A method for laser quenching the surface of a p20 alloy steel

Abstract

The application discloses a kind of P20 alloy steel laser quenching surface strengthening method, comprising the following steps: S1.Preprocessing: P20 alloy steel workpiece surface is treated with alumina grit blasting, after sand blasting, surface roughness Ra=1.5~3.0 μm is made;After sand blasting, the workpiece is cleaned;S2.Laser processing: laser beam is linear uniform speed scanning along the workpiece surface obtained in step S1, laser power is 1.8~2.0 kW, and scanning speed is 4~5 mm / s;S3.Cooling: the workpiece obtained in step S2 is cooled in 20~30 ℃ air cooling.Cooling.The application is realized through sand blasting pretreatment-precision parameter-normal temperature air cooling synergic process system, and the synergic promotion of laser absorption efficiency, heating uniformity, cooling stress release, fundamentally solves the core problem of "single link optimization cannot consider effect and efficiency".

Description

Technical Field

[0001] This invention belongs to the field of material surface strengthening, and specifically relates to a laser quenching surface strengthening method for P20 alloy steel. Background Technology

[0002] P20 alloy steel is a commonly used mold steel, widely used in mold manufacturing, machining, and other fields. It possesses good comprehensive mechanical properties, such as high strength, good toughness, and wear resistance, making it particularly suitable for plastic molds and die-casting molds under medium loads. However, during long-term use, the surface of P20 alloy steel is susceptible to wear, corrosion, and fatigue, leading to performance degradation and shortened service life. Therefore, improving its surface wear resistance, hardness, and fatigue resistance has become a key industry requirement.

[0003] To improve the surface properties of P20 alloy steel, various surface strengthening technologies have been developed in the industry, but all of them have insurmountable defects, as follows:

[0004] (1) Traditional heat treatment technology: Carburizing, nitriding and other traditional methods are the mainstream surface strengthening methods in the early days. They can improve surface hardness and wear resistance to a certain extent, but they have significant shortcomings. The carburizing process requires high temperature and long time heating, which consumes a lot of energy and is prone to uneven thermal expansion and contraction of the workpiece, with a deformation rate of more than 5%. The nitriding treatment time is usually more than 4 hours (some processes reach 32 hours), and the strengthening depth is limited (the thickness of the nitrided layer in traditional processes is usually <0.2 mm), which is difficult to meet the requirements of high-load workpieces. At the same time, improper control of the cooling rate can easily cause cracks.

[0005] (2) Composite surface strengthening technology: To compensate for the shortcomings of traditional technologies, composite processes have emerged. For example, the “shot peening + electrical discharge + laser quenching” process disclosed in Chinese invention patent CN116479338A requires three types of equipment to work together, and the process is complicated. Among them, the electrical discharge treatment requires high-temperature discharge of 8000~25000℃, which can easily cause the workpiece surface to expand in a regular manner, affecting the dimensional accuracy of precision molds. The “nitriding + laser quenching” process disclosed in Chinese invention patent CN120888865A solves the problem of shallow nitriding layer (modified layer thickness ≥1.5 mm), but the nitriding step requires 4~32 hours, the total processing time is ≤16 hours, and it depends on special equipment such as pulsed plasma multi-element co-diffusion furnace, which is costly and has poor versatility, and is not suitable for batch processing of P20 alloy steel in small and medium-sized enterprises.

[0006] (3) Single laser quenching technology: As an emerging surface strengthening technology, laser quenching has the advantages of fast heating speed, small heat-affected zone and high energy utilization rate, and has been gradually applied in the field of metal surface treatment. Its core principle is to use a high-power laser beam to locally and rapidly heat the metal surface to the austenitizing temperature, and then rapidly cool it to form a martensitic structure to achieve surface hardening. However, the existing single laser quenching technology has not optimized the process synergy for the material characteristics of P20 alloy steel (containing elements such as Cr and Mo), and only simply adjusts the laser power or scanning speed, resulting in a series of key problems: ① poor hardness uniformity, with hardness differences in different areas of the surface exceeding 100 HV; ② excessively large heat-affected zone (≥1.5mm), which easily causes workpiece deformation; ③ rapid cooling and heating generate internal stress, with a crack incidence rate exceeding 30%; ④ rapid cooling of the molten pool easily forms pores, affecting the quality of the surface strengthening layer.

[0007] In summary, existing surface strengthening technologies cannot efficiently and stably achieve high-quality surface strengthening of P20 alloy steel. Therefore, optimizing laser quenching process parameters and procedures, constructing a synergistic strengthening system, and ensuring uniform and defect-free surface hardening are key to promoting the large-scale application of laser quenching technology in the processing of P20 alloy steel. Summary of the Invention

[0008] To address the shortcomings of the existing technologies, this invention provides a laser quenching surface strengthening method for P20 alloy steel. Through a synergistic process system of sandblasting pretreatment, precise parameters, and room temperature air cooling, the laser absorption efficiency, heating uniformity, and cooling stress release are synergistically improved.

[0009] The specific technical solution is as follows:

[0010] A method for surface strengthening of P20 alloy steel by laser quenching includes the following steps:

[0011] S1. Pretreatment: The surface of the P20 alloy steel workpiece is sandblasted with alumina sand to achieve a surface roughness Ra of 1.5~3.0 μm; after sandblasting, the workpiece is cleaned.

[0012] S2. Laser processing: The laser beam is linearly and uniformly scanned along the workpiece surface obtained in step S1. The laser power is 1.8~2.0kW and the scanning speed is 4~5mm / s.

[0013] S3. Cooling: Cool the workpiece obtained in step S2 by air cooling at 20~30℃.

[0014] The mechanism of this invention is as follows:

[0015] This invention performs sandblasting pretreatment on the workpiece surface, not simply to remove oil, rust, and oxide scale. Sandblasting improves laser absorption efficiency by controlling surface roughness, laying the foundation for precise parameter control in the subsequent process. Experimental verification shows that the roughness range (Ra=1.5~3.0 μm) of this invention can increase laser absorption efficiency from 60% to over 80% for conventionally cleaned surfaces, avoiding excessively high laser reflectivity due to insufficient roughness (<1.5μm) or uneven heating due to excessive roughness (>3.0μm).

[0016] A linear uniform scanning mode with precise matching of power and scanning speed is adopted. Based on the thermal conductivity of P20 alloy steel (thermal conductivity 40~45 W / (m·K)), the ratio of power to scanning speed is controlled at 0.36~0.5 kW·s / mm. (According to experimental verification, this ratio range can rapidly raise the surface temperature of the workpiece to 850~950℃ (austenitizing temperature), and the heating layer depth is controlled at 0.9~1.1mm. This avoids overheating and ablation caused by excessive power (>2.0 kW) or insufficient heating caused by excessive scanning speed (>5mm / s).

[0017] Using ambient air cooling instead of rapid cooling media (water cooling, oil cooling) or long-term slow cooling, and controlling the cooling rate to match the heating rate, can ensure that austenite is rapidly transformed into martensite (ensuring hardness) and avoid internal stress concentration caused by rapid cooling (cooling rate >100℃ / s). At the same time, no cooling medium is required, simplifying the process and reducing costs.

[0018] Sandblasting pretreatment improves laser absorption efficiency by adjusting surface roughness, laying the foundation for subsequent precise parameter control; the synergistic matching of 1.8~2.0kW laser power and 4~5mm / s scanning speed achieves a heating effect of "rapid heating and appropriate layer depth"; the precise matching of the cooling rate and heating rate at room temperature effectively avoids the generation of internal stress. These three elements form a closed-loop synergistic system, fundamentally solving the core problem of existing technologies where "optimization of a single link cannot simultaneously achieve both effectiveness and efficiency".

[0019] Further, in step S1: using 20~40 mesh alumina sand particles, the surface of the P20 alloy steel workpiece is sandblasted at a pressure of 0.3~0.5 MPa to remove oil stains, rust and oxide scale, and to adjust the surface roughness to 1.5~3.0μm.

[0020] Furthermore, in step S1: after sandblasting, the workpiece is cleaned with ethanol and acetone in sequence to remove residual sand particles and oil stains on the surface, ensuring that there are no contaminants on the surface that could affect the interaction between the laser and the material.

[0021] Specifically, in step S1: the workpiece is ultrasonically cleaned.

[0022] Furthermore, in step S2: the scanning interval is 50%~70% of the laser spot diameter. The overlapping area ensures uniform temperature superposition, avoids heating blind spots, and further guarantees hardness uniformity.

[0023] The laser spot diameter is preferably 2 to 3 mm.

[0024] Furthermore, in step S3, the cooling rate is controlled at 50~80℃ / s. This cooling rate ensures that austenite transforms rapidly into martensite (ensuring hardness) while avoiding stress concentration caused by rapid cooling (cooling rate >100℃ / s). At the same time, no cooling medium is required, simplifying the process and reducing costs.

[0025] Specifically, stacking should be avoided during the cooling process to ensure even airflow.

[0026] The present invention also provides a P20 alloy steel workpiece, which is obtained by the above-mentioned P20 alloy steel laser quenching surface strengthening method.

[0027] Specifically, the surface hardness of the P20 alloy steel workpiece reaches 590~650 HV0.2, the hardness uniformity error is ≤40HV; the heat-affected zone is ≤0.8 mm, and the workpiece deformation rate is ≤0.5%.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention achieves a synergistic improvement in laser absorption efficiency, heating uniformity, and cooling stress release through a collaborative process system of sandblasting pretreatment, precise parameters, and ambient air cooling. Sandblasting pretreatment enhances laser absorption efficiency by controlling surface roughness, laying the foundation for subsequent precise parameter control. The coordinated matching of 1.8~2.0 kW laser power with a scanning speed of 4~5 mm / s enables a heating effect of "rapid heating and appropriate layer depth." The precise matching of the cooling rate and heating rate during ambient air cooling effectively avoids the generation of internal stress. These three elements form a closed-loop synergistic system, fundamentally solving the core problem of existing technologies where "optimization of a single step cannot simultaneously achieve both effectiveness and efficiency."

[0030] The surface hardness and uniformity of P20 alloy steel workpieces treated with the method of this invention are significantly superior to those of existing technologies. The surface hardness reaches 590~650 HV0.2, an improvement of 73.5%~91.2% compared to the substrate (340 HV), approaching the process of nitriding combined with laser quenching (CN120888865A, 700 HV0.1). The hardness uniformity error is ≤40 HV, far superior to existing single laser quenching (error exceeding 100 HV) and the multi-step process of CN116479338A (error approximately 50 HV), solving the core problem of uneven hardness.

[0031] P20 alloy steel workpieces surface-strengthened using the method of this invention are defect-free and exhibit high dimensional stability. The crack and porosity defect rate is reduced to 0, and the heat-affected zone is ≤0.8mm, a 46.7% reduction compared to existing laser quenching (heat-affected zone ≥1.5mm). The workpiece deformation rate is ≤0.5%, superior to CN116479338A (expansion caused by electrical discharge machining) and CN120888865A (nitriding-laser synergistic deformation rate of approximately 1%), meeting the dimensional requirements of precision molds.

[0032] P20 alloy steel workpieces treated with the surface strengthening method of this invention exhibit significantly enhanced wear resistance. Wear depth is reduced to as low as 4682~5679 μm. 3 Compared to the untreated workpiece (45234 μm) 3 It reduces wear by 87.4%~89.6%, and its wear resistance reaches more than 85% of that of the CN120888865A composite process, but the process is simpler and the cost is lower.

[0033] The method of this invention significantly improves processing efficiency and economy. The total processing time is ≤2 h (30 min pretreatment + 30 min laser scanning + 60 min air cooling), which is 87.5% shorter than the total processing time of CN120888865A (≤16 h) and 75% shorter than the multi-step process of CN116479338A (≤8 h). Attached Figure Description

[0034] Figure 1 These are cross-sectional views of the hardness of Examples 1-4;

[0035] Figure 2 The average hardness of the quenched layer in Examples 1-4;

[0036] Figure 3 Wear morphology of an untreated P20 alloy steel workpiece during wear testing;

[0037] Figure 4 The image shows the wear morphology of the workpiece obtained in Example 3 during the wear test.

[0038] Figure 5 The image shows the wear morphology of the workpiece obtained in Example 4 during the wear test. Detailed Implementation

[0039] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention. Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0040] In each specific embodiment, the workpiece used for surface strengthening treatment is a P20 alloy steel mold (100 mm × 50 mm × 20 mm).

[0041] Example 1

[0042] A method for surface strengthening of P20 alloy steel by laser quenching includes the following steps:

[0043] S1. Pretreatment: The surface of the P20 alloy steel workpiece is sandblasted with 30-mesh alumina sand at a pressure of 0.3 MPa to remove oil, rust and oxide scale; the surface roughness of the workpiece after sandblasting is Ra=1.8 μm; after sandblasting, the workpiece is first ultrasonically cleaned in ethanol for 10 min, and then ultrasonically cleaned in acetone for 5 min to remove residual sand and oil on the surface, and then dried for later use.

[0044] S2. Laser processing: The laser beam is linearly and uniformly scanned along the workpiece surface obtained in step S1. The spot diameter is 2 mm and the scanning interval is 1.2 mm. The laser power is 1.8 kW and the scanning speed is 4 mm / s. The ratio of power to scanning speed is 0.45 kW·s / mm.

[0045] S3. The workpiece obtained in step S2 is air-cooled at 22°C at a cooling rate of 55°C / s.

[0046] Example 2

[0047] A method for surface strengthening of P20 alloy steel by laser quenching includes the following steps:

[0048] S1. Pretreatment: The surface of the P20 alloy steel workpiece is sandblasted with 40-mesh alumina sand at a pressure of 0.5 MPa to remove oil, rust and oxide scale; the surface roughness of the workpiece after sandblasting is Ra=2.8 μm; after sandblasting, the workpiece is first ultrasonically cleaned in ethanol for 10 min, and then ultrasonically cleaned in acetone for 5 min to remove residual sand and oil on the surface, and then dried for later use.

[0049] S2. Laser processing: The laser beam is linearly and uniformly scanned along the workpiece surface obtained in step S1. The spot diameter is 3 mm and the scanning interval is 2.0 mm. The laser power is 1.8 kW and the scanning speed is 5 mm / s. The ratio of power to scanning speed is 0.36 kW·s / mm.

[0050] S3. The workpiece obtained in step S2 is air-cooled at 28°C at a cooling rate of 75°C / s.

[0051] Example 3

[0052] A method for surface strengthening of P20 alloy steel by laser quenching includes the following steps:

[0053] S1. Pretreatment: The surface of the P20 alloy steel workpiece is sandblasted with 20-mesh alumina sand at a pressure of 0.4 MPa to remove oil, rust and oxide scale; the surface roughness of the workpiece after sandblasting is Ra=2.2 μm; after sandblasting, the workpiece is first ultrasonically cleaned in ethanol for 10 min, and then ultrasonically cleaned in acetone for 5 min to remove residual sand and oil on the surface, and then dried for later use.

[0054] S2. Laser processing: The laser beam is linearly and uniformly scanned along the workpiece surface obtained in step S1. The spot diameter is 2.5 mm and the scanning interval is 1.5 mm. The laser power is 1.9 kW and the scanning speed is 5 mm / s. The ratio of power to scanning speed is 0.38 kW·s / mm.

[0055] S3. The workpiece obtained in step S2 is air-cooled at 25°C at a cooling rate of 65°C / s.

[0056] Example 4

[0057] A method for surface strengthening of P20 alloy steel by laser quenching includes the following steps:

[0058] S1. Pretreatment: The surface of the P20 alloy steel workpiece is sandblasted with 25-mesh alumina sand at a pressure of 0.4 MPa to remove oil, rust and oxide scale; the surface roughness of the workpiece after sandblasting is Ra=2.5 μm; after sandblasting, the workpiece is first ultrasonically cleaned in ethanol for 10 min, and then ultrasonically cleaned in acetone for 5 min to remove residual sand and oil on the surface, and then dried for later use.

[0059] S2. Laser processing: The laser beam is linearly and uniformly scanned along the workpiece surface obtained in step S1. The spot diameter is 2.8 mm and the scanning interval is 1.8 mm. The laser power is 2.0 kW and the scanning speed is 5 mm / s. The ratio of power to scanning speed is 0.4 kW·s / mm.

[0060] S3. The workpiece obtained in step S2 is air-cooled at 26°C at a cooling rate of 70°C / s.

[0061] Comparative Example 1

[0062] Referring to Example 3, the difference from Example 3 is as follows:

[0063] In step S1: no sandblasting treatment was performed;

[0064] In step S3: water cooling is used.

[0065] Comparative Example 2

[0066] Using the technical solution of Example 1 in CN120888865A as a comparative example, 1Cr17Ni2 alloy steel (similar to P20 composition) was subjected to laser quenching treatment after nitriding for 16 h under the conditions of laser power of 1 kW and scanning speed of 10 mm / s.

[0067] Comparative Example 3

[0068] Referring to Example 3, the difference from Example 3 is that,

[0069] In step S2: the laser power is 1.5 kW and the scanning speed is 6 mm / s.

[0070] Comparative Example 4

[0071] Referring to Example 3, the difference from Example 3 is that,

[0072] In step S1: 10-mesh alumina sand is used to sandblast the surface of the P20 alloy steel workpiece at a pressure of 0.2 MPa; after sandblasting, the surface roughness of the workpiece Ra=4.0 μm.

[0073] test

[0074] The surface hardness, hardened layer thickness, heat-affected zone, wear amount, and deformation rate of the workpieces obtained in each embodiment and comparative example were tested.

[0075] Hardness testing method: Refer to standard GB / T 4340.1-2024 "Metallic materials Vickers hardness test - Part 1: Test method".

[0076] Test method for heat-affected zone: Refer to GB / T 13298-2015 "Metallic Microstructure Inspection Method", cut the quenched workpiece along the cross section, grind (240 grit → 800 grit → 2000 grit wet sandpaper) and polish (diamond polishing paste), then etch it with 4% nitric acid alcohol solution for 5~10s. Observe the changes in microstructure through an HV-1000 optical microscope (magnification 200x). The boundary of the heat-affected zone is the area from the edge of the hardened layer to the matrix structure where there is no obvious change. The maximum distance in this area is the thickness of the heat-affected zone.

[0077] Wear test method: A CSM TRB3 reciprocating friction and wear tester was used. The test type was reciprocating friction and wear. The test parameters were set according to GB / T 39105-2020 "Metallic Materials Sliding Wear Test Method": load 100 N, frequency 6 Hz, the grinding pair was φ6 mm silicon nitride balls, wear track length 6 mm, and test time 30 min. After the test, the wear track area was scanned using an NPFLEX-1000 three-dimensional profilometer to obtain the three-dimensional morphology data of the wear track. The wear track volume (μm³) was calculated using the matching analysis software, and the wear track volume was used as the evaluation index of wear amount.

[0078] The test results are shown in Table 1.

[0079] Table 1 Test results of each embodiment and comparative example

[0080]

[0081] As shown in Table 1, the surface hardness of this invention reaches 590~650 HV0.2, which is 73.5%~91.2% higher than that of the substrate (340 HV), approaching the hardness of nitriding combined laser quenching process (Comparative Example 2, 700 HV0.1). Furthermore, the total processing time of Comparative Example 2 is 16 h, much longer than that of this invention; the equipment cost is 40% higher. The hardness uniformity error is ≤40 HV, far superior to existing single laser quenching (error exceeding 100 HV) and the multi-step process of CN116479338A (error approximately 50 HV). Moreover, the crack and porosity defect rate of this invention is reduced to 0, and the heat-affected zone is ≤0.8 mm, a reduction of 46.7% compared to existing laser quenching (heat-affected zone ≥1.5 mm). The workpiece deformation rate is ≤0.5%, significantly better than the comparative examples. In addition, the wear amount of this invention is as low as 4682~5679 μm. 3 Compared to the untreated workpiece (45234 μm) 3 The wear rate was reduced by 87.4% to 89.6%; compared with Comparative Example 1, the wear amount was reduced by 54.5% to 62.5%. Compared with Comparative Examples 3 and 4, the surface hardness of the present invention (Example 3) was significantly improved, and the hardness error, hardened layer depth, heat-affected zone, wear amount, and deformation rate were all significantly optimized and improved, proving the synergistic effect of the parameters of the present invention.

[0082] The hardness cross-sectional diagrams of Examples 1-4 are shown below. Figure 1 As shown. Figure 1 In the example, 1.8kw 4mm / s is Example 1, 1.8kw 5mm / s is Example 2, 1.9kw 5mm / s is Example 3, and 2.0kw 5mm / s is Example 4.

[0083] The average hardness of the quenched layer in Examples 1-4 is as follows: Figure 2 As shown. Figure 2 In the horizontal axis, parameters 1 to 4 correspond to Examples 1 to 4 respectively.

[0084] The wear morphology of the untreated P20 alloy steel workpiece in the wear test is shown below. Figure 3 The wear morphology of the workpiece obtained in Example 3 during the wear test is shown in [reference needed]. Figure 4 The wear morphology of the workpiece obtained in Example 4 during the wear test is shown in [reference needed]. Figure 5 .

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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 method for surface strengthening of P20 alloy steel by laser quenching, characterized in that, Includes the following steps: S1. Pretreatment: The surface of the P20 alloy steel workpiece is sandblasted with alumina sand to achieve a surface roughness Ra of 1.5~3.0 μm; after sandblasting, the workpiece is cleaned. S2. Laser processing: The laser beam is linearly and uniformly scanned along the workpiece surface obtained in step S1. The laser power is 1.8~2.0kW and the scanning speed is 4~5 mm / s. S3. Cooling: Cool the workpiece obtained in step S2 by air cooling at 20~30℃.

2. The laser quenching surface strengthening method for P20 alloy steel according to claim 1, characterized in that, In step S1: 20-40 mesh alumina sand is used to sandblast the surface of the P20 alloy steel workpiece at a pressure of 0.3-0.5 MPa.

3. The laser quenching surface strengthening method for P20 alloy steel according to claim 1, characterized in that, In step S1: After sandblasting, the workpiece is cleaned with ethanol and acetone in sequence.

4. The laser quenching surface strengthening method for P20 alloy steel according to claim 3, characterized in that, In step S1: the workpiece is ultrasonically cleaned.

5. The laser quenching surface strengthening method for P20 alloy steel according to claim 1, characterized in that, In step S2: the scanning spacing is 50% to 70% of the laser spot diameter.

6. The laser quenching surface strengthening method for P20 alloy steel according to claim 5, characterized in that, In step S2: the diameter of the laser spot is 2~3mm.

7. The laser quenching surface strengthening method for P20 alloy steel according to claim 1, characterized in that, In step S3: the cooling rate is controlled at 50~80℃ / s.

8. A P20 alloy steel workpiece, characterized in that, It is obtained by laser quenching surface strengthening method for P20 alloy steel as described in any one of claims 1 to 6.

9. The P20 alloy steel workpiece according to claim 7, characterized in that, The surface hardness reaches 590~650 HV0.2, and the hardness uniformity error is ≤40HV.

10. The P20 alloy steel workpiece according to claim 8, characterized in that, The heat-affected zone is ≤0.8mm, and the workpiece deformation rate is ≤0.5%.

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