various embodiments can be incorporated into existing metal manufacturing processes at any step that allows line-of-sight access to the product. Some embodiments can apply coatings to substrates over the full range of temperatures expected in steel manufacturing processes. The applied coating preferably does not significantly affect the geometry or structural properties of the underlying metal.

[0116] Nozzle Array 12A and 12B show schematic diagrams of various embodiments of the present disclosure of nozzle arrays according to exemplary embodiments. FIG. 12A shows an embodiment 1200 of a rectangular nozzle array 1210 of cold spray nozzles 1220 oriented to coat the exterior of a rectangular steel component 1250 (e.g., a substrate), such as a steel billet material. The coating spray 1230 is deposited on the rectangular steel component 1250 to form an applied coating 1240. The nozzles 1220 in the nozzle array 1210 are configured to cover the entire surface of the rectangular steel component 1250. That is, the spray nozzle array 1210 surrounds the rectangular steel component 1250 in a linear configuration to ensure that there is an unobstructed straight line between each area of ​​the surface of the rectangular steel component 1250 and at least one of the nozzles 1220 in the spray nozzle array 1210.

[0117] 12B illustrates an embodiment 1255 of a circular nozzle array 1260 of cold spray nozzles 1270 oriented to coat the exterior of a circular steel component 1250 (e.g., a substrate), such as a reinforcing bar. The coating spray 1280 is deposited on the circular steel component 1295 to form an applied coating 1290. The nozzles 1270 in the array of nozzles 1260 are configured to cover the entire surface of the circular steel component 1295. That is, the array of spray nozzles 1270 surrounds the circular steel component 1250 in a circular configuration to ensure that there is an unobstructed straight line between each area of ​​the surface of the circular steel component 1295 and at least one of the nozzles 1260 in the array of spray nozzles 1270. In other embodiments, complex arrays of nozzles are used to coat complex shapes, including girders and beams.

[0118] Nozzle Placement In an exemplary embodiment, the nozzles in the nozzle array are oriented to ensure complete coverage of the coated product. In some embodiments, the nozzles are oriented to ensure that the spray track of each nozzle overlaps with adjacent spray tracks and there are no gaps in the coverage. In some embodiments, some of the spray nozzles may be oriented at least partially longitudinally and at least partially radially. This may allow the array of nozzles to cover parts of the component that may not be covered by an array of spray nozzles positioned only in a single plane. That is, at least some of the spray nozzles in the array of spray nozzles may generate a flow of particles at least partially longitudinally and at least partially radially. Also, one or more nozzles may be oriented in a direction that deviates from a radial line projected through the component. The direction of the deviated radial line may be tilted out of the plane formed by the collection of radial lines.

[0119] Figure 13 illustrates various embodiments of the present disclosure of a nozzle array according to an exemplary embodiment. Figure 13 (left) provides an illustrative example of an embodiment of a nozzle array having a flat circumscribed array 1300 with spray nozzles 1310 in a single plane. A substrate (e.g., a metal component) 1320 is coated with a coating 1330.

[0120] 13 (right) provides an illustration of an embodiment of a nozzle array having a flat staggered array 1350 of coating nozzles 1360. In this embodiment, the array 1350 has spray nozzles 1360 in a helical array. A substrate (e.g., a metal component) 1370 is to be coated with a coating 1330.

[0121] In some embodiments, involving coating of products with raised or recessed features, the nozzle is rotated relative to the surface to achieve complete coverage. In one such embodiment, coating steel reinforcing bars requires coating of the ridges on the surface of the reinforcing bars.

[0122] Figure 14 illustrates various embodiments of the present disclosure of a nozzle array according to an exemplary embodiment. Figure 14 (left) illustrates an embodiment in which a nozzle 1310 is configured to spray particles 1330 to cover a ridge 1320 on the surface of a reinforcing bar. In Figure 14 (left), the nozzle 1310 is located on one side of the ridge and is pointed towards the ridge to ensure that the coating 1340 covers the side of the ridge.

[0123] Figure 14 (right) shows an embodiment 1350 in which a nozzle 1360 is configured to cover the ridge 1320 on the other side of the reinforcement bar (relative to Figure 14 (left)). In Figure 14 (right), the nozzle 1360 is located on the other side of the ridge 1320 (relative to Figure 14 (left)) and is pointed towards the ridge and surface to ensure that the coating 1380 covers the side of the ridge as well as the surface.

[0124] 15 shows a schematic of an exemplary embodiment in which rear spray nozzles are oriented to overlap the coating track from a previous nozzle. A first spray nozzle 1510 sprays a first coating spray track 1520 onto a component 1505 moving in a direction 1515 relative to the first spray nozzle 1510. A second spray nozzle 1530 sprays a second coating spray track 1540. The overlapping spray nozzles 1510 and 1540 result in a coating overlap 1550.

[0125] FIG. 16 illustrates a schematic of an exemplary embodiment 1600 in which successive arrays of spray nozzles 1604 are configured to reach a desired coating thickness. In such an embodiment, each array contributes a portion of the coating thickness, with each subsequent array building on the thickness of the previous array. As illustrated diagrammatically in FIG. 16, a first array 1610 sprays a first coating 1620 on a steel substrate 1608 (e.g., a steel component). A second array 1630 sprays a second coating 1640, and a third array 1650 sprays a third coating 1660. In this manner, the applied coating 1606 can achieve the required thickness.

[0126] In some embodiments, the arrays of spray nozzles are identical and interchangeable. In other embodiments, the arrays are positioned and oriented differently to minimize local variations in coating thickness. In some embodiments, multiple arrays are assembled in series to achieve the required coating thickness. In some embodiments, the nozzles are oriented to cover the entire circumference of the bar, including covering any ridges or other geometric features.

[0127] Coating System Integration In exemplary embodiments, the spray coating system can be integrated into conventional metal manufacturing processes at many potential steps where line of sight access is available. In some embodiments, coating is performed near the end of the manufacturing process after the product has been processed into its final shape. In other embodiments, the coating step can occur before or during the rolling step, with the bond of the coated product being maintained throughout the rolling process. In other embodiments, coating can occur before heating. In other embodiments, coating can occur after cutting of the product.

[0128] FIG. 17A illustrates, in schematic form, various embodiments of the integration of a spray system into a manufacturing line, according to an exemplary embodiment. FIG. 17A illustrates, in schematic form, a coating system installed in a steel bar manufacturing process 1700. In this embodiment, the coating system is located after most of the processing steps. Briefly, the manufacturing processes of heating 1710, rolling 1720, and quenching 1730 of the bar are performed before the coating 1740 is applied. In the coating 1740, the coating system applies a stainless steel coating through several stages in a circular array, in this embodiment. After coating 1740, the coated steel bar is cut to length, cooled, and bundled for distribution.

[0129] FIG. 17B shows a schematic of a coating system installed in a steel bar production process 1700. In this embodiment, the coating system is located before most of the processing steps. Briefly, coating 1770 is performed on the steel billet material prior to the steel production steps. In this embodiment, the coating system applies a stainless steel coating through several stages in a circular array. After the stainless steel coating on the steel billet material, the coated steel billet material undergoes processing steps of bar heating 1775, rolling 1780, and quenching 1785. After quenching, the coated steel billet material is cut to length, cooled, and bundled for distribution.

[0130] Other embodiments include integration into manufacturing processes with other processing steps including casting, extrusion, drawing, etc. The coating system can be incorporated before or after such processing steps.

[0131] Some exemplary embodiments consolidate the coating at a stage where the product has a minimal amount of oxide scale to limit contamination of the applied coating. Examples of such locations include immediately after high pressure water quenching, immediately after rolling, drawing or other deformation processes, etc. In other embodiments, additional processing steps are used to remove any oxide scale from the product prior to coating.

[0132] Coating system size and orientation The size of the exemplary embodiment, including the number of nozzles and coating throughput, may vary and will depend on the details of the existing manufacturing process.

[0133] In some embodiments, the minimum coating thickness is determined by the requirements of the application. For example, in some applications, the maximum corrosion rate is known and a certain coating thickness is required to ensure that the component is protected for the entire duration of its useful life. In other applications, there are requirements regarding the mechanical durability of the coating, including abrasion or scratch resistance, that must be met by a coating of a certain thickness. In other embodiments, the minimum coating thickness is determined by the need to completely cover the component. In the aforementioned embodiments, the coating thickness will be at least 2-4 times the average diameter of the coating powder to allow for complete coverage.

[0134] The required coating throughput of an embodiment can be determined by the desired coating thickness, the throughput of the existing manufacturing process, and the surface area of ​​the product to be coated. The required throughput can then determine a minimum number of nozzles based on the maximum coating deposition rate of each nozzle. The coating system can then be sized to meet the minimum number of nozzles and fully cover the surface of the component to be coated, taking into account the coating area of ​​each nozzle.

[0135] Cold spray of large steel billet material Large billets of steel stock (approximately 7 inches by 7 inches by 25 feet) can be coated, rolled, and processed so that the delivered rebar already has the coating. In some embodiments, a process similar to that described above for FIG. 17B can be used to coat the large billets of stock before they are processed into steel bars. By applying a stainless steel coating to the large billets of stock before the heating, rolling, and quenching steps as described for FIG. 17B, the cost of producing the pre-coated rebar can be lower and throughput can be higher than coating the rebar after the heating, rolling, and quenching steps as illustrated in FIG. 17A.

[0136] The surprising result of forming a corrosion resistant ferritic stainless steel matrix coating on a steel component demonstrates that corrosion resistant steel components can be produced using an array of spray nozzles in a cold spray process.

[0137] New steel alloy composition (Fe-Cr-Si-Al-Mo alloy) (3) Atmospheric and aqueous corrosion of steel is a major challenge in designing effective and durable structures. Modifying the composition of steel to inhibit corrosion can reduce maintenance costs and improve performance, as is the case with stainless steels. Corrosion resistance in steel is typically achieved by adding 14-20% chromium by weight, which forms a surface layer of Cr2O3 (chromia) that protects the steel from corrosion. However, this chromia layer is susceptible to attack in a wide range of environments, including a variety of corrosive environments, acidities (pH), and temperatures. In particular, chloride ions (e.g., Cl - ) and fluoride ions (e.g., F - Attack by halides, including Cr, HNO3, Cr, and HNO4, can remove the protective oxide layer and cause aggressive pitting-type corrosion.

[0138] To enable typical corrosion and halide resistance in ferritic steels, an exemplary embodiment uses high concentrations of molybdenum (e.g., Mo) along with passivating oxide formers such as chromium, aluminum, and silicon. Ferritic steels typically have a body-centered cubic (e.g., BCC) structure. These high concentrations of molybdenum typically quickly repassivate areas where the oxide layer has been damaged by halide attack. This results in a corrosion-resistant stainless steel that has much better resistance to halide attack than existing ferritic steels. Additionally, 316 stainless steel contains 2 wt. % Mo to provide corrosion resistance in chloride environments.

[0139] In some embodiments, silicon and aluminum are incorporated as secondary and tertiary oxide formers to allow for additional corrosion resistance in a wider range of environments. The presence of austenitic stabilizing elements such as nickel and manganese is limited to preserve the ferrite phase. Alloys such as Fe-Cr-Si and Fe-Cr-Al utilize the concept of a secondary protective oxide layer.

[0140] In an exemplary embodiment, ferritic stainless steels can be utilized as a corrosion resistant coating on other material compositions, including carbon steels. This outer coating can be applied in a variety of ways, including cold spray, welded overlay, and coextrusion.

[0141] Application of Fe-Cr-Mo-Al-Si alloys to corrosion resistance FIG. 18 shows a schematic embodiment of an Fe-Cr-Mo-Al-Si based stainless steel alloy as a corrosion resistant coating on a steel component. FIG. 18 shows a schematic embodiment of a multi-layer oxide layer showing how the metal atoms in the alloy diffuse into individual oxide layers on the alloy surface. The bottom material in FIG. 18 is a steel component 1810. An Fe-Cr-Mo-Al-Si alloy coating is deposited on the steel component, with aluminum, silicon, and chromium elements diffusing to form a multi-layer coating of metal oxide layers 1870. An aluminum oxide layer 1820 is closest to the steel component 1810. The next layer after the aluminum oxide layer is a silicon dioxide layer 1830. A chromium oxide layer 1840 is on the surface of the multi-layer oxide coating 1870.

[0142] Chloride ion (Cl - ) penetrates the multi-layer oxide coating and progresses to the inside of the steel components, forming pits (e.g., gaps). The oxide layer of the multi-layer oxide coating has the effect of preventing oxidation corrosion by oxygen, but the Cl - However, the molybdenum atoms in stainless steels are less effective at preventing pitting corrosion caused by Cl. - The MoO3 diffuses into the pitted surface caused by the pitting corrosion and forms a MoO3 passivating naive oxide layer 1860 on the corroded surface. The MoO3 passivating layer prevents and / or resists further corrosion by chloride ions.

[0143] FIG. 19 is an Ellingham diagram showing the relative driving forces for oxide formation between the constituent elements in the present invention. An Ellingham diagram is a graph showing the temperature dependence of the stability of a compound. The Ellingham diagram plots the Gibbs free energy change (ΔG) of each oxidation reaction as a function of temperature. This diagram is particularly useful in identifying which metal oxide layer in a multi-layer oxide coating is likely to form the most stable oxide (highest absolute value of ΔG) and determining the stacking order of the oxide layers, since the more stable oxide layers tend to form closer to the steel components.

[0144] As shown in Figure 19, Al2O3 has the largest absolute value of ΔG and is the layer closest to the steel layer. SiO2 has the next largest absolute value of ΔG and is the layer above the Al2O3 layer. Cr2O3 has the smallest absolute value of ΔG and is the layer above the multi-layer oxide coating.

[0145] The selection of chromium, molybdenum, aluminum, and silicon as primary, secondary, and tertiary corrosion-resistant stainless steel alloying metals is based on optimizing the structure and chemical resistance of the alloy. The structure is optimized to form a body-centered cubic (e.g., BCC) ferritic matrix, and the chemical resistance is optimized to resist corrosion of the steel by both oxygen and chlorides.

[0146] FIG. 20 shows the equilibrium phase composition for a range of Cr and Mo contents for iron, chromium, and molybdenum stainless steel alloys. Exemplary material composition elemental ranges can be selected using the following considerations: Iron (Fe) is selected as the primary alloying element for its abundance, affordability, strength, and ductility. Chromium (Cr) is selected as the primary alloying element to achieve overall corrosion resistance of the alloy. This corrosion resistance is achieved by having a minimum of 16 wt% Cr to form a stable protective Cr2O3 layer, while having no more than 20 wt% Cr to limit or prevent the formation of deleterious metallic phases such as sigma and laves phases. Molybdenum (Mo) is included at a minimum of 3 wt% to improve corrosion resistance in concentrated halide media, especially in high chloride aqueous environments, and is limited to no more than 4-8 wt% to inhibit the formation of chi, sigma, and Laves phase intermetallic compounds. Aluminum (Al) may be included to form an additional Al2O3 protective oxide layer and is limited to 4 wt.% to avoid the formation of brittle Fe3Al precipitates. Silicon (Si) may also be included to form an additional SiO2 protective oxide layer, but not to exceed 2 wt.%, to avoid the formation of brittle Cr3Si precipitates. Manganese (Mn) is added in small amounts (0.1-0.5 wt.%) to consume sulfur impurities in the molten iron through the formation of small MnS precipitates. Carbon (C) and nitrogen (N) are limited to 0.1 wt.% to limit the formation of carbide and nitride phases in the material. Sulfur (S) is limited to 0.05 wt.% to avoid the severe embrittlement that sulfur can cause in steels.

[0147] Range of potential compositions

[0148] Various embodiments of the present invention have the following elements within the specified ranges to achieve the microstructure and utilities described below. According to an embodiment of the present invention, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 12 to 25 weight percent chromium (Cr); 2 to 10 weight percent molybdenum (Mo) and the following: 0-10 weight percent aluminum (Al); 0-5 weight percent silicon (Si); 0-5 weight percent nickel (Ni); 0 to 1.0 weight percent manganese (Mn); 0.0-0.1 weight percent carbon (C); 0.0 to 0.1 weight percent nitrogen (N); and At least one of 0.0 to 0.05 weight percent sulfur (S); The remaining iron (Fe) Includes.

[0149] According to an embodiment of the present invention, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 16 to 20 weight percent chromium (Cr); 3 to 6 weight percent molybdenum (Mo) and the following: 0-4 weight percent aluminum (Al); 0-2 weight percent silicon (Si); 0-0.1 weight percent nickel (Ni); 0.1 to 0.5 weight percent manganese (Mn); 0.0-0.1 weight percent carbon (C); 0.0-0.1 weight percent nitrogen (N); At least one of 0.0 to 0.05 weight percent sulfur (S); The remaining iron (Fe) Includes.

[0150] According to an embodiment of the present invention, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 18% by weight of chromium (Cr); 6 weight percent molybdenum (Mo); 4 weight percent aluminum (Al); 2 weight percent silicon (Si); The remaining iron (Fe) Includes.

[0151] According to an embodiment of the present invention, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 18% by weight of chromium (Cr); 3 weight percent molybdenum (Mo); 4 weight percent aluminum (Al); 2 weight percent silicon (Si); The remaining iron (Fe) Includes.

[0152] According to an embodiment of the present invention, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 18% by weight of chromium (Cr); 8 weight percent molybdenum (Mo); 5 weight percent aluminum (Al); The remaining iron (Fe) Includes.

[0153] According to an embodiment of the present invention, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 18% by weight of chromium (Cr); 8 weight percent molybdenum (Mo); 2 weight percent silicon (Si); The remaining iron (Fe) Includes.

[0154] According to an embodiment of the present invention, a corrosion resistant stainless steel alloy composition having a BCC ferritic matrix comprises: 18% by weight of chromium (Cr); 4% by weight of molybdenum (Mo); The remaining iron (Fe) Includes.

[0155] General manufacturing method Formation Step To synthesize the alloy, one skilled in the art can employ the following steps. It should be noted that this method is a substantial simplification of the lengthy process that would normally be used to synthesize the alloy. Thus, it is expected that the process of synthesizing the alloy will have many steps that one skilled in the art would use. Additionally, some of the steps can be performed in a different order than shown, or simultaneously.

[0156] Thus, one skilled in the art can modify this process accordingly. Moreover, as described above and below, the materials and structures described are only one of many different materials and structures that can be used. One skilled in the art can select appropriate materials and structures depending on the application and other constraints. Thus, the discussion of specific materials and structures is not intended to limit all embodiments.

[0157] One process of various embodiments includes the following steps.

[0158] Providing a mixture of raw materials in appropriate weight fractions as described above for the corrosion resistant stainless steel alloy composition having a BCC ferritic matrix. Providing a furnace for melting the metal mixture. Heating the metal mixture in a furnace to a temperature of about 1600° C. to about 2000° C. to form a liquid metal mixture melt. Cooling the liquid metal mixture melt to an intermediate temperature of about 1000° C. to about 1300° C. over a first period of time to initiate the solidification process. quenching the liquid metal mixture melt to a temperature of about 400° C. to about 600° C. for a second period of time, since quenching limits the formation of carbide precipitates. Tempering the metal mixture at a temperature between about 450° C. and about 600° C. for a period between about 10 minutes and about 60 minutes. Cooling the metal mixture in the absence of active heating, the metal mixture comprising a ferritic stainless steel alloy.

[0159] The first period may be from 5 minutes to 100 minutes. The second period may be from 0.5 seconds to 10 seconds.

[0160] Working Example The following examples are intended to further illustrate the present disclosure and its preferred embodiments.

[0161] Example 1: Cost-effective options Grade 304SS coating, coating thickness 20-40μm, cold spray deposition Example 1 shows the most cost-effective embodiment of the present invention, in which 304SS is used as the corrosion-resistant coating layer because of its excellent general corrosion resistance and the low cost of this coating material compared with other suitable corrosion-resistant coating materials.

[0162] Cold spray deposition was chosen as the method to apply the coating to the carbon steel bars due to its relatively low cost and high throughput. The coating thickness is chosen to be 20-40 μm because this thickness range allows confidence that the corrosion resistant coating completely covers the surface of the material while limiting the use of coating material to reduce the overall cost of the coating. Cold spray deposition is preferably performed on finished or near-finished bars near the end of the manufacturing process.

[0163] Example 2. Grade 316SS coating, coating thickness 25-50μm, cold spray deposition Example 2 represents an embodiment of the invention in which substantial chloride corrosion resistance is achieved in addition to general oxidation resistance using a relatively thin coating layer while keeping costs down. In this example, 316SS is used as the corrosion resistant coating layer, and the increased molybdenum content provides substantial corrosion resistance to chloride attack along with traditional stainless steel protection.

[0164] In this example, cold spray deposition was chosen because it can produce coatings of appropriate thickness at low cost with high throughput. A coating thickness of 25-50 μm was chosen to obtain robust corrosion resistance without increasing cost. Cold spray deposition is preferably performed on finished or near-finished bars near the end of the manufacturing process.

[0165] Example 3. Grade 316SS coating, coating thickness 40-80μm, welded overlay Example 3 illustrates an embodiment of the invention that has substantial chloride corrosion resistance while at the same time being more robust against bending, scratching, or other processes that may damage the surface coating. Again, the use of grade 316SS as the corrosion resistant coating layer provides significant resistance to corrosion in chloride environments.

[0166] In this embodiment, a weld overlay is used to deposit the coating material onto the bar. In this embodiment, a coating thickness of 40-80 μm results in a more robust, mechanically sound coating that can more easily withstand deformation of the bar while maintaining corrosion resistance. Therefore, it is desirable to perform the weld overlay process early in the bar manufacturing process. For example, the weld overlay process can be applied to coat large billets of material that have been rolled to the finished dimensions of the bar.

[0167] Example 4. Fe-18Cr-6Mo-4Al-2Si SS, coating thickness 25-50μm, cold spray deposition Example 4 is a highly corrosion-resistant coating material Fe-18Cr-6Mo-4Al-2Si In this embodiment, Mo is used. In addition to chloride attack resistance due to Mo, this alloy offers excellent overall corrosion resistance by employing several elements that form a protective passivating oxide film. This coating material is generally expensive, but the coating thickness of 25 to 50 μm selected in this example allows for a balance between performance and cost.

[0168] In this example, cold spray deposition is chosen because of its ability to produce coatings of suitable thickness at high throughput, and is preferably performed on finished or near-finished bar stock near the end of the manufacturing process.

[0169] Example 5. Fe-18Cr-6Mo-4Al-2Si SS, coating thickness 40-80μm, weld overlay deposition Example 5 is Fe-18Cr-6Mo-4Al-2Si alloy It provides robust bar protection and performance. The relatively thick coating, between 40 and 80 microns, is able to withstand significant deformation, scratching and other damage that can degrade the coating's performance.

[0170] In this embodiment, a weld overlay is used to deposit a protective coating material onto the bar stock, and therefore the weld overlay process is preferably performed early in the bar manufacturing process, with the weld overlay being applied to a large billet of stock that has been rolled to the finished bar dimensions.

[0171] Example 6. Maximum corrosion resistance composition: Fe-18Cr-6Mo-4Al-2Si-0.1C This example shows the optimization of the composition to obtain the highest possible corrosion resistance by maximizing the content of Mo in addition to the protective oxide formers Cr, Al, and Si to further enhance resistance to halide corrosion attack.

[0172] Figure 21 shows the equilibrium phase fraction plot of an exemplary Fe-Cr-Mo-Al-Si composition, indicating secondary phases that should be limited or avoided entirely. The time-temperature-transformation curves of the exemplary Fe-Cr-Mo-Al-Si composition show how the temperature profile can be controlled to limit / avoid the formation of secondary phases.

[0173] FIG. 22 shows the time-temperature-transformation curves of an exemplary Fe—Cr—Mo—Al—Si composition and illustrates how the temperature profile can be controlled to limit / avoid the formation of secondary phases.

[0174] Due to the high Mo content in this composition, carbide formation of the M6C phase is particularly rapid and rapid quenching to 900 K (about 625 °C) followed by more gradual cooling to room temperature is important to limit the overall volume fraction of carbide precipitates. The advantage of the high Mo content is better resistance to chloride corrosion attack.

[0175] Example 7. Balanced polyoxide composition; Fe-18Cr-3Mo-4Al-2Si This example shows a composition with reduced Mo concentration to reduce material cost and reduce the possibility of forming secondary phases, especially carbide and Laves phase precipitates. This composition still has good overall corrosion resistance, but is less resistant to chloride attack than Example 1. However, the reduced Mo content reduces cost and also relaxes some heat treatment requirements.

[0176] FIG. 23 shows the phase composition map of Fe-18Cr-3Mo-4Al-2Si, indicating the presence of deleterious secondary phases, especially Cr3Si, at low temperatures, which are limited in their final microstructure by thermal process control.

[0177] FIG. 24 shows the time-temperature-transformation diagram for Fe-18Cr-3Mo-4Al-2Si, illustrating the kinetics of secondary phase formation in this example.

[0178] Considering the kinetic information presented in Figure 7, it is desirable to rapidly quench the material, lowering the temperature as quickly as possible from 1200 K to 900 K, to minimize the formation of carbide precipitates. After quenching, it is gradually cooled from 900 K to 700 K, and then air cooled from 700 K to room temperature.

[0179] Example 8. Double oxide-chromium and aluminum; Fe-18Cr-8Mo-5Al This example shows a composition protected with chromia and alumina layers without the use of silicon. Molybdenum is included for halide / pitting protection.

[0180] Example 8 achieves corrosion resistance through the inclusion of Cr, and the high Mo content further enhances halide corrosion resistance. The presence of Al allows for the formation of a secondary protective alumina passivation layer that further enhances the corrosion resistance of this composition. The removal of Si from this composition would be expected to reduce the oxidation resistance of this composition somewhat compared to the other exemplary compositions, but the formation of Cr3Si is also no longer thermodynamically favored, which is beneficial to the microstructure of the material.

[0181] FIG. 25 shows an equilibrium phase fraction plot of an exemplary Fe—Cr—Mo—Al composition, indicating secondary phases that should be limited or avoided entirely.

[0182] FIG. 26 is a time-temperature-transformation diagram for Fe-18Cr-8Mo-5Al showing the kinetics of secondary phase formation in this example.

[0183] In Example 8, the primary detrimental phase of concern is the Laves phase, which begins to become thermodynamically favored below 1000 K and kinetically favored (significant nucleation and growth begins) near 900 K. During the synthesis of this material, it is desirable to rapidly quench and cool the material from 950 K to 750 K in order to limit the formation of Laves phase precipitates which tend to embrittle the material. After quenching to 750 K, it can be gradually cooled to room temperature.

[0184] Example 9. Double oxide; Fe-18Cr-8Mo-2Si Example 9 achieves corrosion resistance through the inclusion of Cr, and also significantly improves halide corrosion resistance due to the high Mo content. The presence of Si allows for the formation of a secondary protective silica (SiO2) passivation layer, further enhancing the corrosion resistance of this composition. The removal of Al from this composition would reduce the oxidation resistance of this composition somewhat compared to the other exemplary compositions, but would be expected to reduce the likelihood of nitride and carbide precipitation. Particularly notable phases that could potentially form are the chi and sigma phases, which can embrittle the material if the volume fraction of these precipitates becomes too large. To limit the volume fraction of these phases, it is desirable to quench the material and cool it rapidly from 1200K to 900K, then gradually cool it down to room temperature.

[0185] FIG. 27 shows the equilibrium phase fraction plot for an Fe—Cr—Mo—Si alloy, indicating secondary phases that should be limited or avoided entirely.

[0186] FIG. 28 shows the time-temperature-transformation diagram for Fe-18Cr-8Mo-2Si, illustrating the kinetics of formation of the secondary phase in this example.

[0187] Example 10. Single oxide-Fe-18Cr-4Mo Example 10 is a simple example in which the only alloying additions to Fe are Cr and Mo. The high Cr concentration provides good overall corrosion resistance, and the addition of 4 wt. % Mo significantly improves corrosion resistance to chloride attack. The Cr and Mo concentrations are low enough that the formation of sigma phase is not thermodynamically favorable, but chi phase can form during the material synthesis process, so it is desirable to perform certain processing steps to avoid the formation of chi phase and the resulting embrittlement of the material.

[0188] FIG. 29 shows the equilibrium phase fraction plot for an Fe—Cr—Mo alloy, indicating secondary phases that should be limited or avoided entirely.

[0189] FIG. 30 shows the time-temperature-transformation diagram for Fe-18Cr-4Mo, illustrating the kinetics of secondary phase formation in this example.

[0190] To minimize the formation of chi phase in the synthesis of Example 10, a quench is required to rapidly reduce the temperature of the material from 1100K to 850K, and then the material is held at 800K for 10 minutes to quickly anneal to remove any defects and chi phase that may have formed during the solidification process. After this brief annealing step, the material can be air-cooled from 800K to room temperature.

[0191] Example 11. Further examples of compositions having various amounts of alloying elements Embodiments include compositions having various amounts of alloying elements, including compositions having other elements not listed here. Further examples of compositions within the scope of the present invention include: [ka]

[0192] The embodiments of the invention described above are intended to be merely illustrative and numerous variations and modifications will be apparent to those skilled in the art. Such variations and modifications are intended to be within the scope of the invention as defined by any of the appended claims.

Claims

1. A steel component comprising: a carbon steel reinforcing bar; and an outer coating metallurgically bonded to the carbon steel reinforcing bar and containing stainless steel, wherein the outer coating forms a corrosion-resistant coating on the carbon steel reinforcing bar, and the average thickness of the outer layer is 10 μm to 500 μm. The steel component.

2. The steel component according to claim 1, wherein there is an interdiffusion region between the carbon steel reinforcing bar and the outer coating, the composition of the interdiffusion region changes continuously from the composition of the coating to the composition of the carbon steel reinforcing bar, and the width of the interdiffusion region is 10 nm to 10 μm.

3. The steel component according to claim 1, wherein the stainless steel coating comprises at least one of cold spray coating, thermal spray coating, plasma spray coating, laser deposition coating, twin wire arc spray coating, or arc welding overlay coating.

4. The steel component according to claim 1, wherein the stainless steel coating comprises at least one of 316 stainless steel, 2205 stainless steel, or 304 stainless steel.

5. The steel component according to claim 4, wherein at least one of 316 stainless steel, 2205 stainless steel, and 304 stainless steel is mixed with metal carbide.

6. The steel component according to claim 5, wherein the metal carbide comprises at least one of chromium carbide, molybdenum carbide, silicon carbide, or manganese carbide.

7. The stainless steel coating comprises: 12 to 25 weight percent chromium (Cr); 2 to 10 weight percent molybdenum (Mo); and the following: 0 to 10 weight percent aluminum (Al); 0 to 5 weight percent silicon (Si); 0 to 5 weight percent nickel (Ni); 0 to 1.0 weight percent manganese (Mn); 0.0 to 0.1 weight percent carbon (C); 0.0 to 0.1 weight percent nitrogen (N); or 0.0 to 0.05 weight percent sulfur (S), at least one or more of them; and the balance being iron (Fe). The steel component according to claim 1.

8. The stainless steel coating comprises: 16 to 20 weight percent chromium (Cr); 3 to 6 weight percent molybdenum (Mo); and the following: 0 to 4 weight percent aluminum (Al); 0 to 2 weight percent silicon (Si); 0 to 0.1 weight percent nickel (Ni); 0.1 to 0.5 weight percent manganese (Mn); 0.0 to 0.1 weight percent carbon (C); 0.0 to 0.1 weight percent nitrogen (N); or at least one of 0.0 to 0.05 weight percent sulfur (S), the balance iron (Fe), and A steel component according to claim 1.

9. The stainless steel coating, Can the reinforcing bar be bent up to 180 degrees around an object with a diameter 3.5 times the diameter of the reinforcing bar without visible cracks occurring in the stainless steel coating, or The stainless steel coating has a sufficient ductility to have an inherent ductility that allows at least 5% elongation before breaking. A steel component according to claim 1.

10. A steel component, comprising A carbon steel reinforcing bar, and An outer layer coating metallurgically bonded to the carbon steel reinforcing bar and containing stainless steel, Including, The outer layer coating forms a corrosion-resistant coating on the carbon steel reinforcing bar, The stainless steel coating contains a ferrite / austenite two-phase fine structure, and The average thickness of the outer layer is 10 μm to 300 μm. A steel component.

11. The stainless steel coating passivates the carbon steel reinforcing bar against corrosion. A steel component according to claim 10.

12. The stainless steel coating is a cold spray coating. A steel component according to claim 10.

13. The stainless steel coating is a weld overlay coating or a twin wire arc spray coating. A steel component according to claim 10.

14. The average particle size of the stainless steel coating is 500 nm to 10 μm. A steel component according to claim 10.

15. The stainless steel coating, 16 to 20 weight percent chromium (Cr), 3 to 6 weight percent molybdenum (Mo), and the following: 0 to 4 weight percent aluminum (Al); 0 to 2 weight percent silicon (Si); 0 to 0.1 weight percent nickel (Ni); 0.1 to 0.5 weight percent manganese (Mn); 0.0 to 0.1 weight percent carbon (C); 0.0 to 0.1 weight percent nitrogen (N); or At least one or more of sulfur (S) in an amount of 0.0 to 0.05 weight percent, and the balance of iron (Fe), and The steel component according to claim 10, comprising.

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