Surface treatment method for enhancing surface friction and thermal fatigue performance of die steel

Abstract

The invention discloses a surface treatment method for enhancing the surface friction and thermal fatigue performance of die steel in the technical field of die steel surface strengthening treatment.The surface treatment method comprises the steps that firstly, attachments on the surface of the die steel are removed, polishing is conducted, so that the surface of the die steel is smooth, and then the die steel is put into a certain proportion of alkaline water flushing liquid to be soaked; washing with clear water after soaking, and ensuring that the washing liquid is completely removed; secondly, the cleaned die steel is put into acid water of a certain proportion to be soaked, the die steel is washed with clear water after being soaked, it is ensured that washing liquid and attachments are completely removed, then water drops on the surface of the die steel are wiped with soft cloth, and the die steel is put into a drying machine to be dried; the dried die steel is put into cold spraying equipment, and cold spraying is carried out after spraying process parameters are set; and the die steel subjected to cold spraying is put into a resistance furnace to be subjected to diffusion treatment, argon is introduced for protection in the diffusion process, and the needed die steel is obtained after diffusion is completed.

Description

Technical Field

[0001] The invention relates to the technical field of die steel surface strengthening treatment, in particular to a surface treatment method for enhancing the friction and thermal fatigue performance of die steel surface. Background Art

[0002] Mold steel is a type of steel used to manufacture cold stamping dies, hot forging dies, die-casting dies and other molds. Molds face complex and diverse actual working conditions in industrial production. Strengthening the surface performance of molds helps to extend the service life of molds and reduce economic losses caused by surface failure behavior. During the use of mold processing, the mold steel surface directly faces the worst working conditions, so improving the failure behavior of the mold steel surface is one of the key points in mold manufacturing.

[0003] The cold spray process uses low-temperature preheated high-pressure gas to generate supersonic airflow through a convergent-divergent Laval nozzle. The powder is sent axially into the high-pressure airflow to form a gas-solid two-phase flow. After acceleration, it hits the substrate in a completely solid state and is deposited on the substrate surface through severe plastic deformation to form a coating.

[0004] When in service, mold steel experiences multiple reciprocating impacts and alternating hot and cold behaviors under high temperature and high pressure environment, and its surface contact friction and thermal fatigue resistance are greatly tested. Summary of the invention

[0005] The purpose of the present invention is to provide a surface treatment method for enhancing the friction and thermal fatigue performance of the mold steel surface, so as to solve the problems mentioned in the above background technology.

[0006] In order to achieve the above object, the present invention provides the following technical solution: a surface treatment method for enhancing the friction and thermal fatigue performance of the mold steel surface, comprising the following steps:

[0007] Step (1), first remove the attachments on the surface of the mold steel, and grind it to make the surface of the mold steel smooth, then soak the mold steel in a certain proportion of alkaline water washing liquid, rinse it with clean water after soaking, and ensure that the washing liquid is completely removed;

[0008] Step (2), then, soak the cleaned mold steel in a certain proportion of acid water, rinse it with clean water after soaking, ensure that the rinse liquid and attachments are completely removed, then wipe the water drops on the surface of the mold steel with a soft cloth, and put it into a dryer for drying;

[0009] Step (3), placing the dried mold steel into a cold spraying device, setting the spraying process parameters, and then performing cold spraying;

[0010] Step (4), the mold steel after cold spraying is placed in a resistance furnace for diffusion treatment, and argon gas is passed through the diffusion process for protection. After the diffusion is completed, the required mold steel is obtained.

[0011] The technical problem to be solved by the present invention can also be achieved by the following technical solution: the alkaline water washing liquid described in step (1) adopts a sodium hydroxide solution with a concentration of 20%, and safety should be paid attention to during the removal of the washing liquid.

[0012] The technical problem to be solved by the present invention can also be achieved by the following technical solution: the acid water in step (2) adopts a nitric acid solution with a concentration of 10%, and safety should be paid attention to during the removal of the acid water.

[0013] The technical problem to be solved by the present invention can also be achieved by the following technical solution: the power of the dryer in step (2) is 850w, and the working time of the dryer is 20min.

[0014] The technical problem to be solved by the present invention can also be achieved by the following technical solution: in step (3), the aluminum layer with a thickness of about 100 um is sprayed quickly.

[0015] The technical problem to be solved by the present invention can also be achieved by the following technical solution: the temperature of the diffusion treatment in step (4) is 500-550° C., and the diffusion time is 2-4 hours.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The spraying heating temperature in the present invention is low, and the particles are basically free from oxidation, burning and grain growth. It is suitable for spraying temperature-sensitive materials such as nanocrystalline and amorphous materials, oxidation-sensitive materials such as aluminum and titanium, and phase-change-sensitive materials such as carbide composite materials.

[0018] The coating of the present invention has a small thermal effect on the substrate, so that the thermal stress between the coating and the substrate is reduced. The residual stress between the coatings is small and mainly compressive stress, which is conducive to obtaining a thicker coating.

[0019] The invention has high spraying efficiency, dense coating and low porosity.

[0020] The spraying powder in the present invention can be recovered and reused. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of a cold spraying device in the present invention;

[0022] Figure 2 It is a schematic diagram of the main technical parameters of cold spraying aluminum in the present invention;

[0023] Figure 3 This is the cross-sectional microstructure diagram of the sample diffused at 500°C for different times in the present invention;

[0024] Figure 4This is the cross-sectional microstructure diagram of the sample diffused at 550°C for different times in the present invention;

[0025] Figure 5 Schematic diagram of the thickness of the aluminized layer under different conditions in the present invention;

[0026] Figure 6 This is a relationship diagram between diffusion time, diffusion temperature and thickness of aluminized layer in the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0028] The technical solution provided by the present invention is:

[0029] A surface treatment method for enhancing the friction and thermal fatigue performance of a mold steel surface is used to enhance the friction, wear and thermal fatigue performance of the mold steel surface, comprising the following steps:

[0030] Step (1): first remove the attachments on the surface of the mold steel and polish it to make the surface of the mold steel smooth. Then, soak the mold steel in a 20% sodium hydroxide solution and rinse it with clean water after soaking to ensure that the rinse liquid is completely removed. Pay attention to safety during the removal of the cleaning liquid.

[0031] Step (2), then, soak the cleaned mold steel in a 10% nitric acid solution, rinse with clean water after soaking, pay attention to safety during the cleaning process, and ensure that the rinse liquid and attachments are completely removed, then use a soft cloth to wipe the water droplets on the surface of the mold steel, and put it into a dryer for drying. The power of the dryer is 850w and the working time of the dryer is 20min.

[0032] Step (3), put the dried mold steel into Figure 1 In the cold spraying equipment shown in FIG. Figure 2 After the spraying process parameters shown, cold spraying is carried out to spray an aluminum layer with a thickness of about 100um, and the spraying is rapid.

[0033] Step (4), the mold steel after cold spraying is placed in a resistance furnace for diffusion treatment. The diffusion treatment temperature is 500-550°C and the diffusion time is 2-4 hours. Argon gas is passed for protection during the diffusion process. After the diffusion is completed, the required mold steel is obtained.

[0034] Example 1

[0035] First, take 3 mold steel samples and polish them separately to make the surface of the mold steel smooth. Then, soak the 3 mold steel samples in 20% sodium hydroxide solution. After soaking, rinse them with clean water to ensure that the rinse fluid is completely removed, and pay attention to safety during the removal of the cleaning fluid.

[0036] Then, the three cleaned mold steel samples were immersed in a 10% nitric acid solution and rinsed with clean water. Pay attention to safety during the cleaning process and ensure that the rinse liquid and attachments are completely removed. Subsequently, use a soft cloth to wipe the water droplets on the surface of the mold steel and put it into the dryer for drying. The power of the dryer is 850w and the working time of the dryer is 20min.

[0037] Next, place the three dried mold steel samples into Figure 1 In the cold spraying equipment shown in FIG. Figure 2 After the spraying process parameters shown, cold spraying is carried out to spray an aluminum layer with a thickness of about 100um, and the spraying is rapid.

[0038] The three mold steel samples after cold spraying were placed in a resistance furnace for diffusion treatment. The diffusion treatment temperature was 500°C. The diffusion time of the three mold steel samples was 2, 3 and 4 h, respectively. Argon gas was used for protection during the diffusion process. After the diffusion was completed, the required mold steel was obtained.

[0039] Comparative Example 1

[0040] First, take 3 mold steel samples and polish them separately to make the surface of the mold steel smooth. Then, soak the 3 mold steel samples in 20% sodium hydroxide solution. After soaking, rinse them with clean water to ensure that the rinse fluid is completely removed, and pay attention to safety during the removal of the cleaning fluid.

[0041] Then, the three cleaned mold steel samples were immersed in a 10% nitric acid solution and rinsed with clean water. Pay attention to safety during the cleaning process and ensure that the rinse liquid and attachments are completely removed. Subsequently, use a soft cloth to wipe the water droplets on the surface of the mold steel and put it into the dryer for drying. The power of the dryer is 850w and the working time of the dryer is 20min.

[0042] Next, place the three dried mold steel samples into Figure 1 In the cold spraying equipment shown in FIG. Figure 2 After the spraying process parameters shown, cold spraying is carried out to spray an aluminum layer with a thickness of about 100um, and the spraying is rapid.

[0043] The three mold steel samples after cold spraying were placed in a resistance furnace for diffusion treatment. The diffusion treatment temperature was 550°C. The diffusion time of the three mold steel samples was 2, 3 and 4 h, respectively. Argon gas was passed for protection during the diffusion process. After the diffusion was completed, the required mold steel was obtained.

[0044] Comparison between Example 1 and Comparative Example 1:

[0045] The cross-sectional structures of the samples in Example 1 and Comparative Example 1 and the bonding state between the infiltration layer and the substrate were observed using a metallographic microscope. The results of Example 1 are as follows: Figure 3 As shown, the results of Comparative Example 1 are as follows Figure 4 As shown, from Figure 3 and Figure 4 It can be seen that the sample after cold spraying aluminum can form an aluminized layer after diffusion treatment. The formed aluminized layer is continuous, uniform and dense. The substrate, aluminized layer and aluminum layer have distinct interfaces and are firmly bonded. This is because after the diffusion treatment of the aluminum coating, the iron and aluminum elements will diffuse at a faster rate, causing phase change recrystallization and refining the coating structure. In addition, along with the mutual diffusion of the coating and matrix elements, the residual stress in the coating disappears, and the bonding performance between the two will be further improved.

[0046] The aluminum layer can be formed after low-temperature diffusion treatment. This is because the moving particles impact the surface of the workpiece during cold spraying, and transfer the mechanical energy they carry to the lattice atoms on the surface, which activates and dislocates the lattice atoms to form vacancies. The continuous impact of the moving particles and their mechanical energy increase the vacancy concentration of the surface layer, forming an atomic sparse area and even a diffusion channel, which improves the behavior of the diffusing atoms, resulting in a significant reduction in the diffusion activation energy. Then the diffusion temperature required to have a sufficient infiltration rate must be greatly reduced. Therefore, the required infiltration rate can be achieved after low-temperature diffusion treatment, promoting the mutual diffusion process of iron and aluminum elements, and gradually forming an alloy layer until the alloy layer grows.

[0047] Example 2

[0048] First, take 6 mold steel samples and polish them separately to make the surface of the mold steel smooth. Then, soak the 6 mold steel samples in 20% sodium hydroxide solution. After soaking, rinse them with clean water to ensure that the rinse fluid is completely removed, and pay attention to safety during the removal of the cleaning fluid.

[0049] Then, the 6 cleaned mold steel samples were immersed in a 10% nitric acid solution and rinsed with clean water. Pay attention to safety during the cleaning process and ensure that the rinse liquid and attachments are completely removed. Subsequently, use a soft cloth to wipe the water droplets on the surface of the mold steel and put it into the dryer for drying. The power of the dryer is 850w and the working time of the dryer is 20min.

[0050] Next, the 6 dried mold steel samples were placed in Figure 1 In the cold spraying equipment shown in FIG. Figure 2 After the spraying process parameters shown, cold spraying is carried out, and the spraying thickness is according to Figure 5 The situation shown is divided into three groups according to different times, each group has two thicknesses of aluminum layer, which are sprayed quickly.

[0051] The three groups of mold steel samples after cold spraying were placed in a resistance furnace for diffusion treatment. The diffusion treatment temperature was 500°C. The diffusion time of the three groups of mold steel samples was 2, 3 and 4 h, respectively. Argon gas was passed for protection during the diffusion process. After the diffusion was completed, the required mold steel was obtained.

[0052] Comparative Example 2

[0053] First, take 6 mold steel samples and polish them separately to make the surface of the mold steel smooth. Then, soak the 6 mold steel samples in 20% sodium hydroxide solution. After soaking, rinse them with clean water to ensure that the rinse fluid is completely removed, and pay attention to safety during the removal of the cleaning fluid.

[0054] Then, the 6 cleaned mold steel samples were immersed in a 10% nitric acid solution and rinsed with clean water. Pay attention to safety during the cleaning process and ensure that the rinse liquid and attachments are completely removed. Subsequently, use a soft cloth to wipe the water droplets on the surface of the mold steel and put it into the dryer for drying. The power of the dryer is 850w and the working time of the dryer is 20min.

[0055] Next, the 6 dried mold steel samples were placed in Figure 1 In the cold spraying equipment shown in FIG. Figure 2 After the spraying process parameters shown, cold spraying is carried out, and the spraying thickness is according to Figure 5 The situation shown is divided into three groups according to different times, each group has two thicknesses of aluminum layer, which are sprayed quickly.

[0056] The three groups of mold steel samples after cold spraying were placed in a resistance furnace for diffusion treatment. The diffusion treatment temperature was 550°C. The diffusion time of the three groups of mold steel samples was 2, 3 and 4 h, respectively. Argon gas was passed for protection during the diffusion process. After the diffusion was completed, the required mold steel was obtained.

[0057] Comparison between Example 2 and Comparative Example 2:

[0058] Figure 6The relationship between the thickness of the aluminized layer and the diffusion time and temperature is shown in Figure 1. It can be seen that with the increase of diffusion temperature and the extension of time, the thickness of the surface aluminized layer tends to increase. The thickness of the aluminized layer formed by diffusion at 550°C is thicker than that formed at 500°C. As the temperature increases, the diffusion coefficient of aluminum in iron increases, which is caused by the increase in the diffusion rate of aluminum in the matrix.

[0059] Depend on Figure 5 It can be seen that the average thickness of the aluminized layer ranges from 18.8um to 59.1um. According to the results of the previous theoretical analysis, the appropriate diffusion conditions can be determined by comparing the experimental and calculated values ​​of the thickness of the aluminized layer formed by diffusion at 500℃ and 550℃.

[0060] Depend on Figure 5 It can be seen that the thickness of the diffusion layer after diffusion at 500℃ for 4h is about 36um, while the calculated value corresponds to a diffusion layer thickness of 60-80um, and 36um is not within this range. The experimental results are very different from the theoretical calculations, so diffusion at 500℃ for 4h is not selected as the diffusion treatment condition.

[0061] Depend on Figure 5 It can be seen that the thickness of the diffusion layer after diffusion at 550℃ for 4h is about 59um, while the calculated value corresponds to a diffusion layer thickness of 40-60um. 59um is within this range. The experimental results are consistent with the theoretical calculations, so diffusion at 550℃ for 4h is selected as the diffusion treatment condition.

[0062] In summary, the more suitable conditions for spray diffusion aluminizing are determined as follows: the aluminum coating thickness is about 100um, the diffusion temperature is 550℃, and the diffusion time is about 4h.

[0063] The advantages of cold spraying are as follows:

[0064] (1) The spraying heating temperature is low, and the particles are basically free of oxidation, burning and grain growth. It is suitable for the spraying of temperature-sensitive materials such as nanocrystalline and amorphous materials, oxidation-sensitive materials such as aluminum and titanium, and phase-change-sensitive materials such as carbide composite materials.

[0065] (2) The coating has little thermal effect on the substrate, which reduces the thermal stress between the coating and the substrate. The residual stress between the coatings is small and mainly compressive stress, which is conducive to obtaining a thicker coating.

[0066] (3) High spraying efficiency, dense coating and low porosity.

[0067] (4) Spray powder can be recycled and reused.

[0068] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A surface treatment method for enhancing the friction and thermal fatigue performance of mold steel surface, characterized in that: The steps include: Step (1), first remove the attachments on the surface of the mold steel, and grind it to make the surface of the mold steel smooth, then soak the mold steel in a certain proportion of alkaline water washing liquid, rinse it with clean water after soaking, and ensure that the washing liquid is completely removed; Step (2), then, soak the cleaned mold steel in a certain proportion of acid water, rinse it with clean water after soaking, ensure that the rinse liquid and attachments are completely removed, then wipe the water drops on the surface of the mold steel with a soft cloth, and put it into a dryer for drying; Step (3), placing the dried mold steel into a cold spraying device, setting the spraying process parameters, and then performing cold spraying; Step (4), the mold steel after cold spraying is placed in a resistance furnace for diffusion treatment, and argon gas is passed through the diffusion process for protection. After the diffusion is completed, the required mold steel is obtained.

2. A surface treatment method for enhancing the friction and thermal fatigue performance of mold steel surface according to claim 1, characterized in that: The alkaline water washing liquid described in step (1) adopts a sodium hydroxide solution with a concentration of 20%. Safety should be paid attention to during the removal of the washing liquid.

3. A surface treatment method for enhancing the friction and thermal fatigue performance of mold steel surface according to claim 2, characterized in that: The acid water described in step (2) is a nitric acid solution with a concentration of 10%. Safety should be paid attention to during the removal of the acid water.

4. A surface treatment method for enhancing the friction and thermal fatigue performance of mold steel surface according to claim 3, characterized in that: The power of the dryer in step (2) is 850w, and the working time of the dryer is 20min.

5. A surface treatment method for enhancing the friction and thermal fatigue performance of mold steel surface according to claim 4, characterized in that: In step (3), the aluminum layer with a thickness of about 100 um is sprayed quickly.

6. A surface treatment method for enhancing the friction and thermal fatigue performance of mold steel surface according to claim 5, characterized in that: The temperature of the diffusion treatment in step (4) is 500-550° C., and the diffusion time is 2-4 hours.

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