Ultra-pure ferritic stainless steel and manufacturing method therefor and application thereof

Abstract

The present invention relates to the technical field of stainless steel product production and manufacturing, and relates to ultra-pure ferritic stainless steel and a manufacturing method therefor and an application thereof. The ultra-pure ferritic stainless steel provided by the present invention comprises the following components in percentage by weight: C ≤ 0.025%, N ≤ 0.025%, Si ≤ 1.00%, Mn ≤ 1.20%, Cr: 18.00%-24.00%, Nb: 0.40%-0.75%, Mo: 1.75%-2.50%, W: 0.80%-1.20%, Cu: 0.30%-0.60%, Al ≤ 0.015%, Ti ≤ 0.01%, P ≤ 0.03%, S ≤ 0.01%, and the balance being Fe and inevitable impurities, wherein the conditions 3.4% ≤ 2Nb + Mo + W ≤ 5.2% and 32% ≤ Cr + 4.7Mo + 2.4W + 11.5Cu ≤ 45% are satisfied. In the present invention, by means of composite strengthening of Nb, W and Mo and reasonable matching of Cu, Al and Ti, the obtained ultra-pure ferritic stainless steel can work and serve at a higher temperature, has good high-temperature strength, high-temperature fatigue life and high-temperature oxidation resistance, has good cold machining performance and good brazing performance, and can be industrially produced.

Description

Ultra-pure ferritic stainless steel, manufacturing method and application thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of stainless steel product manufacturing, and relates to an ultra-pure ferritic stainless steel, a manufacturing method and application thereof, in particular to an ultra-pure ferritic stainless steel with excellent high-temperature resistance and a manufacturing method and application thereof. BACKGROUND

[0002] The ultra-pure ferritic stainless steel has very low C and N contents, generally [C+N]≤250ppm, and a certain amount of stabilizing elements such as Ti and Nb is added. Due to the low content of alloying elements and the absence of expensive alloying elements such as Ni, excellent corrosion resistance, especially intergranular corrosion resistance, can be achieved, which has obvious cost advantages. Therefore, the ultra-pure ferritic stainless steel is widely used in the fields of automobiles, buildings, household appliances and heat exchangers.

[0003] In the automobile exhaust system, automobile exhaust is discharged to the outside through the exhaust manifold, manifold converter, front pipe, main catalytic converter, middle pipe and muffler in turn. Because the temperature of the exhaust and the working environment of each part vary with the location, the performance requirements of the materials used by different parts are also different. The hot end needs to work at a certain high temperature, generally greater than 600℃, and the temperature at the manifold can exceed 800℃.

[0004] Different stainless steel varieties are selected according to the cold and hot end environment of the exhaust system. In order to obtain high high-temperature strength, the addition amount of Nb element is increased, such as 441 commonly used in the hot end of the automobile exhaust system. In order to improve corrosion resistance and oxidation resistance, Mo element is added, such as 436L and 444. In order to simultaneously consider high high-temperature strength and corrosion resistance, 436L and 444 with high Nb content are usually used. The Nb content is generally not more than 0.5%, and around 0.4% can obtain high high-temperature strength. The Mo element is added to about 2% to obtain good corrosion resistance and oxidation resistance.

[0005] With the release and gradual implementation of the "China VI" standard, the emission limit of automobile exhaust pollutants is more stringent, and the working temperature of the hot end is further increased. At the same time, as one of the harmful gases in engine exhaust, the working temperature of the exhaust gas recirculation system (EGR) for purifying nitrogen oxides NOx will also increase. When the temperature exceeds 900℃, the currently commonly used ultra-pure ferritic stainless steel cannot meet the high-temperature resistance and oxidation resistance requirements at higher temperatures. According to the original idea, the addition amount of Nb is further increased to improve the high-temperature strength to some extent, but when the Nb content is high, segregation is prone to occur, causing uneven material performance and affecting the processing performance and use performance. Especially for many high-temperature parts, brazing process is used during processing, and the wetting property of the existing most materials is poor, which limits the application scenarios of the materials.

[0006] Therefore, the original steel grade design has been limited, and a new ultra-pure ferritic stainless steel material that can work at a higher temperature needs to be developed under a new idea.

[0007] SUMMARY

[0008] In view of the defects of the prior art, the application provides an ultra-pure ferritic stainless steel and a manufacturing method and application thereof.

[0009] The ultra-pure ferritic stainless steel provided by the application comprises, by weight percentage, C≤0.025%, N≤0.025%, Si≤1.00%, Mn≤1.20%, Cr: 18.00%-24.00%, Nb: 0.40%-0.75%, Mo: 1.75%-2.50%, W: 0.80%-1.20%, Cu: 0.30%-0.60%, Al≤0.015%, Ti≤0.01%, P≤0.03%, S≤0.01%, and satisfies 3.4%≤2Nb+Mo+W≤5.2%, 32%≤Cr+4.7Mo+2.4W+11.5Cu≤45%, and the balance is Fe and inevitable impurities.

[0010] Further, the ultra-pure ferritic stainless steel comprises, by weight percentage, C≤0.015%, N≤0.015%, Si≤0.80%, Mn≤1.00%, Cr: 18.00%-21.00%, Nb: 0.40%-0.65%, Mo: 1.90%-2.40%, W: 0.90%-1.20%, Cu: 0.3%-0.5%, Al≤0.013%, Ti≤0.01%, P≤0.03%, S≤0.005%, and satisfies 3.6%≤2Nb+Mo+W≤4.9%, 33%≤Cr+4.7Mo+2.4W+11.5Cu≤41%, and the balance is Fe and inevitable impurities.

[0011] Further, the ultra-pure ferritic stainless steel comprises, by weight percentage, C≤0.01%, N≤0.01%, Si: 0.30%-0.80%, Mn: 0.40%-1.00%, Cr: 18.00%-20.00%, Nb: 0.50%-0.60%, Mo: 2.00%-2.30%, W: 1.00%-1.20%, Cu: 0.35%-0.45%, Al≤0.01%, Ti≤0.008%, P≤0.02%, S≤0.003%, and satisfies 4.0%≤2Nb+Mo+W≤4.8%, 34%≤Cr+4.7Mo+2.4W+11.5Cu≤39%, and the balance is Fe and inevitable impurities.

[0012] In another aspect, the present application also provides a method for manufacturing the ultra-pure ferritic stainless steel, comprising a smelting process, a casting process, a hot rolling process, a continuous annealing process after hot rolling, a cold rolling process and a continuous annealing process after cold rolling, wherein the molten steel prepared in the smelting process has the same composition as the ultra-pure ferritic stainless steel.

[0013] Further, in the method for manufacturing the ultra-pure ferritic stainless steel, in the hot rolling process, the heating temperature of the casting blank before hot rolling is 1200-1260℃, and the temperature of the coiling after hot rolling is 620-700℃.

[0014] Further, in the method for manufacturing the ultra-pure ferritic stainless steel, in the continuous annealing process after hot rolling, the annealing temperature is 1000-1060℃, and the holding time is 1.5-2.0 min / mm.

[0015] Further, in the method for manufacturing the ultra-pure ferritic stainless steel, the total deformation rate of the cold rolling process is ≥55%.

[0016] Further, in the method for manufacturing the ultra-pure ferritic stainless steel, in the continuous annealing process after cold rolling, the annealing temperature is 1000-1060℃, and the holding time is 0.9-1.2 min / mm.

[0017] In another aspect, the present application also provides the use of the ultra-pure ferritic stainless steel or the ultra-pure ferritic stainless steel obtained by the method in the preparation of an automobile exhaust system.

[0018] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0019] (1) The ultra-pure ferritic stainless steel obtained by the present application through the composite strengthening of Nb, W and Mo and the reasonable matching of Cu, Al and Ti can meet the working service at a higher temperature, has good high-temperature strength, high-temperature fatigue life and high-temperature oxidation resistance, has good cold working performance and good brazing performance, and can be produced industrially.

[0020] (2) The grain size of the ultra-pure ferritic stainless steel cold plate of the present application is 6-8, the tensile strength is 530-580 MPa, the high-temperature tensile strength at 900℃ is greater than 44 MPa, the high-temperature tensile strength at 1000℃ is greater than 24 MPa, the high-cycle fatigue test at 950℃ under a stress of 15 MPa with a stress ratio R=0.1 is carried out, and the service life is greater than 10 7 times; the high-temperature oxidation test at 900℃ is carried out for 1000 hours, and the oxidation weight gain is 1.4-1.5 mg / cm 2 . BRIEF DESCRIPTION OF DRAWINGS

[0021] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments with reference made to the accompanying drawings. The drawings are for purposes of illustration only and are not intended to limit the application thereto.

[0022] Figure 1 is a microstructure of the finished product of the ultra-pure ferritic stainless steel prepared in Example 1 of the present application;

[0023] Figure 2 is a comparison chart of high temperature strength of the stainless steels prepared in Examples 1-3 and Comparative Examples 4-7 of the present application;

[0024] Figure 3 is a comparison chart of high temperature oxidation weight gain of the stainless steels prepared in Example 1 and Comparative Examples 4-7 of the present application;

[0025] Figure 4 is the results of the solder spread test of the brazing wetting test of the ultra-pure ferritic stainless steel prepared in Example 1 of the present application;

[0026] Figure 5 is the results of the solder spread test of the brazing wetting test of the 444 stainless steel prepared in Comparative Example 5. DETAILED DESCRIPTION

[0027] For the purpose of fully disclosing the present application, specific embodiments are described in detail below. The process of the present application employs, except for the following content, the conventional methods or devices in the art. The following terms are understood to have the meanings generally ascribed to them by those skilled in the art unless otherwise defined.

[0028] When a numerical range is disclosed herein, the range is to be construed as having a lower limit and an upper limit, and each numerical value within the range is included in the range. Further, when the range is for integers, each integer between the lower limit and the upper limit is included in the range. In addition, when multiple ranges are provided to describe a feature or features, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood to include any and all sub-ranges subsumed therein.

[0029] Specifically, in a first aspect, the present application provides an ultra-pure ferritic stainless steel comprising, by weight percentage: C≤0.025%, N≤0.025%, Si≤1.00%, Mn≤1.20%, Cr: 18.00%-24.00%, Nb: 0.40%-0.75%, Mo: 1.75%-2.50%, W: 0.80%-1.20%, Cu: 0.30%-0.60%, Al≤0.015%, Ti≤0.01%, P≤0.03%, S≤0.01%, and satisfying 3.4%≤2Nb+Mo+W≤5.2%, 32%≤Cr+4.7Mo+2.4W+11.5Cu≤45%, the balance being Fe and unavoidable impurities.

[0030] The present application improves the high-temperature strength of the material by Nb, Mo and W complex strengthening, and improves the corrosion resistance and cold working formability of the material by adding Cu. The brazing wettability of the material is improved by controlling the Al and Ti content. The obtained ultra-pure ferritic stainless steel material has good high-temperature strength, high-temperature fatigue life and high-temperature oxidation resistance, and has good cold working performance and brazing processing performance, and can realize industrial production.

[0031] The effects of each element in the ultra-pure ferritic stainless steel of the present application are described in detail as follows:

[0032] C, N: In ferritic stainless steel, the solubility of C in the alpha phase matrix is very low, and the solubility decreases rapidly with the decrease of temperature, which is easy to combine with Cr to form Cr 23 C6, and gathers at the grain boundary, which is also the root of the high-temperature brittleness and intergranular corrosion of ferrite. N has very low solubility in ferritic stainless steel, and also forms chromium nitride. C, N has strong affinity with Nb and Ti, so Nb and Ti are often used as C, N stabilizing elements. Ti(C, N), Nb(C, N) are uniformly distributed in the grain, and will not gather at the grain boundary like Cr 23 C6, which can improve the intergranular corrosion resistance and mechanical properties of ferritic stainless steel. Therefore, C and N should be controlled as low as possible, and the control range of both in the present application is ≤0.025%, preferably ≤0.015%, and most preferably ≤0.010%.

[0033] Si, Mn: Si is a ferrite forming element, and Mn is a weak austenite forming element, and is the main deoxidizer in the smelting process. Silicon inhibits the oxidation of surface metal elements in ferritic stainless steel, and increases the oxidation resistance of the steel to some extent. The Si content is controlled to be ≤1.00%, and the Mn content is controlled to be ≤1.20%; preferably, the Si content is ≤0.80%, and the Mn content is ≤1.00%; most preferably, the Si content is 0.30% to 0.80%, and the Mn content is 0.40% to 1.00%.

[0034] Cr: Chromium is the most important alloying element in stainless steel, and is one of the main alloying elements for oxidation resistance and corrosion resistance in stainless steel. Chromium forms a dense Cr2O3 oxide film on the surface of the material, which hinders the diffusion of oxygen and metal ions, thereby improving the oxidation resistance and strength of the steel. The chromium content in the present application is 18.00% to 24.00%, preferably 18.00% to 21.00%, and most preferably 18.00% to 20.00%.

[0035] Nb, W, Mo: not only can improve the corrosion resistance of stainless steel, but also can enhance its high temperature performance. Mo can significantly promote the enrichment of chromium in the passive film, thereby enhancing the stability of the passive film, strengthening the corrosion resistance of chromium in the steel. Molybdenum improves the strength of stainless steel, including high temperature strength, significantly improves high temperature durability and creep performance, and improves thermal stability. The role of W is similar to that of Mo. The addition of Nb, on the one hand, acts as a stabilizing element for C and N, and on the other hand, can improve the high temperature strength of ferritic stainless steel through solid solution strengthening or precipitation phase strengthening, especially the solid solution strengthening effect is most prominent. In the present application, the content of Nb is controlled at 0.40% to 0.75%, the content of Mo is controlled at 1.75% to 2.50%, and the content of W is controlled at 0.80% to 1.20%; preferably, the content of Nb is controlled at 0.40% to 0.65%, the content of Mo is controlled at 1.90% to 2.40%, and the content of W is controlled at 0.90% to 1.20%; most preferably, the content of Nb is controlled at 0.50% to 0.60%, the content of Mo is controlled at 2.00% to 2.30%, and the content of W is controlled at 1.00% to 1.20%.

[0036] Cu: copper can increase the Cr content in the passive film, thereby improving the corrosion resistance of the passive film, and can improve the pitting potential of the ultra-pure ferritic stainless steel in a certain range, and improve the resistance to crevice corrosion. The precipitation of Cu particles can improve the high temperature and fatigue strength of the steel. Copper can also improve the elongation after fracture of the ultra-pure ferritic stainless steel material in the tensile test, improve its cold formability, and can appropriately compensate for the decrease in cold formability caused by the increase of the strengthening alloying elements. The content of Cu in the present application is controlled at 0.30% to 0.60%, preferably at 0.30% to 0.50%, and most preferably at 0.35% to 0.45%.

[0037] The component control of Nb, W, Mo, Cr, and Cu should also satisfy 3.4%≤2Nb+Mo+W≤5.2%, 32%≤Cr+4.7Mo+2.4W+11.5Cu≤45%.

[0038] Al, Ti: research shows that for ferritic stainless steel, lower Al and Ti content can improve the wettability of the stainless steel material to the brazing filler metal during brazing. It is reasonable to control Al content ≤0.015%, and Ti content ≤0.01%.

[0039] P, S: as harmful elements, phosphorus and sulfur should be controlled as low as possible. In the present application, P: ≤0.03%, S: ≤0.01%.

[0040] On the other hand, the present application also provides a manufacturing method of ultra-pure ferritic stainless steel, which comprises a smelting process, a casting process, a hot rolling process, a continuous annealing process after hot rolling, a cold rolling process, and a continuous annealing process after cold rolling.

[0041] The smelting process can use molten iron as raw material, and needs to go through molten iron pretreatment, converter, VOD furnace, LF furnace smelting, and then continuous casting, or three molten iron, AOD, VOD furnace, LF furnace smelting, and then continuous casting. The smelting can also use scrap steel as raw material, and needs to go through electric furnace, AOD, VOD furnace, LF furnace smelting, and then continuous casting. According to actual needs, die casting can also be carried out. The chemical composition after smelting should meet the design composition described above.

[0042] The hot rolling process and the cold rolling process need to be followed by heat treatment to restore the structure and improve the processing performance of the material. The main process parameters are as follows:

[0043] Preferably, the continuous casting blank is heated before hot rolling, and the hot rolling goes through rough rolling, finish rolling, and coiling to obtain a hot rolled coil. The heating temperature of the blank is 1200-1260℃, which ensures that the blank is fully burned and reduces the load of the rolling mill. The coiling temperature is 620-700℃, which prevents high-temperature brittleness and the precipitation of the second phase, and restores the recrystallization of the hot rolling structure.

[0044] The hot rolling process and the cold rolling process are followed by heat treatment, respectively, to improve the processing performance of the material, and continuous annealing can be used.

[0045] Preferably, the steel coil is subjected to continuous annealing after hot rolling, the annealing temperature is 1000-1060℃, and the holding time is 1.5-2.0min / mm. In this way, the mechanical properties of the material after hot rolling are softened and improved, and the toughness of the material is improved, so as to facilitate subsequent cold rolling processing.

[0046] Preferably, the stainless steel is pickled to remove the surface iron oxide scale after annealing.

[0047] Preferably, the total deformation rate of cold rolling should be ≥55% (preferably ≥65%), thereby refining the grain size of the finished product, improving the elongation of the material, and improving the forming performance of the material.

[0048] The rolling pass, rolling pressure, and pass deformation of cold rolling can be carried out according to the existing technology, and the present application does not make specific limitations thereto.

[0049] Preferably, the steel coil is subjected to continuous annealing after cold rolling, the annealing temperature is 1000-1060℃, and the holding time is 0.9-1.2min / mm. In this way, the mechanical properties of the material after cold rolling are softened and improved, and the toughness of the material is improved, so as to facilitate subsequent processing of the finished material into certain shaped parts.

[0050] Preferably, the stainless steel is pickled to remove the surface iron oxide scale after annealing.

[0051] The manufacturing method of the ultra-pure ferrite stainless steel of the present application, after smelting, continuous casting, hot rolling and cold rolling, the grain size of the ferrite stainless steel cold plate is 6-8, the tensile strength is 530-580 MPa. The high temperature tensile strength at 900℃ is greater than 44 MPa, the high temperature tensile strength at 1000℃ is greater than 24 MPa. At 950℃, the high cycle fatigue test is carried out at 15 MPa according to the stress ratio R=0.1, the service life is greater than 10 7 times. The high temperature oxidation test at 900℃ is carried out for 1000 hours, the oxidation weight gain is 1.4-1.5 mg / cm 2 .

[0052] Example

[0053] The present application is further illustrated by the following examples, but the present application is not limited in the scope of the examples. The experimental methods without specific conditions in the following examples are carried out according to the conventional methods and conditions.

[0054] Example 1

[0055] The molten iron is used as the raw material, after the molten iron pretreatment, converter, VOD furnace, LF furnace smelting, the continuous casting billet is formed, the chemical composition of the casting billet is shown in Table 1.

[0056] The continuous casting billet is sequentially subjected to hot rolling, continuous annealing, cold rolling and continuous annealing treatment to obtain the ultra-pure ferrite stainless steel, the process parameters are shown in Table 2.

[0057] The grain size, normal temperature tensile test and high temperature tensile test of the ultra-pure ferrite stainless steel cold rolling finished product are detected, and the detection results are shown in Table 3.

[0058] Example 2

[0059] The three-removing molten iron is smelted, after AOD, VOD furnace, LF furnace smelting, the continuous casting billet is formed, the chemical composition of the casting billet is shown in Table 1.

[0060] The continuous casting billet is sequentially subjected to hot rolling, continuous annealing, cold rolling and continuous annealing treatment to obtain the ultra-pure ferrite stainless steel, the process parameters are shown in Table 2.

[0061] The grain size, normal temperature tensile test and high temperature tensile test of the ultra-pure ferrite stainless steel cold rolling finished product are detected, and the detection results are shown in Table 3.

[0062] Example 3

[0063] The scrap steel is used as the raw material, after the electric furnace, AOD, VOD furnace, LF furnace smelting, the continuous casting billet is formed, the chemical composition of the casting billet is shown in Table 1.

[0064] The continuous casting billet is sequentially subjected to hot rolling, first continuous annealing, cold rolling and second continuous annealing treatment to obtain the ultra-pure ferrite stainless steel, the process parameters are shown in Table 2.

[0065] The grain size, normal temperature tensile, and high temperature tensile test of the cold-rolled finished product of the ultra-pure ferritic stainless steel are detected, and the detection results are shown in Table 3.

[0066] Comparative Example 4: Stainless Steel 441

[0067] The molten iron is used as a raw material, and after smelting by a molten iron pretreatment, a converter, a VOD furnace, and an LF furnace, a continuous casting billet is formed, and the chemical composition of the continuous casting billet is shown in Table 1.

[0068] The continuous casting billet is sequentially subjected to hot rolling, continuous annealing, cold rolling, and continuous annealing treatment to obtain an ultra-pure ferritic stainless steel, and the process parameters are performed according to the conventional preparation process of stainless steel 441.

[0069] The grain size, normal temperature tensile, and high temperature tensile test of the cold-rolled finished product of the ultra-pure ferritic stainless steel are detected, and the detection results are shown in Table 3.

[0070] Comparative Example 5: Stainless Steel 444

[0071] The molten iron is used as a raw material, and after smelting by a molten iron pretreatment, a converter, a VOD furnace, and an LF furnace, a continuous casting billet is formed, and the chemical composition of the continuous casting billet is shown in Table 1.

[0072] The continuous casting billet is sequentially subjected to hot rolling, continuous annealing, cold rolling, and continuous annealing treatment to obtain an ultra-pure ferritic stainless steel, and the process parameters are performed according to the conventional preparation process of stainless steel 444.

[0073] The grain size, normal temperature tensile, and high temperature tensile test of the cold-rolled finished product of the ultra-pure ferritic stainless steel are detected, and the detection results are shown in Table 3.

[0074] Comparative Example 6: Stainless Steel 444Nb

[0075] The molten iron is used as a raw material, and after smelting by a molten iron pretreatment, a converter, a VOD furnace, and an LF furnace, a continuous casting billet is formed, and the chemical composition of the continuous casting billet is shown in Table 1.

[0076] The continuous casting billet is sequentially subjected to hot rolling, first continuous annealing, cold rolling, and second continuous annealing treatment to obtain an ultra-pure ferritic stainless steel, and the process parameters are performed according to the conventional preparation process of stainless steel 444Nb.

[0077] The grain size, normal temperature tensile, and high temperature tensile test of the cold-rolled finished product of the ultra-pure ferritic stainless steel are detected, and the detection results are shown in Table 3.

[0078] Comparative Example 7: Stainless Steel 445J2

[0079] The molten iron is used as a raw material, and after smelting by a molten iron pretreatment, a converter, a VOD furnace, and an LF furnace, a continuous casting billet is formed, and the chemical composition of the continuous casting billet is shown in Table 1.

[0080] The continuous casting billet is sequentially subjected to hot rolling, continuous annealing, cold rolling and continuous annealing treatment to obtain the ultra-pure ferritic stainless steel, and the process parameters are in accordance with the conventional preparation process of stainless steel 445J2.

[0081] The grain size, normal temperature tensile test and high temperature tensile test of the cold-rolled product of the ultra-pure ferritic stainless steel are detected, and the detection results are shown in Table 3.

[0082] Table 1: Composition summary (wt%) of ferritic stainless steel prepared in Examples 1-3 and Comparative Examples 4-7

[0083] Table 2: Main process parameters of Examples 1-3

[0084] Table 3: Performance summary of ferritic stainless steel of Examples 1-3 and Comparative Examples 4-7

[0085] As shown in Table 3, the grain size of the cold-rolled product of Examples 1-3 is 7-8, and the metallographic structure of the ultra-pure ferritic stainless steel of Example 1 is shown in Figure 1. The elongation after tensile test at normal temperature is 30-30.5%, and the tensile strength is 552-561 MPa.

[0086] High temperature tensile test, the high temperature strength of the stainless steel of Examples 1-3 and Comparative Examples 4-7 is shown in Figure 2, the high temperature tensile strength of the material of the application is greater than 44 MPa at 900℃, and the high temperature tensile strength is greater than 24 MPa at 1000℃, and the high temperature strength is higher than that of Comparative Examples 4-7.

[0087] At 950℃, 15 MPa, high cycle fatigue test is carried out according to stress ratio R=0.1, the service life of the stainless steel of Examples 1-3 is greater than 10 7 times.

[0088] At 900℃ high temperature, 1000 hours continuous oxidation test is carried out on the stainless steel of Example 1 and Comparative Examples 4-7, the high temperature oxidation weight gain of the application and the comparative examples is shown in Figure 3, the oxidation weight gain of the material of the application is 1.44 mg / cm 2 , and the oxidation weight gain is lower than that of Comparative Examples 4-7.

[0089] The cold-rolled product of Example 1 is subjected to brazing wetting test, the filler metal is coated on the surface of the sample, heated at 1100℃ in reducing atmosphere for 30 minutes, and the spreadability of the filler metal is observed, the spread area of the filler metal of the material of the application is obviously larger than that of the stainless steel prepared in Comparative Example 5, as shown in Figure 4. It shows that the material of the application has good filler metal wetting property and good brazing performance.

[0090] It should be noted that the above examples are only used to illustrate the technical solutions of the present application, but not to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalent features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the present application.

Claims

1. An ultra-pure ferritic stainless steel, characterized in that, comprises, by weight percent: C ≤ 0.025%, N ≤ 0.025%, Si ≤ 1.00%, Mn ≤ 1.20%, Cr: 18.00% ~ 24.00%, Nb: 0.40% ~ 0.75%, Mo: 1.75% ~ 2.50%, W: 0.80% ~ 1.20%, Cu: 0.30% ~ 0.60%, Al ≤ 0.015%, Ti ≤ 0.01%, P ≤ 0.03%, S ≤ 0.01%, and satisfies 3.4% ≤ 2Nb + Mo + W ≤ 5.2%, 32% ≤ Cr + 4.7Mo + 2.4W + 11.5Cu ≤ 45%, and the balance is Fe and inevitable impurities.

2. The ultra-pure ferritic stainless steel according to claim 1, characterized in that, comprises, by weight percent: C ≤ 0.015%, N ≤ 0.015%, Si ≤ 0.80%, Mn ≤ 1.00%, Cr: 18.00% ~ 21.00%, Nb: 0.40% ~ 0.65%, Mo: 1.90% ~ 2.40%, W: 0.90% ~ 1.20%, Cu: 0.3% ~ 0.5%, Al ≤ 0.013%, Ti ≤ 0.01%, P ≤ 0.03%, S ≤ 0.005%, and satisfies 3.6% ≤ 2Nb + Mo + W ≤ 4.9%, 33% ≤ Cr + 4.7Mo + 2.4W + 11.5Cu ≤ 41%, and the balance is Fe and inevitable impurities.

3. The ultrapure ferritic stainless steel according to claim 1 or 2, characterized in that, comprises, by weight percent: C ≤ 0.01%, N ≤ 0.01%, Si: 0.30% ~ 0.80%, Mn: 0.40% ~ 1.00%, Cr: 18.00% ~ 20.00%, Nb: 0.50% ~ 0.60%, Mo: 2.00% ~ 2.30%, W: 1.00% ~ 1.20%, Cu: 0.35% ~ 0.45%, Al ≤ 0.01%, Ti ≤ 0.008%, P ≤ 0.02%, S ≤ 0.003%, and satisfies 4.0% ≤ 2Nb + Mo + W ≤ 4.8%, 34% ≤ Cr + 4.7Mo + 2.4W + 11.5Cu ≤ 39%, and the balance is Fe and inevitable impurities.

4. A method of producing an ultrapure ferritic stainless steel, characterized by, comprises a smelting process, a casting process, a hot rolling process, a continuous annealing process after hot rolling, a cold rolling process, and a continuous annealing process after cold rolling, wherein the molten steel prepared by the smelting process has the same composition as the ultra-pure ferritic stainless steel according to any one of claims 1 to 3.

5. The method of producing an ultrapure ferritic stainless steel according to claim 4, characterized by In the hot rolling process, the heating temperature of the cast blank before hot rolling is 1200 ~ 1260℃, and the temperature of the coiling after hot rolling is 620 ~ 700℃.

6. The method of producing an ultrapure ferritic stainless steel according to claim 4, characterized by In the continuous annealing process after hot rolling, the annealing temperature is 1000 ~ 1060℃, and the holding time is 1.5 ~ 2.0 min / mm.

7. The method of producing an ultrapure ferritic stainless steel according to claim 4, characterized by The total deformation rate of the cold rolling process is ≥ 55%.

8. The method of producing an ultrapure ferritic stainless steel according to claim 4, characterized by The annealing temperature of the continuous annealing process after cold rolling is 1000 ~ 1060℃, and the holding time is 0.9 ~ 1.2 min / mm.

9. Use of the ultra-pure ferritic stainless steel according to any one of claims 1 to 3 or the ultra-pure ferritic stainless steel obtained by the manufacturing method according to any one of claims 4 to 8 in the preparation of automobile exhaust systems.

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