Novel high-temperature pitting-corrosion-resistant stainless steel and preparation method thereof

Abstract

The invention relates to novel high-temperature pitting-corrosion-resistant stainless steel and a preparation method thereof, and belongs to the technical field of stainless steel materials, the high-temperature pitting-corrosion-resistant stainless steel comprises, by weight, less than or equal to 0.02% of C, less than or equal to 0.4% of Si, less than or equal to 0.5% of Mn, less than or equal to 0.03% of P, less than or equal to 0.03% of S, less than or equal to 4% of Ni, less than or equal to 14.5% of Cr, less than or equal to 0.3% of Mo, 0.2-0.4% of Al, 0.009-0.013% of Te, 0.03-0.08% of La, 0.5-1% of Nb, 0.01-0.1% of Re, 0.02-0.1% of Ge, 0.05-0.3% of Hf, and the balance Fe and other inevitable impurities. The size of inclusions in the stainless steel is small, the stability is good, the risk of corrosion germination of the inclusions can be effectively reduced, and the stainless steel has excellent high-temperature corrosion resistance.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel materials, in particular to a novel high-temperature pitting corrosion resistant stainless steel and a preparation method thereof. Background Art

[0002] Stainless steel is widely used in various fields of life due to its superior mechanical properties and good corrosion resistance. However, the presence of MnS inclusions in existing stainless steel can easily induce the initiation of pitting corrosion, reduce the pitting corrosion resistance of stainless steel, and make it subject to the risk of accidents caused by corrosion in some specific media and special working conditions. Therefore, it is urgent to improve the stability of MnS inclusions in stainless steel, reduce the risk of corrosion initiation of MnS inclusions, and thus improve the corrosion resistance of stainless steel. Summary of the invention

[0003] In view of one or more technical problems existing in the prior art, the present invention provides a new type of high-temperature pitting corrosion resistant stainless steel and a preparation method thereof. The stainless steel provided by the present invention has small inclusions and good stability, which can effectively reduce the risk of corrosion initiation of inclusions and has excellent high-temperature corrosion resistance.

[0004] In a first aspect, the present invention provides a novel high-temperature pitting corrosion resistant stainless steel, wherein the high-temperature pitting corrosion resistant stainless steel comprises the following components in weight percentage: C≤0.02wt%, Si≤0.4wt%, Mn≤0.5wt%, P≤0.03wt%, S≤0.03wt%, Ni≤4wt%, Cr≤14.5wt%, Mo≤0.3wt%, Al 0.2~0.4wt%, Te 0.009~0.013wt%, La0.03~0.08 wt%, Nb 0.5~1wt%, Re 0.01~0.1wt%, Ge 0.02~0.1wt%, Hf 0.05~0.3wt%, and the rest is Fe and other inevitable impurities; the weight percentage of each component satisfies the following relationship: 60.7wt%≤4Cr+1.5Ni+Al≤64.4wt%; 0.0065<(2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo)<0.045; 7≤(Te+Re+Al) / S≤49.3.

[0005] Preferably, in the high temperature pitting corrosion resistant stainless steel, S accounts for 0.01-0.03wt%, Ni accounts for 3-4wt%, Cr accounts for 14-14.5wt%, and Mo accounts for 0.2-0.3wt%.

[0006] Preferably, the pitting potential of the high temperature pitting corrosion resistant stainless steel in a 3.5% mass fraction NaCl aqueous solution at 25°C is not less than 0.25V, and the passive current density is not greater than 8.70×10 -7 μA / cm 2 .

[0007] Preferably, the pitting potential of the high temperature pitting corrosion resistant stainless steel in a 3.5% mass fraction NaCl aqueous solution at 40°C is not less than 0.30V, and the passive current density is not greater than 8.96×10 -7 μA / cm 2 .

[0008] In a second aspect, the present invention further provides a method for preparing the high temperature pitting corrosion resistant stainless steel according to the first aspect, the preparation method comprising: Converter smelting: transfer molten iron into converter, add nickel ore alloy and chromium ore when tapping, and control the converter tapping end point C≤0.02wt%; P≤0.03wt%, S≤0.03wt% in the molten iron; LF refining: The molten steel after converter smelting is transferred to the LF furnace for refining. During the refining process, lime, slag-removing agent and alloying components need to be added until the content of alloying components in the molten steel meets the requirements; the alloying components include Al, Te, La, Nb, Re, Ge and Hf; Continuous casting: The molten steel after LF refining is continuously cast to obtain high temperature pitting corrosion resistant stainless steel.

[0009] Preferably, before the molten iron is transferred into the converter, the process further includes the steps of performing dephosphorization pretreatment and desulfurization pretreatment on the molten iron.

[0010] Preferably, in the converter smelting process, the nickel ore alloy is used in an amount of 4000-5000 kg / ton of steel; and / or In the converter smelting process, the amount of chromium ore used is 480-490 kg / ton of steel.

[0011] Preferably, in the LF refining process, the amount of lime used is 5-15 kg / ton of steel; and / or The dosage of the slag-removing agent is 30-35 kg / ton of steel.

[0012] Preferably, the LF refining time is 30 to 40 minutes.

[0013] Preferably, the superheat degree of the continuous casting is 20-30°C.

[0014] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention introduces Al into stainless steel, changes the composition of the steel passivation film, improves the stability of the passivation film, and enhances the corrosion resistance of the stainless steel; at the same time, the introduction of Al can reduce the content of Ni, and reduce the production cost of the steel under the premise of ensuring the corrosion resistance of the steel. During the service of the steel, the dissolution of MnS inclusions will induce or accelerate the corrosion of the steel. By introducing Te and La, the inclusions in the stainless steel are modified and softened to form a composite inclusion containing Te-La-Al. After Te is added, a passivation film containing Te will be formed in the steel, which further improves the stability of the passivation film, and at the same time can also alleviate the problem of brittleness of the steel due to the formation of hard aluminum oxide inclusions after Al is added, improve the cutting performance of the steel, and maintain the toughness of the steel. The addition of La can promote the enrichment of Cr and Al in the passivation film, and make Al2O3 grow in a network in the passivation film, improve the compactness of the passivation film, more effectively block the invasion of corrosive substances, and thus enhance the corrosion resistance of the steel. After Nb is added, a composite inclusion with Te-La-Al as the core and Nb as the outer layer can be formed, which further reduces the mismatch between the inclusion and the matrix, improves the stability of the inclusion, thereby reducing the risk of corrosion initiation of the inclusion, and improving the corrosion resistance of the stainless steel. In addition, the addition of Re, Ge and Hf can further improve the comprehensive performance of the material. Re can enhance the oxidation resistance of stainless steel, especially at high temperatures, it can synergize with elements such as chromium and molybdenum to form a stable passivation film, thereby improving the pitting resistance; Ge can promote the uniform distribution of elements such as chromium and molybdenum in stainless steel, and help form a more stable passivation film; at the same time, germanium can also improve the mechanical strength of the passivation film and reduce the occurrence of pitting corrosion, especially in high temperature environments, germanium can effectively prevent local corrosion of the metal surface; the addition of Hf in stainless steel helps to form a stable HfO2 film, which has a high stability at high temperatures, thereby improving the oxidation resistance and pitting resistance of the material, and effectively enhancing the corrosion resistance of stainless steel in high temperature oxidation and chlorine-containing environments. The inclusions in the stainless steel provided by the present invention are small in size and have excellent high temperature corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 The peak fitting results of the passive film Al in the steel provided by Example 2 of the present invention and Comparative Example 1 after the stainless steel material was formed in a 3.5wt.% NaCl solution at 40°C for 72 hours; Figure 2The peak fitting results of the passive film Al in the steel provided in Comparative Example 1 of the present invention after the stainless steel material is formed in a 3.5wt.% NaCl solution at 40°C for 72 hours; Figure 3 The organization diagram of the stainless steel provided in Example 2 of the present invention; Figure 4 The organization diagram of the stainless steel provided in Comparative Example 1 of the present invention; Figure 5 Chip diagram of stainless steel provided in Example 2 of the present invention; Figure 6 The chip diagram of stainless steel provided in Comparative Example 9 of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0018] In a first aspect, the present invention provides a novel high-temperature pitting corrosion resistant stainless steel, wherein the high-temperature pitting corrosion resistant stainless steel comprises the following components in weight percentage: C≤0.02wt%, Si≤0.4wt%, Mn≤0.5wt%, P≤0.03wt%, S≤0.03wt%, Ni≤4wt%, Cr≤14.5wt%, Mo≤0.3wt%, Al 0.2~0.4wt%, Te 0.009~0.013wt%, La0.03~0.08 wt%, Nb 0.5~1wt%, Re 0.01~0.1wt%, Ge 0.02~0.1wt%, Hf 0.05~0.3wt%, and the rest is Fe and other inevitable impurities; the weight percentage of each component satisfies the following relationship: 60.7wt%≤4Cr+1.5Ni+Al≤64.4wt%; 0.0065<(2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo)<0.045; 7≤(Te+Re+Al) / S≤49.3.

[0019] The present invention introduces Al into stainless steel, changes the composition of the steel passivation film, improves the stability of the passivation film, and enhances the corrosion resistance of the stainless steel; at the same time, the introduction of Al can reduce the content of Ni, and reduce the production cost of the steel under the premise of ensuring the corrosion resistance of the steel. During the service of the steel, the dissolution of MnS inclusions will induce or accelerate the corrosion of the steel. Te and La are introduced to modify and soften the inclusions in the stainless steel to form a composite inclusion containing Te-La-Al. After Te is added, a passivation film containing Te will be formed in the steel, which further improves the stability of the passivation film, and at the same time can also alleviate the problem of brittleness of the steel due to the formation of hard aluminum oxide inclusions after Al is added, improve the cutting performance of the steel, and maintain the toughness of the steel. The addition of La can promote the enrichment of Cr and Al in the passivation film, and make Al2O3 grow in a network in the passivation film, improve the compactness of the passivation film, more effectively block the invasion of corrosive substances, and thus enhance the corrosion resistance of the steel. After Nb is added, a composite inclusion with Te-La-Al as the core and Nb as the outer layer can be formed, which further reduces the mismatch between the inclusion and the matrix, improves the stability of the inclusion, thereby reducing the risk of corrosion initiation of the inclusion, and improving the corrosion resistance of the stainless steel. In addition, the addition of Re, Ge and Hf can further improve the comprehensive performance of the material. Re can enhance the oxidation resistance of stainless steel, especially at high temperatures, it can synergize with elements such as chromium and molybdenum to form a stable passivation film, thereby improving the pitting resistance; Ge can promote the uniform distribution of elements such as chromium and molybdenum in stainless steel, and help form a more stable passivation film; at the same time, germanium can also improve the mechanical strength of the passivation film and reduce the occurrence of pitting corrosion, especially in high temperature environments, germanium can effectively prevent local corrosion of the metal surface; the addition of Hf in stainless steel helps to form a stable HfO2 film, which has a high stability at high temperatures, thereby improving the oxidation resistance and pitting resistance of the material, and effectively enhancing the corrosion resistance of stainless steel in high temperature oxidation and chlorine-containing environments. The inclusions in the stainless steel provided by the present invention are small in size and have excellent high temperature corrosion resistance.

[0020] C: C can improve the strength of stainless steel, but excessive C will combine with chromium in the steel to form chromium-rich carbides Cr at the grain boundaries. 23 C6 causes chromium depletion, resulting in intergranular corrosion and decreased corrosion resistance, thereby reducing the corrosion resistance of stainless steel. Therefore, the present invention controls the C content within the above range.

[0021] Si: As the silicon content in stainless steel increases, the pitting potential of the steel in a chloride-containing solution moves in a positive direction, and the segregation of Si promotes the segregation of Cr and the formation of a passivation film. The enrichment of Si on the surface of stainless steel improves the morphology of the oxide film and improves the surface self-passivation ability of stainless steel in an acid solution. However, excessive Si content will lead to a weakening of the corrosion resistance of the steel, because silicon increases the activity of carbon. When the silicon content is high, it helps the precipitation of chromium carbide and promotes the formation of chromium-poor areas, thereby reducing the corrosion resistance of the steel. Therefore, the present invention controls the Si content within the above range.

[0022] Mn: Mn can improve the high temperature strength of steel, but manganese combines with sulfur in steel to form MnS. As the amount of manganese in steel increases, the amount of MnS increases, which increases the risk of stainless steel corrosion. Therefore, the present invention controls the Mn content within the above range.

[0023] P: P is an inevitable impurity element in steel. Therefore, the P content of the present invention should not be too high to reduce its influence on the performance of stainless steel.

[0024] S: MnS inclusions have strong solubility in an acidic environment, which can easily induce pitting corrosion and reduce the pitting corrosion resistance of stainless steel. Therefore, the S content of the present invention should not be too high to reduce its impact on the performance of stainless steel.

[0025] Ni: Ni is one of the main elements of stainless steel, which can increase the austenite content and improve the corrosion resistance of steel.

[0026] Cr: Cr is one of the basic elements for increasing the corrosion resistance of stainless steel. The main function of chromium is to improve the repair ability or regeneration ability of the steel's chemical film and improve the pitting corrosion resistance of stainless steel.

[0027] Mo: Mo can reduce the defect concentration in the passivation film on the surface of stainless steel, so that a very dense and strong passivation film is formed on the surface of stainless steel, which significantly improves the corrosion resistance of stainless steel, especially the resistance to chloride ion pitting corrosion.

[0028] Al: Stainless steel with a certain aluminum content can form a protective Al2O3 film on the surface, which has better anti-oxidation performance than Cr2O3 film. At the same time, adding a certain amount of Al to steel to replace Ni can effectively reduce costs. However, after adding excessive Al, a large amount of ferrite structure will be produced in the steel, which will cause serious local corrosion of the steel and reduce the service performance of the steel. In addition, excessive Al leads to a large amount of enrichment of Al2O3, increases the thickness and brittleness of the passivation film, and makes the protective effect of the passivation film worse. Therefore, the present invention controls the Al content within the above range.

[0029] Te: Te can effectively wrap inclusions in steel, reduce the tendency of inclusions to corrode, and promote the formation of TeO2 in the passivation film, increasing the density of the passivation film. A small amount of Te cannot fully modify the inclusions, while a large amount of Te steel will generate TeO3, which ultimately leads to a decrease in the corrosion resistance of the steel. Therefore, the present invention controls the Te content within the above range.

[0030] La: La does not directly participate in the formation of the passive film, but it can promote the increase of the Cr content in the passive film of steel and the network growth of Al2O3, thereby improving the compactness of the passive film and increasing the corrosion resistance of the steel. A small amount of La has little effect on improving the corrosion resistance of steel, while a large amount of La will cause the size of inclusions in the steel to be too large, thereby increasing the corrosion tendency of the steel and reducing the corrosion resistance of the steel. Therefore, the present invention controls the La content within the above range.

[0031] Nb: Nb wraps inclusions in steel to reduce the potential difference between inclusions and the matrix, and improves the stability of the matrix. A small amount of Nb has an insignificant improvement effect, while a large amount of Nb will cause the inclusion size to be too large, reducing the stability of the inclusion. Therefore, the present invention controls the Nb content within the above range.

[0032] Re: Rhenium can enhance the oxidation resistance of stainless steel. Especially at high temperatures, it can work synergistically with elements such as chromium and molybdenum to form a stable passivation film, thereby improving pitting corrosion resistance.

[0033] Ge: Germanium can promote the uniform distribution of elements such as chromium and molybdenum in stainless steel and help form a more stable passivation film; in addition, germanium can improve the mechanical strength of the passivation film and reduce the occurrence of pitting corrosion, especially in high temperature environments, germanium can effectively prevent local corrosion on the metal surface.

[0034] Hf: The addition of hafnium to stainless steel helps to form a stable HfO2 film, which has high stability at high temperatures, thereby improving the material's oxidation resistance and pitting corrosion resistance.

[0035] According to some preferred embodiments, in the high temperature pitting corrosion resistant stainless steel, S accounts for 0.01-0.03wt%, Ni accounts for 3-4wt%, Cr accounts for 14-14.5wt%, and Mo accounts for 0.2-0.3wt%.

[0036] According to some preferred embodiments, the pitting potential of the high temperature pitting corrosion resistant stainless steel in a 3.5% mass fraction NaCl aqueous solution at 25°C is not less than 0.25V, and the passive current density is not greater than 8.70×10 -7 μA / cm 2 .

[0037] According to some preferred embodiments, the pitting potential of the high temperature pitting resistant stainless steel in a 3.5% mass fraction NaCl aqueous solution at 40°C is not less than 0.30V, and the passive current density is not greater than 8.96×10 -7 μA / cm 2 .

[0038] The stainless steel provided by the present invention has excellent pitting corrosion resistance at both normal temperature and high temperature, and the pitting corrosion resistance is better at high temperature.

[0039] In a second aspect, the present invention further provides a method for preparing the high temperature pitting corrosion resistant stainless steel according to the first aspect, the preparation method comprising: Converter smelting: transfer molten iron into converter, add nickel ore alloy and chromium ore when tapping, and control the converter tapping end point C≤0.02wt%; P≤0.03wt%, S≤0.03wt% in the molten iron; LF refining: The molten steel after converter smelting is transferred to the LF furnace for refining. During the refining process, lime, slag-removing agent and alloying components need to be added until the content of alloying components in the molten steel meets the requirements; the alloying components include Al, Te, La, Nb, Re, Ge and Hf; Continuous casting: The molten steel after LF refining is continuously cast to obtain high temperature pitting corrosion resistant stainless steel.

[0040] According to some preferred embodiments, before the molten iron is transferred into the converter, the molten iron is also subjected to a dephosphorization pretreatment and a desulfurization pretreatment step. The present invention performs a dephosphorization pretreatment and a desulfurization pretreatment on the molten iron before entering the furnace to ensure that the amount of phosphorus and sulfur elements in the molten iron entering the furnace is controlled within a certain range.

[0041] According to some preferred embodiments, during the converter smelting process, the nickel ore alloy is used in an amount of 4000-5000 kg / ton of steel.

[0042] According to some preferred embodiments, in the converter smelting process, the amount of chromium ore used is 480-490 kg / ton of steel.

[0043] According to some preferred embodiments, in the LF refining process, the amount of lime used is 5-15 kg / ton of steel. The present invention helps maintain the chemical reaction balance in the furnace, stabilize the furnace condition, and improve the controllability of the smelting process by adding a slag-removing agent.

[0044] According to some preferred embodiments, the amount of the slag-removing agent is 30-35 kg / ton of steel.

[0045] The present invention forms slag by adding lime to react with impurities such as silicon, manganese, and aluminum in molten iron. The slag can cover the surface of the molten iron to prevent the molten iron from contacting gases such as oxygen and nitrogen in the air, thereby reducing oxidation and nitridation.

[0046] According to some preferred embodiments, the LF refining time is 30 to 40 minutes.

[0047] According to some preferred embodiments, the superheat degree of the continuous casting is 20-30°C.

[0048] In order to more clearly illustrate the technical solutions and advantages of the present invention, the present invention is further described below in conjunction with the examples. The present invention does not specifically limit the sources of the various substances used in the examples and comparative examples, and they can be directly purchased or synthesized by themselves.

[0049] Example 1 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 60.7wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0444, and (Te+Re+Al) / S is 7.97; except for the above components, the rest are Fe and other unavoidable impurities.

[0050] The preparation method of the novel high temperature pitting corrosion resistant stainless steel comprises: Converter smelting: The molten iron before entering the converter is first subjected to pre-dephosphorization and pre-desulfurization treatments to control the residual phosphorus and sulfur in the molten iron before entering the converter, P: 0.01wt%, S: 0.03wt%. Argon bottom blowing throughout the process, high-draw supplementary blowing. When tapping, nickel ore alloy (4000kg / ton of steel, of which Ni accounts for 0.7wt%) and chromium ore (480kg / ton of steel, of which Cr2O3 accounts for 32wt%) are added to the ladle, and the residual carbon content is predicted according to the brightness of the flame, and the blowing is stopped to measure the temperature and take samples to determine the supplementary blowing time, and the end point carbon content is controlled to be the target value in the above table.

[0051] LF refining: The molten steel after converter smelting is transferred to LF furnace for refining. The LF refining time is 30 minutes. During the refining process, lime (10 kg / ton steel) and slag-reducing agent (30 kg / ton steel) are added to adjust the slag condition in time and ensure good fluidity of the refined slag. Then, alloying components (Al, Te, La, Nb, Re, Ge and Hf) are added, and the molten steel is sampled regularly until the content of alloying components (Al, Te, La, Nb, Re, Ge and Hf) in the molten steel reaches the target value in the above table.

[0052] Continuous casting: During the continuous casting process, the superheat of the continuous casting furnace is controlled at 25°C. Under the premise of ensuring no steel leakage, the cooling rate is increased to minimize element segregation.

[0053] Example 2 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 61.55wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0222, and (Te+Re+Al) / S is 27.6; except for the above components, the rest are Fe and other unavoidable impurities.

[0054] The preparation method of the novel high temperature pitting corrosion resistant stainless steel comprises: Converter smelting: The molten iron before entering the converter is first subjected to pre-dephosphorization and pre-desulfurization treatments to control the residual phosphorus and sulfur in the molten iron before entering the converter, P: 0.01wt%, S: 0.013wt%. Argon bottom blowing throughout the process, high-draw supplementary blowing. When tapping, nickel ore alloy (4500kg / ton of steel, of which Ni accounts for 0.7wt%) and chromium ore (480kg / ton of steel, of which Cr2O3 accounts for 32wt%) are added to the ladle, and the residual carbon content is predicted according to the brightness of the flame, and the blowing is stopped to measure the temperature and take samples to determine the supplementary blowing time, and the end point carbon content is controlled to be the target value in the above table.

[0055] LF refining: The molten steel after converter smelting is transferred to LF furnace for refining. The LF refining time is 30 minutes. During the refining process, lime (10 kg / ton steel) and slag-reducing agent (30 kg / ton steel) are added to adjust the slag condition in time and ensure good fluidity of the refined slag. Then, alloying components (Al, Te, La, Nb, Re, Ge and Hf) are added, and the molten steel is sampled regularly until the content of alloying components (Al, Te, La, Nb, Re, Ge and Hf) in the molten steel reaches the target value in the above table.

[0056] Continuous casting: During the continuous casting process, the superheat of the continuous casting furnace is controlled at 25°C. Under the premise of ensuring no steel leakage, the cooling rate is increased to minimize element segregation.

[0057] Example 3 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 64.4wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0066, and (Te+Re+Al) / S is 49.3; except for the above components, the rest are Fe and other unavoidable impurities.

[0058] The preparation method of the novel high temperature pitting corrosion resistant stainless steel comprises: Converter smelting: The molten iron before entering the converter is first subjected to pre-dephosphorization and pre-desulfurization treatments to control the residual phosphorus and sulfur in the molten iron before entering the converter, P: 0.01wt%, S: 0.01wt%. Argon bottom blowing throughout the process, high-draw supplementary blowing. When tapping, nickel ore alloy (5000kg / ton of steel, of which Ni accounts for 0.7wt%) and chromium ore (480kg / ton of steel, of which Cr2O3 accounts for 32wt%) are added to the ladle, and the residual carbon content is predicted according to the brightness of the flame, and the blowing is stopped to measure the temperature and take samples to determine the supplementary blowing time, and the end point carbon content is controlled to be the target value in the above table.

[0059] LF refining: The molten steel after converter smelting is transferred to LF furnace for refining. The LF refining time is 30 minutes. During the refining process, lime (10 kg / ton steel) and slag-reducing agent (30 kg / ton steel) are added to adjust the slag condition in time and ensure good fluidity of the refined slag. Then, alloying components (Al, Te, La, Nb, Re, Ge and Hf) are added, and the molten steel is sampled regularly until the content of alloying components (Al, Te, La, Nb, Re, Ge and Hf) in the molten steel reaches the target value in the above table.

[0060] Continuous casting: During the continuous casting process, the superheat of the continuous casting furnace is controlled at 25°C. Under the premise of ensuring no steel leakage, the cooling rate is increased to minimize element segregation.

[0061] Comparative Example 1 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 61.35wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0222, and (Te+Re+Al) / S is 12.2; in addition to the above components, the rest are Fe and other unavoidable impurities.

[0062] The preparation method of the high temperature pitting corrosion resistant stainless steel in this comparative example is the same as that of Example 2 except that the ratios of the raw materials in the above table are different.

[0063] Depend on Figure 1-2 It can be seen that compared with Comparative Example 1, Al2O3 is generated in the passivation film in Example 2, which can improve the corrosion resistance of the steel at high temperature. Figure 1 and Figure 2 The horizontal axis is the binding energy, and the vertical axis is the strength; Figure 1The bottom (lowest) line is the background, the jagged line is the original line, the top (highest) line is the fitting line of the original line, the lines corresponding to the Al / Al2O3 annotation in the figure are the Al fitting line and the Al2O3 fitting line (because the two have double peaks, they are marked together), and the line corresponding to the Al(OH)3 annotation is the Al(OH)3 fitting line. Figure 2 The bottom (lowest) line is the background, the jagged line is the original line, and the line corresponding to the Al(OH)3 annotation is the coincidence line of the original line fitting line and the Al(OH)3 fitting line.

[0064] Comparative Example 2 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 61.85wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0222, and (Te+Re+Al) / S is 50.7; except for the above components, the rest are Fe and other unavoidable impurities.

[0065] The preparation method of the high temperature pitting corrosion resistant stainless steel in this comparative example is the same as that of Example 2 except that the ratios of the raw materials in the above table are different.

[0066] Depend on Figure 3-4 It can be seen that the stainless steel in Example 2 has a martensite structure, and the steel in Comparative Example 2 has a martensite and a small amount of ferrite structure (the F marked part in the figure). It can be seen that after adding a large amount of Al to the steel, a ferrite structure is generated in the steel, which increases the tendency of local corrosion and reduces the corrosion resistance.

[0067] Comparative Example 3 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 66.8wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0222, and (Te+Re+Al) / S is 27.6; except for the above components, the rest are Fe and other unavoidable impurities.

[0068] The preparation method of the high temperature pitting corrosion resistant stainless steel in this comparative example is the same as that of Example 2 except that the ratios of the raw materials in the above table are different.

[0069] Comparative Example 4 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 61.55wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0222, and (Te+Re+Al) / S is 27.3; except for the above components, the rest are Fe and other unavoidable impurities.

[0070] The preparation method of the high temperature pitting corrosion resistant stainless steel in this comparative example is the same as that of Example 2 except that the ratios of the raw materials in the above table are different.

[0071] Comparative Example 5 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 61.55wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0222, and (Te+Re+Al) / S is 25.3; except for the above components, the rest are Fe and other unavoidable impurities.

[0072] The preparation method of the high temperature pitting corrosion resistant stainless steel in this comparative example is the same as that of Example 2 except that the ratios of the raw materials in the above table are different.

[0073] Comparative Example 6 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 61.55wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0222, and (Te+Re+Al) / S is 23.8; except for the above components, the rest are Fe and other unavoidable impurities.

[0074] The preparation method of the high temperature pitting corrosion resistant stainless steel in this comparative example is the same as that of Example 2 except that the ratios of the raw materials in the above table are different.

[0075] Comparative Example 7 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 61.55wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0222, and (Te+Re+Al) / S is 25.3; except for the above components, the rest are Fe and other unavoidable impurities.

[0076] The preparation method of the high temperature pitting corrosion resistant stainless steel in this comparative example is the same as that of Example 2 except that the ratios of the raw materials in the above table are different.

[0077] Comparative Example 8 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 61.55wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0621, and (Te+Re+Al) / S is 27.6; in addition to the above components, the rest are Fe and other unavoidable impurities.

[0078] The preparation method of the high temperature pitting corrosion resistant stainless steel in this comparative example is the same as that of Example 2 except that the ratios of the raw materials in the above table are different.

[0079] Comparative Example 9 A new type of high temperature pitting corrosion resistant stainless steel, comprising the following components in weight percentage: Among them, the weight fraction of each component satisfies the following relationship: 4Cr+1.5Ni+Al is 61.55wt%, (2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo) is 0.0222, and (Te+Re+Al) / S is 26.9; except for the above components, the rest are Fe and other unavoidable impurities.

[0080] The preparation method of the high temperature pitting corrosion resistant stainless steel in this comparative example is the same as that of Example 2 except that the ratios of the raw materials in the above table are different.

[0081] Depend on Figure 5-6 It can be seen that compared with Comparative Example 9, the chip shape of Example 2 is C-shaped or short spiral, the chips are short and small, the breaking property is good, and the cutting performance of the steel is better.

[0082] Table 1. Electrochemical parameter results of the pitting corrosion resistant stainless steel of each embodiment and comparative example

[0083] As shown in Table 1, the inclusion size of the high temperature pitting corrosion resistant stainless steel provided by the embodiment of the present invention is relatively small (not larger than 1.41 μm), and it has excellent corrosion resistance, especially high temperature corrosion resistance. The pitting potential of the high temperature pitting corrosion resistant stainless steel at 25°C is not less than 0.25 V, and the passivation current density is not greater than 8.70×10 -7 μA / cm 2 ; The pitting potential at 40°C is not less than 0.30V, and the passivation current density is not more than 8.96×10 -7 μA / cm 2 .

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A new type of high temperature pitting corrosion resistant stainless steel, characterized in that: The high temperature pitting corrosion resistant stainless steel comprises the following components in weight percentage: C≤0.02wt%, Si≤0.4wt%, Mn≤0.5wt%, P≤0.03wt%, S≤0.03wt%, Ni≤4wt%, Cr≤14.5wt%, Mo≤0.3wt%, Al 0.2~0.4wt%, Te 0.009~0.013wt%, La 0.03~0.08 wt%, Nb 0.5~1wt%, Re 0.01~0.1wt%, Ge 0.02~0.1wt%, Hf 0.05~0.3wt%, and the rest is Fe and other inevitable impurities; the weight percentage of each component satisfies the following relationship: 60.7wt%≤4Cr+1.5Ni+Al≤64.4wt%; 0.0065<(2Re+Ge+1.5Hf) / (1.2Cr+0.5Mo)<0.045; 7≤(Te+Re+Al) / S≤49.

3.

2. The high temperature pitting corrosion resistant stainless steel according to claim 1, characterized in that: In the high temperature pitting corrosion resistant stainless steel, S accounts for 0.01-0.03wt%, Ni accounts for 3-4wt%, Cr accounts for 14-14.5wt%, and Mo accounts for 0.2-0.3wt%.

3. The high temperature pitting corrosion resistant stainless steel according to claim 1, characterized in that: The pitting potential of the high temperature pitting corrosion resistant stainless steel in a 3.5% mass fraction NaCl aqueous solution at 25°C is not less than 0.25V, and the passive current density is not more than 8.70×10 -7 μA / cm 2 .

4. The high temperature pitting corrosion resistant stainless steel according to claim 1, characterized in that: The pitting potential of the high temperature pitting corrosion resistant stainless steel in a 3.5% mass fraction NaCl aqueous solution at 40°C is not less than 0.30V, and the passive current density is not more than 8.96×10 -7 μA / cm 2 .

5. A method for preparing high temperature pitting corrosion resistant stainless steel according to any one of claims 1 to 4, characterized in that: The preparation method comprises: Converter smelting: transfer molten iron into converter, add nickel ore alloy and chromium ore when tapping, and control the converter tapping end point C≤0.02wt%; P≤0.03wt%, S≤0.03wt% in the molten iron; LF refining: The molten steel after converter smelting is transferred to the LF furnace for refining. During the refining process, lime, slag-removing agent and alloying components need to be added until the content of alloying components in the molten steel meets the requirements; the alloying components include Al, Te, La, Nb, Re, Ge and Hf; Continuous casting: The molten steel after LF refining is continuously cast to obtain high temperature pitting corrosion resistant stainless steel.

6. The preparation method according to claim 5, characterized in that: Before the molten iron is transferred into the converter, the process also includes the steps of dephosphorization pretreatment and desulfurization pretreatment of the molten iron.

7. The preparation method according to claim 5, characterized in that: In the converter smelting process, the nickel ore alloy is used in an amount of 4000-5000 kg / ton of steel; and / or In the converter smelting process, the amount of chromium ore used is 480-490 kg / ton of steel.

8. The preparation method according to claim 5, characterized in that: In the LF refining process, the amount of lime used is 5-15 kg / ton of steel; and / or The dosage of the slag-removing agent is 30-35 kg / ton of steel.

9. The preparation method according to claim 5, characterized in that: The LF refining time is 30 to 40 minutes.

10. The preparation method according to claim 5, characterized in that: The superheat degree of the continuous casting is 20-30°C.

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