A super austenitic stainless steel

Abstract

This invention relates to a super austenitic stainless steel, the composition of which, by weight percentage, is: C≤0.03%, Si≤0.80%, Mn≤0.80%, P≤0.030%, S≤0.010%, Ni: 15.0-20.0%, Cr: 18.0-24.0%, Mo: 5.0-7.0%, Zr: 0.001-0.005%, Y: 0.003-0.008%, with the remainder being Fe and unavoidable impurities. Furthermore, the composition of the super austenitic stainless steel also satisfies the following relationship: ([Mo] / 96) = k ×([Zr] / 91+[Y] / 89), k =718-1135, where [Mo], [Zr], and [Y] represent the weight percentages of Mo, Zr, and Y, respectively.

Description

Technical Field

[0001] This invention relates to a super austenitic stainless steel, belonging to the field of stainless steel. The super austenitic stainless steel provided by this invention overcomes the problem of severe Mo element segregation in traditional super austenitic stainless steel. The Mo element is evenly distributed and has uniform pitting corrosion resistance. Background Technology

[0002] Stainless steel is widely used in various fields of production and daily life. It is classified into many types, such as ferritic stainless steel, austenitic stainless steel, martensitic stainless steel, duplex stainless steel, and so on. As the name suggests, one of the main characteristics of stainless steel is its excellent corrosion resistance. With increasingly rapid industrial progress and increasingly demanding and harsh working environments, the requirements for the corrosion resistance of related stainless steel structural components are also becoming increasingly stringent.

[0003] In the 1980s, in order to meet the requirements of corrosion resistance, scientists proposed the concept of super austenitic stainless steel. It has a similar composition to traditional austenitic stainless steel, but the main difference is that super austenitic stainless steel contains a high content of Mo, usually up to about 6%, in order to improve the pitting corrosion resistance of stainless steel.

[0004] In actual production, it has been found that due to the high Mo content, it is particularly prone to segregation, resulting in uneven distribution of Mo content in the same super austenitic stainless steel product. Since Mo is the main element that improves pitting corrosion resistance, the segregation of Mo will lead to uneven pitting corrosion resistance of super austenitic stainless steel products.

[0005] Therefore, the technical objective of this invention is to mitigate the segregation of Mo in high-Mo-content super austenitic stainless steel and improve the uniformity of Mo content distribution to ensure more uniform pitting corrosion resistance. Summary of the Invention

[0006] This invention provides a super austenitic stainless steel. By introducing trace elements Zr and Y into the super austenitic stainless steel and simultaneously controlling the content relationship between Zr, Y and Mo, the invention effectively improves the distribution of Mo in the matrix, and finally obtains a super austenitic stainless steel with a low Mo segregation coefficient and a relatively uniform Mo element distribution.

[0007] The technical objective of this invention is achieved through the following means.

[0008] The purpose of this invention is to provide a super austenitic stainless steel, characterized in that the composition of the super austenitic stainless steel, by weight percentage, is: C≤0.03%, Si≤0.80%, Mn≤0.80%, P≤0.030%, S≤0.010%, Ni: 15.0-20.0%, Cr: 18.0-24.0%, Mo: 5.0-7.0%, Zr: 0.001-0.005%, Y: 0.003-0.008%, with the remainder being Fe and unavoidable impurities. Furthermore, the composition of the super austenitic stainless steel also satisfies the following relationship: ([Mo] / 96) = k ×([Zr] / 91+[Y] / 89), k =718-1135, where [Mo], [Zr], and [Y] represent the weight percentages of Mo, Zr, and Y, respectively.

[0009] As mentioned earlier, due to its high Mo content, super austenitic stainless steel has been found to suffer from severe Mo segregation during manufacturing. Mo is a key element for improving pitting corrosion resistance, and Mo segregation leads to uneven pitting corrosion resistance in the steel. Taking this technical problem as an opportunity, the inventors of this invention, combined with actual production conditions, conducted extensive research and experiments. They discovered that adding trace amounts of Zr and Y significantly alleviated and improved the Mo segregation problem in super austenitic stainless steel. Furthermore, with a more uniform distribution of Mo content, the pitting corrosion resistance of super austenitic stainless steel exhibited a more uniform trend.

[0010] The role of each element in the super austenitic stainless steel of this invention is described below.

[0011] Carbon: Carbon is an austenite stabilizing element, which is beneficial for improving the strength of super austenitic stainless steel. However, carbon reacts with chromium in stainless steel to form M... 23 Carbides such as C6 can drastically reduce the corrosion resistance of super austenitic stainless steel. Therefore, carbon is controlled as an impurity element in this invention. Considering the addition of raw materials and cost, it is controlled to be below 0.03%, preferably below 0.015%.

[0012] Silicon: Silicon is added as a deoxidizing element. Adding a certain amount of silicon during the smelting of super austenitic stainless steel helps reduce the oxygen content in the steel. Additionally, silicon helps improve the high-temperature oxidation resistance of super austenitic stainless steel. However, excessive silicon content can lead to the formation of non-metallic inclusions, which is detrimental to the toughness, plasticity, and corrosion resistance of super austenitic stainless steel. The super austenitic stainless steel of this invention controls the silicon content to below 0.8%, preferably 0.2-0.6%.

[0013] Manganese: Manganese plays a stabilizing role in austenite and is an austenite-forming element, which can significantly improve the strength of super austenitic stainless steel. In this invention, the manganese content in the super austenitic stainless steel is set to below 0.8%, preferably 0.2-0.6%.

[0014] Phosphorus and sulfur: Phosphorus and sulfur are unavoidable impurity elements in steel. Excessive content of both can lead to the deterioration of various properties of steel, especially corrosion resistance and strength. In this invention, the phosphorus content is controlled below 0.030% and the sulfur content is controlled below 0.01%. Of course, the lower the content of phosphorus and sulfur, the better. However, due to cost factors and raw material conditions, it is preferred that the phosphorus content is 0.005-0.03% and the sulfur content is 0.002-0.01%.

[0015] Nickel: Nickel is an austenite stabilizing element and plays a role in forming austenite. Nickel can significantly improve the strength, corrosion resistance, high temperature strength, and high temperature oxidation resistance of super austenitic stainless steel. This invention controls the nickel content to be 15.0-20.0%. Too high a nickel content will lead to an increase in the cost of super austenitic stainless steel. It is preferred to control the nickel content to be 15.0-18.0%.

[0016] Chromium: Chromium is the most important element to ensure the corrosion resistance of super austenitic stainless steel. However, chromium is a ferrite-forming element. If the content is too high, it will affect the acquisition of the austenite phase in super austenitic stainless steel. In addition, the chromium content will increase the cost. Therefore, the present invention controls the chromium content to be between 18.0-24.0%, preferably between 19.0-23.0%.

[0017] Molybdenum: Molybdenum is an important element in super austenitic stainless steel to improve corrosion resistance and pitting resistance. However, molybdenum is prone to segregation, and the higher the molybdenum content, the more obvious this segregation trend becomes. In addition, excessive molybdenum will also deteriorate plasticity and cause deterioration of processing performance. Taking all factors into consideration, the molybdenum content of this invention is set at 5.0-7.0%.

[0018] Zirconium and Yttrium: Zirconium and yttrium are trace elements added in this invention. The inventors of this invention have discovered that by adding trace amounts of yttrium and zirconium, and simultaneously controlling the content relationship between yttrium and zirconium and molybdenum, the segregation of molybdenum in the super austenitic stainless steel of this invention can be effectively controlled. Although the mechanism is not yet clear, the inventors have summarized and verified this through numerous experiments. Therefore, based on the inventors' experiments, it was found that controlling the zirconium content at 0.001-0.005% and the yttrium content at 0.003-0.008%, while simultaneously controlling ([Mo] / 96) = k ×([Zr] / 91+[Y] / 89) and k When the temperature is 718-1135, the segregation behavior of molybdenum in super austenitic stainless steel can be effectively mitigated.

[0019] As a further improvement, the PREN of the super austenitic stainless steel is ≥40, where PREN = [Cr] + 3.3 × [Mo], and [Cr] and [Mo] represent the weight percentage of Cr and Mo, respectively. By limiting PREN to above 40, excellent pitting corrosion resistance can be obtained, and PREN is preferably controlled above 42.

[0020] As a non-limiting description, the elemental segregation coefficient C of Mo in the super austenitic stainless steel is... Mo Within ±3%, where C Mo = (C2-C1) / C1×100%, where C1 is the theoretical Mo content in the super austenitic stainless steel, and C2 is the actual measured Mo content at any point in the super austenitic stainless steel. This invention, through the synergistic addition of trace amounts of zirconium and yttrium, simultaneously controls the content relationship of zirconium, yttrium, and molybdenum, ultimately obtaining a super austenitic stainless steel with minimal molybdenum segregation, whose Mo segregation coefficient is within ±3%.

[0021] As a non-limiting description, the super austenitic stainless steel is available in product types such as bars, plates, tubes, wires, and sheets. It can be manufactured into any desired shape to meet specific requirements under corresponding working conditions. Because the Mo segregation behavior of the super austenitic stainless steel of this invention is effectively controlled, it exhibits highly uniform pitting corrosion resistance, making it a good alternative to any traditional super austenitic stainless steel in any applicable field.

[0022] As a non-limiting description, the super austenitic stainless steel can be in the form of cast, rolled, forged, etc. The super austenitic stainless steel of the present invention can be made into parts in any state, such as cast, rolled, forged, etc., according to actual application requirements. Since the molybdenum segregation phenomenon of the super austenitic stainless steel of the present invention is not obvious, it is suitable for the preparation of any structural parts in any state suitable for super austenitic stainless steel.

[0023] By way of non-limiting description, the super austenitic stainless steel is used in fields such as petroleum, natural gas, marine engineering, papermaking, waste treatment, coal chemical industry, flue gas treatment, thermal power plants, and nuclear power plants. These fields are often subject to corrosion by sulfur, chlorine, etc. The super austenitic stainless steel of the present invention has uniform resistance to pitting corrosion due to the uniform distribution of Mo element, and therefore has a long service life reliability when applied to the above-mentioned harsh corrosive environments.

[0024] The present invention has the following technical effects.

[0025] This invention improves upon traditional super austenitic stainless steel by addressing the prevalent problem of severe molybdenum segregation. It adds trace amounts of zirconium and yttrium, and synergistically controls the content relationship of zirconium, yttrium, and molybdenum, effectively mitigating the segregation behavior of molybdenum in the super austenitic stainless steel matrix. This results in a super austenitic stainless steel with a more uniform molybdenum content distribution. Since molybdenum is a crucial element affecting the pitting corrosion resistance of super austenitic stainless steel, a uniform molybdenum content distribution is beneficial for obtaining super austenitic stainless steel with consistent pitting corrosion resistance. Detailed Implementation

[0026] To enable those skilled in the art to fully understand the technical solution and beneficial effects of the present invention, the following detailed explanation is provided in conjunction with specific experimental examples.

[0027] Super austenitic stainless steel was smelted according to the designed composition and element content relationship, and experimental samples were obtained by casting. The P content was controlled at 0.015±0.001%, and the S content was controlled at 0.008±0.001%. The designed composition is shown in Table 1. k =([Mo] / 96) / ([Zr] / 91+[Y] / 89), where [Mo], [Zr], and [Y] represent the weight percentages of Mo, Zr, and Y, respectively. The test sample dimensions were 300mm in diameter and 600mm in length. The Mo content was tested at five locations on the sample. The results for Examples 1-8 are recorded in Table 2, and the results for Comparative Examples 9-20 are recorded in Table 3. Sampling and sample preparation were performed according to Section 10 of GB / T20066-2006. The location selected at the center of the sample was designated C, and other locations were randomly selected and designated A, B, D, and E, respectively. The closest distance between the edges of the five locations A, B, and E must be greater than 100mm. In Tables 2-3, C... Mo =(C2-C1) / C1×100%, where C1 is the theoretical content of Mo in super austenitic stainless steel, and C2 is the actual measured Mo content at any point in super austenitic stainless steel.

[0028] Table 1: Design composition of various super austenitic stainless steels, %, balance is Fe.

[0029]

[0030] Table 2: Mo content detection results and Mo content segregation coefficients for Examples 1-8.

[0031]

[0032] Table 3: Mo content detection results and Mo content segregation coefficients of Comparative Examples 9-20.

[0033]

[0034] The above embodiments and comparative examples will be further analyzed and explained below with reference to Tables 1-3.

[0035] In Table 1, test numbers 1-8 all meet the component content requirements of this invention. k As can be seen from Table 2, the experimental results show that the measured Mo content in each part is close to the designed Mo content, and the segregation coefficient is within ±3%, indicating that the Mo element segregation is small and meets the requirements of this invention. This proves that the control of component content and content relationship is achieved. k Controlling the values ​​can effectively reduce the segregation of Mo in super austenitic stainless steel. Test numbers 9-20 show Mo and / or Y and / or Zr and / or k The values ​​do not meet the requirements of this invention. As can be seen from Table 3, the test results show that the measured Mo content in each part deviates significantly from the designed Mo content, and the segregation coefficient is large, indicating that the Mo element segregation is serious and cannot meet the requirements of this invention.

[0036] Comparative Examples 9, 10, and 14, used as comparative examples of Examples 1, 2, and 6 respectively, showed adjustments to the contents of Zr, Y, and Zr. Although the adjusted Zr and Y contents were still within the scope of the present invention, the adjusted contents... k The results in Table 3 show that the Mo element segregation in the test samples of Comparative Examples 9, 10, and 12 is severe and does not meet the requirements of this invention, indicating that... k Controlling the value is crucial to achieving the technical effects of this invention.

[0037] Comparative Examples 11, 13, 17, and 18, serving as comparative examples to Examples 3, 5, 2, and 5 respectively, showed adjustments to the contents of Y, Y, Mo, and Mo. The adjusted contents of Y and Mo were not within the scope required by this invention. k The values ​​still meet the requirements of the present invention, but the final results in Table 3 show that the Mo element segregation in the test samples of Comparative Examples 11, 13, 17 and 18 is serious and cannot meet the requirements of the present invention. This indicates that the control of Y and Mo content is crucial to obtaining the technical effect of the present invention.

[0038] Comparative Examples 12, 15, and 16, serving as comparative examples to Examples 4, 7, and 8 respectively, showed adjustments to the contents of Zr, Zr, and Y. The adjusted Zr and Y contents were not within the range required by this invention. k The values ​​also deviated from the requirements of this invention. The final results in Table 3 show that Mo element segregation was severe in the test samples of Comparative Examples 12, 15, and 16, failing to meet the requirements of this invention. This indicates that the Zr and Y content, as well as... k Controlling the value is crucial to achieving the technical effects of this invention.

[0039] Comparative Examples 19 and 20, serving as comparative examples of Examples 4 and 6 respectively, replaced all of the Y and Zr in the examples with equal amounts of Zr and Y. Specifically, Comparative Example 19 only added Zr, while Comparative Example 20 only added Y. Although the substitution... k The values ​​are still within the scope of this invention, and the contents of Zr and Y elements after substitution are also within the scope of this invention. However, since they are only added individually, the results in Table 3 show that the Mo element content in the test samples of Comparative Examples 19 and 20 also has a large segregation. Although the degree of segregation has been reduced, it still does not meet the requirement of ±3% of this invention. This indicates that the combined addition of Y and Zr is crucial to obtaining the technical effect of this invention.

[0040] In summary, it is easy to see that by adding trace amounts of Zr and Y and synergistically controlling the content relationship between Zr, Y and Mo, this invention ultimately obtains a super austenitic stainless steel with uniform Mo element distribution and slight segregation. Due to its uniform Mo element distribution, it can be expected to have uniform pitting corrosion resistance, high reliability and long service life in corrosive environments, and is suitable for the preparation of various types of structural components.

[0041] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0042] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A super austenitic stainless steel, characterized in that, The composition of the super austenitic stainless steel, by weight percentage, is: C≤0.03%, Si≤0.80%, Mn≤0.80%, P≤0.030%, S≤0.010%, Ni: 15.0-20.0%, Cr: 18.0-24.0%, Mo: 5.0-7.0%, Zr: 0.001-0.005%, Y: 0.003-0.008%, with the remainder being Fe and unavoidable impurities. Furthermore, the composition of the super austenitic stainless steel also satisfies the following relationship: ([Mo] / 96) = k ×([Zr] / 91+[Y] / 89), k =718-1135, where [Mo], [Zr], and [Y] represent the weight percentages of Mo, Zr, and Y, respectively.

2. The super austenitic stainless steel according to claim 1, characterized in that, PREN = [Cr] + 3.3 × [Mo], where [Cr] and [Mo] represent the weight percentages of Cr and Mo, respectively, and PREN ≥ 40.

3. A super austenitic stainless steel according to any one of claims 1-2, characterized in that, The elemental segregation coefficient C of Mo in the super austenitic stainless steel Mo Within ±3%, where C Mo =(C2-C1) / C1×100%, where C1 is the theoretical content of Mo in super austenitic stainless steel, and C2 is the actual measured Mo content at any point in super austenitic stainless steel.

4. A super austenitic stainless steel according to any one of claims 1-2, characterized in that, The super austenitic stainless steel is available in bar, plate, tube, wire, and sheet product types.

5. A super austenitic stainless steel according to any one of claims 1-2, characterized in that, The super austenitic stainless steel is available in cast, rolled, and forged states.

6. A super austenitic stainless steel according to any one of claims 1-2, characterized in that, The super austenitic stainless steel is used in the fields of petroleum, natural gas, marine engineering, papermaking, waste treatment, coal chemical industry, flue gas treatment, thermal power plants, and nuclear power plants.

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