JP2010248620A - Ferritic stainless steel plate excellent in heat resistance and workability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive ferritic stainless steel plate which is excellent in heat resistance and workability. <P>SOLUTION: The ferritic stainless steel plate contains ≤0.02 mass% of C, ≤0.02 mass% of N, ≤2 mass% of Si, ≤2 mass% of Mn, 10 to 20 mass% of Cr, 0.4 to 3 mass% of Cu, 0.01 to 0.5 mass% of Ti, 0.0002 to 0.0030 mass% of B and the remainder consisting of Fe and inevitable impurities. After the ferritic stainless steel plate is hot-rolled, annealing of the hot-rolled plate is omitted and pickling is performed. Then cold-rolling is carried out by a rolling roll with a diameter of 400 mm or more and final annealing is performed to obtain the ferritic stainless steel plate excellent in heat resistance and workability. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a ferritic stainless steel sheet having excellent heat resistance that is optimal for use in exhaust system members that require particularly high temperature strength and oxidation resistance.

  Exhaust system members such as automobile exhaust manifolds, front pipes, and center pipes pass high-temperature exhaust gas exhausted from the engine, so the materials that make up the exhaust members have various characteristics such as oxidation resistance, high-temperature strength, and thermal fatigue characteristics. Is required.

  Conventionally, cast iron is generally used for automobile exhaust members, but stainless steel exhaust manifolds are likely to be used from the viewpoints of strengthening exhaust gas regulations, improving engine performance, and reducing vehicle weight. Became. Although the exhaust gas temperature varies depending on the vehicle type and engine structure, it is often about 600 to 800 ° C., and a material having high high-temperature strength and oxidation resistance in an environment used for a long time in such a temperature range is desired.

  Among stainless steels, austenitic stainless steel has excellent heat resistance and workability, but due to its large thermal expansion coefficient, thermal fatigue failure occurs when applied to a member that repeatedly receives heating and cooling, such as an exhaust manifold. Is likely to occur.

  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), all of which are premised on Nb addition. This increased the high-temperature strength by solid solution strengthening or precipitation strengthening with Nb.

  By the way, when Nb is added, the recrystallization temperature rises, so it is necessary to increase the annealing temperature in the steel plate manufacturing stage. Moreover, since it hardens by addition of Nb, it is necessary to cold-roll after hot-rolled sheet annealing and softening after hot rolling. Further, the toughness is reduced due to Nb precipitates precipitated in the hot rolling process, and troubles such as cracks and breaks may occur in the manufacturing process. In addition, Nb-added steel also has a problem that the r value, which is an indicator of hardening of the product plate, reduction of elongation, and deep drawability, is low. This suppresses the hardenability at room temperature and the development of recrystallized texture due to the presence of solute Nb and precipitated Nb, thereby hindering the pressability and shape freedom when molding an exhaust part. Thus, Nb-added steel has problems in productivity, manufacturability and workability of the steel sheet. In addition, since the manufacturing cost increases due to the addition of Nb, the amount of Nb added can be suppressed if high temperature characteristics can be secured by an additive element other than Nb, and a heat-resistant ferritic stainless steel sheet excellent in workability at low cost can be provided. It becomes possible. Since Mo added to SUS444 has a high alloy cost, there is a problem in that the component cost is significantly increased.

  In addition to Nb and Mo, Patent Documents 1 to 6 disclose techniques relating to Cu addition as alloys that contribute to high temperature strength improvement. In Patent Document 1, addition of Cu of 0.5% or less has been studied for improving low temperature toughness, and Cu addition is not from the viewpoint of heat resistance. Patent Document 2 is a technique that utilizes the action of enhancing the corrosion resistance and weather resistance of steel, and is not an addition from the viewpoint of heat resistance. Patent Documents 3 to 6 disclose techniques for improving high-temperature strength in a temperature range of 600 ° C. or 700 to 800 ° C. using precipitation hardening by Cu precipitates. However, all of these conventional techniques are combined with Nb, and there are problems in manufacturability and cost as well as the above problems in manufacturability. Moreover, although the prior art about the high temperature strength improvement by Cu addition utilizes Cu precipitate, when Cu precipitate is exposed to high temperature for a long time, the coarsening by aggregation and coalescence of a precipitate rapidly Therefore, there is a problem that the precipitation strengthening ability is remarkably lowered. When the engine is subjected to a thermal cycle that accompanies start / stop of the engine, such as an exhaust manifold, there is a risk that thermal fatigue damage will occur due to a significant decrease in high-temperature strength in the long-term use stage. In particular, in the case of a component system in which a large amount of Nb is added, there is a problem that the precipitation strengthening ability due to the Cu precipitates is not exhibited because Cu precipitates are precipitated at the interface between the coarse Laves phase and the parent phase during high-temperature heating. Patent Document 6 discloses a technique for precipitating fine Cu by Nb—Cu—B composite addition. However, composite precipitation with the Laves phase cannot be avoided, and it is premised on the addition of a trace amount of Mo. There was a problem. As described above, there is a study for finely depositing Cu in order to improve the high temperature strength from the viewpoint of heat resistance, but the conventional technology has not led to the fine precipitation of Cu, and it is not possible from the viewpoint of workability and cost. It is enough, and the solution of the problem has not been studied. On the other hand, Patent Documents 7 to 9 disclose steel containing B as a ferritic stainless steel having excellent high-temperature characteristics, but all of them contain B for improving workability, and have high heat resistance. It is not an addition from the viewpoint.

JP 2006-37176 A Japanese Patent No. 3446667 International Publication WO2003 / 004714 Japanese Patent No. 3468156 Japanese Patent No. 3397167 JP 2008-240143 A JP-A-9-279312 JP 2000-169943 A Japanese Patent Laid-Open No. 10-204590

  The present invention provides a ferritic stainless steel that is used in a thermal environment where the maximum temperature of exhaust gas is 600 to 800 ° C. and excellent in heat resistance and workability at low cost.

In the present invention, an object of the present invention is to provide a low-cost ferritic stainless steel sheet for exhaust manifold, in which high temperature characteristics are improved by finely dispersing Cu precipitates by adding Cu in a steel component to which Nb is not added. A new ferritic stainless steel sheet was invented at low cost and excellent in heat resistance and workability by utilizing precipitate refinement by adding Cu-B composite. In order to solve the above-mentioned problems, the present inventors have investigated in detail the high temperature strength developability at about 500 ° C. to 800 ° C. and the normal temperature ductility in steel not containing a large amount of Nb. And as a result of repeating various examinations in order to achieve this purpose, the following knowledge was obtained. As a feature of this, in the case of Cu-added steel, a large amount of Cu precipitates precipitates in the above temperature range, and therefore a method of controlling the form of the precipitates is effective for improving the high temperature strength. Specifically, by adding Ti and Cu in combination, and further adding B, Cu precipitates are uniformly finely precipitated, and it is possible to suppress the strength reduction due to aging heat treatment as well as precipitation strengthening utilization. This is effective for durability stability of components that are subjected to repeated thermal cycles such as an exhaust member and are used for a long period of time. As described above, when Cu is added to the Nb-added steel, Cu precipitates precipitate and act on strengthening, but at the same time, Fe and Nb precipitates (Fe ₂ Nb) called a Laves phase are generated. This is also the same in the Mo-added steel that precipitates of Fe and Mo (Fe ₂ Mo) are generated. In this case, Cu precipitates at the interface between the coarse Laves phase and the matrix phase, so that fine precipitation does not occur, and depending on the temperature conditions, the precipitate rapidly becomes coarse over time. In the case of such a precipitation form, the strengthening ability is lowered and sufficient high-temperature strength cannot be obtained, resulting in low durability. Therefore, in the present invention, in order to obtain the effect of precipitation strengthening with fine Cu precipitates alone and to suppress the coarsening, the fine precipitation technology that does not cause the complex precipitation of the Laves phase and Cu is produced at low cost and exhibits heat resistance performance. It was possible to provide steel materials to be used.

The gist of the present invention for solving the above problems is as follows.
(1) In mass%, C: 0.02% or less, N: 0.02% or less, Si: 2% or less, Mn: 2% or less, Cr: 10-20%, Cu: 0.4-3 %, Ti: 0.01 to 0.5%, B: 0.0002 to 0.0030%, and the balance being Fe and inevitable impurities, ferrite having excellent heat resistance and workability Stainless steel sheet.
(2) In mass%, Nb: 0.01 to 0.3%, Mo: 0.01 to 0.3%, Al: 2.5% or less, V: 1% or less, Zr: 1% or less, The ferritic stainless steel sheet having excellent heat resistance and workability according to claim 1, comprising one or more of Sn: 1% or less.
(3) After hot-rolling ferritic stainless steel having the composition described in (1) or (2), the hot-rolled sheet annealing is omitted and pickling is performed. A method for producing a ferritic stainless steel sheet excellent in heat resistance and workability, characterized by annealing.

  According to the present invention, a ferritic stainless steel sheet excellent in high-temperature strength and workability can be obtained without adding a particularly large amount of Nb. By applying it to exhaust system members such as automobiles in particular, environmental measures and low parts can be obtained. A great effect can be obtained for cost reduction.

It is a figure which shows the 0.2% yield strength in the high temperature tensile test of this invention steel and a comparison steel.

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

  The reason for limitation of the present invention will be described below.

  C deteriorates moldability and corrosion resistance and causes a decrease in high-temperature strength. Therefore, the smaller the content, the better. Therefore, the C content is set to 0.02% or less. However, excessive reduction leads to an increase in refining costs, so 0.001 to 0.009% 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 that is also useful as a deoxidizer and is an element that improves high-temperature strength and oxidation resistance. The high-temperature strength up to about 800 ° C. increases with an increase in the amount of Si, and the effect is manifested at 0.1% or more. However, excessive addition reduces room temperature ductility, so the upper limit is made 2%. Further, considering oxidation resistance, 0.2 to 1.0% is desirable.

  Mn is an element added as a deoxidizer and contributes to an increase in high-temperature strength in the middle temperature range. In addition, it forms on the Mn-based oxide surface layer during long-time use and contributes to the scale adhesion and the effect of suppressing abnormal oxidation. On the other hand, excessive addition of more than 2% lowers ordinary temperature ductility and also forms MnS to lower corrosion resistance, so the upper limit was made 2%. Furthermore, if considering high temperature ductility and scale adhesion, 0.1 to 1.0% is desirable.

  Cr is an essential element for ensuring oxidation resistance and corrosion resistance in the present invention. If it is less than 10%, the effect is not exhibited, and if it exceeds 20%, the workability is deteriorated and the toughness is deteriorated. Furthermore, considering the manufacturability and high temperature ductility, 10 to 18% is desirable.

  As described above, Cu is an element effective for improving the high-temperature strength particularly in the middle temperature range of about 600 to 800 ° C. This is mainly due to precipitation strengthening due to the formation of Cu precipitates in the temperature range. FIG. 1 shows steel A (0.005% C-0.007% N-0.41% Si-0.45% Mn-10.5% Cr-1.25% Cu-0. 15% Ti-0.0009% B), Steel B (0.006% C-0.009% N-0.88% Si-0.31% Mn-13.9% Cr-1.42% Cu- 0.11% Ti-0.0005% B), Steel C (0.004% C-0.011% N-0.11% Si-0.13% Mn-17.5% Cr-1.36% Cu-0.19% Ti-0.0004% B). For comparison, SUH409L (0.005% C-0.007% N-0.35% Si-0.50% Mn-10.5% Cr-0.15% Ti) and Nb- The results for Si steel (0.006% C-0.009% N-0.90% Si-0.35% Mn-13.8% Cr-0.45% Nb) are also shown. Here, the high temperature tensile test was carried out in the rolling direction in accordance with JISG0567, and the 0.2% proof stress was measured. From this, it can be seen that the steel A, steel B, and steel C have higher high-temperature strength than the existing steels SUH409L and Nb-Si steel in any temperature range, although Nb is not added. In the temperature range of about 600 ° C., the strength is high, and it is particularly effective when used in an environment where the exhaust gas temperature is low, and the invention steel can be applied even in an environment below 600 ° C. In the present invention, considering the high temperature proof stress of Nb-Si steel, which is an existing steel used for general purposes, 600 ° C. and 800 ° C. proof stress are 150 MPa or higher and 30 MPa or higher, respectively, as required characteristics of high temperature strength. Such an effect is a precipitation hardening action due to the formation of Cu precipitates, and is manifested by addition of 0.4% or more. Further, in the present invention, as described above, the coarsening of the Cu precipitate due to the composite precipitation with the Laves phase is suppressed, and fine Cu precipitation is caused by the composite addition with Ti and B. On the other hand, excessive addition causes trouble in normal temperature ductility and oxidation resistance. Further, when 3% or more is added, the ear cracking in the hot rolling process becomes prominent and a problem occurs in manufacturability, so the upper limit was made 3%. Considering manufacturability, scale adhesion and weldability, 0.5 to 2.5% is desirable.

  Ti is an element that combines with C, N, and S to improve corrosion resistance, intergranular corrosion resistance, room temperature ductility and deep drawability. In addition, in the compound addition with Cu, addition of an appropriate amount brings about uniform precipitation of Cu precipitates as described above, and improves high-temperature strength and thermal fatigue characteristics. This effect is presumed to be because Ti clusters in the crystal grains or Ti-based fine precipitates become Cu precipitate generation sites, and Cu is not generated coarsely at the grain boundaries. Furthermore, since the recrystallized texture easily develops during recrystallization annealing after cold rolling, it contributes to the improvement of the r value and the press formability is remarkably improved. These effects are manifested from 0.01% or more, but addition of more than 0.5% increases the amount of solid solution Ti and lowers the room temperature ductility, forms coarse Ti-based precipitates, It becomes the starting point of cracks during expansion processing, and press workability deteriorates. Moreover, since oxidation resistance also deteriorates, Ti addition amount was made 0.5% or less. Furthermore, if considering the occurrence of surface flaws and toughness, 0.05 to 0.3% is desirable.

B is an element that improves the secondary workability during product press working. In the present invention, by adding Ti and Cu in combination, Cu precipitates are finely precipitated, which contributes to improvement of high temperature strength. In general, B tends to form (Fe, Cr) ₂₃ (C, B) ₆ or Cr ₂ B in a high temperature range, but these precipitates do not precipitate in Ti—Cu composite added steel. It has been found that there is an effect of finely depositing the Cu precipitate. Cu precipitates are usually very finely precipitated at the initial stage of precipitation and have a large effect of improving the strength, but are coarsened by aging heat treatment, and the strength decrease after aging is large. However, the addition of B suppresses the coarsening of Cu precipitates and increases the strength stability during use. Although the mechanism of the Cu precipitation refinement and coarsening suppression effect by addition of B is not clear, it is presumed that the grain boundary segregation and coarsening of the Cu precipitates are suppressed by the grain boundary segregation of B, and fine precipitation is caused in the grains. . These effects are manifested at 0.0002% or more, but excessive addition deteriorates the hardness, intergranular corrosion and oxidation resistance, and also causes weld cracks, so 0.0002 to 0.0030%. did. Furthermore, if considering corrosion resistance and manufacturing cost, 0.0003 to 0.0015% is desirable.

  In addition to the above elements, Nb, Mo, Al, V, and Zr may be added as necessary.

  Nb may be added as necessary in order to improve the high temperature strength and thermal fatigue characteristics. However, since the formation of a Laves phase occurs and the precipitation strengthening ability due to Cu precipitation is suppressed, addition of a large amount is not desirable. . Further, the workability is hindered and the elongation at break at room temperature required by the present invention cannot be secured, so the upper limit is made 0.3%. Furthermore, 0.01 to 0.2% is desirable from the viewpoint of productivity and manufacturability.

  Mo is an element that further improves high-temperature strength and thermal fatigue characteristics. However, if added in a large amount, the Laves phase precipitates in the same manner as Nb, which is not preferable. Furthermore, since room temperature ductility also falls, addition of trace amount is preferable and 0.01% or more and 0.3% or less are good. More preferably, it is 0.01% or more and 0.2% or less.

  However, when Nb and Mo are added at the same time, there is a concern about deterioration of workability, so the upper limit of the total amount is preferably less than 0.2%.

  In addition to being added as a deoxidizing element, Al is an element added as necessary to improve oxidation resistance. Moreover, it is useful for the strength improvement of 600-700 degreeC as a solid solution strengthening element. The action is stably manifested from 0.01%, but excessive addition hardens to significantly reduce uniform elongation, and toughness is significantly reduced, so the upper limit was made 2.5%. Furthermore, if generation of surface defects, weldability, and manufacturability are taken into consideration, 0.01 to 2.0% is desirable.

  V is an element which is added as necessary because it forms fine carbonitrides and a precipitation strengthening effect is generated, contributing to the improvement of high temperature strength. This effect is stably exhibited by addition of 0.01% or more. However, if added over 1%, the precipitate becomes coarse and the high-temperature strength decreases and the thermal fatigue life decreases, so the upper limit is set to 1%. did. Furthermore, if considering the manufacturing cost and manufacturability, 0.08 to 0.5% is desirable.

  Zr is a carbonitride-forming element like Ti and Nb, contributes to the improvement of high temperature strength and oxidation resistance by increasing the amount of solid solution Ti and Nb, and is stable by adding 0.2% or more. It is an element that is added as necessary to exert its effect. However, since the deterioration of manufacturability due to the addition of more than 1% is remarkable, the content is set to 0.2 to 1%. Furthermore, if considering cost and surface quality, 0.2 to 0.6% is desirable.

  Sn is an element having a large atomic radius and effective for solid solution strengthening, and is an element that is added as necessary because it does not significantly deteriorate the mechanical properties at room temperature. The contribution to high-temperature strength is stably manifested at 0.1% or more, but if added at 1% or more, manufacturability and weldability are significantly deteriorated, so 0.1 to 1% is preferable. Furthermore, if considering oxidation resistance and the like, 0.2 to 0.5% is desirable.

  In the present invention, Nb and Mo were not added or contained at a low concentration, and high temperature strength could be secured. As a result, improvement in room temperature elongation could be realized.

  Next, a manufacturing method will be described. The manufacturing method of the steel plate of this invention consists of each process of steelmaking-hot rolling-pickling-cold rolling-annealing and pickling. In steelmaking, a method in which the steel containing the above essential components and components added as necessary is subjected to furnace melting followed by secondary refining. The molten steel is made into a slab according to a known casting method (continuous casting). The slab is heated to a predetermined temperature and hot-rolled to a predetermined plate thickness by continuous rolling. Regarding cold rolling conditions, is cold rolling of stainless steel sheet usually reverse rolled with a Sendzimir rolling mill with a roll diameter of about 60 to 100 mm or unidirectionally rolled with a tandem rolling mill with a roll diameter of 400 mm or more? It is. Both are rolled in multiple passes.

  In the present invention, in order to increase the r value that is an index of workability, it is preferable to perform cold rolling with a tandem rolling mill having a roll diameter of 400 mm or more. When the roll diameter is as small as 100 mm or less, a large amount of shear strain is introduced in the vicinity of the surface layer during cold rolling, and <111> and <554> crystal orientation development is suppressed during recrystallization annealing in the next process, making it difficult to improve the r value. It becomes. By cold rolling with a large-diameter roll, the crystal orientation is remarkably developed due to suppression of shear strain, which contributes to improvement of the r value. Tandem rolling is unidirectional rolling, and has fewer rolling passes than Sendzimir rolling, and is excellent in productivity. In addition, if the rolling reduction in the cold rolling process is low, a recrystallized structure cannot be obtained after annealing or excessively coarsened to deteriorate the mechanical properties. Therefore, the rolling reduction in the cold rolling process is preferably 30% or more. .

  Moreover, although hot-rolled sheet annealing normally performed in manufacture of a ferritic stainless steel plate may be performed, in the present invention, it is preferable from the viewpoint of improving productivity that the hot-rolled sheet is not annealed. Since normal Nb-added steel has a hot-rolled sheet that is hard, it is annealed before cold rolling, but the steel of the present invention does not add Nb or omits the annealing of the hot-rolled sheet due to the addition of a small amount. This can reduce the manufacturing cost. Further, by omitting the annealing of the hot-rolled sheet, a texture after cold rolling / annealing develops, which leads to an improvement in press formability by improving r value and reducing anisotropy.

  The manufacturing method in other steps is not particularly defined, but hot rolling conditions, hot rolled sheet thickness, cold rolled sheet annealing temperature, atmosphere, and the like 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. In addition, since this invention does not add Nb thru | or low Nb content, the annealing temperature after cold rolling can be made into 850-970 degreeC low temperature. Thereby, high temperature proof stress can be improved compared with the case where annealing temperature exceeds 970 degreeC.

  Steels having the composition shown in Tables 1 and 2 were melted and cast into a slab, and the slab was hot-rolled to form a hot-rolled coil having a thickness of 5 mm. Thereafter, the hot rolled coil was pickled without being annealed, cold-rolled to a thickness of 2 mm, annealed and pickled to obtain a product plate. Here, in cold rolling, unidirectional multi-pass rolling is performed with a rolling mill having a large-diameter roll (diameter 450 mm), and reverse multi-pass rolling is performed with a rolling mill having a small-diameter roll (diameter 100 mm) as a comparison. It was. The annealing temperature of the cold rolled sheet was set to 850 to 970 ° C. in order to make the crystal grain size number about 6 to 8. About the comparative example from which Nb content remove | deviates the upper limit of this invention, the annealing temperature of the cold rolled sheet was 1000-1050 degreeC. No. in the table. 1 to 17 and 37 are steels of the present invention, No. Nos. 18 to 36 are comparative steels. 18 is SUH409L, No. 18; 19 and 20 are steels that have been used as Nb-Si added steels.

  From the product plate thus obtained, a high-temperature tensile test piece was collected, a tensile test was performed at 600 ° C. and 800 ° C., and a 0.2% proof stress was measured (based on JISG0567). A 600 ° C. proof stress of 150 MPa or higher and an 800 ° C. proof strength of 30 MPa or higher were accepted. Further, as an oxidation resistance test, a continuous oxidation test was performed at 900 ° C. in the atmosphere for 200 hours to evaluate whether or not abnormal oxidation occurred (based on JISZ2281). No abnormal oxidation was accepted.

  As normal temperature workability, a JIS No. 13 B test piece was prepared and subjected to a tensile test in the direction parallel to the rolling direction, and the elongation at break was measured. If the elongation at break at room temperature is 35% or more, it becomes possible to process a complicated part.

The evaluation of the r value was performed by taking the JIS No. 13 B tensile test piece and applying 15% strain in the rolling direction, the rolling direction and 45 ° direction, and the rolling direction and 90 ° direction. The average r value was calculated.
r = ln (W ₀ / W) / ln (t ₀ / t) (1)
Here, W ₀ is the plate width before tension, W is the plate width after tension, t ₀ is the plate thickness before tension, and t is the plate thickness after tension.
Average r value = (r ₀ + 2r ₄₅ + r ₉₀ ) / 4 (2)
Here, r ₀ is the r value in the rolling direction, r ₄₅ is the r value in the rolling direction and the 45 ° direction, and r ₉₀ is the r value in the direction perpendicular to the rolling direction. Here, if the average r value is 1.3 or more, it becomes possible to process a complex part. Therefore, it is desirable to have an average r value of 1.3 or more.

  In Tables 1 and 2, the component means mass%. In addition, numerical values outside the scope of the present invention are underlined. As is clear from Tables 1 and 2, No. When steel having the component composition specified in the present invention of 1 to 17 is produced by the ordinary method as described above, the high temperature proof stress at 600 ° C. and 800 ° C. is higher than that of the comparative example, and abnormal oxidation occurs at 900 ° C. It turns out that it is excellent also in oxidation resistance.

  In addition, it can be seen that the mechanical properties at room temperature have a high ductility at break of 35% or more, which is superior to the comparative steel in workability.

  No. of comparative steel. Nos. 18, 19, and 20 are existing steels, but the high-temperature strength is lower than the required value, and comparative steel No. 1 in which Nb is excessively added. 19 and 20 also have a low r value. No. 21 and 22 are inferior in high temperature strength, oxidation resistance, and workability because C and N are outside the upper limits. No. In No. 23, Si is excessively added and the processability is poor. No. In No. 24, Mn is excessively added, which is inferior in oxidation resistance and workability. No. No. 25 has low Cr content and low oxidation resistance as well as low Cr content. No. No. 26 has a low 0.2% yield strength at 600 ° C. and 800 ° C. due to a small amount of Cu added. No. In No. 27, Ti is off the upper limit and the oxidation resistance and workability are poor. No. No. 28 has low ductility because Nb was excessively added with the Ti amount off the lower limit. No. No. 29 has low ductility and r value because Nb is added excessively. No. No. 30 has low oxidation resistance and workability because B is off the upper limit. No. No. 31 has a B addition amount of 0.0001%, which is outside the lower limit, so that the Cu precipitate is coarsened at 800 ° C., the strengthening ability is lowered, and the yield strength is low. No. In Nos. 32 to 36, Mo, Al, V, Zr, and Sn are off the upper limit, so that the room temperature ductility is low, which hinders part processing.

  Among the examples of the present invention, No. 1 using a large diameter roll for cold rolling. 1-17 showed the average r value also as a favorable value of 1.3 or more. No. of the example of the present invention. Steel No. 37 has good high-temperature proof stress and break ductility at normal temperature, but its r-value is lower than the preferred range because the cold-rolled roll diameter is small.

  As is apparent from the above description, according to the present invention, a stainless steel plate excellent in high temperature characteristics and workability can be provided without adding a large amount of expensive alloy elements such as Nb and Mo. By applying to materials, social contributions such as reduction of parts cost and environmental measures by weight reduction are much greater.

Claims (3)

  In mass%, C: 0.02% or less, N: 0.02% or less, Si: 2% or less, Mn: 2% or less, Cr: 10-20%, Cu: 0.4-3%, Ti : Ferritic stainless steel sheet excellent in heat resistance and workability, characterized by containing 0.01 to 0.5%, B: 0.0002 to 0.0030%, the balance being Fe and inevitable impurities .   In mass%, Nb: 0.01 to 0.3%, Mo: 0.01 to 0.3%, Al: 2.5% or less, V: 1% or less, Zr: 1% or less, Sn: 1 The ferritic stainless steel sheet having excellent heat resistance and workability according to claim 1, wherein the ferritic stainless steel sheet is excellent in heat resistance and workability.   After hot-rolling the ferritic stainless steel having the composition according to claim 1 or 2, the hot-rolled sheet annealing is omitted and pickling is performed, and the steel sheet is cold-rolled with a rolling roll having a diameter of 400 mm or more and subjected to final annealing. A method for producing a ferritic stainless steel sheet having excellent heat resistance and workability.

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