Method for calculating residual austenite content of quenched medium-alloy ultrahigh-strength high-toughness steel

Abstract

The invention relates to the technical field of material component-structure calculation, and discloses a method for calculating the residual austenite content of quenched medium-alloy ultrahigh-strength high-toughness steel, which comprises the following steps: S1, determining the components of the medium-alloy ultrahigh-strength high-toughness steel and condition parameters of a quenching process, the condition parameters comprising quenching austenitizing temperature Ta and quenching medium temperature Tq; s2, the martensite transformation starting temperature Ms point is calculated based on the medium-alloy ultrahigh-strength high-toughness steel components and the corresponding coefficient of each component; s3, the residual austenitizing temperature Ta and the quenching medium temperature Tq are calculated on the basis of the martensite transformation starting temperature Ms point, the quenching austenitizing temperature Ta and the quenching medium temperature Tq. According to the method, the Ms point and the residual austenite content are calculated only by determining the components of the steel and quenching process condition parameters and then utilizing a simple empirical formula, complex equipment and tedious operation are not needed, the calculation efficiency is greatly improved, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of material composition-structure calculation, and in particular to a method for calculating the residual content of medium-alloy ultra-high strength and high toughness steel after quenching. Background Art

[0002] The main elements in medium and low alloy ultra-high strength and high toughness steels are generally C, Cr, Mn, Si, Ni, Mo, W, etc. Typical steel grades include 4340 (40CrNi2MoA), D6AC (45CrNiMo1VA), N31 (30CrMnSiNi2A), D406A (30Si2MnCrMoVE), 300M (40Si2Ni2CrMoVA), etc. In the composition-organization design of new medium alloy ultra-high strength and high toughness steels, it is usually necessary to consider that the mechanical properties of medium alloy ultra-high strength and high toughness steels are affected by the transformation of austenite to martensite during quenching, and the amount of retained austenite is the main factor affecting the balance between steel strength and plasticity. In order to reasonably control the amount of retained austenite, a method is often needed to estimate the residual austenite content of medium alloy ultra-high strength and high toughness steels with different compositions under different quenching process conditions.

[0003] In the prior art, the methods for determining the content of retained austenite in steel mainly include metallographic microscopy, X-ray diffraction, and magnetic methods. Although the results of metallographic microscopy are accurate and reliable, the operation is complicated and the equipment requirements are high; although the X-ray diffraction technology has high precision, it also has problems such as expensive equipment and cumbersome operation; the magnetic method has high requirements for equipment precision and operation.

[0004] Therefore, there is a need in the prior art to improve the calculation method of the residual content of medium-alloy ultra-high strength and high toughness steel after quenching. Summary of the invention

[0005] In view of this, the purpose of the embodiment of the present invention is to propose a method for calculating the residual Olympic content of medium-alloy ultra-high strength and high toughness steel after quenching. There is no need to experimentally measure the Ms point, and the residual Olympic content after quenching can be estimated only through the composition and quenching process design.

[0006] Based on the above purpose, the embodiment of the present invention provides a method for calculating the residual content of medium alloy ultra-high strength and high toughness steel after quenching, comprising: S1 determines the composition of the medium alloy ultra-high strength and high toughness steel and the condition parameters of the quenching process, the condition parameters include the quenching austenitizing temperature Ta and the quenching medium temperature Tq; S2 calculates the martensitic transformation starting temperature Ms point based on the composition of medium alloy ultra-high strength and high toughness steel and the corresponding coefficient of each component; S3 calculates the residual austenite content γ% based on the martensitic transformation starting temperature Ms point, the quenching austenitizing temperature Ta, and the quenching medium temperature Tq.

[0007] In some embodiments, in S2, the martensitic transformation starting temperature Ms is calculated according to the following empirical formula: Ms=540-420C-35Mn-12Cr-20Ni-21Mo-10.5W-10.5Si+140V+20Al, The unit of Ms is °C, and each component is expressed in mass percentage.

[0008] In some embodiments, in S3, the Paralympic γ% is calculated according to the following empirical formula: γ%=exp[0.002*(Ta-850)-0.0135*(Ms-Tq)], Wherein, Ta is the quenching austenitizing temperature, in °C; Ms is the martensitic transformation starting temperature, in °C; Tq is the quenching medium temperature, in °C.

[0009] In some embodiments, in S1, the composition of the medium alloy ultra-high strength and high toughness steel includes: in terms of mass percentage, C ranges from 0.25 to 0.45%, Cr ranges from 0.5 to 4.0%, Mn ranges from 0.2 to 1.5%, Si ranges from ≤2.5%, Ni ranges from ≤5%, Mo ranges from 0.2 to 1.5%, W ranges from ≤3.5%, V ranges from 0.01 to 0.40%, Nb ranges from 0.01 to 0.05%, and Al ranges from ≤0.05%.

[0010] In some embodiments, the total content of the main alloy elements ranges from 5 to 10%, and the main alloy includes C, Cr, Mn, Si, Ni, Mo, W, V, Nb, and Al.

[0011] In some embodiments, in S1, the quenching austenitizing temperature Ta ranges from 860 to 930°C, the austenitizing time is 1 hour, and the austenitizing temperature ranges from 860 to 930°C.

[0012] In some embodiments, in S1, the quenching medium temperature Tq ranges from -193 to 25°C.

[0013] In some embodiments, when oil quenching at room temperature is used, Tq=25°C, and when cryogenic treatment is performed within 8 hours after oil quenching at room temperature, Tq=the temperature of cryogenic treatment, wherein, When the cryogenic treatment temperature is -73℃ and the time is 1~2h, Tq=-73℃; When the cryogenic treatment temperature is -193℃ and the time is 1~2h, Tq=-193℃.

[0014] In some embodiments, the quenching process includes one quenching and / or two quenchings, and when the quenching is performed twice, the calculation method uses the parameters of the second quenching process for calculation.

[0015] In some embodiments, the composition of the medium alloy ultra-high strength and high toughness steel is determined by an element analyzer.

[0016] The present invention has at least the following beneficial technical effects: 1) It is only necessary to determine the composition of the steel and the quenching process parameters, and then use a simple empirical formula to calculate the Ms point and the residual content. No complicated equipment and cumbersome operations are required, which greatly improves the calculation efficiency and reduces the cost.

[0017] 2) Wide application scope: The present invention is applicable to medium alloy ultra-high strength and high toughness steel, whose main element content range is relatively wide, such as C range of 0.25-0.45%, Cr range of 0.5-4.0%, etc., covering a variety of medium alloy ultra-high strength and high toughness steels with different composition ratios. This makes the method widely applicable to the calculation of residual content after quenching of medium alloy ultra-high strength and high toughness steels with different compositions, and has strong versatility and practicality.

[0018] 3) Comprehensive consideration of factors: When calculating the Para-Olympic content, not only the influence of the steel composition on the Ms point is considered, but also the key process parameters of austenitizing temperature and quenching medium temperature are comprehensively considered. The relationship between Ms point, quenching medium temperature, austenitizing temperature and Para-Olympic content can be more accurately estimated after quenching. In contrast, some traditional calculation methods may only consider the composition factor and ignore the influence of quenching process conditions on the Para-Olympic content, resulting in inaccurate calculation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is a schematic diagram of an embodiment of a method for calculating the residual content of medium-alloy ultra-high strength and high toughness steel after quenching provided by the present invention. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0022] The terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions; the terms "first", "second", etc. in the specification and claims of the present invention or the above-mentioned drawings are used to distinguish different objects rather than to describe a specific order. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0023] In addition, reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0024] like Figure 1 The present invention provides a method for calculating the residual content of a medium alloy ultra-high strength and high toughness steel after quenching, comprising the following steps: S1 determines the composition of the medium alloy ultra-high strength and high toughness steel and the condition parameters of the quenching process, the condition parameters include the quenching austenitizing temperature Ta and the quenching medium temperature Tq; S2 calculates the martensitic transformation starting temperature Ms point based on the composition of medium alloy ultra-high strength and high toughness steel and the corresponding coefficient of each component; S3 calculates the residual austenite content γ% based on the martensitic transformation starting temperature Ms point, the quenching austenitizing temperature Ta, and the quenching medium temperature Tq.

[0025] In some embodiments, in S2, the martensitic transformation start temperature Ms is calculated using the empirical formula: Ms=540-420C-35Mn-12Cr-20Ni-21Mo-10.5W-10.5Si+140V+20Al, The unit of Ms is °C, and each component is expressed in mass percentage.

[0026] In some embodiments, in S3, the Paralympic γ% empirical formula is: γ%=exp[0.002*(Ta-850)-0.0135*(Ms-Tq)], Wherein, Ta is the quenching austenitizing temperature, in °C; Ms is the martensitic transformation starting temperature, in °C; Tq is the quenching medium temperature, in °C.

[0027] In some embodiments, in S1, the composition of the medium alloy ultra-high strength and high toughness steel includes: by mass percentage, C ranges from 0.25 to 0.45%, Cr ranges from 0.5 to 4.0%, Mn ranges from 0.2 to 1.5%, Si ranges from ≤2.5%, Ni ranges from ≤5%, Mo ranges from 0.2 to 1.5%, W ranges from ≤3.5%, V ranges from 0.01 to 0.40%, Nb ranges from 0.01 to 0.05%, and Al ranges from ≤0.05%. The total content of the main alloy elements ranges from 5 to 10%.

[0028] In some embodiments, in S1, the quenching austenitizing temperature Ta ranges from 860 to 930°C, the austenitizing time is 1 hour, and the austenitizing temperature ranges from 860 to 930°C.

[0029] In some embodiments, in S1, the quenching medium temperature Tq ranges from -193 to 25°C.

[0030] In some embodiments, when oil quenching at room temperature is used, Tq=25°C, and when cryogenic treatment is performed within 8 hours after oil quenching at room temperature, Tq=the temperature of cryogenic treatment, wherein, The cryogenic treatment system includes: when the treatment temperature is -73℃, the treatment time is 1~2h, Tq=-73℃; The deep cryogenic treatment system includes: when the treatment temperature is -193℃, the treatment time is 1~2h, Tq=-193℃.

[0031] In some embodiments, the quenching process includes one quenching and / or two quenchings, and when the quenching is performed twice, the calculation method is based on the process parameters of the second quenching.

[0032] In some embodiments, the composition of the medium alloy ultra-high strength and high toughness steel is determined by an element analyzer.

[0033] The beneficial effects of the method of the present invention include: 1) Improve the accuracy of material property prediction: Accurately calculating the residual austenite content after quenching is crucial for predicting and evaluating the performance of medium-alloy ultra-high-strength and high-toughness steel. The presence of retained austenite will affect the strength, toughness, hardness and fatigue performance of the steel. The present invention can more accurately calculate the residual austenite content, thereby providing more reliable data support for the prediction of material properties, helping to optimize the material composition design and heat treatment process, improve the comprehensive performance of the material, and enable it to better meet the performance requirements in engineering applications.

[0034] 2) Optimize heat treatment process: Through this calculation method, the changing trend of the Paralyzed Aluminum content under different quenching process conditions can be predicted in advance. In actual production, process parameters such as the quenching medium temperature can be adjusted according to the calculation results to obtain the expected Paralyzed Aluminum content, and then optimize the heat treatment process. For example, if you want to obtain a lower Paralyzed Aluminum content to improve the hardness and strength of the material, you can achieve this by appropriately lowering the quenching medium temperature; conversely, if you need to improve the toughness of the material, you can appropriately increase the quenching medium temperature. This helps to improve production efficiency, reduce production costs, and ensure the stability of product quality.

[0035] 3) Promote material research and development and application: This invention provides strong technical support for the development and application of medium-alloy ultra-high strength and high-toughness steel. In the process of new material research and development, researchers can use this method to quickly evaluate the para-Olympic content under different composition and heat treatment process combinations, thereby accelerating the research and development of new materials. In addition, for existing medium-alloy ultra-high strength and high-toughness steel materials, by accurately calculating the para-Olympic content, we can better understand their performance characteristics, expand their application scope in aerospace, automobile manufacturing, engineering machinery and other fields, and improve the added value and market competitiveness of materials.

[0036] The present invention will be further described below in conjunction with examples, but the present invention is not limited to the following examples.

[0037] Example 1 Composition of steel: C=0.28%, Cr=1%, Mn=0.8%, Si=2%, Ni=4.4%, Mo=0.6%, Nb=0.03%, Al=0.02%.

[0038] Quenching process 1: quenching austenitizing at 900℃*1 hour, oil quenching at room temperature, quenching medium temperature Tq=25℃.

[0039] Quenching process 2: quenching austenitization at 900℃*1 hour, oil quenching at room temperature, deep cooling at -73℃ for 1 hour within 8 hours, quenching medium temperature Tq=-73℃.

[0040] Quenching process 3: quenching austenitization at 900℃*1 hour, oil quenching at room temperature, deep cooling at -73℃ for 1 hour within 8 hours, quenching medium temperature Tq=-193℃.

[0041] Quenching process 4: The first quenching, austenitizing at 900℃*1 hour, oil quenching at room temperature, quenching medium temperature Tq=25℃. The second quenching, austenitizing at 860℃*1 hour, oil quenching at room temperature, quenching medium temperature Tq=25℃.

[0042] Quenching process 5: quenching austenitization at 860℃*1 hour, oil quenching at room temperature, deep cooling at -73℃ for 1 hour within 8 hours, quenching medium temperature Tq=-73℃.

[0043] Quenching process 6: quenching austenitization at 860℃*1 hour, oil quenching at room temperature, deep cooling at -73℃ for 1 hour within 8 hours, quenching medium temperature Tq=-193℃.

[0044] Calculation process: Calculate the Ms point: According to the empirical formula for Ms calculation, Ms(℃)=540-420×0.28-35×0.8-12×1-20×4.4-21×0.6-10.5×2+20×0.02=261.8.

[0045] The measured Ms point is 260℃.

[0046] Estimate the Paralympic content γ%: Substitute the Ms point, austenitizing temperature and quenching medium temperature into the Paralympic content calculation formula.

[0047] The Paralympic content estimated by quenching process 1 is: γ%=exp[0.002×(900-850)-0.0135×(261.8-25)]=0.0452, that is, the Paralympic content is about 4.52%.

[0048] The actual measured para-Olympic content γ% after quenching process 1 is 4.49%±1.04%.

[0049] The Paralympic content estimated by quenching process 2 is: γ%=exp[0.002×(900-850)-0.0135×(261.8+73)]=0.0120, that is, the Paralympic content is about 1.20%.

[0050] The actual measured para-Olympic content γ% after quenching process 2 is 1.07%±0.5%.

[0051] The Paralympic content estimated by quenching process 3 is: γ%=exp[0.002×(900-850)-0.0135×(261.8+193)]=0.0020, that is, the Paralympic content is about 0.20%.

[0052] The actual measured residual content γ% after quenching process 3 is 0.44%±0.2%.

[0053] Quenching process 4, the Paralympic content is estimated using the second quenching process parameters: γ%=exp[0.002×(860-850)-0.0135×(261.8-25)]=0.0420, that is, the Paralympic content is about 4.20%.

[0054] The actual measured residual content γ% after quenching process 4 is 4.39%±1.0%.

[0055] The Paralympic content estimated by quenching process 5 is: γ%=exp[0.002(860-850)-0.0135×(261.8+73)]=0.0110, that is, the Paralympic content is about 1.10%.

[0056] The actual measured para-Olympic content γ% after quenching process 5 is 1.01%±0.6%.

[0057] The Paralympic content estimated by quenching process 6 is: exp[0.002(860-850)-0.0135×(261.8+193)]=0.0020, that is, the Paralympic content is about 0.20%.

[0058] The actual measured para-Olympic content γ% after quenching process 6 is 0.35%±0.25%.

[0059] The comparison between the measured and calculated values ​​of Ms point and Paralympic content of Example 1 is shown in Table 1.

[0060] Example 2 Composition of steel: C=0.36%, Cr=1%, Mn=0.5%, Si=2.0%, Ni=4%, Mo=0.5%, Nb=0.04%, Al=0.02%.

[0061] Quenching process 1: quenching austenitizing at 880℃*1 hour, oil quenching at room temperature, quenching medium temperature Tq=25℃.

[0062] Quenching process 2: quenching austenitization at 880℃*1 hour, oil quenching at room temperature, deep cooling at -73℃ for 1 hour within 8 hours, quenching medium temperature Tq=-73℃.

[0063] Calculation process: Calculate Ms point: Ms(℃)=540-420×0.36-35×0.5-12×1-20×4-21×0.5-10.5×2+20×0.02=247.2.

[0064] Measured Ms point: Ms(℃)=250.

[0065] Estimate the Paralympic content γ%: Substitute the Ms point, austenitizing temperature and quenching medium temperature into the Paralympic content calculation formula.

[0066] The estimated Paralympic content of quenching process 1 is: exp[0.002×(880-850)-0.0135×(247.2-25)]=0.0530, that is, the Paralympic content is about 5.30%.

[0067] The actual measured para-Olympic content γ% after quenching process 1 is 5.12%±1%.

[0068] The Paralympic content estimated by quenching process 2 is: γ%=exp[0.002×(880-850)-0.0135×(247.2+73)]=0.0140, that is, the Paralympic content is about 1.40%.

[0069] The actual measured para-Olympic content γ% after quenching process 2 is 1.57±0.35%.

[0070] The comparison between the measured and calculated values ​​of Ms point and Paralympic content of Example 2 is shown in Table 1.

[0071] Example 3 Steel composition: C=0.40%, Si=1.8%, Mn=1.5%, Cr=1%, Ni=0.7%, Mo=0.35%, V=0.04%, FeBal. Quenching process conditions: quenching austenitizing at 900℃*1h, oil quenching at room temperature, quenching medium temperature Tq=25℃.

[0072] Calculation process: Calculate Ms point: Ms(℃)=540-420×0.40-35×1.5-12×1-20×0.7-21×0.35-10.5×1.8+140×0.04=272.85 The measured Ms point is 270℃.

[0073] Estimate the Paralympic content γ%: Substitute the Ms point, austenitizing temperature and quenching medium temperature into the Paralympic content calculation formula.

[0074] Estimated Paralympic content γ%: γ%=exp[0.002×(900-850)-0.0135×(272.85-25)]=0.0389, that is, the Paralympic content is about 3.89%.

[0075] The measured Paralympic content is γ%, 3.61%±0.99%.

[0076] The comparison between the measured and calculated values ​​of Ms point and Paralympic content of Example 3 is shown in Table 1.

[0077] Table 1 Comparison of measured and estimated values ​​of Ms and Para-Olympic content in alloy ultra-high strength and high toughness steel

[0078] Table 1 is a comparison of the calculated Ms points and measured Ms points of different components in Examples 1 to 3, and the measured and calculated values ​​of the Paralympic content.

[0079] It can be seen from the table that there are certain differences between the measured and calculated values ​​of the Ms point and Paralympic content of the medium alloy ultra-high strength and high toughness steel, but in general the calculated values ​​are close to the measured values. The calculated and measured values ​​of the Paralympic content under different quenching process conditions are generally very close, which shows that the calculation formula of the Paralympic content also has high accuracy under different quenching process conditions. In particular, as the austenitizing temperature increases, the trend of the Paralympic content increasing is consistent with the results of the calculated formula. As the quenching medium temperature decreases, the trend of the Paralympic content decreasing is consistent with the results of the calculated formula. R&D personnel can use this method to quickly evaluate the Paralympic content under different composition and heat treatment process combinations, thereby accelerating the research and development process of new materials for medium alloy ultra-high strength steel.

[0080] The above are exemplary embodiments disclosed in the present invention, but it should be noted that various changes and modifications may be made without departing from the scope disclosed in the embodiments of the present invention as defined in the claims. The functions, steps and / or actions of the method claims according to the disclosed embodiments described herein do not need to be performed in any particular order. In addition, although the elements disclosed in the embodiments of the present invention may be described or required in individual form, they may also be understood as multiple unless explicitly limited to the singular.

[0081] It should be understood that, as used herein, the singular forms "a", "an" are intended to include the plural forms as well, unless the context clearly supports an exception. It should also be understood that, as used herein, "and / or" refers to any and all possible combinations including one or more of the associated listed items.

[0082] The serial numbers of the embodiments disclosed in the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0083] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the above embodiments of the present invention, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A method for calculating the residual content of medium alloy ultra-high strength and high toughness steel after quenching, characterized in that: include: S1 determines the composition of the medium alloy ultra-high strength and high toughness steel and the condition parameters of the quenching process, wherein the condition parameters include the quenching austenitizing temperature Ta and the quenching medium temperature Tq; S2: calculating the martensitic transformation starting temperature Ms point based on the composition of the medium alloy ultra-high strength and high toughness steel and the corresponding coefficient of each component; S3 calculates the residual austenite content γ% based on the martensitic transformation starting temperature Ms point, the quenching austenitizing temperature Ta, and the quenching medium temperature Tq.

2. The method for calculating the residual content of medium alloy ultra-high strength and high toughness steel after quenching according to claim 1, characterized in that: In S2, the martensitic transformation starting temperature Ms is calculated according to the following empirical formula: Ms=540-420C-35Mn-12Cr-20Ni-21Mo-10.5W-10.5Si+140V+20Al, The unit of Ms is °C, and each component is expressed in mass percentage.

3. The method for calculating the residual content of medium alloy ultra-high strength and high toughness steel after quenching according to claim 1, characterized in that: In S3, Paralympic γ% is calculated according to the following empirical formula: γ%=exp[0.002*(Ta-850)-0.0135*(Ms-Tq)], Wherein, Ta is the quenching austenitizing temperature, in °C; Ms is the martensitic transformation starting temperature, in °C; Tq is the quenching medium temperature, in °C.

4. The method for calculating the residual content of medium alloy ultra-high strength and high toughness steel after quenching according to claim 1, characterized in that: In S1, the composition of the medium alloy ultra-high strength and high toughness steel includes: in terms of mass percentage, C ranges from 0.25 to 0.45%, Cr ranges from 0.5 to 4.0%, Mn ranges from 0.2 to 1.5%, Si ranges from ≤2.5%, Ni ranges from ≤5%, Mo ranges from 0.2 to 1.5%, W ranges from ≤3.5%, V ranges from 0.01 to 0.40%, Nb ranges from 0.01 to 0.05%, and Al ranges from ≤0.05%.

5. The method for calculating the residual content of medium alloy ultra-high strength and high toughness steel after quenching according to claim 4, characterized in that: The total content of main alloy elements ranges from 5 to 10%, and the main alloys include C, Cr, Mn, Si, Ni, Mo, W, V, Nb, and Al.

6. The method for calculating the residual content of medium alloy ultra-high strength and high toughness steel after quenching according to claim 1, characterized in that: In S1, the quenching austenitizing temperature Ta ranges from 860 to 930°C, the austenitizing time is 1 hour, and the austenitizing temperature ranges from 860 to 930°C.

7. The method for calculating the residual content of medium alloy ultra-high strength and high toughness steel after quenching according to claim 1, characterized in that: In S1, the quenching medium temperature Tq ranges from -193 to 25°C.

8. The method for calculating the residual content of medium alloy ultra-high strength and high toughness steel after quenching according to claim 6, characterized in that: When oil quenching at room temperature is used, Tq=25℃. When deep cryogenic treatment is performed within 8 hours after oil quenching at room temperature, Tq=the temperature of deep cryogenic treatment, where When the temperature of deep cryogenic treatment is -73℃ and the time is 1~2h, Tq=-73℃; When the temperature of deep cryogenic treatment is -193℃ and the time is 1~2h, Tq=-193℃.

9. The method for calculating residual content of medium alloy ultra-high strength and high toughness steel after quenching according to claim 1, characterized in that: The quenching process includes one quenching and / or two quenchings. When the quenching is performed twice, the calculation method uses the parameters of the second quenching process for calculation.

10. The method for calculating the residual content of medium alloy ultra-high strength and high toughness steel after quenching according to claim 1, characterized in that: The composition of the medium alloy ultra-high strength and high toughness steel is determined by an element analyzer.

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