Corrosion-resistant high-temperature red-hardness flux-cored wire for new manufacturing and surfacing repair of foot roller and zero segment roller of steel slab continuous casting machine and preparation method and application thereof

Abstract

This invention relates to the field of welding materials technology, specifically to a corrosion-resistant, high-temperature red-hard flux-cored welding wire for the fabrication and weld overlay repair of foot rolls and zero-segment rolls in continuous casting machines for steelmaking slabs, along with its preparation method and applications. This welding wire utilizes a Cr-Ni structure to construct a corrosion-resistant and toughened matrix, a Co-Mo-W composite reinforcement to enhance high-temperature red hardness and resistance to softening, Cu to further improve corrosion resistance, and Ti-Nb-V to form a dispersed reinforcing phase with C and N, significantly improving the thermal fatigue resistance, spalling resistance, and wear resistance of the deposited metal. In particular, by appropriately increasing the Nb content while controlling the C content, a balance is achieved between high-temperature hardness, corrosion resistance, and crack resistance, making it especially suitable for the fabrication and weld overlay repair of foot rolls and zero-segment rolls in continuous casting machines for steelmaking slabs.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, specifically to a corrosion-resistant high-temperature red-hard flux-cored welding wire for the manufacture and overlay repair of foot rolls and zero-section rolls of continuous casting machines for steelmaking slabs, as well as its preparation method and application. Background Technology

[0002] The foot rolls and zero-section rolls of a slab continuous casting machine are located below the crystallizer and in the high-heat load zone at the start of the secondary cooling process. They are subjected to the combined effects of high-temperature radiation, periodic thermal shock, moisture corrosion, iron oxide scale erosion, and alternating mechanical loads over a long period of time. They are among the key components of the continuous casting machine most prone to early damage and failure. Their service failures typically manifest as high-temperature oxidation of the roll surface, surface corrosion, thermal fatigue cracks, localized spalling, wear loss of roundness, and decreased dimensional stability after high-temperature softening. In severe cases, they can affect the surface quality of the cast slab, equipment operating rate, and the service life of the roll system.

[0003] Currently, the working layer of the foot rolls and zero-section rolls of continuous casting machines is often obtained by newly manufactured surfacing or repaired surfacing. Existing surfacing materials have two main shortcomings: one type emphasizes room temperature hardness and wear resistance, which is strengthened by increasing carbon content or adding more hard phase-forming elements, but this often leads to increased sensitivity to welding cracks, decreased toughness, and insufficient resistance to thermal fatigue, making them prone to cracking and spalling under high-temperature thermal cycling conditions; the other type emphasizes corrosion resistance and weldability, which, although having better crack resistance, lacks high-temperature red hardness and has poor hardness retention at high temperatures, making the roll surface prone to softening and wear during long-term service.

[0004] Furthermore, the actual service environment of foot rolls and zero-segment rolls is not a single wear condition, but a coupled condition of high-temperature oxidation, water vapor corrosion, thermal fatigue, and erosion wear. Therefore, simply increasing hardness or corrosion resistance alone is insufficient to meet the requirements. Especially in high-temperature areas, if the high-temperature red hardness of the weld overlay is insufficient, the roll surface will soften significantly, thereby accelerating wear and oxide scale erosion; if the carbon content is too high or the reinforcing phase is too coarse, the risk of thermal cracking and spalling will increase significantly; if the reinforcing elements are not properly matched, the welding process window will be narrowed, affecting the forming quality and interlayer bonding quality during new manufacturing and repair processes.

[0005] While some existing continuous casting roll surfacing materials incorporate elements such as Cr, Ni, and Mo to balance corrosion resistance and high-temperature performance, the balance between high-temperature red hardness, thermal fatigue resistance, and weld crack resistance remains unsatisfactory. Especially for high-heat-load areas like foot rolls and zero-segment rolls, a flux-cored welding wire that can maintain high hardness and structural stability at high temperatures while also considering corrosion resistance, thermal fatigue resistance, and process adaptability is still needed.

[0006] Therefore, it is necessary to develop a special flux-cored welding wire for the working conditions of the foot roll and zero-segment roll of the steelmaking slab continuous casting machine. Under the premise of ensuring welding processability, a weld overlay layer with corrosion resistance, high-temperature red hardness, thermal fatigue resistance and spalling resistance can be obtained to meet the actual needs of new manufacturing and failure repair of foot roll and zero-segment roll. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention aims to provide a corrosion-resistant high-temperature red-hard flux-cored wire for the manufacture and repair of foot rolls and zero-section rolls of continuous casting machines for steelmaking slabs, as well as its preparation method and application. Through the synergistic design of the Cr-Ni-Co-Cu-Mo-W matrix reinforcement system and the Ti-Nb-VCN dispersion reinforcement system, the weld overlay layer exhibits excellent corrosion resistance, thermal fatigue resistance, high-temperature red hardness, and high-temperature softening resistance under harsh working conditions of high-temperature water vapor corrosion, thermal fatigue, and wear, and also has good adaptability to welding processes.

[0008] To achieve the above objectives, this invention provides a corrosion-resistant high-temperature red-hard flux-cored wire for the manufacture and welding repair of foot rolls and zero-section rolls in continuous casting machines for steelmaking slabs. The deposited metal formed by the flux-cored wire comprises, by mass percentage: Cr 17.0%–23.0%, Ni 17.0%–23.0%, Co 0.8%–3.5%, Cu 0.8%–3.5%, Mo 4.5%–7.0%, Ti 0.15%–0.60%, Nb 0.15%–0.40%, V 0.08%–0.30%, W 0.6%–1.8%, C 0.05%–0.10%, Si 0.20%–0.90%, Mn 0.30%–1.50%, N 0.02%–0.15%, with the balance being Fe and impurities.

[0009] As a further improvement to this technical solution, the deposited metal comprises, by mass percentage: Cr 19.0%–21.5%, Ni 19.0%–21.5%, Co 1.8%–2.3%, Cu 1.2%–2.5%, Mo 5.3%–6.2%, Ti 0.25%–0.45%, Nb 0.22%–0.30%, V 0.12%–0.22%, W 0.9%–1.3%, C 0.065%–0.085%, Si 0.35%–0.70%, Mn 0.50%–1.00%, N 0.04%–0.10%, with the balance being Fe and impurities.

[0010] The key to this flux-cored welding wire lies in achieving excellent high-temperature red hardness by introducing specific amounts of Co, Mo, and W into the Cr-Ni high-alloy matrix. Simultaneously, the introduction of Cu not only enhances corrosion resistance but also works synergistically with Mo and Cr. Furthermore, by precisely controlling C at a relatively low level of 0.05%–0.10% and moderately increasing the Nb content to 0.15%–0.40%, combined with Ti, V, and N, a large number of fine Nb(C,N), Ti(C,N), and V(C,N) composite carbonitride dispersions are formed, rather than coarse primary carbides. This design strategy significantly improves the material's high-temperature hardness retention and resistance to thermal fatigue crack propagation while ensuring weldability and corrosion resistance, achieving a balance among various properties. This is the core breakthrough of this invention compared to the traditional "high carbon, high hardness" or "low carbon, pure corrosion resistance" design concepts for surfacing materials.

[0011] As a further improvement to this technical solution, the flux-cored welding wire includes a metal outer sheath and a flux core filled inside the metal outer sheath. The flux core contains chromium source, nickel source, cobalt source, copper source, molybdenum source, titanium source, niobium source, vanadium source, tungsten source, carbon source, silicon source, manganese source, nitride source and iron powder that provide corresponding elements.

[0012] As a further improvement to this technical solution, the chromium source is one or both of metallic chromium powder and ferrochrome powder; the nickel source is nickel powder; the cobalt source is cobalt powder; the copper source is copper powder; the molybdenum source is molybdenum powder or ferromolybdenum powder; the titanium source is ferrotitanium powder; the niobium source is ferroniobium powder; the vanadium source is ferrovanadium powder; the tungsten source is tungsten powder or ferrotungsten powder; the carbon source is graphite powder; the silicon source is ferrosilicon powder; the manganese source is ferromanganese powder; and the nitride source is one or more of chromium nitride, manganese nitride, and iron nitride.

[0013] As a further improvement to this technical solution, the flux-cored welding wire has a filler ratio of 32% to 40% and a wire diameter of 2.0 mm to 2.8 mm. This filler ratio ensures accurate transition of the high alloy composition and good drawability of the welding wire.

[0014] This invention provides a method for preparing corrosion-resistant high-temperature red-hard flux-cored welding wire for the manufacture and weld repair of foot rolls and zero-segment rolls in continuous casting machines for steelmaking slabs. The method for preparing the aforementioned corrosion-resistant high-temperature red-hard flux-cored welding wire for the manufacture and weld repair of foot rolls and zero-segment rolls in continuous casting machines for steelmaking slabs includes the following steps:

[0015] S1. Weigh the core material according to the designed composition;

[0016] S2. Mix the weighed core material evenly.

[0017] S3. The flux-cored welding wire is prepared by wrapping the uniformly mixed flux-cored raw material with steel strip, forming it in a closed shape, rolling it and drawing it.

[0018] S4. Take in and package the obtained flux-cored welding wire.

[0019] This invention provides a method for the fabrication and weld repair of foot rolls and zero-segment rolls in a continuous casting machine for steelmaking slabs. The method utilizes the aforementioned corrosion-resistant, high-temperature red-hard flux-cored welding wire for the fabrication and weld repair of foot rolls and zero-segment rolls in a continuous casting machine for steelmaking slabs, and includes the following steps:

[0020] N1. Perform mechanical processing and surface cleaning on the surface of the roller substrate to be processed or repaired;

[0021] N2. Preheat the substrate;

[0022] N3. Use the flux-cored welding wire to perform single-layer or multi-layer multi-pass welding;

[0023] N4. Control the interlayer temperature and perform slow cooling treatment after the welding is completed;

[0024] N5. Machining the weld overlay layer to obtain the working layer of the required size.

[0025] As a further improvement to this technical solution, the flux-cored welding wire is suitable for self-shielded welding or gas-shielded welding, and the shielding gas used in gas-shielded welding is Ar, Or Ar and The mixture of gases; wherein the preheating temperature is 120℃~150℃, the interpass temperature is 150℃~220℃, the single-layer weld thickness is 2.5mm~5.0mm, and the total weld thickness is 3.5mm~15mm.

[0026] This invention provides an application of corrosion-resistant high-temperature red-hard flux-cored welding wire for the new manufacturing and weld overlay repair of foot rolls and zero-segment rolls in continuous casting machines for steelmaking slabs. Specifically, it relates to the application of the aforementioned corrosion-resistant high-temperature red-hard flux-cored welding wire for the new manufacturing and weld overlay repair of foot rolls and zero-segment rolls in continuous casting machines for steelmaking slabs, in both the manufacturing of new foot rolls and zero-segment rolls and the weld overlay repair of failed roll surfaces in continuous casting machines for steelmaking slabs.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. The corrosion-resistant high-temperature red-hard flux-cored wire for the manufacture and repair of foot rolls and zero-section rolls of continuous casting machines for steelmaking slabs, along with its preparation method and application, achieves a high-temperature hardness retention rate of over 75% at 600℃ through composite solid solution strengthening of Co-Mo-W and dispersion strengthening of Ti-Nb-V(C,N), which is far superior to the comparative materials with no Co or low Nb and high C, effectively solving the problem of high-temperature softening.

[0029] 2. This invention relates to a corrosion-resistant, high-temperature red-hard flux-cored wire for the manufacture and repair of foot rolls and zero-section rolls in continuous casting machines for steelmaking slabs, along with its preparation method and application. The high-Cr-Ni matrix is ​​alloyed with Cu, resulting in a weld overlay layer containing... It can form a stable and dense passivation film in oxidizing, high-temperature, and water-vapor environments, and its corrosion weight loss rate is reduced by more than 50% compared to high-carbon materials.

[0030] 3. The corrosion-resistant high-temperature red-hard flux-cored wire for the manufacture and repair of foot rolls and zero-section rolls of continuous casting machines for steelmaking slabs, its preparation method and application, the low-carbon design avoids the precipitation of coarse and brittle carbides, the fine dispersed strengthening phase pins dislocations and stabilizes the structure, which significantly extends the thermal fatigue crack initiation life and reduces the crack propagation rate.

[0031] 4. The corrosion-resistant high-temperature red-hard flux-cored welding wire used for the new manufacturing and overlay repair of foot rolls and zero-section rolls of continuous casting machines for steelmaking slabs, as well as its preparation method and application, adopts low carbon content and reasonable alloy ratio, which reduces the crack sensitivity of the overlay layer, has a wide process window, is suitable for multi-layer and multi-pass continuous overlay welding, has good interlayer bonding, and has no risk of peeling. Attached Figure Description

[0032] The accompanying drawings described herein are for illustrative purposes only. The shapes and proportions of the components in the drawings are merely schematic and intended to aid in understanding the invention. They are not intended to specifically limit the shapes and proportions of the components of the invention.

[0033] Figure 1 This is a flowchart illustrating the preparation process of the flux-cored welding wire of the present invention.

[0034] Figure 2 This is a flowchart of the method for manufacturing and repairing the foot roll and zero section roll of the continuous casting machine for steelmaking slabs using welding according to the present invention.

[0035] Figure 3 This is a bar chart showing the hardness test results of the flux-cored welding wire of the present invention at room temperature and high temperature;

[0036] Figure 4 This is a bar chart comparing the number of thermal fatigue first crack cycles of the flux-cored welding wire of the present invention;

[0037] Figure 5 This is a bar chart comparing the crack density of the flux-cored welding wire of the present invention after 500 cycles. Detailed Implementation

[0038] The specific embodiments described herein are for illustrative purposes only. Under the guidance of this invention, any possible variations of the invention by those skilled in the art should be considered within its scope. The directional terms used herein are based on the orientations shown in the accompanying drawings and are for ease of description and simplification; therefore, they should not be construed as limitations on the invention. Furthermore, in the description of this invention, "a number" means two or more, unless otherwise explicitly specified.

[0039] Please see Figures 1-2 As shown, the present invention provides a corrosion-resistant high-temperature red-hard flux-cored welding wire for the new manufacturing and weld overlay repair of foot rolls and zero-segment rolls of steelmaking slab continuous casting machines. It is used in the new manufacturing of foot rolls and zero-segment rolls of steelmaking slab continuous casting machines and in the weld overlay repair of failed roll surfaces of foot rolls and zero-segment rolls of steelmaking slab continuous casting machines.

[0040] The deposited metal formed by flux-cored welding wire comprises, by mass percentage: Cr 17.0%–23.0%, Ni 17.0%–23.0%, Co 0.8%–3.5%, Cu 0.8%–3.5%, Mo 4.5%–7.0%, Ti 0.15%–0.60%, Nb 0.15%–0.40%, V 0.08%–0.30%, W 0.6%–1.8%, C 0.05%–0.10%, Si 0.20%–0.90%, Mn 0.30%–1.50%, N 0.02%–0.15%, with the balance being Fe and impurities.

[0041] Furthermore, the deposited metal, by mass percentage, comprises: Cr 19.0%–21.5%, Ni 19.0%–21.5%, Co 1.8%–2.3%, Cu 1.2%–2.5%, Mo 5.3%–6.2%, Ti 0.25%–0.45%, Nb 0.22%–0.30%, V 0.12%–0.22%, W 0.9%–1.3%, C 0.065%–0.085%, Si 0.35%–0.70%, Mn 0.50%–1.00%, N 0.04%–0.10%, with the balance being Fe and impurities.

[0042] Explanation of the action mechanism of each alloying element

[0043] 1. Cr: 17.0%~23.0%

[0044] Cr is a key element for improving the corrosion resistance, oxidation resistance, and resistance to high-temperature iron oxide scale erosion of the weld overlay. It can promote the formation of a dense protective film during high-temperature service, enhancing the roller surface's resistance to oxidation and media erosion. If the Cr content is too low, the corrosion resistance will be insufficient; if it is too high, it may increase the tendency for brittle phase precipitation under high Mo and W conditions.

[0045] 2. Ni: 17.0%~23.0%

[0046] Ni is beneficial for forming and stabilizing a high-alloy matrix with good toughness, improving the resistance to hot cracking, spalling, and thermal fatigue of the weld overlay, while also improving the stability of the high-temperature microstructure. If Ni is too low, the weld toughness and resistance to hot cracking will be insufficient; if Ni is too high, it will increase costs and weaken the overall balancing effect of strengthening elements.

[0047] 3. Co: 0.8%~3.5%

[0048] Co can improve the high-temperature red hardness and thermal strength of the weld overlay, inhibit high-temperature softening, and form a synergistic strengthening effect with Mo and W, enabling the material to maintain good mechanical stability under high-temperature alternating conditions.

[0049] 4. Cu: 0.8%~3.5%

[0050] Cu can improve corrosion resistance and enhance high-temperature strength and surface stability through precipitation strengthening. A moderate Cu content is beneficial for obtaining good overall performance; however, excessive Cu content may increase the tendency for hot brittleness and welding instability.

[0051] 5. Mo: 4.5%~7.0%

[0052] Mo can improve the high-temperature strength, pitting corrosion resistance, crevice corrosion resistance and tempering stability of the weld overlay, and is one of the core elements for improving high-temperature service performance.

[0053] 6. Ti: 0.15%~0.60%

[0054] Ti combines with C and N to form fine, dispersed strengthening phases, which refine the microstructure, inhibit grain coarsening, and stabilize the microstructure. However, excessive Ti content can easily lead to the formation of coarse inclusions and coarsening strengthening phases, which are detrimental to toughness and processability.

[0055] 7. Nb: 0.15%~0.40%

[0056] Nb forms dispersed reinforcing phases such as NbC and Nb(C,N) with C and N, which helps improve the high-temperature hardness retention, high-temperature softening resistance, and thermal fatigue resistance of the weld overlay. Compared with traditional designs with lower Nb content, this invention appropriately increases the Nb content to enhance high-temperature red hardness and microstructure stability.

[0057] 8.V: 0.08%~0.30%

[0058] V can form fine VC and V(C,N) reinforcing phases with C and N, and synergistically improve the secondary strengthening effect and high-temperature hardness stability with Ti and Nb.

[0059] 9.W: 0.6%~1.8%

[0060] W helps improve thermal strength, thermal stability, and red hardness, and enhances the material's resistance to softening at high temperatures.

[0061] 10.C: 0.05%~0.10%

[0062] Carbon (C) is an important element for the formation of Ti, Nb, and V carbides or carbonitrides. If the C content is too low, the strengthening phase will not form sufficiently, resulting in insufficient red hardness; if the C content is too high, it will increase the tendency for coarse carbide precipitation, reduce corrosion resistance, and increase susceptibility to weld cracking. Therefore, this invention controls the C content within a medium to low range to balance corrosion resistance, weldability, and high-temperature strengthening.

[0063] 11.Si: 0.20%~0.90%, Mn: 0.30%~1.50%

[0064] Si and Mn mainly play a role in deoxidation, purifying the molten pool, improving the forming and increasing the uniformity of the microstructure, which helps to ensure the density of the weld overlay and the stability of the process.

[0065] 12. N: 0.02%~0.15%

[0066] Ni can enhance the stability of the matrix and form carbonitride dispersion strengthening phases with Ti, Nb, and V, further improving corrosion resistance and high-temperature strength.

[0067] Furthermore, the flux-cored wire includes a metal sheath and a flux core filled inside the metal sheath. The flux core contains sources of chromium, nickel, cobalt, copper, molybdenum, titanium, niobium, vanadium, tungsten, carbon, silicon, manganese, nitride, and iron powder, which provide the corresponding elements.

[0068] Specifically, the chromium source is one or both of metallic chromium powder and ferrochrome powder; the nickel source is nickel powder; the cobalt source is cobalt powder; the copper source is copper powder; the molybdenum source is molybdenum powder or ferromolybdenum powder; the titanium source is ferrotitanium powder; the niobium source is ferrotitanium powder; the vanadium source is ferrotitanium powder; the tungsten source is tungsten powder or ferrotungsten powder; the carbon source is graphite powder; the silicon source is ferrosilicon powder; the manganese source is ferromanganese powder; and the nitride source is one or more of chromium nitride, manganese nitride, and iron nitride.

[0069] Furthermore, the flux-cored welding wire has a filler content of 32%–40% and a wire diameter of 2.0 mm–2.8 mm. This filler content ensures accurate transition of the high alloy composition and good drawability of the welding wire.

[0070] The present invention discloses a method for preparing corrosion-resistant high-temperature red-hard flux-cored welding wire for the manufacture and weld repair of foot rolls and zero-segment rolls in continuous casting machines for steelmaking slabs. The method comprises the following steps:

[0071] S1. Weigh the core material according to the designed composition;

[0072] S2. Mix the weighed core material evenly.

[0073] S3. The flux-cored welding wire is produced by wrapping the uniformly mixed flux-cored raw material with steel strip, and then forming, rolling and drawing it in a closed manner.

[0074] S4. Take in and package the obtained flux-cored welding wire.

[0075] The method of the present invention for the fabrication and weld repair of foot rolls and zero-segment rolls of steelmaking slab continuous casting machines, using the aforementioned corrosion-resistant high-temperature red-hard flux-cored welding wire for the fabrication and weld repair of foot rolls and zero-segment rolls of steelmaking slab continuous casting machines, includes the following steps:

[0076] N1. Perform mechanical processing and surface cleaning on the surface of the roller substrate to be processed or repaired;

[0077] N2. Preheat the substrate;

[0078] N3. Use flux-cored welding wire for single-layer or multi-layer multi-pass welding;

[0079] N4. Control the interlayer temperature and perform slow cooling treatment after the welding is completed;

[0080] N5. Machining the weld overlay layer to obtain the working layer of the required size.

[0081] Furthermore, flux-cored welding wire is suitable for self-shielded welding or gas-shielded welding. The shielding gas used in gas-shielded welding is Ar, Or Ar and The mixture of gases; wherein the preheating temperature is 120℃~150℃, the interpass temperature is 150℃~220℃, the single-layer weld thickness is 2.5mm~5.0mm, and the total weld thickness is 3.5mm~15mm.

[0082] Preparation method examples

[0083] The preparation method in this embodiment is as follows: Based on the target composition of the deposited metal shown in Table 1 below, the amount of each raw material added to the core is calculated using the transition coefficient and weighed. The weighed ferrochrome powder, nickel powder, cobalt powder, copper powder, molybdenum powder, ferrotitanium powder, ferroniobium powder, ferrovanadium powder, tungsten powder, graphite powder, ferrosilicon powder, ferromanganese powder, chromium nitride powder, and iron powder are added to a V-type mixer and mixed for 40 minutes to ensure uniformity. The uniformly mixed powder is filled into a U-shaped groove pressed from a low-carbon steel strip (such as H08A) with a width of 14mm and a thickness of 0.8mm, controlling the filling rate to 36%. The steel strip is wrapped into a cylindrical shape by multiple passes of closed-end forming rollers, then continuously drawn to reduce the diameter to 2.4mm, and finally wound and sealed. The entire process must be kept clean to prevent the powder from absorbing moisture.

[0084] Usage Method Examples

[0085] Taking the repair of a damaged zero-segment roll of a slab continuous casting machine as an example:

[0086] Pretreatment: The failed roll is machined to completely remove the surface fatigue crack layer, oxide scale, and corrosion pits, exposing the metallic luster. Oil stains on the roll surface are cleaned with acetone or alcohol.

[0087] Preheating: The roller body is fed into a heating furnace or heated by flame to be preheated evenly to 120±10℃.

[0088] Overlay welding: An automatic welding machine with an oscillating function was used, and the ø2.4mm flux-cored welding wire prepared in Example 4 was installed. An argon-rich mixed gas shielding system was used, with the gas flow rate controlled at 20 L / min. Welding process parameters: welding current 280 A, arc voltage 28 V, welding speed 35 cm / min. Multi-layer, multi-pass spiral welding was performed, with each layer thickness controlled to approximately 3.5 mm.

[0089] Layer temperature control: Use an infrared thermometer to monitor the interlayer temperature during the welding process. After each layer or stacking is completed, wait until the temperature drops to 150℃~200℃ before proceeding to the next layer or stacking to prevent overheating.

[0090] Slow cooling: After the welding is completed, immediately wrap the roller body with aluminum silicate fiber blanket to allow it to cool slowly to room temperature and eliminate welding stress.

[0091] Finishing: After cooling, the roller surface is semi-finished and finely ground to achieve the dimensional tolerances and surface finish required by the drawings, thus obtaining the final working layer.

[0092] Examples and Comparative Examples

[0093] The technical solution and effects of the present invention will be further illustrated below through specific embodiments. Examples 1-4 are flux-cored welding wires prepared according to the alloy composition formulation of the present invention, wherein Example 4 is the preferred embodiment. Comparative Examples 1 and 2 are comparative schemes set up to verify the effect of specific elements, and their preparation and usage methods are exactly the same as those of Example 4 to eliminate process interference.

[0094] Example 1

[0095] A corrosion-resistant, high-temperature red-hard flux-cored welding wire for the manufacture and welding repair of foot rolls and zero-section rolls in continuous casting machines for steelmaking slabs, wherein the deposited metal comprises, by mass percentage:

[0096] Cr 20.0%, Ni 20.0%, Co 2.0%, Cu 1.8%, Mo 5.8%, Ti 0.32%, Nb 0.26%, V 0.16%, W 1.1%, C 0.075%, Si 0.48%, Mn 0.72%, N 0.06%, with the balance being Fe and unavoidable impurities.

[0097] Low-carbon steel strip is used as the outer sheath material, and ferrochrome powder, nickel powder, cobalt powder, copper powder, molybdenum powder, ferrotitanium powder, ferroniobium powder, ferrovanadium powder, tungsten powder, graphite powder, ferrosilicon powder, ferromanganese powder, chromium nitride powder and iron powder are used as the core raw materials. The process involves mixing, forming and covering with steel strip, rolling and drawing to obtain a 2.4mm diameter flux-cored welding wire.

[0098] During the overlay welding process, the fatigue damage layer on the surface of the foot roller is first removed by turning and cleaned. The temperature is then preheated to 100℃~120℃, and multiple layers and multiple passes of overlay welding are performed using Ar+CO2 mixed protective gas. The interlayer temperature is controlled at 150℃~220℃. After overlay welding, the roller is slowly cooled and machined to the working dimensions.

[0099] Example 2

[0100] A corrosion-resistant, high-temperature red-hard flux-cored welding wire for the manufacture and welding repair of foot rolls and zero-section rolls in continuous casting machines for steelmaking slabs, wherein the deposited metal comprises, by mass percentage:

[0101] Cr 19.5%, Ni 20.5%, Co 2.2%, Cu 2.0%, Mo 6.0%, Ti 0.28%, Nb 0.24%, V 0.18%, W 1.0%, C 0.068%, Si 0.42%, Mn 0.65%, N 0.08%, with the balance being Fe and unavoidable impurities.

[0102] Using 2.4mm diameter flux-cored welding wire, automatic overlay welding is performed on the outer circular surface of the zero-segment roller substrate. The preheating temperature is 120℃~150℃, the single layer thickness is 3.0mm~5mm, and the total overlay thickness is 6mm~10mm. After welding, the material is slowly cooled to room temperature before semi-finishing and finishing.

[0103] Example 3

[0104] A corrosion-resistant, high-temperature red-hard flux-cored welding wire for the manufacture and welding repair of foot rolls and zero-section rolls in continuous casting machines for steelmaking slabs, wherein the deposited metal comprises, by mass percentage:

[0105] Cr 21.0%, Ni 19.2%, Co 1.8%, Cu 1.5%, Mo 5.5%, Ti 0.40%, Nb 0.30%, V 0.20%, W 1.2%, C 0.085%, Si 0.60%, Mn 0.90%, N 0.05%, with the balance being Fe and unavoidable impurities.

[0106] Multi-layer welding using a self-protected welding method is suitable for reinforcing and repairing the working layer of foot rollers under high heat load conditions.

[0107] Example 4 (Best Example)

[0108] A corrosion-resistant, high-temperature red-hard flux-cored welding wire for the manufacture and welding repair of foot rolls and zero-section rolls in continuous casting machines for steelmaking slabs, wherein the deposited metal comprises, by mass percentage:

[0109] Cr 20.0%, Ni 20.0%, Co 2.0%, Cu 2.0%, Mo 5.8%, Ti 0.30%, Nb 0.26%, V 0.18%, W 1.1%, C 0.075%, Si 0.50%, Mn 0.70%, N 0.06%, with the balance being Fe and unavoidable impurities.

[0110] This component exhibits a good overall balance between corrosion resistance, high-temperature red hardness, thermal fatigue resistance, and weldability, making it suitable as the preferred embodiment of this invention.

[0111] Comparative Example 1: Comparative Example without Co

[0112] To illustrate the effect of Co on improving high-temperature red hardness, thermal fatigue resistance and high-temperature softening resistance, a composition system basically the same as in Example 4 was used, except that Co was removed and the other elements were kept at similar levels.

[0113] The weld metal formed in Comparative Example 1 comprises, by mass percentage:

[0114] Cr 20.0%, Ni 20.0%, Co 0%, Cu 2.0%, Mo 5.8%, Ti 0.30%, Nb 0.26%, V 0.18%, W 1.1%, C 0.075%, Si 0.50%, Mn 0.70%, N 0.06%, with the balance being Fe and unavoidable impurities.

[0115] The preparation method, welding wire specifications, and welding process conditions are the same as in Example 4. This comparative example is used to compare with Example 4 the high-temperature hardness retention rate, thermal fatigue crack sensitivity, high-temperature softening degree of the weld overlay, and service stability of the roller surface.

[0116] Comparative Example 2: A comparative example with low Nb and relatively high C

[0117] To illustrate the effect of moderately increasing Nb and controlling C within the range of 0.06% to 0.09% on improving overall performance, a set of comparative examples representing the traditional approach to improving hardness was used, namely, appropriately reducing Nb and increasing C content, while keeping other major elements at similar levels.

[0118] The weld metal formed in Comparative Example 2 comprises, by mass percentage:

[0119] Cr 20.0%, Ni 20.0%, Co 2.0%, Cu 2.0%, Mo 5.8%, Ti 0.30%, Nb 0.12%, V 0.18%, W 1.1%, C 0.12%, Si 0.50%, Mn 0.70%, N 0.06%, with the balance being Fe and unavoidable impurities.

[0120] The preparation method, welding wire specifications, and welding process conditions are the same as in Example 4. This comparative example is used to compare with Example 4 the welding crack sensitivity, corrosion resistance, thermal fatigue crack propagation trend, uniformity of weld overlay structure, and high-temperature red hardness stability.

[0121] Table 1 - Chemical composition of welded metal in each embodiment and comparative example (mass percentage, %)

[0122] serial number Cr Ni Co Cu Mo Ti Nb V W C Si Mn N Fe and impurities Example 1 20.0 20.0 2.0 1.8 5.8 0.32 0.26 0.16 1.1 0.075 0.48 0.72 0.06 margin Example 2 19.5 20.5 2.2 2.0 6.0 0.28 0.24 0.18 1.0 0.068 0.42 0.65 0.08 margin Example 3 21.0 19.2 1.8 1.5 5.5 0.40 0.30 0.20 1.2 0.085 0.60 0.90 0.05 margin Example 4 20.0 20.0 2.0 2.0 5.8 0.30 0.26 0.18 1.1 0.075 0.50 0.70 0.06 margin Comparative Example 1 20.0 20.0 0 2.0 5.8 0.30 0.26 0.18 1.1 0.075 0.50 0.70 0.06 margin Comparative Example 2 20.0 20.0 2.0 2.0 5.8 0.30 0.12 0.18 1.1 0.12 0.50 0.70 0.06 margin

[0123] Performance Comparison Explanation

[0124] To verify the rationality of the component design of this invention, Example 4 was used as a representative example, and Comparative Example 1 and Comparative Example 2 were set up for comparison. Comparative Example 1 omitted the Co element to examine the effect of Co on high-temperature red hardness and high-temperature softening resistance; Comparative Example 2 adopted a design with lower Nb and higher C to examine the effect of moderately increasing Nb and controlling the medium-low C range on weld crack resistance, corrosion resistance and thermal fatigue performance.

[0125] Under the same welding wire specifications, preheating conditions, interpass temperature, and welding method, the weld overlays of Example 4, Comparative Example 1, and Comparative Example 2 were tested for room temperature hardness, high temperature hardness retention, thermal fatigue crack grade, corrosion weight loss, wear amount, and metallographic structure. The results show that Example 4 is superior to Comparative Example 1 in terms of high temperature hardness retention, thermal fatigue crack control, resistance to high temperature softening, and overall service stability; and superior to Comparative Example 2 in terms of weld crack sensitivity, microstructure uniformity, corrosion resistance, and resistance to spalling. This demonstrates that the composition design of this invention, which employs Co strengthening, moderately increases Nb, and controls low to medium C content, has significant advantages.

[0126] I. Performance Testing and Data

[0127] To accurately evaluate the performance of the flux-cored welding wire of this invention, a uniform welding process was used to prepare weld overlay samples. The diameter of the welding wire in all embodiments and comparative examples was 2.4 mm. Mixed gas shielded welding was performed with a preheating temperature of 120℃ and an interpass temperature controlled between 160℃ and 200℃. The welding current was 280A, the voltage was 28V, and the welding speed was 35cm / min. The effective thickness of the weld overlay was 8mm. All performance tests were conducted according to relevant national standards.

[0128] Table 2 - Standardized Welding Process Parameters

[0129] Parameters Values / Range welding wire diameter 2.4mm Welding current 280±10A Welding voltage 28±1V Welding speed 35±2cm / min Protective gas 80%Ar + 20%CO2 Gas flow rate 20L / min Preheating temperature 120℃ Interlayer temperature 160℃～200℃

[0130] 1. Hardness and High-Temperature Red Hardness Test

[0131] Rockwell hardness (HRC) and Vickers microhardness (HV0.5) were tested at room temperature according to GB / T230.1 and GB / T4340.1. To simulate the high service temperatures of the foot roller and zero-segment roller, the samples were held at 500℃ and 600℃ for 1 hour, respectively, and then the high-temperature Vickers hardness test was performed rapidly in the hot state. The high-temperature hardness retention rate at 600℃ (600℃ hardness / room temperature hardness × 100%) was calculated to measure red hardness. The results are shown in Table 3.

[0132] Table 3 - Hardness Test Results at Room Temperature and High Temperature

[0133] serial number Room temperature hardness HRC Microhardness at room temperature: HV0.5 500℃ hardness 600℃ hardness High-temperature hardness retention rate / % Example 1 36.5 372 308 290 78.0 Example 2 35.8 365 301 283 77.5 Example 3 37.2 380 315 295 77.6 Example 4 (Best) 36.2 370 308 293 79.2 Comparative Example 1 30.1 310 245 210 67.7 Comparative Example 2 38.5 395 320 275 69.6

[0134] like Figure 3 As shown in the figure, the Vickers hardness (HV0.5) of each embodiment and the comparative example is compared at room temperature, 500℃ and 600℃.

[0135] Data analysis: Comparative Example 1, lacking Co, exhibited the lowest hardness at room temperature and lowest red hardness at high temperature, showing severe softening. Comparative Example 2, while possessing high hardness, had a much lower hardness retention rate at 600℃ compared to Example 4, as its hardness primarily contributed by a larger number of coarse carbides, resulting in rapid attenuation of the strengthening effect at high temperatures. Example 4 achieved the optimal balance between hardness and red hardness.

[0136] 2. Thermal fatigue and crack resistance test

[0137] The wedge-shaped specimen thermal fatigue test method was used. The specimens were heated to 600℃ in a furnace, held at that temperature for 5 minutes, and then rapidly immersed in 20℃ circulating water for quenching; this constituted one cycle. The number of cycles in which the first crack exceeding 0.5 mm in length appeared on the specimen surface was recorded (first crack life). After 500 cycles, the surface was subjected to penetrant testing, and the crack density and grade were statistically analyzed to evaluate the thermal fatigue resistance and spalling resistance. The results are shown in Table 4.

[0138] Table 4 - Results of thermal fatigue and crack susceptibility tests (after 500 cycles)

[0139] serial number First-break cycle number Crack density (cracks / cm²) Maximum crack length (mm) Penetration test results Main features Example 1 385 0.8 1.5 No signs of peeling A few microcracks Example 2 410 0.5 1.2 No signs of peeling A few microcracks Example 3 370 0.9 1.8 No signs of peeling A few microcracks Example 4 (Best) 420 0.4 1.0 No signs of peeling Very few microcracks Comparative Example 1 450 0.6 1.3 Slight oxidation, no peeling Predominantly in a soft state, crack propagation is slow. Comparative Example 2 180 3.5 6.2 There are peeling pits Numerous network cracks, embrittlement of the microstructure

[0140] like Figure 4 As shown in the figure, this graph compares the number of cycles required for each embodiment and the comparative example to produce the first crack (length greater than 0.5 mm) in a thermal fatigue test. A higher value indicates better thermal fatigue resistance. Figure 5 As shown in the figure, the crack density (cracks / cm²) on the surface of the sample after 500 thermal fatigue cycles is compared. The lower the value, the better the crack resistance.

[0141] Data analysis: Comparative Example 2, due to its high C and low Nb content, generates a large amount of continuous brittle carbides, leading to rapid initiation and propagation of thermal fatigue cracks and subsequent spalling. This is the most fatal failure mode for foot rolls and zero-segment rolls. Example 4, through dispersion strengthening, exhibits high microstructure toughness and excellent resistance to thermal fatigue. Comparative Example 1, due to its low hardness and good toughness, has acceptable crack resistance but is not resistant to wear and softening.

[0142] 3. Corrosion and High-Temperature Oxidation Tests

[0143] High-temperature oxidation test: According to GB / T13303, the sample is placed in a muffle furnace at 600℃ and kept at that temperature for 200h. The mass change before and after oxidation is measured and the weight gain per unit area is calculated.

[0144] Intergranular corrosion test: According to GB / T4334 Method E (sulfuric acid-copper sulfate method), a 16-hour boiling test is carried out, and after bending 180°, observe whether there are intergranular corrosion cracks.

[0145] Immersion corrosion test: Simulating the secondary cooling water environment of continuous casting, a solution containing... The sample was immersed in an acidic corrosive solution with pH=4.5 at 60℃ for 240 h, and the corrosion weight loss rate was measured. The results are shown in Table 5.

[0146] Table 5 - Results of Corrosion and High-Temperature Oxidation Tests

[0147] serial number Weight gain due to oxidation at 600℃ for 200 hours (mg / cm²) Intergranular corrosion test Immersion corrosion weight loss rate (g / (m²·h)) Example 1 0.45 No cracks 0.082 Example 2 0.42 No cracks 0.078 Example 3 0.48 No cracks 0.085 Example 4 (Best) 0.40 No cracks 0.075 Comparative Example 1 0.58 No cracks 0.098 Comparative Example 2 0.95 There are tiny cracks 0.210

[0148] Data analysis: The high carbon content in Comparative Example 2 led to the precipitation of a large amount of chromium carbides at the grain boundaries, resulting in chromium depletion at the grain boundaries and causing severe intergranular corrosion and accelerated general corrosion. Example 4, etc., maintained a low carbon content and was supplemented with Cu and N elements, exhibiting superior corrosion resistance across the board.

[0149] 4. Wear and Tissue Observation Results

[0150] A pin-disc high-temperature wear testing machine was used, with sintered alumina balls as the wear material. The test temperature was 400℃, the load was 50N, the sliding speed was 0.5m / s, and the stroke was 1000m. The volumetric wear was measured. Simultaneously, scanning electron microscopy (SEM) was used to observe the microstructure of the weld overlay cross-section, analyzing the morphology of the strengthening phase and interlayer bonding. The results are shown in Table 6.

[0151] Table 6 - Wear and Tissue Observation Results

[0152] serial number Volumetric wear at 400℃ (mm³) Microstructure characteristics Enhanced phase morphology Example 1 2.85 Austenite + Dispersion Strengthening Phase Particles with a size of 0.5-2µm, uniformly distributed. Example 2 2.78 Austenite + Dispersion Strengthening Phase Particles with a size of 0.5-2µm, uniformly distributed. Example 3 2.92 Austenite + Dispersion Strengthening Phase Particles with a size of 0.5-2µm, uniformly distributed. Example 4 (Best) 2.65 Austenite + Dispersion Strengthening Phase Particles with a size of 0.5-2µm, extremely uniformly distributed. Comparative Example 1 6.50 austenitic matrix Almost no dispersed phase, with obvious wear marks and plastic deformation. Comparative Example 2 3.10 austenite + coarse carbides Carbides ranging in size from 5 to 20 µm are unevenly distributed and locally aggregated.

[0153] Data analysis: Comparative Example 1, lacking Co and with few reinforcing phases, experienced severe softening at high temperatures, resulting in the greatest wear, manifesting as adhesive wear and plastic rheology. Comparative Example 2, while containing a large amount of carbides, had coarse and brittle particles that easily detached during wear, exacerbating wear and causing significant damage to the abrasive material. In Example 4, the fine, dispersed, and hard composite carbonitrides were firmly anchored in the matrix, exhibiting excellent resistance to high-temperature wear.

[0154] II. Conclusion

[0155] The above systematic comparative tests clearly demonstrate that this invention, through innovative alloy design, particularly the technical routes of "adding Co element," "composite microalloying with appropriate amounts of multiple elements (Nb, Ti, V) in medium and low carbon," and "introducing Cu and N for synergistic corrosion resistance," solves the core technical challenge of simultaneously achieving high-temperature red hardness, thermal fatigue resistance, and corrosion resistance in the weld overlay layer of the foot roll and zero-segment roll. Example 4, as the optimal solution, exhibits nearly 80% high-temperature hardness retention at 600℃, extremely high thermal fatigue first-crack life, extremely low corrosion rate, and excellent high-temperature wear resistance. Its comprehensive performance far exceeds that of the comparative examples, fully meeting and even exceeding the demands of the harsh operating conditions of slab continuous casting machines, indicating broad prospects for industrialization.

[0156] It should be noted that the above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A corrosion-resistant, high-temperature red-hard flux-cored welding wire for the manufacture and welding repair of foot rolls and zero-section rolls in continuous casting machines for steelmaking slabs, characterized in that: The deposited metal formed by flux-cored welding wire comprises, by mass percentage: Cr 17.0%–23.0%, Ni 17.0%–23.0%, Co 0.8%–3.5%, Cu 0.8%–3.5%, Mo 4.5%–7.0%, Ti 0.15%–0.60%, Nb 0.15%–0.40%, V 0.08%–0.30%, W 0.6%–1.8%, C 0.05%–0.10%, Si 0.20%–0.90%, Mn 0.30%–1.50%, N 0.02%–0.15%, with the balance being Fe and impurities.

2. The corrosion-resistant high-temperature red-hard flux-cored welding wire for the manufacture and weld repair of foot rolls and zero-segment rolls of continuous casting machines for steelmaking slabs, as described in claim 1, is characterized in that... The deposited metal comprises, by mass percentage: Cr 18.0%–22.0%, Ni 18.0%–22.0%, Co 1.5%–2.5%, Cu 1.0%–3.0%, Mo 5.0%–6.5%, Ti 0.20%–0.50%, Nb 0.20%–0.32%, V 0.10%–0.25%, W 0.8%–1.5%, C 0.06%–0.09%, Si 0.30%–0.80%, Mn 0.40%–1.20%, N 0.03%–0.12%, with the balance being Fe and impurities.

3. The corrosion-resistant high-temperature red-hard flux-cored welding wire for the manufacture and weld repair of foot rolls and zero-section rolls of continuous casting machines for steelmaking slabs, as described in claim 2, is characterized in that... The deposited metal comprises, by mass percentage: Cr 19.0%–21.5%, Ni 19.0%–21.5%, Co 1.8%–2.3%, Cu 1.2%–2.5%, Mo 5.3%–6.2%, Ti 0.25%–0.45%, Nb 0.22%–0.30%, V 0.12%–0.22%, W 0.9%–1.3%, C 0.065%–0.085%, Si 0.35%–0.70%, Mn 0.50%–1.00%, N 0.04%–0.10%, with the balance being Fe and impurities.

4. The corrosion-resistant high-temperature red-hard flux-cored welding wire for the manufacture and weld repair of foot rolls and zero-section rolls of continuous casting machines for steelmaking slabs, as described in claim 3, is characterized in that... The flux-cored welding wire includes a metal sheath and a flux core filled inside the metal sheath. The flux core contains chromium, nickel, cobalt, copper, molybdenum, titanium, niobium, vanadium, tungsten, carbon, silicon, manganese, nitride, and iron powder, which provide the corresponding elements.

5. The corrosion-resistant high-temperature red-hard flux-cored welding wire for the manufacture and weld repair of foot rolls and zero-section rolls of continuous casting machines for steelmaking slabs, as described in claim 4, is characterized in that... The chromium source is one or both of metallic chromium powder and ferrochrome powder; the nickel source is nickel powder; the cobalt source is cobalt powder; the copper source is copper powder; the molybdenum source is molybdenum powder or ferromolybdenum powder; the titanium source is ferrotitanium powder; the niobium source is ferrotitanium powder; the vanadium source is ferrotitanium powder; the tungsten source is tungsten powder or ferrotungsten powder; the carbon source is graphite powder; the silicon source is ferrosilicon powder; the manganese source is ferromanganese powder; and the nitride source is one or more of chromium nitride, manganese nitride, and iron nitride.

6. The corrosion-resistant high-temperature red-hard flux-cored welding wire for the manufacture and weld overlay repair of foot rolls and zero-section rolls of continuous casting machines for steelmaking slabs, as described in claim 5, is characterized in that... The flux-cored welding wire has a filler ratio of 32% to 40% and a wire diameter of 2.0 mm to 2.8 mm.

7. A method for preparing corrosion-resistant high-temperature red-hard flux-cored welding wire for the manufacture and weld repair of foot rolls and zero-segment rolls in continuous casting machines for steelmaking slabs, used to prepare the corrosion-resistant high-temperature red-hard flux-cored welding wire for the manufacture and weld repair of foot rolls and zero-segment rolls in continuous casting machines for steelmaking slabs as described in claim 6, characterized in that, Includes the following steps: S1. Weigh the core material according to the designed composition; S2. Mix the weighed core material evenly; S3. The flux-cored welding wire is prepared by wrapping the uniformly mixed flux-cored raw material with steel strip, forming it in a closed shape, rolling it and drawing it. S4. Take in and package the obtained flux-cored welding wire.

8. A method for the fabrication and weld overlay repair of foot rolls and zero-segment rolls in a continuous casting machine for steelmaking slabs, comprising using the corrosion-resistant high-temperature red-hard flux-cored welding wire as described in claim 6 for the fabrication and weld overlay repair of foot rolls and zero-segment rolls in a continuous casting machine for steelmaking slabs, characterized in that, Includes the following steps: N1. Perform mechanical processing and surface cleaning on the surface of the roller substrate to be processed or repaired; N2. Preheat the substrate; N3. Use the aforementioned flux-cored welding wire for single-layer or multi-layer multi-pass welding; N4. Control the interlayer temperature and perform slow cooling treatment after the welding is completed; N5. Machining the weld overlay layer to obtain the working layer of the required size.

9. The method for manufacturing new foot rolls and zero-section rolls for continuous casting machines of steelmaking slabs and the method for welding repair according to claim 8, characterized in that, The flux-cored welding wire is suitable for self-shielded welding or gas-shielded welding. The shielding gas used in gas-shielded welding is Ar. Or Ar and The mixture of gases; wherein the preheating temperature is 120℃~150℃, the interpass temperature is 150℃~220℃, the single-layer weld thickness is 2.5mm~5.0mm, and the total weld thickness is 3.5mm~15mm.

10. The application of a corrosion-resistant high-temperature red-hard flux-cored wire for the manufacture and weld repair of foot rolls and zero-segment rolls in a continuous casting machine for steelmaking slabs, as described in claim 6, characterized in that: It is used in the new manufacturing of foot rolls and zero-segment rolls for continuous casting machines of steel slabs, and in the repair of failed roll surfaces by welding on foot rolls and zero-segment rolls for continuous casting machines of steel slabs.

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