Thick low-temperature-resistant high-toughness duplex stainless steel

Abstract

The invention belongs to the technical field of metal materials, and particularly relates to thick low-temperature-resistant high-toughness duplex stainless steel which comprises the following components in percentage by weight: 0.01-0.03% of C; 0.80% to 1.20% of Si; 0.80% to 1.20% of Mn; less than or equal to 0.020% of P; s is less than or equal to 0.010%; ni: 5.00% to 6.80%; cr: 22.50% to 25.00%; mo: 4.00% to 5.50%; 0.013% to 0.020% of Nb; the alloy comprises the following components in percentage by weight: 0.15%-0.20% of Ti, 0.16%-0.23% of N and 0.001%-0.003% of Y; and the balance of Fe and inevitable impurities. Through optimal design of chemical components and reasonable formulation of smelting, continuous casting, heating rolling and solid solution processes, the steel plate has good comprehensive mechanical properties and internal quality, and equipment service conditions under the low-temperature working condition are met.

Description

Technical Field

[0001] The invention belongs to the technical field of metal materials, and in particular relates to a thick-gauge, low-temperature-resistant, high-toughness duplex stainless steel. Background Art

[0002] Duplex stainless steel is a high-quality material with excellent comprehensive mechanical properties, superior corrosion resistance, and good weldability. It is widely used in the petrochemical, offshore shipbuilding, nuclear power, and pressure vessel industries. Furthermore, the addition of nitrogen to the steel grade can replace nickel, stabilizing the austenite structure. Due to the proportional distribution of austenite and ferrite, duplex stainless steel exhibits high mechanical properties under the action of synergistic deformation. Furthermore, due to the unique characteristics of the austenite structure, it also offers excellent corrosion resistance, making it an ideal engineering material.

[0003] Existing patent CN116145052A discloses a duplex stainless steel with excellent low-temperature impact toughness and its preparation process. Its chemical composition, by mass fraction, includes C: 0.04-0.08, Mn: 2.2-3.3, Cr: 20.15-21.20, Ni: 3.1-3.4, Cu: 0.02-0.4, N: 0.10-0.12, V: 0.12-0.20, Re: 0.04-0.06, Nb: 0.03-0.07, Ti: 0.09-0.12, and the balance is Fe. The resulting stainless steel exhibits excellent plasticity while enhancing corrosion resistance to produce a highly tough ferritic hot-rolled stainless steel. This effectively avoids the problem of stamping cracking, particularly when used in winter or in northern regions, where its high toughness is particularly advantageous. However, the document only provides information on the low-temperature toughness of 12mm thick hot-rolled steel plates, which does not meet the performance requirements for low-temperature-resistant duplex stainless steel.

[0004] Existing patent CN116240349A describes a method for manufacturing highly formable, economical duplex stainless steel sheet. Its chemical composition is C ≤ 0.030%, Si ≤ 1.00%, Mn: 2.50%-3.50%, P ≤ 0.035%, S ≤ 0.003%, Cr: 19.50%-20.50%, Ni: 0.90%-1.50%, Mo ≤ 0.50%, N: 0.18%-0.25%, Cu ≤ 0.80%, with the remainder being iron and unavoidable impurities. This method produces economical duplex stainless steel cold-rolled sheet suitable for heat exchangers, pump components, and other applications requiring high formability and corrosion resistance, thus meeting industrial needs. However, the chemical composition of that invention differs from the present invention, and its high nitrogen content increases the difficulty and cost of smelting control. Moreover, the invention only provides 3.2 mm cold-rolled coils and only provides elongation, which cannot meet the design requirements of duplex stainless steel for engineering use.

[0005] Patent CN115725902A discloses a cost-effective duplex stainless steel containing the rare earth metal Ce and its preparation method. Its chemical composition is as follows: C ≤ 0.03%, Si ≤ 0.75%, Mn 2-4%, S ≤ 0.02%, P ≤ 0.04%, Cr 20.5-21.5%, Ni 1.5-2.5%, Mo ≤ 0.6%, N 0.15-0.20%, Cu 0.5-1.5%, Ce 0.01-0.07%, with the balance being Fe and unavoidable impurities. This method is simple to manufacture, and by adding a trace amount of Ce (0.01-0.07%) to the cost-effective duplex stainless steel, the resulting micro-alloyed cost-effective duplex stainless steel exhibits superior elongation, impact toughness, and corrosion resistance compared to conventional cost-effective duplex stainless steel. However, the addition of a relatively high amount of rare earth elements results in high production costs, and the lack of a thickness range makes it unsuitable for all equipment manufacturing applications. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a thick-gauge, low-temperature-resistant, high-toughness duplex stainless steel. Through the optimization design of chemical composition and the rational formulation of smelting, continuous casting, hot rolling, and solid solution processes, the steel plate has good comprehensive mechanical properties and internal quality, meeting the service conditions of equipment under low-temperature conditions.

[0007] To achieve the above objectives, the present invention adopts the following technical solutions:

[0008] Disclosed is a thick-gauge, low-temperature-resistant, high-toughness duplex stainless steel, comprising the following components by weight: C: 0.01%-0.03%; Si: 0.80%-1.20%; Mn: 0.80%-1.20%; P≤0.020%; S≤0.010%; Ni: 5.00%-6.80%; Cr: 22.50%-25.00%; Mo: 4.00%-5.50%; Nb: 0.013%-0.020%; Ti: 0.15%-0.20%, N: 0.16%-0.23%, Y: 0.001%-0.003%; the remainder being Fe and unavoidable impurities.

[0009] A thick-gauge, low-temperature-resistant, high-toughness duplex stainless steel with a plate thickness of 10 to 60 mm.

[0010] The above ingredients work as follows:

[0011] (1) Carbon: Carbon is the main strengthening element in stainless steel. It stabilizes austenite, expands the austenite phase, and improves the mechanical properties of the steel. However, as the carbon content in the steel increases, more chromium forms carbides with the carbon, which reduces the corrosion resistance of the steel. The carbon content in the steel should not be too high. Therefore, the carbon content in the present invention is controlled within the range of 0.01% to 0.03%.

[0012] (2) Si: Silicon can produce a significant solid solution strengthening effect in steel, which can increase the yield strength of steel. At the same time, it forms a silicon-rich oxide film on the surface of stainless steel, which can effectively improve the corrosion resistance of stainless steel. However, excessive addition will reduce the hot working performance of steel. Therefore, the present invention requires that the Si content in steel be controlled within 0.80% to 1.20%.

[0013] (3) Mn: Manganese remains in the steel as a deoxidizing element. It can increase the solubility of nitrogen in the steel, thereby improving the performance of the steel and saving nickel. On the other hand, manganese has a strong affinity for sulfur, inhibiting the harmful effects of sulfur in the steel and improving the high-temperature thermoplasticity of duplex stainless steel. However, an increase in the Mn content will reduce the corrosion resistance and plasticity of the stainless steel. It is required that the Mn content in the steel be controlled within an appropriate range, that is, 0.80% to 1.20%.

[0014] (4) Ni: Nickel is one of the most important strengthening elements that contribute to the excellent corrosion resistance and mechanical properties of stainless steel. It can stabilize the austenite structure, greatly improve the strength and low-temperature toughness of the steel, and enhance the ability of the two-phase structure to coordinate deformation. However, excessive addition will increase the sensitivity of duplex stainless steel to intergranular corrosion, and economic efficiency must also be considered. Therefore, the present invention requires that the Ni content in the steel be controlled to 5.00% to 6.80%.

[0015] (5) Cr: Chromium is one of the most important elements in stainless steel. In duplex stainless steel, chromium can promote the formation of delta ferrite and interact with austenite-forming elements such as carbon and nickel to form a stable two-phase structure. At the same time, chromium can improve the corrosion resistance of austenite. Considering that the addition of chromium will promote the formation of Cr 23 To prevent the precipitation of harmful phases such as C6, the present invention requires that the Cr content in the steel be controlled at 22.50% to 25.00%.

[0016] (6) Mo: Molybdenum and chromium can produce a synergistic effect, which can improve the corrosion resistance of stainless steel. At the same time, molybdenum can be dissolved in the austenite matrix, improving the heat resistance of austenite grains, inhibiting the growth of austenite grains during hot working, playing a role in grain refinement, and improving high-temperature mechanical properties. However, excessive molybdenum will reduce the stress corrosion resistance of the two-phase structure in stainless steel. Therefore, the present invention requires that the Mo content in the steel be controlled to 4.00-5.50%.

[0017] (7) Nb: Niobium is dispersed in the matrix of stainless steel in the form of carbonitrides, which produces second phase strengthening and grain refinement, can increase the yield strength of steel, reduce the brittle transition temperature, and can effectively reduce Cr 23The formation of C6 compounds improves the intergranular corrosion resistance of stainless steel. At the same time, niobium can also improve the deformation resistance of ferrite structure and improve the hot working performance of steel. Therefore, the present invention requires that the Nb content of steel be controlled to 0.013% to 0.020%.

[0018] (8) P: Phosphorus is a harmful element that increases the brittleness of steel, deteriorates its plasticity and toughness, and has an adverse effect on welding. At the same time, the presence of phosphorus will also increase the cold cracking tendency of steel and reduce the low-temperature toughness of steel. Therefore, the lower the P content in steel, the better. The present invention requires it to be less than 0.020%.

[0019] (9) S: Sulfur forms FeS and MnS sulfides at the austenite grain boundaries in steel, which reduces the impact toughness and weldability of the steel. It is easy to produce hot cracks during hot working, which reduces the performance and corrosion resistance of the steel. Therefore, the S content in steel should be limited to less than 0.010%.

[0020] (10) N: Nitrogen improves the stability of austenite and increases the toughness and low-temperature toughness of steel. However, excessive nitrogen content increases the difficulty of smelting and affects the surface quality of steel. Therefore, the nitrogen content is controlled within a range of 0.16% to 0.23%.

[0021] (11) Ti: Titanium exists in steel primarily as carbonitride precipitations at grain boundaries and within grains. During hot rolling, the precipitations act as recrystallization nuclei, promoting the recrystallization process and significantly improving the mechanical properties of the steel. They also act as nitrogen fixation agents. Therefore, the Ti content is controlled within a range of 0.15% to 0.20%.

[0022] (12) Y: The addition of the rare earth element yttrium can prevent excessive bonding between Ti and N, thereby inhibiting the large-scale precipitation of TiN in the steel, which leads to a reduction in the solid solution strengthening effect of N atoms and significantly improves the low-temperature toughness of the steel. At the same time, the Y element can modify alumina inclusions and play a role in purifying the molten steel. However, considering the strong affinity of Y atoms with oxygen, large-scale addition is likely to introduce new non-metallic inclusions. Therefore, the present invention requires that the Y content be controlled within 0.001% to 0.003%.

[0023] A method for manufacturing thick-gauge, low-temperature-resistant, high-toughness duplex stainless steel, comprising the following steps: smelting, continuous casting, rolling, and solutionizing.

[0024] 1) Smelting: EAF+LF+VOD is used for smelting;

[0025] 2) Continuous casting: control the superheat at 25-30°C, the continuous casting billet speed at 1.0-1.6 m / min, the crystallizer electromagnetic stirring current intensity at 300-350 A, the frequency at 2.5-3.0 Hz, the billet temperature in the secondary cooling zone at 950-1150°C, the billet surface temperature return to no more than 165°C, the specific water content at 1.25-1.85 kg / L, the electromagnetic stirring at the end of solidification at the position where the solid phase ratio in the center of the billet is 0.25-0.35, the current intensity at 100-120 A, the frequency at 6.0-8.0 Hz, and a reduction of 10-19 mm;

[0026] 3) Rolling: The preheating temperature of the slab is 1000-1150℃, the heating temperature of the slab is 1225-1250℃, the total time of the soaking section and the heating section of the heating furnace is 3.5-4.5h, the total time in the furnace is 5-6h, and the air-fuel ratio is controlled at 1:1.8-1:2.4; the first pass reduction rate is 10%-15% and high-pressure water descaling is performed with a water pressure of 18-25MPa. The second and third pass reduction rates are both not less than 20%, and the rolling number does not exceed 10. The final rolling temperature is above 1000℃. After rolling, the steel plate immediately enters pre-straightening, then air-cools to 675-750℃, and then is hot sent into the furnace for solution treatment;

[0027] 4) Solution treatment: The heating time in the temperature rising stage is controlled at 1.2-1.6 min / mm, the solution temperature is 1050-1080°C, the holding time is 1.8-2.2 min / mm, and then cooled to room temperature in high-pressure water at a cooling rate of 13-20°C / s.

[0028] Step 1) Smelting process: pre-treatment of molten iron, adding scrap steel, melting, primary dephosphorization treatment, continue to heat up 50-80℃, after removing the slag, enter the LF process, feed the calcium wire at 0.35-0.4kg / t, and carry out pre-desulfurization treatment of reducing slag at the same time. After adjusting the chemical composition to the target composition, remove the protective slag and enter the VOD process for oxygen blowing and decarbonization. Nitrogen addition and denitrification processes are carried out in the ladle by blowing nitrogen from the bottom of the ladle. The nitrogen blowing starting temperature is 1635-1655℃, the nitrogen blowing pressure is 1.8-2.1MPa, and the flow rate is 135-150m 3 / h, nitrogen blowing time is 55 to 65 minutes.

[0029] Step 4) The steel plate is solution treated in a walking beam solution furnace.

[0030] Compared with the existing technology, the beneficial effects of the present invention are:

[0031] The present invention designs alloy elements and formulates appropriate rolling and heat treatment processes according to the characteristics of duplex stainless steel, thereby ensuring that the performance of the steel plate meets the design requirements.

[0032] (1) The products produced by the process of the present invention have excellent strength indicators through rolling and solution treatment. The room temperature yield strength after solution treatment (R p0.2 ) and tensile strength (Rm) are 511~572MPa and 688~789MPa respectively; 350℃ high temperature tensile yield strength (R p0.2 The tensile strength (Rm) and tensile strength (Rm) are 333-373 MPa and 624-680 MPa, respectively. The tensile properties of the steel plates in different states far exceed the required specifications and are significantly improved compared to other steel grades, meeting the mechanical performance requirements under different working conditions.

[0033] (2) After solution treatment, the steel grade of the present invention has an impact absorption energy of 400 J at 0°C and an impact absorption energy of 212 J under -196°C test conditions, and has excellent low-temperature toughness.

[0034] (3) After solution treatment, the steel of the present invention has a tensile section shrinkage in the thickness direction of the steel plate of not less than 42%, and has good plasticity.

[0035] (4) The present invention utilizes a microalloying design concept by adding niobium (Nb) to produce fine, dispersed second-phase particles, inhibiting grain growth and refining the austenite grain structure. This effectively improves the low-temperature toughness of duplex stainless steel by enhancing the ability of the two-phase structure to deform synergistically. The addition of yttrium (Y), a low-cost rare earth element, modifies harmful inclusions such as sulfides and oxides that significantly lower the ductile-brittle transition temperature, purifying the molten steel and further improving the steel's low-temperature toughness. Compared to other rare earth elements, this is more economical.

[0036] (5) The present invention designs a process route of smelting → continuous casting → rolling → solution treatment. In particular, based on the characteristics of high alloy content, molten steel fluidity, and poor shrinkage-feeding capacity of the solidification zone of the steel grade, it proposes to apply electromagnetic stirring and a certain amount of reduction at the end of solidification to improve the uniformity of the steel. At the same time, according to the microstructure characteristics of products of different thicknesses, the rolling and solution treatment processes are designed to promote the transformation of ferrite to austenite during the hot working process. After the solution heat treatment, the ratio of ferrite content to austenite content of the steel plate is between 0.923 and 1.128, further achieving the effect of grain refinement, so that the microstructure of the product with a thickness of 10 to 60 mm has good uniformity. During the stress process, the two-phase microstructure deforms synergistically, and the steel plate has excellent strength and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the metallographic diagram of the duplex stainless steel of the present invention. DETAILED DESCRIPTION

[0038] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein in the specification of the application are for the purpose of describing specific embodiments only and are not intended to limit this application. Mentioning "embodiments" herein means that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of this 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 can be combined with other embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0039] A method for manufacturing thick-gauge, low-temperature-resistant, high-toughness duplex stainless steel, comprising the following steps: smelting, continuous casting, rolling, and solutionizing.

[0040] 1) Smelting: EAF+LF+VOD is used for smelting. After adding scrap steel + molten iron for pretreatment, melting and primary dephosphorization are carried out, the temperature is continuously raised to 50-80°C, and after removing the slag, the LF process is entered. Calcium wire is fed at 0.35kg / t, and pre-desulfurization treatment is carried out to make reducing slag. After adjusting the chemical composition to the target composition, the protective slag is removed and the process is transferred to the VOD process for oxygen blowing and decarbonization. Nitrogen addition and denitrification are carried out in the ladle by blowing nitrogen from the bottom of the ladle. The nitrogen blowing starting temperature is 1635-1655°C, the nitrogen blowing pressure is 1.8-2.1MPa, and the flow rate is 135-150m 3 / h, nitrogen blowing time is 55 to 65 minutes.

[0041] 2) Continuous casting: Control the superheat at 25-30°C, the continuous casting billet pulling speed at 1.0-1.6 m / min, the crystallizer electromagnetic stirring current intensity at 300-350 A, the frequency at 2.5-3.0 Hz, the billet temperature in the secondary cooling zone at 950-1150°C, the billet surface temperature return no more than 165°C, the specific water content at 1.25-1.85 kg / L, the electromagnetic stirring at the end of solidification is set at a position where the solid phase ratio in the center of the billet is 0.25-0.35, the current intensity at 100 A-120 A, the frequency at 6.0-8.0 Hz, and a reduction of 10-19 mm. By controlling the superheat, secondary cooling intensity and water distribution system, the billet edge and corner defects are effectively improved, and defects such as shrinkage cavities, internal cracks in the billet, and segregation are reduced. By means of crystallizers, electromagnetic stirring at the end of solidification and other means to accelerate the solidification process, break up the dendrites in the central area, increase the yield of equiaxed crystals, reduce component segregation and central porosity, the purpose of refining grains and improving billet quality has been achieved.

[0042] 3) Rolling: Preheating temperature 1000-1150°C, slab heating temperature 1225-1250°C, total time in the soaking and heating sections of the heating furnace 3.5-4.5 hours, total furnace time 5-6 hours. Maintain an air-fuel ratio of 1:1.8-1:2.4; first-pass reduction 10-15% with high-pressure water descaling at 18-25 MPa. Second and third-pass reductions should be no less than 20%. Rolling should occur in no more than 10 passes, with a final rolling temperature above 1000°C. After rolling, the steel plate rapidly enters pre-straightening, followed by air cooling to 675-750°C.

[0043] 4) Solution treatment: The steel plate is solution treated in a step-beam solution furnace. The heating time in the heating stage is controlled at 1.2-1.6 min / mm, the solution temperature is 1050-1080°C, the holding time is 1.8-2.2 min / mm, and then cooled to room temperature in high-pressure water at a cooling rate of 13-20°C / s.

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0045] The chemical compositions of each example are shown in Table 1.

[0046] Table 1 Chemical composition (wt%)

[0047]

[0048] The smelting process of each embodiment is shown in Table 2.

[0049] Table 2 Smelting process parameters

[0050]

[0051] The continuous casting process of each embodiment is shown in Table 3.

[0052] Table 3 Continuous casting process parameters

[0053]

[0054] The thermal processing technology of each embodiment is shown in Table 4.

[0055] Table 4 Hot working process parameters

[0056]

[0057] Table 5 Solution treatment process

[0058]

[0059] The low-temperature-resistant, high-toughness duplex stainless steel of Example 1 was produced from molten steel smelted in a converter, refined outside the furnace, and vacuum-treated before being cast into continuous-cast ingots with a cross-section of 195 mm. The resulting steel plates were rolled to a 10 mm gauge. The composition, smelting process, continuous casting process, hot working process, and solutionizing process are shown in Example 1 in Tables 1 to 5. The mechanical properties are shown in Table 6-1.

[0060] Table 6-1 Mechanical properties results

[0061]

[0062] The 10mm specification steel plate has undergone solution treatment, and all performance indicators fully meet the requirements. At the same time, the steel plate has good high-temperature performance and good toughness and strength matching, fully meeting the requirements of low-temperature resistant and high-toughness duplex stainless steel.

[0063] The low-temperature-resistant, high-toughness duplex stainless steel of Example 2 was produced from molten steel smelted in a converter, refined outside the furnace, and vacuum-treated before being cast into continuous-cast ingots with a cross-section of 195 mm. The resulting steel plates were rolled to a 15 mm gauge. The composition, smelting process, continuous casting process, hot working process, and solutionizing process are shown in Example 2 in Tables 1 to 5. The mechanical properties are shown in Table 6-2.

[0064] Table 6-2 Mechanical properties results

[0065]

[0066] The 15mm specification steel plate has undergone solution treatment, and all performance indicators fully meet the requirements. At the same time, the steel plate has good high-temperature performance and good toughness and strength matching, fully meeting the requirements of low-temperature resistant and high-toughness duplex stainless steel.

[0067] The low-temperature-resistant, high-toughness duplex stainless steel of Example 3 was produced from molten steel smelted in a converter, refined outside the furnace, and vacuum-treated before being cast into continuous-cast ingots with a cross-section of 195 mm. The resulting steel plates were rolled to a size of 20 mm. The composition, smelting process, continuous casting process, hot working process, and solutionizing process are shown in Example 3 in Tables 1 to 5. The mechanical properties are shown in Table 6-3.

[0068] Table 6-3 Mechanical properties results

[0069]

[0070] The 20mm specification steel plate has undergone solution treatment, and all performance indicators fully meet the requirements. At the same time, the steel plate has good high-temperature performance and good toughness and strength matching, fully meeting the requirements of low-temperature resistant and high-toughness duplex stainless steel.

[0071] The low-temperature-resistant, high-toughness duplex stainless steel of Example 4 was produced from molten steel smelted in a converter, refined outside the furnace, and vacuum-treated before being cast into continuous-cast ingots with a cross-section of 195 mm. The resulting steel plates were rolled to a size of 25 mm. The composition, smelting process, continuous casting process, hot working process, and solutionizing process are shown in Example 4 in Tables 1 to 5. The mechanical properties are shown in Tables 6-4.

[0072] Table 6-4 Mechanical properties results

[0073]

[0074] The 25mm specification steel plate has undergone solution treatment, and all performance indicators fully meet the requirements. At the same time, the steel plate has good high-temperature performance and good toughness and strength matching, fully meeting the requirements of low-temperature resistant and high-toughness duplex stainless steel.

[0075] The low-temperature-resistant, high-toughness duplex stainless steel of Example 5 was produced from molten steel smelted in a converter, refined outside the furnace, and vacuum-treated before being cast into continuous-cast ingots with a cross-section of 195 mm. The resulting steel plates were rolled to a size of 30 mm. The composition, smelting process, continuous casting process, hot working process, and solutionizing process are shown in Example 5 in Tables 1 to 5. The mechanical properties are shown in Tables 6-5, respectively.

[0076] Table 6-5 Mechanical properties results

[0077]

[0078] The 30mm specification steel plate has undergone solution treatment, and all performance indicators fully meet the requirements. At the same time, the steel plate has good high-temperature performance and good toughness and strength matching, fully meeting the requirements of low-temperature resistant and high-toughness duplex stainless steel.

[0079] The low-temperature-resistant, high-toughness duplex stainless steel of Example 6 was produced from molten steel smelted in a converter, refined outside the furnace, and vacuum-treated before being cast into continuous-cast ingots with a cross-section of 195 mm. The resulting steel plates were rolled to a size of 35 mm. The composition, smelting process, continuous casting process, hot working process, and solutionizing process are shown in Example 6 in Tables 1 to 5. The mechanical properties are shown in Tables 6-6.

[0080] Table 6-6 Mechanical properties results

[0081]

[0082] The 35mm specification steel plate has undergone solution treatment, and all performance indicators fully meet the requirements. At the same time, the steel plate has good high-temperature performance and good toughness and strength matching, fully meeting the requirements of low-temperature resistant and high-toughness duplex stainless steel.

[0083] The low-temperature-resistant, high-toughness duplex stainless steel of Example 7 was produced from molten steel smelted in a converter, refined outside the furnace, and vacuum-treated before being cast into continuous-cast ingots with a cross-section of 195 mm. The resulting steel plates were rolled to a size of 40 mm. The composition, smelting process, continuous casting process, hot working process, and solutionizing process are shown in Example 7 in Tables 1 to 5. The mechanical properties are shown in Tables 6 and 7, respectively.

[0084] Table 6-7 Mechanical properties results

[0085]

[0086] The 45mm specification steel plate has undergone solution treatment, and all performance indicators fully meet the requirements. At the same time, the steel plate has good high-temperature performance and good toughness and strength matching, fully meeting the requirements of low-temperature resistant and high-toughness duplex stainless steel.

[0087] The low-temperature-resistant, high-toughness duplex stainless steel of Example 8 was produced from molten steel smelted in a converter, refined outside the furnace, and vacuum-treated before being cast into continuous-cast ingots with a cross-section of 195 mm. The resulting steel plates were rolled to a size of 45 mm. The composition, smelting process, continuous casting process, hot working process, and solutionizing process are shown in Tables 1 to 5 for Example 8. The mechanical properties are shown in Tables 6 to 8, respectively.

[0088] Table 6-8 Mechanical properties results

[0089]

[0090] The 45mm specification steel plate has undergone solution treatment, and all performance indicators fully meet the requirements. At the same time, the steel plate has good high-temperature performance and good toughness and strength matching, fully meeting the requirements of low-temperature resistant and high-toughness duplex stainless steel.

[0091] The low-temperature-resistant, high-toughness duplex stainless steel of Example 9 was produced from molten steel smelted in a converter, refined outside the furnace, and vacuum-treated before being cast into continuous-cast ingots with a cross-section of 195 mm. The resulting steel plates were rolled to a size of 50 mm. The composition, smelting process, continuous casting process, hot working process, and solutionizing process are shown in Tables 1 to 5 of Example 9. The mechanical properties are shown in Tables 6 to 9, respectively.

[0092] Table 6-9 Mechanical properties results

[0093]

[0094] The 50mm specification steel plate has undergone solid solution treatment, and all performance indicators fully meet the requirements. At the same time, the steel plate has good high-temperature performance and good toughness and strength matching, fully meeting the requirements of low-temperature resistant and high-toughness duplex stainless steel.

[0095] The low-temperature-resistant, high-toughness duplex stainless steel of Example 10 was produced from molten steel smelted in a converter, refined outside the furnace, and vacuum-treated before being cast into continuous-cast ingots with a cross-section of 195 mm. The resulting steel plates had a gauge of 55 mm. The composition, smelting process, continuous casting process, hot working process, and solutionizing process are shown in Tables 1 to 5 of Example 10. The mechanical properties are shown in Tables 6 to 10, respectively.

[0096] Table 6-10 Mechanical properties results

[0097]

[0098] The 55mm specification steel plate has undergone solution treatment, and all performance indicators fully meet the requirements. At the same time, the steel plate has good high-temperature performance and good toughness and strength matching, fully meeting the requirements of low-temperature resistant and high-toughness duplex stainless steel.

[0099] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and basic spirit of the invention, and the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A thick-gauge, low-temperature-resistant, high-toughness duplex stainless steel, characterized in that: The components are as follows by weight percentage: C: 0.01% to 0.03%; Si: 0.80% to 1.20%; Mn: 0.80% to 1.20%; P≤0.020%; S≤0.010%; Ni: 5.00% to 6.80%; Cr: 22.50% to 25.00%; Mo: 4.00% to 5.50%; Nb: 0.013% to 0.020%; Ti: 0.15% to 0.20%, N: 0.16% to 0.23%, Y: 0.001% to 0.003%; the remaining content is Fe and unavoidable impurities; the steel plate thickness is 10 to 60 mm; the manufacturing method of duplex stainless steel, the process steps are smelting, continuous casting, rolling, and solid solution, and the specific steps include: 1) Smelting: EAF+LF+VOD is used for smelting; 2) Continuous casting: control the superheat at 25-30°C, the continuous casting billet speed at 1.0-1.6 m / min, the crystallizer electromagnetic stirring current intensity at 300-350 A, the frequency at 2.5-3.0 Hz, the billet temperature in the secondary cooling zone at 950-1150°C, the billet surface temperature return to no more than 165°C, the specific water content at 1.25-1.85 kg / L, the electromagnetic stirring at the end of solidification at the position where the solid phase ratio in the center of the billet is 0.25-0.35, the current intensity at 100-120 A, the frequency at 6.0-8.0 Hz, and a reduction of 10-19 mm; 3) Rolling: The preheating temperature of the slab is 1000-1150℃, the heating temperature of the slab is 1225-1250℃, the total time of the soaking section and the heating section of the heating furnace is 3.5-4.5h, the total time in the furnace is 5-6h, and the air-fuel ratio is controlled at 1:1.8-1:2.4; the first pass reduction rate is 10%-15% and high-pressure water descaling is performed with a water pressure of 18-25MPa. The second and third pass reduction rates are both not less than 20%, and the rolling number does not exceed 10. The final rolling temperature is above 1000℃. After rolling, the steel plate immediately enters pre-straightening, then air-cools to 675-750℃, and then is hot sent into the furnace for solution treatment; 4) Solution treatment: The heating time in the temperature rising stage is controlled at 1.2-1.6 min / mm, the solution temperature is 1050-1080°C, the holding time is 1.8-2.2 min / mm, and then cooled to room temperature in high-pressure water at a cooling rate of 13-20°C / s.

2. The thick-gauge low-temperature-resistant and high-toughness duplex stainless steel according to claim 1, characterized in that: Step 1) Smelting process: pre-treatment of molten iron, adding scrap steel, melting, primary dephosphorization treatment, continue to heat up 50-80℃, after removing the slag, enter the LF process, feed calcium wire at 0.35-0.4kg / t, and carry out pre-desulfurization treatment of reducing slag at the same time. After adjusting the chemical composition to the target composition, remove the protective slag and enter the VOD process for oxygen blowing and decarbonization. Nitrogen addition and denitrification processes are carried out in the ladle by blowing nitrogen from the bottom of the ladle. The nitrogen blowing temperature is 1635-1655℃, the nitrogen blowing pressure is 1.8-2.1MPa, and the flow rate is 135-150m 3 / h, nitrogen blowing time is 55 to 65 minutes.

3. The thick-gauge low-temperature-resistant and high-toughness duplex stainless steel according to claim 1, characterized in that: Step 4) The steel plate is solution treated in a walking beam solution furnace.

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