Wire raw material and preparation method for surface gradient coating of continuous casting roll

Abstract

The present invention discloses a wire raw material and a preparation method for a surface gradient coating of a continuous casting roll. The mass fractions of the wire for the bonding layer are: component A 55% - 65%, component B 15% - 20%, WC 5% - 10%, MgO 1.5% - 3.0%, Y2O3 0.1% - 0.5%; the mass fractions of the wire for the transition layer are: component A 35% - 55%, component B 25% - 30%, WC 10% - 15%, MgO 3.0% - 4.0%, Y2O3 0.5% - 1.0%; the mass fractions of the wire for the hard surface layer are: component A 15% - 30%, component B 30% - 43%, WC 15% - 20%, MgO 4.0% - 5.0%, Y2O3 1.0% - 1.5%. The coating prepared on the surface of the continuous casting roll by the present invention presents a multi-layer gradient structure, and has excellent wear resistance and resistance to thermal fatigue and cold fatigue; the process operation is simple, the production efficiency is high, and the practicability is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of continuous casting roll surface treatment, and relates to a wire raw material and a preparation method for a surface gradient coating of a continuous casting roll based on submerged arc welding repair technology. Background Art

[0002] The secondary cooling support guide rolls and straightening rolls of a continuous casting machine are collectively referred to as continuous casting rolls. As the core components of continuous casting equipment, continuous casting rolls undertake the functions of bearing, driving the billet and the movable mold. Their quality, strength and service life have a great impact on the operation rate of continuous casting equipment. Continuous casting rolls need to bear heavy loads, thermal stresses, mechanical alternating loads, high-temperature rapid cooling and heating, etc. under the service state. Therefore, it is required that the roll surface should have appropriate hardness, strong wear resistance, thermal fatigue resistance, good thermal conductivity, large cross-sectional shrinkage rate and good acid and alkali corrosion resistance, and the roll core should have good toughness.

[0003] The main failure forms of continuous casting rolls are wear and cracks: when the diameter of the continuous casting roll is worn by 4 mm or cracks with the risk of roll breakage appear on the roll surface, the continuous casting roll is taken off the machine and scrapped. From the investigation of production plants and literature data, since the residual value of scrapped continuous casting rolls is relatively high, if the repair technology is not adopted after scrapping, the annual consumption value of rolls for a single stand is more than several million yuan. Therefore, the repair work of continuous casting rolls has been taken seriously by each plant.

[0004] At present, the commonly used material for continuous casting rolls at home and abroad is 42CrMo steel, and the repair material is stainless steel. For example: Patent document CN105479038A discloses a surfacing weld layer for a continuous casting roll made of a ferritic stainless steel alloy. The surfacing weld layer includes a bottom layer and a surface layer stacked on the continuous casting roll. The bottom layer includes 0.04 - 0.08 parts of C, 1.0 - 1.5 parts of Mn, 0.4 - 0.8 parts of Si, 16 - 22 parts of Cr, and the balance of Fe. The surface layer includes 0.04 - 0.08 parts of C, 1.3 - 1.8 parts of Mn, 0.4 - 0.8 parts of Si, 10 - 15 parts of Cr, 3.5 - 5 parts of Ni, 0.5 - 1 part of Mo, and the balance of Fe. However, the service life of the continuous casting roll repaired with stainless steel is still relatively short. Patent document CN105965174A discloses a surfacing material for the bottom surface of a continuous casting roll, which contains the following components by weight percentage: C 0.03 - 0.1%; P ≤ 0.025%; S ≤ 0.03%; Si 0.3 - 0.5%; Mn 1 - 1.5%; Cr 16 - 20%; Ba 1 - 3%; Mn 0.5 - 1.2%; Ni 1.2 - 1.8%; W 2 - 3%; V 1 - 2%; Nb 7 - 10%; Pt 0.1 - 0.3%; Zr 0.05 - 0.2%; TiO2 0.1 - 0.5%; CaF2 0.6 - 1.2%; the balance is Fe. However, the material disclosed in this patent can only be used for the repair of carbon steel parts or the bottom layer or transition layer of other surfacing materials, and cannot be used as the hard surface layer. Patent document CN113894465A discloses a submerged arc self-shielded surfacing flux-cored wire for continuous casting roll surfacing, which adopts molybdenum, niobium, and copper composite precipitation strengthening technology. The chemical composition of the weld metal deposited by the wire is: C 0.02% - 0.08%, Mn 0.5% - 1.50%, Si 0.2% - 0.8%, Cr 14.50% - 16.50%, Ni 3.0% - 5.5%, Mo 0.3% - 0.8%, Cu 2.5% - 5.0%, Nb 0.10% - 0.50%, N 0.05% - 0.12%, and the balance is Fe. Patent document CN103921015A discloses a submerged arc welding flux for repairing continuous casting rolls and its preparation method. The characteristics are that the flux includes the following components by weight percentage: MgO 34 - 43%, SiO2 9 - 21%, Al2O3 12 - 22%, CaF2 7 - 15%, CaO 1 - 16%, TiO2 6 - 14%, MnO 7 - 11%. However, the above documents do not involve the surfacing layer and the surfacing process design; moreover, the physical property differences between the above repair materials and the base material are relatively large, and there are still differences in thermal properties. High residual stresses will be generated at the interfaces of each component during high-temperature rapid cooling and heating, which will further lead to internal cracking or spalling of the material.

[0005] There is also a literature [Sun Dale, Li Xiaobing, etc. Development of Surfacing Materials and Processes for Long-Life Continuous Casting Rolls. Journal of Northeastern University (Natural Science Edition). 29(5) 2008, 693 - 696.] which studies that on the basis of 1Cr13NiMo surfacing materials, functional alloying elements Nb, V and Re with a mass fraction not exceeding 2% are added to develop new surfacing welding strips and matching sintered fluxes. The structure, strength and thermal fatigue properties of the surfacing deposited metal are significantly better than imported welding materials; however, with the market putting forward higher requirements for the wear resistance and thermal cracking resistance of continuous casting rolls, its mechanical properties still cannot meet the on-site use requirements. Therefore, it is necessary to design new repair materials, coating structures and repair processes to further improve the wear resistance, thermal cracking resistance and corrosion resistance of the continuous casting roll surface. This is of great significance for reducing production costs, improving economic benefits and realizing green manufacturing. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a surface gradient coating of a continuous casting roll based on the submerged arc automatic welding technology, so as to overcome the problems of insufficient composition, structure, process and mechanical properties and cracking between layers existing in the prior art, ensure the comprehensive mechanical properties of the surfacing layer, improve the structure of the surfacing layer, and at the same time be beneficial to reducing the residual stress of the surfacing layer and preventing surfacing process defects, etc. It can be used to directly manufacture a brand-new surface gradient coating of a continuous casting roll or repair a failed continuous casting roll.

[0007] The present invention is realized through the following technical solutions:

[0008] A wire raw material for the surface gradient coating of a continuous casting roll of the present invention is characterized by comprising a metal powder A component, a metal powder B component and a metal oxide powder C component:

[0009] The mass fraction components of the A component are: carbon C: ≤0.15%, silicon Si: ≤1.00%, manganese Mn: ≤1.00%, sulfur S: ≤0.035%, phosphorus P: ≤0.030%, chromium Cr: 11.00% - 14.00%, nickel Ni: 3.50% - 5.50%, molybdenum Mo: 0.30% - 0.60%, vanadium V: 0.50% - 1.50%, and the balance is iron Fe;

[0010] The mass fraction components of the B component are: carbon C: 0.08% - 0.12%, silicon Si: 0.60% - 1.00%, sulfur S: ≤0.035%, phosphorus P: ≤0.030%, manganese Mn: 2.00% - 5.00%, molybdenum Mo: 3.00% - 6.00%, vanadium V: 2.50% - 4.50%, and the balance is iron Fe;

[0011] The mass fraction components of Component C are as follows: tungsten carbide WC: 5.00% - 20.00%; magnesium oxide MgO: 1.50% - 5.00%; yttrium oxide Y2O3: 0.10% - 1.50%.

[0012] Among them, the particle sizes of the said Component A and Component B are respectively 30 - 50 μm; the particle sizes of the tungsten carbide WC, magnesium oxide MgO and yttrium oxide Y2O3 are all 20 - 30 μm.

[0013] To further improve the wear resistance and thermal cracking resistance of the surface coating of the continuous casting roll, the present invention is based on the powder of 1Cr13Ni4Mo2V (i.e., Component A), and adds Component B containing Mn, Mo, V, as well as WC powder, MgO powder and rare earth oxide Y2O3 powder; among them, the WC powder is the main hard particle, the MgO powder is the second-phase toughening particle, and Y2O3 is the grain growth inhibitor.

[0014] However, the research of the present invention shows that in the surface repair technology of the continuous casting roll with 42CrMo as the substrate, if the above high-hardness coating is directly coated on the substrate, due to the large difference in physical properties between the substrate and the coating, when the continuous casting roll is in long-term service, it is still inevitable to cause high residual stress to accumulate at the interfaces of each component, and finally lead to internal cracking or peeling of the coating.

[0015] To overcome this problem, the welding wire raw material of a surface gradient coating of a continuous casting roll described in the present invention is characterized in that the welding wire used to make the 3-layer coating with a gradient change in raw material composition:

[0016] The first layer is the backing welding wire, which has a good combination with the continuous casting roll substrate. Therefore, the first layer coating contains the following raw materials by mass fraction: Component A 55% - 65%, Component B 15% - 20%, and Component B can increase the wear resistance and thermal cracking resistance of the coating; WC 5% - 10%, MgO 1.5% - 3.0%, Y2O3 0.1% - 0.5%, and Component C can increase the wear resistance of the coating.

[0017] The second layer is the transition layer welding wire, which contains the following raw materials by mass fraction: Component A 35% - 55% and Component B 25% - 30% together as the bonding phase, coating the hard particles WC 10% - 15%, while MgO 3.0% - 4.0% and Y2O3 0.5% - 1.0% are respectively used as the second-phase toughening particles and grain inhibitors, playing the role of dispersion strengthening, grain refinement and increasing the wear resistance of the substrate; in addition, since there are also alloy carbides in the continuous casting roll substrate, the main carbides are MC, M 23 C6 and M6C (where M represents alloying elements such as W, Mo, V, etc.), which precipitate in the micro-molten pool of submerged arc welding, M 23C6 precipitates at grain boundaries and between dendrites during slow cooling. The fine and dispersed carbides have good strengthening effects. Therefore, when the fine carbides (mainly M 23 C6) are distributed at grain boundaries, they can prevent grain boundary slip and improve the creep strength of the matrix. Research shows that the microstructure of the substrate alloy of the continuous casting roll is the dispersion-strengthened phase of (CoCrW)6C-type carbides, and its content is about 2-~4 wt%.

[0018] The third layer is the hardfacing wire electrode, which directly contacts the continuous casting billet during service and is the most critical part of the entire coating. It contains the following raw materials by mass fraction: 15%~30% of component A, 30%~43% of component B, 15%~20% of WC coated with hard particles, 4.0%~5.0% of MgO, and 1.0%~1.5% of Y2O3, and its various mechanical property indexes reach the best values. The research results of the present invention show that when the content of component B with high wear resistance and high hot crack resistance increases to 30%~43%, the repaired coating has the best hardness, toughness, wear resistance, high corrosion resistance and cost performance.

[0019] Cr element: Cr can not only act as an alloy binder phase, bonding to WC, but also solid-solve with Ni element to strengthen the matrix, improve the strength, toughness, corrosion resistance and high-temperature resistance of the matrix. Research shows that as the Cr content in the coating increases, the content of the eutectic structure of Cr and C elements also increases, and the morphology of the eutectic structure changes from honeycomb-like to lamellar, and the matrix will have more stable mechanical properties. Therefore, Cr element can effectively hinder the coarsening of the second phase composed of WC, VC, MgO, Y2O3, etc., thereby improving the thermal stability of the coating at high temperatures. When the Cr content is insufficient, it cannot meet the corrosion resistance requirements of the hardfacing layer of the continuous casting roll; but when the Cr content is too high, too much Cr will make the coating hardness too high, prone to brittle spalling and microcracks.

[0020] Si element: Si is an indispensable reducing agent and deoxidizing element in the submerged arc welding process. Si can dissolve into austenite to improve the yield strength and elastic limit of the matrix, improve the oxidation resistance of the matrix, and reduce the occurrence of hot cracks after the continuous casting roll is used. Experiments show that an appropriate amount of Si can improve the wear resistance of the matrix. The increase in the Si content can inhibit dendrite growth, reduce intermetallic compounds, play a role in dispersing carbides, and make the mechanical properties of the matrix more stable. However, when the Si content is excessive, it will reduce the hardenability of the matrix.

[0021] Mn element: The present invention focuses on reducing production costs and selects inexpensive Mn in the raw material components to reduce rare and precious metal Ni. The test results show that the Mn element can not only dissolve in the matrix but also exist in the form of carbides, improving the strength of the matrix and reducing the risk of roll breakage during the use of continuous casting rolls. However, when the Mn content is too high, it will significantly reduce the starting temperature (Ms) of martensite transformation, increase the content of retained austenite in the submerged arc welding repair coating of continuous casting rolls, and increase the risk of roll breakage.

[0022] Mo element: As a strong carbide-forming element, Mo can improve the stability of MC-type carbides and the tempering stability of the repair layer, inhibiting the generation of thermal cracks during the use of stretch-reducing rolls; in addition, about 20% of Mo enters the M7C3-type carbides, which can effectively improve the hardness, wear resistance, and service life of the surface coating of continuous casting rolls.

[0023] V element: As a forming element of stable carbide MC, V can strengthen the matrix of the repair layer through precipitation strengthening and carbide dispersion strengthening, obtaining high-temperature strength and toughness.

[0024] W element: W is a typical solid-solution strengthening element, which can increase the wear resistance of the surface coating of continuous casting rolls. At the same time, it reduces the stacking fault energy and diffusion coefficient of the alloy, slows down the high-temperature diffusion rate of Cr, etc., strengthens the atomic binding force in the solid solution and slows down the softening rate, thereby increasing the service life of the surface coating.

[0025] The third object of the present invention is to provide a method for preparing a surface gradient coating of a continuous casting roll, which is characterized in that by using the submerged arc automatic welding technology, three layers of gradient coatings are surfacing welded on the surface of the continuous casting roll, including the following steps:

[0026] S1, drying the three kinds of welding wires and the continuous casting roll of the present invention for 2 - 8 h, and preheating the continuous casting roll to a temperature of 120 - 260 °C;

[0027] S2, carrying out the welding operation by circumferential surfacing welding. The first layer in direct contact with the continuous casting roll is the backing layer welding wire, the second layer upwards is the transition layer welding wire in sequence, and the third layer is the hard surface layer welding wire layer; lap cladding is adopted between the continuous casting roll substrate and the three layers of coatings, and the lap rate is 20% - 45% (the lap rate is the ratio of the lap width between adjacent cladding passes to the width of a single cladding layer during multi-pass cladding);

[0028] S3, after the three layers of coatings are prepared, cooling the surfacing layer to room temperature. At this time, the thickness of each layer is 1.5 - 3.5 mm, and the total thickness of the surfacing layer is not less than 5 mm;

[0029] S4. Place the continuously cast roll after welding in a heat treatment at 520 - 550 °C for 2 - 8 hours to eliminate the internal stress of the continuously cast roll, and take it out of the furnace at 200 - 250 °C, then the finished continuously cast roll is obtained, which can be further finely processed or subjected to factory inspection.

[0030] Preferably, during the cladding process, from the first layer to the third layer, the content of component A in the welding wire gradually decreases, while the contents of component B and component C gradually increase; the interlayer temperature (i.e., the temperature when starting to build the next single - pass cladding layer after each single - pass cladding layer is completed) is controlled at 100 - 250 °C, and it is kept warm while rotating.

[0031] Preferably, in step S2, after each layer of coating is welded, the welding head is lifted upward by 2.5 - 3 mm, and then continue with the next layer of welding until the three - layer coating is prepared.

[0032] Preferably, in step S3, in order to ensure dimensional accuracy, there should be a machining allowance of 2.5 - 3 mm on one side for the roll surface and the total length of the continuously cast roll at room temperature.

[0033] Preferably, the parameters of the submerged - arc automatic welding are as follows: the shielding gas is argon or nitrogen; the current is 250 - 450 A, the welding voltage is 25 - 35 V, and the welding speed is 350 - 550 mm / min; since the raw material ratio of each layer of coating is different, from the 1st layer to the 3rd layer, the content of high - melting - point alloys such as WC and MgO gradually increases. In order to ensure complete melting of the alloy and guarantee the quality of metallurgical bonding, it is necessary to increase the current and voltage, that is, provide greater energy per unit area to ensure the welding quality; due to the increase in laser power, the heat input to the substrate during the welding process gradually increases. Therefore, more preferably, variable - parameter operation should be adopted for each layer to increase the welding speed so as not to increase the molten pool and the heat - affected zone and deteriorate the quality of the bonding layer.

[0034] Current A Voltage V Welding speed mm / min The first layer 250～300 25～28 350～400 The second layer 350～400 28～32 450～500 The third layer 400～450 32～35 500～550

[0035] Preferably, the hardness of the hard surface layer of the finished continuously cast roll is HRC42 ± 2.

[0036] The beneficial effects of the present invention are as follows:

[0037] The coating material of the present invention adds alloying elements with wear resistance and thermal crack resistance on the basis of traditional welding materials, and prepares gradient coatings with different ratios on the surface of 42CrMo continuous casting rolls, presenting a gradient coating structure with multi-layer gradient gradual change rather than sudden disordered change; the obtained coating has excellent wear resistance and resistance to thermal and cold fatigue, improves the performance of the continuous casting roll, and can meet different requirements such as heat crack resistance, wear resistance, corrosion resistance, and long service life of the continuous casting roll; adopting the submerged arc automatic welding technology, the process operation is simple, and it can realize the industrial large-scale production of rapid manufacturing or repair of the roll surface of the continuous casting roll, with high production efficiency, good weld quality, greatly reducing the manufacturing difficulty and saving the manufacturing cost, high practicability, simple operation, and high economic benefits. Detailed implementation manners

[0038] The following further illustrates the present invention in conjunction with specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0039] For the experimental methods without specific conditions noted in the following embodiments, they are usually carried out according to conventional conditions or the conditions provided by the manufacturers.

[0040] Embodiment 1

[0041] For the repair of the surface of a continuous casting roll in this embodiment, automatic submerged arc welding is used for circumferential surfacing to weld 3 gradient coatings. The welding wire used for each layer includes raw materials with the following mass fractions:

[0042] The first layer is the backing layer welding wire: 55% of component A, 15% of component B, 5% of WC, 2% of MgO, 0.3% of Y2O3;

[0043] The second layer is the transition layer welding wire: 35% of component A, 25% of component B, 10% of WC, 3% of MgO, 0.5% of Y2O3;

[0044] The third layer is the hard facing layer welding wire: 15% of component A, 30% of component B, 15% of WC, 4.5% of MgO, 1.3% of Y2O3;

[0045] Among them, the mass fraction components of component A are: 0.15% of C, 1.00% of Si, 1.00% of Mn, 14.00% of Cr, 5.50% of Ni, 0.60% of Mo, 1.50% of V, and the balance is Fe; the mass fraction components of component B are: 0.12% of C, 1.00% of Si, 5.00% of Mn, 6.00% of Mo, 4.50% of V, and the balance is Fe.

[0046] The preparation method of the gradient coating on the surface of the continuous casting roll adopts the submerged arc automatic welding technology, and 3 gradient coatings are surfacing welded on the surface of the continuous casting roll, including the following steps:

[0047] S1. Dry the backing layer welding wire, transition layer welding wire, hard surface layer welding wire and the continuous casting roll for 5 h, and preheat the continuous casting roll to 150 °C; control the interlayer temperature at 160 °C, keep warm while rotating.

[0048] S2. Carry out the welding operation by circumferential surfacing. The first layer in direct contact with the continuous casting roll is the backing layer welding wire, the second layer upwards in sequence is the transition layer welding wire, and the third layer is the hard surface layer welding wire; use argon as the shielding gas. The parameters of submerged arc automatic welding are as follows:

[0049] The 1st layer: current 260 A, voltage 28 V, welding speed 360 mm / min, lapping rate 30%; the 2nd layer: current 350 A, voltage 28 V, welding speed 450 mm / min, lapping rate 25%; the 3rd layer: current 400 A, voltage 32 V, welding speed 500 mm / min, lapping rate 30%. After welding each layer of coating is completed, lift the welding head upwards by 2.5 - 3 mm, and continue with the next layer of welding until the preparation of the 3 - layer coating is completed; the surfacing process is completed at one time, and measure the temperature of the surfacing workpiece at any time.

[0050] S3. After the preparation of the 3 - layer coating is completed, cool the surfacing layer to room temperature. To ensure dimensional accuracy, there should be a machining allowance of 2.5 mm on one side for the roll surface and the total length of the continuous casting roll at normal temperature; at this time, the thickness of each layer is 2.8 mm, and the total thickness of the surfacing layer is 8.4 mm.

[0051] S4. Place the welded continuous casting roll in heat treatment at 530 °C for 6 hours to eliminate the internal stress of the continuous casting roll, and take it out of the furnace at 220 °C, then the finished continuous casting roll is obtained. The hardness of the hard surface layer of the finished continuous casting roll is HRC43.

[0052] Example 2

[0053] For the surface repair of a continuous casting roll in this example, automatic submerged arc welding of 3 gradient coatings is carried out by circumferential surfacing. Each layer of welding wire used includes raw materials with the following mass fractions:

[0054] The 1st layer is the backing layer welding wire: 60% of component A, 18% of component B, 8% of WC, 2.5% of MgO, 0.5% of Y2O3.

[0055] The 2nd layer is the transition layer welding wire: 40% of component A, 28% of component B, 12% of WC, 3.5% of MgO, 0.8% of Y2O3.

[0056] The 3rd layer is the hard surface layer welding wire: 25% of component A, 38% of component B, 18% of WC, 4.6% of MgO, 1.1% of Y2O3.

[0057] Among them, the mass fraction components of component A are: 0.12% C, 0.80% Si, 0.80% Mn, 0.005% S, 13.00% Cr, 5.00% Ni, 0.50% Mo, 1.20% V, and the balance is Fe; the mass fraction components of component B are: 0.10% C, 0.80% Si, 4.00% Mn, 5.00% Mo, 4.00% V, and the balance is Fe.

[0058] The preparation method of the surface gradient coating of the continuous casting roll adopts the submerged arc automatic welding technology, and three layers of gradient coatings are surfacing welded on the surface of the continuous casting roll, including the following steps:

[0059] S1, dry the backing wire, transition layer wire, hard surface layer wire and the continuous casting roll for 6h, preheat the continuous casting roll to a temperature of 200°C; control the interlayer temperature at 220°C, rotate and keep warm.

[0060] S2, carry out the welding operation by means of circumferential surfacing welding. The first layer in direct contact with the continuous casting roll is the backing wire, the second layer upwards in sequence is the transition layer wire, and the third layer is the hard surface layer wire; the shielding gas is argon; the parameters of the submerged arc automatic welding are:

[0061] The first layer: current 280A, voltage 25V, welding speed 350mm / min, lap rate 20%; the second layer: current 360A, voltage 29V, welding speed 460mm / min, lap rate 20%; the third layer: current 420A, voltage 33V, welding speed 520mm / min, lap rate 25%; after welding each layer of coating is completed, the welding head is lifted upwards by 2.5 - 3mm, and continue to weld the next layer until the three layers of coatings are prepared; the surfacing process is completed at one time, and the temperature of the surfacing workpiece is measured at any time.

[0062] S3, after the three layers of coatings are prepared, cool the surfacing layer to room temperature. In order to ensure the dimensional accuracy, there should be a machining allowance of 2.8mm on one side for the roll surface and the total length of the continuous casting roll at normal temperature; at this time, the thickness of each layer is 2.5mm, and the total thickness of the surfacing layer is 7.5mm.

[0063] S4, place the welded continuous casting roll in heat treatment at 550°C for 6 hours to eliminate the internal stress of the continuous casting roll, and take it out of the furnace at 230°C, then the finished continuous casting roll is obtained, and the hardness of the hard surface layer of the finished continuous casting roll is HRC41.

[0064] Example 3

[0065] For the surface repair of a continuous casting roll in this example, three gradient coatings are automatically submerged arc welded by means of circumferential surfacing welding. Each layer of wire used includes raw materials with the following mass fractions:

[0066] The first layer is the backing layer welding wire: 58% of component A, 19% of component B, 9% of WC, 2.8% of MgO, 0.2% of Y2O3;

[0067] The second layer is the transition layer welding wire: 45% of component A, 29% of component B, 13% of WC, 3.8% of MgO, 0.6% of Y2O3;

[0068] The third layer is the hardfacing layer welding wire: 28% of component A, 40% of component B, 19% of WC, 4.8% of MgO, 1.2% of Y2O3;

[0069] Among them, the mass fraction components of component A are: 0.10% of C, 0.60% of Si, 0.80% of Mn, 0.005% of S, 0.011% of P, 12.00% of Cr, 4.00% of Ni, 0.40% of Mo, 1.00% of V, and the balance is Fe; the mass fraction components of component B are: 0.09% of C, 0.70% of Si, 0.015% of P, 3.20% of Mn, 4.35% of Mo, 3.15% of V, and the balance is Fe.

[0070] The preparation method of the surface gradient coating of the continuous casting roll adopts the submerged arc automatic welding technology, and three layers of gradient coatings are surfacing welded on the surface of the continuous casting roll, including the following steps:

[0071] S1, dry the backing layer welding wire, transition layer welding wire, hardfacing layer welding wire and the continuous casting roll for 6h, preheat the continuous casting roll to a temperature of 180°C; control the interlayer temperature at 235°C, rotate and keep warm;

[0072] S2, carry out the welding operation by circumferential surfacing. The first layer in direct contact with the continuous casting roll is the backing layer welding wire, the second layer upwards in sequence is the transition layer welding wire, and the third layer is the hardfacing layer welding wire; the shielding gas is argon; the parameters of the submerged arc automatic welding are:

[0073] The first layer: current 290A, voltage 26V, welding speed 380mm / min, lap rate 25%; the second layer: current 380A, voltage 30V, welding speed 480mm / min, lap rate 25%; the third layer: current 440A, voltage 34V, welding speed 530mm / min, lap rate 25%; after welding each layer of the coating is completed, the welding head is lifted upwards by 2.5 - 3mm, and continue to weld the next layer until the three layers of coatings are prepared; the surfacing process is completed at one time, and measure the temperature of the surfacing workpiece at any time;

[0074] S3. After the three-layer coating is prepared, the surfacing layer is cooled to room temperature. To ensure dimensional accuracy, there should be a machining allowance of 2.5 mm on one side for the roll surface and the total length of the continuous casting roll at room temperature. At this time, the thicknesses of the three layers are 2.5 mm, 2.0 mm, and 3 mm respectively, and the total thickness of the surfacing layer is 7.5 mm.

[0075] S4. The welded continuous casting roll is heat-treated at 520 °C for 8 hours to eliminate the internal stress of the continuous casting roll, and then taken out of the furnace at 200 °C, thus obtaining the finished continuous casting roll. The hardness of the hard surface layer of the finished continuous casting roll is HRC42.

[0076] Example 4

[0077] For the surface repair of a continuous casting roll in this example, automatic submerged arc welding is used to deposit three gradient coatings in a circumferential surfacing manner. The welding wire for each layer includes raw materials with the following mass fractions:

[0078] The first layer is the backing layer welding wire: 65% of component A, 20% of component B, 10% of WC, 3.0% of MgO, 0.4% of Y2O3;

[0079] The second layer is the transition layer welding wire: 50% of component A, 30% of component B, 15% of WC, 4% of MgO, 1% of Y2O3;

[0080] The third layer is the hard surface layer welding wire: 30% of component A, 43% of component B, 20% of WC, 5% of MgO, 1.5% of Y2O3;

[0081] Among them, the mass fraction components of component A are: 0.08% of C, 0.40% of Si, 0.40% of Mn, 0.008% of S, 11.25% of Cr, 3.50% of Ni, 0.30% of Mo, 0.50% of V, and the balance is Fe; the mass fraction components of component B are: 0.08% of C, 0.60% of Si, 0.008% of S, 0.010% of P, 2.00% of Mn, 3.00% of Mo, 2.50% of V, and the balance is Fe.

[0082] For the preparation method of the surface gradient coating of this continuous casting roll, submerged arc automatic welding technology is adopted to deposit three gradient coatings on the surface of the continuous casting roll, including the following steps:

[0083] S1. The backing layer welding wire, transition layer welding wire, hard surface layer welding wire and the continuous casting roll are dried for 8 h, and the continuous casting roll is preheated to a temperature of 250 °C. The interlayer temperature is controlled at 120 °C, and it is kept warm while rotating.

[0084] S2. Carry out the welding operation by circumferential surfacing. The first layer in direct contact with the continuous casting roll is the backing layer wire electrode. The second layer above it in sequence uses the transition layer wire electrode, and the third layer uses the hard facing layer wire electrode; argon is used as the shielding gas. The parameters for submerged arc automatic welding are as follows:

[0085] Layer 1: current 300 A, voltage 27 V, welding speed 380 mm / min, and the lapping rate is 45%; Layer 2: current 400 A, voltage 32 V, welding speed 500 mm / min, and the lapping rate is 20%; Layer 3: current 450 A, voltage 35 V, welding speed 550 mm / min, and the lapping rate is 35%. After welding each layer of the coating is completed, the welding head is lifted upward by 2.5 - 3 mm, and continue with the next layer of welding until the preparation of the 3 - layer coating is completed; the surfacing process is completed at one time, and the temperature of the surfacing workpiece is measured at any time;

[0086] S3. After the preparation of the 3 - layer coating is completed, cool the surfacing layer to room temperature. To ensure dimensional accuracy, there should be a machining allowance of 2.5 mm on one side for the roll surface and the total length of the continuous casting roll at room temperature; at this time, the thicknesses of the 3 - layer coatings are 3.0 mm, 2.5 mm, and 3.0 mm respectively, and the total thickness of the surfacing layer is 8.5 mm;

[0087] S4. Place the welded continuous casting roll in heat treatment at 550 °C for 6 hours to eliminate the internal stress of the continuous casting roll, and take it out of the furnace at 230 °C, then the finished continuous casting roll is obtained. The hardness of the hard facing layer of the finished continuous casting roll is HRC44.

[0088] Comparative Example 1

[0089] Comparative Example 1 is the comparative example of Example 1. Automatic submerged arc welding is carried out by circumferential surfacing. The raw materials of its wire electrodes are all Component A (1Cr13Ni4Mo2V composition). The mass fraction components of Component A are: 0.15% C, 1.00% Si, 1.00% Mn, 14.00% Cr, 5.50% Ni, 0.60% Mo, 1.50% V, and the balance is Fe.

[0090] The preparation method of the surface gradient coating of this continuous casting roll adopts submerged arc automatic welding technology to surfacing 3 layers of non - gradient coatings on the surface of the continuous casting roll, including the following steps:

[0091] S1. Dry the backing layer wire electrode, transition layer wire electrode, hard facing layer wire electrode and the continuous casting roll for 5 h, and preheat the continuous casting roll to a temperature of 150 °C; control the inter - layer temperature at 160 °C, and keep warm while rotating;

[0092] S2. Carry out the welding operation by circumferential surfacing to surfacing 3 layers. Argon is used as the shielding gas. The parameters for submerged arc automatic welding are as follows:

[0093] Layer 1: current 260 A, voltage 28 V, welding speed 360 mm / min, overlap rate 30%; Layer 2: current 350 A, voltage 28 V, welding speed 450 mm / min, overlap rate 25%; Layer 3: current 400 A, voltage 32 V, welding speed 500 mm / min, overlap rate 30%. After welding each layer of the coating is completed, the welding head is lifted upward by 2.5 - 3 mm, and continue to weld the next layer until the preparation of the 3-layer coating is completed; the surfacing process is completed at one time, and the temperature of the surfacing workpiece is measured at any time;

[0094] S3, after the preparation of the 3-layer coating is completed, the surfacing layer is cooled to room temperature. In order to ensure dimensional accuracy, there should be a machining allowance of 2.5 mm on one side for the roll surface and the total length of the continuous casting roll at room temperature; at this time, the thickness of each layer is 2.8 mm, and the total thickness of the surfacing layer is 8.4 mm;

[0095] S4, the welded continuous casting roll is heat-treated at 530 °C for 6 hours to eliminate the internal stress of the continuous casting roll, and is taken out of the furnace at 220 °C, then the finished continuous casting roll is obtained, and the hardness of the hard surface layer of the finished continuous casting roll is HRC36.

[0096] Comparative Example 2

[0097] Comparative Example 2 is the comparative example of Example 2. Automatic submerged arc welding is used to weld 3 gradient coatings in a circumferential surfacing manner. The wire used for each layer includes raw materials with the following mass fractions:

[0098] The first layer is the backing wire: 60% of component A, 18% of component B;

[0099] The second layer is the transition wire: 40% of component A, 28% of component B;

[0100] The third layer is the hard surface wire: 25% of component A, 38% of component B;

[0101] Among them, the mass fraction components of component A are: 0.12% C, 0.80% Si, 0.80% Mn, 0.005% S, 13.00% Cr, 5.00% Ni, 0.50% Mo, 1.20% V, and the balance is Fe; the mass fraction components of component B are: 0.10% C, 0.80% Si, 4.00% Mn, 5.00% Mo, 4.00% V, and the balance is Fe.

[0102] The preparation method of the surface gradient coating of this continuous casting roll adopts submerged arc automatic welding technology to surfacing 3 gradient coatings on the surface of the continuous casting roll, including the following steps:

[0103] S1. Bake the backing layer wire, transition layer wire, hard facing layer wire and the continuous casting roll for 6 hours, and preheat the continuous casting roll to 200°C; control the interlayer temperature at 220°C, keep it warm while rotating.

[0104] S2. Carry out the welding operation by circumferential surfacing. The first layer in direct contact with the continuous casting roll is the backing layer wire, the second layer upwards in sequence is the transition layer wire, and the third layer is the hard facing layer wire; use argon as the shielding gas. The parameters for submerged arc automatic welding are as follows:

[0105] Layer 1: Current 280A, voltage 25V, welding speed 350mm / min, lapping rate 20%; Layer 2: Current 360A, voltage 29V, welding speed 460mm / min, lapping rate 20%; Layer 3: Current 420A, voltage 33V, welding speed 520mm / min, lapping rate 25%; After welding each layer of coating is completed, lift the welding head upwards by 2.5 - 3mm, and continue with the next layer of welding until the three layers of coating are prepared; The surfacing process is completed at one time, and measure the temperature of the surfacing workpiece at any time.

[0106] S3. After the three layers of coating are prepared, cool the surfacing layer to room temperature. To ensure dimensional accuracy, there should be a machining allowance of 2.8mm on one side for the roll surface and the total length of the continuous casting roll at room temperature; At this time, the thickness of each layer is 2.5mm, and the total thickness of the surfacing layer is 7.5mm.

[0107] S4. Place the welded continuous casting roll in heat treatment at 550°C for 6 hours to eliminate the internal stress of the continuous casting roll, and take it out of the furnace at 230°C, then the finished continuous casting roll is obtained. The hardness of the hard facing layer of the finished continuous casting roll is HRC38.

[0108] Put the repaired continuous casting rolls of Examples 1 - 4 and Comparative Examples 1 - 2 into use on the machine, and compare with the single - time machine - use time of the continuous casting roll made of the original material. The average single - time machine - use time is shown in Table 1.

[0109] Table 1 Comparison of the continuous casting rolls of Examples 1 - 4 and Comparative Examples 1 - 2 with the continuous casting roll made of the original material

[0110]

[0111] As can be seen from Table 1, the repaired continuous casting roll of the present invention has performance characteristics such as gradient distribution of composition and structure, high wear resistance, and good resistance to thermal cracking. According to the technical scheme of this invention patent for surfacing repair, the single - time machine - use days of the continuous casting roll have increased significantly. At best, it can be increased to 2 times. At the same time, compared with the surfacing method with a single composition and structure, the single - time machine - use days have also been significantly improved, which has reference and promotion significance for surfacing of rolls in similar working condition stands.

Claims

1. A welding wire for forming a surface gradient coating on a continuous casting roll, characterized in that, The raw materials for making the welding wire include metal powder component A, metal powder component B, and metal oxide powder component C: The mass fraction components of component A are: carbon C: 0.08 - 0.15%, silicon Si: 0.4 - 1.00%, manganese Mn: 0.4 - 1.00%, sulfur S: ≤0.035%, phosphorus P: ≤0.030%, chromium Cr: 11.00% - 14.00%, nickel Ni: 3.50% - 5.50%, molybdenum Mo: 0.30% - 0.60%, vanadium V: 0.50% - 1.50%, and the balance is iron Fe; The mass fraction components of component B are: carbon C: 0.08% - 0.12%, silicon Si: 0.60% - 1.00%, sulfur S: ≤0.035%, phosphorus P: ≤0.030%, manganese Mn: 2.00% - 5.00%, molybdenum Mo: 3.00% - 6.00%, vanadium V: 2.50% - 4.50%, and the balance is iron Fe; The components of component C are: tungsten carbide WC; magnesium oxide MgO; yttrium oxide Y2O3; The welding wire made from the above raw materials is used to make a three-layer coating with a gradient composition: The first layer is the backing layer welding wire, containing the following raw materials by mass fraction: component A 55% - 65%, component B 15% - 20%, WC 5% - 10%, MgO 1.5% - 3.0%, Y2O3 0.1% - 0.5%; The second layer is the transition layer welding wire, containing the following raw materials by mass fraction: component A 35% - 50%, component B 25% - 30%, WC 10% - 15%, MgO 3.0% - 4.0%, Y2O3 0.5% - 1.0%; The third layer is the hardfacing layer welding wire, containing the following raw materials by mass fraction: component A 15% - 30%, component B 30% - 43%, WC 15% - 20%, MgO 4.0% - 5.0%, Y2O3 1.0% - 1.5%.

2. The welding wire for forming a surface gradient coating on a continuous casting roll according to claim 1, characterized in that, The particle sizes of the component A and component B are 30 - 50μm; the particle sizes of the tungsten carbide WC, magnesium oxide MgO, and yttrium oxide Y2O3 are all 20 - 30μm.

3. A method for preparing a surface gradient coating on a continuous casting roll, characterized in that, Using the submerged arc automatic welding technology and the welding wire described in claim 1 or 2, a three-layer gradient coating is surfacing welded on the surface of the continuous casting roll, including the following steps: S1, drying the welding wire and the continuous casting roll for 2 - 8h, and preheating the continuous casting roll to a temperature of 120 - 260°C; S2, performing the welding operation in a circumferential surfacing welding method. The first layer in direct contact with the continuous casting roll uses the backing layer welding wire, the second layer upwards in sequence uses the transition layer welding wire, and the third layer uses the hardfacing layer welding wire, and lap cladding is used, and the lap rate is 20% - 45%; S3, after the three-layer coating is prepared, cooling the surfacing layer to room temperature. At this time, the thickness of each layer is 1.5 - 3.5mm, and the total thickness of the surfacing layer is not less than 5mm; S4, placing the welded continuous casting roll at 520 - 550°C for heat treatment for 2 - 8 hours, and taking it out of the furnace at 200 - 250°C to obtain the finished continuous casting roll.

4. The preparation method according to claim 3, characterized in that, In the step S2, after each layer of the coating is welded, the welding head is lifted upwards by 2.5 - 3mm, and the next layer of welding is continued until the three-layer coating is prepared.

5. The preparation method according to claim 3, characterized in that, The parameters of the submerged arc automatic welding are as follows: current 250 - 450 A, welding voltage 25 - 35 V, welding speed 350 - 550 mm / min.

6. The preparation method according to claim 3, characterized in that, The parameters of the submerged arc automatic welding are as follows: 。 7. The preparation method according to claim 3, characterized in that, The hardness of the hard surface layer of the finished continuous casting roll is HRC42 ± 2.

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