A method for improving the ductility of a martensitic steel plate

Abstract

The application discloses a method for improving the ductility of a martensite steel plate, and belongs to the technical field of metal material heat treatment. The method comprises the following steps: S1, heating the martensite steel plate to 1040-1060 DEG C, and introducing a protective gas during the heating process; S2, then introducing Ar+CO2+CO+H2 or N2+CO2+CO+H2 mixed gas to perform decarburization treatment on the martensite steel plate to obtain a decarburized steel plate; S3, performing quenching treatment on the decarburized steel plate to obtain a quenched steel plate; and S4, performing tempering treatment on the quenched steel plate. The martensite steel plate prepared by the method can keep high strength and significantly improve the ductility.

Description

Technical Field

[0001] This application belongs to the field of heat treatment technology for metallic materials, specifically relating to a method for improving the ductility of martensitic steel plates. Background Technology

[0002] Martensitic steel is a type of carbon or alloy steel that has undergone quenching to obtain a martensitic structure. Due to its high strength, high hardness, and good wear resistance, it is widely used in aerospace, automotive manufacturing, mechanical engineering, surgical instruments, and military equipment. However, despite its excellent performance in many applications, martensitic steel has always suffered from low plasticity and poor ductility, which to some extent limits its application in certain fields.

[0003] To improve the mechanical properties of martensitic steel, especially its ductility, researchers have conducted extensive studies and experiments. Currently, the main methods for improving the ductility of martensitic steel are through two aspects: optimizing chemical composition and improving heat treatment processes. Existing methods can improve the ductility of martensitic steel to a certain extent, but often at the expense of strength.

[0004] Therefore, there is an urgent need to develop a method that can significantly improve the ductility of martensitic steel while maintaining high strength. Summary of the Invention

[0005] In view of this, this application provides a method for improving the ductility of martensitic steel plates, which can significantly improve the ductility of martensitic steel while maintaining its high strength.

[0006] In a first aspect, this application provides a method for improving the ductility of martensitic steel plates, comprising the following steps:

[0007] Step S1: Heat the martensitic steel plate to 1040℃~1060℃, and introduce protective gas during the heating process;

[0008] Step S2: Then, a mixture of Ar+CO2+CO+H2 or N2+CO2+CO+H2 gas is introduced to decarburize the martensitic steel plate to obtain a decarburized steel plate.

[0009] Step S3: Quench the decarburized steel plate to obtain a quenched steel plate;

[0010] Step S4: Temper the quenched steel plate.

[0011] By adopting the above technical solution, the martensitic steel plate treatment method of this application can significantly improve the ductility of martensitic steel while maintaining its high strength. The heat treatment in step S1 ensures a uniform internal structure of the steel, while the protective gas prevents oxidation of the steel plate surface, maintaining the purity of the material and providing a foundation for subsequent processing. Combined with the decarburization treatment in step S2, the carbon concentration in the thickness direction of the steel plate exhibits a gradient distribution. Simultaneously controlling the decarburization treatment temperature, time, and atmosphere controls the characteristics of the carbon concentration gradient distribution, enabling the carbon gradient steel plate to generate an inherent synergistic strengthening effect during deformation. Combined with the quenching treatment in step S3, the main structure of the steel plate forms martensite, giving the steel plate high strength. Finally, the tempering treatment in step S4 optimizes the microstructure, further eliminates internal stress, and improves ductility while maintaining high strength.

[0012] Optionally, in step S1, the composition of the martensitic steel plate is: C: 0.22%~0.30%, Si: 0.2%~0.4%, Mn: 1.15%~1.45%, Cr: 0.1%~0.3%, B: 0.0005%~0.001%, with the remainder being Fe and unavoidable impurity elements.

[0013] By adopting the above technical solution, this application selects a specific martensitic steel plate composition, which can further improve the strength and ductility of the martensitic steel plate.

[0014] Optionally, in step S1, the thickness of the martensitic steel plate is 1.4mm to 1.6mm.

[0015] By adopting the above technical solution, this application selects martensitic steel plates of a specific thickness, which can ensure the uniformity of heat treatment and help to form a more uniform martensitic structure, thereby further improving the overall strength and ductility of the martensitic steel plates.

[0016] Optionally, in step S1, the protective gas is selected from at least one of argon or nitrogen, and the gas flow rate is 500 mL·min. -1 ~600mL·min -1 Argon or nitrogen gas must have a purity of ≥99.99%.

[0017] By adopting the above technical solution, the high-purity protective gas of this application can effectively isolate oxygen, prevent steel from oxidizing at high temperatures, and maintain the purity of the material surface. By controlling the gas flow rate, it is ensured that the protective gas can uniformly cover the steel plate surface during the heating process, avoiding localized oxidation.

[0018] Optionally, in step S2, the total gas flow rate of the mixed gas is 800 mL·min. -1 ~1000 mL·min -1H2 gas flow rate accounts for 1% of the total gas flow rate, while CO2 and CO account for 40% of the total gas flow rate.

[0019] By adopting the above technical solution, this application can control the total gas flow rate to ensure the formation of a uniform protective atmosphere on the steel plate surface, preventing localized oxidation or uneven decarburization. Since the steel plate also contains small amounts of alloying elements such as Mn, Si, Cr, and B, oxidation of these elements (except Fe and C) is unavoidable under CO2-CO atmosphere decarburization. Therefore, introducing 1% H2 during decarburization can inhibit the oxidation of these alloying elements. Adjusting the ratio of CO2 to CO can control the degree and depth of decarburization, improving ductility while maintaining the overall performance of the material.

[0020] In summary, this application introduces a protective gas during the heating process in step S1 to prevent unintended oxidation and uncontrollable random decarburization of all elements in the steel during the heating stage, ensuring uniform composition of the steel plate in its initial state and providing consistent starting conditions for subsequent precise control of decarburization. In step S2, a mixture of Ar+CO2+CO+H2 or N2+CO2+CO+H2 gas is introduced at the decarburization temperature for decarburization treatment, along with 1% H2. This enables controllable surface decarburization while suppressing the oxidation of other alloying elements besides carbon. This process, through precise control of the atmosphere, temperature, and time, constructs a carbon concentration gradient distribution along the thickness direction of the steel plate. This gradient structure generates a synergistic strengthening effect during deformation: the low-carbon surface region enhances plasticity, the transition region relieves stress, and the high-carbon central region ensures high strength, ultimately achieving both high strength and high ductility.

[0021] Optionally, the CO2 / CO ratio is slightly less than the critical CO2 / CO value for Fe oxidation at the actual decarbonization temperature in the CO2-CO system;

[0022] The critical CO2 / CO ratio for Fe oxidation is: , e is the base of the natural logarithm, and T is the decarburization temperature of the decarburization process, in °C.

[0023] By adopting the above technical solution, this application controls the CO2-CO pressure ratio during the decarbonization process by precisely controlling the CO2-CO flow rate, thereby controlling V. CO2 / CO Setting the value slightly below the critical value can prevent Fe oxidation while ensuring decarburization, thereby further ensuring the overall strength of the martensitic steel plate and improving its ductility.

[0024] Optionally, in step S2, the decarburization temperature T is 1040℃~1060℃.

[0025] Optionally, in step S2, the decarburization time t = 7.19 + 12.75[C] + 1.23 × 105 ×e (-157000 / RT) Where C is the carbon content of the martensitic steel plate, e is the base of the natural logarithm, R is the gas constant, and T is the decarburization temperature.

[0026] Optionally, in the above formula, [C] represents the carbon content of the martensitic steel plate, in %; for example, when the carbon content is 0.22%, [C] = 0.22; the base of the natural logarithm, e, is taken as 2.718; and the gas constant R is taken as 8.314.

[0027] By adopting the above technical solution, this application improves the microstructure of the material by precisely controlling the parameters of the decarburization process, further enhancing the ductility of the material, and balancing the high strength of the martensitic steel plate.

[0028] Optionally, in step S3, the quenching process includes: water quenching the decarburized steel plate.

[0029] By adopting the above technical solution, the quenching treatment in this application uses water quenching, which can achieve a rapid and uniform cooling effect. On the one hand, it can promote the full progress of martensitic phase transformation, thereby improving the strength and hardness of the steel plate; on the other hand, it can ensure that the high-temperature carbon concentration gradient is retained, giving the surface layer of the material high plasticity while maintaining high strength in the center, effectively enhancing the synergistic effect of the material's strength and plasticity.

[0030] Optionally, in step S4, the tempering temperature T for the tempering treatment... 回 =408.37[C]+16.83[Si]+186.63[Mn], tempering time is 1.8~2.2h.

[0031] Optionally, [C], [Si], and [Mn] represent the carbon content, silicon content, and manganese content of the martensitic steel plate, respectively, in percentage (%). For example, when the carbon content is 0.22%, the silicon content is 0.22%, and the manganese content is 1.15%, we take [C] = 0.22, [Si] = 0.22, and [Mn] = 1.15.

[0032] By adopting the above technical solution, this application further optimizes the mechanical properties by controlling the tempering temperature and tempering time, and significantly improves the ductility of the material while maintaining a certain strength.

[0033] Optionally, after tempering, the finished steel plate is obtained.

[0034] By adopting the above technical solution, the martensitic steel plate obtained in this application can significantly improve the ductility of martensitic steel while maintaining high strength, thus meeting the needs of different industries for martensitic steel plates that combine high strength and good ductility.

[0035] In summary, the present invention has at least one of the following beneficial technical effects:

[0036] 1. The martensitic steel plate treatment method of this application can significantly improve the ductility of martensitic steel while maintaining its high strength.

[0037] 2. The decarburization treatment in step S2 of this application, combined with the heating treatment in step S1, as well as the quenching and tempering treatments, can produce martensitic steel plates with both high strength and good ductility. Attached Figure Description

[0038] Figure 1 The martensitic structure of the martensitic steel plate before treatment in Example 1;

[0039] Figure 2 The engineering stress-strain curve of the martensitic steel plate before treatment in Example 1;

[0040] Figure 3 The microstructure of the edge (left image) and center (right image) of the finished steel plate cross-section after treatment in Example 1;

[0041] Figure 4 The following is the engineering stress-strain curve of the finished steel plate after treatment in Example 1;

[0042] Figure 5 This is a schematic diagram of the tensile specimen used in the experimental testing of this application;

[0043] Figure 5 Marking instructions: A, 1.25mm (arc length); B, 25mm; C, 5mm; D, 70mm; E, 10mm. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0045] To improve the ductility of martensitic steel, existing technologies typically employ optimized chemical composition and improved heat treatment processes. While these methods enhance the ductility of martensitic steel to some extent, they often sacrifice its strength.

[0046] To address the aforementioned problems, this application proposes a method for improving the ductility of martensitic steel plates, comprising the following steps:

[0047] Step S1: Heat the martensitic steel plate to 1040℃~1060℃, and introduce protective gas during the heating process;

[0048] Step S2: Then, a mixture of Ar+CO2+CO+H2 or N2+CO2+CO+H2 gas is introduced to decarburize the martensitic steel plate to obtain a decarburized steel plate.

[0049] Step S3: Quench the decarburized steel plate to obtain a quenched steel plate;

[0050] Step S4: Temper the quenched steel plate.

[0051] The solution of this application will be described below with reference to the following specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available products, and the devices or equipment used are all purchased from conventional market sales channels. Specific Implementation

[0053] Examples 1-3

[0054] Example 1

[0055] This embodiment provides a method for improving the ductility of martensitic steel plates, including the following steps:

[0056] Step S1: Place a 1.5mm thick martensitic steel plate into a tubular furnace with an inner diameter of 80mm and heat it to 1050℃. During the heating process, argon gas with a purity ≥99.99% and a flow rate of 550mL·min is introduced as a protective gas. -1 The composition of the martensitic steel plate includes: C: 0.22%, Si: 0.22%, Mn: 1.15%, Cr: 0.16%, B: 0.0008%, with the remainder being Fe and unavoidable impurity elements.

[0057] Step S2: Then, a mixed gas of Ar + CO2 + CO + H2 is introduced to decarburize the martensitic steel plate, resulting in a decarburized steel plate; wherein the total gas flow rate of the mixed gas is 1000 mL·min. -1 The H2 gas flow rate accounts for 1% of the total gas flow rate, while CO2 and CO account for 40%. The decarburization temperature is 1050℃, and the calculated critical CO2 / CO ratio for Fe oxidation is 0.409. The CO2 / CO ratio in the decarburization atmosphere is set to 0.4. The carbon content (C) of the martensitic steel plate is 0.22%, and the decarburization time is 10 min. The decarburization time is calculated using the formula t = 7.19 + 12.75[C] + 1.23 × 10⁻⁶. 5 ×e (-157000 / RT) Substituting [C]=0.22, e=2.718, R=8.314, T=1050, we can calculate the result.

[0058] Step S3: Quench the decarburized steel plate by placing the steel plate on the hydraulic press workbench, pressing the steel plate with the pressure head, and then injecting water into the water tank of the hydraulic press workbench to quench the steel plate to obtain quenched steel plate.

[0059] Step S4: Temper the quenched steel plate to obtain the finished steel plate; the tempering temperature is 308℃ and the tempering time is 2h.

[0060] Example 2

[0061] This embodiment provides a method for improving the ductility of martensitic steel plates, including the following steps:

[0062] Step S1: Place a 1.5mm thick martensitic steel plate into a tubular furnace with an inner diameter of 80mm and heat it to 1040℃. During the heating process, argon gas with a purity ≥99.99% and a flow rate of 550mL·min is introduced as a protective gas. -1 The composition of the martensitic steel plate includes: C: 0.22%, Si: 0.22%, Mn: 1.15%, Cr: 0.16%, B: 0.0008%, with the remainder being Fe and unavoidable impurity elements.

[0063] Step S2: Then, a mixed gas of Ar + CO2 + CO + H2 is introduced to decarburize the martensitic steel plate, resulting in a decarburized steel plate; wherein the total gas flow rate of the mixed gas is 1000 mL·min. -1 The H2 gas flow rate accounts for 1% of the total gas flow rate, and CO2 and CO account for 40% of the total gas flow rate; the decarburization temperature is 1040℃, the calculated critical CO2 / CO value for Fe element oxidation is 0.415, the CO2 / CO ratio in the decarburization atmosphere is set to 0.4, the carbon content C of the martensitic steel plate is 0.22%, and the decarburization time is 10min;

[0064] Step S3: Quench the decarburized steel plate by placing the steel plate on the hydraulic press workbench, pressing the steel plate with the pressure head, and then injecting water into the water tank of the hydraulic press workbench to quench the steel plate to obtain quenched steel plate.

[0065] Step S4: Temper the quenched steel plate to obtain the finished steel plate; the tempering temperature is 308℃ and the tempering time is 2h.

[0066] Example 3

[0067] This embodiment provides a method for improving the ductility of martensitic steel plates, including the following steps:

[0068] Step S1: Place a 1.5mm thick martensitic steel plate into a tubular furnace with an inner diameter of 80mm and heat it to 1060℃. During the heating process, argon gas with a purity ≥99.99% and a flow rate of 550mL·min is introduced as a protective gas. -1The composition of the martensitic steel plate includes: C: 0.22%, Si: 0.22%, Mn: 1.15%, Cr: 0.16%, B: 0.0008%, with the remainder being Fe and unavoidable impurity elements.

[0069] Step S2: Then, a mixed gas of Ar + CO2 + CO + H2 is introduced to decarburize the martensitic steel plate, resulting in a decarburized steel plate; wherein the total gas flow rate of the mixed gas is 1000 mL·min. -1 The H2 gas flow rate accounts for 1% of the total gas flow rate, and CO2 and CO account for 40% of the total gas flow rate; the decarburization temperature is 1060℃, the calculated critical CO2 / CO value for Fe element oxidation is 0.403, the CO2 / CO ratio in the decarburization atmosphere is set to 0.4, the carbon content C of the martensitic steel plate is 0.22%, and the decarburization time is 10min;

[0070] Step S3: Quench the decarburized steel plate by placing the steel plate on the hydraulic press workbench, pressing the steel plate with the pressure head, and then injecting water into the water tank of the hydraulic press workbench to quench the steel plate to obtain quenched steel plate.

[0071] Step S4: Temper the quenched steel plate to obtain the finished steel plate; the tempering temperature is 308℃ and the tempering time is 2h.

[0072] Comparative Examples 1-3

[0073] Comparative Example 1

[0074] The difference between Comparative Example 1 and Example 1 is that in step S1 of Comparative Example 1, the martensitic steel plate is heated to 1000°C.

[0075] Comparative Example 2

[0076] The difference between Comparative Example 2 and Example 1 is that in step S1 of Comparative Example 2, the martensitic steel plate is heated to 1100°C.

[0077] Comparative Example 3

[0078] The difference between Comparative Example 3 and Example 1 is that in step S2 of Comparative Example 3, the CO2 / CO ratio in the decarbonization atmosphere is set to 0.65.

[0079] Experimental testing

[0080] Testing method: Samples are cut from the finished steel plate using wire cutting. Figure 5 (Schematic diagram of tensile specimen) The dumbbell-shaped specimen with the required dimensions is tested for mechanical properties using an electronic universal testing machine according to the GB / T 228-2010 standard, and the tensile strength and elongation of the specimen are detected.

[0081] The finished steel plates obtained after being processed by the methods of Examples 1-3 and Comparative Examples 1-3 were tested for tensile strength and elongation. The test results are shown in Table 1.

[0082] Table 1

[0083]

[0084] As can be seen from the test results in Table 1, the methods for improving the ductility of martensitic steel plates in Examples 1-3 of this application can effectively improve the ductility of martensitic steel plates while maintaining high strength.

[0085] In Comparative Example 1, the martensitic steel plate was heated at a relatively low temperature in step S1, resulting in a limited increase in elongation and a decrease in tensile strength.

[0086] In Comparative Example 2, a higher heating temperature was used on the martensitic steel plate in step S1. Although the elongation was improved compared to the martensitic steel plate before treatment, the tensile strength was significantly reduced.

[0087] In Comparative Example 3, when the CO2 / CO ratio in the decarburization atmosphere of step S2 was set higher than the critical CO2 / CO value for Fe oxidation, both tensile strength and elongation decreased.

[0088] Examples 4-10

[0089] Example 4

[0090] The difference between Example 4 and Example 1 is that in step S2 of Example 4, the decarburization time is selected as 8 minutes.

[0091] Example 5

[0092] The difference between Example 5 and Example 1 is that in step S2 of Example 4, the decarburization time is 12 minutes.

[0093] Example 6

[0094] The difference between Example 6 and Example 1 is that in step S2 of Example 6, the total gas flow rate of the mixed gas is 800 mL·min. -1 .

[0095] Example 7

[0096] The difference between Example 7 and Example 1 is that in step S2 of Example 7, the total gas flow rate of the mixed gas is 900 mL·min. -1 .

[0097] Example 8

[0098] The difference between Example 8 and Example 1 is that the method in Example 8 includes the following steps:

[0099] Step S1: Place a 1.5mm thick martensitic steel plate into a tubular furnace with an inner diameter of 80mm and heat it to 1050℃. During the heating process, argon gas with a purity ≥99.99% and a flow rate of 550mL·min is introduced as a protective gas. -1 The composition of the martensitic steel plate includes: C: 0.25%, Si: 0.3%, Mn: 1.3%, Cr: 0.2%, B: 0.0008%, with the remainder being Fe and unavoidable impurity elements.

[0100] Step S2: Then, a mixed gas of Ar + CO2 + CO + H2 is introduced to decarburize the martensitic steel plate, resulting in a decarburized steel plate; wherein the total gas flow rate of the mixed gas is 1000 mL·min. -1 The H2 gas flow rate accounts for 1% of the total gas flow rate, and CO2 and CO account for 40% of the total gas flow rate; the decarburization temperature is 1050℃, the calculated critical CO2 / CO value for Fe element oxidation is 0.409, the CO2 / CO ratio in the decarburization atmosphere is set to 0.4, the carbon content C of the martensitic steel plate is 0.22%, and the decarburization time is 10min;

[0101] Step S3: Quench the decarburized steel plate by placing the steel plate on the hydraulic press workbench, pressing the steel plate with the pressure head, and then injecting water into the water tank of the hydraulic press workbench to quench the steel plate to obtain quenched steel plate.

[0102] Step S4: Temper the quenched steel plate to obtain the finished steel plate; the tempering temperature is 350℃ and the tempering time is 2h.

[0103] Example 9

[0104] The difference between Example 9 and Example 1 is that in step S4 of Example 9, the tempering time is 2.2h.

[0105] Example 10

[0106] The difference between Example 10 and Example 1 is that in step S4 of Example 10, the tempering time is 1.8h.

[0107] The finished steel plates obtained after processing using the methods in Examples 4 to 10 were tested for tensile strength and elongation. The test results are shown in Table 2.

[0108] Table 2

[0109]

[0110] As can be seen from the test results in Table 2, the difference between Examples 4 and 5 and Example 1 is that the decarburization time in step S2 is different. Specifically, the decarburization time in Example 1 is calculated using the formula t = 7.19 + 12.75[C] + 1.23 × 10⁻⁶. 5 ×e (-157000 / RT) Calculations show that the finished steel plate obtained after treatment using the method in Example 1 has the highest tensile strength and the best ductility.

[0111] The difference between Examples 6 and 7 and Example 1 is that the total gas flow rate of the mixed gas in step S2 is different. Among them, the finished steel plate obtained after treatment by the method of Example 1 has the highest tensile strength and the best ductility.

[0112] The difference between Example 8 and Example 1 is that the composition of the martensitic steel plate is different, and the tensile strength of the finished steel plate obtained by Example 8 is increased.

[0113] The difference between Examples 9 and 10 and Example 1 is that the tempering time in step S4 is different. The finished steel plate obtained in Example 1 has better tensile strength and ductility.

[0114] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the principles of this application should be included within the protection scope of this application.

Claims

1. A method for improving the ductility of martensitic steel plates, characterized in that, Includes the following steps: Step S1: Heat the martensitic steel plate to 1040℃~1060℃, and introduce a protective gas during the heating process; the composition of the martensitic steel plate is: C: 0.22%~0.30%, Si: 0.2%~0.4%, Mn: 1.15%~1.45%, Cr: 0.1%~0.3%, B: 0.0005%~0.001%, with the remainder being Fe and unavoidable impurity elements; Step S2: Then, a mixed gas of Ar + CO2 + CO + H2 or N2 + CO2 + CO + H2 is introduced to decarburize the martensitic steel plate, resulting in a decarburized steel plate; the total gas flow rate of the mixed gas is 800 mL·min. -1 ~1000 mL·min -1 H2 gas flow rate accounts for 1% of the total gas flow rate, while CO2 and CO account for 40% of the total gas flow rate; the CO2 / CO ratio is 0.

4. Step S3: The decarburized steel plate is quenched to obtain a quenched steel plate; Step S4: Temper the quenched steel plate.

2. The method according to claim 1, characterized in that, In step S1, the thickness of the martensitic steel plate is 1.4mm to 1.6mm.

3. The method according to claim 1, characterized in that, In step S1, the protective gas is selected from at least one of argon or nitrogen, and the gas flow rate is 500 mL·min. -1 ~600mL·min -1 The purity of the argon or nitrogen gas is ≥99.99%.

4. The method according to claim 1, characterized in that, In step S2, the decarburization temperature T of the decarburization treatment is 1040℃~1060℃.

5. The method according to any one of claims 1 or 4, characterized in that, In step S2, the decarburization time is calculated as t = 7.19 + 12.75[C] + 1.23 × 10⁻⁶. 5 ×e (-157000 / RT) Sure, in, t: Decarbonization time, in minutes (min); [C]: Carbon content of martensitic steel plate, in % (mass fraction), directly taken as 0.22~0.30; e is the base of the natural logarithm; R: Gas constant, with a value of 8.314; T: Decarburization temperature, expressed in degrees Celsius.

6. The method according to claim 1, characterized in that, In step S3, the quenching process includes: water quenching the decarburized steel plate.

7. The method according to claim 1, characterized in that, In step S4, the tempering temperature T of the tempering treatment 回 =408.37[C]+16.83[Si]+186.63[Mn], tempering time is 1.8~2.2h; where, T 回 Tempering temperature, in degrees Celsius (°C); [C], [Si], and [Mn] represent the mass fractions of carbon, silicon, and manganese in martensitic steel plates, respectively, in % (%), with values ​​of 0.22~0.30, 0.2~0.4, and 1.15~1.45.

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