Steel with high hardness and high corrosion resistance and preparation method thereof

Abstract

The invention discloses steel with high hardness and high corrosion resistance and a preparation method thereof, and belongs to metal material surface modification.The preparation method comprises the steps that after the steel is ground, cleaned and dried, carburizing treatment is conducted; carrying out heat treatment on the carburized steel; and with Cr as a target material, ion implantation is conducted on the steel subjected to heat treatment, and finished steel is obtained. According to the method, the ion Cr injection technology and carburizing treatment are creatively combined, technological parameters are optimized according to the characteristics of the carburizing layer, the corrosion resistance and the wear resistance are cooperatively improved, and the treated workpiece keeps high hardness and high wear resistance of the carburizing layer and also has excellent corrosion resistance.

Description

Technical Field

[0001] This application belongs to the field of surface modification of metallic materials, and specifically relates to a steel with high hardness and high corrosion resistance and its preparation method. Background Technology

[0002] Carburizing steel is one of the most widely used structural steels in the machinery manufacturing industry. Through carburizing and subsequent heat treatment, it can achieve a combination of properties such as high surface hardness and high wear resistance, while maintaining sufficient strength and toughness in the core. Therefore, carburizing steel is often used to manufacture key components such as gears, bearings, and drive shafts.

[0003] However, conventional carburizing treatment primarily focuses on improving surface hardness and wear resistance, often resulting in a decrease in surface corrosion resistance. For example, in carburized stainless steel CSS-42L, the increased carbon concentration after carburizing directly leads to a significant reduction in corrosion resistance. Furthermore, the carburized layer typically consists of high-carbon martensite, retained austenite, and carbides, making it susceptible to electrochemical corrosion in humid atmospheres, industrial environments, or media containing chloride ions. This leads to pitting and rust on the surface of components, significantly reducing their fatigue life and service reliability.

[0004] To improve the corrosion resistance of steel, chromium plating, electroless nickel plating, or nitriding are commonly applied to its surface. However, these methods have some limitations when applied to carburized steel: electroplating causes environmental pollution and has limited adhesion to the substrate, making it prone to peeling under heavy loads and impact loads; while electroless nickel plating offers good corrosion resistance, its hardness is usually lower than that of carburized layers, resulting in insufficient wear resistance; and although nitriding can improve surface hardness, its improvement in corrosion resistance is limited, and it may affect fatigue performance due to the formation of brittle phases.

[0005] Ion implantation is a modification technique that forcibly implants high-energy ions into the surface of a material. It can significantly improve the physical and chemical properties of a workpiece surface without altering its dimensions, and the implanted layer exhibits extremely strong adhesion with the substrate, without a distinct interface. Chromium (Cr) is a key element in the formation of passivation films, and the corrosion resistance of stainless steel stems from its high Cr content. Therefore, introducing Cr into the surface of carburized steel via ion implantation can impart corrosion resistance similar to that of stainless steel.

[0006] However, the effectiveness of ion implantation is highly dependent on the selection of process parameters. For carburized layers with complex composition and microstructure, not all parameters of ion implantation of Cr will have a positive effect. If the implantation energy (accelerating voltage) is too low, Cr ions cannot effectively penetrate the surface oxide layer; if the implantation energy is too high, it may destroy the original favorable microstructure of the carburized layer, or cause Cr ions to be implanted too deeply, resulting in concentration dilution and failure to form an effective Cr-rich protective layer near the surface. If the implantation dose (determined by implantation time and beam current density) is insufficient, the surface Cr concentration will be insufficient, and a continuous protective passivation film cannot be formed; if the implantation dose is too high, it may lead to surface damage, excessive lattice distortion, or even peeling, and is also costly.

[0007] Therefore, developing a combined carburizing and ion-implanting process for carburized steel that can significantly improve its corrosion resistance without compromising its original excellent mechanical properties is an urgent problem to be solved in this field. Summary of the Invention

[0008] To address the above problems, this application provides a method for improving the hardness and corrosion resistance of steel, comprising: After grinding, cleaning and drying, the steel is subjected to carburizing treatment; Heat treatment is performed on the carburized steel. Using Cr as the target material, heat-treated steel is ion implanted to obtain the finished steel product. Furthermore, the steel includes 10CrNi3Mo, 16Cr3NiWMoVE, 18Cr2Ni4WA, 12Co14Ni6Cr5Mo4WV, 20CrMnTi, or 20CrMo.

[0009] Furthermore, the carburizing temperature is 900℃-1000℃, the pressure is 100Pa-1000Pa, and the carburizing agent is acetylene, methane, propane, or ethylene.

[0010] Furthermore, the heat treatment is carried out 1-3 times, including holding at 800℃-1100℃ for 0.5h-1.5h, gas quenching or oil quenching, cold treatment at -60℃ to -100℃ for 1h-3h, holding at 450℃-550℃ for 1h-3h, and air cooling or oil cooling.

[0011] Furthermore, the purity of Cr is not less than 99.9%.

[0012] Furthermore, the accelerating voltage for ion implantation is 40kV-60kV, and the time is 4h-13h.

[0013] Furthermore, the ion implantation temperature is 100℃-400℃.

[0014] Furthermore, the vacuum chamber pressure for ion implantation is no higher than 5.0 × 10⁻⁶. -3 Pa.

[0015] Furthermore, the beam current density of ion implantation is 10-50 μA / cm².

[0016] This application also discloses a steel with high hardness and high corrosion resistance, which is prepared by the above method. The surface of the steel has a composite layer, in which the mass percentage concentration of C element is not less than 8% and the mass percentage concentration of Cr element is not less than 8%.

[0017] Compared with the prior art, this application has the following advantages: 1. This application creatively combines ion implantation Cr technology with carburizing treatment, optimizes process parameters for the characteristics of the carburized layer, and achieves a synergistic improvement in corrosion resistance and wear resistance. The treated workpiece maintains the high hardness and high wear resistance of the carburized layer, and also has excellent corrosion resistance.

[0018] 2. Under the specific accelerating voltage and implantation time window of this application, high-energy Cr ions can be effectively implanted into the carburized layer to form a reinforced layer. This reinforced layer is dense and defect-free, and is metallurgically bonded to the substrate. The bonding force is far greater than that of traditional coatings, and it is not easy to peel off. Moreover, the Cr element enriched in this reinforced layer can quickly form a stable and dense passivation film mainly composed of Cr2O3 on the surface, which greatly hinders the erosion of corrosive media.

[0019] 3. The ion implantation process in this application is a dry process with no wastewater or exhaust gas emissions, which is environmentally friendly and suitable for various complex-shaped carburized steel parts. In addition, the workpiece temperature is low during the process, which will not cause tempering and softening of the matrix structure, thus ensuring the overall performance of the parts.

[0020] Other features and advantages of this application will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A flowchart illustrating a method for preparing a high-hardness and high-corrosion-resistant steel according to an embodiment of this application is shown. Figure 2 A scanning electron microscope (SEM) image of the sample surface cross-section of Example 1 of this application is shown; Figure 3 It shows Figure 2 Energy dispersive spectroscopy (EDS) at section A of the sample surface in Example 1 of this application; Figure 4 It shows Figure 2 Energy dispersive spectroscopy (EDS) at section B of the sample surface in Example 1 of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] To address the insufficient corrosion resistance of alloy steels whose surface hardness is improved through carburizing, and the insufficient surface hardness of alloy steels with Cr ion implantation, such as... Figure 1 As shown, this application provides a method for preparing steel with high hardness and high corrosion resistance, comprising: S1: After grinding, cleaning, and drying, the steel undergoes carburizing treatment. Steel types include 10CrNi3Mo, 16Cr3NiWMoVE, 18Cr2Ni4WA, 12Co14Ni6Cr5Mo4WV, 20CrMnTi, or 20CrMo. The carburizing temperature is 900℃-1000℃, the pressure is 100Pa-1000Pa, and the carburizing agent is acetylene, methane, propane, or ethylene. The diffusion ratio and pulse number vary depending on specific requirements.

[0025] S2: Heat treatment is performed on the carburized steel. The heat treatment is carried out 1-3 times, and the heat treatment process is carried out according to the standard requirements of the steel, including holding at 800℃-1100℃ for 0.5h-1.5h, air quenching or oil quenching, cold treatment at -60℃ to -100℃ for 1h-3h, holding at 450℃-550℃ for 1h-3h, and air cooling or oil cooling.

[0026] S3: Using Cr as the target material, with a Cr purity of not less than 99.9%, ion implantation is performed on heat-treated steel. The accelerating voltage for ion implantation is 40kV-60kV, the implantation time is 4h-13h, the ion implantation temperature is 100℃-400℃, and the vacuum chamber pressure for ion implantation does not exceed 5.0×10⁻⁶. -3At a current density of 10-50 μA / cm², ion implantation yields finished steel. The effectiveness of ion implantation heavily depends on the selection of process parameters. If the accelerating voltage is too low, Cr ions cannot effectively penetrate the surface oxide layer; if the implantation energy is too high, it may damage the original favorable microstructure of the carburized layer or cause Cr ions to be implanted too deeply, resulting in concentration dilution and preventing the formation of an effective Cr-rich protective layer near the surface; if the implantation dose (determined by implantation time and current density) is insufficient, the surface Cr concentration will be insufficient, preventing the formation of a continuous protective passivation film; if the implantation dose is too high, it may lead to surface damage, excessive lattice distortion, or even peeling, and is also costly. Under the specific accelerating voltage and implantation time window of this application, high-energy Cr ions can be effectively implanted into the carburized layer to form a reinforced layer. This reinforced layer is dense, defect-free, and metallurgically bonded to the substrate, with a bonding strength far exceeding that of traditional coatings, making it difficult to peel off.

[0027] This application also discloses a steel with high hardness and high corrosion resistance, which is prepared by the above method. The surface of the steel has a composite layer, in which the mass percentage concentration of C element is not less than 8% and the mass percentage concentration of Cr element is not less than 8%.

[0028] To better illustrate this solution, the following embodiments and comparative examples are provided.

[0029] Example 1 S1: A standard sample was made of 12Co14Ni6Cr5Mo4WV steel. The surface was ground and then ultrasonically cleaned with acetone and alcohol. After drying, it was placed in a vacuum carburizing furnace. The carburizing temperature was 920℃, the carburizing agent was acetylene, the carburizing pressure was 200Pa, and the carburizing time was 4 hours.

[0030] S2: The carburized sample was held at 1090℃ for 0.5h, air-quenched, cold-treated at -80℃ for 2h, held at 500℃ for 2h, and air-cooled. This heat treatment cycle was repeated 3 times. The effective hardened layer depth of the heat-treated sample was approximately 1.2mm, and the surface hardness was 62HRC.

[0031] S3: Using 99.95% pure Cr as the target material, ion implantation was performed on the heat-treated sample, and the vacuum was evacuated to a background vacuum of 3.0 × 10⁻⁶. -3 The accelerating voltage was set to 50 kV, the beam current density to 30 μA / cm², and the sample temperature to 200 °C. The ion source was turned on, and implantation was performed for 8 hours. After implantation, the sample was cooled to room temperature under vacuum and then removed.

[0032] Example 2 The steps are the same as in Example 1, except that the carburizing temperature is 1000℃, the pressure is 1000Pa, the accelerating voltage is 35kV, and the injection time is 12h.

[0033] Example 3 The steps are the same as in Example 1, except that the carburizing temperature is 900℃, the pressure is 100Pa, the accelerating voltage is 65kV, and the injection time is 4h.

[0034] Comparative Example 1 The same batch of carburized samples as in Example 1 were used, but without Cr implantation.

[0035] Comparative Example 2 The same batch of standard samples as in Example 1 were used for ion implantation, but without the carburizing treatment of S1 and the heat treatment of S2.

[0036] Taking the sample treated in Example 1 as an example, cross-sectional SEM and EDS analyses were performed on the sample from Example 1. Figure 2 As shown, a modified layer with a thickness of approximately 100nm-200nm was formed on the surface of the carburized layer, and this layer has a dense structure. Figure 3 As shown, the Cr element concentration at point A (within 50 nm of the surface) reaches over 8% by mass percentage. Figure 4 As shown, the mass fraction of Cr at location B, which is far from the surface layer, is 4.5%.

[0037] The samples from Examples 1-3 and Comparative Example 1 were subjected to potentiodynamic polarization curve tests in a 3.5 wt% NaCl solution. The results are shown in Table 1. The self-corrosion potential of the samples from Examples 1-3 was shifted by more than 80 mV compared with that of Comparative Example 1, the corrosion current density was reduced, and the corrosion resistance was significantly improved.

[0038] Table 1

[0039] The Vickers hardness gradient test was performed on the sample surfaces of Example 1 and Comparative Example 2. The results are shown in Table 2. The surface hardness of Example 1 is significantly higher than that of Comparative Example 2, indicating that the composite process of this application can ensure both corrosion resistance and hardness.

[0040] Table 2

[0041] In summary, the vacuum carburizing and ion implantation Cr composite process provided in this application can effectively and significantly improve the hardness and corrosion resistance of steel surfaces, and has extremely high industrial application value.

[0042] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing steel with high hardness and high corrosion resistance, characterized in that, include: After grinding, cleaning and drying, the steel is subjected to carburizing treatment; Heat treatment is performed on carburized steel. Using Cr as the target material, heat-treated steel is ion implanted to obtain the finished steel product.

2. The method for preparing a steel with high hardness and high corrosion resistance according to claim 1, characterized in that, The steel includes 10CrNi3Mo, 16Cr3NiWMoVE, 18Cr2Ni4WA, 12Co14Ni6Cr5Mo4WV, 20CrMnTi, or 20CrMo.

3. The method for preparing a steel with high hardness and high corrosion resistance according to claim 1, characterized in that, The carburizing treatment is carried out at a temperature of 900℃-1000℃ and a pressure of 100Pa-1000Pa, and the carburizing agent is acetylene, methane, propane or ethylene.

4. The method for preparing a steel with high hardness and high corrosion resistance according to claim 1, characterized in that, The heat treatment is performed 1-3 times, and the heat treatment includes holding at 800℃-1100℃ for 0.5h-1.5h, gas quenching or oil quenching, cooling at -60℃ to -100℃ for 1h-3h, holding at 450℃-550℃ for 1h-3h, and air cooling or oil cooling.

5. The method for preparing a steel with high hardness and high corrosion resistance according to claim 1, characterized in that, The purity of the Cr is not less than 99.9%.

6. The method for preparing a steel with high hardness and high corrosion resistance according to claim 1, characterized in that, The accelerating voltage for ion implantation is 40kV-60kV, and the time is 4h-13h.

7. The method for preparing a steel with high hardness and high corrosion resistance according to claim 1, characterized in that, The ion implantation temperature is 100℃-400℃.

8. The method for preparing a steel with high hardness and high corrosion resistance according to claim 1, characterized in that, The vacuum chamber pressure during ion implantation is no higher than 5.0 × 10⁻⁶. -3 Pa.

9. The method for preparing a steel with high hardness and high corrosion resistance according to claim 1, characterized in that, The beam current density of the ion implantation is 10-50 μA / cm².

10. A type of steel with high hardness and high corrosion resistance, characterized in that, The steel is prepared by the method according to any one of claims 1-9, wherein the surface of the steel has a composite layer, and the mass percentage concentration of C element in the composite layer is not less than 8%, and the mass percentage concentration of Cr element is not less than 8%.

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