A wear-resistant alloy layer on the inner wall of a pulverized coal conveying elbow by laser cladding and its additive manufacturing process

Abstract

The present invention belongs to the technical field of additive manufacturing. The present invention discloses a wear-resistant alloy layer on the inner wall of a pulverized coal conveying elbow and an additive manufacturing process therefor. After preheating the pulverized coal conveying elbow, the present invention alternately laser clads a high-speed steel layer and a high-chromium cast iron layer on the inner wall of the pulverized coal conveying elbow to obtain a pulverized coal conveying elbow with a wear-resistant alloy layer. The bonding strength between the wear-resistant alloy layer of the pulverized coal conveying elbow obtained in the present invention and the elbow matrix reaches 765-772 MPa, and the wear-resistant alloy layer will not fall off at high temperatures above 900 °C, having excellent heat resistance and stability; the service life of the pulverized coal conveying elbow obtained in the present invention is long, and the service life can meet the overhaul time of the unit, ensuring normal operation during operation, while reducing the number of overhauls; the obtained pulverized coal conveying elbow has high stability, reducing air pollution caused by a large amount of pulverized coal spraying out, and avoiding direct economic losses caused by a large amount of fine coal being sprayed out due to elbow breakage.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and particularly to a wear-resistant alloy layer obtained by laser cladding on the inner wall of a pulverized coal conveying elbow and an additive manufacturing process therefor. Background Art

[0002] Pulverized coal conveying pipelines are used to convey pulverized coal from the outlet of a coal mill to a burner. Their operating characteristics are high flow velocity of pulverized coal, high particle hardness, and a certain temperature. Under such operating conditions, the equipment wears severely, especially at the elbows. Without any protective measures, the elbows are generally worn through in less than a year, greatly reducing the service life of the pulverized coal conveying pipeline. Moreover, most of the pulverized coal conveying pipelines are on high-altitude supports, making maintenance inconvenient.

[0003] In order to extend the service life of pulverized coal conveying pipelines, currently, the elbows of pulverized coal conveying pipelines are usually treated. Existing pulverized coal conveying elbows all paste alumina ceramic sheets on the inner wall of the elbows using glue. The aging of the glue will cause the glue to come off, resulting in the shedding of the alumina ceramic sheets, causing local or large-area exposure of the low-carbon steel elbow base material. The wear resistance of the base material is poor, and it will be worn through after a short period of use, leading to pulverized coal leakage. In addition, in order to convey and dry pulverized coal, hot air is usually used to convey pulverized coal. The hot air temperature is generally about 350°C. During the conveying process, pulverized coal accumulates in the elbow. After the pulverized coal accumulates, it will cause spontaneous combustion, the high temperature will melt the glue, resulting in the shedding of the alumina ceramic sheets, the exposure of the base material, and the wear-through of the elbow, leading to pulverized coal leakage. Therefore, there is an urgent need in the art to develop a pulverized coal conveying elbow with excellent high-temperature resistance, wear resistance, and high inner-layer peel strength. Summary of the Invention

[0004] The object of the present invention is to provide a wear-resistant alloy layer obtained by laser cladding on the inner wall of a pulverized coal conveying elbow and an additive manufacturing process therefor, so as to solve the problems existing in the pulverized coal conveying elbows that paste alumina ceramic sheets on the inner wall of the elbows using glue, such as easy aging of the glue, poor temperature resistance, resulting in low bonding strength between the alumina ceramic sheets and the elbow base material, easy shedding, causing exposure of the base material, wear-through of the elbow, and leading to pulverized coal leakage.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a wear-resistant alloy layer obtained by laser cladding on the inner wall of a pulverized coal conveying elbow. The wear-resistant alloy layer comprises alternately distributed high-speed steel layers and high-chromium cast iron layers. The high-speed steel comprises components with the following mass fractions: C 2-2.2%, Si 0.8-1%, Mn 0.5-0.7%, S 0.01-0.03%, P 0.02-0.04%, Ni 0.3-0.5%, Cr 4-4.2%, Mo 5.2-5.4%, V 5-5.2%, Nb 0.4-0.6%, W 1.7-1.9%, and the balance is Fe. The high-chromium cast iron comprises components with the following mass fractions: C 4.2-4.4%, B 1.7-1.9%, Si 1.9-2.1%, Cr 38-42%, Ni 4-6%, Mn 0.2-0.4%, Mo 0.4-0.6%, and the balance is Fe.

[0007] Preferably, the number of layers of the wear-resistant alloy layer is 6-14 layers.

[0008] Preferably, the thickness of each high-speed steel layer and each high-chromium cast iron layer is independently 0.8-1.5 mm.

[0009] The present invention also provides an additive manufacturing process for laser cladding the wear-resistant alloy layer on the inner wall of the pulverized coal conveying elbow, comprising the following steps:

[0010] After preheating the pulverized coal conveying elbow, alternately laser clad high-speed steel and high-chromium cast iron on the inner wall of the pulverized coal conveying elbow to obtain a pulverized coal conveying elbow with a wear-resistant alloy layer;

[0011] The first wear-resistant alloy layer in contact with the inner wall of the pulverized coal conveying elbow is a high-speed steel layer.

[0012] Preferably, the preheating temperature is 240-290 °C.

[0013] Preferably, the power of the laser cladding is 2500-3500 W; the spot diameter of the laser cladding is 4.2-4.8 mm; the scanning rate of the laser cladding is 650-750 mm / min; the overlapping rate of the laser cladding is 45-55%.

[0014] Preferably, during the laser cladding process, the powder feeding amounts of the high-speed steel and the high-chromium cast iron are independently 250-350 g / min.

[0015] Preferably, the laser cladding is carried out under a protective gas; the protective gas is argon, nitrogen or helium.

[0016] It can be seen from the above technical solutions that, compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] The coal powder conveying elbow obtained by the present invention does not require a binder, solving the problem of excessive wear on the inner wall of the elbow. At the same time, the bonding strength between the wear-resistant alloy layer and the elbow matrix of the obtained coal powder conveying elbow is high, solving the problem of easy detachment of the alumina ceramic chips on the inner wall of the elbow;

[0018] The bonding strength between the wear-resistant alloy layer and the elbow matrix of the coal powder conveying elbow obtained by the present invention reaches 765 - 772 MPa, and the wear-resistant alloy layer will not fall off at high temperatures above 900 °C, having excellent heat resistance and stability;

[0019] The coal powder conveying elbow obtained by the present invention has a long service life, and its service life can meet the overhaul time of the unit, ensuring normal operation during operation and reducing the number of inspections at the same time; the obtained coal powder conveying elbow has high stability, reducing air pollution caused by a large amount of coal powder spraying, and avoiding direct economic losses caused by a large amount of fine coal being ejected due to elbow breakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0021] Figure 1 Effect diagram of pretreatment for the Q235B carbon steel elbow described in Example 1;

[0022] Figure 2 Inner wall effect diagram of the coal powder conveying elbow with a wear-resistant alloy layer obtained in Example 1;

[0023] Figure 3 Finished product diagram of the coal powder conveying elbow with a wear-resistant alloy layer obtained in Example 1;

[0024] Figure 4 3D morphology diagram of the wear scar volume of the elbow of Q235B described in Example 1 and the obtained coal powder conveying elbow with a wear-resistant alloy layer, where a is the 3D morphology diagram of the wear scar volume of the elbow of Q235B, and b is the 3D morphology diagram of the wear scar volume of the coal powder conveying elbow with a wear-resistant alloy layer;

[0025] Figure 5 3D morphology diagram of the wear scar volume of the coal powder conveying elbow with a wear-resistant alloy layer obtained in Example 2;

[0026] Figure 6 3D morphology diagram of the wear scar volume of the coal powder conveying elbow with tungsten carbide obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention provides a wear-resistant alloy layer on the inner wall of a pulverized coal conveying elbow by laser cladding. The wear-resistant alloy layer comprises alternately distributed high-speed steel layers and high-chromium cast iron layers. The high-speed steel comprises components with the following mass fractions: C 2-2.2%, Si 0.8-1%, Mn 0.5-0.7%, S 0.01-0.03%, P 0.02-0.04%, Ni 0.3-0.5%, Cr 4-4.2%, Mo 5.2-5.4%, V 5-5.2%, Nb 0.4-0.6%, W 1.7-1.9%, and the balance is Fe. The high-chromium cast iron comprises components with the following mass fractions: C 4.2-4.4%, B 1.7-1.9%, Si 1.9-2.1%, Cr 38-42%, Ni 4-6%, Mn 0.2-0.4%, Mo 0.4-0.6%, and the balance is Fe.

[0028] In the high-speed steel of the present invention, the mass fraction of C is preferably 2.02-2.18%, more preferably 2.1%; the mass fraction of Si is preferably 0.83-0.95%, more preferably 0.9%; the mass fraction of Mn is preferably 0.52-0.61%, more preferably 0.6%; the mass fraction of S is preferably 0.015-0.025%, more preferably 0.02%; the mass fraction of P is preferably 0.025-0.038%, more preferably 0.03%; the mass fraction of Ni is preferably 0.31-0.48%, more preferably 0.4%; the mass fraction of Cr is preferably 4.06-4.15%, more preferably 4.1%; the mass fraction of Mo is preferably 5.27-5.32%, more preferably 5.3%; the mass fraction of V is preferably 5.08-5.15%, more preferably 5.1%; the mass fraction of Nb is preferably 0.42-0.56%, more preferably 0.5%; the mass fraction of W is preferably 1.77-1.82%, more preferably 1.8%; and the balance is Fe.

[0029] In the high-chromium cast iron of the present invention, the mass fraction of C is preferably 4.22-4.36%, more preferably 4.32-4.34%; the mass fraction of B is preferably 1.79-1.87%, more preferably 1.85-1.86%; the mass fraction of Si is preferably 1.99-2.09%, more preferably 2.05-2.08%; the mass fraction of Cr is preferably 38.8-40.5%, more preferably 39.56-39.85%; the mass fraction of Ni is preferably 4.5-5.8%, more preferably 5.62-5.79%; the mass fraction of Mn is preferably 0.27-0.31%, more preferably 0.3%; the mass fraction of Mo is preferably 0.45-0.58%, more preferably 0.54-0.56%; and the balance is Fe.

[0030] In the present invention, the number of layers of the wear-resistant alloy layer is preferably 6 to 14 layers, and more preferably 9 to 12 layers.

[0031] In the present invention, the thickness of each layer of high-speed steel layer and each layer of high-chromium cast iron layer is independently preferably 0.8 to 1.5 mm, and more preferably 1 to 1.2 mm.

[0032] The present invention also provides an additive manufacturing process for laser cladding a wear-resistant alloy layer on the inner wall of the pulverized coal conveying elbow, comprising the following steps:

[0033] After preheating the pulverized coal conveying elbow, laser cladding high-speed steel and high-chromium cast iron alternately on the inner wall of the pulverized coal conveying elbow to obtain a pulverized coal conveying elbow with a wear-resistant alloy layer;

[0034] The first layer of wear-resistant alloy layer in contact with the inner wall of the pulverized coal conveying elbow is a high-speed steel layer.

[0035] In the present invention, before the preheating, the pulverized coal conveying elbow is pretreated; the pretreatment is to polish the inner wall of the pulverized coal conveying elbow; the purpose of polishing is to remove the oxide layer and fatigue layer on the inner wall of the pulverized coal conveying elbow.

[0036] In the present invention, the preheating temperature is preferably 240 to 290 °C, and more preferably 250 to 280 °C; the purpose of preheating is to reduce the structural stress between the inner wall of the pulverized coal conveying elbow and the wear-resistant alloy layer.

[0037] In the present invention, the laser cladding uses a fiber laser and an internal hole laser head.

[0038] In the present invention, the power of the laser cladding is preferably 2500 to 3500 W, and more preferably 2800 to 3200 W; the spot diameter of the laser cladding is preferably 4.2 to 4.8 mm, and more preferably 4.5 to 4.7 mm; the scanning rate of the laser cladding is preferably 650 to 750 mm / min, and more preferably 700 to 730 mm / min; the overlapping rate of the laser cladding is preferably 45 to 55%, and more preferably 48 to 50%.

[0039] In the laser cladding process of the present invention, the powder feeding amounts of high-speed steel and high-chromium cast iron are independently preferably 250 to 350 g / min, and more preferably 300 to 320 g / min.

[0040] In the laser cladding process of the present invention, the powder particle diameters of high-speed steel and high-chromium cast iron are independently preferably 50 to 175 μm, and more preferably 60 to 150 μm.

[0041] In the present invention, the laser cladding is carried out under a protective gas; the protective gas is preferably argon or helium.

[0042] The present invention utilizes laser cladding to prepare a wear-resistant alloy layer on the inner wall of the elbow. The wear-resistant alloy layer is composed of two wear-resistant alloys stacked on top of each other to adapt to the alternation of wear resistance and hardening, thereby improving the stability of the wear-resistant alloy layer.

[0043] The technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0044] The coal powder conveying elbows used in the following examples and comparative examples are Q235B carbon steel elbows.

[0045] Example 1

[0046] The Q235B carbon steel elbow (with dimensions of R800 and 90°) was cut into two equal parts of elbows (with dimensions of R800 and 45°). Then, an angle grinder was used to polish the inner wall to remove rust and oxide layers on the inner wall. The pretreated elbow was placed on a heating belt and preheated to 250 °C. Segmented laser cladding was carried out using a fiber laser and an internal hole laser head, with argon as the protective gas and carrier gas powder feeding. The power of the laser cladding was maintained at 3000 W, the spot diameter was 4.5 mm, the scanning rate was 700 mm / min, the overlap rate was 50%, and the powder feeding amounts of high-speed steel and high-chromium cast iron were both 300 g / min. The first layer of laser cladding material in contact with the inner wall of the coal powder conveying elbow was high-speed steel, and the second layer was high-chromium cast iron. Then, laser cladding was alternately carried out until the 9th layer. The thickness of each layer of laser cladding material was 1 mm. The high-speed steel powder (with a particle size of 50 μm) included the following components by mass fraction: C 2.1%, Si 0.9%, Mn 0.6%, S 0.02%, P 0.03%, Ni 0.4%, Cr 4.1%, Mo 5.3%, V 5.1%, Nb 0.5%, W 1.8%, and the rest was Fe; the high-chromium cast iron powder (with a particle size of 50 μm) included the following components by mass fraction: C 4.34%, B 1.85%, Si 2.08%, Cr 39.85%, Ni 5.62%, Mn 0.3%, Mo 0.54%, and the rest was Fe. After the laser cladding was completed, the elbow was spliced and the straight section of the elbow was welded using gas shielded welding as required. Then, the angle and radius were calibrated in sequence, the surface was painted with anti-rust paint, and packaged to obtain a coal powder conveying elbow with a wear-resistant alloy layer.

[0047] The 3D morphology detection of the wear marks of the Q235B carbon steel elbow and the obtained coal powder conveying elbow with a wear-resistant alloy layer in this example was carried out, and the obtained results are as Figure 4 shown.

[0048] The anti-peeling strength of the inner wall of the pulverized coal conveying elbow with a wear-resistant alloy layer obtained in this example is 765 MPa, and the wear-resistant alloy layer of the obtained pulverized coal conveying elbow with a wear-resistant alloy layer does not fall off at a high temperature of 900 °C.

[0049] Example 2

[0050] The difference from Example 1 is that the size of the elbow is R700; the number of laser cladding layers is 10 layers. Others are the same as in Example 1.

[0051] The 3D morphology of the wear scar of the pulverized coal conveying elbow with a wear-resistant alloy layer obtained in this example was detected, and the obtained results are as Figure 5 shown.

[0052] The anti-peeling strength of the inner wall of the pulverized coal conveying elbow with a wear-resistant alloy layer obtained in this example is 772 MPa, and the wear-resistant alloy layer of the obtained pulverized coal conveying elbow with a wear-resistant alloy layer does not fall off at a high temperature of 900 °C.

[0053] Example 3

[0054] The difference from Example 1 is that the size of the elbow is R1200; the number of laser cladding layers is 10 layers. Others are the same as in Example 1.

[0055] The anti-peeling strength of the inner wall of the pulverized coal conveying elbow with a wear-resistant alloy layer obtained in this example is 768 MPa, and the wear-resistant alloy layer of the obtained pulverized coal conveying elbow with a wear-resistant alloy layer does not fall off at a high temperature of 900 °C.

[0056] Comparative Example 1

[0057] The difference from Example 1 is that the laser cladding material is tungsten carbide powder with a particle size of 50 μm. Others are the same as in Example 1.

[0058] The 3D morphology of the wear scar of the pulverized coal conveying elbow with tungsten carbide obtained in this comparative example was detected, and the obtained results are as Figure 6 shown.

[0059] Comparative Example 2

[0060] The inner wall of the elbow of Q235B (size R800, 90°) was polished with an angle grinder to remove the rust and oxide layer on the inner wall; a 10-mm-thick alumina ceramic sheet was pasted on the inner wall of the pretreated elbow using GWJ series adhesive (the coating thickness of the GWJ series adhesive is 0.2 mm); then the angle and radius were calibrated, anti-rust paint was applied to the surface, and packaging was carried out in sequence to obtain a pulverized coal conveying elbow with a wear-resistant alloy layer.

[0061] The anti-peeling strength of the inner wall of the pulverized coal conveying elbow obtained in this comparative example is 15 MPa, and the alumina ceramic chips on the pulverized coal conveying elbow obtained fall off during the spontaneous combustion phenomenon caused by the accumulation of pulverized coal.

[0062] It can be seen from Examples 1 to 3 and Comparative Examples 1 to 2 that the anti-peeling strength of the wear-resistant alloy layer on the inner wall of the pulverized coal conveying elbow obtained by the present invention reaches 765-772 MPa, which is significantly better than the 15 MPa achieved by the existing pulverized coal conveying elbows; at the same time, the obtained pulverized coal conveying elbow can withstand a high temperature of 900 °C, and the temperature resistance performance is greatly improved compared with the existing pulverized coal conveying elbows.

[0063] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A wear-resistant alloy layer with laser cladding on the inner wall of a pulverized coal conveying elbow, characterized in that, The wear-resistant alloy layer comprises alternately distributed high-speed steel layers and high-chromium cast iron layers; the high-speed steel comprises components with the following mass fractions: C 2-2.2%, Si 0.8-1%, Mn 0.5-0.7%, S 0.01-0.03%, P 0.02-0.04%, Ni 0.3-0.5%, Cr 4-4.2%, Mo 5.2-5.4%, V 5-5.2%, Nb 0.4-0.6%, W 1.7-1.9%, and the balance is Fe; the high-chromium cast iron comprises components with the following mass fractions: C 4.2-4.4%, B 1.7-1.9%, Si 1.9-2.1%, Cr 38-42%, Ni 4-6%, Mn 0.2-0.4%, Mo 0.4-0.6%, and the balance is Fe; The first wear-resistant alloy layer in contact with the inner wall of the pulverized coal conveying elbow is a high-speed steel layer.

2. The wear-resistant alloy layer of laser cladding on the inner wall of the pulverized coal conveying elbow according to claim 1, wherein The number of layers of the wear-resistant alloy layer is 6-14 layers.

3. The wear-resistant alloy layer of laser cladding on the inner wall of the pulverized coal conveying elbow according to claim 1 or 2, characterized in that, The thickness of each high-speed steel layer and each high-chromium cast iron layer is independently 0.8-1.5 mm.

4. The additive manufacturing process of the laser cladding wear-resistant alloy layer on the inner wall of the pulverized coal conveying elbow according to any one of claims 1 to 3, characterized in that, It includes the following steps: After preheating the pulverized coal conveying elbow, alternately laser cladding high-speed steel and high-chromium cast iron on the inner wall of the pulverized coal conveying elbow to obtain a pulverized coal conveying elbow with a wear-resistant alloy layer; The first wear-resistant alloy layer in contact with the inner wall of the pulverized coal conveying elbow is a high-speed steel layer.

5. The additive manufacturing process of the laser cladding wear-resistant alloy layer on the inner wall of the pulverized coal conveying elbow according to claim 4, characterized in that, The preheating temperature is 240-290 °C.

6. The additive manufacturing process of the laser cladding wear-resistant alloy layer on the inner wall of the pulverized coal conveying elbow according to claim 4 or 5, characterized in that, The power of the laser cladding is 2500-3500 W; the spot diameter of the laser cladding is 4.2-4.8 mm; the scanning rate of the laser cladding is 650-750 mm / min; the overlapping rate of the laser cladding is 45-55%.

7. The additive manufacturing process of the laser cladding wear-resistant alloy layer on the inner wall of the pulverized coal conveying elbow according to claim 6, characterized in that, During the laser cladding process, the powder feeding amounts of the high-speed steel and the high-chromium cast iron are independently 250-350 g / min.

8. The additive manufacturing process of the laser cladding wear-resistant alloy layer on the inner wall of the pulverized coal conveying elbow according to claim 5 or 7, characterized in that, The laser cladding is carried out under a protective gas; the protective gas is argon, nitrogen or helium.

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