Copper-containing 420 stainless steel material based on BJ printing and preparation method thereof

Abstract

The invention belongs to the technical field of metal materials, and particularly discloses a copper-containing 420 stainless steel material based on BJ printing and a preparation method thereof.The copper-containing 420 stainless steel material based on BJ printing is prepared by dissolving copper salt in a water-based binder, and conducting binder jet printing, curing, degreasing and vacuum sintering in the hydrogen atmosphere, so that copper is reduced in situ and forms dispersed or network-shaped distribution along the grain boundary; uniform distribution of the copper element is achieved in the printing process, in-situ reduction is conducted in the subsequent heat treatment stage to form a dispersed distribution or network-shaped copper phase, and therefore the sintering densification behavior and the heat conduction performance are synchronously optimized on the premise that the inherent advantages of the binder spraying technology are not damaged. The density of the obtained material is larger than or equal to 98.4%, the heat conductivity coefficient reaches 22.8 W / (K.m) and is improved by 87.7% compared with a copper-free sample, and the mechanical property is excellent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal preparation, and particularly relates to a copper-containing 420 stainless steel material based on BJ printing and a preparation method thereof. BACKGROUND

[0002] As a key technical path in the intelligent manufacturing system, additive manufacturing has played an increasingly important role in the process of global industrial transformation and upgrading in recent years. The additive manufacturing technology based on metal materials has become an important support means in the fields of high-end equipment manufacturing, mold development and thermal management devices, etc. due to its high design freedom, high material utilization rate and suitability for complex structure integrated forming.

[0003] Among many metal additive manufacturing processes, binder jetting (BJ) printing technology has gradually become a technology route that attracts attention in industrialized applications due to its characteristics of not requiring a high-energy beam source, high forming efficiency, low equipment cost and suitability for mass production. However, when the binder jetting technology is applied to traditional 420 stainless steel materials, the inherent contradiction between its inherent metallurgical properties and forming mechanism gradually emerges. In the binder jetting forming process, the prepared parts are often difficult to reach more than 95% of the theoretical density due to the limitation of the original packing density between powder particles, the hindering effect of binder residues on sintering densification, and the low self-diffusion coefficient and sintering activity of 420 stainless steel itself. More importantly, the intrinsic thermal conductivity of 420 stainless steel matrix is usually lower than 15 W / (K·m) due to the lack of high-thermal-conductivity phases, which seriously restricts its functional expansion in application scenarios involving heat exchange, rapid cooling or high heat load conditions. Although existing research attempts to introduce high-thermal-conductivity metal phases through post-processing copper infiltration or composite sintering to improve thermal performance, such methods not only have complex processes and high costs, but also easily lead to composition segregation, poor interface bonding or dimensional deformation, etc., which are difficult to meet the core demands of binder jetting technology for efficient, stable and batch production.

[0004] Therefore, how to construct a 420 stainless steel material system based on binder jetting printing technology, and optimize its solidification, debinding and sintering system to realize the synergistic improvement of high density and high thermal conductivity, has become a key challenge and technical problem to be solved for technical personnel in the field. SUMMARY

[0005] The application provides a copper-containing 420 stainless steel material based on BJ printing and a preparation method thereof. The material realizes the synergistic improvement of high density and high thermal conductivity through a binder jetting forming process. The core is to introduce copper source in the form of soluble salt into a water-based binder system, realize uniform distribution of copper elements during printing, and form dispersed distribution or network copper phase in situ through reduction in the subsequent heat treatment stage, so as to simultaneously optimize sintering densification behavior and thermal conductivity performance without destroying the inherent advantages of the binder jetting process.

[0006] To achieve the above-mentioned application purposes, the application provides a preparation method of a copper-containing 420 stainless steel material based on BJ printing, which comprises the following steps: Step one, copper salt is prepared into a solution and then added into a water-based binder, and stirred uniformly at room temperature to form a copper-containing binder solution; Step two, a binder jetting printer is used to jet the copper-containing binder solution onto a flat 420 stainless steel powder layer to build a three-dimensional initial blank layer by layer; Step three, the initial blank is placed in an oven for heating, cross-linking and curing to obtain a green body; Step four, the cured green body is transferred to a debinding furnace for debinding treatment to remove the binder; Step five, the debound blank is loaded into a vacuum sintering furnace, hydrogen is introduced for heating and sintering, and then the furnace is cooled to obtain the copper-containing 420 stainless steel material.

[0007] Further, the copper salt in step one is copper nitrate pentahydrate (Cu(NO3)2·5H2O), and the addition amount of the copper salt is 25-50% of the mass of the water-based binder. The water-based binder comprises the following components in a weight percentage: 8-10% polyvinyl alcohol, 3-5% glycerol, 0.1-0.5% surfactant, and the rest is deionized water. The binder has suitable surface tension, viscosity and drying shrinkage, and meets the jetting stability requirements of the binder jetting print head.

[0008] Further, the 420 stainless steel powder in step two comprises the following components in a weight percentage: C 0.28%-0.40%, Si ≤1.0%, Mn ≤1.0%, P ≤0.04%, S ≤0.03%, Cr 12.0%-14.0%, Ni ≤0.75%, and the rest is Fe and unavoidable impurities. The particle size of the 420 stainless steel powder is 0-25 μm, the oxygen content is ≤800 ppm, and the Hall flow rate is ≤25 s / 50 g.

[0009] Further, the step two, the working frequency of the nozzle of the binder jetting printer is 10 kHz, the droplet volume is 30 pL, the layer thickness is set to 50 pm, the powder roller speed is 50 rpm, the doctor blade pressure is 0.3 MPa, the moving powder falling time is 270 ms; and the penetration time is 5000-10000 ms. The parameters in the application avoid excessive penetration to cause layer blur or insufficient penetration to cause weakened interlayer bonding.

[0010] Further, the step three, the heating cross-linking and curing temperature is 120-130 DEG C, and the curing time is 120-150 min. If the curing temperature is lower than 100 DEG C or the holding time is shorter than 60 min, the cross-linking is insufficient, the green strength is insufficient, and the structure is easy to collapse before debinding; if the curing temperature is higher than 150 DEG C, the binder components may be heat aged, the brittleness is increased, and the green body is cracked in the subsequent processing.

[0011] Further, the step four, the debinding temperature in the debinding furnace is 550-650 DEG C, the heating rate is 2-4 DEG C / min, and the debinding time is 120-150 min. If the debinding temperature is lower than 550 DEG C, the binder pyrolysis is not complete, the residual carbon reacts with chromium to form chromium carbide in the sintering stage, the chromium-poor area is formed, and the corrosion resistance is reduced; if the debinding temperature is higher than 650 DEG C, the 420 stainless steel powder is surface oxidized in the absence of a protective atmosphere, a dense oxide film is formed, and the formation of the subsequent sintering neck is hindered.

[0012] Further, the step five, the vacuum sintering temperature is 1300-1350 DEG C, the heating rate is 5-10 DEG C / min, the sintering time is 4-6 h, and the vacuum degree is less than or equal to 10-2 Pa.

[0013] Beneficial effects: 1. The application combines the binder jetting printing technology and the vacuum sintering process, and realizes the forming of the copper-containing 420 stainless steel material without secondary sintering or separate copper infiltration, simplifies the process flow, and reduces the production cost. Meanwhile, the 420 stainless steel prepared by the application has high density and high thermal conductivity, and significantly improves the mechanical properties and thermal properties of the part. The density is not less than 98.4%, the thermal conductivity is not less than 22.8 W / (K.m), the thermal diffusivity is not less than 5.38 mm2 / s, the Vickers hardness is not less than 320 HV0.5, and is suitable for manufacturing industrial parts with strict requirements on thermal management performance, including but not limited to injection mold inserts, die casting mold cores, micro-channel heat exchanger substrates, semiconductor packaging heat dissipation bases and high-precision medical instrument structural parts.

[0014] 2. This invention deeply integrates copper with the forming process carrier (binder), utilizing the inherent characteristic of the binder in the binder spraying process—that it exists only at the particle contact points—to precisely position the copper source in the future sintering neck region. This allows for the in-situ generation of a highly thermally conductive phase during sintering, avoiding both the compositional inhomogeneity problems of traditional powder mixing and the risks of interface defects and dimensional instability caused by copper infiltration in post-processing. This strategy breaks through the mutual constraints between "densification" and "thermal conductivity enhancement" in traditional metallurgical approaches, establishing a new paradigm based on process-material co-design. This method is suitable for large-scale production, featuring high efficiency, stability, and low cost, and can meet the needs of high-performance industrial applications such as molds, heat exchangers, and precision parts. Attached Figure Description

[0015] Figure 1 An optical micrograph of the copper-containing 420 stainless steel material prepared in Example 1 of this invention; Figure 2 An optical micrograph of the copper-containing 420 stainless steel material prepared in Example 2 of this invention; Figure 3 An optical micrograph of the copper-containing 420 stainless steel material prepared in Example 3 of this invention; Figure 4 An optical micrograph of the 420 stainless steel material prepared in Comparative Example 1 of this invention; Figure 5 This is an optical micrograph of the copper-containing 420 stainless steel material prepared in Comparative Example 2 of the present invention; Figure 6 This is an optical micrograph of the copper-containing 420 stainless steel material prepared in Comparative Example 3 of the present invention. Detailed Implementation

[0016] The technical solution of this application will be further described below through specific embodiments, which will be described in detail with reference to the accompanying drawings.

[0017] Unless otherwise specified, all materials used in this application are derived from commercially available materials.

[0018] Example 1 This invention provides a method for preparing copper-containing 420 stainless steel material based on BJ printing, comprising the following steps: Step 1: After preparing the copper salt solution, add it to the water-based adhesive and stir evenly at room temperature to form a copper-containing adhesive solution; Specifically, a copper-containing water-based binder solution is prepared. The binder system uses deionized water as the solvent, and polyvinyl alcohol (PVA), glycerol and a small amount of surfactant are added as functional components. Among them, the molecular weight of polyvinyl alcohol is in the range of 85000-124000, and the addition amount is 8% of the total mass; glycerol is used as a plasticizer, and the addition amount is 3% of the total mass; the surfactant is selected as sodium dodecyl sulfate, and the addition amount is 0.1% of the total mass. The above components are mixed by stirring at room temperature for 30 minutes to form a transparent and uniform base binder solution, which meets the requirements of rheological properties and jetting stability of the binder jetting print head. Subsequently, Cu(NO3)2·5H2O solution is added to the above base binder at a proportion of 50% of the mass of the set water-based binder. The dissolution process is carried out at room temperature, and the stirring is continued for 5 minutes to ensure that the solute is fully dispersed and completely dissociated to form a copper-containing binder solution.

[0019] Step two, using a binder jetting printer, the copper-containing binder solution is jetted onto the flat 420 stainless steel powder layer to build a three-dimensional initial billet layer by layer; Specifically, a binder jetting three-dimensional printing device is used to build the initial billet. The chemical composition of the 420 stainless steel powder used is as follows: C 0.28%-0.40%, Si ≤1.0%, Mn ≤1.0%, P ≤0.04%, S ≤0.03%, Cr 12.0%-14.0%, Ni ≤0.75%, and the balance is Fe and unavoidable impurities. The powder is subjected to ball milling and shaping treatment, and has a near-spherical shape, a particle size distribution of 0-25μm, a tap density ≥4.2 g / cm³, a Hall flow rate less than 25 s / 50 g, and an oxygen content less than 800 ppm, ensuring good powder flowability and sintering activity. During the printing process, the powder laying system lays a single layer of powder with a doctor blade pressure of 0.3 MPa and a powder roller speed of 50 rpm, and the layer thickness is set to 50μm. The working frequency of the nozzle is 10 kHz, the droplet volume is 30 pL, the moving and falling powder time is 270 ms, and the penetration time is 5000-10000 ms. The aforementioned copper-containing binder solution is selectively jetted onto the powder layer. The binder penetration depth is controlled in the range of 80-120μm through process verification, which avoids the blurring of the interlayer boundary due to excessive penetration and prevents the weakening of the interlayer bonding due to insufficient penetration. Through repeated powder laying and jetting operations, a three-dimensional initial billet is finally built.

[0020] Step three, placing the initial billet in an oven for heating, cross-linking and curing to obtain a green body; Specifically, the initial billet is placed in a constant temperature oven and kept at 120℃ for 120 minutes. Under this temperature and time condition, the polyvinyl alcohol molecular chain undergoes cross-linking reaction to form a three-dimensional network structure, and at the same time, the water and low boiling point components slowly evaporate, so that the green body obtains sufficient mechanical strength to withstand the mechanical stress in the subsequent handling and debinding process.

[0021] Step four, transfer the solidified green body to a debinding furnace for debinding treatment to remove the binder; Specifically, the solidified green body is transferred to a debinding furnace with controllable atmosphere. The debinding process is carried out in air or inert gas (such as nitrogen) atmosphere, and the temperature is raised from room temperature to 600℃ at a rate of 2℃ / min, and kept at this temperature for 120 minutes. At this stage, the organic binder components (including polyvinyl alcohol, glycerol and surfactant) pyrolyze to generate small molecule gas products and diffuse out of the body.

[0022] Step five, load the debound body into a vacuum sintering furnace, introduce hydrogen gas for temperature rising and sintering, and then cool down in the furnace to obtain a copper-containing 420 stainless steel material.

[0023] Specifically, the debound body is loaded into a vacuum sintering furnace, and vacuum is first applied to remove residual oxygen and moisture in the furnace, and then high-purity hydrogen gas is introduced to maintain a positive pressure in the furnace. The temperature is raised to 1320℃ at a rate of 5℃ / min, and kept at this temperature for 4 hours, and then cooled down to room temperature in the furnace. It is worth noting that sintering must be carried out in a hydrogen atmosphere: if an inert atmosphere such as argon or nitrogen is used, the copper oxide cannot be reduced and remains in the form of CuO inclusions in the matrix, which severely disrupts the continuity of the matrix and reduces the density and thermal conductivity; if only vacuum sintering is used without hydrogen gas, the reduction kinetics is limited and the reduction is incomplete, and an effective copper phase cannot be formed.

[0024] The micrograph of the copper-containing 420 stainless steel material prepared based on BJ printing in this example is shown in Figure 1 .

[0025] Example 2 The difference between this example and Example 1 is that the concentration of the copper salt solution in Step one is 35wt%, and the other steps and parameters are consistent with Example 1. The micrograph of the copper-containing 420 stainless steel material prepared based on BJ printing in this example is shown in Figure 2 .

[0026] Example 3 The difference between this example and Example 1 is that the concentration of the copper salt solution in Step one is 45wt%, and the other steps and parameters are consistent with Example 1. The micrograph of the copper-containing 420 stainless steel material prepared based on BJ printing in this example is shown in Figure 3 .

[0027] Comparative Example 1 The difference between this comparative example and Example 1 is that no copper-containing binder is used, only the conventional water-based binder as described in Example 1 is used, and the other steps and parameters are consistent with Example 1. The micrograph of the 420 stainless steel material prepared based on BJ printing in this comparative example is shown inFigure 4 as shown.

[0028] Comparative Example 2 The difference between this comparative example and Example 1 is that the concentration of the copper salt solution in Step 1 is 15wt%, and other steps and parameters are consistent with Example 1. The micrograph of the copper-containing 420 stainless steel material based on BJ printing prepared in this comparative example is as shown in Figure 5 .

[0029] Comparative Example 3 The difference between this comparative example and Example 1 is that the concentration of the copper salt solution in Step 1 is 25wt%, and other steps and parameters are consistent with Example 1. The micrograph of the copper-containing 420 stainless steel material based on BJ printing prepared in this comparative example is as shown in Figure 6 .

[0030] The 420 stainless steel materials prepared in the above examples and comparative examples were subjected to performance testing, and the test results are shown in Table 1 below. Table 1 Performance table of 420 stainless steel materials prepared in examples and comparative examples Number Copper salt concentration wt% Density g / cm3 Densification % Thermal conductivity W / (K.m) Example 1 50 6.833 96.1 24.894 Example 2 35 7.187 98.4 22.817 Example 3 45 7.021 97.9 23.763 Comparative Example 1 0 6.528 92.3 12.159 Comparative Example 2 15 6.746 94.3 17.332 Comparative Example 3 25 6.977 96.8 19.589 The thermal diffusivity coefficients of the 420 stainless steel materials prepared in Example 1 and Comparative Example 1 were also tested, and the test results are shown in Tables 2 and 3 below, respectively.

[0031] Table 2 Thermal diffusivity test results table of 420 stainless steel material prepared in Example 1 Number of shots Temperature °C Thermal spreading system 2 / s]]> Confidence interval Calculated Cp. J / (g*K) Laser voltage V Pulse width ms 1 25.0 5.387 0.9 0.597 250.0 0.60 2 25.0 5.386 0.5 0.598 250.0 0.60 3 25.0 5.385 0.5 0.600 250.0 0.60 4 25.0 5.372 0.5 0.552 250.0 0.60 5 25.0 5.377 0.5 0.602 250.0 0.60 Average 25.0 5.381 0.590 Table 3 Thermal diffusivity test results table of 420 stainless steel material prepared in Comparative Example 1 Number of shots Temperature °C Thermal diffusivity mm2 / s Confidence interval Calculated Cp. J / (g*K) Laser voltage V Pulse width ms 1 25.3 2.232 0.5 0.824 250.0 0.60 2 25.1 2.229 0.5 0.844 250.0 0.60 3 25.0 2.226 0.5 0.831 250.0 0.60 4 25.0 2.227 0.5 0.838 250.0 0.60 5 25.0 2.226 0.5 0.845 250.0 0.60 Average 25.1 2.228 0.836 The copper-containing 420 stainless steel material prepared in the present application has a density of not less than 96%, a thermal conductivity of not less than 22.8 W / (K·m), and a thermal diffusivity of not less than 5.38 mm² / s, and is suitable for manufacturing industrial parts with strict requirements on thermal management performance. Typical application scenarios include injection mold inserts, die casting mold cores, micro-channel heat exchanger substrates, and semiconductor packaging heat dissipation bottoms. The material system is fully compatible with existing binder jetting equipment platforms, and does not require additional copper infiltration, hot isostatic pressing, or secondary infiltration processes, realizing integrated innovation from material design to forming process.

[0032] To sum up, the application integrates the functional element copper into the water-based binder in the form of a soluble salt, uses the characteristics of the binder naturally positioned at the particle contact points in the binder spraying process, and makes the copper source accurately distributed in the future sintering neck area. All the process parameters are optimized and experimentally verified to ensure the certainty, repeatability and industrial feasibility of the technical scheme. The technical effects of the application can be achieved by the skilled person in the art without creative labor according to the specific embodiments.

[0033] It is obvious for those skilled in the art that the application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the application. Therefore, the embodiments should be regarded as exemplary and non-limiting from any point of view. In addition, it should be understood that although the present application is described in the form of embodiments, it does not only contain one technical solution, and the description manner of the specification is only for the sake of clarity. The skilled person in the art should consider the specification as a whole, and the technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by the skilled person in the art.

Claims

1. A method for preparing copper-containing 420 stainless steel material based on BJ printing, characterized in that: Includes the following steps: Step 1: After preparing the copper salt into a solution, add it to the water-based adhesive and stir evenly at room temperature to form a copper-containing adhesive solution; Step 2: Using an adhesive jet printer, spray the copper-containing adhesive solution onto the evenly laid 420 stainless steel powder. Layer by layer, a three-dimensional initial blank is constructed; Step 3: Place the initial blank in an oven and heat it for cross-linking and curing to obtain the green blank; Step 4: Transfer the cured green body to a degreasing oven for degreasing treatment to remove the binder; Step 5: The degreased billet is placed into a vacuum sintering furnace, heated by hydrogen gas, and then cooled in the furnace to obtain a copper-containing product. 420 stainless steel material.

2. The method for preparing copper-containing 420 stainless steel material based on BJ printing according to claim 1, characterized in that: In step one, the copper salt is copper nitrate pentahydrate, and the amount of copper salt added is 35-50% of the mass of the water-based adhesive. The water-based adhesive includes the following components by weight fraction: 8-10% polyvinyl alcohol, 3-5% glycerol, 0.1-0.5% surfactant, and the remainder is deionized water.

3. The method for preparing copper-containing 420 stainless steel material based on BJ printing according to claim 1, characterized in that: The 420 stainless steel powder in step two comprises the following weight fractions: C 0.28%~0.40%, Si ≤1.0%, Mn ≤1.0%, P ≤0.04%, S ≤0.03%, Cr 12.0%~14.0%, Ni ≤0.75%, with the balance being Fe and unavoidable impurities; the 420 stainless steel powder has a particle size of 0-25μm, an oxygen content ≤800ppm, and a Hall flow rate ≤25s / 50g.

4. The method for preparing copper-containing 420 stainless steel material based on BJ printing according to claim 3, characterized in that: In step two, the nozzle operating frequency of the adhesive jet printer is 10 kHz, the droplet volume is 30 pL, the layer thickness is set to 50 μm, the powder spreading roller speed is 50 rpm, the doctor blade pressure is 0.3 MPa, the powder falling time is 270 ms, and the penetration time is 5000-10000 ms.

5. The method for preparing copper-containing 420 stainless steel material based on BJ printing according to claim 1, characterized in that: In step three, the heating cross-linking curing temperature is 120-130℃, and the curing time is 120-150 min.

6. The method for preparing copper-containing 420 stainless steel material based on BJ printing according to claim 1, characterized in that: In step four, the degreasing temperature in the degreasing furnace is 550-650℃, the heating rate is 2-4℃ / min, and the degreasing time is 120-150min.

7. The method for preparing copper-containing 420 stainless steel material based on BJ printing according to claim 1, characterized in that: In step five, the vacuum sintering temperature is 1300-1350℃, the heating rate is 5-10℃ / min, the sintering time is 4-6h, and the vacuum degree is ≤10⁻² Pa.

8. A copper-containing 420 stainless steel material prepared by the preparation method according to any one of claims 1-7.

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