Preparation method of high-wear-resistance tungsten carbide coating for inner surface of stainless steel

Abstract

The invention discloses a preparation method of a high-wear-resistance tungsten carbide coating for the inner surface of stainless steel, and belongs to the technical field of high-wear-resistance coating materials.The preparation method comprises the steps that a stainless steel sample is put into an electroplating pool to be electroplated, and a middle transition layer is formed on the surface of the stainless steel sample block; and the electroplated stainless steel sample block is subjected to surface cleaning and then placed in a CVD reaction hearth to be subjected to vapor deposition, and a tungsten carbide coating is formed on the surface of the stainless steel sample block. The method solves the problems that the inner surface of the stainless steel cannot be effectively coated, the coating thickness is not uniform, the coating hardness is insufficient and the like through conventional PVD, thermal spraying and other surface treatment processes, preparation of the high-hardness and high-thickness tungsten carbide coating on the inner surface of the stainless steel is achieved, the coating binding force is good, and the coating quality is high. The stainless steel can be widely applied to complex-structure stainless steel parts in the fields of aerospace, power generation equipment, petrochemical engineering and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of highly wear-resistant coating materials, and particularly to a preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel. Background Art

[0002] Stainless steel products are widely used in fields such as construction, automobiles, machinery, and chemical engineering, and have good corrosion resistance and processing performance. With the continuous improvement of technology, the quality of stainless steel has also been gradually improved, and super ferritic stainless steel, super martensitic stainless steel, etc. have emerged. These steels show good use effects in existing conventional corrosion and wear conditions, but when facing harsh conditions such as high speed, high temperature, and high erosion speed, the use effects are poor. Therefore, people have taken various ways to improve, such as replacing other more wear-resistant and corrosion-resistant materials. Although the service life has been improved, problems such as high cost and difficult processing have restricted the application and promotion; forming a combination of steel parts and more wear-resistant materials, but due to the too large performance differences between the materials, it is difficult to adapt. How to find a suitable way to improve performance is extremely urgent.

[0003] The damage of materials starts from the surface. Improving the surface performance can effectively extend the service life. Therefore, surface treatment of stainless steel products is an effective and low-cost improvement method. Conventional surface treatment processes cannot effectively solve problems such as coating the inner hole of pipes due to reasons such as high coating temperature and difficult coating process for the inner surface.

[0004] Therefore, aiming at the problems existing in the prior art, sorting out the difficulties of inner surface coating, and providing a preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel are technical problems that need to be urgently solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel, which solves the problems that conventional surface treatment processes such as PVD and thermal spraying cannot effectively coat the inner surface of stainless steel, the coating thickness is uneven, and the coating hardness is insufficient, and realizes the preparation of a tungsten carbide coating with high hardness and high thickness on the inner surface of stainless steel. The coating has good bonding strength and can be widely applied to complex-structured stainless steel parts in fields such as aerospace, power generation equipment, and petrochemical industry.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel, comprising the following steps:

[0008] (1) Clean the oil stain on the surface of the stainless steel sample block, and then put it into an electroplating bath for electroplating to form an intermediate transition layer on the surface of the stainless steel sample block;

[0009] (2) Clean the surface of the electroplated stainless steel sample block, and then place it in the CVD reaction furnace for chemical vapor deposition to form a tungsten carbide coating on the surface of the stainless steel sample block.

[0010] Furthermore, the stainless steel sample block is made of austenitic stainless steel or martensitic precipitation hardening stainless steel.

[0011] The beneficial effect of adopting the above further solution is that: the stainless steel materials used in the present invention are widely used in the fields of aerospace, power generation equipment, petrochemical industry, etc. Surface modification on this type of stainless steel material can effectively ensure the corrosion resistance of austenitic stainless steel remains unchanged while improving wear resistance, and at the same time further improve the wear resistance of martensitic precipitation hardening stainless steel.

[0012] Furthermore, in step (1), the electrolyte used for electroplating is an aqueous solution of Ni salt, Cr salt or Cu salt.

[0013] The concentration of the aqueous solution is 30 - 300 g / L.

[0014] Furthermore, the electroplating temperature is 20 - 70 °C, and the current density is 1 - 10 A / dm 2 .

[0015] The beneficial effect of adopting the above further solution is that: by controlling the electroplating temperature and current density, the present invention improves the stability of the electroplated layer, ensures that the electroplated layer is tightly combined, promotes the size of the electroplated layer to be stable and uniform, and does not have the problem of local overthickness.

[0016] Furthermore, the thickness of the intermediate transition layer is 5 - 30 microns.

[0017] The beneficial effect of adopting the above further solution is that: the thickness of the transition layer defined above in the present invention can effectively improve the bonding force between the tungsten carbide coating and the steel part, can effectively absorb the stress caused by the difference in thermal expansion coefficient, and will not cause the intermediate layer to be deformed under stress during work due to the overthickness of the transition layer, resulting in the coating falling off and not playing a wear-resistant role.

[0018] Furthermore, in step (2), the chemical vapor deposition temperature is 500 - 700 °C, and the chemical vapor deposition time is 4 - 12 h.

[0019] The beneficial effect of adopting the above further solution is that: by making the chemical vapor deposition temperature lower than the phase transformation temperature of the steel part material, the present invention can effectively protect the steel part from obvious performance changes at this temperature. The appropriate chemical vapor deposition time can effectively control the coating thickness and reduce the coating non-uniformity caused by the local concentration difference of raw materials in the reaction kettle.

[0020] Furthermore, in the chemical vapor deposition process, the tungsten source is WF6;

[0021] The carbon source is a gaseous hydrocarbon with 1 to 4 carbon atoms, preferably methyl ether, methyl ethyl ether, neopentane or ethylene.

[0022] Furthermore, H2 is also introduced during the chemical vapor deposition process.

[0023] Furthermore, during the chemical vapor deposition process, the tungsten source flow rate is 6 - 12 scmm, the carbon source flow rate is 150 - 200 sccm, and the H2 flow rate is 180 - 200 scmm.

[0024] The beneficial effect of adopting the above further scheme is that: by controlling the raw material flow rate, the present invention effectively promotes the efficient progress of the reaction, effectively solves the problems of different deposition rates of different raw materials and different raw material products with different concentrations, and realizes the production of the target product.

[0025] Further, the thickness of the tungsten carbide coating is 20 - 150 microns.

[0026] The beneficial effect of adopting the above further scheme is that: the controllable range of the coating thickness is wide, which can effectively meet the requirements of different working conditions and realize the formulation of personalized solutions.

[0027] The beneficial effect of the present invention is that: in this field, the performance of stainless steel is greatly affected by temperature. Especially when the temperature exceeds 800 °C, the properties such as hardness of stainless steel will have obvious fluctuations. The temperatures required for conventional PVD, CVD, thermal spraying and other processes have reached above 900 °C, which leads to the performance fluctuations of stainless steel itself and also affects the organizational structure of stainless steel itself, and is extremely likely to cause the phenomena of coating cracking and delamination. At the same time, due to equipment and process limitations, most surface treatment processes cannot effectively prepare uniform coatings required for complex inner surfaces. The present invention combines the advantages of CVD for preparing inner surface coatings, uses hydrogen as a reducing agent, and by introducing special gaseous tungsten sources and carbon sources, controls the fluid flow field distribution in the furnace, so that the tungsten source and carbon source can react on the surface at 500 - 700 °C to produce a highly wear-resistant and thick tungsten carbide coating (the tungsten carbide coating contains a series of tungsten carbides such as WC, W2C, W3C, W12C, etc.), whose hardness is 1000 - 1600 HV. Compared with the uncoated stainless steel parts, in scenarios such as oil drilling tools, its service life is extended by 3 - 5 times compared with the uncoated parts. Through a critical load of 50 N, the coating does not show peeling, the thickness is 40 - 150 microns, which is much higher than the thickness of conventional CVD coatings, and the coating can be repeatedly coated, reducing the loss of parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic structural diagram of the tungsten carbide coating prepared on a stainless steel substrate according to the figure of the present invention;

[0029] Figure 2 It is a cross-sectional SEM image of the tungsten carbide coating prepared in Example 1;

[0030] Figure 3 SEM cross-sectional view of the tungsten carbide coating prepared in Example 4;

[0031] Figure 4 XRD pattern of the tungsten carbide coating prepared in Example 2;

[0032] Figure 5 XRD pattern of the tungsten carbide coating prepared in Example 3;

[0033] Figure 6 SEM cross-sectional view of the tungsten carbide coating prepared in Comparative Example 1. Detailed implementation manners

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0035] Example 1

[0036] Select a 17-4PH steel part with an inner diameter of 50 mm, an outer diameter of 60 mm, and a height of 30 mm for testing. After cleaning the inner and outer surfaces of the sample block, prepare the intermediate electroplated layer. At 25 °C, the current density is 2 A / dm 2 , using NiSO4·7H2O\NiCl2·6H2O as the nickel source, prepare a Ni-based intermediate electroplated layer with a thickness of 9 microns in the electroplated intermediate layer. Then place the sample in the reaction furnace, evacuate and introduce dimethyl ether (flow rate: 150 scmm), WF6 (flow rate: 6 sccm), and hydrogen (flow rate: 200 scmm). Let them mix and enter the furnace. The deposition pressure is 100 Pa, and deposit for 4 hours at 620 °C in the gas phase. The prepared coating is dense, has good adhesion, no obvious delamination, and the hardness reaches 1000-1100 HV 0.2 , and the thickness reaches 31 microns.

[0037] Example 2

[0038] The same as Example 1, the difference is that the ratios of dimethyl ether (flow rate: 200 scmm), WF6 (flow rate: 12 sccm), and hydrogen (flow rate: 180 scmm) are adjusted. The thickness and hardness of the prepared coating reach 1100-1200 HV 0.2 , and the thickness reaches 46 microns.

[0039] Example 3

[0040] Same as Example 2, except that the gas deposition time was adjusted to 8 hours. The hardness of the prepared coating reached 1100 - 1300 HV 0.2 , and the thickness reached 63 microns.

[0041] The coated specimens were wire cut, and after wire cutting, the specimens were placed in acetone and absolute ethanol for cleaning to remove foreign substances adhered to the surface, such as dust, oil, and grease. Metallographic and morphological analysis was observed using a scanning electron microscope, the coating hardness was detected according to the national standard GB / T9790 - 2021, and XRD was used for coating phase analysis. The results are as Figure 4 , Figure 5 shown.

[0042] Example 4

[0043] A 316L steel part with an inner diameter of 50 mm, an outer diameter of 60 mm, and a height of 30 mm was selected for the test. After cleaning the inner and outer surfaces of the sample block, the intermediate electroplated layer was prepared. At 25 °C, the current density was 2 A / dm 2 , using NiSO4·7H2O\NiCl2·6H2O as the nickel source, a Ni-based intermediate electroplated layer was prepared with a coating thickness of 17 microns. The specimen was placed in the reaction furnace chamber, evacuated, and methyl ether (flow rate: 180 scmm), WF6 (flow rate: 8 sccm), and hydrogen (flow rate: 200 scmm) were introduced. After mixing, they entered the furnace chamber, and the deposition pressure was 100 Pa. Coating was carried out at 650 °C for 8 hours. The prepared coating was dense, had good adhesion, no obvious delamination, and the hardness reached 1180 - 1320 HV 0.2 , and the thickness reached 62 microns.

[0044] Example 5

[0045] Same as Example 4, except that the coating time was adjusted to 4 hours. The hardness of the prepared coating reached 1140 - 1260 HV 0.2 , and the thickness reached more than 35 microns.

[0046] Example 6

[0047] Same as Example 4, except that hydrogen (flow rate: 180 scmm) was adjusted. The hardness of the prepared coating reached 1200 - 1360 HV 0.2 , and the thickness reached more than 60 microns.

[0048] Comparative Example 1

[0049] A steel part with an inner diameter of 50 mm, an outer diameter of 60 mm, and a height of 30 mm was selected for the test. After cleaning the inner and outer surfaces of the sample block, the intermediate electroplated layer was prepared. At 25 °C, the current density was 2 A / dm 2, using NiSO4·7H2O\NiCl2·6H2O as the nickel source, a Ni-based intermediate electroplated layer was prepared, and then a tungsten carbide coating was deposited by a conventional CVD process at 900-1100°C. The coating thickness was 8 microns. Due to the too high reaction temperature, the coating peeled off, as shown in Figure 6 .

[0050] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel, characterized in that, It includes the following steps: (1) Clean the oil stain on the surface of the stainless steel sample block, and then put it into the electroplating bath for electroplating to form an intermediate transition layer on the surface of the stainless steel sample block; (2) Clean the surface of the electroplated stainless steel sample block, and then place it in the CVD reaction furnace for chemical vapor deposition to form a tungsten carbide coating on the surface of the stainless steel sample block.

2. The preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel according to claim 1, characterized in that, The stainless steel sample block is made of austenitic stainless steel or martensitic precipitation hardening stainless steel.

3. The preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel according to claim 1, wherein, In step (1), the electrolyte used for electroplating is an aqueous solution of Ni salt, Cr salt or Cu salt.

4. The preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel according to claim 3, characterized in that, The electroplating temperature is 20 - 70 °C, and the current density is 1 - 10 A / dm 2 .

5. The preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel according to claim 4, wherein The thickness of the intermediate transition layer is 5-30 microns.

6. The preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel according to claim 1, characterized in that, In step (2), the chemical vapor deposition temperature is 500-700 °C, and the chemical vapor deposition time is 4-12 h.

7. The preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel according to claim 6, wherein, During the chemical vapor deposition process, the tungsten source is WF6; The carbon source is a gaseous hydrocarbon with 1 to 4 carbon atoms.

8. The preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel according to claim 7, characterized in that, During the chemical vapor deposition process, H2 is also introduced.

9. The preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel according to claim 8, characterized in that, During the chemical vapor deposition process, the flow rate of the tungsten source is 6-12 scmm, the flow rate of the carbon source is 150-200 sccm, and the flow rate of H2 is 180-200 scmm.

10. The preparation method of a highly wear-resistant tungsten carbide coating for the inner surface of stainless steel according to claim 1, wherein, The thickness of the tungsten carbide coating is 20-150 microns.

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