Nitrocarburizing process for die-casting die without white bright layer
By optimizing the nitrocarburizing process, the white bright layer and brittle structure of the die-casting mold were eliminated, the hardness and diffusion layer depth were improved, the problems of hard and brittle structure and white bright layer in the existing technology were solved, and the service life of the mold was extended.
Patent Information
- Application Number
- CN202610256342.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-04
- Publication Date
- 2026-05-08
AI Technical Summary
Existing nitrocarburizing processes form hard and brittle vein-like structures and a bright white layer on the surface of die-casting molds, which cannot withstand the high impact loads of large die-casting machines.
By optimizing the nitrogen-carbon co-diffusion process through steps such as quenching, tempering, vacuum treatment, nitrogen treatment, and nitrogen potential control, the white layer is eliminated, the microstructure of the infiltrated layer is improved, and the depth and hardness of the infiltrated layer are increased.
It has achieved an increase in the hardness of die-casting molds to 700-900HV0.3, a diffusion layer depth of 180-210μm, elimination of the white bright layer, improved metallographic stability to level 1, excellent surface condition, and avoidance of oxidation.
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Abstract
Description
Technical Field
[0001] This invention relates to surface treatment technology for metal materials, and more particularly to a nitrogen-carbon co-infiltration process for die-casting molds without a white bright layer. Background Technology
[0002] Molds are the mother of manufacturing; a good mold material can often significantly improve manufacturing efficiency and reduce costs.
[0003] With the introduction of Tesla's integrated die-casting concept, the market's requirements for mold steel are becoming increasingly stringent.
[0004] The most common materials for large die-casting molds are 4Cr5Mo2V and 4Cr5MoSi1V. During their service, they are repeatedly in contact with high-temperature molten aluminum alloys, which causes thermal fatigue cracks and corrosion on the surface.
[0005] To improve the corrosion resistance of die-casting molds, they are usually subjected to nitrocarburizing, which increases the surface hardness while maintaining the hardness of the matrix, in order to resist the corrosion of high-temperature molten aluminum alloys.
[0006] Nitrogen-carbon infiltration refers to the process of introducing a certain ratio of ammonia and carbon dioxide at a specific temperature, which decomposes to produce active nitrogen and carbon atoms, simultaneously penetrating the metal surface to form a carbonitride layer. This infiltrated layer has advantages such as high hardness, high wear resistance, high corrosion resistance, and high fatigue strength. However, this treatment method also has disadvantages, producing a hard and brittle vein-like structure and a white, shiny layer, making it unsuitable for impact loads. Given that modern large die-casting machines typically have clamping forces reaching 10,000 tons, the market demand for nitriding without a white, shiny layer is urgent. Summary of the Invention
[0007] In view of the aforementioned deficiencies in the prior art, the technical problem to be solved by the present invention is that the existing nitrocarburizing process produces a hard and brittle vein-like structure and a white, shiny layer, which is unsuitable for impact loads. The present invention provides a nitrocarburizing process for die-casting molds without a white, shiny layer, eliminating the white, shiny layer, improving the diffusion layer structure, and increasing the diffusion layer depth to extend the mold's service life.
[0008] To achieve the above objectives, the present invention provides a nitrocarburizing process for die-casting molds without a white gloss layer, comprising the following steps:
[0009] The die-casting mold is quenched and tempered several times to adjust its hardness.
[0010] Then clean the surface of the die-casting mold with alcohol;
[0011] The cleaned die-casting mold is placed in a gas nitriding furnace and evacuated, and then nitrogen gas is introduced.
[0012] Add the nitriding furnace to 560℃, introduce ammonia and carbon dioxide into the nitriding furnace, adjust the nitrogen potential and keep it at the temperature for 2-4 hours to make the die casting mold in the strong penetration period.
[0013] Adjust the nitrogen potential and hold at that temperature for 4-8 hours to ensure the die-casting mold is in the diffusion phase;
[0014] After purging with nitrogen atmosphere and holding at that temperature for 2-4 hours, remove from the furnace and air cool.
[0015] Furthermore, the die-casting mold is quenched and tempered three times.
[0016] Furthermore, the die-casting mold is quenched and tempered three times. Specifically, after heating and holding the die-casting mold at a certain temperature, it is oil-quenched to below the Ms point, then air-cooled to room temperature, and then tempered three times. Each tempering is followed by air-cooling to room temperature before the next tempering.
[0017] Furthermore, the die-casting mold is quenched and tempered several times to adjust its hardness to 48-50 HRC.
[0018] Further, the cleaned die-casting mold is placed in a gas nitriding furnace and evacuated, and then nitrogen is introduced. Specifically, the mold is placed in a gas nitriding furnace and evacuated, and then nitrogen is introduced to 15 kPa.
[0019] Further, the nitriding furnace is brought to 560°C, and ammonia and carbon dioxide are introduced into the nitriding furnace. The nitrogen potential is adjusted to 1.2-1.8, and the furnace is kept at this temperature for 2-4 hours to bring the die-casting mold into a strong permeation period.
[0020] Furthermore, the nitrogen potential during the diffusion period is adjusted to 0.4-0.6.
[0021] Furthermore, nitrogen atmosphere is used for purging and heat preservation for 2-4 hours. Specifically, nitrogen atmosphere is used for purging and cooling to 550℃. The heat preservation time is set to 2-4 hours according to the effective thickness of the mold.
[0022] Furthermore, a nitrogen atmosphere is used for purging, and the temperature is maintained for 2-4 hours. Specifically, the temperature is lowered to 550°C, ammonia and carbon dioxide are no longer introduced, and nitrogen is purged at a flow rate of 2.0 L / h for 2-4 hours.
[0023] Further, the nitriding furnace is heated to 560°C, and ammonia and carbon dioxide are introduced into the nitriding furnace. After adjusting the nitrogen potential, the furnace is kept at this temperature for 2-4 hours to ensure that the die-casting mold is in a strong permeation period. The ratio of ammonia to carbon dioxide introduced is 20:1.
[0024] Technical effect
[0025] This invention provides a nitriding and carbonizing process for die-casting molds without a white gloss layer, enabling the die-casting molds to achieve the required nitriding hardness, resulting in a hardness of 700-900 HV. 0.3 Meanwhile, the diffusion layer depth can reach 180-210 μm; in addition, the present invention can eliminate the white bright layer, reduce the vein structure, and make the diffusion layer metallographic stability at level 1; furnace cooling to below 150°C and air cooling can prevent the mold from oxidizing in the air, making its surface condition better.
[0026] The following will further explain the concept, specific structure, and technical effects of the present invention in order to fully understand the purpose, features, and effects of the present invention. Detailed Implementation
[0027] To make the technical problems, solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0028] In the following description, specific details, such as particular internal procedures and techniques, are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will appreciate that the invention may be practiced in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of the invention with unnecessary detail.
[0029] This invention provides a nitrocarburizing process for die-casting molds without a white gloss layer, comprising the following steps:
[0030] Step 100: Quench and temper the die-casting mold three times to adjust its hardness. Specifically, after heating and holding the die-casting mold at a certain temperature, oil quench it to below the Ms point, then air cool it to room temperature, and then temper it three times. After each tempering, air cool it to room temperature before the next tempering is performed to adjust the hardness of the die-casting mold to 44-50 HRC.
[0031] Step 200: Then clean the surface of the die-casting mold with alcohol;
[0032] Step 300: Place the cleaned die-casting mold into a gas nitriding furnace and evacuate it. Then, introduce nitrogen gas until the pressure reaches 15 kPa.
[0033] Step 400: Add the nitriding furnace to 560°C, introduce ammonia and carbon dioxide into the nitriding furnace, adjust the nitrogen potential to 1.2-2.4, and keep it at this temperature for 2-4 hours to bring the die-casting mold into a strong permeation period; the ratio of ammonia to carbon dioxide introduced is 20:1.
[0034] Step 500: Adjust the nitrogen potential and hold at that temperature for 4-8 hours to bring the die-casting mold into the diffusion phase; during the diffusion phase, adjust the nitrogen potential to 0.4-0.6. Steps 400 and 500 are mainly for soft nitriding treatment and to obtain a nitrided layer of a certain depth.
[0035] Step 600 involves purging with a nitrogen atmosphere and holding at that temperature for 2-4 hours, then removing the furnace and air-cooling. Specifically, this involves purging with a nitrogen atmosphere, cooling to 550°C, and holding at that temperature for 2-4 hours. More specifically, purging with a nitrogen atmosphere and holding at that temperature for 2-4 hours includes cooling to 550°C, ceasing the introduction of ammonia and carbon dioxide, and purging with nitrogen at a flow rate of 2.0 L / h for 2-4 hours. This step primarily removes the white, shiny layer.
[0036] Example 1
[0037] In this embodiment, 4Cr5Mo2V was used for the experiment.
[0038] The nitriding steps in this embodiment are as follows:
[0039] Step 1: After heating and holding the sample at 1030℃, oil quench it to below the Ms point, and then air cool it to room temperature. Then, it undergoes a cycle of 540℃ for 2 hours followed by air cooling to room temperature, a second cycle of 610℃ for 2 hours followed by air cooling to room temperature, and a third cycle of 540℃ for 2 hours followed by air cooling to room temperature, to harden the sample to between 48-50 HRC. The sample is then cut into 10mm*10mm*10mm cubes.
[0040] Step 2: Clean the surface oil stains with ethanol and polish off the oxide layer.
[0041] Step 3: Place the prepared sample into a gas nitriding furnace, evacuate the furnace, and then introduce nitrogen gas to 15 kPa.
[0042] Step 4: Heat to 560℃, introduce ammonia and carbon dioxide in a ratio of 20:1, adjust the nitrogen potential to 1.2, enter the strong osmosis period, and keep warm for 2.5 hours.
[0043] Step 5: Adjust the nitrogen potential to 0.4, enter the diffusion period, and keep warm for 4 hours.
[0044] Step 6: Cool down to 550℃, stop introducing ammonia and carbon dioxide, purge with nitrogen at a flow rate of 2.0L / h, and keep warm for three hours.
[0045] Step 7: Cool in the furnace to below 150°C and remove from the furnace, then air cool to room temperature.
[0046] Example 2
[0047] In this embodiment, 4Cr5Mo2V was used for the experiment.
[0048] Step 1: After heating and holding the sample at 1030℃, oil quench it to below the Ms point, and then air cool it to room temperature. Then, it undergoes a cycle of 540℃ for 2 hours followed by air cooling to room temperature, a second cycle of 610℃ for 2 hours followed by air cooling to room temperature, and a third cycle of 540℃ for 2 hours followed by air cooling to room temperature, to harden the sample to between 48-50 HRC. The sample is then cut into 10mm*10mm*10mm cubes.
[0049] Step 2: Clean the surface oil stains with ethanol and polish off the oxide layer.
[0050] Step 3: Place the prepared sample into a gas nitriding furnace, evacuate the furnace, and then introduce nitrogen gas to 15 kPa.
[0051] Step 4: Heat to 560℃, introduce ammonia and carbon dioxide in a ratio of 20:1, adjust the nitrogen potential to 1.2, enter the strong osmosis period, and keep warm for 2.5 hours.
[0052] Step 5: Adjust the nitrogen potential to 0.4, enter the diffusion period, and keep warm for 4 hours.
[0053] Step 6: Cool down to 550℃, stop introducing ammonia and carbon dioxide, purge with nitrogen at a flow rate of 2.0L / h, and keep warm for 2.5 hours.
[0054] Step 7: Cool in the furnace to below 150°C and remove from the furnace, then air cool to room temperature.
[0055] The diffusion depth, surface hardness, white gloss layer, and metallographic rating of the two embodiments described above were tested according to GB / T11354-2005, and the results are shown in Table 1.
[0056] Table 1
[0057]
[0058] As shown in Table 1, the 4Cr5Mo2V steel treated by the present invention has excellent nitriding effect, high surface hardness, high diffusion depth, no brittle white bright layer, and the vein structure is well controlled.
[0059] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.
Claims
1. A nitrocarburizing process for die-casting molds without a white gloss layer, characterized in that, Includes the following steps: The die-casting mold is quenched and tempered several times to adjust its hardness. Then, use alcohol to clean the surface of the die-casting mold; The cleaned die-casting mold is placed in a gas nitriding furnace and evacuated, and then nitrogen gas is introduced. Add the nitriding furnace to 560°C, introduce ammonia and carbon dioxide into the nitriding furnace, adjust the nitrogen potential and keep it at that temperature for 2-4 hours to bring the die-casting mold into a strong permeation period; Adjust the nitrogen potential and maintain the temperature for 4-8 hours to ensure that the die-casting mold is in the diffusion phase; After purging with nitrogen atmosphere and holding at that temperature for 2-4 hours, remove from the furnace and air cool.
2. The nitriding and carbonizing process for a die-casting mold without a white gloss layer as described in claim 1, characterized in that, The die-casting mold is quenched and tempered three times.
3. The nitriding and carbonizing process for a die-casting mold without a white gloss layer as described in claim 1, characterized in that, The die-casting mold is quenched and tempered three times. Specifically, after heating and holding the die-casting mold, it is oil-quenched to below the Ms point, then air-cooled to room temperature, and then tempered three times. Each tempering is followed by air-cooling to room temperature before the next tempering.
4. The nitriding and carbonizing process for a die-casting mold without a white gloss layer as described in claim 1, characterized in that, The die-casting mold is quenched and tempered several times to adjust its hardness to 44-50 HRC.
5. The nitriding and carbonizing process for a die-casting mold without a white gloss layer as described in claim 1, characterized in that, The cleaned die-casting mold is placed in a gas nitriding furnace and evacuated, and then nitrogen is introduced. Specifically, the mold is placed in a gas nitriding furnace and evacuated, and then nitrogen is introduced to 15 kPa.
6. The nitriding and carbonizing process for a die-casting mold without a white gloss layer as described in claim 1, characterized in that, Add the nitriding furnace to 560°C, introduce ammonia and carbon dioxide into the nitriding furnace, adjust the nitrogen potential to 1.2-1.8, and keep it at this temperature for 2-4 hours to bring the die-casting mold into a strong permeation period.
7. The nitriding and carbonizing process for a die-casting mold without a white gloss layer as described in claim 1, characterized in that, The nitrogen potential is adjusted to 0.4-0.6 during the diffusion period.
8. The nitriding and carbonizing process for a die-casting mold without a white gloss layer as described in claim 1, characterized in that, Use nitrogen atmosphere for purging and maintain the temperature for 2-4 hours. Specifically, use nitrogen atmosphere for purging and cool down to 550℃. Set the holding time to 2-4 hours based on the effective thickness of the mold.
9. The nitriding and carbonizing process for a die-casting mold without a white gloss layer as described in claim 1, characterized in that, Use nitrogen atmosphere for purging and maintain the temperature for 2-4 hours. Specifically, this includes cooling to 550°C, stopping the introduction of ammonia and carbon dioxide, purging with nitrogen at a flow rate of 2.0 L / h, and maintaining the temperature for 2-4 hours.
10. The nitriding and carbonizing process for a die-casting mold without a white gloss layer as described in claim 1, characterized in that, The nitriding furnace is heated to 560°C. Ammonia and carbon dioxide are introduced into the nitriding furnace. After adjusting the nitrogen potential, the furnace is kept at this temperature for 2-4 hours to ensure that the die-casting mold is in a strong permeation period. The ratio of ammonia to carbon dioxide introduced is 20:1.