Method for removing oxide skin of hot stamping part

Abstract

The invention discloses a method for removing an oxide skin of a hot stamping part, which comprises the following steps that an austenite blank is subjected to hot stamping forming and laser cutting to obtain the part, the surface of the part is provided with the oxide skin, the thickness of the part is less than or equal to 1.2 mm, and the thickness of the oxide skin is less than 10 microns; the part is immersed in a pickling solution to be subjected to pickling, and oxide skin on the surface of the part is removed; sequentially carrying out water washing, alkali washing and water washing on the part subjected to acid washing; immersing the part into a chemical solution to form a nano film on the surface of the part; and the part is subjected to tempering treatment, so that the internal residual stress of the part is released, and the hydrogen embrittlement risk is avoided. According to the method for removing the oxide skin of the hot stamping part, by controlling the pickling process and the subsequent tempering treatment, the part is prevented from being excessively pickled, the hydrogen embrittlement risk is reduced, and meanwhile the deformation problem caused by shot blasting treatment is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot stamping part processing, in particular to a method for removing oxide skin of a hot stamping part. BACKGROUND

[0002] The hot stamping process can produce high-strength and complex-geometry parts by heating the steel plate to the austenite zone and rapidly transferring it to the mold for forming and quenching. However, during hot forming, the bare steel plate is prone to react with oxygen at high temperature to form an oxide skin. The oxide skin affects the quality of the part surface and subsequent painting, so in the post-processing process, the oxide skin needs to be removed.

[0003] In industry, shot blasting is usually used to treat the oxide skin on the surface of parts with large thickness, but for thin parts, shot blasting can easily cause surface indentation, warping or overall deformation of the parts, significantly affecting product performance and dimensional accuracy.

[0004] Pickling is a commonly used method for removing oxide skin, which uses chemical reaction between acid and oxide layer to dissolve and separate the oxide. Pickling is widely used in surface treatment of steel coils, steel strips, steel pipes and other primary metal materials, however, traditional pickling process has some drawbacks when applied to three-dimensional complex-shaped or formed metal parts.

[0005] Pickling mainly targets two-dimensional metal plates or strips, and for parts that have been three-dimensionally formed, due to their complex shape, indentation and dead angles, the acid solution is difficult to uniformly contact the entire surface, and local cleaning may not be complete. During pickling, the acid solution not only dissolves the oxide skin, but also may cause corrosion of the metal substrate to some extent, especially if it is not neutralized and dried in time after pickling, which can easily cause secondary rust on the part surface, affecting subsequent processes.

[0006] Moreover, hydrogen molecules can penetrate into the metal lattice during pickling, which can easily induce hydrogen embrittlement. Hydrogen embrittlement not only weakens the toughness and strength of the material, but also can cause delayed fracture of the part during use, seriously affecting the reliability and safety of the product. SUMMARY

[0007] To overcome the above shortcomings, the present application aims to provide a method for removing oxide skin of a hot stamping part, which controls the pickling process and subsequent tempering treatment to prevent the part from being overpickled and reduce the risk of hydrogen embrittlement, while avoiding the deformation problem caused by shot blasting.

[0008] Technical solution: The present application discloses a method for removing oxide skin of a hot stamping part, comprising the following steps:

[0009] The austenitic blank is hot-stamped to form a part, the part is laser cut, the surface of the part has an oxide skin, the thickness of the part is less than or equal to 1.2 mm, and the thickness of the oxide skin is less than 10 um;

[0010] The part is immersed in an acid pickling solution for pickling to remove the oxide skin on the surface of the part;

[0011] The pickled part is sequentially subjected to water washing, alkali washing, and water washing;

[0012] The part is immersed in a chemical solution to form a nanometer film on the surface of the part;

[0013] The part is subjected to tempering treatment to release the residual stress inside the part and avoid hydrogen embrittlement risk;

[0014] The time interval between the acid pickling and the water washing is less than 60 s, the time interval between the alkali washing and the water washing is less than 60 s, and the time interval from the formation of the nanometer film on the surface of the part to the tempering treatment is less than 8 h.

[0015] Further, the concentration of hydrochloric acid in the acid pickling solution ranges from 10% to 20%, the concentration of the slow-release agent is 1-5 g / L, and the acid pickling time is 1-5 min.

[0016] Further, in the step of "immersing the part in an acid pickling solution for pickling", the part is also cleaned by ultrasonic waves, wherein the ultrasonic power is 1-3 KW.

[0017] Further, the alkali washing solution includes sodium hydroxide, and the concentration of the sodium hydroxide is 1-5%.

[0018] Further, in the step of "immersing the part in a chemical solution to form a nanometer film on the surface of the part", the chemical solution at least includes one or both of sodium molybdate and sodium silicate, the concentration of the sodium molybdate is 1-10%, the concentration of the sodium silicate is 1-10%, the chemical solution also includes a flash rust inhibitor, the concentration of the flash rust inhibitor is 0.1-5%, and the thickness of the nanometer film is 20-200 nm.

[0019] Further, after the step of "immersing the part in a chemical solution to form a nanometer film on the surface of the part", the part on which the nanometer film is formed is taken out of the alkali washing tank, and the part is blown dry by hot air with a temperature of 60-90°C for 30 min.

[0020] Further, in the step of "tempering the part", the tempering temperature is 150-200°C, and the tempering time is 10-30 min.

[0021] Further, after the step of "tempering the part", the part is also subjected to oil spraying treatment to avoid rusting of the part.

[0022] The beneficial effects of the present application are:

[0023] (1) The present application combines pickling solution and ultrasonic wave for cleaning, thereby effectively stripping the thin layer of oxide scale on the surface of hot stamping parts, while avoiding over-corrosion or damage to the surface of the parts;

[0024] (2) The present application improves the pickling process. To avoid rusting after pickling, water washing, alkali washing and secondary water washing are sequentially performed after pickling, thereby neutralizing residual acid solution, removing attached impurities and improving the cleanliness of the surface of the parts, providing a good foundation for subsequent processing;

[0025] (3) A uniform and dense nano film is formed on the surface of the parts, effectively preventing rusting problems that may occur during storage and transportation of the parts;

[0026] (4) The present application effectively releases internal stress caused by the penetration of hydrogen atoms during the pickling process by adding a tempering step, thereby reducing the risk of hydrogen embrittlement of the parts. BRIEF DESCRIPTION OF DRAWINGS

[0027] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. In addition, the shapes and scale sizes of the components in the drawings are only illustrative and are used to help understand the present application and are not specific limitations on the shapes and scale sizes of the components of the present application. Those skilled in the art can select various possible shapes and scale sizes to implement the present application according to specific circumstances under the teaching of the present application. In the drawings:

[0028] Figure 1 Metallographic display of the part after removing the oxide scale by the method of the present application;

[0029] Figure 2 Metallographic display of the part after removing the oxide scale by the prior art shot blasting treatment;

[0030] Figure 3 Schematic diagram of the part after pickling according to the prior art;

[0031] Figure 4 Schematic diagram of the part after nano film treatment according to the present application;

[0032] Figure 5 Comparison diagram of the dimensional change of the part after pickling and shot blasting;

[0033] Figure 6 Surface resistance test diagram of the part after pickling and film treatment;

[0034] Figure 7 Surface resistance test diagram of the part after shot blasting treatment. DETAILED DESCRIPTION

[0035] The present application will be further illustrated in conjunction with the accompanying drawings and specific embodiments.

[0036] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances. The embodiments will be described below according to the overall structure of the present application.

[0037] The present application provides a method for removing the oxide scale of hot stamping parts, comprising the following steps:

[0038] The austenitic blank is hot stamping formed, and the part is obtained after laser cutting, the surface of the part has an oxide scale, the thickness of the part is less than or equal to 1.2mm, and the thickness of the oxide scale is less than 10um;

[0039] The part is immersed in a pickling solution for pickling to remove the oxide scale on the surface of the part;

[0040] The pickled part is sequentially washed with water, alkali and water;

[0041] The part is immersed in a chemical solution to form a nano film on the surface of the part;

[0042] The part is tempered to release the residual stress inside the part and avoid the risk of hydrogen embrittlement.

[0043] Specifically, during the hot stamping forming process, the austenitic blank reacts with oxygen in the air at high temperature to rapidly form an oxide scale on the surface, and the oxide scale is usually composed of a mixture of FeO, Fe3O4 and Fe2O3 and other iron oxides. The present application uses a pickling solution to chemically treat the part, reacts the acidic components in the pickling solution with the oxide scale to generate soluble metal salts and desorb, thereby achieving the purpose of removing the oxide scale. At the same time, the time and temperature of pickling are controlled to avoid excessive corrosion of the blank.

[0044] To prevent the pickling solution of the residual liquid after pickling from causing secondary corrosion to the surface of the part, the part after pickling needs to be sequentially subjected to water washing, alkali washing and re-water washing treatment. The water washing can be divided into multiple water washing to remove the pickling solution remaining on the surface of the part to the greatest extent, and the alkali washing solution after alkali washing. The preliminary water washing can take away most of the pickling solution remaining, and the alkali washing can neutralize the acidic substances adhering to the metal surface through the alkaline solution and remove the impurities generated in the pickling process at the same time, and then the water washing is performed again, so as to ensure that the surface of the part is clean and free of residual pickling solution or alkali washing solution, and prevent corrosion and rusting of the surface of the part. The alkali washing solution at least includes sodium hydroxide, and the concentration thereof is between 1-5%. Preferably, the time interval between the water washing after pickling and the water washing after alkali washing is less than 60s, and the time interval between the water washing after alkali washing and the water washing after pickling is preferably less than 30s.

[0045] After the part is cleaned, it is further immersed in a chemical solution to form a nanometer thin film on the surface, that is, to form a uniform and dense passivation layer on the metal surface. The passivation layer can effectively seal the active sites on the surface of the part, prevent oxygen, moisture and other corrosive media from directly contacting the surface of the part, and thus improve the corrosion resistance and long-term stability of the part. After the nanometer thin film is formed on the surface of the part, the part is preferably tempered within 8h.

[0046] Finally, the part is subjected to tempering treatment, the part is heated to 150-200℃, and the tempering time is 10-30min. The tempering treatment can release the stress generated in the part due to hydrogen penetration during pickling, thereby reducing the risk of hydrogen embrittlement. In addition, tempering can also promote the density of the nanometer thin film on the surface of the part, thereby improving the physical stability thereof. The surface of the part is further subjected to oil spraying treatment to form an oil film, which provides physical isolation protection, prevents water vapor and corrosive gas from directly contacting the surface of the part during storage or transportation, and improves the rust resistance of the part.

[0047] Compared with the physical shot blasting peeling method, the pickling can remove the oxide layer adhering to the surface of the part, and is more suitable for hot stamping parts with complex shapes and can also ensure that the quality of the surface of the part is uniform and consistent without deformation, thereby providing a good foundation for subsequent processes. In the present application, the pickling solution at least includes hydrochloric acid, and the concentration of the hydrochloric acid is 10-20%. The pickling solution also includes a slow-release agent, and the concentration of the slow-release agent is 1-5g / L. The pickling time is controlled within 1-5min, so as to reduce the risk of hydrogen embrittlement as much as possible.

[0048] Preferably, since in the process of hot stamping, the surface of the part tends to form a relatively dense oxide skin with strong adhesion, it is difficult to dissolve only by pickling. Therefore, when the part is immersed in the pickling solution for pickling, the part is cleaned at the same time by using ultrasonic waves, which further promotes the falling off of the oxide skin. The ultrasonic waves are located on both sides of the tank wall of the pickling tank, and the ultrasonic power is 1-3KW. The high-frequency vibration in the pickling solution induces "cavitation effect", which destroys the adhesion structure of the oxide skin, so that the oxide skin falls off from the surface of the part.

[0049] Further, in the step of "immersing the part in a chemical solution to form a nanometer film on the surface of the part", the chemical solution contains at least one or both of sodium molybdate and sodium silicate, wherein the concentration of sodium molybdate is 1-10%, the concentration of sodium silicate is 1-10%, and the chemical solution also contains a flash rust inhibitor with a concentration of 0.1-5% to prevent the part from rusting quickly during the film forming process. After the part is immersed in the chemical solution, a nanometer film with a thickness of 20-200nm can be formed on the metal surface, thereby improving the rust resistance of the part.

[0050] Preferably, after the nanometer film is formed on the surface of the part, in order to ensure that the film layer can be fixed densely and uniformly on the surface of the part, hot air with a temperature of 60-90℃ is used to dry the part, and the drying time is 30min. After the nanometer film is initially formed, it needs to be dried in time, otherwise the solvent or moisture in the residual liquid may not evaporate uniformly, which may cause the nanometer film to shrink or wrinkle, and further cause uneven distribution of the film layer, uneven thickness or local failure. The present application promotes the rapid and uniform dehydration of the nanometer film by constant temperature hot air drying, thereby significantly improving the structural stability and adhesion of the nanometer film.

[0051] Further, since the part may absorb trace amounts of hydrogen atoms during pickling, the part may have problems such as hydrogen embrittlement or fracture during subsequent use. Therefore, the part needs to be tempered and oiled again. Specifically, the part needs to be placed in a hot air furnace or oven and heated to 150-200℃ for 10-30min.

[0052] After the tempering treatment is completed, the part is oiled to form a protective film on the surface of the part, which is aimed at isolating air, moisture and other corrosive gases from contacting the part to prevent the part from rusting.

[0053] The following specific examples are used to further illustrate the application:

[0054] Example 1

[0055] A 1.0mm blank is hot stamped, and the piece after hot stamping is laser cut to obtain a part;

[0056] The part is put into the pickling tank for pickling to remove the oxide scale, wherein the concentration of hydrochloric acid is 15%, the concentration of the buffer is 2g / L, and the pickling time is 5 minutes;

[0057] Then the pickled part is washed with water for multiple times to remove the residual pickling solution on the surface, and then is put into a 1% concentration of sodium hydroxide solution to neutralize the residual small amount of pickling solution;

[0058] Then the alkaline washed part is washed with water for multiple times to remove the residual alkaline solution;

[0059] Then the part is soaked in a mixed solution of 60°C, 3% concentration of sodium molybdate and 3% concentration of anti-flash rust agent for 30 seconds;

[0060] After the part is taken out, the part is dried with hot air of 80°C for 10 minutes;

[0061] Then the part is tempered at a temperature of 180 degrees for 20 minutes;

[0062] Finally, the part is treated with oil spraying.

[0063] Example Two

[0064] First, the 0.8mm blank is hot stamped, and the hot stamped sheet is laser cut to obtain the part;

[0065] Then the part is put into the pickling tank for pickling to remove the oxide scale, wherein the concentration of hydrochloric acid is 10%, the concentration of the buffer is 5g / L, and the ultrasonic power is 1.5KW, and the pickling time is 2 minutes. Through the combination of ultrasonic and pickling, the removal of the oxide scale can be accelerated, and the pickling time and the risk of hydrogen embrittlement can be reduced;

[0066] Then the pickled part is washed with water for multiple times to remove the residual pickling solution on the surface, and then is put into a 2% concentration of sodium hydroxide solution to neutralize the residual small amount of pickling solution;

[0067] Then the alkaline washed part is washed with water for multiple times to remove the residual alkaline solution;

[0068] Then the part is soaked in a mixed solution of 40°C, 10% concentration of sodium molybdate, 5% concentration of sodium silicate and 2% concentration of anti-flash rust agent for 10 seconds;

[0069] After the part is taken out, the part is dried with hot air of 80°C for 30 minutes;

[0070] Then the part is tempered at a temperature of 180 degrees for 20 minutes;

[0071] Finally, the part is treated with oil spraying.

[0072] The prior art methods for treating the surface scale of a part mainly include shot blasting and pickling, as shown in Figure 1 and Figure 2 The surface of a part treated by shot blasting still has some scale not removed completely, and the surface of the part has slight deformation, while the surface of a part treated by the method of the present application has almost no scale. Further referring to Figure 5 , after the size of a part treated by pickling and a part treated by shot blasting is measured respectively, the part treated by pickling has no deformation and change in size, while the part treated by shot blasting has a change in size of about 0.5 mm, so shot blasting is not used for a part with a thin thickness.

[0073] As shown in Figure 3 and Figure 4 , Figure 3 A part treated by a common pickling step, after direct pickling and multiple water washing, the surface of the part is active and has no film protection, and rust will be produced on the surface of the part in a short time, Figure 4 A part treated by the method of the present application, after the part is treated by a nano film, a protective film is formed on the surface of the part, so rust will not be produced. Further referring to Figure 6 and Figure 7 , after a part is pickled by the method of the present application, the surface resistance of the part is 0.313 mΩ, but if the part is treated by shot blasting, the surface resistance of the part is 7.825 mΩ, the different surface resistances of the parts treated by the two methods depend on whether the scale on the surface of the part is removed completely, the more scale remains, the greater the surface resistance will be. Further, the smaller the surface resistance of the part is, the better the welding performance of the part will be, usually the surface resistance of a processed part needs to be less than 1.5 mΩ, but the surface resistance of a part treated by shot blasting to remove scale cannot meet the requirement.

[0074] So far, the technical solution of the present application has been described in combination with the preferred embodiments shown in the drawings, but those skilled in the art can easily understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without departing from the principles of the present application, and the technical solutions after the changes or replacements will fall within the protection scope of the present application.

Claims

1. A method of removing scale from a hot stamped part, characterized by, The method comprises the following steps: hot stamping forming an austenitic blank, and laser cutting to obtain a part, the surface of the part having an oxide skin, the thickness of the part being less than or equal to 1.2 mm, and the thickness of the oxide skin being less than 10 um; immersing the part in an acid pickling solution to remove the oxide skin on the surface of the part; sequentially washing the part after acid pickling, alkali washing, and washing with water; immersing the part in a chemical solution to form a nano film on the surface of the part; tempering the part to release the residual stress in the part and avoid hydrogen embrittlement risk; wherein the time interval between acid pickling and washing with water is less than 60 s, the time interval between alkali washing and washing with water is less than 60 s, and the time interval from forming the nano film on the surface of the part to tempering is less than 8 h.

2. The method of removing scale from a hot stamped part of claim 1, wherein, The concentration of hydrochloric acid in the acid pickling solution ranges from 10% to 20%, the concentration of the slow-release agent ranges from 1 g / L to 5 g / L, and the acid pickling time ranges from 1 min to 5 min.

3. The method of removing scale from a hot stamped part of claim 1, wherein, In the step of "immersing the part in an acid pickling solution to perform acid pickling", the part is also cleaned by ultrasonic waves, wherein the power of the ultrasonic waves ranges from 1 KW to 3 KW.

4. The method of removing scale from a hot stamped part of claim 1, wherein, The alkali washing solution comprises sodium hydroxide, and the concentration of the sodium hydroxide ranges from 1% to 5%.

5. The method of removing scale from a hot stamped part of claim 1, wherein, In the step of "immersing the part in a chemical solution to form a nano film on the surface of the part", the chemical solution at least comprises one or both of sodium molybdate and sodium silicate, the concentration of the sodium molybdate ranges from 1% to 10%, the concentration of the sodium silicate ranges from 1% to 10%, the chemical solution further comprises a flash rust inhibitor, the concentration of the flash rust inhibitor ranges from 0.1% to 5%, and the thickness of the nano film ranges from 20 nm to 200 nm.

6. The method of removing scale from a hot stamped part of claim 1, wherein, After the step of "immersing the part in a chemical solution to form a nano film on the surface of the part", the part on which the nano film is formed is taken out of the alkali washing tank, and the part is blown dry by hot air at a temperature ranging from 60°C to 90°C for 30 min.

7. The method of removing scale from a hot stamped part of claim 1, wherein, In the step of "tempering the part", the tempering temperature ranges from 150°C to 200°C, and the tempering time ranges from 10 min to 30 min.

8. The method of removing scale from a hot stamped part of claim 1, wherein, After the step of "tempering the part", the part is also subjected to oil spraying to avoid rusting.

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