A laser cladding powder for improving the friction coefficient of the cladding layer after multi-layer cladding.

Abstract

A laser cladding powder for improving the friction coefficient of the cladding layer after multi-layer cladding has the following chemical composition by weight percentage: C: 0.10–0.30%, Si: 0.6–1.5%, Cr: 15.2–19.4%, Ni: 45.1–54.5%, Co: 8–13%, Mo: 8.00–12.00%, W: 2.40–6.00%, Mn: 0.100–0.400%, Nb: 0.020–0.040%, with the balance being Fe, and simultaneously satisfying: Co+W: 11.9–17.2%, Cr+Ni: 62.6–70.3%. The powder of this invention avoids steel adhesion during laser cladding, improves the wear resistance of the multi-layer laser cladding material under high temperature and high pressure conditions, ensures no cracking during cooling and production after multi-layer cladding, reduces the number of times steel gets stuck during use, and is suitable for surface modification of pipe rolling tools, significantly reducing the wear rate of pipe rolling tools.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, specifically relating to a laser cladding powder that improves the friction coefficient of the cladding layer after multi-layer cladding. Background Technology

[0002] Seamless steel pipe is an economical steel material. During the production process of seamless steel pipe, especially in the production of high alloy steel, the rolling tools wear out very much. In the later stages of service, the wear is often very severe, which not only affects the surface quality of the seamless pipe, but also reduces its service life, resulting in more downtime and increased cost per ton of steel.

[0003] Laser cladding is a surface modification technology that uses pre-placed cladding materials or adds them synchronously during processing. Selected cladding materials containing different active elements are placed on the surface of a substrate. Under the irradiation and heating effect of a high-energy-density laser beam, the cladding materials and the substrate surface melt together and then rapidly cool and solidify, producing a cladding layer that is metallurgically bonded to the substrate. The cladding layer has excellent wear resistance, corrosion resistance, fatigue resistance, and oxidation resistance.

[0004] Chinese patent CN101974724A discloses "an iron-based alloy powder for laser cladding," whose composition by weight percentage is 0.60–1.00% C, 0.35–0.70% Si, 0.30–0.60% Mn, 5.0–7.0% Cr, 2.5–4.0% Ni, 1.5–2.5% Mo, 1.0–1.5% W, 0.70–1.0% V, 0.20–0.40% Ti, 0.50–0.70% B, 0.20–0.40% Nb, 0.10–0.30% Ce, with the remainder being Fe. The iron-based laser cladding alloy coating has a hardness of 62–67 HRC, exhibiting high hardness, but it does not consider wear resistance and cannot effectively solve the problem of cracking in the cladding layer.

[0005] Chinese patent CN102168211A discloses a "high-temperature cobalt-based alloy for heat-resistant pads in steel rolling furnaces," with the following chemical composition by weight percentage: C 0.05–0.20%, Si 0.5–2.0%, Mn 0.5–1.5%, Cr 27–30%, Co 39–41%, Ni 14–18%, W 2–5%, Ce 0.02–0.2%, and the remainder being Fe. It exhibits high creep strength, oxidation resistance, and corrosion resistance at a service temperature of 1300℃, effectively extending the service life of the manufactured heat-resistant pads. However, due to the excessively high Co content, it cannot effectively solve the problem of cracking of the cladding layer after multi-layer cladding and during use. Furthermore, the high Co content increases hardness, reduces the surface friction coefficient, and easily leads to steel jamming during rolling.

[0006] Chinese patent CN 111748726A discloses "a high wear-resistant material for perforated rolls," with the following chemical element mass percentages: C: 0.5-0.65%, Si: 0.2-0.6%, Mn: 1.5-1.8%, Cr: 0-0.4%, Mo: 0.3-0.8%, Ti: 1.2-3.0%, Ni: 0.3-0.7%, with the balance being Fe and other unavoidable impurities. The wear amount is 7.6-8.5 mm. Based on rolling 20,000 rolls per roll change cycle, the wear amount per 10,000 rolls is 3.8-4.25 mm, indicating insufficient wear resistance.

[0007] Chinese patent CN102677049A discloses a laser repair process for the surface of high-carbon alloy rolls. This process uses alloy powder with Cr and Mo elements to strengthen the iron-based alloy. By adding appropriate amounts of B and Si, the alloy forms an austenitic matrix after solidification to meet hardness requirements, while also exhibiting good wettability and self-fluxing properties. This prevents cracking during the cladding process, achieving a roll surface hardness of over 55 HRC. However, excessive hardness can easily lead to steel jamming when applied to perforated roll surfaces, and it is prone to cracking during multi-layer cladding. Furthermore, it does not emphasize wear resistance under high temperature and pressure.

[0008] Because tube rolling tools need to operate under high temperature and high pressure for extended periods, the material's microstructure and properties must exhibit high-temperature stability. High-temperature wear is the most significant failure mode for tube rolling tools. Existing cladding materials suffer from problems such as cracking and steel jamming during multi-layer cladding cooling and use, ultimately preventing their application in laser cladding of large-size, large-surface-area tube rolling tools, resulting in poor cladding formation and performance. Summary of the Invention

[0009] The purpose of this invention is to provide a laser cladding powder that improves the friction coefficient of the cladding layer after multi-layer cladding. This powder can prevent steel from sticking during the cladding process, and the cladding layer still has good wear resistance under high temperature and high pressure conditions after multi-layer laser cladding. It ensures that the cladding layer does not crack during cooling and production after multi-layer cladding, reduces the number of times steel gets stuck, and is suitable for surface modification of pipe rolling tools, which greatly reduces the wear rate of pipe rolling tools.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A laser cladding powder for improving the friction coefficient of the cladding layer after multi-layer cladding has the following chemical composition by weight percentage: C: 0.10–0.30%, Si: 0.6–1.5%, Cr: 15.2–19.4%, Ni: 45.1–54.5%, Co: 8–13%, Mo: 8.00–12.00%, W: 2.40–6.00%, Mn: 0.100–0.400%, Nb: 0.020–0.040%, with the balance being Fe, and simultaneously satisfying: Co+W: 11.9–17.2%, Cr+Ni: 62.6–70.3%.

[0012] Furthermore, the balance is Fe.

[0013] Preferably, the average size of the laser cladding powder is between 75 and 150 μm.

[0014] Furthermore, the hardness of the cladding layer obtained after laser cladding is between 215 and 239 HB.

[0015] Furthermore, the cladding layer obtained after laser cladding exhibits a friction coefficient of 3.9–5.0 under a load of 30 N and a temperature of 600 °C.

[0016] In the composition design of the laser cladding powder described in this invention:

[0017] C: Hardness is improved through solid solution strengthening and precipitation strengthening by forming precipitates with other carbide-forming elements. Excessive C content leads to high hardenability, making the material prone to cracking during cooling and use after multi-layer cladding, resulting in performance degradation and economic losses. Therefore, this invention controls the C content to 0.10–0.30%.

[0018] Si provides self-fluxing properties to the powder and has strong deoxidizing and slag-forming capabilities. During the deposition process, it reacts with oxygen in the molten pool and oxides on the surface of the molten pool to form low-melting-point borosilicates that float to the surface of the molten pool, reducing the amount of oxygen and slag in the molten pool and improving the wettability of the matrix and the deposited layer, as well as the forming properties of the deposited material. Therefore, the Si content is controlled at 1.5% to 3.0% in this invention.

[0019] Ni: By adding a certain amount of Ni, the ferrite matrix is ​​stably transformed into an austenitic matrix, thereby improving high-temperature strength and creep resistance. If the Ni content is too low, the austenitic structure will lack stability and the high-temperature wear resistance will be poor. If too much Ni is added, the matrix hardness will decrease, resulting in poor wear resistance. Therefore, the Ni content in this invention is controlled at 45.1% to 54.5%.

[0020] Cr: In this invention, the Cr content is controlled at 15.2-19.4%, and the weight percentage of Cr and Ni is controlled at 62.6-70.3%. This facilitates the formation of stable chromium and nickel oxides and chromium-nickel spinel phase (NiCr2O4) under high-temperature service conditions, forming an oxide layer of 5-100 μm. On the one hand, the oxide film isolates the cladding layer from the high-temperature tube blank, preventing steel adhesion; on the other hand, it improves the stability of the cladding layer, which is beneficial for improving the oxidation resistance and wear resistance of the cladding layer and reducing the number of times steel jams. However, excessive Cr content will reduce the amount of other alloying elements added, which is not conducive to improving hardness and is detrimental to wear resistance.

[0021] Co: Co has a high melting point, and adding Co is beneficial for improving the material's load-bearing capacity at high temperatures, resistance to hot corrosion, cold and hot fatigue performance, and resistance to high-temperature creep. However, excessive Co content leads to increased brittleness, making the material prone to cracking during cooling after multi-layer laser cladding and during use, resulting in surface cracks. High Co content also causes high surface hardness and a low coefficient of friction in the cladding layer, leading to steel jamming. Therefore, this invention controls the Co content to be between 8% and 13%.

[0022] W is the main element for improving high-temperature strength. Its main function is to dissolve in austenite, strengthen austenite and increase the recrystallization temperature of austenite, reduce the alloy stacking fault energy, and reduce the creep rate. In the high-temperature environment in contact with the steel billet, it plays a role in improving red hardness and ensures that the cladding layer still has high hardness during friction and wear. Therefore, the W content in this invention is controlled at 2.40-6.00%.

[0023] Meanwhile, by controlling the total elemental content of Co+W between 11.9% and 17.2%, the volume percentage of the γ' phase is increased to enhance solid solution strengthening and ensure good hardness of the cladding layer. This avoids both excessively low hardness of the cladding layer during use, which can lead to severe plastic deformation, cracking, and oxide film peeling, and excessively high hardness, which can cause cracking of the weld overlay due to reduced plasticity during the cladding process.

[0024] Mo: Mo is also a key element for improving high-temperature strength. Mo promotes the formation of MoC-type carbides and plays a role in stabilizing the Cr oxide film. Adding an appropriate amount of Mo is beneficial to the stable existence of the oxide film, preventing steel adhesion, improving corrosion resistance, increasing the friction coefficient of the cladding layer, and ensuring the material's corrosion resistance, wear resistance, and anti-sticking properties. Therefore, this invention controls the Mo content to be between 8.00% and 12.00%.

[0025] Nb: Nb can promote grain boundary oxidation, allowing the oxide film to penetrate deep into the grain boundaries and form an interlocking structure, thereby improving the bonding strength between the oxide film and the substrate. Therefore, the Nb content in this invention is controlled at 0.020–0.040%.

[0026] The compositional design features of the laser cladding powder described in this invention are as follows:

[0027] First, the total elemental content of Cr+Ni is limited to 62.6-70.3%, which allows for the formation of stable chromium and nickel oxides and chromium-nickel spinel phase (NiCr2O4) under high-temperature service conditions. This forms an oxide film on the surface of the cladding layer, improving the stability of the cladding layer, preventing the piercing roll cladding layer substrate and the billet metal from being isolated, and avoiding steel sticking.

[0028] Secondly, through extensive experiments, the inventors discovered that excessively high Co content leads to excessively high hardness and a low coefficient of friction in the cladding layer, causing problems such as steel jamming and cracking during use, thus affecting the normal operation of the rolling mill tools. Therefore, the Co content must be limited to a certain range to avoid steel jamming and cracking.

[0029] Third, the total elemental content of Co+W is limited to 11.9-17.2% to increase the volume percentage of the γ' phase and enhance the solid solution strengthening effect, so as to ensure that the cladding layer has good hardness. This avoids the oxide film from cracking and peeling due to excessively low hardness and severe deformation of the cladding layer during use, and also avoids cracking during the cladding process due to excessively high hardness of the cladding layer.

[0030] Fourth, the low-C design can prevent cracking of the weld layer.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. This invention forms a 5-100µm thick oxide film on the surface of the cladding layer by controlling the content of Ni and Cr elements and their total content. Simultaneously, the addition of Mo and Nb elements promotes the stable existence of the oxide film, preventing steel adhesion during cladding. This also improves the stability of the cladding layer, enhances its oxidation resistance and friction coefficient, and prevents cracking during use. Traditional methods of improving wear resistance utilize alloying elements such as Cr and Mo to form fine carbides, which act as dispersion reinforcement, enhancing the high-temperature wear resistance of the substrate.

[0033] 2. This invention combines low C, low Co and medium W design, and controls the total content of Co+W elements to 11.9-17.2%, which avoids excessive hardness of the cladding layer causing cracks during use, reduces the occurrence of steel jamming problems, and also avoids excessively low hardness of the cladding layer during use, which can lead to cracks and peeling of the oxide film.

[0034] 3. The powder described in this invention is used to perform laser cladding on the surface of the rolling mill tool. The resulting cladding layer still has a high coefficient of friction under high temperature and high pressure conditions. The coefficient of friction of the cladding layer obtained after laser cladding is 3.9 to 5.0 under 600℃ and 30N load, and the hardness of the cladding layer is guaranteed to be 215 to 239HB. This effectively solves the problem of cracking or steel jamming during use after multiple layers of cladding on the surface of the rolling mill tool, and increases the service life of the rolling mill tool. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments.

[0036] The specific chemical composition of the laser cladding powders used in this invention and comparative examples is shown in Table 1.

[0037] The embodiments and comparative examples of this invention use a 3kW semiconductor laser to prepare three cladding layers on a certain roll using a laser cladding process, in order to improve the wear resistance of the roll throughout its use.

[0038] The rollers obtained after laser cladding in the embodiments and comparative examples of the present invention were used on the rolling line for 7 days and then removed from the line. During and after use, the surface cladding layer of the rollers was observed to see whether there was cracking, steel jamming, and wear. The specific results are shown in Table 2.

[0039] The high-temperature friction coefficient of the cladding layer of the rollers obtained after laser cladding in the embodiments and comparative examples of the present invention was measured at 600℃ and 30N load. The specific results are shown in Table 2.

[0040] The hardness of the cladding layer was measured according to the national standard GB / T 231 "Britell Hardness Test for Metallic Materials". The specific results are shown in Table 2.

[0041] As can be seen from Table 2, the wear of the cladding layer obtained in the embodiments of the present invention under high temperature and high pressure conditions is 2.3 to 2.9 mm / 10,000 pieces, the coefficient of friction is 3.9 to 5.0, the hardness is 215 to 239 HB, and no cracking occurs during use, and the number of times steel is stuck is greatly reduced.

[0042] In Comparative Example 1, the content of Co and Co+W was too low, and the content of Ni and Cr+Ni was too high, resulting in a low content of high melting point alloying elements. The hardness could meet the requirements of this invention, but the wear resistance was poor. Although it did not crack during use, it jammed the steel many times.

[0043] In Comparative Example 2, the Co+W content was too high and the Cr+Ni content was too low, resulting in high hardness. During use, cracks occurred, and the cracks were wide. The coefficient of friction was low, and the steel jamming was severe.

[0044] Comparative Example 3 has a high Co+W content, a relatively high Mn content, and a relatively low Nb content. It has high strength, but micro-cracks occur during use, the friction coefficient is low, and steel jamming is severe.

[0045] In Comparative Example 4, the Co+W content was too high, the Cr+Ni content was too low, the Mn content was too high, and the Nb content was too low. The strength was high, and cracks appeared in the cladding layer after multi-layer cladding.

[0046] In Comparative Example 5, the Co+W content was too high and the Cr+Ni content was too low, resulting in high strength and cracking of the cladding layer after multi-layer cladding.

[0047] Comparative Example 6 has a higher Mo content and a lower Nb content. Its strength meets the requirements of this invention and it did not crack during use. However, it has a lower coefficient of friction, a larger amount of wear, and a higher number of times it jams.

[0048]

[0049]

[0050]

Claims

1. A laser cladding powder for improving the friction coefficient of the cladding layer after multi-layer cladding, wherein the chemical composition by weight percentage is: C: 0.10-0.30%, Si: 0.6-1.5%, Cr: 15.2-19.4%, Ni: 45.1-54.5%, Co: 8-13%, Mo: 8.00-12.00%, W: 2.40-6.00%, Mn: 0.100-0.400%, Nb: 0.020-0.040%, with the balance being Fe, and simultaneously satisfying: Co+W: 11.9-17.2%, Cr+Ni: 62.6-70.3%.

2. The powder for laser cladding according to claim 1, characterized in that, The average size of the powder is 75–150 μm.

3. The powder for laser cladding according to claim 1, characterized in that, The hardness of the cladding layer obtained after laser cladding is 215-239 HB.

4. The laser cladding powder according to claim 1 or 3, characterized in that, The friction coefficient of the cladding layer obtained after laser cladding is 3.9 to 5.0 under a load of 30N and a temperature of 600℃.

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