Method for eliminating precipitated phase of hot-rolled structure of economical austenitic stainless steel

Abstract

The invention discloses a method for eliminating a precipitated phase of a hot-rolled structure of economical austenitic stainless steel, and relates to the technical field of stainless steel material treatment. According to the method for eliminating the precipitated phase of the hot-rolled structure of the economical austenitic stainless steel, chemical components and process parameters are synergistically optimized, so that the carbonitride precipitated phase does not appear in the hot-rolled hot coil structure, and the grain boundary binding force is remarkably enhanced; the problem of performance deterioration caused by a precipitated phase of the traditional economical austenitic stainless steel is fundamentally solved; by eliminating a precipitated phase, the material achieves balanced and excellent performance in the aspects of mechanical properties such as strength and toughness, and meanwhile, the reasonable proportion of Cr and Ni ensures that the material has good corrosion resistance and plasticity and toughness; the hot rolling structure is pure, the grain boundary weakening phenomenon caused by a precipitated phase does not exist, the risks of cracking, damage and the like do not exist in the online machining process, and the safety and stability of subsequent machining are greatly improved.

Description

Technical Field

[0001] This application belongs to the field of stainless steel material processing technology, and in particular relates to a method for eliminating precipitated phases in the hot-rolled structure of economical austenitic stainless steel. Background Technology

[0002] With the rapid development of society and the economy, the concept of low-carbon and environmental protection has taken root in people's hearts. The civilian stainless steel field has put forward higher requirements for the economy, high strength and environmental protection of materials. On the one hand, traditional carbon steel is difficult to meet the needs of high-end civilian scenarios in terms of corrosion resistance and strength, while conventional austenitic stainless steel has a high cost due to its high Cr and Ni content, which limits its large-scale promotion and application. On the other hand, the market urgently needs a low-cost, high-strength stainless steel material that can reduce the amount of material used by reducing the thickness, thus achieving low-carbon and environmental protection, and also reduce the difficulty of subsequent installation, adapting to the wide range of needs in the fields of construction and transportation.

[0003] Against this backdrop, economical austenitic stainless steel emerged. This type of steel, by optimizing its chemical composition and reducing the content of precious metals such as Cr and Ni, significantly lowers production costs while maintaining basic corrosion resistance. Simultaneously, by increasing the content of C and N elements, it utilizes interstitial strengthening and martensitic transformation strengthening effects to significantly enhance material strength, perfectly meeting the core needs of the civilian sector. However, the introduction of high C and N elements also brings significant technical challenges: during hot rolling and subsequent cooling, the steel is highly prone to precipitating carbonitride phases. These precipitates are mainly concentrated at the austenitic grain boundaries, significantly weakening grain boundary bonding. This not only leads to a decrease in the material's mechanical properties (such as toughness and plasticity) but also reduces its corrosion resistance, seriously affecting the safety of hot-rolled processing and even causing product scrap, thus limiting the industrial application of this type of economical austenitic stainless steel.

[0004] Current technologies for controlling precipitates in austenitic stainless steel primarily focus on high-alloy steels, employing complex heat treatment processes (such as solution treatment) to eliminate precipitates. However, these methods are costly and energy-intensive, contradicting the low-cost positioning of economical austenitic stainless steels. For low-alloy, high-C / N content economical austenitic stainless steels, no effective precipitate control scheme has yet been developed. Existing hot rolling and coiling processes cannot avoid the carbonitride precipitation-sensitive temperature range, resulting in the persistent precipitate problem in the hot-rolled microstructure, becoming a key bottleneck restricting its large-scale application. Therefore, developing a low-cost, high-efficiency precipitate elimination method suitable for economical austenitic stainless steels has become an urgent technical problem to be solved in the industry. Summary of the Invention

[0005] To address some or all of the technical problems existing in the prior art, this application provides a method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel.

[0006] This application provides a method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel, comprising the following steps: Step S1: Material selection, austenitic stainless steel is selected; Step S2: Slab rough rolling. The slab of the above material is heated to 1200±50℃, and the initial rolling temperature is controlled at 1150-1200℃. Rolling is carried out in 5-7 passes. Step S3: Finish rolling of the billet. The billet after rough rolling is finished in 5-7 passes, and the final rolling temperature is controlled at 900-1050℃. Step S4: Hot coiling. After finishing rolling, the coil is put into laminar flow cooling. The coiling temperature is controlled at 300-500℃ to complete the hot coiling and thus eliminate the precipitates in the hot-rolled structure.

[0007] Preferably, the chemical composition of the austenitic stainless steel is as follows: C≤0.18%, Cr: 13.0%~16.0%, Ni: 0.50%~1.50%, Cu≤1.0%, N: 0.10%~0.25%, Mn: 7.0~10.0%, Si≤1.0%.

[0008] Preferably, the chemical composition of the austenitic stainless steel is as follows: C: 0.10%, Cr: 13.4%, Ni: 0.51%, Cu: 0.15%, N: 0.20%, Mn: 9.4%, Si: 0.4%.

[0009] Preferably, the billet is heated to 1230 ℃, the initial rolling temperature is 1200 ℃, and 5 rolling passes are used.

[0010] Preferably, the rough-rolled billet is subjected to 7 passes of finish rolling, and the final rolling temperature is controlled at 1000℃.

[0011] Preferably, after finishing rolling, laminar flow cooling is applied, and the coiling temperature is controlled at 480℃.

[0012] Preferably, the chemical composition of the austenitic stainless steel is as follows: C: ≤0.14%, Cr: 13.8%, Ni: 1.33%, Cu: 0.89%, N: 0.21%, Mn: 9.90%, Si: 0.45%.

[0013] Preferably, the billet is heated to 1220°C, the initial rolling temperature is 1180°C, and 7 rolling passes are used.

[0014] Preferably, the rough-rolled billet is subjected to 7 passes of finish rolling, and the final rolling temperature is controlled at 980℃.

[0015] Preferably, after finishing rolling, laminar flow cooling is applied, and the coiling temperature is controlled at 420℃.

[0016] The method for eliminating precipitates in the hot-rolled microstructure of economical austenitic stainless steel disclosed in this application has the following advantages and positive effects: By synergistically optimizing the chemical composition and process parameters, no carbonitride precipitates appeared in the microstructure of the hot-rolled coil, and the grain boundary bonding force was significantly enhanced, fundamentally solving the performance defects caused by precipitates in traditional economical austenitic stainless steel. The grain refinement effect was significant, and the material achieved balanced and excellent performance in terms of mechanical properties such as strength and toughness. At the same time, the reasonable ratio of Cr and Ni elements ensured that the material had good corrosion resistance. The hot-rolled coil microstructure was pure, without grain boundary weakening caused by precipitates, and there was no risk of cracking or breakage during online processing, which greatly improved the safety and stability of subsequent processing. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are only for further understanding of the embodiments of this application and constitute a part of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 The metallographic image shows the microstructure of hot-rolled coils produced without using the method described in this application. Figure 2 This is a metallographic image of the microstructure of a hot-rolled coil produced using the method described in this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0019] The method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel according to this application includes the following steps: Step S1: Material selection, using austenitic stainless steel; the specific chemical composition of the austenitic stainless steel is: C≤0.18%, Cr: 13.0%~16.0%, Ni: 0.50%~1.50%, Cu≤1.0%, N: 0.10%~0.25%, Mn: 7.0~10.0%, Si≤1.0%; by controlling the key components C, N, Cr, and Ni, the risk of carbonitride precipitation is reduced while ensuring the material's economy, corrosion resistance, and high strength.

[0020] Step S2: Slab rough rolling. The slab of the above material is heated to 1200±50℃, and the initial rolling temperature is controlled at 1150-1200℃. Rolling is carried out in 5-7 passes. The slab heating temperature ensures that the slab structure is fully homogenized, and the initial rolling temperature ensures that the hot rolling is in a good austenitic plastic deformation range.

[0021] Step S3: Finish rolling of the billet. The billet after rough rolling is finished in 5-7 passes, and the final rolling temperature is controlled at 900-1050℃. Multi-pass rolling is used to ensure that the deformation rate of each pass is reduced, thereby reducing the risk of carbonitride precipitation caused by deformation heat. The control of the final rolling temperature ensures that the microstructure is austenitic during hot rolling, thereby reducing the risk of C and N precipitation.

[0022] Step S4: Hot coiling. After finishing rolling, the coil is placed in laminar flow cooling, with the coiling temperature controlled at 300-500℃ to complete the hot coiling process, thereby eliminating precipitates in the hot-rolled microstructure. If the coiling temperature is too high, the hot coil will remain in the carbonitride precipitation-sensitive temperature range for an extended period during cooling, resulting in a large amount of carbonitride precipitation at grain boundaries. If the coiling temperature is too low, the high strength of the steel will make coiling difficult, easily causing scratches on the surface of the hot coil and potentially leading to scrapped coils.

[0023] This application provides two specific embodiments.

[0024] Example 1: The specific chemical composition of austenitic stainless steel is as follows: C: 0.10%, Cr: 13.4%, Ni: 0.51%, Cu: 0.15%, N: 0.20%, Mn: 9.4%, Si: 0.4%.

[0025] The billet is rough rolled, heated to 1230 ℃, and the initial rolling temperature is 1200 ℃, using 5 rolling passes.

[0026] The billet is finished by 7 passes of finishing rolling after rough rolling, and the final rolling temperature is controlled at 1000℃.

[0027] Hot coiling is performed, and after finishing rolling, it is put into laminar flow cooling. The coiling temperature is controlled at 480℃ to complete the hot coil rolling, thereby eliminating the precipitated phases in the hot-rolled structure.

[0028] Metallographic examination of the hot-rolled coils revealed no carbonitride precipitates, and the grain boundaries were clear and intact, with no precipitate adhesion or grain boundary weakening. The microstructure exhibited a uniform single austenite structure with regular grain size distribution and no obvious grain coarsening or unevenness.

[0029] Example 2: Material selection: The specific chemical composition of austenitic stainless steel is as follows: C: ≤0.14%, Cr: 13.8%, Ni: 1.33%, Cu: 0.89%, N: 0.21%, Mn: 9.90%, Si: 0.45%.

[0030] The billet is rough rolled, heated to 1220℃, and the initial rolling temperature is 1180℃, using 7 rolling passes.

[0031] The billet is finished by 7 passes of finishing rolling after rough rolling, with the final rolling temperature controlled at 980℃.

[0032] Hot coiling is performed, and after finishing rolling, it is put into laminar flow cooling. The coiling temperature is controlled at 420℃ to complete the hot coiling, thereby eliminating the precipitated phases in the hot-rolled structure.

[0033] Metallographic examination of the hot-rolled coils revealed excellent microstructure purity, with no carbonitride precipitates found. The austenitic matrix structure was continuous and uniform, with regular grain size distribution, clear grain boundaries, no impurities, and strong bonding.

[0034] The overall workflow of this invention follows the sequence of "material selection → rough rolling of cast billet → fine rolling of cast billet → hot coiling", with each link working together to comprehensively control the generation of precipitates from the source to the end.

[0035] The specific workflow is as follows: First, based on the performance requirements of economical austenitic stainless steel, the content range of key elements such as C, N, Cr, and Ni is precisely controlled to reduce the thermodynamic risk of carbonitride precipitation while ensuring economy and high strength. Secondly, the billet with the controlled composition is fed into a continuous heating furnace and heated at a preset temperature to ensure that the microstructure is homogenized. Then, it is subjected to multiple rough rolling passes at a suitable initial rolling temperature to gradually disperse the deformation and reduce the precipitation caused by deformation heat. Next, the rough-rolled billet enters the finishing mill, where multiple passes of finishing rolling further refine the grains and control the final rolling temperature within the austenitic stable range to ensure the purity of the microstructure after rolling. Finally, the finished strip is coiled on a coiler. During the coiling process, laminar cooling is applied to rapidly reduce the hot-rolling temperature, control the coiling temperature within a preset range, shorten the residence time in the precipitation-sensitive temperature range, and ultimately eliminate the precipitates in the hot-rolled microstructure.

[0036] As attached Figure 1 The image shows organizational features that were not created using the method described in this application.

[0037] Appendix Figure 1In the hot-rolled microstructure, there are a large number of discrete / aggregate structures marked with arrows. These are carbonitride precipitates, which are distributed in the grain boundaries and intragranular regions, resulting in poor microstructure uniformity and weakening of grain boundaries by the precipitates. At the same time, the microstructure exhibits a mixed multiphase state without obvious single matrix microstructure characteristics.

[0038] The presence of these precipitates directly reduces the toughness, plasticity, and corrosion resistance of the material, while weakening the grain boundary bonding force and increasing the risk of cracking and breakage during subsequent processing.

[0039] As attached Figure 2 The diagram shows the organizational features of an organization employing the method described in this application.

[0040] Appendix Figure 2 In the hot-rolled state, there are no obvious precipitates, and the microstructure exhibits a uniform and continuous matrix structure (which conforms to the single austenitic microstructure characteristics of economical austenitic stainless steel); the grain boundaries are clear and there are no precipitates attached, and the overall structure is pure and the uniformity is significantly improved.

[0041] This application targets economical austenitic stainless steel grades. By controlling the chemical composition, hot rolling, and coiling processes, the risk of carbonitride precipitation is reduced, the rolling temperature is increased, and the coiling temperature is decreased, ultimately eliminating precipitates in the hot-rolled microstructure. Through these measures, the produced hot-rolled coils are free of precipitates, ensuring safe production and producing hot-rolled coils with satisfactory microstructure and properties.

[0042] It should be noted that, unless otherwise expressly specified and limited, the term "connection" or its synonyms should be interpreted broadly in this document. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. Furthermore, expressions such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. At the same time, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. In addition, the terms "front," "rear," "left," "right," "upper," and "lower" in this document refer to the placement states shown in the accompanying drawings.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel, characterized in that, Includes the following steps: Step S1: Material selection, austenitic stainless steel is selected; Step S2: Slab rough rolling. The slab of the above material is heated to 1200±50℃, and the initial rolling temperature is controlled at 1150-1200℃. Rolling is carried out in 5-7 passes. Step S3: Finish rolling of the billet. The billet after rough rolling is finished in 5-7 passes, and the final rolling temperature is controlled at 900-1050℃. Step S4: Hot coiling. After finishing rolling, the coil is put into laminar flow cooling. The coiling temperature is controlled at 300-500℃ to complete the hot coiling and thus eliminate the precipitates in the hot-rolled structure.

2. The method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel according to claim 1, characterized in that, The specific chemical composition of the austenitic stainless steel is as follows: C≤0.18%, Cr: 13.0%~16.0%, Ni: 0.50%~1.50%, Cu≤1.0%, N: 0.10%~0.25%, Mn: 7.0~10.0%, Si≤1.0%.

3. The method for eliminating precipitates in the hot-rolled microstructure of economical austenitic stainless steel according to claim 2, characterized in that, The specific chemical composition of the austenitic stainless steel is as follows: C: 0.10%, Cr: 13.4%, Ni: 0.51%, Cu: 0.15%, N: 0.20%, Mn: 9.4%, Si: 0.4%.

4. The method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel according to claim 3, characterized in that, The billet is heated to 1230 ℃, and the initial rolling temperature is 1200 ℃. It is rolled in 5 passes.

5. The method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel according to claim 4, characterized in that, The rough-rolled billet is finished by 7 passes of finishing rolling, with the final rolling temperature controlled at 1000℃.

6. The method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel according to claim 5, characterized in that, After finishing rolling, the coil is subjected to laminar flow cooling, and the coiling temperature is controlled at 480℃.

7. The method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel according to claim 2, characterized in that, The specific chemical composition of the austenitic stainless steel is as follows: C: ≤0.14%, Cr: 13.8%, Ni: 1.33%, Cu: 0.89%, N: 0.21%, Mn: 9.90%, Si: 0.45%.

8. The method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel according to claim 7, characterized in that, The billet is heated to 1220℃, and the initial rolling temperature is 1180℃. It is rolled in 7 passes.

9. The method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel according to claim 8, characterized in that, The rough-rolled billet is finished by 7 passes of finishing rolling, with the final rolling temperature controlled at 980℃.

10. The method for eliminating precipitated phases in the hot-rolled microstructure of economical austenitic stainless steel according to claim 9, characterized in that, After finishing rolling, the coiling is subjected to laminar flow cooling, and the coiling temperature is controlled at 420℃.

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