Method for calculating residual austenite content of medium-alloy super-high-strength high-toughness steel after quenching

Abstract

The application relates to the technical field of material composition-structure calculation, and discloses a method for calculating residual austenite content of medium-alloy super-high-strength high-toughness steel after quenching, S1 determines the composition of the medium-alloy super-high-strength high-toughness steel and condition parameters of a quenching process, the condition parameters include a quenching austenitizing temperature Ta and a quenching medium temperature Tq; S2 calculates a martensite transformation starting temperature Ms point based on the composition of the medium-alloy super-high-strength high-toughness steel and corresponding coefficients of each component; and S3 calculates the residual austenite content gamma % based on the martensite transformation starting temperature Ms point, the quenching austenitizing temperature Ta and the quenching medium temperature Tq. According to the method, the composition of the steel and the quenching process condition parameters are determined, then the Ms point and the residual austenite content are calculated by using simple empirical formulas, without the need of complicated equipment and cumbersome operation, so that the calculation efficiency is greatly improved, and the cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material composition-structure calculation, and particularly relates to a method for calculating residual austenite content of medium-alloy super-high-strength high-toughness steel after quenching. BACKGROUND

[0002] Typical steel types include 4340 (40CrNi2MoA), D6AC (45CrNiMo1VA), N31 (30CrMnSiNi2A), D406A (30Si2MnCrMoVE), 300M (40Si2Ni2CrMoVA), etc. In the composition-structure design of new medium-alloy super-high-strength high-toughness steel, the mechanical properties of the medium-alloy super-high-strength high-toughness steel are usually considered to be affected by the austenite-to-martensite transformation during quenching, and the amount of residual austenite is a main factor affecting the strength and plasticity balance of the steel. In order to reasonably control the amount of residual austenite, a method is often needed to estimate the residual austenite content of different composition medium-alloy super-high-strength high-toughness steel under different quenching process conditions.

[0003] In the prior art, the methods for measuring the residual austenite content in steel mainly include metallographic microscopic technology, X-ray diffraction technology, and magnetic method. The metallographic microscopic technology is accurate and reliable, but the operation is complex and requires high equipment; the X-ray diffraction technology is high in precision, but also has problems such as expensive equipment and complicated operation; and the magnetic method requires high equipment precision and operation.

[0004] Therefore, there is a need to improve the method for calculating the residual austenite content of medium-alloy super-high-strength high-toughness steel after quenching in the prior art. SUMMARY

[0005] Therefore, the purpose of the embodiments of the present application is to provide a method for calculating the residual austenite content of medium-alloy super-high-strength high-toughness steel after quenching, which does not need to measure the Ms point by experiment, but only needs to estimate the residual austenite content after quenching through the composition and quenching process design.

[0006] To achieve the above purpose, the embodiments of the present application provide a method for calculating the residual austenite content of medium-alloy super-high-strength high-toughness steel after quenching, which comprises the following steps:

[0007] S1 determining the composition of the medium-alloy super-high-strength high-toughness steel and the condition parameters of the quenching process, wherein the condition parameters include a quenching austenitizing temperature Ta and a quenching medium temperature Tq;

[0008] S2 calculating a martensite transformation starting temperature Ms point based on the composition of the medium-alloy super-high-strength high-toughness steel and the corresponding coefficients of each composition;

[0009] S3 calculates the retained austenite content γ% based on the martensite transformation start temperature Ms, and the quenching austenitizing temperature Ta, and the quenching medium temperature Tq.

[0010] In some embodiments, in S2, the martensite transformation start temperature Ms is calculated according to the following empirical formula:

[0011] Ms = 540 - 420C - 35Mn - 12Cr - 20Ni - 21Mo - 10.5W - 10.5Si + 140V + 20Al,

[0012] wherein the unit of Ms is ℃, and each component is in mass percentage.

[0013] In some embodiments, in S3, the retained austenite γ% is calculated according to the following empirical formula:

[0014] γ% = exp[0.002*(Ta-850) - 0.0135*(Ms-Tq)],

[0015] wherein Ta is the quenching austenitizing temperature, in ℃; Ms is the martensite transformation start temperature, in ℃; and Tq is the quenching medium temperature, in ℃.

[0016] In some embodiments, in S1, the medium-alloyed super-high-strength high-toughness steel composition includes: in mass percentage, C ranging from 0.25% to 0.45%, Cr ranging from 0.5% to 4.0%, Mn ranging from 0.2% to 1.5%, Si ≤ 2.5%, Ni ≤ 5%, Mo ranging from 0.2% to 1.5%, W ≤ 3.5%, V ranging from 0.01% to 0.40%, Nb ranging from 0.01% to 0.05%, and Al ≤ 0.05%.

[0017] In some embodiments, the total content of the main alloying elements ranges from 5% to 10%, and the main alloying elements include C, Cr, Mn, Si, Ni, Mo, W, V, Nb, and Al.

[0018] In some embodiments, in S1, the quenching austenitizing temperature Ta ranges from 860 ℃ to 930 ℃, the austenitizing time is 1 h, and the austenitizing temperature ranges from 860 ℃ to 930 ℃.

[0019] In some embodiments, in S1, the quenching medium temperature Tq ranges from -193 ℃ to 25 ℃.

[0020] In some embodiments, when using normal-temperature oil quenching, Tq = 25 ℃, and when performing cryogenic treatment within 8 hours after normal-temperature oil quenching, Tq = the temperature of the cryogenic treatment.

[0021] The cryogenic treatment temperature is -73 DEG C, and the time is 1-2 hours, and Tq=-73 DEG C;

[0022] The cryogenic treatment temperature is -193 DEG C, and the time is 1-2 hours, and Tq=-193 DEG C.

[0023] In some embodiments, the quenching process comprises one quenching and / or two quenchings, and the calculation method takes the parameters of the second quenching process to calculate.

[0024] In some embodiments, the composition of the medium-alloy ultra-high-strength high-toughness steel is determined by an elemental analyzer.

[0025] The present application has at least the following beneficial technical effects:

[0026] 1) Only by determining the composition of the steel and the quenching process condition parameters, and then using a simple empirical formula to calculate the Ms point and the residual austenite content, without complex equipment and tedious operation, the calculation efficiency is greatly improved, and the cost is reduced.

[0027] 2) Wide application range: The present application is suitable for medium-alloy ultra-high-strength high-toughness steel, and the content range of main elements is wide, such as the range of C is 0.25-0.45%, the range of Cr is 0.5-4.0%, etc., which covers a variety of medium-alloy ultra-high-strength high-toughness steels with different component proportions. This makes the method widely applicable to the calculation of residual austenite content after quenching of medium-alloy ultra-high-strength high-toughness steels with different compositions, and has strong universality and practicality.

[0028] 3) Comprehensive consideration: When calculating the residual austenite content, not only the influence of the composition of the steel on the Ms point is considered, but also the austenitizing temperature and the quenching medium temperature, which are key process parameters. Through the relationship between the Ms point, the quenching medium temperature, the austenitizing temperature and the residual austenite content, the residual austenite content after quenching can be more accurately estimated. In comparison, some traditional calculation methods may only consider the composition factor and ignore the influence of quenching process conditions on the residual austenite content, resulting in inaccurate calculation results. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other embodiments can also be obtained without creative labor on the basis of these drawings.

[0030] Figure 1 The schematic diagram of the medium-alloy ultra-high-strength high-toughness steel quenching residual austenite content calculation method provided by the present application. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the present application clearer, the embodiments of the present application are further described in detail below with reference to the drawings.

[0032] The terms "comprise" and "have" and any variations thereof in the specification and claims of the present application and the above description of the drawings are intended to cover non-exclusive inclusion; the terms "first", "second" and the like in the specification and claims of the present application or the above description of the drawings are used to distinguish different objects, not to describe a specific order. The meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0033] In addition, the reference to "embodiments" herein means that the specific features, structures or characteristics described in conjunction with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0034] As Figure 1 A method for calculating the residual austenite content of a medium-alloy ultra-high-strength high-toughness steel provided by the present application after quenching is shown, comprising the following steps:

[0035] S1 determines the composition of the medium-alloy ultra-high-strength high-toughness steel and the condition parameters of the quenching process, including quenching austenitizing temperature Ta and quenching medium temperature Tq;

[0036] S2 calculates the martensite transformation starting temperature Ms point based on the composition of the medium-alloy ultra-high-strength high-toughness steel and the corresponding coefficient of each component;

[0037] S3 calculates the residual austenite content γ% based on the martensite transformation starting temperature Ms point, and the quenching austenitizing temperature Ta and the quenching medium temperature Tq.

[0038] In some embodiments, in S2, the martensite transformation starting temperature Ms is calculated by the empirical formula:

[0039] Ms=540-420C-35Mn-12Cr-20Ni-21Mo-10.5W-10.5Si+140V+20Al,

[0040] Wherein, the unit of Ms is ℃, and each component is in mass percent.

[0041] In some embodiments, in S3, the residual austenite γ% is calculated by the empirical formula:

[0042] γ%=exp[0.002*(Ta-850)-0.0135*(Ms-Tq)],

[0043] Wherein, Ta is the quenching austenitizing temperature, unit is ℃; Ms is the martensite transformation start temperature, unit is ℃; Tq is the quenching medium temperature, unit is ℃.

[0044] In some embodiments, in S1, the medium alloy super high strength and high toughness steel composition comprises: in 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 alloying elements ranges from 5 to 10%.

[0045] In some embodiments, in S1, the quenching austenitizing temperature Ta ranges from 860 to 930℃, the austenitizing time is 1h, and the austenitizing temperature ranges from 860 to 930℃.

[0046] In some embodiments, in S1, the quenching medium temperature Tq ranges from -193 to 25℃.

[0047] In some embodiments, when the normal temperature oil quenching is adopted, Tq=25℃, and when the cryogenic treatment is performed within 8 hours after the normal temperature oil quenching, Tq is the temperature of the cryogenic treatment, wherein,

[0048] The cryogenic treatment system comprises: when the treatment temperature is -73℃, the treatment time is 1-2h, and Tq=-73℃.

[0049] The cryogenic treatment system comprises: when the treatment temperature is -193℃, the treatment time is 1-2h, and Tq=-193℃.

[0050] In some embodiments, the quenching process comprises one-time quenching and / or two-time quenching, and the calculation method is based on the second quenching process parameter when the two-time quenching is adopted.

[0051] In some embodiments, the medium alloy super high strength and high toughness steel composition is determined by an elemental analyzer.

[0052] The beneficial effects of the method of the present application include:

[0053] 1) Improve the accuracy of material performance prediction: Accurate calculation of residual austenite content after quenching is crucial for predicting and evaluating the performance of medium alloy ultra-high strength high toughness steel. The presence of residual austenite can affect the strength, toughness, hardness and fatigue performance of the steel. This invention can more accurately calculate the residual austenite content, thereby providing more reliable data support for the prediction of material performance, helping to optimize the composition design and heat treatment process of the material, and improving the comprehensive performance of the material, so that it better meets the performance requirements in engineering applications.

[0054] 2) Optimize heat treatment process: Through this calculation method, the trend of residual austenite content under different quenching process conditions can be predicted in advance. In actual production, process parameters such as quenching medium temperature can be adjusted according to the calculation results to obtain the expected residual austenite content, thereby optimizing the heat treatment process. For example, if you want to obtain lower residual austenite content to improve the hardness and strength of the material, you can achieve this by appropriately reducing 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 cost, and at the same time ensure the stability of product quality.

[0055] 3) Promote material research and application: This invention provides strong technical support for the development and application of medium alloy ultra-high strength high toughness steel. In the process of new material research and development, researchers can use this method to quickly evaluate the residual austenite content under different combinations of composition and heat treatment process, thereby accelerating the research and development process of new materials. In addition, for existing medium alloy ultra-high strength high toughness steel materials, by accurately calculating the residual austenite content, the performance characteristics of the material can be better understood, the application range of the material in the fields of aerospace, automobile manufacturing, engineering machinery, etc. can be expanded, and the added value and market competitiveness of the material can be improved.

[0056] The invention will be further described below in conjunction with examples, but the invention is not limited to the following examples.

[0057] Example 1

[0058] The composition of the steel: C=0.28%, Cr=1%, Mn=0.8%, Si=2%, Ni=4.4%, Mo=0.6%, Nb=0.03%, Al=0.02%.

[0059] Quenching process 1: quenching austenitizing at 900℃*1 hour, quenching at room temperature, quenching medium temperature Tq=25℃.

[0060] Quenching process 2: quenching austenitizing at 900℃*1 hour, quenching at room temperature, -73℃ deep cooling for 1 hour within 8 hours, quenching medium temperature Tq=-73℃.

[0061] Quenching process 3: austenitizing at 900°C for 1 hour, oil quenching at room temperature, deep cooling at -73°C for 1 hour within 8 hours, quenching medium temperature Tq = -193°C.

[0062] Quenching process 4: first quenching, austenitizing at 900°C for 1 hour, oil quenching at room temperature, quenching medium temperature Tq = 25°C. Second quenching, quenching austenitizing at 860°C for 1 hour, oil quenching at room temperature, quenching medium temperature Tq = 25°C.

[0063] Quenching process 5: quenching austenitizing at 860°C for 1 hour, oil quenching at room temperature, deep cooling at -73°C for 1 hour within 8 hours, quenching medium temperature Tq = -73°C.

[0064] Quenching process 6: quenching austenitizing at 860°C for 1 hour, oil quenching at room temperature, deep cooling at -73°C for 1 hour within 8 hours, quenching medium temperature Tq = -193°C.

[0065] Calculation process:

[0066] Calculate Ms point: according to the empirical formula of Ms calculation, Ms (°C) = 540-420x0.28-35x0.8-12x1-20x4.4-21x0.6-10.5x2+20x0.02 = 261.8.

[0067] Measured Ms point 260°C.

[0068] Estimate residual austenite content γ%: substitute Ms point, austenitizing temperature and quenching medium temperature into the residual austenite content calculation formula.

[0069] Quenching process 1 estimated residual austenite content: γ% = exp[0.002x(900-850)-0.0135x(261.8-25)] = 0.0452, that is, the residual austenite content is about 4.52%.

[0070] Quenching process 1 measured residual austenite content γ%, 4.49% ± 1.04%.

[0071] Quenching process 2 estimated residual austenite content: γ% = exp[0.002x(900-850)-0.0135x(261.8+73)] = 0.0120, that is, the residual austenite content is about 1.20%.

[0072] Quenching process 2 measured residual austenite content γ%, 1.07% ± 0.5%.

[0073] Quenching process 3 estimated residual austenite content: γ% = exp[0.002x(900-850)-0.0135x(261.8+193)] = 0.0020, that is, the residual austenite content is about 0.20%.

[0074] Quenching process 3: measured residual austenite content γ%, 0.44%±0.2%.

[0075] Quenching process 4: estimated residual austenite content with second quenching process parameters: γ%=exp[0.002(860-850)-0.0135(261.8-25)]=0.0420, i.e. residual austenite content is about 4.20%.

[0076] Quenching process 4: measured residual austenite content γ%, 4.39%±1.0%.

[0077] Quenching process 5: estimated residual austenite content: γ%=exp[0.002(860-850)-0.0135(261.8+73)]=0.0110, i.e. residual austenite content is about 1.10%.

[0078] Quenching process 5: measured residual austenite content γ%, 1.01%±0.6%.

[0079] Quenching process 6: estimated residual austenite content: exp[0.002(860-850)-0.0135(261.8+193)]=0.0020, i.e. residual austenite content is about 0.20%.

[0080] Quenching process 6: measured residual austenite content γ%, 0.35%±0.25%.

[0081] Comparison of measured and calculated values of Ms point and residual austenite content of Example 1 is shown in Table 1.

[0082] Example 2

[0083] Composition of the steel: C=0.36%, Cr=1%, Mn=0.5%, Si=2.0%, Ni=4%, Mo=0.5%, Nb=0.04%, Al=0.02%.

[0084] Quenching process 1: quenching austenitization at 880°C*1 hour, quenching in oil at room temperature, quenching medium temperature Tq=25°C.

[0085] Quenching process 2: quenching austenitization at 880°C*1 hour, quenching in oil at room temperature, deep cooling at -73°C for 1 hour within 8 hours, quenching medium temperature Tq=-73°C.

[0086] Calculation process:

[0087] Calculation of Ms point: Ms(°C)=540-420*0.36-35*0.5-12*1-20*4-21*0.5-10.5*2+20*0.02=247.2.

[0088] Measured Ms point: Ms(°C)=250.

[0089] Estimation of residual austenite content γ%: Ms point, austenitizing temperature and quenching medium temperature are substituted into the residual austenite content calculation formula.

[0090] Estimation of residual austenite content of quenching process 1: exp[0.002x(880-850)-0.0135x(247.2-25)]=0.0530, i.e. the residual austenite content is about 5.30%.

[0091] Measured residual austenite content γ% of quenching process 1, 5.12%±1%.

[0092] Estimation of residual austenite content of quenching process 2: γ%=exp[0.002x(880-850)-0.0135x(247.2+73)]=0.0140, i.e. the residual austenite content is about 1.40%.

[0093] Measured residual austenite content γ% of quenching process 2, 1.57±0.35%.

[0094] Comparison of measured and calculated values of Ms point and residual austenite content of Example 2 is shown in Table 1.

[0095] Example 3

[0096] Composition of steel: C=0.40%, Si=1.8%, Mn=1.5%, Cr=1%, Ni=0.7%, Mo=0.35%, V=0.04%, Fe Bal.

[0097] Quenching process condition: quenching austenitizing 900°C*1h, normal temperature oil quenching, quenching medium temperature Tq=25°C.

[0098] Calculation process:

[0099] Calculation of Ms point: Ms(°C)=540-420x0.40-35x1.5-12x1-20x0.7-21x0.35-10.5x1.8+140x0.04=272.85

[0100] Measured Ms point 270°C.

[0101] Estimation of residual austenite content γ%: Ms point, austenitizing temperature and quenching medium temperature are substituted into the residual austenite content calculation formula.

[0102] Estimation of residual austenite content γ%: γ%=exp[0.002x(900-850)-0.0135x(272.85-25)]=0.0389, i.e. the residual austenite content is about 3.89%.

[0103] Measured residual austenite content γ%, 3.61%±0.99%.

[0104] The measured values of Ms point and residual austenite content of Example 3 are compared with the calculated values in Table 1.

[0105] Comparison of measured and estimated values of Ms and residual austenite content of the alloy super-high strength and high toughness steel in Table 1

[0106]

[0107] Table 1 is the comparison of the calculated Ms point and the measured Ms point, and the comparison of the measured value and the calculated value of the residual austenite content of different components in Examples 1-3.

[0108] As can be seen from the table, there is a certain difference between the measured value and the calculated value of the Ms point and the residual austenite content of the medium alloy super-high strength and high toughness steel, but overall the calculated value can be well close to the measured value. The calculated value and the measured value of the residual austenite content under different quenching process conditions are very close overall, which shows that the residual austenite content calculation formula also has high accuracy under different quenching process conditions. The measured and calculated formula results are consistent with the trend that the residual austenite content increases as the austenitizing temperature increases. The measured and calculated formula results are consistent with the trend that the residual austenite content decreases as the quenching medium temperature decreases. The researchers can use this method to quickly evaluate the residual austenite content under different component and heat treatment process combinations, thereby accelerating the research and development process of medium alloy super-high strength steel new materials.

[0109] The above is the exemplary embodiment disclosed by the present application, but it should be noted that various changes and modifications can be made without departing from the scope of the embodiments disclosed by the present application defined by the claims. The functions, steps and / or acts of the method claims described herein need not be performed in any particular order. Furthermore, although the elements of the embodiments disclosed by the present application can be described or claimed in individual form or in a singular way, they can also be understood as plural unless explicitly limited to a singular.

[0110] It should be understood that, as used herein, the singular forms "a", "an" and "the" are intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that "and / or" as used herein refers to any and all possible combinations of one or more of the associated listed items.

[0111] The above embodiment sequence number of the embodiments of the present application is only for description, and does not represent the advantages and disadvantages of the embodiments.

[0112] Those skilled in the art should understand that the above discussion of any embodiment is only exemplary, and is not intended to mean that the scope of the embodiments disclosed by the present application (including claims) is limited to these examples; under the idea of the embodiments of the present application, the above embodiments or technical features in different embodiments can also be combined, and there are many other changes of different aspects of the embodiments of the present application as above. In order to be brief, they are not provided in details. Therefore, any omission, modification, equivalent replacement, improvement, etc. made in the spirit and principle of the embodiments of the present application shall be included in the protection scope of the embodiments of the present application.

Claims

1. A method for calculating the residual austenite content of medium-alloy ultra-high strength and high toughness steel after quenching, characterized in that, include: S1 determines the composition and quenching process conditions of medium alloy ultra-high strength and high toughness steel, including the quenching austenitizing temperature Ta and the quenching medium temperature Tq. S2 calculates the martensitic transformation initiation temperature Ms point based on the composition of the medium alloy ultra-high strength and high toughness steel and the corresponding coefficient of each composition; S3 calculates the residual austenitic content γ% based on the martensitic transformation initiation temperature Ms, the quenching austenitizing temperature Ta, and the quenching medium temperature Tq. In S2, the martensitic transformation initiation temperature Ms is calculated according to the following empirical formula: Ms=540-420C-35Mn-12Cr-20Ni-21Mo-10.5W-10.5Si+140V+20Al, Where Ms is in °C, and each component is expressed as a mass percentage. In S3, Paralympic γ% is calculated using the following empirical formula: γ%=exp[0.002*(Ta-850)-0.0135*(Ms-Tq)], Where Ta is the quenching austenitizing temperature in °C; Ms is the martensitic transformation initiation temperature in °C; and Tq is the quenching medium temperature in °C.

2. The method for calculating the residual austenite 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, by mass percentage: C ranging from 0.25% to 0.45%, Cr ranging from 0.5% to 4.0%, Mn ranging from 0.2% to 1.5%, Si ranging from ≤2.5%, Ni ranging from ≤5%, Mo ranging from 0.2% to 1.5%, W ranging from ≤3.5%, V ranging from 0.01% to 0.40%, Nb ranging from 0.01% to 0.05%, and Al ranging from ≤0.05%.

3. The method for calculating the residual austenite content of medium alloy ultra-high strength and high toughness steel after quenching according to claim 2, characterized in that, The total content of the main alloying elements ranges from 5% to 10%, and the main alloying elements include C, Cr, Mn, Si, Ni, Mo, W, V, Nb, and Al.

4. The method for calculating the residual austenite 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.

5. The method for calculating the residual austenite 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℃.

6. The method for calculating the residual austenite content of medium alloy ultra-high strength and high toughness steel after quenching according to claim 4, characterized in that, When using room temperature oil quenching, Tq = 25℃. When deep cryogenic treatment is performed within 8 hours after room temperature oil quenching, Tq = the temperature of deep cryogenic treatment, where... 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℃.

7. The method for calculating the residual austenite 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 two quenchings are performed, the calculation method uses the parameters of the second quenching process.

8. The method for calculating the residual austenite 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 was determined using an elemental analyzer.

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