Heat treatment, surface treatment and maintenance method of pre-hardening integrated die-casting die

Abstract

The invention discloses a heat treatment method of a pre-hardening integrated die-casting die, which comprises the following steps: heating a material for preparing the pre-hardening integrated die-casting die to 960-1000 DEG C, preserving heat, and quenching by adopting a water mist cooling mode; heat preservation is conducted at 600-630 DEG C, air cooling is conducted after heat preservation, and first tempering is completed; and heat preservation is conducted at the temperature of 560-590 DEG C, air cooling is conducted after heat preservation, secondary tempering is completed, and the hardness is controlled to be 38-42 HRC. According to the heat treatment, surface treatment and maintenance method for the pre-hardening integrated die-casting die, a proper heat treatment process is provided for a pre-hardening integrated die-casting die material to obtain good obdurability matching, an efficient surface treatment method is provided to prolong the service life of the die, and a professional maintenance method is provided; therefore, the service life of the die is prolonged, the production cost of an integrated die-casting enterprise is reduced, and cost reduction and efficiency improvement of the enterprise are promoted.

Description

Technical Field

[0001] The invention relates to the field of alloy steel manufacturing, and in particular to a heat treatment, surface treatment and maintenance method for a pre-hardened integrated die-casting mold. Background Art

[0002] The manufacturing cost of integrated die-casting molds is extremely high. Each set of integrated die-casting molds can only support a production capacity of 50,000 to 60,000 times. During the die-casting process, the mold is subjected to high-speed erosion of molten metal and repeated heating and cooling. The processing environment is very harsh and the mold loss is large. In addition, the manufacturing cycle of integrated die-casting molds is long. After roughing, heat treatment requires large vacuum heat treatment equipment. In order to avoid the risk of deformation and cracking of large mold inserts during heat treatment, sufficient machining allowances need to be left for heat treatment, resulting in a longer production cycle and higher costs.

[0003] According to the mold material disclosed in the patent "A special material for pre-hardened integrated die-casting mold and its preparation method" (application number: 202410608604.8), through reasonable alloy composition design and combined with the advantages of pre-hardening treatment, the material cost, heat treatment cost and processing cost of the integrated die-casting mold are effectively reduced, the overall manufacturing cycle is shortened, and the mold deformation, cooling water channel hole deformation and offset, and mold cracking caused by heat treatment of large mold inserts during processing are avoided, ensuring that the die-casting parts have good product quality.

[0004] At present, the mold core materials commonly used in integrated die-casting production are all prepared by roughing-heat treatment-finishing. Heat treatment is performed during the mold processing process. The risk of mold deformation and cracking during quenching is relatively high. The above-mentioned pre-hardened integrated die-casting mold directly achieves acceptable hardness for machining through pre-hardening treatment before cavity processing, but the strength and toughness are not matched. In addition, the surface of the mold is subjected to high-temperature molten metal erosion and repeated high and low temperature cycles during service. The physical properties and stress state of the mold core cavity surface determine the service life of the mold. The service life of integrated die-casting molds is generally low in harsh working environments, resulting in extremely high application costs. There is a lack of efficient surface treatment methods to improve the surface state of the mold cavity. In addition, unreasonable use of the mold during service also aggravates the cracking and failure of the mold. Problems such as improper use of release agents, failure to clean the cavity surface in time after the mold has been in service for a certain number of times, and failure to maintain the cavity surface in time when slight cracks appear will all lead to a mold service life lower than expected. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is that the pre-hardened integrated die-casting mold material prepared by the existing pre-hardened integrated die-casting mold special material and its preparation method lacks a suitable heat treatment process, and the performance of the integrated die-casting mold is poor, and there is a lack of efficient surface treatment methods to improve the surface state of the mold. In addition, there is a lack of reasonable maintenance methods during the service life of the mold, which leads to problems such as low service life and mismatch of strength and toughness. Therefore, the present invention provides a heat treatment, surface treatment and maintenance method for a pre-hardened integrated die-casting mold, provides a suitable heat treatment process for the pre-hardened integrated die-casting mold material to obtain a good strength and toughness match, provides an efficient surface treatment method to increase the service life of the mold, and provides a professional maintenance method to perform maintenance or repair in time, thereby increasing the service life of the mold, reducing the production cost of the integrated die-casting enterprise, and promoting the enterprise to achieve cost reduction and efficiency improvement.

[0006] To achieve the above object, the present invention provides a heat treatment method for a pre-hardened integrated die-casting mold, comprising the following steps:

[0007] The material for preparing the pre-hardened integrated die-casting mold is heated to 960-1000°C for insulation, and quenched by water mist cooling;

[0008] Keep warm at 600-630℃, then air cool to complete the first tempering;

[0009] Keep warm at 560-590℃, air cool after keeping warm, complete the second tempering, and control the hardness at 38-42HRC.

[0010] In a preferred embodiment of the present invention, a surface treatment method for a pre-hardened integrated die-casting mold is provided, characterized in that it comprises the following steps:

[0011] After the pre-hardened integrated die-casting mold is opened, the cavity surface is shot peened, and three passes of shot peening are completed using a shot peening process with a shot peening intensity of 0.1 to 0.33 mmA;

[0012] After the cavity surface of the pre-hardened integrated die-casting mold is shot peened, the mold is nitrided and oxidized, and the process temperature is controlled at 540-560°C.

[0013] Furthermore, the shot material used in the shot peening is 0.4 mm steel cut wire shot, the spraying distance is set to 15-20 mm, and the spraying flow rate is set to 4-8 kg / min; wherein, the shot peening intensity of the first shot peening process is 0.33 mmA, and the spraying pressure is 4 bar; the shot peening intensity of the second shot peening process is 0.2 mmA, and the spraying pressure is 2 bar; the shot peening intensity of the third shot peening process is 0.1 mmA, and the spraying pressure is 1 bar.

[0014] Furthermore, the mold is heated and replaced with an atmosphere in a vacuum environment before the nitriding treatment. Then, the die is nitrided according to the die-casting mold nitriding process. The nitriding atmosphere is N 2 -NH 3 ; Finally, the atmosphere is replaced with water vapor, the temperature is lowered to 540℃ for oxidation treatment, and then air-cooled.

[0015] In another preferred embodiment of the present invention, a maintenance method for a pre-hardened integrated die-casting mold is provided, characterized in that it comprises the following steps:

[0016] The mold is stress relieved before use and stress relieved and maintained after the set number of uses;

[0017] The mold is preheated before production, and the overall temperature reaches 200-250℃;

[0018] After a single die-casting production, the mold release agent is evenly and finely sprayed onto the cavity surface to form effective adhesion;

[0019] The mold is cleaned and maintained after each use.

[0020] Furthermore, the mould is subjected to stress relief treatment before use, and stress relief treatment and maintenance is performed after the set number of uses, specifically including: the stress relief treatment temperature is set at 520-560°C, and the mould is subjected to nitriding and oxidation treatment after fine machining and trial moulding; the mould is subjected to the first stress relief treatment when it has been used normally for 5,000 times in production; the mould is subjected to the second stress relief treatment when it has been used for 15,000 times; the mould is subjected to the third stress relief treatment when it has been used for 25,000 times; thereafter, the mould is subjected to stress relief treatment every 20,000 times of production.

[0021] Furthermore, the mold is preheated before production, wherein the preheating includes using one or more of a blowtorch, liquefied gas, and natural gas to uniformly preheat the cavity surface, and using an infrared temperature gun to measure the instantaneous temperature of the mold surface.

[0022] Furthermore, after a single die-casting production, the mold release agent is evenly and finely sprayed onto the cavity surface to form effective adhesion. Specifically, the mold surface temperature after spraying is ensured to be no less than 250°C, and the mold release agent spraying time is controlled to be the time when the mold surface temperature after spraying is no less than 250°C.

[0023] Furthermore, the mold is cleaned every time after being taken off the machine, specifically including cleaning the oil stains on the surface of the mold cavity; cleaning the aluminum sticking on the surface of the cavity, and if the aluminum sticking is serious, light polishing is performed to prevent poor adhesion of the release agent; cleaning the flying skin, burrs, residues, and dirt on the mold parting surface and the slider mating parts; after the mold is cleaned, the surface is evenly sprayed with WD40-type protective agent for protection, and wiped off before being put on the machine; use compressed air to clean the residual water in the cooling water pipe to prevent waterway corrosion.

[0024] Furthermore, if slight cracks appear on the surface of the mold after it is removed from the machine, the mold is subjected to stress relief treatment and single-pass shot peening treatment in the cracked local area, with a shot peening intensity of 0.1 mmA and a spray pressure of 1 bar.

[0025] Technical Effects

[0026] The present invention provides a method for heat treatment, surface treatment and maintenance of a pre-hardened integrated die-casting mold. In the heat treatment method, a pre-hardening method is adopted, and quenching is performed by water mist cooling before mold processing, so as to effectively avoid mold deformation, cooling water channel hole deformation and offset, mold cracking and other problems caused by heat treatment of large mold inserts during processing, reduce heat treatment costs, shorten the overall manufacturing cycle of the integrated die-casting mold, obtain a uniform martensitic structure through a reasonable heat treatment process, and control the hardness to 38-42HRC. The surface treatment process designed by the present invention forms a micro-deformation layer on the surface of the mold cavity through shot peening, introduces residual compressive stress, improves the hardness of the cavity surface, and provides a channel for the diffusion of nitrogen in the subsequent nitriding process, thereby promoting the effect of nitriding treatment. The thickness of the nitriding layer is significantly increased. Compared with nitriding treatment, the shot peening combined with nitriding composite surface treatment method used in the present invention has more excellent surface treatment effect and performance performance, which is beneficial to improving the service life of the mold. In addition, the maintenance method for the above-mentioned pre-hardened integrated die-casting mold provided by the present invention is beneficial to extending the service life of the mold, reducing the enterprise's mold replacement cost, improving production efficiency, reducing the production cost of integrated die-casting enterprises, and promoting enterprises to reduce costs and increase efficiency.

[0027] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the hardness of the sample of the pre-hardened integrated die-casting mold of Example 1 of the present invention after quenching at different temperatures;

[0029] Figure 2 It is a schematic diagram of the grain size rating of the sample of the pre-hardened integrated die-casting mold of Example 1 of the present invention after quenching at different temperatures;

[0030] Figure 3Schematic diagram of the tempering characteristics of the pre-hardened integrated die-casting mold of Example 1 of the present invention;

[0031] Figure 4 Schematic diagram of the impact toughness comparison of the pre-hardened integrated die-casting mold sample in the quenched and tempered state in Example 1 of the present invention;

[0032] Figure 5 It is a schematic diagram of the quenched and tempered microstructure of Examples 1 to 3 of the present invention;

[0033] Figure 6 is a schematic diagram of the metallographic structure of the cross section of the sample after surface treatment in Example 2 and Example 3 of the present invention;

[0034] Figure 7 It is a schematic diagram of the hardness gradient of the cross section of the sample after surface treatment in Example 2 and Example 3 of the present invention;

[0035] Figure 8 Schematic diagram of the surface and cross-sectional crack morphology of the specimens of Example 1 and Example 2 after thermal fatigue test in the present invention;

[0036] Fig. 9 Schematic diagram of the surface and cross-sectional crack morphology of the specimens of Example 2 and Example 3 after thermal fatigue test in the present invention;

[0037] Fig.10 It is a schematic diagram of the comparison of dynamic melting weight loss of samples in Examples 1 to 3 of the present invention. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0039] In the following description, specific details such as specific internal procedures and techniques are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0040] The invention provides a heat treatment method for a pre-hardened integrated die-casting mold, wherein, in terms of mass percentage, the chemical composition of the pre-hardened integrated die-casting mold steel is C: 0.23-0.33%, Si: 0.35-1.00%, Mn: 0.35-1.00%, Cr: 2.50-3.50%, Mo: 0.30-0.60%, Ni: 0-1.0%, V: 0.20-0.50%, Nb: 0-0.05%, and the balance is Fe.

[0041] An embodiment of the present invention provides a heat treatment method for a pre-hardened integrated die-casting mold, comprising the following steps:

[0042] The material for preparing the pre-hardened integrated die-casting mold is heated to 960-1000° C. and kept warm, and quenched by water mist cooling;

[0043] Keep warm at 600-630℃, then air cool to complete the first tempering;

[0044] Keep warm at 560-590℃, air cool after keeping warm, complete the second tempering, and control the hardness at 38-42HRC.

[0045] In another preferred embodiment of the present invention, a surface treatment method for a pre-hardened integrated die-casting mold is provided, comprising the following steps:

[0046] After the pre-hardened integrated die-casting mold is opened, shot peening is performed on the cavity surface, and three shot peening processes are completed using a shot peening process with a shot peening intensity of 0.1 to 0.33 mmA; among them, the shot material used in the shot peening process is 0.4 mm steel cut wire shot, the spraying distance is set to 15-20 mm, and the spraying flow rate is set to 4 to 8 kg / min; among them, the shot peening intensity of the first shot peening process is 0.33 mmA, and the spraying pressure is 4 bar; the shot peening intensity of the second shot peening process is 0.2 mmA, and the spraying pressure is 2 bar; the shot peening intensity of the third shot peening process is 0.1 mmA, and the spraying pressure is 1 bar.

[0047] After the pre-hardened integrated die-casting mold cavity surface is shot peened, the mold is nitrided and oxidized, and the process temperature is controlled at 540-560°C. Specifically, the mold is heated in a vacuum environment and the atmosphere is replaced in the early stage of nitriding; then the die-casting mold is nitrided according to the nitriding process, and the nitriding atmosphere is N 2 -NH 3 ; Finally, the atmosphere is replaced with water vapor, the temperature is lowered to 540℃ for oxidation treatment, and then air-cooled.

[0048] In another preferred embodiment of the present invention, a maintenance method for a pre-hardened integrated die-casting mold is provided, characterized in that it comprises the following steps:

[0049] Step 1, the mold is subjected to stress relief treatment before use, and stress relief treatment and maintenance are performed after the set number of uses; the mold is subjected to stress relief treatment before use, and stress relief treatment and maintenance are performed after the set number of uses, specifically including: the stress relief treatment temperature is set at 520-560°C, and the mold is subjected to nitriding and oxidation treatment after fine machining and mold trial completion; the mold is subjected to the first stress relief treatment when the mold is used normally in production for a total of 5,000 times; the mold is subjected to the second stress relief treatment when the mold is used for a total of 15,000 times; the mold is subjected to the third stress relief treatment when the mold is used for a total of 25,000 times; thereafter, the mold is subjected to stress relief treatment once every 20,000 times of production.

[0050] Step 2, the mold is preheated before production, and the overall temperature reaches 200-250°C; the mold is preheated before production, wherein the preheating includes using one or more of a blowtorch, liquefied gas, and natural gas to uniformly preheat the cavity surface, and using an infrared temperature gun to measure the instantaneous temperature of the mold surface.

[0051] Step 3: After a single die-casting production, the mold release agent is evenly and finely sprayed onto the surface of the cavity to form effective adhesion. Specifically, the release agent spraying time should not be too long, and should not exceed the time when the mold surface temperature is not lower than 250°C, ensuring that the mold surface temperature after spraying is not lower than 250°C.

[0052] Step 4, the mold is cleaned and maintained after each time it is taken off the machine. Specifically, the mold is cleaned after each time it is taken off the machine, including cleaning the oil stains on the surface of the mold cavity; cleaning the aluminum sticking on the surface of the cavity, if the aluminum sticking is serious, light polishing is performed to prevent poor adhesion of the release agent; cleaning the flying skin, burrs, residues, and dirt on the mold parting surface and the slider mating parts; after the mold is cleaned, the surface is evenly sprayed with WD40 type protective agent for protection, and wiped off before being put on the machine; use compressed air to clean the residual water in the cooling water pipe to prevent waterway corrosion. If there is slight cracking on the surface of the mold after it is taken off the machine, the mold is subjected to stress relief treatment and single-pass shot peening treatment in the local cracked area, with a shot peening intensity of 0.1mmA and a spray pressure of 1bar. If there is frequent aluminum sticking on the surface of the mold after it is taken off the machine, the mold surface is subjected to oxynitriding treatment.

[0053] The following will use specific embodiments to illustrate a heat treatment, surface treatment and maintenance method for a pre-hardened integrated die-casting mold provided by the present invention.

[0054] The specific application dimensions and weights of Examples 1 to 3 are shown in Table 1, and the chemical composition and mass percentage of each Example are shown in Table 2.

[0055] Table 1 Application dimensions and weight of each embodiment

[0056]

[0057]

[0058] Table 2 Chemical composition of each example (mass fraction, %)

[0059] Example C Si Mn Cr Mo Ni V Nb P S 1 0.29 0.69 0.72 3.12 0.51 0.88 0.35 0.030 0.009 0.001 2 0.30 0.70 0.69 3.36 0.46 0.92 0.30 0.028 0.009 0.004 3 0.31 0.69 0.73 3.25 0.52 0.85 0.33 0.033 0.012 0.002

[0060] Example 1

[0061] The heat treatment method in this embodiment is as follows:

[0062] Step 1, heating the material to 960° C. and keeping the temperature, and quenching the material by water mist cooling;

[0063] Step 2, heat preservation at 620°C, air cooling after heat preservation, and completing the first tempering;

[0064] Step 3, keep warm at 580°C, air cool after keeping warm, complete the second tempering, and obtain a hardness of 39-40HRC.

[0065] Example 2

[0066] The heat treatment method in this embodiment is as follows:

[0067] Step 1, heating the material to 960° C. and keeping the temperature, and quenching the material by water mist cooling;

[0068] Step 2, heat preservation at 620°C, air cooling after heat preservation, and completing the first tempering;

[0069] Step 3, heat preservation at 580°C, air cooling after heat preservation, and completing the second tempering to obtain a hardness of 39-40HRC;

[0070] Step 4: After the module is pre-hardened, the mold is opened and the surface of the module cavity is nitrided and oxidized. In the early stage of nitriding, the temperature is increased and the atmosphere is replaced in a vacuum environment. The nitriding atmosphere is N 2 -NH 3 ;

[0071] Step 5, after the nitridation process is completed, the atmosphere is replaced with water vapor, the temperature is lowered to 540°C to complete the oxidation treatment, and then air-cooled.

[0072] Example 3

[0073] The heat treatment method in this embodiment is as follows:

[0074] Step 1, heating the material to 960° C. and keeping the temperature, and quenching the material by water mist cooling;

[0075] Step 2, heat preservation at 620°C, air cooling after heat preservation, and completing the first tempering;

[0076] Step 3, heat preservation at 580°C, air cooling after heat preservation, and completing the second tempering to obtain a hardness of 39-40HRC;

[0077] Step 4: After the module is pre-hardened, the mold is opened, and then the cavity surface is shot peened three times with 0.4 mm steel cut wire shot. The first shot peening is completed with a shot distance of 15-20 mm, a shot flow of 4-8 kg / min, a shot pressure of 4 bar, and a shot peening intensity of 0.33 mmA.

[0078] Step 5, the second shot peening process is completed with a spray distance of 15-20 mm, a spray flow rate of 4-8 kg / min, a spray pressure of 2 bar, and a shot peening intensity of 0.2 mmA;

[0079] Step 6, the third shot peening process is completed with a spray distance of 15 to 20 mm, a spray flow rate of 4 to 8 kg / min, a spray pressure of 1 bar, and a shot peening intensity of 0.1 mmA;

[0080] Step 7: After the shot peening treatment is completed, the surface of the module cavity is nitrided and oxidized. In the early stage of the nitriding treatment, the temperature is increased and the atmosphere is replaced in a vacuum environment. The nitriding atmosphere is N 2 -NH 3 ;

[0081] Step 8, after the nitridation process is completed, the atmosphere is replaced with water vapor, the temperature is lowered to 540°C to complete the oxidation treatment, and then air-cooled.

[0082] After Examples 1 to 3 were processed by the above-mentioned preparation method, samples were taken for performance testing.

[0083] a. Quenched hardness and grain size

[0084] The material of the present invention (sampled from Example 1) was subjected to water quenching test at a quenching temperature of 880-1040°C. The hardness after quenching was as shown in the attached figure. Figure 1 As shown in the figure, when the quenching temperature reaches 960℃, the alloy elements in the steel are basically dissolved, and the quenching hardness reaches a peak value of 54.1HRC. As the quenching temperature continues to increase, the quenching hardness remains at 53.5~54HRC. The grain size ratings of the samples after quenching at different temperatures are shown in the attached figure. Figure 2 As shown in the figure, with the increase of quenching temperature, the grain size continues to increase, and the grain size rating gradually decreases. When the quenching temperature is higher than 1000℃, the grain size is larger, the fine grain strengthening effect will be weakened, and the mold material cannot guarantee good comprehensive mechanical properties.

[0085] b. Tempering characteristics

[0086] The material of the present invention (sampled as Example 1) is quenched at 960°C and then tempered at 200°C to 650°C. The tempering characteristic curve is shown in the attached figure. Figure 3 As shown, according to the target hardness, the optimal tempering temperature is set to 620°C, and the hardness is 39-40HRC.

[0087] c. Quenching and tempering impact toughness

[0088] The material of the present invention (sampled as Example 1) was tempered after quenching at different temperatures, and the final hardness was 39-40HRC. The quenched and tempered material was subjected to transverse impact test. The sample size was 10mm×10mm×55mm, and a V2 notch was opened. The impact test results are shown in the attached Figure 4 As shown in the figure, with the increase of quenching temperature, the original austenite grains become larger and larger, and the impact toughness of the material continues to decrease.

[0089] d. Quenched and tempered microstructure

[0090] After the heat treatment of Examples 1 to 3 of the present invention was completed, samples were taken near the cavity surface to observe the microstructure. Figure 5 As shown, the matrix structure is a dense tempered martensite structure, the lath size is small, and the morphology meets the standards of high-quality die-casting mold steel.

[0091] e. Nitriding layer thickness

[0092] The surface treatment method of Example 2 of the present invention is oxynitriding treatment, and Example 3 adopts a composite surface treatment method of oxynitriding treatment followed by shot peening treatment. The metallographic photograph of the cross section of the sample after surface treatment is shown in the attached figure. Figure 6 As shown, Example 3 obviously has a deeper nitriding layer thickness. Figure 7 The hardness gradient comparison of the sample cross section at the surface of Example 2 and Example 3 further obtains the specific nitriding layer thickness. The nitriding layer thickness of Example 2 is 150 μm, and the nitriding layer thickness of Example 3 is 226 μm. Compared with nitriding treatment, the composite surface treatment method designed by the present invention can increase the nitriding layer thickness by 50%.

[0093] f. Thermal fatigue performance

[0094] The thermal cycle was carried out from room temperature to 700°C. After 2000 thermal cycles, the thermal fatigue surface and cross-sectional crack morphologies of Example 1 and Example 2 of the present invention were compared. Figure 8 As shown in the figure, it can be seen that the surface of Example 2 is not cracked, while the surface of Example 1 has dense and deep network fatigue cracks. The surface treatment has a significant improvement on the thermal fatigue performance of the mold cavity. After 6000 hot and cold cycles, the thermal fatigue surface and cross-sectional crack morphology of the comparative samples of Example 2 and Example 3 are shown in the attached figure. Fig. 9As shown, the higher number of hot and cold cycles leads to significantly longer and wider main cracks on the surface of the sample of Example 2, and the cracking depth of the thermal fatigue main crack reaches 2330μm, which is extremely deep. After the same number of hot and cold cycles, the cracks on the surface of the sample of Example 3 are shallower, and the cracking condition is significantly better than that of the sample of Example 2. The cracking depth of the thermal fatigue main crack is 893μm. Compared with the surface nitriding treatment, the composite surface treatment method designed by the present invention can significantly improve the thermal fatigue resistance of the mold.

[0095] g. Thermal melting resistance

[0096] In the embodiments 1 to 3 of the present invention, dynamic melting loss experiments were carried out in 700°C molten ADC12 aluminum alloy, and the weight loss of the samples during dynamic melting loss within 60 minutes was compared. Fig.10 As shown. Fig.10 It can be seen that after 15min, 30min and 60min of aluminum liquid melting loss, the weight loss of Example 1 is relatively serious, while after surface treatment, there is no obvious melting loss phenomenon in Example 2 and Example 3, indicating that nitriding treatment and the composite surface treatment designed by the present invention can improve the mold's resistance to aluminum liquid melting loss.

[0097] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A heat treatment method for a pre-hardened integrated die-casting mold, characterized in that: The following steps are involved: The material for preparing the pre-hardened integrated die-casting mold is heated to 960-1000°C for insulation, and quenched by water mist cooling; Keep warm at 600-630℃, then air cool to complete the first tempering; Keep warm at 560-590℃, air cool after keeping warm, complete the second tempering, and control the hardness at 38-42HRC.

2. A surface treatment method for a pre-hardened integrated die-casting mold, characterized in that: The following steps are involved: After the pre-hardened integrated die-casting mold is opened, the cavity surface is shot peened, and three shot peening processes are completed using a shot peening process with a shot peening intensity of 0.1 to 0.33 mmA; After the cavity surface of the pre-hardened integrated die-casting mold is shot peened, the mold is nitrided and oxidized, and the process temperature is controlled at 540-560°C.

3. The surface treatment method of a pre-hardened integrated die-casting mold according to claim 2, characterized in that: The shot material used in the shot peening treatment is 0.4 mm steel cut wire shot, the spraying distance is set to 15-20 mm, and the spraying flow rate is set to 4-8 kg / min; wherein, the shot peening intensity of the first shot peening process is 0.33 mmA, and the spraying pressure is 4 bar; the shot peening intensity of the second shot peening process is 0.2 mmA, and the spraying pressure is 2 bar; the shot peening intensity of the third shot peening process is 0.1 mmA, and the spraying pressure is 1 bar.

4. The surface treatment method of a pre-hardened integrated die-casting mold according to claim 2, characterized in that: In the early stage of nitriding treatment, the mold is heated up and the atmosphere is replaced in a vacuum environment; then the nitriding treatment is carried out according to the die-casting mold nitriding process, and the nitriding atmosphere is N2-NH3; finally, the atmosphere is replaced with water vapor, and the temperature is lowered to 540℃ for oxidation treatment, and then air-cooled.

5. A maintenance method for a pre-hardened integrated die-casting mold, characterized in that: The following steps are involved: The mold is stress relieved before use and stress relieved and maintained after the set number of uses; The mold is preheated before production, and the overall temperature reaches 200-250°C; After a single die-casting production of the mold, the mold release agent is evenly and finely sprayed onto the surface of the cavity to form effective adhesion; The mold is cleaned and maintained after each time it is taken off the machine.

6. A method for maintaining a pre-hardened integrated die-casting mold according to claim 5, characterized in that: The mold is subjected to stress relief treatment before use, and stress relief treatment and maintenance after being used for a set number of times, including: the stress relief treatment temperature is set at 520-560°C, and the mold is subjected to nitriding and oxidation treatment after fine machining and mold trial; the first stress relief treatment is carried out when the mold is used normally in production for a total of 5,000 times; the second stress relief treatment is carried out when the mold is used for a total of 15,000 times; the third stress relief treatment is carried out when the mold is used for a total of 25,000 times; thereafter, the mold is subjected to stress relief treatment every 20,000 times of production.

7. A method for maintaining a pre-hardened integrated die-casting mold according to claim 5, characterized in that: The mold is preheated before production, wherein the preheating includes using one or more of a blowtorch, liquefied gas, and natural gas to uniformly preheat the cavity surface, and using an infrared temperature gun to measure the instantaneous temperature of the mold surface.

8. A method for maintaining a pre-hardened integrated die-casting mold according to claim 5, characterized in that: After a single die-casting production of the mold, the release agent is evenly and finely sprayed onto the surface of the cavity to form effective adhesion. Specifically, the surface temperature of the mold after spraying is ensured to be no less than 250°C, and the release agent spraying time is controlled to be the time when the surface temperature of the mold after spraying is no less than 250°C.

9. A method for maintaining a pre-hardened integrated die-casting mold according to claim 5, characterized in that: The mold is cleaned after each time it is taken off the machine, specifically including cleaning the oil stains on the surface of the mold cavity; cleaning the aluminum sticking on the surface of the cavity, and if the aluminum sticking is serious, light polishing is performed to prevent poor adhesion of the release agent; cleaning the flying skin, burrs, residues, and dirt on the mold parting surface and the slider matching parts; after the mold is cleaned, the surface is evenly sprayed with WD40-type protective agent for protection, and wiped off before being put on the machine; using compressed air to clean the residual water in the cooling water pipe to prevent waterway corrosion.

10. A method for maintaining a pre-hardened integrated die-casting mold according to claim 9, characterized in that: If slight cracks appear on the surface of the mold after it is removed from the machine, the mold will be subjected to stress relief treatment and single-pass shot peening treatment in the cracked local area. The shot peening intensity is 0.1mmA and the injection pressure is 1bar.

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