Manufacturing method and application of hot isostatic pressing anti-corrosion steel mold

Abstract

The invention belongs to the technical field of forming and manufacturing of energetic materials, and particularly relates to a manufacturing method and application of a hot isostatic pressing anti-corrosion steel mold. A preparation method of a hot isostatic pressing anti-corrosion steel mold comprises the following steps that S1, raw material powder is prepared, specifically, alloy powder is prepared, and raw material components comprise, by mass, 1%-3% of C, 30%-35% of Cr, 10%-15% of W, 1%-2% of Si, 0.5%-2% of Fe and 45%-60% of Co; s2, powder filling and degassing are conducted, specifically, a steel ladle sleeve is prepared, the powder and the steel mold are placed in the steel ladle sleeve, and sealing welding is conducted after vacuumizing; s3, hot isostatic pressing, wherein the sheath is placed in a hot isostatic pressing environment for heat preservation and pressure maintaining; and S4, heat treatment. According to the steel mold manufactured through the method, Co occupies a main body, carbides of Cr and W are evenly dispersed and distributed in cobalt-based alloy, and corrosion resistance and abrasion resistance are excellent. And an optimized hot isostatic pressing forming process is adopted, and compared with a forming mold used at present, the manufactured mold has more excellent corrosion resistance and wear resistance and is more suitable for manufacturing of PBX raw materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of forming manufacturing technology of energetic materials, and particularly relates to a hot isostatic pressing anticorrosion steel mold manufacturing method and application. BACKGROUND

[0002] As a key tool in the pressing process, the performance of the mold directly determines the dimensional accuracy, density uniformity and final use performance of the energetic material product, and has a crucial influence on the safety and forming quality of the entire manufacturing process. In the forming process of energetic materials such as high polymer bonded explosives, molds are generally used to press the powder raw materials. At present, high-strength structural steel such as 42CrMo is widely used as mold material in the industry. This kind of steel can withstand the pressing pressure required for forming under conventional process conditions due to its high room temperature strength, good toughness and certain processing performance, which meets the basic production needs.

[0003] With the continuous development of energetic material formula systems, the service environment of the mold in actual production has put forward more severe challenges. PBX raw materials often contain corrosive components such as chloride, nitrate and sulfate. Under the action of temperature and pressure cycles in the pressing process, the corrosion activity of these components is significantly enhanced, which can sharply accelerate the corrosion reaction of the mold steel matrix. This causes corrosion pits and rust layers to gradually appear on the surface of the mold cavity, which significantly increases the surface roughness and enhances the adhesion with the raw materials. As a direct result, the formed products are prone to defects such as scratches, missing corners, and sticking to the mold, the dimensional accuracy of the products is difficult to guarantee, the batch quality stability decreases, and in severe cases, the products may even be scrapped, which significantly increases the production cost. At the same time, corrosion also greatly shortens the service life of the mold. Even if the surface is repaired, it is often impossible to restore the use due to the size of the cavity being out of tolerance or the corrosion being too deep, and the mold needs to be replaced as a whole. Therefore, the corrosion failure problem of the traditional mold steel has become a core bottleneck that restricts the stability of the forming quality of energetic materials and the long-term service of the mold.

[0004] To cope with the above challenges, the current forming process puts forward higher requirements for the comprehensive performance of the mold. The ideal mold material not only needs to have excellent corrosion resistance to resist the corrosion of corrosive media for a long time and maintain the smoothness and stability of the cavity surface, but also must have high wear resistance and fatigue resistance to withstand the friction and wear and alternating stress in long-term repeated pressing, prolong the fault-free operation period, and avoid affecting the consistency of the product due to premature deformation of the cavity.

[0005] Under this background, it is an urgent need in the field of energetic material forming equipment to develop a mold that can simultaneously meet the requirements of excellent corrosion resistance, high wear resistance and long service life.

[0006] Hot isostatic pressing technology, as an advanced process for preparing fully dense materials through high temperature and high pressure, provides the possibility for the development of new composite molds, which can theoretically solve the balance problem of corrosion resistance and wear resistance. However, when the existing HIP technology is applied to mold manufacturing, there are still problems such as single material system selection, and insufficient matching of process parameters and specific requirements of PBX material forming, which leads to the difficulty of targeted optimization of mold performance. Therefore, it is urgent to carry out material innovation and process optimization based on HIP technology, to fundamentally break through the performance limitations of traditional mold steel by designing high corrosion-resistant alloy system and controlling composite structure, and to provide reliable technical support for improving the forming quality and production efficiency of energetic materials.

[0007] In addition, on the one hand, there are differences in the understanding of those skilled in the art; on the other hand, the inventors have studied a large number of literatures and patents when making the invention, but due to the limited space, all the details and contents are not listed in detail, which does not mean that the invention does not have these prior art characteristics, on the contrary, the invention has all the characteristics of the prior art, and the applicant reserves the right to add relevant prior art in the background art. SUMMARY

[0008] The present application belongs to the field of forming and manufacturing technology of energetic materials, and specifically relates to a hot isostatic pressing corrosion-resistant steel mold and a preparation method thereof. The present application provides a preparation method of a corrosion-resistant steel mold for PBX forming. The corrosion resistance of the steel mold is effectively improved. The service life of the steel mold is greatly improved.

[0009] In view of the above technical problems, one of the purposes of the present application is to provide a preparation method of a hot isostatic pressing corrosion-resistant steel mold, comprising the following steps: S1 Preparation of raw material powder: preparing alloy powder, wherein the raw material components include 1-3% C, 30-35% Cr, 10-15% W, 1-2% Si, 0.5-2% Fe, and 45-60% Co in terms of mass fraction; S2 Powder filling and degassing: preparing a ladle cover, placing the powder and the steel mold in the ladle cover, and sealing after vacuumizing; S3 Hot isostatic pressing: placing the cover in a hot isostatic pressing environment for heat preservation and pressure preservation; S4 Heat treatment.

[0010] According to a preferred embodiment, in S3, the pressure preservation condition is 120-150 Mpa.

[0011] According to a preferred embodiment, in S3, the heat preservation condition is 1120-1150℃.

[0012] According to a preferred embodiment, in S2, the vacuum degree of vacuumizing in the cover is 0.1-0.01 Pa.

[0013] According to a preferred embodiment, in S2, the cladding is selected from one of low carbon steel, stainless steel, cobalt-based alloy.

[0014] According to a preferred embodiment, in S2, vacuumizing is performed at a temperature range of 50-200℃.

[0015] According to a preferred embodiment, in S4, the heat treatment comprises the following step: quenching at 1100-1150℃.

[0016] According to a preferred embodiment, in S1, the raw material components are selected from the following group: 2% C, 30% Cr, 15% W, 1% Si, 2% Fe, 50% Co; 2% C, 30% Cr, 5% W, 1% Si, 2% Fe, 60% Co; or 2% C, 20% Cr, 15% W, 1% Si, 2% Fe, 60% Co.

[0017] One of the purposes of the present application is also to provide a hot isostatic pressing corrosion-resistant steel mold, which is prepared based on the above preparation method.

[0018] According to a preferred embodiment, the mold is provided with a corrosion-resistant layer with a thickness of not less than 3 mm, and the strength of the corrosion-resistant layer is not less than 2100 MPa.

[0019] According to a preferred embodiment, the preparation method further comprises: S5 precisely machining the steel mold to the accurate size. Preferably, the precise machining method comprises one or more of turning, grinding, mechanical polishing, and chemical polishing.

[0020] One of the purposes of the present application is also to provide the application of the hot isostatic pressing corrosion-resistant steel mold prepared based on the above preparation method in the forming manufacturing of high polymer bonded explosives.

[0021] The beneficial effects of the present technical solution are: As Figure 1 It can be known that the phase composition of the mold corrosion-resistant layer is mainly Co and CrC. Figure 2 The phase color can know the distribution of each microstructure. The corrosion-resistant layer prepared by the isostatic pressing process has a main body of Co, which has a corrosion-resistant effect; the carbide of Cr is uniformly dispersed in the cobalt-based alloy, which improves the wear resistance. The steel mold has a corrosion-resistant layer with a thickness of more than 3 mm, which still has a PBX corrosion-resistant effect after wear (Table 3, Figure 4 ). The corrosion-resistant layer of the steel mold optimized by the isostatic pressing process has a strength of 2100 MPa, an impact toughness of 21 J, and a surface wear resistance (ASTM G65 wear volume loss) of 7.5 mm 3After 72 h PBX corrosion and salt spray test, the steel mold does not appear obvious corrosion.

[0022] It can be seen that the steel mold prepared by the application is mainly occupied by Co, and the carbides of Cr and W are uniformly dispersed in the cobalt-based alloy, and the corrosion resistance and wear resistance are excellent. By adopting the optimized hot isostatic pressing forming process, the mold prepared has more excellent corrosion resistance and wear resistance than the currently used forming mold, and is more suitable for the manufacture of PBX raw materials.

[0023] The cobalt-based alloy in the corrosion-resistant layer is the main body, which can form a dense and stable passivation film, and the specific Cr and W carbides can improve the wear resistance of the material and reduce surface damage (such as scratches), thereby indirectly maintaining the integrity of the passivation film. The metal matrix is isolated from the external corrosive medium, preventing the corrosive medium from reacting with the metal, thereby playing a protective role. The thickness of the passivation film can reach 3mm and has self-repairing ability. Even in some cases where the passivation film is slightly damaged, in the presence of oxygen, the cobalt on the surface of the metal will rapidly oxidize again, allowing the passivation film to be repaired and continue to play a protective role. Thus, the corrosion resistance of the mold corrosion-resistant layer is enhanced. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy analysis (XPS) spectra of the hot isostatic pressing composite sample involved in Example 1, wherein, Figure 1 A is the XRD spectrum, Figure 1 B is the XPS spectrum; Figure 2 The energy spectrum analysis module (EDS) and electron backscatter diffraction instrument (EBSD) test result graph of the hot isostatic pressing composite sample involved in Example 1; Figure 3 The corrosion-resistant layer depth test of the hot isostatic pressing composite sample involved in Example 1; Figure 4 The corrosion resistance test of the hot isostatic pressing composite sample involved in Example 1 and the sample of Comparative Example 1; Figure 5 The mechanical property and wear resistance test of the hot isostatic pressing composite sample involved in Example 1. DETAILED DESCRIPTION

[0025] In the description of the application, the terms are used only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. In the description of the application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0026] The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents or instruments used are commercially available reagents and materials unless the manufacturer is not specified; the specific conditions are not specified in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer, and the source of the raw materials used in the present application is not limited, and the raw materials used in the present application are commercially available unless otherwise specified.

[0027] Example 1 This example relates to a method for preparing a material for a hot isostatic pressing corrosion-resistant steel mold.

[0028] The preparation method comprises the following steps: (1) Preparation of raw material powder: alloy powder is prepared by gas atomization process, and the raw material components include 2wt% C, 30wt% Cr, 15wt% W, 1wt% Si, 2wt% Fe, and 50wt% Co; (2) Powder filling and degassing: a ladle cover is prepared, and the powder and the steel mold are placed in the ladle cover, and after vacuumizing at a certain temperature, it is sealed and welded; (3) Hot isostatic pressing: the cover is placed in a hot isostatic pressing environment for heat preservation (1130°C) and pressure preservation (130 MPa) for 3 hours, since the inside of the cover is a vacuum environment, the powder is densified under high temperature and high pressure environment and simultaneously metallurgically combined with the steel mold; (4) After heat treatment, the precise steel mold size is obtained by precise mechanical machining.

[0029] Example 2 This example is consistent with the preparation method described in Example 1, and the difference is that the hot isostatic pressing condition of (3) is heat preservation (1100°C) and pressure preservation (130 MPa) for 3 hours in the environment.

[0030] Example 3 This example is consistent with the preparation method described in Example 1, and the difference is that the hot isostatic pressing condition of (3) is heat preservation (1180°C) and pressure preservation (130 MPa) for 3 hours in the environment.

[0031] Example 4 This example is consistent with the preparation method described in Example 1, and the difference is that the hot isostatic pressing condition of (3) is heat preservation (1130°C) and pressure preservation (110 MPa) for 3 hours in the environment.

[0032] Example 5 This example is consistent with the preparation method described in Example 1, and the difference is that the hot isostatic pressing condition of (3) is heat preservation (1130°C) and pressure preservation (150 MPa) for 3 hours in the environment.

[0033] Example 6 The preparation method of this example is consistent with that described in Example 1, except that the raw material components of (1) include 2wt% C, 30wt% Cr, 5wt% W, 1wt% Si, 2wt% Fe, and 60wt% Co.

[0034] Example 7 The preparation method of this example is consistent with that described in Example 1, except that the raw material components of (1) include 2wt% C, 20wt% Cr, 15wt% W, 1wt% Si, 2wt% Fe, and 60wt% Co.

[0035] The technical solutions of Examples 1-6 are shown in Table 1. The technical solutions of Examples 1, 7, and 8 are shown in Table 1.

[0036] Table 1

[0037] Table 2

[0038] Comparative Example 1 Comparative Example 1 is a mold without hot isostatic pressing compounding.

[0039] Test Example (I) Structure diagram of corrosion-resistant layer The sample after hot isostatic pressing compounding in Example 1 was detected by XRD and XPS, and the XRD and XPS spectra are shown in Figure 1 Figure 1 In the XRD spectrum of a, the main crystalline phases of the composite layer are metallic cobalt (Co) and chromium carbide (CrC). The three sharp peaks of Co, especially the highest peak, indicate that Co is the main phase or base bonding phase in the composite layer, and its crystallinity is very good. The peaks are relatively sharp, indicating that the grains in the composite layer are complete and the crystal structure is complete.

[0040] Figure 1 The XPS spectrum of b identifies various elements stably present in the composite layer, and the results show that C, Cr, W, Si, Fe, Co, and O are stably present in the composite layer. In combination with Figure 1 a, it is confirmed again that CrC hard phase exists.

[0041] (II) Micro-area comprehensive analysis The composite layer of Example 1 was microscopically detected by EDS+EBSD.

[0042] As Figure 2 can be seen, the distribution of each microstructure, the corrosion-resistant layer prepared by this isostatic pressing process has a Co main body, which plays a corrosion-resistant role, and the chromium carbide is uniformly dispersed in the cobalt-based alloy, which improves the wear resistance.​

[0043] (III) Performance Test The corrosion resistance was tested by high temperature salt spray test, in which the sample was placed in a salt spray corrosion environment at 80°C, and the corrosion of the sample was observed.

[0044] Figure 3 The composite layer of Example 1 is shown According to The sample prepared in Example 4 showed point-like corrosion marks after 72 h of corrosion at 120°C in PBX, and the PBX corrosion resistance was lower than that of the other examples with higher isostatic pressing pressure (none of which corroded after 96 h). The pressing temperature had a large effect on the mechanical properties of the product, such as strength, impact toughness, and surface wear resistance, and the mechanical properties of the samples at different temperatures are shown in Table 1. Figure 5 The final preferred isostatic pressing pressure is 120-150 Mpa, and the temperature is 1120-1150°C.

[0045] Examples 1, 6, and 7 used the same hot isostatic pressing process, and the wear resistance of the samples (ASTM G65 wear volume loss) was 8.5 mm 3 , 12 mm 3 , and 11.5 mm 3 , respectively. This result shows that a specific content of Cr and W carbide components can improve the wear resistance of the material. Under the premise of a constant hot isostatic pressing process, the wear resistance of the material differs, and the decisive factor is the specific ratio of the content of the carbide components. Example 1 exhibits the best wear resistance (wear volume loss of 8.5 mm 3 ), and the wear volume of Examples 6 and 7 significantly increases, which shows that there is an optimal range of Cr and W carbide content that can maximize the improvement of wear resistance. The component content of Example 1 is likely to be most conducive to the formation of a carbide strengthening phase with high hardness and high stability, and to achieve an ideal state of dispersion distribution in the matrix, thereby most effectively resisting abrasive wear; and a deviation (too high or too low) in the component content can lead to deterioration of the quantity, morphology, or distribution of the strengthening phase, resulting in a noticeable decrease in wear resistance. Therefore, by precisely regulating the Cr and W carbide, the wear resistance of the material can be optimized.

[0046] Figure 3The results of the corrosion depth test of the composite layer of Example 1 are shown. The hardness test curve of the material shows that the hardness value is stably maintained at a high level of about 700 HV in the range of about 3.5 mm in depth from the surface layer to the inside, forming a wide range of hardness platform. This result clearly shows that the corrosion layer is not only a surface hardness, but also a hard composite material with uniform overall performance; its high and uniform hardness is due to the uniform dispersion of hard phases such as chromium carbide in the cobalt-based binder phase, which ensures that the material has excellent and durable wear resistance and compressive strength, and can effectively resist wear and deformation during long-term service. Combined with its corrosion resistance, the material successfully breaks through the performance bottleneck of traditional die steel, providing a key guarantee for realizing the long-term stability of energetic material product size and significantly extending the service life of the mold.

[0047] Table 3 is a statistical table of the corrosion resistance of the examples and the comparative examples after wear. Figure 4 The corrosion resistance of Example 1 and Comparative Example 1 was tested. The comparison results show that the example material has significant corrosion resistance whether it is for PBX powder or high temperature salt spray. Specifically, the example remains intact within 72 hours and only has a small corrosion spot at 96 hours; while the comparative example has large area corrosion at 24 hours and continues to intensify over time. Further from Table 3, even if the surface wear depth of the example reaches 0.5 mm, it can still be free of corrosion in the PBX raw material at 120°C within 72 hours, while the comparative example rapidly corrodes even in the non-worn state.

[0048] The corrosion-resistant reinforced steel mold manufactured by the example method can continue to be oxidized in air to form a dense passivation film even after wear and tear, and continue to play a protective role. Shallow wear does not damage the corrosion resistance of the surface of the steel mold. It can be said that the corrosion resistance of the example material does not depend on the original surface state, but is due to the intrinsic properties of the overall material. The uniform composite structure formed by the hard phase and the binder phase can still provide continuous and effective corrosion protection even after wear, so that the mold cavity size and surface quality can remain stable even after normal wear during long-term service, fundamentally breaking through the corrosion failure bottleneck of traditional mold materials.

[0049] As shown in Figure 5 , the wear resistance (ASTM G65 wear volume loss) of Example 1 is 7-10 mm 3 , which is significantly better than the wear resistance (ASTM G65 wear volume loss) of the 42CrMo mold of the comparative example, which is 30-50 mm 3 . This result further proves that the specific Cr, W carbide component content can improve the wear resistance of the material.

[0050] Table 3

[0051] It should be noted that the above-mentioned embodiments illustrate rather than limit the application, and that those skilled in the art will be able to devise modifications which, though perhaps not explicitly described or shown herein, nonetheless fall within the scope of the application. Accordingly, the patentable scope of the application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a hot isostatic pressing corrosion-resistant steel mold, characterized in that, Includes the following steps: S1 Raw material powder preparation: Prepare alloy powder, wherein, by mass fraction, the raw material components include 1-3% C, 30-35% Cr, 10-15% W, 1-2% Si, 0.5-2% Fe, and 45-60% Co; S2 Powder filling and degassing: Prepare a steel sleeve, place the powder and steel mold in the steel sleeve, and seal it after vacuuming; S3 Hot Isostatic Pressing: The cladding is placed in a hot isostatic pressing environment for heat and pressure preservation; S4 heat treatment.

2. The preparation method according to claim 1, characterized in that, In S3, the pressure holding condition is 120-150 MPa.

3. The preparation method according to claim 1, characterized in that, In S3, the heat preservation condition is 1120-1150℃.

4. The preparation method according to claim 1, characterized in that, In S2, the vacuum level inside the casing is 0.1-0.01 Pa.

5. The preparation method according to claim 1, characterized in that, In S2, the cladding is selected from one of low-carbon steel, stainless steel, or cobalt-based alloy.

6. The preparation method according to claim 1, characterized in that, In S2, a vacuum is drawn within a temperature range of 50-200℃.

7. The preparation method according to claim 1, characterized in that, In S4, the heat treatment includes the following steps: quenching at 1100-1150℃.

8. A hot isostatic pressing corrosion-resistant steel mold, characterized in that, The hot isostatic pressing corrosion-resistant steel mold prepared by any one of claims 1 to 9.

9. The hot isostatic pressing corrosion-resistant steel mold according to claim 8, characterized in that, The mold is provided with an anti-corrosion layer of not less than 3 mm, and the strength of the anti-corrosion layer is not less than 2100 MPa.

10. The application of hot isostatic pressing corrosion-resistant steel molds in the molding and manufacturing of polymer-bonded explosives, characterized in that... The hot isostatic pressing corrosion-resistant steel mold is a hot isostatic pressing corrosion-resistant steel mold prepared by any one of the preparation methods described in claims 1 to 9.

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