JP5025671B2 - Ferritic stainless steel sheet excellent in high temperature strength and method for producing the same - Google Patents

Description

  The present invention relates to a ferritic stainless steel sheet excellent in high-temperature strength and particularly suitable for use in exhaust system members that require high-temperature strength, and a method for producing the same.

  Exhaust system members such as exhaust manifolds and mufflers for automobiles allow high-temperature exhaust gas discharged from the engine to pass therethrough, and therefore, materials constituting the exhaust members are required to have various characteristics such as high-temperature strength and oxidation resistance.

  Conventionally, cast iron was generally used for automobile exhaust members, but an exhaust manifold made of stainless steel seems to be used from the viewpoints of stricter exhaust gas regulations, improved engine performance, and lighter vehicle body. Became. Although the exhaust gas temperature varies depending on the vehicle type, in recent years, the temperature is often about 800 to 900 ° C., and the temperature of the exhaust manifold through which the high-temperature exhaust gas discharged from the engine passes is as high as 750 to 850 ° C. However, exhaust gas regulations are being further strengthened and fuel efficiency is being improved, and the exhaust gas temperature is considered to increase further.

  Among the stainless steels, austenitic stainless steels are superior in high-temperature strength and workability, but due to their large thermal expansion coefficient, thermal fatigue failure occurs when applied to a member that repeatedly receives heating and cooling, such as an exhaust manifold. And scale peeling easily occurs.

  On the other hand, since ferritic stainless steel has a smaller thermal expansion coefficient than austenitic stainless steel, it is excellent in thermal fatigue characteristics and scale peel resistance. Further, compared with austenitic stainless steel, it does not contain Ni, so the material cost is low and it is used for general purposes. However, since ferritic stainless steel has lower high-temperature strength than austenitic stainless steel, a technique for improving high-temperature strength has been developed. For example, there are SUS430J1 (Nb-added steel), Nb-Si-added steel, and SUS444 (Nb-Mo-added steel). Based on Nb addition, the high-temperature strength is improved by adding Si and Mo. Among them, SUS444 has the highest strength because about 2% of Mo is added. However, SUS444 cannot cope with the increase in exhaust gas temperature, and a ferritic stainless steel having a high-temperature strength equal to or higher than SUS444 and oxidation resistance equivalent to SUS444 is desired.

  In addition to the above examples, various additive elements have been studied. Patent Documents 1 and 2 disclose techniques for performing Cu-Ti composite addition. In Cu and Ti additions in Patent Document 1, additions of 0.5% or less have been studied for improving low-temperature toughness, and they are not additions from the viewpoint of heat resistance. Patent Document 2 discloses a technique for improving the high-temperature strength in the temperature range of 700 ° C. to 850 ° C. using precipitation hardening by Cu precipitates, but the proof stress at 850 ° C. is almost equivalent to the SUS444 level. Therefore, it was not considered as an exhaust part of SUS444 or higher. The conventional technology for improving the high-temperature strength by adding Cu utilizes Cu precipitates. However, when Cu precipitates are exposed to high temperatures for a long time, coarsening due to aggregation and coalescence of precipitates occurs rapidly. There is a problem that the precipitation strengthening ability is remarkably lowered. Patent Documents 3 and 4 disclose techniques for limiting the total precipitation amount. In Patent Document 3, a method of controlling the total precipitation amount to 0.05 to 0.6% or less for improving formability has been studied, and is not a method from the viewpoint of heat resistance. In Patent Document 4, in order to obtain a workability equivalent to that of a cold-rolled annealed plate in an annealed stainless steel pipe, a method of reducing the total precipitation amount to 1% or less has been studied, but for improving low-temperature toughness and workability. Cu is added, and precipitation strengthening due to Cu precipitates is not considered. Patent Document 5 discloses a technique of adding B based on Nb—Mo-added steel. However, the addition of B in Patent Document 5 has been studied for the addition of 0.0003 to 0.001% in order to improve cold workability and secondary workability, and is not an addition from the viewpoint of heat resistance. The B addition in the conventional knowledge is for the purpose of improving workability, and improves the grain boundary strength due to grain boundary segregation to improve the secondary workability, and the influence on the high temperature characteristics has not been clear.

  The inventors have recently disclosed a technique for obtaining high-temperature strength in a temperature range of about 750 ° C. by adding Nb—Cu—B in Patent Document 6. However, even when this technology is used, the temperature range of 850 ° C. or higher remains at the same level as that of SUS444, and does not satisfy the demand for a ferritic stainless steel having a high-temperature strength of SUS444 or higher and an oxidation resistance equivalent to that of SUS444.

JP 2006-37176 A Japanese Patent No. 3397167 JP 2005-298854 A Japanese Patent No. 3678321 International Publication WO 2004/053171 JP 2008-240143 A

  An object of this invention is to provide the ferritic stainless steel which has high high temperature strength by utilizing the reinforcement mechanism different from a prior art, and its manufacturing method.

In order to solve the above problems, the present inventors have taken into consideration the use conditions in the exhaust manifold, and in the temperature range of 800 to 900 ° C., a large amount of precipitates precipitate and grow. In order to increase the strength as an exhaust member based on precipitation strengthening by precipitating ε-Cu precipitated by addition of Nb and Mo-based Laves phases and Cu from the conventional material, these are Laves. As a result of examining the means for finely dispersing the phase and ε-Cu, it has been found that the Nb—Mo—Cu—Ti—B composite addition is effective for fine precipitation. In particular, B generally tends to form (Fe, Cr) ₂₃ (C, B) ₆ or Cr ₂ B in a high temperature range, but these precipitates are present in Nb—Mo—Cu—Ti—B composite added steel. It was found that the product did not precipitate and had the effect of finely depositing the Laves phase and the ε-Cu phase. The Laves phase reduces the amount of dissolved Nb and Mo and usually coarsens, so there is almost no high-temperature strengthening ability after aging in particular, but it has fine precipitation due to the addition of B, so it has precipitation strengthening ability. Contributes to the improvement of high-temperature strength, and increases the strength stability when used for a long time. In addition, ε-Cu usually precipitates very finely at the initial stage of precipitation and has a large effect of improving the strength, but is coarsened by aging heat treatment, and the strength decrease after aging is large. However, the addition of B suppresses the coarsening of ε-Cu and increases the strength stability during use. Although the mechanism of the effect of suppressing precipitation refinement and coarsening due to the addition of B is not clear, the interfacial energy is reduced by the grain boundary segregation of B, so that the grain boundary precipitation of the Laves phase and ε-Cu is suppressed and the grain is refined. Presumed to be deposited. Moreover, it is guessed that suppressing the grain boundary diffusion of Nb, Mo and Cu suppresses the coarsening of these precipitates.

  Further, the Nb—Mo—Cu—Ti—B composite added steel is subjected to cold rolling annealing at 1070 ° C. or more, preferably 1100 ° C. or more, so that the total amount of precipitates is kept to 2% by mass or less and used as an exhaust system member. It is found that by increasing the amount of precipitates, it is possible to provide a ferritic stainless steel having a high temperature strength of SUS444 or higher, that is, 0.2% proof stress at 850 ° C. of 40 MPa or more and oxidation resistance equivalent to SUS444. It was.

  FIG. 1 shows 18.5 to 19% Cr-0.004 to 0.006% C-0.2 to 0.3% Si-0.9 to 1.1% Mn-1.8 to 2% Mo-1. .8-2% Cu-0.6-0.7 Nb-0.1-0.2% Ti-0.009-0.011% N steel sheet and B to which B is not added to the basic composition of steel The relationship between the precipitation frequency and the particle size of precipitates (mainly the Laves phase and ε-Cu) in the case of aging heat treatment at 850 ° C. for 10 minutes after annealing at 1100 ° C. × 60 s using 0.0002% added steel sheet It is the result shown. In the B-added steel, the average particle size tends to be finer than that in the B-free steel, and it can be seen that the Laves phase and ε-Cu are refined by the addition of B.

  FIG. 2 shows that 18.5 to 20% Cr-0.002 to 0.008% C-0.3 to 0.4% Si-0.9 to 1.2% Mn-1.8 to 2.5 % Mo-1.5-2% Cu-0.6-0.9Nb-0.1-0.2% Ti-0.008-0.011% N-0.0003-0.0008B Steel Product Plate It is the result which showed the relationship between the precipitation amount of and 850 degreeC high temperature intensity | strength. It can be seen from FIG. 2 that the yield strength at 850 ° C. increases as the precipitation amount of the product plate decreases, and has a yield strength equivalent to SUS444 at 2% by mass or less. Further, in FIG. 3, 18.7% Cr-0.005% C-0.3% Si-1.1% Mn-1.9% Mo-1.8% Cu-0.85Nb-0.14% Ti It is the result which showed the relationship between the precipitation amount of the product plate of -0.011% N-0.001B steel, and the final annealing temperature. FIG. 3 shows that the total amount of precipitates decreases as the final annealing temperature is increased. 2 and 3, it can be seen that a 0.2% proof stress at 850 ° C. of 34 MPa or more can be secured even if annealing is performed at a normal final annealing temperature of 1000 ° C.

  In addition, when Cu is added in an amount of 2% or more, the high temperature strength is sufficiently ensured by precipitation strengthening of ε-Cu, so that high temperature characteristics exceeding SUS444 can be realized even if Mo, which is an expensive additive element, is reduced. Newly discovered. However, when Cu was increased and Mo was reduced, it became clear that an abnormal oxidation phenomenon occurred rarely and the oxidation resistance was lowered. As a result of detailed studies on this problem, it was found that this phenomenon occurs only when Si is reduced, and that abnormal oxidation does not occur when Si is added in an amount of 0.15 mass% or more.

  As described above, in the present invention, in the effect of finely precipitating the Laves phase and ε-Cu due to B, the present invention has found an operational effect different from that of the conventional invention and has led to the present invention that improves the high-temperature strength. And the ferritic stainless steel sheet excellent in the high temperature strength which reduced the precipitate by annealing at 1070 degreeC or more, precipitated the precipitate when using it for an exhaust system member, and exhibited precipitation strengthening to the maximum was invented.

The gist of the present invention for solving the above problems is as follows.
(1) In mass%, C: 0.01% or less, N: 0.02% or less, Si: 0.05-1%, Mn: more than 0.6-2%, Cr: 15-30%, Mo: 1~4%, Cu: 1~ 3.3%, Nb: 0.2~1.5%, Ti: 0.05~0.5%, B: containing .0002-.01% and, Ri is Na Fe and unavoidable impurities balance, excellent ferritic stainless steel high-temperature strength of 0.2% proof stress of 850 ° C. may be higher than 32 MPa.
(2) In mass%, C: 0.01% or less, N: 0.02% or less, Si: 0.15 to 1%, Mn: more than 0.6 to 2%, Cr: 15 to 30%, Mo: 0.1 to less than 1%, Cu: more than 2 to 3.5%, Nb: 0.2 to 1.5%, Ti: 0.05 to 0.5%, B: 0.0002 to 0. containing 01% Ri is Na Fe and unavoidable impurities balance, excellent ferritic stainless steel high-temperature strength of 0.2% proof stress of 850 ° C. may be higher than 32 MPa.
(3) The ferritic stainless steel sheet having excellent high temperature strength as described in (1) or (2), wherein the total precipitation amount is 2% or less by mass%.
(4) High temperature according to any one of (1) to (3), characterized by containing one or more of Al: 0.1% or more and 4% or less and V: 1% or less in mass% Ferritic stainless steel sheet with excellent strength.
(5) It is characterized by containing one or more of W: 5% or less, Sn: 1% or less, Zr: 2% or less, Hf: 2% or less, Ta: 5% or less in mass% ( A ferritic stainless steel sheet having excellent high-temperature strength as described in any one of 1) to (4).
(6) The method for producing a ferritic stainless steel sheet having excellent high-temperature strength according to any one of (3) to (5), wherein the final annealing temperature of the cold-rolled sheet is 1070 ° C. or higher.

  Here, for the case where the lower limit is not specified, it indicates that an inevitable impurity level is included.

  According to the present invention, a high temperature characteristic of SUS444 or higher can be obtained, and in particular, by applying it to an exhaust system member such as an automobile, it becomes possible to cope with a high exhaust gas temperature.

It is a figure which shows the particle size distribution of the precipitate of B addition steel and B additive-free steel after aging heat processing for 10 minutes at 850 degreeC. It is a figure which shows the relationship between the precipitation amount of a cold rolled sheet, and 0.2% yield strength of 850 degreeC. It is a figure which shows the relationship between the final annealing temperature and precipitation amount of a cold rolled sheet.

  The reason for limiting the present invention will be described below.

  C deteriorates moldability and corrosion resistance and causes a decrease in high-temperature strength. Therefore, the lower the content, the better. Therefore, the C content is set to 0.01% or less. However, excessive reduction leads to an increase in refining costs, so 0.001 to 0.005% is desirable.

  N, like C, deteriorates moldability and corrosion resistance and brings about a decrease in high-temperature strength. Therefore, the smaller the content, the better. Therefore, the N content is set to 0.02% or less. However, excessive reduction leads to an increase in refining costs, so 0.003 to 0.015% is desirable.

  Si is an element useful as a deoxidizer, but is an extremely important element for improving high-temperature characteristics and oxidation resistance. Concerning the high temperature strength, the Si content of 0.05% or more promotes the precipitation of an intermetallic compound mainly composed of Fe, Nb, and Mo called a Laves phase at a high temperature. On the other hand, the addition of more than 1% causes the Laves phase to excessively precipitate, agglomerate / coarse, and the precipitation strengthening ability disappears, so the upper limit is made 1%. Si is also an element that improves the oxidation resistance. In order to exhibit the effect, it is necessary to add 0.05% or more. On the other hand, when it exceeds 1%, scale peeling tends to occur and the processability at room temperature also decreases. From the above, the range of Si is 0.05 to 1%.

  Further, when Cu is more than 2% and Mo is less than 1%, abnormal oxidation is particularly likely to occur. Therefore, Si needs to be 0.15% or more to prevent this. In this case, too, addition of more than 1% tends to cause scale peeling, so the upper limit is made 1%.

  Mn is an element added as a deoxidizing agent, and forms a Mn-based oxide on the surface layer during long-time use, contributing to scale adhesion and an effect of suppressing abnormal oxidation. The effect is manifested at over 0.6%. On the other hand, excessive addition of more than 2% lowers the uniform elongation at room temperature, forms MnS, lowers the corrosion resistance, and brings about deterioration of oxidation resistance. From these viewpoints, the upper limit was made 2%. Furthermore, if considering high temperature ductility and scale adhesion, 0.6 to 1.5% is desirable.

  Cr is an essential element for ensuring oxidation resistance in the present invention. If it is less than 15%, the effect is not exhibited, and if it exceeds 30%, the workability is deteriorated or the toughness is deteriorated, so the content is made 15 to 30%. Furthermore, considering the high temperature ductility and the manufacturing cost, 17 to 22% is desirable.

  Mo improves corrosion resistance, suppresses high-temperature oxidation, and is effective for precipitation strengthening by fine precipitation of the Laves phase and high-temperature strength improvement by solid solution strengthening. However, excessive addition promotes coarse precipitation of the Laves phase, lowers precipitation strengthening ability, and degrades workability. Furthermore, in the Nb—Mo—Cu—Ti—B-added steel of the present invention, solid solution Mo can be increased by adding Cu, and the Laves phase refinement by adding B can be obtained by adding 1% or more of Mo. The effect is affected by the amount of Cu added, and when Cu is added in an amount of 1% or more and 2%, the effect of improving the strengthening ability by Cu is somewhat small, so Mo needs to be added in an amount of 1% or more. Excessive Mo addition exceeding 4% promotes coarsening of the Laves phase, does not contribute to high-temperature strength, and increases costs, so the upper limit is made 4%.

  However, when Cu is added in excess of 2%, the effect of improving the strengthening ability due to Cu is large, and the workability is also improved, so the addition of Mo can be reduced. Since Mo is expensive, the cost can be reduced. The lower limit is 0.1%, and the effect is manifested by addition of more Mo. Also, when Cu is added in excess of 2%, the upper limit of Mo can be made 4%, but it is not necessary to utilize precipitation strengthening and solid solution strengthening by the Laves phase, so the upper limit of Mo is extremely less than 1%. It can also be reduced.

  Ti is an element that combines with C, N, and S to improve the r value that serves as an index of corrosion resistance, intergranular corrosion resistance, and deep drawability. In addition, in the combined addition with Nb and Mo, addition of an appropriate amount brings about an increase in the amount of solid solution during cold rolling annealing of Nb and Mo, an improvement in high temperature strength, and an improvement in hot ductility, thereby improving thermal fatigue characteristics. Furthermore, these effects are manifested from 0.05% or more, but by adding more than 0.5%, the amount of solid solution Ti is increased and the uniform elongation is lowered, and coarse Ti-based precipitates are formed, It becomes the starting point of cracks during hole expansion processing and deteriorates hole expansion. Therefore, the Ti addition amount is set to 0.05 to 0.5%. Furthermore, if considering the occurrence of surface flaws and toughness, 0.1 to 0.3% is desirable.

  Nb is an element necessary for improving the high-temperature strength by solid solution strengthening and precipitate refinement strengthening. In addition, C and N are fixed as carbonitrides, contributing to the development of the recrystallization texture that affects the corrosion resistance and r value of the product plate. Furthermore, it contributes to precipitation strengthening by fine precipitation of the Laves phase and solid solution strengthening by solid solution Nb, and this effect is manifested by addition of 0.2% or more. On the other hand, excessive addition reduces the uniform elongation and deteriorates the hole expandability. Furthermore, if considering the intergranular corrosion property, the manufacturability and the manufacturing cost of the welded portion, 0.4 to 0.9% is desirable.

  B is an element that improves the secondary workability at the time of press working of the product. In the present invention, fine precipitation of Nb, Mo-based precipitates and ε-Cu by adding Nb—Mo—Cu—Ti—B as described above. Contributes to the improvement of high temperature strength. These effects are manifested at 0.0002% or more. However, excessive addition deteriorates the hardness and intergranular corrosion, and also causes weld cracks. Therefore, the content was made 0.0002 to 0.01%. Furthermore, if considering moldability and manufacturing cost, 0.0003 to 0.005% is desirable.

  Cu is an element effective for improving the high-temperature strength as described above. This is a precipitation hardening effect due to the precipitation of ε-Cu, and is remarkably exhibited by addition of 1% or more. On the other hand, if it is less than 1%, the precipitation hardening effect is not remarkably exhibited. On the other hand, excessive addition causes a reduction in uniform elongation and excessively high room temperature proof stress, which impairs press formability. Further, if added in an amount of 3.5% or more, an austenite phase is formed in a high temperature range and abnormal oxidation occurs on the surface, so the upper limit was made 3.5%. The upper limit of Cu is preferably 3%. In consideration of manufacturability and scale adhesion, 1.2 to 2% is desirable.

  Al is an element added as a deoxidizing element, but is also an element that improves oxidation resistance. It is also useful for improving the strength as a solid solution strengthening element. The effect of improving the strength is stably manifested from 0.1%, but excessive addition hardens it to significantly reduce uniform elongation and toughness to remarkably decrease, so the upper limit was made 4%. Furthermore, if considering the occurrence of surface defects, weldability, and manufacturability, 0.1 to 2.5% is desirable. When Al is added for the purpose of deoxidation, less than 0.1% of Al remains in the steel as an inevitable impurity.

  V forms fine carbonitrides and causes a precipitation strengthening action, which contributes to an improvement in high temperature strength. This effect is stably manifested by addition of 0.01% or more. However, if added over 1%, the precipitates become coarse and the high-temperature strength decreases, and the thermal fatigue life and workability decrease. 1%. Furthermore, if considering the manufacturing cost and manufacturability, 0.08 to 0.5% is desirable.

  W is an element having the same effect as Mo and improving the high temperature strength. This effect appears stably from 1% or more, but if added excessively, it dissolves in the Laves phase, coarsening precipitates and degrading manufacturability and workability. preferable. Furthermore, if considering cost, oxidation resistance, etc., 1.2 to 3% is desirable.

  Sn is an element having a large atomic radius and effective for solid solution strengthening, and does not greatly deteriorate the mechanical properties at room temperature. The contribution to the high-temperature strength is stably manifested at 0.1% or more, but if added at 1% or more, manufacturability and workability are remarkably deteriorated, so 0.1 to 1% is preferable. Furthermore, if considering oxidation resistance and the like, 0.2 to 0.8% is desirable.

  Zr is a strong carbonitride-forming element over Ti and Nb. Therefore, if Zr is added, it contributes to improvement in high-temperature strength and oxidation resistance by increasing the amount of solid solution Ti and Nb. Adds a stable effect. However, since addition of more than 2% significantly deteriorates manufacturability and workability, the content is set to 0.2 to 2%. Furthermore, if considering cost and surface quality, 0.2 to 0.9% is desirable.

  Hf is a strong carbonitride-forming element higher than Ti and Nb, so if Hf is added, it contributes to improving high temperature strength and oxidation resistance by increasing the amount of solid solution Ti and Nb, and 0.2% or more. Adds a stable effect. However, since addition of more than 2% significantly deteriorates manufacturability and workability, the content is set to 0.2 to 2%. Furthermore, if considering cost and surface quality, 0.2 to 1% is desirable.

  Since Ta is a strong carbonitride-forming element over Ti and Nb, if Ta is added, it contributes to improving high-temperature strength and oxidation resistance by increasing the amount of dissolved Ti and Nb, and 0.2% or more Adds a stable effect. However, since addition of more than 5% causes remarkable deterioration of manufacturability and workability, the content is set to 0.2 to 5%. Furthermore, if considering cost and surface quality, 0.2 to 3% is desirable.

  The total precipitation amount in the cold-rolled annealed sheet is desirably 2% by mass or less. This is because, at 800 to 900 ° C. used as an exhaust system member, fine precipitation of precipitates is promoted and high temperature strength is easily maintained (see FIG. 2).

  The higher the final annealing temperature of the cold-rolled sheet, the larger the amount of precipitates in the cold-rolled sheet, so that the total amount of precipitates in the cold-rolled annealed sheet can be reduced. As a result, the amount of fine precipitates deposited when used as an exhaust system member is increased, contributing to refinement of the precipitates. When the final annealing temperature of the cold-rolled sheet is 1070 ° C. or higher, the total amount of precipitates in the cold-rolled annealed sheet is 2% by mass or less, and 40 MPa can be obtained as the 0.2% yield strength at 850 ° C. If it exceeds 1200 ° C, the crystal grains become too large, so 1200 ° C is set as the upper limit of the final annealing temperature. Considering high-temperature strength stability, cost, and surface quality, the final annealing temperature is desirably 1100 ° C. or higher and 1200 ° C. or lower.

  The manufacturing method of the steel sheet is not particularly specified except that the final annealing temperature of the cold-rolled sheet is preferably 1070 ° C. or higher, but the hot-rolling conditions, hot-rolled sheet thickness, presence / absence of hot-rolled sheet annealing, The rolling conditions, hot-rolled sheet and annealing temperature, atmosphere, etc. may be appropriately selected. Further, temper rolling or tension leveler may be applied after cold rolling and annealing. Further, the product plate thickness may be selected according to the required member thickness.

  Steels having the composition shown in Tables 1 and 2 were melted and cast into slabs, and the slabs were hot-rolled to form hot rolled coils having a thickness of 5 mm. Thereafter, the hot rolled coil was pickled, cold-rolled to a thickness of 2 mm, annealed and pickled to obtain a product plate. The annealing temperature of the cold-rolled sheet was set to 1000 to 1150 ° C. in consideration of the total precipitation amount. No. in Table 1 1 to 36 are steels of the present invention, No. 1 in Table 2. Reference numerals 37 to 57 are comparative steels.

  From the product plate thus obtained, a high-temperature tensile test piece was collected so that the rolling direction was the tensile direction, a tensile test was performed at 850 ° C., and 0.2% proof stress was measured (according to JIS G 0567). Compliant, figures are rounded off to the nearest decimal point). Moreover, the total deposit of a product board calculated | required the sample of the cold rolled annealing board in the electrolytic extraction residue. Furthermore, as an oxidation resistance test, a continuous oxidation test was performed for 200 hours at 850 ° C. and 950 ° C. in the atmosphere to evaluate whether or not abnormal oxidation and scale peeling occurred (based on JIS Z 2281). As normal temperature workability, a JIS No. 13 B test piece defined in JIS Z 2201 was prepared, a tensile test in a direction parallel to the rolling direction was performed, and elongation at break was measured (conforms to JIS Z 2241). Here, if the elongation at break at room temperature is 25% or more, it can be processed into a general exhaust part.

  As is clear from Tables 1 and 2, the steel having the component composition defined in the present invention has a 0.2% proof stress of 850 ° C. of 34 MPa or more and SUS444 (No. 56 steel) of 850 ° C. of 0.2. It can be seen that the% yield strength is higher than 32 MPa, the elongation at break at room temperature is secured at 25% or more, and there is no abnormal oxidation or scale peeling at 850 ° C. and 950 ° C. and excellent oxidation resistance.

  Moreover, in the present invention examples in which the Al content is 0.1% or more and 4% or less, improvement of 0.2% proof stress is observed. About Al content less than 0.1%, it is Al as an inevitable impurity derived from Al added for the purpose of deoxidation.

  Further, No. 1 manufactured at an annealing temperature of 1070 ° C. or higher so that the total precipitation amount is 2% or less. In the case of 1 to 30 steel, the 0.2% proof stress at 850 ° C. is 40 MPa or more, the elongation at break at room temperature is 30% or more, the oxidation resistance at 850 ° C. and 950 ° C. is no problem, and very excellent characteristics Is shown.

  It is a comparative steel, No. The 37, 38, and 39 steels have C, N, and Si that are outside the upper limits, respectively, and their oxidation resistance is lower than that of the inventive steel. No. 41 steel has Cr lower than the lower limit, and its oxidation resistance is lower than that of invention steel. No. Steel No. 43 has less Cu, Mo is off the lower limit, and the high-temperature yield strength is slightly low. Moreover, since Si is slightly low at 0.1%, there is no problem with oxidation resistance at 850 ° C., but it is inferior at 950 ° C. No. Forty steel, Mn is added excessively, resulting in poor oxidation resistance and low ductility at room temperature. No. In Steel Nos. 42 and 44, Cr and Mo are out of the upper limits, respectively, while the high-temperature proof stress is high, but the total precipitation amount is large and the room temperature ductility is low. No. In 45 steel, Cu is out of the upper limit, and the high temperature proof stress is high, but the room temperature ductility is low, and the oxidation resistance is also inferior. No. In Steel Nos. 46 and 47, Ti and Nb are outside the upper limit, and although the high-temperature proof stress is high, the total precipitation amount is large and the room temperature ductility is low. No. In 48 steel, Al is out of the upper limit, and high temperature proof stress is high, but cold ductility is low. No. As for steel No. 49, Si is less than the lower limit of 0.11% as a component of less than 1%, and oxidation resistance is not a problem at 850 ° C., but abnormal oxidation occurred at 950 ° C., so that the oxidation resistance is low. Inferior. No. Steel Nos. 50 to 56 have B, V, W, Sn, Zr, Hf, and Ta additions outside the upper limit, and although the high temperature strength is high, the total precipitation amount is large, so that the room temperature ductility is low, which hinders part processing. No. 57 steel is SUS444, Cu is out of the lower limit, and the high temperature proof stress is low.

Claims (6)

In mass%, C: 0.01% or less, N: 0.02% or less, Si: 0.05 to 1%, Mn: more than 0.6 to 2%, Cr: 15 to 30%, Mo: 1 -4%, Cu: 1 to 3.3 %, Nb: 0.2 to 1.5%, Ti: 0.05 to 0.5%, B: 0.0002 to 0.01%, the balance There Fe and Ri name from unavoidable impurities, excellent ferritic stainless steel high-temperature strength of 0.2% proof stress of 850 ° C. may be higher than 32 MPa. In mass%, C: 0.01% or less, N: 0.02% or less, Si: 0.15 to 1%, Mn: more than 0.6 to 2%, Cr: 15 to 30%, Mo: 0 0.1 to less than 1%, Cu: more than 2 to 3.5%, Nb: 0.2 to 1.5%, Ti: 0.05 to 0.5%, B: 0.0002 to 0.01% containing, and Ri is Na Fe and unavoidable impurities balance, excellent ferritic stainless steel high-temperature strength of 0.2% proof stress of 850 ° C. may be higher than 32 MPa.   The ferritic stainless steel sheet having excellent high temperature strength according to claim 1 or 2, wherein the total precipitation amount is 2% or less in terms of mass%.   The ferrite having excellent high-temperature strength according to any one of claims 1 to 3, characterized by containing at least one of Al: 0.1% to 4% and V: 1% in mass%. Stainless steel sheet.   It contains at least one of W: 5% or less, Sn: 1% or less, Zr: 2% or less, Hf: 2% or less, Ta: 5% or less in mass%. 4. A ferritic stainless steel sheet excellent in high temperature strength according to any one of 4 above.   The method for producing a ferritic stainless steel sheet having excellent high-temperature strength according to any one of claims 3 to 5, wherein the final annealing temperature of the cold-rolled sheet is 1070 ° C or higher.

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