A punch coating and a method for producing the same

Abstract

The application discloses a punch coating and a preparation method thereof, and belongs to the field of material surface strengthening. The method aims at solving the problems of easy cracking of the punch coating, large heat affected zone of the substrate and uneven performance of the punch coating caused by high heat input of traditional laser cladding technology. The core of the application lies in the adoption of the ultra-high-speed laser cladding technology, and the synergistic control of the 012Al alloy powder composition, the optimization of the cladding path and the process parameters. The method can effectively reduce the heat input, utilize the residual heat of subsequent cladding to perform in-situ heat treatment on the service end of the first cladding, promote the release of residual stress and the precipitation of hard carbide, and finally obtain the punch coating with dense structure, no cracks, high hardness (average 56 HRC, 58 HRC at the service end) and significantly prolonged service life by combining with subsequent stress relief annealing.

Description

Technical Field

[0001] This invention relates to the field of material surface strengthening, and discloses a punch coating and its preparation method. Background Technology

[0002] Punch components used in industrial applications such as die casting and hot extrusion are subjected to high temperatures, high pressures, and cyclic mechanical impacts over extended periods. Their surfaces are prone to high-temperature wear, thermal fatigue cracks, and molten metal adhesion, leading to a significant reduction in service life. While manufacturing the entire punch using high-alloy tool steels such as 012Al can meet the base strength requirements, the material cost is prohibitively high, and localized wear failure can render the entire component unusable, resulting in resource waste. Therefore, the industry commonly employs a composite design approach of "substrate + coating," where a high-performance wear-resistant coating is applied to a low-cost substrate surface, thus balancing economic efficiency and surface performance.

[0003] Among numerous surface strengthening technologies, laser cladding has attracted widespread attention due to its advantages such as achieving metallurgical bonding between the coating and the substrate, fine microstructure, and high hardness. However, traditional laser cladding technology has a high heat input, which easily leads to an excessively large heat-affected zone (typically 170–300 μm) on the substrate. This not only causes workpiece deformation but also generates defects such as pores and cracks in the coating. At the same time, the performance of the bonding area is degraded due to thermal stress concentration, seriously affecting the reliability and service life of the coating. In contrast, ultra-high-speed laser cladding technology, through extremely high scanning speeds (20–500 m / min) and a unique laser-powder-molten pool energy distribution method, significantly reduces the heat input, reducing the depth of the heat-affected zone to 20–50 μm and the coating dilution rate to <5%. This effectively suppresses thermal damage and crack formation in the substrate, while the powder utilization rate can reach over 90%, offering advantages in both energy saving and material conservation.

[0004] Nevertheless, during laser cladding, the substrate temperature continues to rise due to heat accumulation, leading to a decrease in the coating's solidification and cooling rate. This, in turn, causes fluctuations in the coating's microstructure (such as grain size and hard phase distribution) and macroscopic properties (such as hardness and wear resistance). For components like punches that require highly consistent surface properties, such fluctuations directly affect their service stability under high-temperature and high-load conditions. Therefore, a systematic process design is essential to actively control heat input, temperature field, and material system to ensure the uniformity and reliability of the coating performance.

[0005] Currently, the preparation of a crack-free, high-performance coating for 012Al steel punches is a technical challenge that urgently needs to be overcome. Therefore, it is necessary to develop a punch coating and its preparation method. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the technical problem solved by the present invention is to provide a method for preparing 012Al coating by ultra-high speed laser cladding, which constructs a high-performance punch coating by synergistically controlling powder characteristics, cladding path and process parameters, reducing cracking tendency and heat input control, and achieving good microstructure and performance matching.

[0007] The specific solution of the present invention is as follows:

[0008] This invention provides a punch coating and its preparation method, mainly including the following steps:

[0009] 1. Characteristics of alloy powder (by mass percentage)

[0010] C: 0.50~0.55; Si: 0.8~1.0; Cr: 3.8~4.0; Mo: 2.8~3.5; V: 1.0~1.2; Mn: 0.8~1.1; Al: 0.3~0.4; O≤0.008; S:≤0.005%; P:≤0.005%. Particle size 15~53 µm, flowability 18.2 s / 50g.

[0011] 2. Coating process

[0012] This invention also provides a method for preparing the above-mentioned high-performance high-speed steel coating, which mainly includes the following steps:

[0013] (1) Preheating of workpiece: Place the workpiece and powder in an 80℃ vacuum oven and keep them warm for 3 to 5 hours. The holding time should be controlled according to the size of the workpiece.

[0014] (2) Coating parameters: The cladding direction is from the main service end to the non-service end. A semiconductor laser is used to perform laser cladding on the surface of the substrate. The process parameters are: spot diameter 3 mm, laser beam focus positive defocus 2 mm, laser power 1500~5000 W, scanning line speed 25~30 m / min, overlap rate 60%, powder feeding rate 75~90 g / min, to obtain a 012Al steel coating with a thickness of 1~2 mm;

[0015] (3) Stress relief parameters: After the coating punch is air-cooled to room temperature, it should be immediately placed in a vacuum oven at 200-400℃ for 2-3 hours to release stress, which can prevent cracking during subsequent coating machining.

[0016] (4) Processing test: The mechanical properties and microstructure of the coating were characterized. The coating had only pores of about 3 micrometers in size that could not be avoided by the process. Almost no cracks were observed. The average hardness of the coating was 56 HRC and the hardness of the service end was 58 HRC.

[0017] The technical principles of this invention will now be introduced:

[0018] In this invention, based on the material properties of 012Al steel, the wear resistance of its coating mainly originates from the high-hardness vanadium carbides dispersed in the matrix; while the red hardness benefits from the secondary hardening effect produced by alloying elements such as molybdenum and vanadium, as well as the stable tempered structure formed during the coating process. These reinforcing phases are uniformly distributed in the tough martensitic matrix, jointly ensuring that the coating possesses both excellent wear resistance and resistance to softening deformation under harsh conditions of high temperature and high pressure.

[0019] In this invention, the cladding path strategy and key process parameters are specifically optimized. By sequentially cladding from the working end to the non-working end of the workpiece, the accumulated residual heat generated by subsequent laser processing can create a continuous in-situ thermal effect on the first-clad area (especially the working end). This effect not only promotes the release of residual stress within the coating but also further drives the precipitation and growth of carbides such as VC, thereby progressively improving the overall performance of the coating at the working end. Furthermore, this path strategy, combined with subsequent systematic stress relief processes, can significantly reduce the macroscopic residual stress and microscopic cracking tendency of the coating, effectively extending the service life of the coating.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention achieves a synergistic balance between high performance and low defects in the 012Al coating. By controlling material composition, cladding strategy, cladding process, and stress relief, minimal defects are achieved, resulting in an average coating hardness of 56 HRC, with the hardness at the critical service end further increased to 58 HRC, significantly improving the wear resistance and load-bearing capacity of the punch surface.

[0022] This invention achieves gradient performance enhancement and stress regulation through a cladding path strategy. By adopting a sequential cladding path "from the main service end to the non-service end", a continuous "in-situ post-heating" effect is formed, reducing the participating stress and improving the characteristics of the strengthening phase. Attached Figure Description

[0023] Figure 1 The microstructure of the 012Al coating in the example is shown. Detailed Implementation

[0024] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0025] Example

[0026] A punch coating and its preparation method, characterized by comprising the following steps:

[0027] 1) Matrix and Powder: The matrix is ​​a die-casting punch (100mm in diameter) made of H13 steel hot work die steel. The spraying powder is 012Al alloy powder that meets the requirements of this invention, and its composition (mass percentage) is strictly controlled as follows: C: 0.52, Si: 0.9, Cr: 3.9, Mo: 3.2, V: 1.1, Mn: 0.9, Al: 0.35, O: 0.006, S: 0.003, P: 0.004, with a particle size distribution of 15-53 µm;

[0028] 2) Pretreatment: The punch substrate and 012Al alloy powder are placed in an 80℃ vacuum oven and kept at that temperature for 4 hours. The vacuum degree is ≤1×10⁻²Pa, which effectively removes moisture and adsorbed gases.

[0029] 3) Cladding: A semiconductor laser is used, with a laser power of 2000 W, a scanning speed of 25 m / min, a spot diameter of 3 mm, an overlap rate of 60%, and a powder feeding rate of 75 g / min. The cladding path strictly follows the sequence from the working end (top) of the punch to the non-working end (tail).

[0030] 4) Post-treatment: After the cladding is completed, the workpiece is air-cooled to room temperature, and then immediately placed in a vacuum oven at 300℃ for 2.5 hours for stress-relieving annealing.

[0031] The resulting coating thickness was approximately 1.2 mm. Testing revealed a dense and uniform coating with only a small number of inherent process pores of approximately 3 micrometers in size, and no macroscopic or microscopic network cracks were observed. The average hardness of the coating was 56 HRC, while the hardness of the working end region significantly increased to 58 HRC, forming an ideal performance gradient.

[0032] Comparative Example 1

[0033] A punch coating and its preparation method, characterized by comprising the following steps:

[0034] 1) Matrix and Powder: The matrix is ​​a die-casting punch (100 mm in diameter) made of H13 steel hot work die steel. The spraying powder is 012Al alloy powder that meets the requirements of this invention, and its composition (mass percentage) is strictly controlled as follows: C: 0.52, Si: 0.9, Cr: 3.9, Mo: 3.2, V: 1.1, Mn: 0.9, Al: 0.35, O: 0.006, S: 0.003, P: 0.004, with a particle size distribution of 15-53 µm;

[0035] 2) Pretreatment: The punch substrate and 012Al alloy powder are placed in an 80℃ vacuum oven and kept at that temperature for 4 hours. The vacuum degree is ≤1×10⁻²Pa, which effectively removes moisture and adsorbed gases.

[0036] 3) Cladding: A semiconductor laser is used, with a laser power of 2000 W, a scanning speed of 25 m / min, a spot diameter of 3 mm, an overlap rate of 60%, and a powder feeding rate of 75 g / min. The cladding path is changed to proceed from the tail end of the punch towards the working end.

[0037] 4) Post-treatment: After the cladding is completed, the workpiece is air-cooled to room temperature, and then immediately placed in a vacuum oven at 300℃ for 2.5 hours for stress-relieving annealing.

[0038] The resulting coating thickness was approximately 1.2 mm. Testing revealed a dense and uniform coating with only a small number of inherent process pores of approximately 3 micrometers in size. Due to the continuous conduction of heat generated during cladding to the uncoated, cold working end area, the heat accumulation effect intensified in this region. Obvious microcracks appeared at the edge of the working end of the coating, and the hardness in this area fluctuated significantly (52–55 HRC), indicating uneven performance.

[0039] Comparative Example 2

[0040] A punch coating and its preparation method, characterized by comprising the following steps:

[0041] 1) Matrix and Powder: The matrix is ​​a die-casting punch (100 mm in diameter) made of H13 steel hot-work die steel. The spraying powder is 012Al alloy powder conforming to the requirements of this invention, with its composition (mass percentage) strictly controlled as follows: C: 0.52, Si: 0.9, Cr: 3.9, Mo: 3.2, V: 1.1, Mn: 0.9, Al: 0.35, O: 0.012, S: 0.003, P: 0.004, and a particle size distribution of 15–53 µm.

[0042] 2) Pretreatment: The punch substrate and 012Al alloy powder are placed in an 80℃ vacuum oven and kept at that temperature for 4 hours. The vacuum degree is ≤1×10⁻²Pa, which effectively removes moisture and adsorbed gases.

[0043] 3) Cladding: A semiconductor laser is used, with laser power increased to 6000 W, scanning speed reduced to 8 m / min, spot diameter 3 mm, overlap rate 60%, and powder feeding rate 95 g / min. The cladding path is changed to proceed from the tail end of the punch towards the working end.

[0044] 4) Post-treatment: After the cladding is completed, the workpiece is air-cooled to room temperature, and then immediately placed in a vacuum oven at 300℃ for 2.5 hours for stress-relieving annealing.

[0045] The resulting coating thickness was approximately 1.7 mm. Testing revealed numerous process-inherent pores of approximately 5 micrometers in size. High heat input significantly widened the heat-affected zone of the substrate, leading to microstructural coarsening. Due to the slow cooling rate, hard phases such as VC did not precipitate significantly in their finer form. More importantly, the substantial thermal stress between the coating and the substrate resulted in penetrating macroscopic cracks. Although the coating achieved an average hardness of 54 HRC, it was brittle and prone to spalling under impact loads.

[0046] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A punch coating, characterized in that, The coating is prepared by ultra-high-speed laser cladding process, and its material is 012Al alloy powder. The chemical composition of the 012Al alloy powder, by mass percentage, is: C: 0.50–0.55%; Si: 0.8–1.0%; Cr: 3.8–4.0%; Mo: 2.8–3.5%; V: 1.0–1.2%; Mn: 0.8–1.1%. Al: 0.3-0.4%; O≤0.008%; S≤0.005%; P≤0.005%, the powder has a particle size of 15-53 µm and a flowability of 18.2 s / 50g; the coating has a thickness of 1-2 mm, an average hardness of 56 HRC, a service end hardness of 58 HRC, and no macroscopic cracks or microscopic network cracks in the coating except for process-inherent pores with a size ≤3 µm.

2. A method for preparing the punch coating as described in claim 1, characterized in that, Includes the following steps: (1) Pretreatment of workpiece and powder: Place the punch substrate and 012Al alloy powder in an 80℃ vacuum oven for 3-5 hours to remove moisture and adsorbed gas; (2) Ultra-high speed laser cladding: a semiconductor laser is used to perform cladding in the order from the main service end of the punch to the non-service end. The process parameters are: spot diameter 3 mm, laser beam focus positive defocus 2 mm, laser power 1500~5000 W, scanning line speed 25~30 m / min, overlap rate 60%, powder feeding rate 75~90 g / min. (3) Stress relief treatment: After cladding, the workpiece is air-cooled to room temperature and immediately placed in a vacuum oven at 200-400℃ for 2-3 hours; (4) Performance testing: The coating is characterized in terms of structure and performance to ensure that the hardness and defect control meet the requirements.

3. The preparation method according to claim 2, characterized in that, The cladding path described in step (2) proceeds sequentially from the working end (top) of the punch to the non-working end (tail). The accumulated residual heat generated by subsequent cladding forms an in-situ thermal effect on the first cladding area, promoting the release of residual stress and the precipitation and growth of VC carbides.

4. The preparation method according to claim 2, characterized in that, The thickness of the laser cladding coating in step (2) is 1 to 1.5 mm, and the width of the heat-affected zone of the substrate is ≤50 µm by controlling the heat input.

5. The preparation method according to claim 2, characterized in that, The preferred parameters for the stress relief treatment in step (3) are: temperature 300℃, holding time 2.5 hours, and vacuum degree ≤1×10 -2 Pa.

6. The preparation method according to claim 2, characterized in that, The VC carbides in the 012Al alloy powder are dispersed in the martensitic matrix, and the hardness of the coating at the service end is ≥58 HRC, with an average coating hardness of 56 HRC.

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