A heat treatment process for improving the demolding performance of alloy steel based on gradient coating

Abstract

This invention discloses a heat treatment process for improving the demolding performance of alloy steel based on gradient coating, belonging to the field of alloy steel surface modification and heat treatment technology. Addressing industry pain points such as high surface roughness, high demolding resistance, easy sticking and tearing, and poor adhesion of conventional hard coatings in existing mold alloy steel, this invention proposes a composite modification process involving substrate tempering pretreatment, refined surface etching, a low-stress metal transition underlayer, a friction-reducing and wear-resistant gradient functional coating, a low surface energy hydrophobic lubricating surface layer, and integrated tempering and shaping of the coating. This invention innovatively couples and synergizes gradient coating preparation with heat treatment, controlling the hardness and structural stress of the substrate through heat treatment, achieving a gradual transition of mechanical properties through the gradient coating, and constructing a low surface energy lubricating film on the surface, significantly reducing the interfacial adhesion and frictional resistance between the steel mold and the molding material.

Description

Technical Field

[0001] This invention belongs to the field of alloy steel surface modification and heat treatment technology, specifically, it relates to a heat treatment process for improving the demolding performance of alloy steel based on gradient coating. Background Technology

[0002] Mold alloy steel is a core material in the molding and processing industry, widely used in the compression molding process of plastics, non-ferrous metals, rubber, and powder materials. During molding operations, high-temperature molten materials easily wet the surface of the mold steel, generating strong adhesion through molecular adsorption, leading to difficulties in demolding. Traditional mold alloy steel, after conventional quenching and tempering treatment, generally suffers from problems such as high surface roughness, high surface energy, and high coefficient of friction, which can easily cause defects such as workpiece scratches, sticking to the mold, and tearing at the edges and corners during demolding. Frequent manual demolding not only significantly reduces production efficiency but also damages the mold cavity surface and shortens the mold's service life. Simply relying on mechanical polishing to reduce surface roughness can lead to wear and failure of the mold surface during long-term use, resulting in poor long-term demolding ability and requiring frequent polishing maintenance. Using a single release agent by spraying can contaminate the molded workpiece and has poor heat resistance. In high-temperature molding environments, it is easy to carbonize and leave residues, forming carbon deposits that affect mold precision and product quality. Although conventional hard coatings have high hardness, they also have a high coefficient of friction and weak interfacial bonding with the substrate. Under the mechanical stress of repeated demolding, they are prone to peeling and flaking, which in turn exacerbates the demolding difficulty. Existing technologies generally treat heat treatment and coating preparation as two separate processes, which leads to a mismatch between the residual stress of the substrate and the deposition stress of the coating. This makes the coating prone to cracking and peeling, and fails to achieve a long-term stable demolding effect. Most coatings use a single structure, and there is a sudden change in the physical properties (such as hardness and elastic modulus) between the substrate and the coating. Under thermal cycling conditions, the interfacial stress concentration is severe, resulting in a short service life of the coating. In summary, the industry currently lacks a coupled process that can organically combine heat treatment to regulate the properties of the substrate with gradient coating to modify the surface properties, making it impossible to simultaneously meet the multiple requirements of high substrate strength, high coating adhesion, and low surface adhesion. Therefore, developing a composite process that combines heat treatment strengthening with gradient lubrication coating to specifically improve the demolding performance of alloy steel has significant industrial practical value and economic benefits.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a heat treatment process based on gradient coating to improve the demolding performance of alloy steel, thereby solving the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows: A heat treatment process for improving the demolding performance of alloy steel based on gradient coating includes the following sequential process steps: Step (1) Substrate pretreatment: Grinding and polishing, sandblasting to remove impurities, and ultrasonic cleaning with organic solvents are performed on the alloy steel mold workpiece to remove surface oxide scale, oil stains and processing burrs. After drying, the surface roughness is controlled at Ra 0.8~2.5 μm. Among them, brown corundum micro sand is used for sandblasting, the sandblasting pressure is 0.20~0.40 MPa, and anhydrous ethanol and acetone mixed solvent is used for ultrasonic cleaning, with a cleaning time of 15~30 min. Step (2) Tempering heat treatment: The cleaned alloy steel workpiece is sent into a vacuum heat treatment furnace and heated to 860-950 ℃ at a rate of 4-9 ℃ / min, held for 1.5-2.5 h, and then cooled by oil quenching; then a two-stage tempering is performed, with the first stage tempering at 520-580 ℃ for 1.0-2.0 h and the second stage tempering at 400-460 ℃ for 0.8-1.5 h, followed by air cooling to room temperature; wherein, quenching oil is used for oil quenching, with a cooling rate of 25-40 ℃ / min, and nitrogen is introduced throughout the two-stage tempering process to prevent surface oxidation and discoloration; Step (3) Surface etching activation: Place the heat-treated workpiece in a vacuum coating equipment and evacuate to 2.5 × 10⁻⁶. -3 ~6.0×10 -3 High-purity argon gas was introduced, and plasma bias etching was performed at a bias voltage of -100 to -160 V, an etching power of 320 to 580 W, and a processing time of 15 to 35 min. The flow rate of the high-purity argon gas was controlled at 30 to 80 sccm, and the vacuum level was maintained within ±0.5 × 10⁻⁶ during the etching process. -3 Pa; Step (4) Preparation of metal transition layer: NiCo alloy transition layer is deposited by magnetron sputtering at a deposition temperature of 240-320 ℃ and a sputtering power of 150-240 W. The layer thickness is 5-15 μm to improve the bonding strength between the coating and the substrate. The mass ratio of NiCo alloy transition layer is 55%-70% Ni and 30%-45% Co. The layer is free of pores and cracks. Step (5) Preparation of friction-reducing and wear-resistant gradient coating: Adjust the target material ratio and reaction gas flow rate layer by layer to prepare a metal-ceramic composite gradient coating. The content of hard ceramic phase inside the coating gradually changes from 10% to 45%, the total thickness of the gradient layer is 20-40 μm, and the deposition temperature is 280-380 ℃. The metal phase of the gradient coating is NiCo alloy, and the ceramic phase is one or a combination of two of TiC and Si3N4. The metal-ceramic composite gradient coating adopts a 3-8 layer continuous gradient structure, with the ceramic phase content increasing by 5%-8% in each layer, and there is no obvious interface between the layers. Step (6) Low surface energy lubricant seal: A fluorine-doped diamond-like lubricant seal is deposited on the gradient coating surface. The seal thickness is 3-10 μm, and the deposition temperature is 310-400 ℃ to reduce the surface energy of the coating. The fluorine-doped diamond-like seal contains 4%-9% fluorine by mass. Step (7) Coating tempering and setting: The coated workpiece is sent into a vacuum tempering furnace with a vacuum degree ≤ 4.0 × 10 -2 Pa is heated to 360–420 ℃ at a rate of 2–4 ℃ / min, held at that temperature for 1.0–2.2 h, and then slowly cooled to room temperature in the furnace to complete the modification treatment. The furnace cooling rate is controlled at 1.2–3.5 ℃ / min, and the material is removed from the furnace only when cooled to below 150 ℃ to eliminate coating deposition stress and residual stress from the substrate heat treatment.

[0006] Optionally, the alloy steel can be any one of cold work die steel, hot work die steel, alloy structural steel, or wear-resistant die alloy steel.

[0007] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art. Of course, any product implementing the present invention does not necessarily need to achieve all of the following advantages at the same time: 1. This invention achieves excellent demolding performance and extremely low interfacial adhesion by constructing a low surface energy hydrophobic lubricating surface layer on the mold surface. There is no sticking, no tearing, and no carbon residue during the demolding process.

[0008] 2. This invention adopts a gradient coating structure design with continuous and gradual changes in metal and ceramic, which realizes a smooth transition of hardness and elastic modulus layer by layer, avoids abrupt changes in physical properties and stress concentration at the interface between the substrate and the coating, and the coating has high bonding strength. Under the mechanical stress of repeated demolding and the action of hot and cold cycles, there is no peeling, detachment or cracking.

[0009] 3. This invention couples and coordinates gradient coating preparation with heat treatment process, adopting a process sequence of first tempering and strengthening the substrate, then modifying the surface of the coating, and finally tempering and shaping the coating at low temperature. This not only ensures that the substrate has excellent structural strength and deformation resistance, but also gives the mold surface good lubrication and mold release properties, thus achieving the best match between the properties of the substrate and the coating.

[0010] 4. The friction-reducing and wear-resistant gradient coating and low surface energy lubricating seal prepared by this invention have extremely low friction coefficients and excellent wear resistance and scratch resistance. Long-term mold opening and closing does not easily produce scratches and wear, thus extending the service life of the mold.

[0011] 5. The modified alloy steel mold prepared by this invention has a long-lasting and stable demolding effect, eliminating the need for frequent spraying of demolding agents, avoiding the problems of demolding agent contamination of the molded workpiece and high-temperature carbonization residue, while reducing the number of mold cleaning and maintenance operations, lowering production costs, and improving production efficiency.

[0012] 6. The present invention has a mature process, good repeatability, and low production cost. It is compatible with existing vacuum heat treatment furnaces and magnetron sputtering equipment. It is applicable to various forming mold alloy steels such as cold work mold steel, hot work mold steel, alloy structural steel, and wear-resistant mold alloy steel. It can be widely used in industrial mold manufacturing fields such as plastic injection molding, die casting, rubber pressing, and powder metallurgy molding. It has industrialization promotion value and economic benefits.

[0013] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0014] The accompanying drawings described below are merely some embodiments. Those skilled in the art can obtain other drawings based on these drawings without any creative effort. In the drawings: Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0015] The invention will now be described in further detail with reference to the accompanying drawings.

[0016] Please see Figure 1 As shown, this embodiment provides a heat treatment process for improving the demolding performance of alloy steel based on gradient coating, including the following sequential process steps: Step (1) Substrate pretreatment: Grinding and polishing, sandblasting to remove impurities, and ultrasonic cleaning with organic solvents are performed on the alloy steel mold workpiece to remove surface oxide scale, oil stains and processing burrs. After drying, the surface roughness is controlled at Ra 0.8~2.5 μm. Among them, brown corundum micro sand is used for sandblasting, the sandblasting pressure is 0.20~0.40 MPa, and anhydrous ethanol and acetone mixed solvent is used for ultrasonic cleaning, with a cleaning time of 15~30 min. Step (2) Tempering heat treatment: The cleaned alloy steel workpiece is sent into a vacuum heat treatment furnace and heated to 860-950 ℃ at a rate of 4-9 ℃ / min, held for 1.5-2.5 h, and then cooled by oil quenching; then a two-stage tempering is performed, with the first stage tempering at 520-580 ℃ for 1.0-2.0 h and the second stage tempering at 400-460 ℃ for 0.8-1.5 h, followed by air cooling to room temperature; wherein, quenching oil is used for oil quenching, with a cooling rate of 25-40 ℃ / min, and nitrogen is introduced throughout the two-stage tempering process to prevent surface oxidation and discoloration; Step (3) Surface etching activation: Place the heat-treated workpiece in a vacuum coating equipment and evacuate to 2.5 × 10⁻⁶. -3 ~6.0×10 -3 High-purity argon gas was introduced, and plasma bias etching was performed at a bias voltage of -100 to -160 V, an etching power of 320 to 580 W, and a processing time of 15 to 35 min. The flow rate of the high-purity argon gas was controlled at 30 to 80 sccm, and the vacuum level was maintained within ±0.5 × 10⁻⁶ during the etching process. -3 Pa; Step (4) Preparation of metal transition layer: NiCo alloy transition layer is deposited by magnetron sputtering at a deposition temperature of 240-320 ℃ and a sputtering power of 150-240 W. The layer thickness is 5-15 μm to improve the bonding strength between the coating and the substrate. The mass ratio of NiCo alloy transition layer is 55%-70% Ni and 30%-45% Co. The layer is free of pores and cracks. Step (5) Preparation of friction-reducing and wear-resistant gradient coating: Adjust the target material ratio and reaction gas flow rate layer by layer to prepare a metal-ceramic composite gradient coating. The content of hard ceramic phase inside the coating gradually changes from 10% to 45%, the total thickness of the gradient layer is 20-40 μm, and the deposition temperature is 280-380 ℃. The metal phase of the gradient coating is NiCo alloy, and the ceramic phase is one or a combination of two of TiC and Si3N4. The metal-ceramic composite gradient coating adopts a 3-8 layer continuous gradient structure, with the ceramic phase content increasing by 5%-8% in each layer, and there is no obvious interface between the layers. Step (6) Low surface energy lubricant seal: A fluorine-doped diamond-like lubricant seal is deposited on the gradient coating surface. The seal thickness is 3-10 μm, and the deposition temperature is 310-400 ℃ to reduce the surface energy of the coating. The fluorine-doped diamond-like seal contains 4%-9% fluorine by mass. Step (7) Coating tempering and setting: The coated workpiece is sent into a vacuum tempering furnace with a vacuum degree ≤ 4.0 × 10 -2Pa is heated to 360–420 ℃ at a rate of 2–4 ℃ / min, held at that temperature for 1.0–2.2 h, and then slowly cooled to room temperature in the furnace to complete the modification treatment. The furnace cooling rate is controlled at 1.2–3.5 ℃ / min, and the material is removed from the furnace only when cooled to below 150 ℃ to eliminate coating deposition stress and residual stress from the substrate heat treatment.

[0017] The alloy steel described in this embodiment is any one of cold work die steel, hot work die steel, alloy structural steel, and wear-resistant die alloy steel.

[0018] Example 1 (Cold work die alloy steel Cr12MoV) Substrate pretreatment: Brown corundum micro-blasting was performed at a pressure of 0.30 MPa; ultrasonic cleaning was performed for 22 min using a mixed solvent of anhydrous ethanol and acetone; after drying, the surface roughness Ra was 1.2 μm. Tempering heat treatment: The temperature is raised to 910℃ in a vacuum furnace at 6℃ / min and held for 2.0h. The oil quenching cooling rate is 32℃ / min. The first tempering is held at 550℃ for 1.5h, and the second tempering is held at 430℃ for 1.2h. Nitrogen protection is maintained throughout the process, and the temperature is air-cooled to room temperature. Surface etching activation: vacuum degree 4.2×10 -3 Pa; High-purity argon gas was introduced at a flow rate of 55 sccm; Plasma bias voltage was -130V, power was 450W, and etching time was 22 min; Vacuum fluctuation was ≤ ±0.4 × 10⁻⁶. -3 Pa; Metal transition substrate: magnetron sputtered NiCo alloy (65% Ni, 35% Co), deposition temperature 290℃, power 200W, thickness 10μm; the substrate is free of pores and cracks; Friction-reducing and wear-resistant gradient coating: TiC-NiCo composite gradient coating, with a total of 5 layers; the ceramic phase content increases by 5% to 8% in each layer from 12%, 18%, 25%, 34%, to 42%; the total thickness is 30μm, the deposition temperature is 330℃, and there is no obvious interface between the layers; Low surface energy lubricating seal: Fluorine-doped diamond-like layer, 6 μm thick, deposition temperature 350 °C; Coating tempering and setting: vacuum degree 2.5×10 -2 Pa, heat to 390℃ at 3℃ / min, hold for 1.6h; cool with furnace at 2.2℃ / min, cool to 120℃ and remove from furnace.

[0019] Example 2 (Hot work die alloy steel H13) Matrix pretreatment: brown fused alumina sandblasting at a pressure of 0.25 MPa; ultrasonic cleaning with anhydrous ethanol and acetone for 18 min; Ra 1.8 μm after drying; Heat treatment: heating to 880℃ at 5℃ / min, holding for 2.2h, oil quenching cooling rate 28℃ / min; first-stage tempering at 530℃ for 1.8h, second-stage tempering at 410℃ for 1.0h, nitrogen protection, air cooling to room temperature; Surface etching activation: vacuum degree 3.5×10 -3 Pa; Argon flow rate 45 sccm; Bias voltage -115V, power 380W, etching 18min; Vacuum fluctuation ≤ ±0.3×10 -3 Pa; Metal transition substrate: NiCo alloy (60% Ni, 40% Co), deposition temperature 270℃, power 180W, thickness 7μm; free of pores and cracks; Friction-reducing and wear-resistant gradient coating: Si3N4-NiCo composite gradient coating, with a total of 4 layers; the ceramic phase content increases by 5% to 8% in each layer from 11%, 17%, 26%, to 40%; the total thickness is 25μm, and the deposition temperature is 310℃; there are no obvious interfaces between the layers. Low surface energy lubricating seal: fluorine-doped diamond-like carbon layer, 4.5 μm thick, deposition temperature 330 °C; Coating tempering and setting: vacuum degree 3.0×10 -2 Pa, heat to 370℃ at 2.5℃ / min, hold for 2.0h; cool with furnace at 1.8℃ / min, cool to 110℃ and remove from furnace.

[0020] It should be noted that all electrical devices involved in this application can be powered by batteries or external power sources.

[0021] It should be noted that the accompanying drawings and textual descriptions in this application are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments.

[0022] This invention is not limited to the embodiments described above. Anyone should understand that structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention. Technical aspects, shapes, and structures not described in detail in this invention are all publicly known technologies.

Claims

1. A heat treatment process for improving the demolding performance of alloy steel based on gradient coating, characterized in that, Includes the following steps: Step (1): Grind and polish the workpiece, sandblast to remove impurities, and ultrasonically clean it with organic solvent to remove surface oxide scale, oil stains and processing burrs. After drying, the surface roughness is controlled at Ra 0.8~2.5 μm. Step (2): The cleaned workpiece is sent into a vacuum heat treatment furnace and heated to 860-950 ℃ at a rate of 4-9 ℃ / min. It is held for 1.5-2.5 h and then cooled by oil quenching. Then, it undergoes two-stage tempering: the first stage tempering is held at 520-580 ℃ for 1.0-2.0 h, and the second stage tempering is held at 400-460 ℃ for 0.8-1.5 h. It is then air-cooled to room temperature. Step (3): Place the tempered workpiece in a vacuum coating equipment and evacuate it to a vacuum level of 2.5 × 10⁻⁶. -3 ~6.0×10 -3 Pa, high-purity argon gas is introduced, and plasma bias etching is performed with a bias voltage of -100 to -160 V, an etching power of 320 to 580 W, and a processing time of 15 to 35 min; Step (4): Deposit a NiCo alloy transition underlayer using magnetron sputtering at a deposition temperature of 240–320 °C, a sputtering power of 150–240 W, and an underlayer thickness of 5–15 μm to improve the bonding strength between the coating and the substrate. Step (5): Adjust the target material ratio and reaction gas flow rate layer by layer to prepare a metal-ceramic composite gradient coating. The content of hard ceramic phase inside the coating gradually changes from 10% to 45%, the total thickness of the gradient layer is 20-40 μm, and the deposition temperature is 280-380℃. Step (6): Deposit a fluorine-doped diamond-like lubricant seal layer on the gradient coating surface. The seal layer thickness is 3-10 μm and the deposition temperature is 310-400 ℃ to reduce the surface energy of the coating. Step (7): Place the coated workpiece into a vacuum tempering furnace with a vacuum degree ≤ 4.0 × 10⁻⁶. -2 Pa is heated to 360–420 °C at a rate of 2–4 °C / min, held at that temperature for 1.0–2.2 h, and then slowly cooled to room temperature in the furnace to complete the modification treatment.

2. The heat treatment process for improving the demolding performance of alloy steel based on gradient coating according to claim 1, characterized in that, The alloy steel is any one of cold work die steel, hot work die steel, alloy structural steel, and wear-resistant die alloy steel.

3. The heat treatment process for improving the demolding performance of alloy steel based on gradient coating according to claim 1, characterized in that, Step (1) Sandblasting uses brown corundum micro-abrasive, with a sandblasting pressure of 0.20-0.40 MPa. Ultrasonic cleaning uses a mixture of anhydrous ethanol and acetone as solvents, with a cleaning time of 15-30 min.

4. The heat treatment process for improving the demolding performance of alloy steel based on gradient coating according to claim 1, characterized in that, Step (2) uses quenching oil with a cooling rate of 25-40 ℃ / min. Nitrogen gas is introduced throughout the two-stage tempering process to prevent surface oxidation and discoloration.

5. The heat treatment process for improving the demolding performance of alloy steel based on gradient coating according to claim 1, characterized in that, In step (3), the flow rate of high-purity argon gas is controlled at 30–80 sccm, and the vacuum fluctuation range during etching is kept within ±0.5 × 10⁻⁶. -3 Pa.

6. The heat treatment process for improving the demolding performance of alloy steel based on gradient coating according to claim 1, characterized in that, Step (4) The NiCo alloy transition layer has a mass ratio of 55% to 70% Ni and 30% to 45% Co. The layer is free of pores and cracks.

7. The heat treatment process for improving the demolding performance of alloy steel based on gradient coating according to claim 1, characterized in that, Step (5) The gradient coating metal phase is NiCo alloy, and the ceramic phase is one or a combination of two of TiC and Si3N4.

8. The heat treatment process for improving the demolding performance of alloy steel based on gradient coating according to claim 1, characterized in that, The metal-ceramic composite gradient coating described in step (5) adopts a 3-8 layer continuous gradient structure, with the ceramic phase content of each layer increasing by 5%-8%, and there is no obvious interface between the layers.

9. The heat treatment process for improving the demolding performance of alloy steel based on gradient coating according to claim 1, characterized in that, Step (6) The mass fraction of fluorine in the fluorine-doped diamond-like coating is 4% to 9%.

10. The heat treatment process for improving the demolding performance of alloy steel based on gradient coating according to claim 1, characterized in that, Step (7) Slowly cool the furnace to room temperature. During the cooling process, the rate is controlled at 1.2 to 3.5 °C / min. Cool to below 150 °C before removing from the furnace to eliminate coating deposition stress and residual stress from substrate heat treatment.

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