Weldable hydrogen embrittlement-resistant high-strength corrosion-resistant austenitic steel based on material calculation and preparation method thereof

Abstract

The invention relates to weldable hydrogen embrittlement-resistant high-strength corrosion-resistant austenitic steel based on material calculation and a preparation method thereof. The weldable hydrogen embrittlement-resistant high-strength corrosion-resistant austenitic steel comprises the following components in percentage by weight: less than 0.03% of C, 0.27%-0.3% of N, 0.18%-0.22% of Si, 2.3%-2.5% of Mn, 15%-18% of Cr, 18%-20% of Ni, 1.4%-1.6% of Mo, 1.9%-2.1% of Co, 0.3%-1% of Nb, 0.3%-1% of V and the balance of Fe and impurities. The yield strength of the finished product is larger than 800 MPa, the tensile strength is larger than 1000 MPa, and the ductility is larger than 23%. The weldability is good; the self-corrosion potential is greater than-0.6 V, and the self-corrosion current is less than 1.5 * 10 <-5 > A / cm < 2 >. And the hydrogen embrittlement sensitivity coefficient at room temperature is less than 18%. According to the method, smelting components are accurately designed through multi-dimensional component calculation, the smelting, casting, hot rolling and heat treatment processes are optimized through full-process calculation, and the weldability, hydrogen brittleness resistance, corrosion resistance and mechanical properties of the austenitic stainless steel are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of special steel preparation, and in particular to a high-strength and corrosion-resistant austenitic steel which is weldable and resistant to hydrogen embrittlement based on multi-dimensional full-process calculation, and a preparation method thereof. Background Art

[0002] In today's industrial field, especially in harsh environments such as aerospace, chemical industry and marine engineering, higher requirements are placed on the performance of materials. Austenitic steel (or austenitic stainless steel) is widely used due to its excellent corrosion resistance and good mechanical properties. However, the traditional chromium-nickel austenitic steel has a FCC (face-centered cubic lattice) crystal structure and multiple slip systems. Its yield strength (YS) is only 200-400MPa and its tensile strength (UTS) is 600-750MPa. The strength is low, and it is difficult to continue to improve its strength on the basis of austenite. In addition, even if some measures are taken to enhance its mechanical properties, other properties of austenitic steel, such as corrosion resistance, weldability, and hydrogen embrittlement resistance, will be seriously weakened.

[0003] At present, the research and development of austenitic steel with high strength, corrosion resistance, excellent weldability and hydrogen embrittlement resistance has the following problems: 1) The inherent contradiction between mechanical properties and functional characteristics such as corrosion resistance, weldability and hydrogen embrittlement resistance is difficult to reconcile and cannot be taken into account at the same time; 2) On the basis of ensuring a certain corrosion resistance, weldability and hydrogen embrittlement resistance, it is impossible to further improve the tensile mechanical properties, mainly because the yield strength is difficult to exceed 800MPa; 3) The research and development methods are simple, and most of the composition design and preparation process parameters lack preliminary accurate calculations. Even if material calculation methods are used, only one aspect of the composition or preparation process parameters is calculated. There is no comprehensive integrated calculation of the whole process, and the efficiency is very low.

[0004] The Chinese invention patent with application number 202310621125.5 discloses "a high-strength and high-corrosion-resistant nuclear power austenitic stainless steel and its manufacturing method". Austenitic stainless steel has excellent pitting corrosion resistance, pitting potential> 0.95V, pitting equivalent index PREN> 60, but its mechanical properties are not particularly excellent, and the room temperature yield strength (Rp 0.2 ) and tensile strength (Rm) are 435MPa and 748MPa respectively, which need to be further improved.

[0005] The Chinese invention patent with application number 200680018090.0 discloses a "submarine hull steel with enhanced weldability". The hull steel has enhanced weldability, but the yield strength is 480-620MPa, which still cannot meet the high-strength standard. Moreover, as a martensitic steel, its plasticity is poor.

[0006] The Chinese invention patent with application number 202410430874.4 discloses a "hydrogen embrittlement-resistant austenitic stainless steel and its preparation method", which makes full use of large-sized atoms of rare earth Y and strong carbide-forming element Nb to implement composite microalloying, and improves the hydrogen embrittlement resistance of austenitic stainless steel by modifying and optimizing the size distribution of micron and submicron inclusions and nanometer carbides, changing their interface characteristics with the matrix, and forming deep internal interface irreversible hydrogen traps. However, its room temperature yield strength is only 610MPa at most, and rare earth elements are expensive, resulting in high production costs.

[0007] The present invention aims at the inherent defects of the above-mentioned austenitic stainless steel and the problems existing in the related research and development work, and provides a high-strength corrosion-resistant austenitic steel with excellent weldability and hydrogen embrittlement resistance and a preparation method thereof based on the full process and comprehensive multi-dimensional material calculation. The present invention has the following advantages: 1) The prepared austenitic steel has good weldability, corrosion resistance and hydrogen embrittlement resistance, as well as excellent mechanical properties, and its tensile yield strength is not less than 800MPa, and its elongation at break is not less than 23%; 2) The preparation process adopts full process calculation, including both the initial composition design and the subsequent smelting and heat treatment process parameter design, and accurately optimizes the mechanical properties and related functional characteristics of the material; 3) Through material calculation, mechanical properties, corrosion resistance, weldability, hydrogen embrittlement resistance and other aspects are comprehensively considered, providing multi-dimensional guidance for the design and preparation of alloy products; 4) Through multi-dimensional full process material calculation, combined with rapid preparation process, performance and organizational characterization, the research and development cost of austenitic steel is greatly reduced, and the product development efficiency is improved. Summary of the invention

[0008] The present invention overcomes the shortcomings of austenitic steel that cannot take into account both mechanical properties and other functional characteristics, as well as the low efficiency of the preparation process and the lack of overall multi-dimensional calculation of the entire process, and provides a high-strength and corrosion-resistant austenitic steel with excellent weldability and resistance to hydrogen embrittlement based on full-process and multi-dimensional material calculation and a preparation method thereof; the material design method described in the present invention is simple and low-cost, and is suitable for the design and development of new multifunctional high-strength austenitic steel. The smelting composition is accurately designed through component calculation, and the smelting, casting, hot rolling and heat treatment processes are optimized, which can further improve the weldability, hydrogen embrittlement resistance, corrosion resistance and mechanical properties of austenitic steel, so that austenitic steel can be widely used in aerospace, chemical and marine engineering scenarios with harsh service conditions.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A weldable, hydrogen embrittlement-resistant, high-strength, corrosion-resistant austenitic steel is provided based on material calculation. The steel comprises, by mass percentage, C less than 0.03%, N: 0.27% to 0.3%, Si: 0.18% to 0.22%, Mn: 2.3% to 2.5%, Cr: 15% to 18%, Ni: 18% to 20%, Mo: 1.4% to 1.6%, Co: 1.9% to 2.1%, Nb: 0.3% to 1%, V: 0.3% to 1%, and the remainder is Fe and unavoidable impurities.

[0011] The properties of austenitic steel finished products are: yield strength>800MPa, tensile strength>1000MPa, elongation>23%; self-corrosion potential>-0.6V, self-corrosion current<1.5×10 -5 A / cm 2 ; The hydrogen embrittlement sensitivity coefficient at room temperature is less than 18%.

[0012] A method for preparing weldable hydrogen embrittlement-resistant high-strength corrosion-resistant austenitic steel based on material calculation comprises the following steps:

[0013] Step 1: Mix and batch the ingredients. The principles of ingredient design are as follows:

[0014] (1) To ensure that the matrix has sufficient austenite stability and martensitic transformation does not occur under low temperature and cold deformation conditions, the theoretical martensitic transformation point M is controlled. s and M εs ;in:

[0015] M s (K)=731-227([C]+[N])-17.6[Ni]-22.5[Mn]-17.3[Cr]-16.2[Mo]-18.2[Co]<

[0016] 4K;

[0017] M εs (K)=630-261.4([C]+[N])-13.7[Mn]-13.1[Cr]-17.9[Ni]-38.5[Al]-17.4[Co]<

[0018] 4K;

[0019] (2) To ensure corrosion resistance, control the corrosion equivalent PREN value, PREN = [Cr] + 16 [N] + 3.3 [Mo] ≥ 25%;

[0020] (3) To ensure the yield strength, control the room temperature yield strength; yield strength

[0021] (4) To ensure the hydrogen embrittlement resistance, control the hydrogen embrittlement corrosion equivalent, hydrogen embrittlement corrosion equivalent IF = 37.193-51.248[C]-2.5884[Ni]-1.0174[Mn]-0.46770[Cr]-34.396[N]≤-7;

[0022] (5) To ensure weldability, control the welding hot crack equivalent ([Nb]+[V]+[Ti]) / ([C]-0.02)>8.5;

[0023] Step 2: Melt and cast the prepared raw materials to obtain ingots; the specific process is as follows:

[0024] (1) placing the prepared raw materials in a vacuum induction suspension melting furnace;

[0025] (2) When the furnace is evacuated to the set vacuum degree, a gas washing operation is performed, and high-purity nitrogen with a mass concentration of ≥ 99.999% is introduced to replace the gas in the furnace; the nitrogen partial pressure is determined by Sievert's law, and the relationship between the nitrogen partial pressure and the solubility of nitrogen in steel is as follows:

[0026]

[0027] Where P N2 is the nitrogen partial pressure, is the interaction coefficient of alloying element j on nitrogen activity in molten steel, and is a function related to temperature T; [j] is the content of alloying elements in the molten steel;

[0028] (3) Close all valves, turn on the circulating water, slowly adjust the smelting power from small to large to the set maximum power, and start smelting; after all the solid raw materials are melted into liquid metal, count for 15 to 20 minutes. After the timer ends, slowly adjust the power to the minimum. After cooling for at least 30 minutes, open the furnace door, take out the ingot, turn it over, and repeat the above operation for the second smelting;

[0029] Step 3: hot rolling the ingot to obtain a hot rolled alloy; the specific process is as follows:

[0030] (1) using thermodynamic calculation software, performing thermodynamic calculation of each phase on the composition of the austenitic steel calculated in step 1, obtaining a curve of phase content in the steel varying with temperature, and determining the temperature range in which the structure of the steel is entirely austenitic based on the curve;

[0031] (2) placing the ingot in a high-temperature heat treatment furnace for heat treatment, controlling the heat treatment temperature within the temperature range determined in process (1), and maintaining the temperature for more than 30 minutes;

[0032] (3) Setting the initial roll height of the two-roll mill, quickly transferring the heat-treated ingot into the two-roll mill for rolling, and setting the reduction amount for each pass;

[0033] (4) After the last rolling pass is completed, the rolled plate that has been rolled to the target thickness is quickly placed in water for quenching;

[0034] Step 4: Perform aging treatment on the hot-rolled alloy, as follows:

[0035] (1) Perform thermodynamic calculations on the alloy of the selected composition and determine the aging temperature based on the precipitation equilibrium precipitation results obtained;

[0036] (2) The heat treatment furnace is heated to the aging temperature determined in step (1), the hot rolled plate is placed in the heat treatment furnace, kept at the temperature for more than 30 minutes, and then placed in water for rapid cooling to obtain a finished steel plate.

[0037] In the step three process (1), the thermodynamic calculation software includes one or more of Thermal Calc software, JMat-Pro software and FactSage software.

[0038] In the process (2) of step three, the range of the heat treatment temperature is the lowest temperature value t to t+100 in the temperature range determined in process (1), in units of °C.

[0039] In the step three process (3), the number of rolling passes is no more than 5, and the cumulative reduction is ≤85%.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The material calculation in the preparation method of the present invention is a full-process calculation, including both the initial composition design and the subsequent smelting and heat treatment process parameter design, to accurately optimize the mechanical properties and related functional characteristics of the material;

[0042] (2) Through material calculation, mechanical properties, corrosion resistance, weldability, hydrogen embrittlement resistance and other aspects are comprehensively considered to provide multi-dimensional guidance for the design and preparation of alloy products;

[0043] (3) Through multi-dimensional full-process material calculation, combined with rapid preparation process, performance and organizational characterization, the R&D cost of austenitic steel has been greatly reduced and the development efficiency has been improved;

[0044] (4) Based on material calculation and composition design, the present invention obtains high-strength corrosion-resistant austenitic steel with excellent weldability and hydrogen embrittlement resistance by optimizing smelting, hot rolling and heat treatment processes. The finished product has a yield strength of >800MPa, a tensile strength of >1000MPa, and an elongation of >23%; good weldability; self-corrosion potential >-0.6V, and self-corrosion current <1.5×10 -5 A / cm 2 The hydrogen embrittlement sensitivity coefficient at room temperature is less than 18%. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is the thermodynamic calculation result of the set composition in the steel of Example 1 of the present invention (aging temperature is 920°C).

[0046] Figure 2 It is the thermodynamic calculation result of the set composition in the steel of Example 2 of the present invention (aging temperature is 950°C). DETAILED DESCRIPTION

[0047] The invention provides a high-strength and corrosion-resistant austenitic steel with excellent weldability and hydrogen embrittlement resistance based on material calculation and component design. The steel comprises, by mass percentage, C less than 0.03%, N: 0.27% to 0.3%, Si: 0.18% to 0.22%, Mn: 2.3% to 2.5%, Cr: 15% to 18%, Ni: 18% to 20%, Mo: 1.4% to 1.6%, Co: 1.9% to 2.1%, Nb: 0.3% to 1%, V: 0.3% to 1%, and the remainder is Fe and unavoidable impurities.

[0048] The composition of the steel of the present invention meets the multi-dimensional composition design criteria, and the composition design principles are as follows, wherein [X] is the mass percentage of the X element (in %).

[0049] (1) Ensure that the matrix has sufficient austenite stability, and that martensitic transformation does not occur under low temperature and cold deformation conditions, and control the theoretical martensitic transformation point M s and M εs Below 4K, the criteria are as follows:

[0050] Ms(K)=731-227([C]+[N])-17.6[Ni]-22.5[Mn]-17.3[Cr]-16.2[Mo]-18.2[Co]<4K;

[0051] Mεs(K)=630-261.4([C]+[N])-13.7[Mn]-13.1[Cr]-17.9[Ni]-38.5[Al]-17.4[Co]<4K;

[0052] (2) Ensure good corrosion resistance and control the corrosion resistance equivalent PREN (in %) value to be no less than 25. The criteria are as follows:

[0053] PREN=[Cr]+16[N]+3.3[Mo]≥25

[0054] (3) Ensure room temperature yield strength Above 800MPa, the criterion formula is as follows:

[0055]

[0056] in, It is the yield strength without considering the effect of temperature.

[0057] (4) Ensure good hydrogen embrittlement resistance and control the hydrogen embrittlement corrosion equivalent IF to be no greater than -7. The judgment formula is as follows:

[0058] IF=37.193-51.248[C]-2.5884[Ni]-1.0174[Mn]-0.46770[Cr]-34.396[N]≤-7

[0059] (5) Ensure good weldability. The criteria are as follows:

[0060] Welding hot crack equivalent ([Nb]+[V]+[Ti]) / ([C]-0.02)>8.5

[0061] The austenitic steel prepared by the present invention has a yield strength of >800MPa, a tensile strength of >1000MPa, an elongation of >23%, good weldability, excellent corrosion resistance, self-corrosion potential >-0.6V, and self-corrosion current <1.5×10 -5 A / cm 2 ; Excellent resistance to hydrogen embrittlement, the hydrogen embrittlement sensitivity coefficient at room temperature is less than 18%.

[0062] The preparation of a weldable, hydrogen embrittlement-resistant, high-strength, corrosion-resistant austenitic steel based on material calculation described in the present invention includes the steps of batching → vacuum suspension melting → heat treatment → hot rolling → aging treatment. The specific steps are as follows:

[0063] Step 1: Mix and batch the ingredients. The principles of ingredient design are as follows:

[0064] (1) According to the composition design principle, the detailed composition calculation of each element in the steel is carried out, including determining the mass percentage of each element, especially the precise content of key elements such as vanadium (V), niobium (Nb), carbon (C), nitrogen (N), manganese (Mn), etc.

[0065] (2) Based on the results of the composition calculation, select the corresponding raw materials. Weigh the selected raw materials according to the calculated ratio to ensure that the addition amount of each element is accurate. For some elements that are difficult to add directly (such as C), they can be added in the form of pre-prepared alloys or compounds. The addition of N is mainly controlled by adjusting the nitrogen partial pressure during smelting.

[0066] Step 2: Melt and cast the prepared raw materials to obtain ingots.

[0067] (1) Wipe the furnace body and crucible clean with gauze soaked in alcohol, and place the prepared raw materials in a vacuum induction suspension melting furnace. The protective atmosphere required for smelting is high-purity nitrogen (mass concentration ≥ 99.999%). Melting is a high-temperature process, which is mainly used to convert solid raw materials into liquid alloys and remove impurities and gases contained in the raw materials. Passing nitrogen can ensure that there will be no chemical reaction with the molten steel, thereby maintaining the chemical composition of the molten steel stable.

[0068] (2) Use a diffusion pump to evacuate to a set vacuum level (e.g. 9×10 -3 Pa), the vacuum induction suspension melting furnace is scrubbed and high-purity nitrogen is introduced to remove excess gas as much as possible. Repeat the above vacuum operation process and introduce an appropriate amount of high-purity nitrogen. It should be noted that at a certain temperature, the saturated solubility of nitrogen is determined by the alloy elements and the smelting nitrogen partial pressure. Therefore, after selecting the alloy composition and the precise content of N, the Sievert law can be used to determine the nitrogen partial pressure. The specific relationship between the nitrogen partial pressure and the solubility of nitrogen in steel is as follows:

[0069]

[0070] Where P N2 is the nitrogen partial pressure, is the interaction coefficient of alloy element j in molten steel on nitrogen activity. Because the alloy element concentration is low and the smelting pressure is low, it can be approximated as the first-order interaction coefficient. It is a function of temperature. [j] is the alloying element content in the molten steel.

[0071] (3) Close all valves, turn on the circulating water, and slowly adjust the smelting power from small to large to the set maximum power (such as 90kW), and start smelting. The main purpose of slowly adjusting the power is to prevent the raw materials from splashing. After all the solid raw materials are melted into liquid metal, count for 15 to 20 minutes. After the timing ends, slowly adjust the power to the minimum, mainly to avoid the phenomenon of too large casting riser caused by too fast cooling rate. After cooling for at least 30 minutes, open the furnace door to take out the ingot, turn it over and repeat the above operation for the second smelting. The main purpose is to make the elements in the ingot more evenly distributed.

[0072] Step 3: hot rolling the ingot to obtain a hot-rolled alloy.

[0073] (1) Using thermodynamic calculation software, perform thermodynamic calculations on the composition of the austenitic steel calculated in step 1 for each phase, obtain a curve of the phase content in the steel varying with temperature, and determine the temperature range in which the structure of the steel is entirely austenitic based on the curve.

[0074] (2) The ingot is placed in a high-temperature heat treatment furnace for heat treatment. The heat treatment temperature is selected within the above temperature range and kept at this temperature for more than 30 minutes. In addition to heating before rolling, the heat treatment has another purpose, which is to allow the precipitation phases such as (V, Nb) (C, N) and Cr2N to be dissolved into the matrix as much as possible, so that the precipitation in the subsequent hot rolling process can play a role in refining the grains.

[0075] (3) Set the initial roll gap height of the two-roll mill (e.g., 25 mm), quickly place the heat-treated ingot into the two-roll mill for rolling, and set the reduction amount for each pass (e.g., the reduction amount for each pass is set to 25 mm → 20 mm → 15 mm → 10 mm → 5.5 mm in sequence).

[0076] (4) After the last rolling pass is completed, the rolled plate that has been rolled to the target thickness is quickly placed in water for quenching. The purpose is to make the rolled plate quickly pass through the phase transformation zone of about 700°C when cooling, prevent the austenite from transforming into ferrite, and ensure that the matrix is ​​austenite.

[0077] Step 4: Aging treatment of the hot rolled alloy.

[0078] (1) Thermodynamic calculations are performed on the selected components, and the aging temperature is determined based on the precipitation equilibrium results. The main purpose is to fully precipitate (V, Nb)(C, N) while dissolving all Cr2N. This is because the (V, Nb)(C, N) precipitation phase has the effects of precipitation strengthening and grain refinement. Although Cr2N has a strengthening effect, it is easy to become the site of pitting initiation, thereby accelerating corrosion and weakening the corrosion resistance of the austenitic steel.

[0079] (2) The heat treatment furnace is set to heat to the determined aging temperature, and the hot-rolled plate is placed in the heat treatment furnace, kept at the temperature for more than 30 minutes, and then placed in water for rapid cooling.

[0080] The following embodiments are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0081] [Example 1]

[0082] This embodiment prepares a high-strength, corrosion-resistant austenitic steel with excellent weldability and resistance to hydrogen embrittlement based on multi-dimensional full-process material calculation. The specific steps are as follows:

[0083] Step 1: Design and prepare ingredients.

[0084] (1) According to the criteria in the composition design principle, the alloy composition is determined by mass percentage to be C: 0.03%, N: 0.28%, Si: 0.2%, Mn: 2.43%, Cr: 18%, Ni: 18%, Mo: 1.5%, Co: 2%, Nb: 0.3%, V: 1%, and the balance is Fe and unavoidable impurities.

[0085] (2) According to the results of the composition design, select the corresponding raw materials. Weigh the selected raw materials according to the calculated ratio to ensure that the addition amount of each element is accurate. The total amount of raw materials is 1 kg. Among them, C is added in the form of Fe-5C master alloy, and N is added by controlling the nitrogen partial pressure.

[0086] Step 2: Melt and cast the prepared raw materials to obtain ingots.

[0087] (1) Wipe the furnace body and crucible with gauze dampened with alcohol, and place the prepared raw materials in the cylindrical crucible of the vacuum induction suspension melting furnace. The protective atmosphere during smelting is high-purity nitrogen (mass concentration ≥ 99.999%). Melting is a high-temperature process, which is mainly used to convert solid raw materials into liquid alloys and remove impurities and gases contained in the raw materials. The nitrogen can ensure that there will be no chemical reaction with the molten steel, thereby maintaining the chemical composition of the molten steel stable.

[0088] (2) Use mechanical pumps and diffusion pumps to evacuate the air, and the vacuum degree reaches 9×10 -3 When the pressure is 20 kPa, high-purity nitrogen gas of 20 kPa is introduced to wash the vacuum induction suspension melting furnace to remove excess gas as much as possible. Repeat the above vacuum operation and then introduce high-purity nitrogen gas of 84 kPa. The nitrogen partial pressure is determined by the relationship between the nitrogen partial pressure and the solubility of nitrogen in steel.

[0089] (3) Close the main pumping valve, turn off the diffusion pump, turn on the cooling water, start the motor for smelting, slowly adjust the smelting power to 90kW, and slowly increase the current to prevent the raw materials from splashing. When all the raw materials in the crucible are liquid, start timing for 15 minutes. After 15 minutes, slowly adjust the motor power to the minimum and turn off the motor. After cooling for 30 minutes, open the furnace door, take out the ingot from the crucible, turn it over, and put it back into the crucible for a second smelting to ensure that the composition of the ingot is more uniform.

[0090] Step 3: hot rolling the ingot to obtain a hot-rolled alloy.

[0091] (1) Using thermodynamic calculation software, perform thermodynamic calculations on the components calculated in step 1 for each phase, and obtain a curve of the phase content in the steel changing with temperature (e.g. Figure 1According to the curve, the temperature range in which the structure of the steel is entirely austenite phase is determined, and the heat treatment temperature of 1250°C is selected within the temperature range.

[0092] (2) Cut off both sides of the cylindrical ingot, leaving a 30 mm thick plate in the middle, and heat treat it in a high temperature heat treatment furnace for 30 min. The heat treatment can make the precipitated phases such as (V, Nb) (C, N) and Cr2N dissolved into the matrix as much as possible, and the precipitation in the subsequent hot rolling process can play a role in refining the grains.

[0093] (3) The solution-solutionized ingot is quickly placed in a two-roll mill for rolling, with the reduction of each pass being 25 mm, 20 mm, 15 mm, 10 mm, and 5.5 mm, respectively. It should be noted that after each rolling pass, the process (2) must be repeated and placed in a high-temperature heat treatment furnace for insulation, and after rolling along the rolling direction, the rolled plate must be horizontally rotated 90° and then straightened by the rolling mill to make the rolled plate smoother.

[0094] (4) After the last rolling pass, the 5 mm thick rolled plate is immediately placed in water for quenching. The purpose is to make the rolled plate quickly pass through the phase change zone of about 700 ° C when cooling, prevent the austenite from transforming into ferrite, and ensure that the matrix is ​​austenite.

[0095] Step 4: Aging treatment of the hot rolled alloy.

[0096] (1) Through thermodynamic calculation of the set composition, the aging temperature was determined to be 920℃, the aging holding time was 30min, and then it was quickly cooled in water to obtain the final high-strength and corrosion-resistant austenitic steel sample with excellent weldability and resistance to hydrogen embrittlement. The role of aging is to fully precipitate (V, Nb)(C, N) and dissolve all Cr2N at the same time, because the (V, Nb)(C, N) precipitation phase can play the role of precipitation strengthening and fine grain strengthening, while Cr2N has a strengthening effect, but it is easy to become the location of pitting initiation and thus accelerate corrosion, weakening the corrosion resistance of austenitic steel.

[0097] (2) The aged samples were machined to obtain steel bars and steel plates, which were taken out for tensile strength, corrosion resistance, weldability, hydrogen embrittlement resistance and other performance tests. The test results are shown in Tables 1 to 4.

[0098] [Example 2]

[0099] This embodiment prepares a high-strength, corrosion-resistant austenitic steel with excellent weldability and resistance to hydrogen embrittlement based on multi-dimensional full-process material calculation. The specific steps are as follows:

[0100] Step 1: Design and prepare ingredients.

[0101] (1) According to the criteria in the composition design principle, the alloy composition is determined by mass percentage to be C: 0.02%, N: 0.29%, Si: 0.2%, Mn: 2.43%, Cr: 16%, Ni: 18%, Mo: 1.5%, Co: 1.9%, Nb: 0.8%, V: 0.5%, and the balance is Fe and unavoidable impurities.

[0102] (2) According to the results of the composition calculation, select the corresponding raw materials. Weigh the selected raw materials according to the calculated ratio to ensure that the addition amount of each element is accurate. The total amount of raw materials is 1 kg. Among them, C is added in the form of Fe-5C master alloy, and N is added by controlling the nitrogen partial pressure.

[0103] Step 2: Melt and cast the prepared raw materials to obtain ingots.

[0104] (1) Wipe the furnace body and crucible with gauze dampened with alcohol, and place the prepared raw materials in the cylindrical crucible of the vacuum induction suspension melting furnace. The protective atmosphere during smelting is high-purity nitrogen (mass concentration ≥ 99.999%). Melting is a high-temperature process, which is mainly used to convert solid raw materials into liquid alloys and remove impurities and gases contained in the raw materials. The nitrogen can ensure that there will be no chemical reaction with the molten steel, thereby maintaining the chemical composition of the molten steel stable.

[0105] (2) Use mechanical pumps and diffusion pumps to evacuate the air, and the vacuum degree reaches 9×10 -3 When the pressure is 20 kPa, high-purity nitrogen gas of 20 kPa is introduced to wash the vacuum induction suspension melting furnace to remove excess gas as much as possible. Repeat the above vacuum operation and then introduce high-purity nitrogen gas of 90 kPa. The nitrogen partial pressure is determined by the relationship between the nitrogen partial pressure and the solubility of nitrogen in steel.

[0106] (3) Close the main pumping valve, turn off the diffusion pump, turn on the cooling water, start the motor for smelting, slowly adjust the smelting power to 90kW, and slowly increase the current to prevent the raw materials from splashing. When all the raw materials in the crucible are liquid, start timing for 15 minutes. After 15 minutes, slowly adjust the motor power to the minimum and turn off the motor. After cooling for 30 minutes, open the furnace door, take out the ingot from the crucible, turn it over, and put it back into the crucible for a second smelting to ensure that the composition of the ingot is more uniform.

[0107] Step 3: hot rolling the ingot to obtain a hot rolled alloy;

[0108] (1) Using thermodynamic calculation software, perform thermodynamic calculations on the components calculated in step 1 for each phase, and obtain a curve of the phase content in the steel changing with temperature (e.g. Figure 2 According to the curve, the temperature range in which the structure of the steel is entirely austenite phase is determined, and the heat treatment temperature of 1255°C is selected within the temperature range.

[0109] (2) Cut off both sides of the cylindrical ingot, leaving a 30 mm thick plate in the middle, and heat treat it in a high temperature heat treatment furnace for 30 min. Heat treatment can make the precipitated phases such as (V, Nb)(C, N) and Cr2N dissolved into the matrix as much as possible, and precipitation can play a role in refining the grains in the subsequent hot rolling process.

[0110] (3) The solution-solutionized ingot is quickly placed in a two-roll mill for rolling, with the reduction of each pass being 25 mm, 20 mm, 15 mm, 10 mm, and 5.5 mm, respectively. It should be noted that after each rolling pass, the process (2) must be repeated and placed in a high-temperature heat treatment furnace for insulation, and after rolling along the rolling direction, the rolled plate must be horizontally rotated 90° and then straightened by the rolling mill to make the rolled plate smoother.

[0111] (4) After the last rolling pass, the 5 mm thick rolled plate is immediately placed in water for quenching. The purpose is to make the rolled plate quickly pass through the phase change zone of about 700 ° C when cooling, prevent the austenite from transforming into ferrite, and ensure that the matrix is ​​austenite.

[0112] Step 4: Aging treatment of the hot rolled alloy.

[0113] (1) Through thermodynamic calculation of the set composition, the aging temperature was determined to be 950℃, the aging holding time was 30min, and then it was quickly cooled in water to obtain the final high-strength and corrosion-resistant austenitic steel sample with excellent weldability and resistance to hydrogen embrittlement. The role of aging is to fully precipitate (V, Nb)(C, N) and dissolve all Cr2N at the same time, because the (V, Nb)(C, N) precipitation phase can play the role of precipitation strengthening and fine grain strengthening, while Cr2N has a strengthening effect, but it is easy to become the location of pitting initiation and thus accelerate corrosion, weakening the corrosion resistance of the austenitic steel.

[0114] (2) The aged samples were machined to obtain steel bars and steel plates, which were taken out for tensile strength, corrosion resistance, weldability, hydrogen embrittlement resistance and other performance tests. The test results are shown in Tables 1 to 4.

[0115] Table 1 Mechanical properties of the samples

[0116] Example Yield Strength(Mpa) Tensile strength(MPa) Elongation at break (%) 1 801 1005 24.3 2 807 1012 23.3

[0117] Table 2 Corrosion resistance of samples

[0118] Example <![CDATA[Self - corrosion potential E corr (V)]]> <![CDATA[Self-corrosion current I corr (A / cm 2 )]]> 1 -0.582 <![CDATA[1.46×10 -5 ]]> 2 -0.591 <![CDATA[1.48×10 -5 ]]>

[0119] Table 3 Hydrogen embrittlement resistance of samples

[0120]

[0121] Table 4 Tensile fracture position of the specimen after welding

[0122] Example Fracture location 1 Broken in parent material 2 Broken in parent material

[0123] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A weldable, hydrogen embrittlement-resistant, high-strength, corrosion-resistant austenitic steel based on material calculation, characterized in that: Calculated by mass percentage, the components of the steel are C <0.03%, N: 0.27%~0.3%, Si: 0.18%~0.22%, Mn: 2.3%~2.5%, Cr: 15%~18%, Ni: 18%~20%, Mo: 1.4%~1.6%, Co: 1.9%~2.1%, Nb: 0.3%~1%, V: 0.3%~1%, and the balance is Fe and unavoidable impurities.

2. The weldable hydrogen embrittlement-resistant high-strength corrosion-resistant austenitic steel based on material calculation according to claim 1 is characterized in that: The properties of austenitic steel finished products are: yield strength>800MPa, tensile strength>1000MPa, elongation>23%; self-corrosion potential>-0.6V, self-corrosion current<1.5×10 -5 A / cm 2 ; The hydrogen embrittlement sensitivity coefficient at room temperature is less than 18%.

3. A method for preparing weldable hydrogen embrittlement-resistant high-strength corrosion-resistant austenitic steel based on material calculation as claimed in claim 1 or 2, characterized in that: The steps include: Step 1: Mix and batch the ingredients. The principles of ingredient design are as follows: (1) To ensure that the matrix has sufficient austenite stability and martensitic transformation does not occur under low temperature and cold deformation conditions, the theoretical martensitic transformation point M is controlled. s and M εs ; in: M s (K)=731-227([C]+[N])-17.6[Ni]-22.5[Mn]-17.3[Cr]-16.2[Mo]-18.2[Co]< 4K； M εs (K)=630-261.4([C]+[N])-13.7[Mn]-13.1[Cr]-17.9[Ni]-38.5[Al]-17.4[Co]< 4K； (2) To ensure corrosion resistance, control the corrosion equivalent PREN value, PREN = [Cr] + 16 [N] + 3.3 [Mo] ≥ 25%; (3) To ensure the yield strength, control the room temperature yield strength; yield strength (4) To ensure the hydrogen embrittlement resistance, control the hydrogen embrittlement corrosion equivalent, hydrogen embrittlement corrosion equivalent IF = 37.193-51.248[C]-2.5884[Ni]-1.0174[Mn]-0.46770[Cr]-34.396[N]≤-7; (5) To ensure weldability, control the welding hot crack equivalent ([Nb]+[V]+[Ti]) / ([C]-0.02)>8.5; Step 2: Melt and cast the prepared raw materials to obtain ingots; the specific process is as follows: (1) placing the prepared raw materials in a vacuum induction suspension melting furnace; (2) When the furnace is evacuated to the set vacuum degree, a gas washing operation is performed, and high-purity nitrogen with a mass concentration of ≥ 99.999% is introduced to replace the gas in the furnace; the nitrogen partial pressure is determined by Sievert's law, and the relationship between the nitrogen partial pressure and the solubility of nitrogen in steel is as follows: Where P N2 is the nitrogen partial pressure, is the interaction coefficient of alloying element j on nitrogen activity in molten steel, and is a function related to temperature T; [j] is the content of alloying elements in the molten steel; (3) Close all valves, turn on the circulating water, slowly adjust the smelting power from small to large to the set maximum power, and start smelting; after all the solid raw materials are melted into liquid metal, count for 15 to 20 minutes. After the timer ends, slowly adjust the power to the minimum. After cooling for at least 30 minutes, open the furnace door, take out the ingot, turn it over, and repeat the above operation for the second smelting; Step 3: hot rolling the ingot to obtain a hot-rolled alloy; the specific process is as follows: (1) using thermodynamic calculation software, performing thermodynamic calculation of each phase on the composition of the austenitic steel calculated in step 1, obtaining a curve of phase content in the steel varying with temperature, and determining the temperature range in which the structure of the steel is entirely austenitic based on the curve; (2) placing the ingot in a high-temperature heat treatment furnace for heat treatment, controlling the heat treatment temperature within the temperature range determined in process (1), and maintaining the temperature for more than 30 minutes; (3) Setting the initial roll height of the two-roll mill, quickly transferring the heat-treated ingot into the two-roll mill for rolling, and setting the reduction amount for each pass; (4) After the last rolling pass is completed, the rolled plate that has been rolled to the target thickness is quickly placed in water for quenching; Step 4: Perform aging treatment on the hot-rolled alloy, as follows: (1) Perform thermodynamic calculations on the alloy of the selected composition and determine the aging temperature based on the precipitation equilibrium precipitation results obtained; (2) The heat treatment furnace is heated to the aging temperature determined in step (1), the hot rolled plate is placed in the heat treatment furnace, kept at the temperature for more than 30 minutes, and then placed in water for rapid cooling to obtain a finished steel plate.

4. A method for preparing weldable hydrogen embrittlement-resistant high-strength corrosion-resistant austenitic steel based on material calculation as claimed in claim 3, characterized in that: In the step three process (1), the thermodynamic calculation software includes one or more of Thermal Calc software, JMat-Pro software and FactSage software.

5. A method for preparing weldable hydrogen embrittlement-resistant high-strength corrosion-resistant austenitic steel based on material calculation as claimed in claim 3, characterized in that: In the process (2) of step three, the range of the heat treatment temperature is the lowest temperature value t to t+100 in the temperature range determined in process (1), in units of °C.

6. A method for preparing weldable hydrogen embrittlement-resistant high-strength corrosion-resistant austenitic steel based on material calculation as claimed in claim 3, characterized in that: In the step three process (3), the number of rolling passes is no more than 5, and the cumulative reduction is ≤85%.

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