Nb2205-containing duplex stainless steel plate and preparation method thereof

Abstract

The invention belongs to the technical field of stainless steel variety development, and particularly relates to an Nb2205-containing duplex stainless steel plate and a preparation method thereof. The duplex stainless steel plate containing Nb2205 comprises the following components in percentage by weight: less than or equal to 0.030% of C, less than or equal to 1.00% of Si, less than or equal to 2.00% of Mn, less than or equal to 0.030% of P, less than or equal to 0.005% of S, 21.00%-23.00% of Cr, 5.50%-6.50% of Ni, 3.00%-3.50% of Mo, 0.15%-0.20% of N, 0.04%-0.05% of Nb and the balance of iron. According to the Nb2205-containing duplex stainless steel plate, on the premise that the room-temperature strength, corrosion resistance and low-temperature toughness of traditional 2205 duplex stainless steel are guaranteed, the 110 DEG C high-temperature strength is greatly improved, and the design requirements of special fields are met.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel variety development technology, specifically relating to a duplex stainless steel sheet containing Nb2205 and its preparation method. Background Technology

[0002] Duplex stainless steel refers to stainless steel in which austenite and ferrite coexist in its room temperature microstructure, typically in a ratio close to 1:1. This type of steel possesses high strength and good resistance to chloride ions (Cl). - With its outstanding advantages such as resistance to pitting corrosion, stress corrosion, and weldability, it is widely used in petrochemical, salt production, hydraulic engineering, shipbuilding, and civil applications. Due to the adoption of nitrogen-for-nitrogen (N) substitution in its composition design, the Ni content is significantly reduced compared to ordinary austenitic and super austenitic stainless steels, resulting in lower manufacturing costs and making it a resource-saving steel.

[0003] Due to its unique microstructure, 2205 duplex stainless steel is generally recommended for use at temperatures not exceeding 300℃. However, in certain applications, a high-temperature strength of 110℃ is required to meet room-temperature requirements, meaning a longitudinal yield strength Rt0.5 of not less than 450MPa. Existing standard compositions typically have a longitudinal yield strength Rt0.5 of 410–430MPa, which cannot satisfy these specific requirements. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a duplex stainless steel sheet containing Nb2205 and its preparation method.

[0005] Specifically, the present invention is achieved through the following technical solutions: A duplex stainless steel sheet containing Nb2205, comprising, by weight percentage: C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.030%, S≤0.005%, Cr: 21.00%~23.00%, Ni: 5.50%~6.50%, Mo: 3.00%~3.50%, N: 0.15%~0.20%, Nb: 0.04%~0.05%, with the balance being iron.

[0006] The above-mentioned method for preparing Nb2205-containing duplex stainless steel sheet includes: (1) Use an electric furnace to smelt molten steel and then perform AOD smelting on the molten steel. After tapping the steel, remove the slag and control the slag layer thickness to be 70~200mm. (2) Move the ladle to the LF station, add CaO and CaF2, energize to slag, add ferroniobium, and perform micro-alloying treatment on the molten steel. (3) After the added CaO and CaF2 melt, aluminum powder is added to the slag surface and aluminum blocks are added to the molten steel; after adjusting the temperature of the molten steel, Ca wire is fed into the molten steel; (4) After feeding the wire, the molten steel is weakly stirred, and then the ladle is put into the continuous casting station. After settling and casting, a continuous casting billet is obtained. (5) Roll the continuously cast billet into a plate and perform solution heat treatment.

[0007] In the above-mentioned method for preparing Nb2205 duplex stainless steel plates, the electric furnace uses dephosphorized molten iron from a converter, along with scrap steel and ferrochrome, as raw materials, or uses scrap steel and ferrochrome as raw materials in its entirety.

[0008] In the above-mentioned method for preparing Nb2205 duplex stainless steel sheet, at the LF station, the amount of CaO added is 0.3% to 0.6% of the weight of molten steel, ensuring that the binary basicity of the LF slag is ≥4.

[0009] In the above-mentioned method for preparing Nb2205 duplex stainless steel sheet, at the LF station, the amount of CaF2 added is 0.2% to 0.5% of the weight of the molten steel.

[0010] In the above-mentioned method for preparing Nb2205 duplex stainless steel sheet, the niobium content in the ferroniobium is 60-65%, and the Nb content in the steel is controlled to be 0.04-0.05%.

[0011] In the above-mentioned method for preparing Nb2205 duplex stainless steel sheet, the amount of aluminum powder added is 0.1% to 0.2% of the weight of molten steel, and the amount of aluminum block added is 0.010% to 0.025% of the weight of molten steel.

[0012] In the above-mentioned method for preparing Nb2205 duplex stainless steel sheet, the amount of Ca wire added is 0.5-0.7 kg / t molten steel; the gas flow rate for weak stirring is 50-150 NL / min; and the duration of weak stirring is 15-20 min.

[0013] In the above-mentioned method for preparing Nb2205 duplex stainless steel sheet, the standing time is 15-20 minutes; the solution heat treatment temperature is 1050-1100℃, and the sheet is water-cooled after being removed from the furnace.

[0014] The technical solution of the present invention has the following beneficial effects: (1) The Nb2205 duplex stainless steel sheet of the present invention has a high-temperature yield strength Rt0.5 of not less than 450MPa at 110℃.

[0015] (2) The Nb2205 duplex stainless steel sheet of the present invention, while ensuring the room temperature strength, corrosion resistance and low temperature toughness of traditional 2205 duplex stainless steel, significantly improves the high temperature strength at 110℃, which meets the design requirements of special fields. Attached Figure Description

[0016] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention.

[0017] Figure 1 The average grain size of a 14mm thick 2205 substrate without Nb. Figure 2 The average grain size is that of a 14mm thick 2205 substrate containing 0.043% Nb. Figure 3 The variation trend of low-temperature toughness corresponding to different Nb contents; Figure 4 The variation trend of high-temperature yield strength with different Nb contents at 110℃ is shown. Detailed Implementation

[0018] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0019] Based on existing 2205 duplex stainless steel, this invention adopts the technical concept of Nb microalloying to develop a duplex stainless steel sheet that balances high-temperature strength and low-temperature toughness, as well as its manufacturing method. Its characteristic is that, based on the existing composition of 2205 duplex stainless steel, by rationally determining the amount of Nb added and related process measures, the high-temperature strength at 110℃ is significantly improved while ensuring the room temperature strength, corrosion resistance and low-temperature toughness of traditional 2205 duplex stainless steel.

[0020] Specifically, the Nb2205 duplex stainless steel sheet provided by this invention comprises, by weight percentage: C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.030%, S≤0.005%, Cr: 21.00%~23.00%, Ni: 5.50%~6.50%, Mo: 3.00%~3.50%, N: 0.15%~0.20%, Nb: 0.04%~0.05%, with the balance being iron.

[0021] In the Nb2205 duplex stainless steel sheet of the present invention, solid solution of Nb causes significant lattice distortion, hinders dislocation movement, and leads to stress concentration and local work hardening; fine and dispersed precipitation of Nb phase pins dislocations, increasing the slip resistance of grain boundaries and phase boundaries; trace amounts of Nb promote grain refinement. The above three aspects work together to play an important role in improving high-temperature strength.

[0022] Figure 1The average grain size of a 14 mm thick, Nb-free 2205 substrate is shown to be 4.32 μm. Figure 2 The average grain size of a 2205 plate with a thickness of 14 mm and containing 0.043% Nb is shown to be 3.61 μm. Grain refinement has a significant effect on improving the instantaneous high-temperature strength of the material.

[0023] The inventors of this invention studied the effect of Nb content on intensity changes, and the results are shown in [the table below]. Figure 3 .pass Figure 3 It can be seen that trace amounts of Nb can significantly improve yield strength, and the effect on improving yield strength at room temperature is significantly better than that at high temperature; when the Nb content is too high, the effect on improving yield strength decreases.

[0024] The inventors of this invention also studied the effect of Nb content on low-temperature toughness changes, and the results are shown in […]. Figure 4 .pass Figure 4 It can be seen that when the Nb content is 0.043%, the grains are refined and the toughness is significantly improved; when the Nb content exceeds 0.05%, the precipitated phase grows significantly and the low-temperature toughness is greatly reduced.

[0025] in, Figures 1 to 4 The data shown uses stainless steel sheets, and except for the Nb content, the contents of all other components are within the following ranges: C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.030%, S≤0.005%, Cr: 21.00%~23.00%, Ni: 5.50%~6.50%, Mo: 3.00%~3.50%, N: 0.15%~0.20%, with the balance being iron.

[0026] On the other hand, the present invention also provides a method for preparing Nb2205 duplex stainless steel sheet, comprising the following steps: (1) Use an electric furnace to smelt molten steel and then perform AOD smelting on the molten steel. After tapping the steel, remove the slag and control the slag layer thickness to be 70~200mm. (2) Move the ladle to the LF station, add CaO and CaF2, energize to slag, add ferroniobium, and perform micro-alloying treatment on the molten steel. (3) After the added CaO and CaF2 melt, aluminum powder is added to the slag surface and aluminum blocks are added to the molten steel; after adjusting the temperature of the molten steel, Ca wire is fed into the molten steel; (4) After feeding the wire, the molten steel is weakly stirred, and then the ladle is put into the continuous casting station. After settling and casting, a continuous casting billet is obtained. (5) Roll the continuously cast billet into a plate and perform solution heat treatment.

[0027] In some preferred embodiments, the electric furnace uses dephosphorized molten iron from a converter, along with scrap steel and ferrochrome, as raw materials, or uses scrap steel and ferrochrome as raw materials entirely.

[0028] The AOD smelting is carried out according to conventional methods, which will not be described in detail in this invention.

[0029] In some preferred embodiments, the amount of CaO added is 0.3% to 0.6% of the weight of molten steel, for example: 0.3%, 0.4%, 0.5% or 0.6%, to ensure that the binary basicity of the LF slag is ≥4; the amount of CaF2 added is 0.2% to 0.5% of the weight of molten steel, for example: 0.2%, 0.3%, 0.4% or 0.5%.

[0030] In some preferred embodiments, the niobium content in the ferroniobium is 60-65%, and the Nb content in the steel is controlled to be 0.04-0.05%.

[0031] In some preferred embodiments, the amount of aluminum powder added is 0.1% to 0.2% of the weight of molten steel, for example, 0.1%, 0.12%, 0.14%, 0.16%, 0.18% or 0.2%; the amount of aluminum block added is 0.010% to 0.025% of the weight of molten steel, for example, 0.010%, 0.015%, 0.020% or 0.025%.

[0032] In some preferred embodiments, the amount of Ca wire added is 0.5 to 0.7 kg / t of molten steel, for example, 0.5 kg / t of molten steel, 0.55 kg / t of molten steel, 0.6 kg / t of molten steel, 0.65 kg / t of molten steel, or 0.7 kg / t of molten steel.

[0033] In some preferred embodiments, the gas flow rate for the weak stirring is 50–150 NL / min, for example: 50 NL / min, 60 NL / min, 70 NL / min, 80 NL / min, 90 NL / min, 100 NL / min, 110 NL / min, 120 NL / min, 130 NL / min, 140 NL / min, or 150 NL / min. The accurate flow rate setting is based on the condition that the slag surface is slightly agitated and the molten steel is not exposed to air. The duration of the weak stirring is 15–20 min, for example, 18 min.

[0034] In some preferred embodiments, the settling time is 15 to 20 minutes, for example: 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes.

[0035] Rolling the continuously cast billet into a plate can be done using conventional methods, which will not be described in detail here.

[0036] In some preferred embodiments, the solution heat treatment temperature is 1050–1100°C, the holding time is 9–11 min / mm, and the product is water-cooled after removal from the furnace. The solution treatment temperature is, for example, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, or 1100°C; the holding time is 9 min / mm, 10 min / mm, or 11 min / mm.

[0037] The Nb2205 duplex stainless steel sheet prepared according to the method of the present invention significantly improves the high-temperature strength at 110℃ while ensuring the room temperature strength, corrosion resistance and low-temperature toughness of traditional 2205 duplex stainless steel, thus meeting the design requirements of special fields.

[0038] Example The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments, unless otherwise specified, were performed according to conventional methods and conditions. The raw materials used in the following embodiments were all commercially available.

[0039] Example 1 1. The electric furnace uses stainless steel scrap, ferrochrome, and nickel plates as raw materials. The composition of the steel produced by the electric furnace is: C 1.90%, Si 0.13%, Mn 0.14%, P 0.020%, S 0.024%, Cr 23.05%, Ni 3.75%, N 0.014%.

[0040] 2. AOD is smelted using conventional methods. During the reduction period, the metal in the low-aluminum FeSi reduction slag is used. The steel composition of AOD is: C 0.021%, Si 0.55%, Mn 1.13%, P 0.018%, S 0.003%, Cr 22.58%, Ni 5.65%, Mo 3.13%, N 0.1650%. The tapping temperature is 1664℃ and the steel output is 188 tons.

[0041] 3. After tapping AOD steel, slag is removed, and the slag layer thickness is 140mm.

[0042] 4. After the ladle enters the LF station, it is energized, and ferroniobium containing 65% Nb is added according to the standard of 1.6kg / ton, along with 550kg of CaO and 400kg of CaF2, and then slag is melted by energizing.

[0043] 5. After the slag melts, add 240 kg of aluminum powder to the slag surface and add 32 kg of aluminum shot to the steel.

[0044] 6. According to the production schedule, after adjusting the temperature of the molten steel to 1535℃, feed 110 kg of Ca wire.

[0045] 7. After wire feeding, stir at a flow rate of 120 NL / min for 16 minutes before tapping. The composition of the tapped steel is: C 0.023%, Si 0.61%, Mn 1.14%, P 0.019%, S 0.001%, Cr 22.56%, Ni 5.60%, Mo 3.14%, N 0.1665%, Nb 0.042%, and the tapping temperature is 1514℃.

[0046] 8. Casting begins 20 minutes after the ladle leaves the LF station, with protection provided throughout the casting process.

[0047] 9. Steel plate heat treatment: 1060℃, furnace dwell time 3min / mm, water cooling after exiting the furnace.

[0048] Sheet material specifications: Thickness 14mm (Standard: ASTM A240 / A240M)

[0049] Note: In the table, "--" indicates that the corresponding test item is not related to the sample orientation and does not require testing.

[0050] Example 2 1. The electric furnace uses stainless steel scrap, ferrochrome, and nickel plates as raw materials. The composition of the steel produced by the electric furnace is: C 1.85%, Si 0.15%, Mn 0.18%, P 0.021%, S 0.025%, Cr 23.65%, Ni 3.82%, N 0.0145%.

[0051] 2. AOD is smelted using conventional methods, with low-aluminum FeSi reduction during the reduction period. The AOD steel composition is: C 0.023%, Si 0.57%, Mn 1.22%, P 0.020%, S 0.001%, Cr 22.65%, Ni 5.61%, Mo 3.13%, N 0.1650%, tapping temperature 1661℃, and steel output 180 tons.

[0052] 3. After tapping AOD steel, slag is removed, and the slag layer thickness is 140mm.

[0053] 4. After the ladle enters the LF station, it is energized, and ferroniobium containing 65% Nb is added according to the standard of 1.8kg / ton, along with 550kg of CaO and 400kg of CaF2, and then slag is smelted by energizing.

[0054] 5. After the slag melts, add 240 kg of aluminum powder to the slag surface and add 32 kg of aluminum shot to the steel.

[0055] 6. According to the production schedule, after adjusting the temperature of the molten steel to 1535℃, feed 100 kg of Ca wire.

[0056] 7. After wire feeding, stir at a flow rate of 120 NL / min for 18 minutes before tapping. The composition of the tapped steel is: C 0.023%, Si 0.55%, Mn 1.25%, P 0.019%, S 0.001%, Cr 22.62%, Ni 5.62%, Mo 3.15%, N 0.1665%, Nb 0.048%. The tapping temperature is 1514℃.

[0057] 8. Casting begins 18 minutes after the ladle leaves the LF station, with full protection during the casting process.

[0058] 9. Steel plate heat treatment: 1060℃, furnace dwell time 3min / mm, water cooling after exiting the furnace. Sheet material specifications: Thickness 14mm (Standard: ASTM A240 / A240M)

[0059] Note: In the table, "--" indicates that the corresponding test item is not related to the sample orientation and does not require testing.

[0060] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0061] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0062] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A duplex stainless steel sheet containing Nb2205, characterized in that, By weight percentage, it includes: C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.030%, S≤0.005%, Cr: 21.00%~23.00%, Ni: 5.50%~6.50%, Mo: 3.00%~3.50%, N: 0.15%~0.20%, Nb: 0.04%~0.05%, with the balance being iron.

2. The method for preparing Nb2205-containing duplex stainless steel sheet according to claim 1, characterized in that, include: (1) Use an electric furnace to smelt molten steel and then perform AOD smelting on the molten steel. After tapping the steel, remove the slag and control the slag layer thickness to be 70~200mm. (2) Move the ladle to the LF station, add CaO and CaF2, energize to slag, add ferroniobium, and perform micro-alloying treatment on the molten steel. (3) After the added CaO and CaF2 melt, aluminum powder is added to the slag surface and aluminum blocks are added to the molten steel; after adjusting the temperature of the molten steel, Ca wire is fed into the molten steel; (4) After feeding the wire, the molten steel is weakly stirred, and then the ladle is put into the continuous casting station. After settling and casting, a continuous casting billet is obtained. (5) Roll the continuously cast billet into a plate and perform solution heat treatment.

3. The preparation method according to claim 2, characterized in that, The electric furnace uses dephosphorized molten iron from a converter, along with scrap steel and ferrochrome, as raw materials, or uses scrap steel and ferrochrome as raw materials entirely.

4. The preparation method according to claim 2, characterized in that, At the LF station, the amount of CaO added is 0.3% to 0.6% of the weight of molten steel to ensure that the binary basicity of the LF slag is ≥4.

5. The preparation method according to claim 2, characterized in that, At the LF station, the amount of CaF2 added is 0.2% to 0.5% of the weight of the molten steel.

6. The preparation method according to claim 2, characterized in that, The niobium content in the ferroniobium is 60-65%, and the Nb content in the steel is controlled at 0.04-0.05%.

7. The preparation method according to claim 2, characterized in that, The amount of aluminum powder added is 0.1% to 0.2% of the weight of molten steel, and the amount of aluminum block added is 0.010% to 0.025% of the weight of molten steel.

8. The preparation method according to claim 2, characterized in that, The amount of Ca added is 0.5-0.7 kg / t of molten steel; the gas flow rate for the weak stirring is 50-150 NL / min; and the duration of the weak stirring is 15-20 min.

9. The preparation method according to claim 2, characterized in that, The settling time is 15-20 minutes; the solution heat treatment temperature is 1050-1100℃, and the product is cooled by water after being removed from the furnace.

10. A duplex stainless steel sheet containing Nb2205, characterized in that, It is prepared by the preparation method according to any one of claims 2-9.

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