Low-cost duplex stainless steel with high strength, plasticity and corrosion resistance as well as preparation method and application of low-cost duplex stainless steel

Abstract

The invention provides low-cost duplex stainless steel with high strength and plasticity and corrosion resistance and a preparation method and application thereof, the general formula of the stainless steel is FeaCrbNicModMMn < e > Si < f > Ng Ti < h > C , a = 56-63 wt%, b = 24-26 wt%, c = 2-7 wt%, d = 3.5-4.5 wt%, e = 7.5-12 wt%, f = 0.2-0.5 wt%, g = 0.1-0.5 wt%, h = 0.1-0.5 wt% and i = 0.01-0.03 wt%, and a, b, c, d, e, f, g, h and i are the mass percentages of the corresponding elements respectively. The stainless steel not only has excellent mechanical properties of high strength and high plasticity, but also shows excellent corrosion resistance, and can meet strict service environment requirements in ocean engineering.

Description

Technical Field

[0001] This invention relates to alloy technology, and more particularly to a low-cost duplex stainless steel that combines high strength, plasticity, and corrosion resistance, its preparation method, and its applications. Background Technology

[0002] As the core of marine engineering materials, metallic structural materials are widely used in warships, carrier-based aircraft, offshore wind power equipment, and ships. However, the high temperature, high humidity, and high salinity of the marine environment place extremely high demands on the comprehensive performance of metallic materials, including high strength, high toughness, corrosion resistance, and wear resistance. While traditional 304 and 316L stainless steels, as well as E690 and Q355 low-alloy steels, possess good toughness and corrosion resistance, their yield strength is typically low, making it difficult to meet the strength requirements of modern high-end equipment. On the other hand, high-strength alloy steels are prone to corrosion in the extreme marine environment, leading to premature material failure and preventing long-term service. Therefore, developing new marine steels that combine high strength, toughness, and corrosion resistance has become the biggest challenge currently facing the field of marine engineering materials.

[0003] Furthermore, traditional duplex stainless steel relies on high levels of precious metals such as Ni to balance its microstructure and performance, resulting in high costs and limiting its adoption in low-cost applications such as building structures and general process equipment.

[0004] Therefore, developing duplex stainless steel that combines high strength and plasticity, excellent corrosion resistance and low cost not only has important theoretical value, but also provides more competitive material options for industrial applications, which meets the strategic needs of sustainable development and resource conservation. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by proposing a low-cost duplex stainless steel that combines high strength and plasticity with corrosion resistance. This stainless steel not only possesses excellent mechanical properties of high strength and high plasticity, but also exhibits excellent corrosion resistance, thus meeting the stringent service environment requirements in marine engineering.

[0006] It should be noted that, in this invention, unless otherwise specified, the specific meaning of "comprising" in relation to composition and description includes both open-ended meanings such as "comprising," "including," etc., and closed-ended meanings such as "composed of," "consisting of," etc., and similar meanings.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: a low-cost duplex stainless steel with both high strength and corrosion resistance, having the general formula Fe. a Cr b Ni c Mo d Mn e Si fN g Ti h C i Where a = 56-63 wt%, b = 24-26 wt%, c = 2-7 ​​wt%, d = 3.5-4.5 wt%, e = 7.5-12 wt%, f = 0.2-0.5 wt%, g = 0.1-0.5 wt%, h = 0.1-0.5 wt%, i = 0.01-0.03 wt%, and a, b, c, d, e, f, g, h, and i are the mass percentages of the corresponding elements.

[0008] Furthermore, the yield strength of the low-cost duplex stainless steel, which combines high strength, plasticity, and corrosion resistance, is 752 MPa-1057 MPa.

[0009] Furthermore, the tensile strength of the low-cost duplex stainless steel, which combines high strength, plasticity, and corrosion resistance, is 926MPa-1258MPa.

[0010] Furthermore, the elongation of the low-cost duplex stainless steel, which combines high strength, plasticity, and corrosion resistance, is 15.8% to 27.6%.

[0011] Furthermore, the corrosion current density of the low-cost duplex stainless steel, which combines high strength and plasticity with corrosion resistance, is 1.199 × 10⁻⁶. -6 -3.67×10 -7 A / cm 2 It has a corrosion potential of -305.2 to -258.5 mV and a low cost.

[0012] Furthermore, the low-cost duplex stainless steel that combines high strength, plasticity, and corrosion resistance has a ferritic and austenitic duplex structure.

[0013] Another object of the present invention discloses a method for preparing a low-cost duplex stainless steel that combines high strength, plasticity, and corrosion resistance, comprising the following steps:

[0014] Step 1: According to the general formula Fe a Cr b Ni c Mo d Mn e Si f N g Ti h C i Weigh the raw materials: iron blocks, chromium blocks, nickel blocks, molybdenum blocks, manganese blocks, titanium blocks, silicon blocks, and carbon powder. Nitrogen is added in the form of CrN. The proportion of each element in the alloy is a mass percentage.

[0015] Step 2: Place the weighed raw materials into the water-cooled crucible of the vacuum melting furnace. After evacuating the vacuum melting furnace, fill it with inert gas for protection, adjust the induced current, and carry out vacuum melting to completely melt the elements. Cool to obtain duplex stainless steel ingots.

[0016] Step 3: Hold the duplex stainless steel ingot at 1150℃~1200℃ for 30~90 minutes, then air cool; then hot roll at 1000℃~1050℃ until the thickness is reduced by 45%~50%, then continue hot rolling at 800℃~850℃ until the thickness is reduced by 85%~90%, then air cool; hold at 1000℃~1200℃ for 30~60 minutes, then water quench to obtain a low-cost duplex stainless steel with both high strength and corrosion resistance.

[0017] Furthermore, the iron blocks, chromium blocks, nickel blocks, molybdenum blocks, manganese blocks, titanium blocks, silicon blocks, and chromium nitride are all industrial-grade pure raw materials with a purity of 99.5 wt.% or higher.

[0018] Furthermore, during the vacuum melting process in step two, the vacuum is evacuated to 3×10⁻⁶. -3 Pa ~ 5.5×10 -3 Pa, then backflush argon gas to 0.05~0.06 Pa.

[0019] Furthermore, the vacuum melting temperature in step two is 2100℃ ~ 2300℃.

[0020] Furthermore, in step two, the voltage for each arc ignition melting is 10-15V, and the current for each arc ignition melting is 300-350A.

[0021] Furthermore, during the vacuum melting process described in step two, the alloy ingot is turned over and melted six to eight times.

[0022] Furthermore, during hot rolling as described in step three, the rolling pressure remains consistent.

[0023] Another objective of this invention is to disclose the application of a low-cost duplex stainless steel with both high strength and corrosion resistance in the field of marine engineering materials.

[0024] This invention relates to a low-cost duplex stainless steel that combines high strength, plasticity, and corrosion resistance, along with its preparation method and applications. Compared with existing technologies, it has the following advantages:

[0025] 1) This invention presents a low-cost duplex stainless steel with both high strength, ductility, and corrosion resistance. It is composed of iron, chromium, nickel, molybdenum, manganese, titanium, silicon, and nitrogen in a specific ratio, and is produced by a vacuum electric arc furnace. This series of low-cost duplex stainless steel materials all contain ferrite (α, body-centered cubic structure) and austenite (γ, face-centered cubic structure) in their structure, and the microstructure and mechanical properties of the alloy can be controlled by adjusting the proportions of different metal elements. The stainless steel of this invention exhibits high strength and high ductility. Testing shows that the yield strength of the low-cost duplex stainless steel with both high strength, ductility, and corrosion resistance is 589 MPa-712 MPa. The tensile strength of the low-cost duplex stainless steel with both high strength, ductility, and corrosion resistance is 926 MPa-1258 MPa. The elongation of the low-cost duplex stainless steel with both high strength, ductility, and corrosion resistance is 15.8%~27.6%.

[0026] 2) Simultaneously, this series of duplex stainless steel materials exhibits excellent corrosion resistance. Testing revealed that the corrosion current density of this low-cost duplex stainless steel, which combines high strength and plasticity with corrosion resistance, is 1.199 × 10⁻⁶. -6 -3.67×10 -7 A / cm 2 The corrosion potential is -305.2 to -258.5 mV.

[0027] 3) With lower cost, this series of stainless steels significantly reduces the content of expensive nickel and molybdenum elements, and instead adds inexpensive manganese and nitrogen elements to stabilize the austenitic phase and improve strength and corrosion resistance. While ensuring that the material has excellent strength, plasticity and corrosion resistance, the cost of raw materials is significantly reduced, achieving a good balance between performance and price.

[0028] The low-cost duplex stainless steel of this invention, which combines high strength, plasticity, and corrosion resistance, has good application prospects and large-scale promotion potential in the field of marine engineering materials. Attached Figure Description

[0029] Figure 1 Fe prepared in Example 1 a Cr b Ni c Mo d Mn e Si f N g Ti h C i XRD pattern of high-strength, ductile, and corrosion-resistant duplex stainless steel;

[0030] Figure 2 Fe prepared in Example 1 a Cr b Ni c Mo d Mn e Sif N g Ti h C i Microscopic morphology images of high-strength, high-plasticity, and corrosion-resistant duplex stainless steel;

[0031] Figure 3 Fe prepared in Example 1 a Cr b Ni c Mo d Mn e Si f N g Ti h C i Tensile stress-strain curve of high-strength, plastic and corrosion-resistant duplex stainless steel.

[0032] Figure 4 Fe prepared in Example 1 a Cr b Ni c Mo d Mn e Si f N g Ti h C i Comparison of potentiodynamic polarization curves between high-strength, plastic and corrosion-resistant duplex stainless steel ingots and 316L stainless steel. Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0034] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0035] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0036] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0037] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0038] In this specification, the terms "optional" or "optional" are used to indicate the use or omission of certain substances, components, procedures, application conditions, etc.

[0039] In this instruction manual, when "room temperature" or "room temperature" is used, the temperature can be 15-25℃.

[0040] Unless otherwise specified, all reagents or instruments used in this instruction manual are commercially available products.

[0041] The present invention will be further described in detail below with reference to the embodiments.

[0042] A method for preparing a low-cost duplex stainless steel with both high strength, ductility, and corrosion resistance, characterized in that the formula for the low-cost duplex stainless steel with both high strength, ductility, and corrosion resistance is: Fe a Cr b Ni c Mo d Mn e Si f N g Ti h C i The proportions of each element are by mass percentage.

[0043] The specific preparation method is as follows: The alloy is melted in a vacuum electric arc furnace. The raw materials—iron blocks, chromium blocks, nickel blocks, molybdenum blocks, manganese blocks, titanium blocks, silicon blocks, and chromium nitride—are uniformly mixed and placed in a water-cooled copper crucible. The vacuum melting furnace is then evacuated to a vacuum degree of 3 × 10⁻⁶. -3 Pa ~ 5.5 × 10 -3 At a pressure of 0.05-0.06 Pa, argon gas is backflushed to a pressure of 0.05-0.06 Pa before smelting. Ti alloy ingots are smelted first to absorb residual oxygen in the vacuum arc furnace. During alloy smelting, the alloy needs to be turned over and smelted at least 6-8 times, each time for one to two minutes, to ensure uniform composition. After cooling, duplex stainless steel ingots are obtained.

[0044] The duplex stainless steel ingots obtained from smelting were held at 1150℃~1200℃ for 30~90 minutes, followed by air cooling. Then, they were hot-rolled at 1000℃~1050℃ until the thickness was reduced by 45%~50%, followed by hot rolling at 800℃~850℃ until the thickness was reduced by 85%~90%, and then air-cooled. Finally, they were held at 1000℃~1200℃ for 30~60 minutes and water-quenched to obtain high-strength, ductile, and corrosion-resistant duplex stainless steel.

[0045] In the following examples, the mechanical properties and corrosion resistance of the prepared low-cost duplex stainless steel, which combines high strength, ductility, and corrosion resistance, were tested. The prepared low-cost duplex stainless steel was cut into samples of the desired shapes, and then subjected to mechanical and corrosion resistance experiments. The specific testing process is as follows:

[0046] 1. Mechanical property test:

[0047] The detection method is as follows:

[0048] A gauge length of 10 mm and a cross-sectional area of ​​2 × 1.5 mm were cut from a low-cost duplex stainless steel ingot. 2 The dog-bone shaped plate was used to prepare the sample, which was then stretched at room temperature with a strain rate of 0.001 s⁻¹. -1 The stress-strain curves for tensile engineering were obtained after processing with Matlab.

[0049] 2. Corrosion resistance testing

[0050] The detection method is as follows:

[0051] Several corrosion-resistant samples were cut from low-cost duplex stainless steel ingots. The samples were small circular pieces with a diameter of 15 mm and a thickness of 2 mm. The cut samples were polished with SiC sandpaper up to 2000#, ultrasonically cleaned with distilled water and anhydrous ethanol, and dried for later use.

[0052] A three-electrode electrochemical workstation was used, with a low-cost duplex stainless steel sample as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode. Under isothermal conditions of 25℃, the potentiodynamic polarization curves of this series of duplex stainless steels in 3.5 wt% NaCl solution were measured. The self-corrosion current density and corrosion potential were obtained to quantitatively evaluate the corrosion resistance of different duplex stainless steels in 3.5 wt% NaCl solution.

[0053] Example 1

[0054] This embodiment discloses a low-cost duplex stainless steel with both high strength and plasticity and corrosion resistance, whose general formula is Fe. 59.87 Cr 25 Ni2Mo4Mn8Si 0.5 N 0.5 Ti 0.1 C 0.03 The proportions of each element are by mass percentage.

[0055] The method for preparing the low-cost duplex stainless steel with high strength, ductility, and corrosion resistance includes the following steps:

[0056] (1) According to the alloy composition Fe 59.87 Cr 25 Ni2Mo4Mn8Si 0.5 N 0.5 Ti 0.1 C 0.03 Material preparation, wherein the proportions of each element in the alloy are by mass percentage;

[0057] (2) Add iron blocks, chromium blocks, nickel blocks, molybdenum blocks, manganese blocks, silicon blocks, and chromium nitride to the electric arc furnace in sequence, and evacuate the electric arc furnace to a vacuum degree of 3×10⁻⁶. -3 After Pa, argon gas is introduced into the furnace to a pressure of 0.05 Pa for melting. After the alloying elements are evenly mixed, the furnace is cooled to obtain an ingot.

[0058] (3) The duplex stainless steel ingot obtained from smelting is held at 1200℃ for 30 minutes and then air-cooled. Then it is hot-rolled at 1000℃ until the thickness is reduced by 50%, and then hot-rolled again at 800℃ until the thickness is reduced by 85%, and then air-cooled. It is then held at 1050℃ for 30 minutes and water-quenched to obtain a low-cost duplex stainless steel with both high strength and corrosion resistance.

[0059] Figure 1 Fe prepared in Example 1 59.87 Cr 25 Ni2Mo4Mn8Si 0.5 N 0.5 Ti 0.1 C 0.03 The XRD pattern of the high-strength, ductile, and corrosion-resistant duplex stainless steel shows that the alloy has a duplex structure consisting of ferrite (α) phase and austenite (γ) phase.

[0060] Figure 2 Fe prepared in Example 1 59.87 Cr 25 Ni2Mo4Mn8Si 0.5 N 0.5 Ti 0.1 C 0.03 Microscopic morphology images of high-strength, ductile, and corrosion-resistant duplex stainless steel show a microstructure consisting of a dark ferrite matrix with randomly distributed light-colored island-like austenite phases.

[0061] Mechanical properties were tested on the duplex stainless steel tensile sheets prepared in this embodiment. The results showed a yield strength of 1017 MPa, a breaking strength of 1188 MPa, and an elongation of 21.5%. The tensile stress-strain curve of the duplex stainless steel ingot under as-cast conditions is shown below. Figure 3 As shown.

[0062] The duplex stainless steel sample prepared in this embodiment was cut and subjected to electrochemical potentiodynamic polarization curve testing, and compared with 316L stainless steel; the corrosion current density of this alloy was measured to be 3.67 × 10⁻⁶. -7 A / cm 2 With a corrosion potential of -291.6V, it exhibits superior corrosion resistance compared to 316L stainless steel alloy in simulated seawater environments.

[0063] Figure 4 Fe prepared in Example 159.87 Cr 25 Ni2Mo4Mn8Si 0.5 N 0.5 Ti 0.1 C 0.03 A comparison of the potentiodynamic polarization curves of high-strength, plasticity-resistant, and corrosion-resistant duplex stainless steel ingots and 316L stainless steel. It can be seen that, compared to 316L stainless steel, Example 1 exhibits a lower self-corrosion current density, a larger passivation range, and superior corrosion resistance.

[0064] Example 2

[0065] This embodiment discloses a low-cost duplex stainless steel with both high strength and plasticity and corrosion resistance, whose general formula is Fe. 57.87 Cr 25 Ni2Mo4Mn 10 Si 0.5 N 0.5 Ti 0.1 C 0.03 The preparation method of the low-cost duplex stainless steel with high strength, plasticity and corrosion resistance described in this embodiment is the same as that in Example 1.

[0066] Its yield strength was tested to be 1036 MPa, its tensile strength to be 1203 MPa, its elongation to be 21.3%, and its corrosion current density to be 5.87 × 10⁻⁶ MPa. -7 A / cm 2 The corrosion potential is -305.2V.

[0067] Example 3

[0068] This embodiment discloses a low-cost duplex stainless steel with both high strength and plasticity and corrosion resistance, whose general formula is Fe. 56.77 Cr 24 Ni2Mo4Mn 12 Si 0.5 N 0.5 Ti 0.2 C 0.03 The preparation method of the low-cost duplex stainless steel with high strength, plasticity, and corrosion resistance described in this embodiment is the same as that in Example 1.

[0069] Its yield strength was tested to be 1057 MPa, its fracture strength to be 1253 MPa, its elongation to be 20.5%, and its corrosion current density to be 3.43 × 10⁻⁶ MPa. -7 A / cm 2 The corrosion potential is -297.6V.

[0070] Example 4

[0071] This embodiment discloses a low-cost duplex stainless steel with both high strength and plasticity and corrosion resistance, whose general formula is Fe. 56.87 Cr25 Ni4Mo4Mn9Si 0.5 N 0.5 Ti 0.1 C 0.03 The preparation method of the low-cost duplex stainless steel with high strength, plasticity and corrosion resistance described in this embodiment is the same as that in Example 1.

[0072] Its yield strength was tested to be 782 MPa, its tensile strength to be 986 MPa, its elongation to be 16.1%, and its corrosion current density to be 1.199 × 10⁻⁶ MPa. -6 A / cm 2 The corrosion potential is -258.5V.

[0073] In summary, the Fe in this invention a Cr b Ni c Mo d Mn e Si f N g Ti h C i Duplex stainless steel exhibits excellent strength and plasticity even in the as-cast state. Its high Cr content gives it excellent corrosion resistance, and its low Ni content further reduces its cost.

[0074] This invention is not limited to the description of a low-cost duplex stainless steel with high strength, plasticity and corrosion resistance as described in any one of Examples 1–4. Changes in element content and preparation methods are all within the scope of protection of this invention.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-cost duplex stainless steel possessing both high strength and corrosion resistance, characterized in that, The general formula is Fe a Cr b Ni c Mo d Mn e Si f N g Ti h C i Where a = 56-63 wt%, b = 24-26 wt%, c = 2-7 ​​wt%, d = 3.5-4.5 wt%, e = 7.5-12 wt%, f = 0.2-0.5 wt%, g = 0.1-0.5 wt%, h = 0.1-0.5 wt%, i = 0.01-0.03 wt%, and a, b, c, d, e, f, g, h, and i are the mass percentages of the corresponding elements.

2. The low-cost duplex stainless steel with high strength, plasticity, and corrosion resistance according to claim 1, characterized in that, The yield strength of the low-cost duplex stainless steel, which combines high strength, plasticity, and corrosion resistance, is 752 MPa-1057 MPa. And / or, the tensile strength of the low-cost duplex stainless steel that combines high strength, plasticity and corrosion resistance is 926MPa-1258MPa; And / or, the elongation of the low-cost duplex stainless steel, which combines high strength, plasticity, and corrosion resistance, is 15.8% to 27.6%; And / or, the corrosion current density of the low-cost duplex stainless steel, which combines high strength and plasticity with corrosion resistance, is 1.199 × 10⁻⁶. -6 -3.67×10 -7 A / cm 2 The corrosion potential is -305.2 to -258.5 mV.

3. The low-cost duplex stainless steel with high strength, ductility, and corrosion resistance according to claim 1, characterized in that, The low-cost duplex stainless steel, which combines high strength, plasticity, and corrosion resistance, has a ferritic and austenitic duplex structure.

4. A method for preparing a low-cost duplex stainless steel with high strength, ductility, and corrosion resistance as described in any one of claims 1-3, characterized in that, Includes the following steps: Step 1: According to the general formula Fe a Cr b Ni c Mo d Mn e Si f N g Ti h C i Weigh the raw materials: iron blocks, chromium blocks, nickel blocks, molybdenum blocks, manganese blocks, titanium blocks, silicon blocks, and carbon powder. Nitrogen is added in the form of CrN. Step 2: Place the weighed raw materials into the water-cooled crucible of the vacuum melting furnace. After evacuating the vacuum melting furnace, fill it with inert gas for protection, adjust the induced current, and carry out vacuum melting to completely melt the elements. Cool to obtain duplex stainless steel ingots. Step 3: Hold the duplex stainless steel ingot at 1150℃~1200℃ for 30~90 minutes, then air cool; then hot roll at 1000℃~1050℃ until the thickness is reduced by 45%~50%, then continue hot rolling at 800℃~850℃ until the thickness is reduced by 85%~90%, then air cool; hold at 1000℃~1200℃ for 30~60 minutes, then water quench to obtain a low-cost duplex stainless steel with both high strength and corrosion resistance.

5. The method for preparing low-cost duplex stainless steel with both high strength and corrosion resistance according to claim 4, characterized in that, The iron blocks, chromium blocks, nickel blocks, molybdenum blocks, manganese blocks, titanium blocks, silicon blocks, and chromium nitride are all industrial-grade pure raw materials with a purity of 99.5 wt.% or higher.

6. The method for preparing low-cost duplex stainless steel with both high strength and corrosion resistance according to claim 4, characterized in that, In step two, during the vacuum melting process, the vacuum is evacuated to 3×10⁻⁶. -3 Pa ~ 5.5×10 -3 Pa, then backflush argon gas to 0.05~0.06 Pa.

7. The method for preparing low-cost duplex stainless steel with both high strength and corrosion resistance according to claim 4, characterized in that, The vacuum melting temperature described in step two is 2100℃~2300℃.

8. The method for preparing low-cost duplex stainless steel with both high strength and corrosion resistance according to claim 4, characterized in that, In step two, the voltage for each arc ignition melting is 10-15V, and the current for each arc ignition melting is 300-350A.

9. The method for preparing low-cost duplex stainless steel with both high strength and corrosion resistance according to claim 4, characterized in that, During the vacuum melting process described in step two, the alloy ingot is turned over and melted six to eight times.

10. The application of a low-cost duplex stainless steel with high strength, plasticity and corrosion resistance as described in any one of claims 1-3 in the field of marine engineering materials.

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