Duplex stainless steel tube blank and method for producing the same

Abstract

The present application relates to a kind of duplex stainless steel pipe blank and its preparation method, wherein the preparation method includes that the molten steel obtained by smelting is poured into ingot;According to the surface temperature of the ingot after forging, the ingot is treated by post-processing pipe blank according to the deformation amount of the ingot temperature control pass.The pipe blank includes the following components according to the mass percentage distribution ratio: C≤0.028%, Si:0.40-0.80%, Mn≤1.00%, P≤0.020%, S≤0.010%, Cr:22.4~22.8%, Ni:5.2~5.8%, Mo:3.1~3.5%, N:0.16~0.20%, Al:0.01-0.03%, the balance is Fe;And Mn / N≥4, [O]Content≤0.0035%.The duplex stainless steel pipe blank of the present application has excellent hot working plasticity, and can be used for producing high-quality duplex stainless steel forgings.

Description

Technical Field

[0001] This invention belongs to the field of forging technology, specifically relating to a duplex stainless steel tube blank and its preparation method. Background Technology

[0002] Duplex stainless steel has a structure in which austenite (γ) and ferrite (α) coexist. During hot working, the two phases have significantly different coefficients of thermal expansion and deformation resistance, which can easily lead to internal stress concentration. The optimal hot working temperature range for duplex stainless steel is relatively narrow; exceeding this range can easily result in a decrease in plasticity, thereby increasing the risk of cracking.

[0003] Cracking during processing can lead to increased scrap rates, and rework can impact production efficiency. Material replacement can also result in high costs. Hot working cracks can cause internal or surface cracks in materials, significantly reducing the mechanical properties of components, such as strength and toughness. Components with cracks may suddenly fracture due to stress concentration during subsequent use, especially in high-pressure, corrosive, or alternating load environments; in other words, components with cracks pose a significant safety hazard during use.

[0004] Therefore, to solve the problem of hot working cracking in duplex stainless steel, a comprehensive study is needed on material properties and processing technology. Summary of the Invention

[0005] In order to solve all or some of the above problems, the present invention aims to provide a duplex stainless steel tube blank and its preparation method.

[0006] According to one aspect of the present invention, a duplex stainless steel tube blank is provided, comprising, by weight percentage, the following components: C ≤ 0.028%, Si: 0.40-0.80%, Mn ≤ 1.00%, P ≤ 0.020%, S ≤ 0.010%, Cr: 22.4-22.8%, Ni: 5.2-5.8%, Mo: 3.1-3.5%, N: 0.16-0.20%, Al: 0.01-0.03%, with the balance being Fe; and Mn / N ≥ 4, [O] content ≤ 0.0035%.

[0007] Furthermore, it possesses two phases: austenite and ferrite.

[0008] The present invention also provides a method for preparing a duplex stainless steel tube blank, wherein the duplex stainless steel tube blank is as described in any of the above claims, and the preparation method includes:

[0009] The molten steel obtained from smelting is poured into steel ingots;

[0010] The steel ingot is forged according to the temperature of the ingot to control the deformation amount of each pass;

[0011] The steel ingot is post-treated according to the surface temperature of the forged steel ingot to obtain the duplex stainless steel tube blank.

[0012] Furthermore, before casting the molten steel obtained from smelting into steel ingots, the preparation method further includes: smelting in a medium-frequency furnace, smelting in an argon-oxygen refining furnace, and refining outside the ladle to obtain molten steel.

[0013] Furthermore, in the argon-oxygen refining furnace smelting, deoxidation is carried out through Si / Al composite deoxidation, reducing the oxygen content in the molten steel to less than 0.0035%.

[0014] Furthermore, before forging the steel ingot according to the temperature-controlled deformation per pass, the preparation method further includes:

[0015] The steel ingot is placed in a heating furnace and heated to 1250°C.

[0016] Furthermore, the forging process of the steel ingot based on the temperature-controlled deformation per pass specifically involves:

[0017] The first stage of forging is carried out on steel ingots with a temperature range of 1200℃-1250℃, with the deformation amount controlled at ≤30% per pass, until the temperature of the steel ingot is less than 1200℃. The second stage of forging is carried out on steel ingots with a temperature range of 1100℃-1200℃, with the deformation amount controlled at ≥50% per pass, until the temperature of the steel ingot is less than or equal to 1100℃. Finally, the third stage of forging is carried out on steel ingots with a temperature less than or equal to 1100℃, with the deformation amount controlled at ≤20% per pass.

[0018] Furthermore, the step of post-processing the steel ingot according to the surface temperature of the forged steel ingot to obtain the duplex stainless steel tube blank specifically involves:

[0019] If the surface temperature of the forged steel ingot is greater than 950°C, an online solution treatment process is adopted to treat the steel ingot, and the water temperature is controlled below 80°C to cool the solution-treated steel ingot to obtain the duplex stainless steel tube blank.

[0020] If the surface temperature of the forged steel ingot is less than or equal to 950°C, then an offline solution treatment process is adopted to treat the steel ingot, and the solution-treated steel ingot is water-cooled to below 200°C and then air-cooled to obtain the duplex stainless steel tube blank.

[0021] Furthermore, if the surface temperature of the forged steel ingot is less than or equal to 950°C, then an offline solution treatment process is adopted to treat the steel ingot, and the solution-treated steel ingot is water-cooled to below 200°C and then air-cooled to obtain the duplex stainless steel tube blank. Specifically:

[0022] If the surface temperature of the forged steel ingot is less than or equal to 950°C, the steel ingot is placed in a heating furnace and heated to 1050°C, and a holding time is set for holding. The holding time is determined by the radius of the steel ingot. The steel ingot is then removed, water-cooled to below 200°C, and then air-cooled to obtain the duplex stainless steel tube blank.

[0023] Furthermore, the heat preservation time is equal to the radius of the steel ingot in millimeters multiplied by any value within the range of one to two, and the heat preservation time is in minutes.

[0024] As can be seen from the above technical solution, the duplex stainless steel tube blank and its preparation method provided by the present invention have the following beneficial effects:

[0025] The duplex stainless steel tube blank of the present invention has two phases: austenite and ferrite. The duplex stainless steel tube blank of the present invention has excellent hot working plasticity and can be used to produce high-quality duplex stainless steel forgings. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating a method for preparing a duplex stainless steel tube blank according to an embodiment of the present invention. Detailed Implementation

[0027] 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.

[0028] When a range of values ​​is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0029] A duplex stainless steel tube blank according to an embodiment of the present invention comprises the following components by weight percentage: C≤0.028%, Si: 0.40-0.80%, Mn≤1.00%, P≤0.020%, S≤0.010%, Cr: 22.4~22.8%, Ni: 5.2~5.8%, Mo: 3.1~3.5%, N: 0.16~0.20%, Al: 0.01-0.03%, with the balance being Fe; and Mn / N≥4, [O] content≤0.0035%.

[0030] Regarding the above proportions of the duplex stainless steel tube blank in this embodiment, a small amount of C can improve strength through solid solution strengthening, but the carbides formed by carbon and chromium will lead to local chromium depletion and reduce corrosion resistance. Therefore, this embodiment limits the C content to less than or equal to 0.028%. This content can reduce carbide precipitation and avoid intergranular corrosion during welding or at high temperatures.

[0031] Si, as a deoxidizer, can reduce oxide inclusions during smelting and improve high-temperature oxidation resistance; Al, as an auxiliary deoxidizer, can refine grains. However, excessive Si and Al may promote brittle phases, so the content of Si and Al needs to be controlled appropriately to balance deoxidation and avoid brittleness. In this example, the Si content is 0.40-0.80%, and the Al content is 0.01-0.03%.

[0032] Mn can stabilize austenite (partially replacing nickel) and promote nitrogen dissolution. Excessive Mn may reduce pitting corrosion resistance. Therefore, in this embodiment, the Mn content is controlled below 1.00%, and the synergistic optimization of Mn and N is: Mn / N ≥ 4.

[0033] Nitrogen (N) is a strong austenitic stabilizer that maintains the dual-phase structure, significantly improving pitting resistance and enhancing solid solution strengthening. However, excessive N content may lead to nitride precipitation, reducing the hot workability of the steel. Therefore, in this embodiment, the N content is controlled at 0.16–0.20%.

[0034] Cr forms a Cr2O3 passivation film, providing basic corrosion resistance and promoting ferrite phase formation. Cr needs to be balanced with austenite-forming elements (Ni, N) to maintain the two-phase ratio. Therefore, in this embodiment, the Cr content must be controlled between 22.4% and 22.8%.

[0035] Ni is an austenite phase stabilizing element that improves toughness and processing performance, while Mo is a key alloying element in duplex stainless steel, significantly enhancing resistance to pitting and crevice corrosion. However, both Ni and Mo are precious metals, and excessively high content will increase manufacturing costs. Therefore, in this embodiment, the Ni content is controlled at 5.2–5.8%, and the Mo content is controlled at 3.1–3.5%.

[0036] Oxygen is an impurity element that easily forms oxide inclusions, reducing toughness and corrosion resistance. In this embodiment, the oxygen content is controlled below 0.0035%, which can reduce the volume fraction and size of hard oxide inclusions, reduce the risk of stress concentration, and reduce the initiation of microcracks during high-temperature deformation.

[0037] The duplex stainless steel tube blank in this embodiment has two phases: austenite and ferrite.

[0038] The duplex stainless steel tube blank in this embodiment has excellent hot workability and can be used to produce high-quality duplex stainless steel forgings.

[0039] This invention also provides a method for preparing duplex stainless steel tube blanks, wherein the duplex stainless steel tube blanks are as described in any of the above embodiments, such as... Figure 1 As shown, the preparation method of this embodiment includes:

[0040] Step S001: Cast the molten steel obtained from smelting into steel ingots;

[0041] Step S002: Forge the steel ingot according to the temperature of the steel ingot and control the deformation amount of each pass;

[0042] Step S003: Perform post-treatment on the steel ingot according to the surface temperature of the forged steel ingot to obtain duplex stainless steel tube blank.

[0043] In this embodiment, before casting the molten steel into steel ingots in step S001, the preparation method further includes: smelting in a medium-frequency furnace, smelting in an argon-oxygen refining furnace, and refining outside the ladle to obtain molten steel. During the argon-oxygen refining furnace stage, deoxidation is performed using a Si / Al composite deoxidation method to reduce the oxygen content in the molten steel to less than 0.0035%. After argon-oxygen refining, the molten steel undergoes an outside-the-ladle refining process to adjust the alloy composition before being cast into steel ingots.

[0044] Before forging the steel ingot according to the temperature control of the deformation per pass in step S002, the preparation method of this embodiment further includes placing the steel ingot in a heating furnace and heating it to 1250°C. After heating in the heating furnace, the highest temperature of the steel ingot is obtained as 1250°C.

[0045] Specifically, step S002 involves controlling the deformation amount per pass based on the temperature of the steel ingot during forging: controlling the deformation amount per pass to ≤30%, performing the first stage forging on steel ingots with temperatures between 1200℃ and 1250℃ until the temperature of the steel ingot is below 1200℃; again controlling the deformation amount per pass to ≥50%, performing the second stage forging on steel ingots with temperatures between 1100℃ and 1200℃ until the temperature of the steel ingot is less than or equal to 1100℃; finally, controlling the deformation amount per pass to ≤20%, performing the third stage forging on steel ingots with temperatures less than or equal to 1100℃.

[0046] In this embodiment, the forging process of the steel ingot includes a first stage (initial stage), a second stage (stabilization stage), and a third stage (final forging stage). Each stage is divided according to temperature. The first stage is for steel ingots with a temperature range of 1200℃-1250℃ after furnace heating; the second stage is for steel ingots with a temperature range of 1100℃-1200℃ after the first stage; and the third stage is for steel ingots with a temperature less than or equal to 1100℃ after the second stage. Specifically, the first stage forging uses small deformation, i.e., deformation per pass ≤ 30%; the second stage forging uses large deformation, i.e., deformation per pass ≥ 50%; and the third stage forging uses small deformation, i.e., deformation per pass ≤ 20%.

[0047] Specifically, step S003 involves post-processing the steel ingot according to its surface temperature after forging to obtain a duplex stainless steel tube blank. If the surface temperature of the forged steel ingot is greater than 950°C, an online solution treatment process is used to treat the steel ingot, and the water temperature is controlled below 80°C to cool the solution-treated steel ingot to obtain a duplex stainless steel tube blank. If the surface temperature of the forged steel ingot is less than or equal to 950°C, an offline solution treatment process is used to treat the steel ingot, and the solution-treated steel ingot is water-cooled to below 200°C and then air-cooled to obtain a duplex stainless steel tube blank.

[0048] Specifically, if the surface temperature of the forged steel ingot is less than or equal to 950°C, an offline solution treatment process is adopted to treat the steel ingot, and the solution-treated steel ingot is water-cooled to below 200°C and then air-cooled to obtain a duplex stainless steel tube blank. The process is as follows: if the surface temperature of the forged steel ingot is less than or equal to 950°C, the steel ingot is placed in a heating furnace and heated to 1050°C, and a holding time is set for holding. The holding time t is determined by the radius R of the steel ingot; and the steel ingot is removed, water-cooled to below 200°C and then air-cooled to obtain a duplex stainless steel tube blank.

[0049] Regarding the aforementioned holding time t, the value of the holding time is equal to the value of the radius of the steel ingot in millimeters multiplied by any value in the range of one to two. The unit of the holding time is minutes, that is, t = R * (1-2) min, where R is in millimeters (mm).

[0050] The duplex stainless steel tube blank prepared in the embodiments of the present invention has two phases, austenite and ferrite, and the tube blank prepared in the embodiments of the present invention has excellent hot working plasticity and can be used to produce high-quality duplex stainless steel forgings.

[0051] The preparation methods of the embodiments of the present invention will be described below through Examples 1, 2, and 3. The composition of the tube blank in Examples 1, 2, and 3 is shown in Table 1 below:

[0052] Table 1: Composition of the tube blanks in Examples 1, 2, and 3

[0053]

[0054]

[0055] Example 1:

[0056] The actual composition of the duplex stainless steel tube billet is shown in Table 1. The preparation method is as follows: molten steel is obtained through a "medium frequency furnace + AOD + ladle refining" process, with an oxygen content of 0.0033%; the tube billet radius of the cast ingot is 140mm; a "multi-stage temperature-controlled forging" process is adopted: the deformation per pass in the initial forging stage is 28%; the deformation per pass in the stabilizing stage is 50%; the deformation per pass in the final forging stage is 17%; the surface temperature of the tube billet at the end of forging is 990℃, and online solution heat treatment is employed.

[0057] Example 2:

[0058] The actual composition of the duplex stainless steel tube billet is shown in Table 1. The preparation method is as follows: molten steel is obtained through a "medium frequency furnace + AOD + ladle refining" process, with an oxygen content of 0.0032%; the tube billet radius of the cast steel ingot is 110mm, and a "multi-stage temperature-controlled forging" process is adopted: the deformation per pass in the initial forging stage is 26%; the deformation per pass in the stabilizing stage is 52%; the deformation per pass in the final forging stage is 19%; the surface temperature of the tube billet at the end of forging is 1010℃, and online solution heat treatment is employed.

[0059] Example 3:

[0060] The actual composition of the duplex stainless steel tube billet is shown in Table 1. The preparation method is as follows: the molten steel is obtained by smelting through "medium frequency furnace + AOD + ladle refining" process, with an oxygen content of 0.0033%; the tube billet of the cast steel ingot has a radius of 90mm, and adopts the "multi-stage temperature controlled forging" process: the deformation amount of the forging passes in the initial stage is 27%; the deformation amount of the forging passes in the stable stage is 55%; the deformation amount of the forging passes in the final forging stage is 18%; the surface temperature of the tube billet is 940℃ at the end of forging, and offline solution heat treatment is adopted. After the tube billet is loaded into the furnace, it is raised to 1050℃, and the set holding time is t = 90 * 1.5 = 135min. After being taken out of the furnace, it is water-cooled and cooled to 190℃ on the surface of the tube billet before being taken out and air-cooled to room temperature.

[0061] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art should understand that these embodiments are merely illustrative of the invention and should not be construed as limiting its scope. It should be noted that any variations and substitutions equivalent to these embodiments should be considered to be covered within the scope of the claims. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing duplex stainless steel tube blanks, characterized in that, The duplex stainless steel tube blank, calculated by weight percentage, comprises the following components: C≤0.028%, Si: 0.40-0.80%, Mn≤1.00%, P≤0.020%, S≤0.010%, Cr: 22.4~22.8%, Ni: 5.2~5.8%, Mo: 3.1~3.5%, N: 0.16~0.20%, Al: 0.01-0.03%, with the balance being Fe; and Mn / N≥4, [O] content≤0.0035%. The preparation method includes: The molten steel obtained from smelting is poured into steel ingots; The steel ingot is forged according to the temperature of the ingot to control the deformation amount of each pass; The steel ingot is post-treated according to the surface temperature of the forged steel ingot to obtain the duplex stainless steel tube blank. The forging process of the steel ingot is specifically carried out by controlling the deformation amount of each pass based on the temperature of the steel ingot. The first stage of forging is performed on steel ingots with a temperature range of 1200℃-1250℃, with the deformation per pass controlled to ≤30%, until the temperature of the steel ingot is below 1200℃; the second stage of forging is performed on steel ingots with a temperature range of 1100℃-1200℃, with the deformation per pass controlled to ≥50%, until the temperature of the steel ingot is less than or equal to 1100℃; finally, the third stage of forging is performed on steel ingots with a temperature less than or equal to 1100℃, with the deformation per pass controlled to ≤20%. The specific steps for post-processing the steel ingot based on its surface temperature after forging to obtain the duplex stainless steel tube blank are as follows: If the surface temperature of the forged steel ingot is greater than 950°C, an online solution treatment process is adopted to treat the steel ingot, and the water temperature is controlled below 80°C to cool the solution-treated steel ingot to obtain the duplex stainless steel tube blank. If the surface temperature of the forged steel ingot is less than or equal to 950°C, then an offline solution treatment process is adopted to treat the steel ingot, and the solution-treated steel ingot is water-cooled to below 200°C and then air-cooled to obtain the duplex stainless steel tube blank.

2. The preparation method according to claim 1, characterized in that, Before casting the molten steel obtained from smelting into steel ingots, the preparation method further includes: smelting in a medium-frequency furnace, smelting in an argon-oxygen refining furnace, and refining outside the ladle to obtain molten steel.

3. The preparation method according to claim 2, characterized in that, In argon-oxygen refining furnace smelting, deoxidation is carried out through Si / Al composite deoxidation, reducing the oxygen content in the molten steel to less than 0.0035%.

4. The preparation method according to claim 1, characterized in that, Before forging the steel ingot according to the temperature-controlled deformation per pass, the preparation method further includes: The steel ingot is placed in a heating furnace and heated to 1250°C.

5. The preparation method according to claim 1, characterized in that, If the surface temperature of the forged steel ingot is less than or equal to 950°C, then an offline solution treatment process is adopted to treat the steel ingot, and the solution-treated steel ingot is water-cooled to below 200°C and then air-cooled to obtain the duplex stainless steel tube blank. Specifically: If the surface temperature of the forged steel ingot is less than or equal to 950°C, the steel ingot is placed in a heating furnace and heated to 1050°C, and a holding time is set for holding. The holding time is determined by the radius of the steel ingot. The steel ingot is then removed, water-cooled to below 200°C, and then air-cooled to obtain the duplex stainless steel tube blank.

6. The preparation method according to claim 5, characterized in that, The heat preservation time is equal to the radius of the steel ingot in millimeters multiplied by any value in the range of one to two, and the heat preservation time is in minutes.

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