A stainless steel resistant to high temperature intergranular oxidation and a manufacturing method thereof

Abstract

A stainless steel resistant to high-temperature intergranular oxidation and a method for manufacturing the same. The stainless steel comprises the following components by mass: C 0.03-0.08%, Si 0.25-1.0%, Mn 0.5-2.0%, Cr 24.0-26.0%, Ni 19.0-22.0%, Mo ≤ 0.5%, N 0.02-0.06%, Nb 0.05-0.1%, P ≤ 0.045%, S ≤ 0.030%, with the remainder consisting of Fe and other unavoidable impurities. Furthermore, the following requirements must be met simultaneously: an oxide layer index of 1.1 ≤ Cr / (Ni+Si) ≤ 1.3; and an intergranular oxidation index of Nb / (C+N) ≥ 0.5. At 1000°C, the stainless steel exhibits a tensile strength (Rm) ≥ 80 MPa, an elongation (EL) ≥ 60%, and a weight gain (after oxidation for 100 hours) ≤ 3 mg / cm. 2 The oxide layer is dense and does not fall off; it can be used in power boilers, annealing furnaces, aerospace engines and other fields.

Description

Technical Field

[0001] The present invention relates to the field of austenitic stainless steel, and in particular to stainless steel resistant to high-temperature intergranular oxidation and a manufacturing method thereof. Background Art

[0002] With the development of strategic emerging industries such as new materials, new equipment, and new generation information technology, the requirements for stainless steel quality and performance are constantly increasing. High strength, high corrosion resistance, and long life have become the main strategic development directions of stainless steel products. Austenitic heat-resistant stainless steel, as a key material in high-temperature environments, is widely used in thermal power boilers, steel annealing furnaces, aerospace engine components, and other fields. Traditional austenitic heat-resistant stainless steel relies on chromium and nickel elements to form Cr2O3 and NiO oxide layers for antioxidant protection. However, in extremely high-temperature service environments, oxygen atoms tend to diffuse rapidly along the grain boundaries of heat-resistant stainless steel, and the diffusion rate of Cr atoms in the grain boundaries is much higher than the diffusion rate within the grains, resulting in the rapid formation of network Cr2O3 and Cr on the surface grain boundaries. 23 C6, resulting in grain spalling of the surface grains and a significant increase in the oxidation rate, which greatly restricts the high-temperature service life of heat-resistant stainless steel. Studies have shown that when the temperature exceeds 1000°C, the volatilization of manganese and chromium oxides in the oxide film intensifies, further weakening the density of the protective layer. Although the intergranular oxidation sensitivity has been slightly improved by low-carbon design, the self-repair ability of the oxide film under complex thermomechanical loads is still insufficient. Therefore, there is an urgent need to improve the shortcomings of heat-resistant stainless steel under high temperature conditions, where oxygen atoms diffuse and oxidize along the grain boundaries due to grain boundary weakening, resulting in grain spalling and rapid oxidation.

[0003] Chinese patent number CN201510338198.9 discloses "a titanium-containing austenitic stainless steel with excellent oxidation resistance and its manufacturing method." Its composition (wt%) is designed to be C 0.025-0.05, Si 0.6-1.0, Mn 1.2-2.0, S ≤ 0.03, P ≤ 0.0356, Cr 17.0-19.0, Ni 9.0-12.0, N 0.01-0.03, Ti ≤ 0.2, Nb ≤ 0.2, Ce 0.01-0.03, with the remainder being Fe and unavoidable impurities. This patent primarily addresses the problems of excessive Ti content in 321 stainless steel, which can lead to casting nozzle nodules and poor surface quality. This improvement is achieved by replacing Ti with Nb, rather than improving high-temperature oxidation resistance through Nb alloying.

[0004] Chinese patent number CN202210391130.7 discloses a method for preparing a high-temperature oxidation-resistant coating on the surface of 316L stainless steel. The method involves hot-dip coating of aluminum silicon to produce Fe2Al5, FeAl2, and FeAl phases. This layer forms an aluminum oxide layer at high temperatures, thus protecting the substrate. However, this method is time-consuming and costly, making it difficult to apply on a large scale.

[0005] Chinese patent number CN201710789347.2 discloses "a high-performance, high-temperature resistant ferritic stainless steel and its preparation method". Its composition design (wt%) is C≤0.5, Si0.2~2.6, Cr 17.0~27.0, Mo0.2~2.0, Nb0.2~1.8, V0.05~0.6, Ti0.1~0.7, and the rest is Fe and unavoidable impurities. The Si element is used to improve the resistance to high-temperature oxidation, and the Nb element is used to form Fe-Nb compounds to improve the high-temperature mechanical properties. The room temperature tensile strength and elongation of the alloy are greater than 510Mpa and 6.0% respectively. At 1000℃, the tensile strength is greater than 15MPa, and the average oxidation rate at 1000℃ is less than 0.1g / m 2 / h, compared with high nickel austenitic stainless steel, its strength and oxidation resistance are poor.

[0006] The above patented products have the disadvantages of insufficient high-temperature oxidation resistance, complex process and high cost, and insufficient high-temperature strength. Summary of the Invention

[0007] The present invention aims to provide a stainless steel resistant to high temperature intergranular oxidation and a method for manufacturing the same. The stainless steel has excellent high temperature oxidation resistance and high temperature mechanical properties. At 1000°C, the stainless steel has a tensile strength Rm ≥ 80 MPa, an elongation EL ≥ 60%, and a weight gain of ≤ 3 mg / cm after oxidation for 100 h. 2 The oxide layer is dense and does not fall off; in addition, the present invention does not require a complicated heat treatment process and has high production efficiency; the stainless steel can be applied to thermal power energy boilers, steel annealing heating furnaces, aerospace engine components and other fields.

[0008] To achieve the above objectives, the technical solutions of the present invention are as follows:

[0009] The present invention improves the disadvantage of heat-resistant stainless steel under high temperature conditions that oxygen atoms rapidly diffuse and oxidize along grain boundaries due to sensitization, resulting in accelerated oxidation and grain spalling, by using niobium alloying technology.

[0010] Specifically, the stainless steel resistant to high temperature intergranular oxidation of the present invention has the following chemical components by weight:

[0011] C: 0.03~0.08%,

[0012] Si: 0.25~1.0%,

[0013] Mn: 0.5~2.0%,

[0014] Cr: 24.0~26.0%,

[0015] Ni: 19.0~22.0%,

[0016] Mo: ≤0.5%,

[0017] N: 0.02~0.06%,

[0018] Nb: 0.05~0.10%,

[0019] P≤0.045%,

[0020] S≤0.030%,

[0021] The balance includes Fe and other unavoidable impurities, and must satisfy the following relationship:

[0022] Oxide layer index: 1.1≤Cr / (Ni+Si)≤1.3;

[0023] Intergranular oxidation index: Nb / (C+N)≥0.5.

[0024] Furthermore, the balance is Fe and other inevitable impurities.

[0025] Furthermore, the chemical composition of the stainless steel further includes one or more of: V≤0.2%, B≤0.0050%, and Ca≤0.0050%, in percentage by mass.

[0026] The mechanical properties of the stainless steel described in the present invention at 1000°C meet the following requirements: tensile strength Rm ≥ 80 MPa, elongation EL ≥ 60%. When held at 1000°C in air for 100 hours, the weight of the sample after holding, including the oxide scale (including broken oxides), increases by ≤ 3 mg / cm compared to the original pickled surface sample. 2 , the oxide layer is dense and does not fall off.

[0027] In the composition design of the high-temperature intergranular oxidation resistant stainless steel of the present invention:

[0028] C. A higher C content will increase the strength of the steel, but the plasticity, toughness and weldability will decrease. In order to ensure that the microalloyed steel has good welding performance, a low carbon content should generally be used. In addition, C can also form a variety of second phase particles in microalloyed steel, such as M with Cr. 23 Precipitates such as C6 and M7C3 can form fine and dispersed nano-scale precipitates with V, Nb, and T. These precipitated second-phase particles can play a role in grain refinement and precipitation strengthening.

[0029] Si is beneficial to improving the oxidation resistance of stainless steel, but too high a content will significantly reduce the plasticity of stainless steel. Si can enhance the density of the Cr2O3 film, especially in the early stage of high-temperature oxidation, where Si will form a composite layer of SiO2 and Cr2O3, further inhibiting the diffusion of oxidation.

[0030] Mn is one of the austenite stabilizing elements. It can expand the austenite region, which is beneficial to the production of stainless steel hot rolling process. Mn can reduce the activity of C and N in ferrite and austenite, and increase the solid solubility of N in austenite.

[0031] Cr, Cr is the main alloying element of stainless steel and plays a decisive role in corrosion resistance. In oxidizing media, Cr can generate Cr2O3 on the surface of steel, forming a stable and dense protective film, thereby producing a passivation effect to prevent further corrosion of the steel. Under high temperature conditions, Cr2O3 is chemically stable at high temperatures and can effectively isolate oxygen from the substrate, slowing down the oxidation reaction. When the Cr content exceeds 20%, the oxide film becomes denser and more tightly bonded to the substrate, significantly improving the resistance to high-temperature oxidation. High carbon will combine with Cr to form carbides (such as Cr 23 C6), resulting in “chromium depletion” of the matrix near the grain boundary and weakening the continuity of the oxide film.

[0032] Ni optimizes the composition and structure of the Cr2O3 layer, enhancing its density and adhesion, thereby improving the stainless steel's oxidation resistance at high temperatures. Cr is a core element in the formation of the oxide film in austenitic stainless steel, and the addition of Ni helps stabilize the Cr oxide film in high-temperature environments, reducing cracking or flaking. The Ni oxide film has a low thermal expansion coefficient, preventing it from rupturing under thermal shock conditions. Together with Cr2O3, it forms a double-layer protective structure, further enhancing oxidation resistance.

[0033] N: Elemental N can significantly increase the yield strength of steel and enhance austenite stability. By increasing lattice distortion, N increases the grain boundary migration energy of stainless steel at high temperatures, thereby inhibiting grain growth and improving high-temperature strength and creep properties. It can also increase the density of the chromium oxide layer and reduce the diffusion rate of oxygen atoms into the inner layers of the body.

[0034] Nb, the addition of Nb element can inhibit the 23 The precipitation of C6 improves the corrosion resistance of stainless steel, while the formation of Nb(CN) enhances the strength and hardness of stainless steel at both room and high temperatures. Nb helps form a stable passivation film, reduces the precipitation of harmful phases, and enhances corrosion resistance in atmospheric and dilute acid or salt environments. It also helps control grain growth during hot working, increasing the start and end temperature ranges for hot working and making the hot working process more controllable. Furthermore, Nb combines with C at grain boundaries, inhibiting the diffusion of Cr and O at these boundaries and improving grain boundary oxidation in stainless steel.

[0035] In addition to the above essential elements, one or more of V≤0.20%, B≤0.0050%, and Ca≤0.0050% may be selectively added to obtain the desired properties, calculated as a mass percentage.

[0036] V is a ferrite-forming element. Too high a V content is not conducive to the stability of the austenite structure. An upper limit control must be implemented on V. A small amount of V can form fine VN precipitates with N, which plays a strengthening role and is beneficial to improving the strength of the material. Therefore, the V content is controlled to be ≤0.20%.

[0037] A trace amount of B element in stainless steel can improve the high-temperature plasticity of the material, thereby improving the processing performance. Therefore, the B content is controlled to ≤0.0050%.

[0038] The trace amount of Ca element in stainless steel mainly plays the role of modifying steelmaking inclusions, so that inclusions with poor plasticity are modified into inclusions with good ductility. Therefore, the Ca content is controlled to be ≤0.0050%.

[0039] The innovative design features of the stainless steel composition resistant to high temperature intergranular oxidation of the present invention are:

[0040] 1. An innovative oxide layer index was proposed. By regulating the ratio of Cr, Ni, and Si within the alloy composition range to 1.1 ≤ Cr / (Ni+Si) ≤ 1.3, the stainless steel forms a dense oxide layer at temperatures above 900°C, protecting the substrate from oxidation. When Cr / (Ni+Si) < 1.1, the Cr2O3 layer content increases, with a volume ratio of Cr to its oxide of approximately 2.03 (the volume ratio of Ni to its oxide is approximately 1.7). This results in excessive internal stress in the Cr2O3 layer, which is prone to cracking and detachment, making it less effective in protecting the substrate from oxidation. When Cr / (Ni+Si) > 1.3, the Ni-rich layer content increases. The formation of the nickel-rich layer relies primarily on the rapid diffusion of Ni, while the oxygen diffusion rate is insufficient to maintain the continuous self-repair of the oxide film, resulting in an increased oxidation rate. Consequently, the oxide layer formed by the Ni and Cr elements in a specific ratio, together in a double-layer protective structure, forms a compact oxide layer that inhibits further diffusion of oxygen atoms into the metal substrate. The Si element can form a Si-rich layer at the interface between the metal matrix and the Ni and Cr oxide layers, further inhibiting the oxidation of the matrix metal. Figure 1 As shown, the outermost layer is a Ni-rich oxide layer, the second layer is a Cr2O3 layer, and the innermost layer is a SiO2 layer.

[0041] 2. An innovative intergranular oxidation index was proposed. By adding Nb and regulating the Nb / C / N ratio (Nb / (C+N) ≥ 0.5), this approach can mitigate the rapid, deep oxidation failure of stainless steel caused by grain boundary oxidation at high temperatures. Studies have shown that the diffusion rate of oxygen at grain boundaries is tens of times higher than within the grain interior, while the diffusion rate of chromium at grain boundaries is three orders of magnitude higher. Nb preferentially forms nanoscale carbonitrides in steel. These precipitates pin grain boundaries and alter the grain boundary structure. The fine carbonitrides distributed within the grain boundaries physically block the diffusion pathways for oxygen and chromium atoms, reducing their diffusion rate. Nb atoms in solid solution (atomic radius 0.143 nm) are much larger than Fe atoms (0.124 nm) and tend to accumulate at grain boundaries (concentrations can reach 1.0 atomic percent). For oxygen atoms, the Nb solution reduces the free volume at the grain boundaries, increasing the energy barrier for oxygen diffusion. For Cr atoms, the drag effect of Nb slows their segregation along grain boundaries. In addition, the bonding energy of Nb with O (ΔHf(Nb-O)=753 kJ / mol) is significantly higher than that of Cr (ΔHf(Cr-O)=402 kJ / mol), and Nb preferentially occupies the active sites for oxygen diffusion. When Nb / (C+N)≥0.5, grain boundary oxidation is significantly suppressed, such as Figure 2 shown.

[0042] When Nb / (C+N) is less than 0.5, Nb cannot be sufficiently enriched at the grain boundaries and cannot block the diffusion of O atoms, and the grain boundaries are obviously oxidized, such as Figure 3 As shown in the figure, as the oxidation progresses, the grain boundaries are completely oxidized and the grains are peeled off, resulting in the continuous oxidation and thinning of the stainless steel substrate, and finally leading to oxidation perforation failure.

[0043] In summary, the present invention adopts a unique alloy ratio design of Cr / Ni / Si elements and Nb / C / N, thereby having excellent resistance to high-temperature oxidation and resistance to high-temperature intergranular oxidation and spalling, ensuring good service performance in high-temperature environments and avoiding safety accidents caused by high-temperature oxidation failure.

[0044] The method for manufacturing high-temperature intergranular oxidation-resistant stainless steel of the present invention comprises the following steps:

[0045] 1) Smelting and casting

[0046] Smelting and casting the stainless steel into slabs according to the composition of the stainless steel;

[0047] 2) Hot rolling

[0048] The slab undergoes heating and holding, dephosphorization, rough rolling, finishing rolling, layer cooling, and coiling. The slab heating temperature is 1250-1300°C for 180-240 minutes, the finishing rolling temperature is 900-1000°C, and after layer cooling, the steel plate temperature is lowered to 650-700°C. After coiling, the coil is air-cooled.

[0049] 3) Heat treatment

[0050] The coil is subjected to solution annealing treatment at a temperature of 1050-1150°C for a time of T = (1-1.5) H, where T is in min and H represents the plate thickness in mm.

[0051] 4) Pickling

[0052] The surface of the coil is shot blasted and pickled.

[0053] Preferably, in step 1), blast furnace-AOD smelting and LF refining are adopted, and continuous casting is performed to form ingots.

[0054] Preferably, in step 2), the length of the steel coil rolled by the finishing roller is controlled to be ≤5000m, and the finishing roller needs to be replaced if the length exceeds 5000m, or the number of coils rolled by the finishing roller is controlled to be ≤10, and the finishing roller needs to be replaced if the length exceeds 10.

[0055] Preferably, in step 4), the surface roughness Ra of the coil after shot blasting is 3.0-5.0 μm.

[0056] Preferably, in step 4), the shot blasting time is 90-120 s, and the shot blasting power is 80-110 kW.

[0057] Preferably, in step 4), the pickling includes a sulfuric acid section + a mixing section, the sulfuric acid concentration in the sulfuric acid section is 400-500 g / L, the nitric acid concentration in the mixing section is 140-160 g / L, the hydrofluoric acid concentration is 30-50 g / L, and the pickling temperature is 45-65°C.

[0058] In the manufacturing method of the present invention:

[0059] In step 2), the steel of the present invention has high resistance to high temperatures due to the addition of high amounts of Ni and Nb. Therefore, the slab heating temperature is set between 1250°C and 1300°C to reduce the hot rolling load, and the heating and holding time is 180 to 240 minutes. The finishing rolling temperature is between 900°C and 1000°C to prevent a dwell time between 700°C and 900°C, which can lead to the precipitation of brittle phases and carbides and reduce the corrosion resistance and plasticity of the stainless steel.

[0060] Furthermore, due to the niobium alloying and high-nickel alloy design, the stainless steel of this invention exhibits high resistance to high temperatures, which increases the pressure on the rolls. Furthermore, the oxide scale is relatively dense, making it easy for the steel strip to scratch the rolls during finishing rolling, leading to the oxide scale being embedded in the stainless steel matrix. Therefore, during hot rolling, the length of the steel coil rolled by the finishing rolls must be controlled to ≤5000m, or the number of coils rolled by the finishing rolls must be controlled to ≤10. If the number exceeds 10 coils, the rolls must be replaced to prevent serious scratching of the rolls, which could lead to the oxide scale being embedded in the steel strip.

[0061] In step 3), the coil is subjected to solution annealing treatment to improve the corrosion resistance of the stainless steel, soften the structure, and eliminate work hardening. The solution annealing temperature is 1050~1150℃, and the solution annealing time T=(1~1.5)H, where T is in min and H is the plate thickness in mm.

[0062] In step 4), the surface roughness Ra of the coil after shot blasting is 3.0-5.0 μm. Excessive surface roughness will reduce the surface's oxidation resistance and corrosion resistance. Excessive roughness will inhibit the pickling effect, making it impossible to remove residual rust on the surface.

[0063] Preferably, in step 4), the shot blasting time is 90~120s, and the shot blasting power is 80~110kW. The shot blasting power has an important influence on the crushing of the oxide layer and the surface roughness. If the shot blasting power and time are too large, the surface roughness will increase, affecting the surface oxidation resistance and corrosion resistance, and also causing the cold-rolled surface to be rough. If the shot blasting power and time are too small, although the roughness is reduced, the oxide scale cannot be completely removed, resulting in residual oxide scale on the pickling surface. Due to the regulation of the oxide layer index, the composite oxide layer formed by the stainless steel of the present invention during solution annealing has high density and strong bonding with the matrix, making it difficult to remove the oxide layer by pickling. Therefore, compared with the conventional stainless steel pickling process, the shot blasting power is increased and the shot blasting time is extended to break up the oxide layer, so that the acid can enter the interior of the oxide layer along the cracks in the oxide layer, reducing the difficulty of pickling. However, the shot blasting power should not be too large, otherwise it will damage the surface and cause surface hardening.

[0064] In step 4), the sulfuric acid concentration in the sulfuric acid section is 400-500 g / L, the nitric acid concentration in the mixing section is 140-160 g / L, and the hydrofluoric acid concentration is 30-50 g / L. Because the composite oxide layer formed by annealing stainless steel in the present invention is highly dense and strongly adheres to the substrate, and shot blasting has limited ability to remove oxide scale, the concentration of the pickling solution must be increased compared to traditional stainless steel pickling solutions to achieve good product surface quality.

[0065] High-temperature oxidation-resistant stainless steel has a high resistance to high-temperature deformation. During hot rolling, the edges of the steel strip easily scratch the finishing rollers, causing rust to be rolled into the edges of the steel strip. To improve this defect, the present invention optimizes the process to control the length of the steel coil rolled by the finishing rollers to ≤5000m during the hot rolling process, or to control the number of rolls rolled by the finishing rollers to ≤10 rolls. If the number exceeds 10 rolls, the finishing rollers must be replaced, thereby obtaining a steel coil with no surface rust or scale residue. In addition, during the pickling stage, because the optimized oxide layer is compact and has strong adhesion to the substrate, increased shot blasting intensity and shot blasting time are required to break the oxide layer into a loose state, reducing the difficulty of pickling. Thus, the present invention has obtained a steel coil with a good surface by optimizing the rolling rollers and shot blasting process.

[0066] Beneficial effects of the present invention:

[0067] 1. The present invention optimizes the structure and thermal expansion coefficient of the oxide layer and improves the high-temperature oxidation resistance of the oxide layer by regulating the oxide layer index: 1.1≤Cr / (Ni+Si)≤1.3.

[0068] 2. The present invention regulates the intergranular oxidation index, i.e., Nb / (C+N) ≥ 0.5. NbC inhibits the diffusion rate of O and Cr atoms along the grain boundaries, thereby improving high-temperature strength and alleviating the defect of grain spalling caused by grain boundary oxidation at high temperatures.

[0069] 3. By optimizing the hot rolling and pickling shot blasting processes, the surface defects of hot rolled oxide scale penetrating into the base material and the oxide scale being difficult to remove by pickling are avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 This is a SEM photo of the composite Cr, Ni, and Si oxide layer in the stainless steel of the present invention;

[0071] Figure 2 This is a SEM photograph of the grain boundary of the oxide layer when Nb / (C+N) in the composition of the stainless steel of the present invention is ≥0.5;

[0072] Figure 3 This is a SEM photograph of the grain boundary of the oxide layer when Nb / (C+N) is less than 0.5 in the composition of the stainless steel of the present invention. DETAILED DESCRIPTION

[0073] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0074] The chemical compositions of the embodiments and comparative examples are shown in Table 1, with the remainder comprising Fe and other unavoidable impurities. The manufacturing process parameters for the embodiments and comparative examples are shown in Table 2. The performance results of the embodiments and comparative examples are shown in Table 3.

[0075] Compared with Examples 1 to 8, the oxide layer index of Comparative Example 1 is less than 1.1, and the Ni content is relatively high, which reduces the diffusion of oxygen atoms, resulting in insufficient self-repair of the oxide layer, increasing the oxidation rate, and reducing the service life.

[0076] Compared with Examples 1 to 8, the oxide layer index of Comparative Example 2 is greater than 1.3, and the Cr content is too high, which increases the proportion of the Cr2O3 layer, causes the oxide layer to expand in volume and fragment, and aggravates oxidation.

[0077] Compared with Examples 1 to 8, Comparative Example 3 has insufficient Nb content and an intergranular oxidation index of less than 0.5, which leads to intergranular oxidation, grain spalling, oxide layer rupture, and aggravated oxidation.

[0078] In Comparative Example 4, compared with Example 1, the shot blasting power was reduced to 70 kW, and the oxide scale was insufficiently fragmented, resulting in the inability to completely remove the surface oxide scale by pickling, and residual oxide scale defects appeared on the surface.

[0079] Compared with Example 1, in Comparative Example 5, the shot blasting time is less than 90 seconds, resulting in residual oxide scale defects on the surface.

[0080] Compared with Examples 1 to 8, in Comparative Example 6, since the continuous rolling length of the finishing roller reaches 6410 m, the surface of the finishing roller is severely worn, resulting in the embedding of oxide scale into the steel matrix.

[0081] Compared with Examples 1 to 8, Comparative Example 7 does not add Nb element. On the one hand, intergranular oxidation is aggravated at high temperature and the oxidation resistance is reduced. On the other hand, there is no precipitation phase such as NbC, which reduces the high temperature strength.

[0082] The above embodiments and comparative examples illustrate that only qualified stainless steel products can be obtained according to the composition design and process parameters of the present invention.

[0083] The stainless steel of the present invention has excellent mechanical properties: the tensile strength of the stainless steel in the example is higher than 80 MPa at 1000°C, and the elongation is about 70-80%. When the sample is kept at 1000°C in air for 100 hours, the weight of the sample after the holding period, including the oxide scale (including broken oxides), increases by ≤3 mg / cm compared to the original pickled surface sample. 2 , the oxide layer is dense and does not fall off.

[0084]

[0085]

[0086]

Claims

1. A stainless steel resistant to high temperature intergranular oxidation, characterized in that: The mass percentage of its components is: C：0.03~0.08%， Si: 0.25~1.0%, Mn: 0.5~2.0%, Cr：24.0~26.0%， Ni: 19.0~22.0%, Mo≤0.5%, N：0.02~0.06%， Nb: 0.05~0.10%, P≤0.045%， S≤0.030%， The balance includes Fe and other unavoidable impurities, and must satisfy the following relationship: Oxide layer index: 1.1≤Cr / (Ni+Si)≤1.3; Intergranular oxidation index: Nb / (C+N)≥0.

5.

2. The high temperature intergranular oxidation resistant stainless steel according to claim 1, characterized in that: The remainder of the composition is Fe and other inevitable impurities.

3. The high temperature intergranular oxidation resistant stainless steel according to claim 1 or 2, characterized in that: The composition of the stainless steel further includes one or more of: V≤0.2%, B≤0.0050%, and Ca≤0.0050%, in percentage by mass.

4. The high temperature intergranular oxidation resistant stainless steel according to claim 1 or 2, characterized in that: The stainless steel has a tensile strength Rm ≥ 80 MPa, an elongation EL ≥ 60% at 1000°C, and a weight gain of ≤ 3 mg / cm after oxidation for 100 hours. 2 , the oxide layer is dense and does not fall off.

5. The high temperature intergranular oxidation resistant stainless steel according to claim 3, characterized in that: The stainless steel has a tensile strength Rm ≥ 80 MPa, an elongation EL ≥ 60% at 1000°C, and a weight gain of ≤ 3 mg / cm after oxidation for 100 hours. 2 , the oxide layer is dense and does not fall off.

6. The method for producing high-temperature intergranular oxidation-resistant stainless steel according to any one of claims 1 to 5, wherein: The steps include: 1) Smelting and casting Smelting and casting the stainless steel into slabs according to the composition of the stainless steel; 2) Hot rolling The slab undergoes heating and holding, dephosphorization, rough rolling, finishing rolling, layer cooling, and coiling. The slab heating temperature is 1250-1300°C for 180-240 minutes, the finishing rolling temperature is 900-1000°C, and after layer cooling, the steel plate temperature is lowered to 650-700°C. After coiling, the coil is air-cooled. 3) Heat treatment The coil is subjected to solution annealing treatment at a temperature of 1050-1150°C for a time of T = (1-1.5) H, where T is in min and H represents the plate thickness in mm. 4) Pickling The surface of the coil is shot blasted and pickled.

7. The method for producing high-temperature intergranular oxidation resistant stainless steel according to claim 6, wherein: In step 1), blast furnace-AOD smelting and LF refining are adopted, and continuous casting is performed to form ingots.

8. The method for producing high-temperature intergranular oxidation resistant stainless steel according to claim 6, wherein: In step 2), the length of the steel coil rolled by the finishing roller is controlled to be ≤5000m. If the length exceeds 5000m, the finishing roller needs to be replaced. Alternatively, the number of coils rolled by the finishing roller is controlled to be ≤10. If the length exceeds 10, the finishing roller needs to be replaced.

9. The method for producing high-temperature intergranular oxidation resistant stainless steel according to claim 6, wherein: In step 4), the surface roughness Ra of the coil after shot blasting is 3.0~5.0μm.

10. The method for producing high-temperature intergranular oxidation resistant stainless steel according to claim 6 or 9, characterized in that: In step 4), the pickling includes a sulfuric acid section + a mixing section. The sulfuric acid concentration in the sulfuric acid section is 400-500 g / L, the nitric acid concentration in the mixing section is 140-160 g / L, and the hydrofluoric acid concentration is 30-50 g / L. The pickling temperature is 45-65°C.

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