JP2010507021A - Ferritic stainless steel excellent in workability of welds and corrosion resistance of steel materials and method for producing the same - Google Patents

Abstract

A ferritic stainless steel and a method for producing the same are provided. Ferritic stainless steel is, by weight, C: 0.01% or less, N: 0.01% or less, Si: 1.0% or less, Mn: 1.0% or less, Cr: 10.0-20. 0%, Al: 0.15% or less, Ca: 0.0005-0.002%, Zr: 0.0018-0.01%, O: 0.004-0.008%, and the balance Fe And other inevitable impurities. This ferritic stainless steel may further include one or more of Nb: 0.01 to 0.5% and Ti: 0.01 to 0.5%. According to this ferritic stainless steel, a ferritic stainless steel that improves the workability of the welded portion by refining the solidified crystal grains of the welded portion by adding Ca and Zr in combination, and also has excellent corrosion resistance of the steel material. Can be provided.

Description

  The present invention relates to a material excellent in workability of a welded portion and corrosion resistance of a steel material. More specifically, the corrosion resistance is improved by controlling the component and size of the oxide of the steel material, and the solidification nucleus of the oxide. The present invention relates to a ferritic stainless steel that can improve the workability of a welded part by refining the solidified crystal grains of the welded part using the action of generation.

  In recent years, stricter exhaust gas regulations and lighter weight have led to demands for improved fuel efficiency in the automobile industry, and automakers have superior heat resistance and corrosion resistance in place of existing castings or aluminized steel sheets as exhaust system parts. Ferritic stainless steel is used.

  The exhaust system component material is largely configured in a shell shape and a pipe shape, and many of them are manufactured and assembled by welding. Therefore, ensuring the quality characteristics of the welded portion is a very important factor that affects the performance of exhaust system parts. As an example, the exhaust system material is processed into a predetermined shape after processing a steel plate or a welded pipe (a pipe manufactured by a method such as high-frequency welding, TIG welding, or laser welding) into a product. Since the exhaust system parts have a very complicated shape, a part of the steel plate or pipe being formed is subjected to severe processing. When ferritic stainless steel pipe material is subjected to secondary processing such as bending or expansion of the weld, weld cracking occurs in the weld metal or weld heat-affected zone, which is related to the excellent workability of the base metal. In many cases, the workability of the welded portion is lowered and it is difficult to exert its characteristics. Such a phenomenon remarkably occurs due to brittle cracks in the pipe weld when it is molded under low temperature or high speed processing conditions such as in winter.

  According to the conventional known technology, the factors that reduce the workability of the welded part are largely summarized into four types: residual stress during pipe forming, hardening, impurity elements such as C and N, and coarsening of solidified crystal grains. it can. In order to reduce the residual stress, the method of annealing the entire pipe and excluding the deformation near the weld is the most effective. In patent document 1, the pipe manufactured by welding is annealed in the temperature range of 850-1000 degreeC, and the method of cooling with the cooling rate of 1 degreeC / sec or more is proposed. According to this method, it is reported that the workability and toughness of the pipe can be improved to the extent of cold-rolled annealed plates. However, an increase in the manufacturing unit cost is unavoidable when annealing is performed, and sufficient quality characteristics are ensured when annealing is performed on highly alloyed pipes in order to ensure high heat resistance and oxidation resistance. I can't.

  The hardening phenomenon of the welded portion has a close relationship with alloy elements such as Si, Mn, Ti, and Nb and the amount of impurity elements such as C and N. Alloy elements are added as basic elements for exhibiting the characteristics of the manufacturing process and products, and their content is often difficult to control. Therefore, a method of reducing the amount of impurity elements C and N is positive. Has been developed and applied. In the known technology, impurity elements such as C and N are added to elements such as Ti, Nb, and Zr, which are stabilizing elements, along with improvements in steelmaking processes such as vacuum oxygen decarburization (VOD) refining technology. Nitride or carbide is added to form the current, but the current VOD process reduces the amount of C + N to about 100 ppm, and it has been pointed out that there is a problem of lowering productivity and increasing unit price due to the addition of steelmaking process. ing. In order to reduce the amount of solid solution C and N by adding a stabilizing element such as Ti, Nb and Zr to form a nitride or carbide, the amount of the stabilizing element is 8 times the amount of C + N. Based on the addition of the above, when it is a weld metal, it may be added up to 20 times recently.

  However, when a large amount of Ti is added, coarse oxidized inclusions or precipitates are formed, and surface cracks and surface defects are likely to occur during rolling, and when Zr is added, nozzle clogging occurs during steelmaking. There is a problem of doing. Also, when rapidly heated and cooled like a welded part, the precipitates can be generated for a very short time, so even if the content of Ti, Nb, Zr, etc. is simply increased, sufficient precipitates are formed. On the contrary, there are cases where workability cannot be ensured by increasing the amount of Ti, Nb, Zr and C, N, etc. in the solid solution.

  On the other hand, in recent years, there has been proposed a method for improving workability by refining the solidification structure of steel and weld metal. The control method of the solidified structure is roughly divided into improvement of equipment such as electromagnetic induction stirring of molten steel (see Non-Patent Document 1) and technology for promoting ferrite nucleation of inclusions by adding alloy components. In the method using electromagnetic induction stirring, it is known that an equiaxed crystal ratio of about 40 to 60% of the steel material is secured by optimizing the stirring position of the molten steel during solidification. Although the above technique can improve the workability of the steel material, there is a problem that the effect cannot be ensured when the steel material is remelted like welding.

  For the refinement of the solidification structure using inclusions, a method using TiN precipitates (references 1 and 2) and oxides (references 3 to 10) is known. In the following description, (%) indicates wt%.

  1. Non-Patent Document 2: A method in which 0.4% Ti and 0.016% N are contained in the molten metal, and TiN is generated with a molten steel superheat degree DT of 40 ° C. or lower.

  2. Patent Document 2: A technology that contains 0.01% or more of a single TiN inclusion and secures an equiaxed crystal ratio of 60% at the slab stage.

  3. Patent Document 3 and Patent Document 4: 0.001 to 0.02% Mg and 0.001 to 0.2% Al are added to form a Mg-Al based composite oxide, and the solidification structure of the welded portion is fine. How to turn.

4). Patent Document 5: After adding 0.0005 to 0.01% Mg into molten steel deoxidized to an oxygen content of 0.01% or less, Mg-based oxidation is performed by starting solidification of the molten steel within 180 seconds. What contains the size of the object in the steel material with a density distribution of 0.01 to 5 mm, 3 pieces / mm ² .

  5. Patent Document 6: A method of forming a composite inclusion of Mg—Al-based oxide and Ti-based nitride in steel by setting the content ratio of Mg and Al to 0.3 to 0.5%.

  6). Patent Document 7: Using Mg inclusions formed by adding 0.0005 to 0.01% Mg to refine the solidified structure and optimize the hot rolling conditions to process the material without cold rolling To improve performance.

  7). Patent Document 8: Technology for improving workability, surface characteristics, and corrosion resistance by adding Mg and Ca contents of 0.006% or less to refine the solidified crystal grains of the steel material.

8). Patent Document 9: A composite inclusion of 0.01 to 5 mm Mg-based oxide and TiN precipitate is distributed in a steel material at a density of 3 pieces / mm ² or more.

  9. Patent Document 10: Addition of 0.001 to 0.05% of rare earth metal Y to form inclusions such as Al-Y, Mg-Y, Al-Mg-Y, and refine solidified crystal grains Technology to prevent brittle cracking in steel plate manufacturing process and steel pipe manufacturing process.

10. Patent Document 11: 0.01-0.3% Ti and 0.01-0.2% Al are added, and Ar, O ₂ , CO ₂ , He, etc. are used as protective gases, and 0 in the weld metal A method of distributing Ti and Al nitride of 3 mm or more to a density of 1.5 × 10 ⁴ pieces / mm ² or more.

  11. Patent Document 12: containing 0.0003 to 0.003% Ca and 0.01% or less O, and controlling the contents of O and S in the range of S / 1.25 + O / 5 ≧ 0.003, and selectively A method in which 0.001 to 0.3% of Zr is added to form CaS or CaO in the steel material, and the role of nucleation of the ferrite (111) surface is promoted during hot rolling.

  In the above technique, Documents 1 and 2 are techniques for crystallizing TiN in the molten metal to refine the solidification structure of the steel ingot. However, these techniques are difficult when temperature control of the molten metal is difficult as in welding. It is difficult to apply, and a large amount of Ti and TiN damages the toughness of the steel, which may further increase the problem of brittle cracking of ferritic stainless steel.

  The techniques of Documents 3 to 10 are methods in which Mg, Y or the like is added alone or in combination to generate oxides in the molten metal and promote solidification nucleation, but Mg, Y, etc., which are excellent in oxidation reactivity When added to the molten metal, it is difficult to predict the recovery rate, so the quality of each steel material varies frequently and there are handling problems such as explosiveness.

  The technique of Document No. 11 is a method of generating CaS and CaO in a molten metal and promoting the generation of a ferrite (111) surface having excellent workability during hot rolling. However, according to this technique, coarse oxidation inclusions or sulfides are formed by adding Zr after Ca is charged and removing residual oxygen. Such coarse inclusions reduce the surface quality of the steel material, resulting in a decrease in corrosion resistance due to an increase in the interfacial area between the inclusions and the matrix, and adding a large amount of Zr increases the production unit price. There are also problems.

  In this way, the need for ferritic stainless steel that can ensure the workability of welded parts of steel and the corrosion resistance of steel has been highlighted, but no alternative has been presented. is there.

Japanese Unexamined Patent Publication No. 1997-125209 Japanese Unexamined Patent Publication No. 2000-160299 Japanese Unexamined Patent Publication No. 1997-217151 Japanese Unexamined Patent Publication No. 1997-271900 Japanese Unexamined Patent Application Publication No. 1998-324956 Japanese Unexamined Patent Publication No. 2001-020046 Japanese Unexamined Patent Publication No. 2001-181808 Japanese Unexamined Patent Publication No. 2001-288543 Japanese Unexamined Patent Publication No. 2001-294991 Japanese Unexamined Patent Publication No. 2002-285292 Japanese Unexamined Patent Publication No. 2002-336990 Japanese Laid-Open Patent Publication No. 2003-221652

Iron and steel (Vol. 66 (1980), No. 6, 66th edition, p. 38) Iron and steel (Vol. 66 (1980), p. 110)

  An object of the present invention is to solve the above-described problems of the prior art, and to provide a ferritic stainless steel excellent in workability of a welded portion and corrosion resistance of a steel material and a method for producing the same.

  According to one aspect of the present invention, the ferritic stainless steel of the present invention is, by weight, C: 0.01% or less, N: 0.01% or less, Si: 1.0% or less, Mn: 1.%. 0% or less, Cr: 10.0-20.0%, Al: 0.15% or less, Ca: 0.0005-0.002%, Zr: 0.0018-0.01%, O: 0.004 -0.008% and the balance Fe and other inevitable impurities. This ferritic stainless steel may further include at least one of Nb: 0.01 to 0.5% and Ti: 0.01 to 0.5%.

  According to another aspect of the present invention, the method for producing hot-rolled or cold-rolled ferritic stainless steel according to the present invention includes a step of producing a molten stainless steel in an electric furnace, and a step of refining the produced molten stainless steel. A step of continuously casting the refined molten metal to obtain a steel ingot, a step of rolling the cast steel ingot, and a step of annealing the rolled rolled steel material, whereby weight% C: 0.01% or less, N: 0.01% or less, Si: 1.0% or less, Mn: 1.0% or less, Cr: 10.0-20.0%, Al: 0.15 %: Ca: 0.0005-0.002%, Zr: 0.0018-0.01%, O: 0.004-0.008%, Ti: 0.01-0.5%, and Ferrite containing balance Fe and other inevitable impurities Providing stainless steel, in said step of refining comprises the step of charging the Ca was added to Zr in the molten metal. The refining step may further include a step of controlling oxygen to 0.01% or less before adding Zr to the molten metal.

  As described above, according to the ferritic stainless steel of the present invention, by adding Ca and Zr in combination, the solidified crystal grains of the welded portion are refined to improve the workability of the welded portion, and the corrosion resistance of the steel material is improved. In addition, it is possible to provide an excellent ferritic stainless steel.

  Hereinafter, the present invention will be described in detail.

  In order to improve the low temperature workability and corrosion resistance of ferritic stainless steel welds, the present invention refines the solidified crystal grains of the welds and forms sufficient carbonitrides to reduce the amount of residual C and N. It is characterized by.

  Hereinafter, the reason for limiting the components of the ferritic stainless steel of the present invention will be described.

  C, N: C and N are elements that reduce the workability of the base metal and the welded portion, so it is preferable to make the amount as small as possible, and in consideration of an increase in manufacturing cost, C: 0.01% or less , N: 0.01% or less.

  Si, Mn, Al, P, S: These are present in the steel invariably, but if present in a large amount, the workability is lowered and the corrosion resistance characteristic of stainless steel is lowered. %, Mn: 1.0% or less, Al: 0.15% or less, P: 0.040% or less, and S: 0.010% or less.

  When Cr: Cr is less than 10%, the corrosion resistance, which is a basic characteristic of stainless steel, is insufficient. Therefore, when Cr: 10% or more and the amount of Cr increases, the toughness of the welded portion may deteriorate. Therefore, Cr: 20% or less.

  Ca: Ca is an essential element for improving the weldability which is the subject of the present invention. In order to improve weldability, 0.0005% or more is necessary. However, if it is 0.002% or more, the size of oxidized inclusions increases and adversely affects corrosion resistance. %.

  Zr: Zr is an essential element for improving the weldability, which is the subject of the present invention, like Ca. In addition, Zr may improve the corrosion resistance of the steel material by minimizing the size of the oxide particles, and may form nitrides or carbides to form oxides and composite inclusions. In order to improve weldability and corrosion resistance, 0.002% or more is necessary, but if it is 0.01% or more, there is a problem of nozzle clogging during the steel making process along with an increase in cost due to an increase in addition amount. Since points occur, the upper limit is made 0.01%.

  O: O is an element that forms Zr and Ca-based oxides. When the content is 0.004% or less, formation of the oxide is difficult, and when the content is 0.008% or more, the effect of quality improvement is small. Therefore, when the workability of the weld is strongly required, the oxygen content is preferably 0.005% or less.

  Ti: Ti is an element that improves workability. If it is 0.01% or more, its effect appears, but if added over 0.5%, workability deteriorates due to an increase in the amount of solid solution Ti. There is a problem of doing.

  An alloying element may be further included depending on physical properties required for the steel including the above-described component system. For example, for improving the corrosion resistance, at least one of Mo, Ni and Cu can be further added in an amount of 0.1 to 2.0%. When the content of at least one of Mo, Ni, and Cu is 0.1% or more, an effect of improving the corrosion resistance is obtained, and when it exceeds 2.0%, the workability is deteriorated and the manufacturing cost is increased. Further, Nb may be contained up to 0.5%, but if it exceeds 0.5%, there is a problem that workability is deteriorated due to an increase in the amount of solid solution Nb. Therefore, when Nb is added to form NbN, NbC or the like to improve workability, it is preferably added in the range of 0.01 to 0.5%.

As the steel satisfying the composition range according to the present invention, there is a Ca-Zr-based or Ca-Zr-Ti-based oxide. These may be included in a size of 1 to 3 μm and a density of 5 to 10 pieces / mm ² . In this case, Ti-based or Nb-based precipitates of 1 μm or less may be included at a density of 39000 / mm ² or more.

  Below, the manufacturing method of the ferritic stainless steel of this invention is demonstrated.

  The ferritic stainless steel of the present invention described above is manufactured through the following steps. First, a molten stainless steel is manufactured in an electric furnace, and the manufactured molten stainless steel is refined, and then the refined molten metal is continuously cast to obtain a steel ingot, and the steel ingot is rolled to obtain a rolled steel material. This rolled steel material is annealed.

  Moreover, in embodiment of this invention, in order to obtain Ca-Zr and a Ca-Zr-Ti type | system | group oxide, the process of charging Ca after adding Zr to a molten metal in a refining step is included. In this case, the amount of oxide can be adjusted more effectively by controlling the oxygen to 0.01% or less. Conventionally, it is a technique for removing residual oxygen by adding Zr after Ca is charged, but in this case, coarse CaO or CaS is formed to reduce the quality and corrosion resistance of the steel surface, and a large amount of Zr is added. There is a problem that the manufacturing unit price increases.

  When Ca and oxygen react to form single CaO, the size of the oxide is too large, causing the problems described above. When ZrO is formed, the size is reduced and acts as a solidification nucleus. Can not do it. Accordingly, an object of the present invention is to form a complex oxide of Ca and Zr and control the size of the oxide to a size suitable for acting as a solidification nucleus.

  However, since Ca is more reactive with oxygen than Zr, when Zr is added after adding Ca first, or when it is added at the same time, a large amount of Zr is required to obtain the effect of the present invention. If Zr is added in a large amount, ZrO and ZrN are generated in a large amount, which causes a problem of brittle cracking and an increase in manufacturing unit cost.

  The present invention is characterized in that Zr is added before Ca is added. When a small amount of Zr is added first, ZrO is formed to lower the concentration of oxygen, and then Ca is added to form a complex oxide with Zr to optimize the size of the oxide and to process it. And corrosion resistance can be improved.

  Ti reacts with nitrogen to form TiN, and the nitrogen concentration is lowered to improve workability. Ti is added before the refining step, that is, before Zr and Ca, but TiN has a melting point lower than that of the Ca—Zr or Ca—Zr—Ti oxide, and the Ca—Zr or Ca— It is formed after the formation of the Zr-Ti-based oxide, and is formed so that TiN surrounds a part of the Ca-Zr-based or Ca-Zr-Ti-based oxide, and the Ca-Zr-based or Ca-Zr-Ti Forms complex inclusions with system oxides. Nb, like Ti, forms a nitride to form a complex inclusion with a Ca—Zr-based or Ca—Zr—Ti-based oxide, and can be added selectively or together with Ti.

  Since the oxide and composite inclusions have a high melting point, even if they are further welded after being formed in the molten metal step, they exist in the newly solidified structure and act as solidification nuclei. This is particularly effective for improving the workability and corrosion resistance of welds.

  Here, Ti or Nb that forms Ti-based or Nb-based precipitates reacts with carbon in the molten metal, and forms precipitates in the form of TiC or NbC to improve workability. The main component of the precipitate is carbide, but a part of the precipitate may be nitride.

  An example of the refining method according to the present invention is shown in Table 1 below.

  In Table 1, when Ca is added before Zr, Ca has a higher reactivity with oxygen than Zr, and CaO and ZrO single form oxides are formed. On the other hand, when Zr is added before Ca, a composite oxide such as a Ca—Zr-based oxide is formed, and in this case, the recovery rate of Zr is improved.

  According to the present invention, the weldability is improved by any of the welding methods that pass through the melting and solidification processes, such as GTA welding, laser welding, and plasma welding, regardless of the type of welding method. The welding conditions can be selected in accordance with various conditions such as material composition, steel plate thickness, and purpose.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this only describes the preferable Example of this invention, and does not limit the scope of the present invention.

Example 1
10 types of ferritic stainless steels having different compositions shown in Table 2 are melted, and a steel sheet with a thickness of 1.5 mm is manufactured by hot rolling, annealing, pickling, cold rolling, second pickling, etc. GTA welding was performed. In Table 2, no. No. 1 has a basic alloy composition of STS409L. Nos. 2 to 3 are obtained by adding Ca alone. 4 to 9 show the composite addition of Ca and Zr when the content of C + N is changed. No. 10 is a comparative example when the oxygen amount is not controlled. Nb is 0.014% in Example 4, 0.012% in Example 9, and 0.013% in the remaining examples.

  The production method of the present invention includes a step of producing a molten stainless steel having the composition shown in Table 1 in an electric furnace, a step of refining the produced molten stainless steel, and a step of continuously casting the refined molten metal to obtain a steel ingot. And rolling the cast steel ingot, and annealing the rolled steel ingot, and the refining step controls oxygen to O: 0.004 to 0.008%. And a step of adding Ca after adding Zr to the molten metal immediately before the continuous casting.

  The amount of oxygen is controlled using Si or Al deoxidizer in the AOD or VOD step, and since Ca and Zr are volatile, the amount remaining during addition in the electric furnace process or AOD or VOD process is reduced. Therefore, it was added immediately before the continuous casting process. Here, a Fe—Ca-based material for Ca and a pure metal plate material for Zr were used.

  GTA welding was performed using a bead-on plate using a DC type welding machine (maximum welding current 350 A). The welding conditions were: welding current: 110 A, welding speed: 0.32 m / min, tungsten electrode diameter: 2.5 mm, electrode tip angle: 100 °, arc length: 1.5 mm, protective gas Ar (15 (l / min)) )Met.

  The size of the crystal grains in the weld was measured using an optical microscope. The cross section of the welded portion was polished using sandpaper and an abrasive, and was observed after electrolytic etching with a Nital solution. The hardness distribution of the welded portion was measured using a micro Vickers hardness tester with a load of 200 g and a holding time of 10 seconds at intervals of 0.2 mm.

  In the method of measuring the distribution of oxide and precipitate particles, the number and size of oxide and precipitate particles having a size of 1 μm or more are measured using an electron probe microanalyzer (EPMA), and each mirror surface is measured on the EPMA. The polished test piece was placed, the elements forming the oxide and the precipitate were mapped and measured in 10 fields of view of 5000 times, and then the occupation ratio was calculated. For oxides and precipitates of less than 1 μm, replicas were copied onto a mesh and analyzed with 10 fields of view at 10,000 to 100,000 magnifications using a transmission electron microscope.

  The DBTT characteristics of the welded portion were tested by a Charpy impact test on a test piece having a quarter size (1.5 mm thickness × 10 mm width × 55 mm length) in a test temperature range of −60 to 100 ° C. In the pitting corrosion test, a φ15 disk specimen was polished with sandpaper # 600 and then left in the air for 5 hours or longer to form a passive film. As a solution, 800 ml of 3.5% NaCl was used.

  Table 3 shows the results of evaluating the impact characteristics of the welded portion and the corrosion resistance of the steel materials for 10 types of test materials. When Examples 4 to 9, which are examples of the present invention, are compared with the Ca and Zr additive-free materials and Ca single additive materials of Examples 1 to 3, when Ca and Zr are added together, the size and hardness of the crystal grains of the welded portion And the variation in DBTT characteristics and impact energy of the welds was improved. In the example in which both Ca and Zr are added, the pitting potential value increases, and the corrosion resistance of the steel can be improved. In particular, when Ca and Zr are added in combination, even if the content of C and N is about 180 ppm, the low temperature impact characteristics of the weld and the corrosion resistance of the steel material can be ensured, and the operating time of the refining process can be reduced. It is determined that the effect of shortening can be obtained. Further, in the example of the present invention in which the oxygen concentration was controlled to 0.01% or less, the weldability was improved and the corrosion resistance was excellent as compared with Example 10 in which the oxygen concentration was not controlled.

(Example 2)
Five types of ferritic stainless steels having different compositions shown in Table 4 were melted, and a steel plate material having a thickness of 1.5 mm was manufactured by hot rolling, annealing, cold rolling, etc., and GTA welding was performed. In Table 4, no. No. 11 has a basic alloy composition of STS409L. No. 12 is obtained by adding only Ca. 13-15 shows what added Ca and Zr combined when the content of C + N was changed. Nb is 0.013% in Examples 11, 12, 14, and 15, and 0.014% in Example 13.

  The production method of the present invention includes a step of producing a molten stainless steel having the above composition in an electric furnace, a step of refining the produced molten stainless steel, a step of continuously casting the refined molten metal to obtain a steel ingot, and the above Rolling the cast steel ingot, and annealing the rolled steel ingot, and the refining step is a step of adding Ca after adding Zr to the molten metal immediately before continuous casting And including.

  Since Ca and Zr have volatility, there is a problem in that the amount remaining during addition in the electric furnace process, AOD or VOD process is reduced, so they were added immediately before the continuous casting process. Here, a Fe—Ca-based material for Ca and a pure metal plate material for Zr were used.

  GTA welding was performed using a bead-on plate using a DC type welding machine (maximum welding current 350 A). The welding conditions were: welding current: 110 A, welding speed: 0.32 m / min, tungsten electrode diameter: 2.5 mm, electrode tip angle: 100 °, Arc length 1.5 mm, protective gas Ar (15 (l / min)) Met.

  The size of the crystal grains in the weld was measured using an optical microscope. The cross section of the welded portion was polished using sandpaper and an abrasive, electrolytically etched with a nital solution, and then observed. The hardness distribution of the welded portion was measured using a micro Vickers hardness tester with a load of 200 g and a holding time of 10 seconds at intervals of 0.2 mm.

  In the method of measuring the distribution of oxide and precipitate particles, the number and size of oxide and precipitate particles having a size of 1 μm or more are measured using EPMA, and each mirror-polished test piece is placed on EPMA. The elements forming the oxides and precipitates were mapped and measured in 10 fields of view of 5000 times, and the occupation ratio was calculated. For oxides and precipitates of less than 1 μm, replicas were copied onto a mesh and analyzed with 10 fields of view at 10,000 to 100,000 magnifications using a transmission electron microscope.

  The DBTT characteristics of the welded portion were tested by a Charpy impact test on a test piece having a quarter size (1.5 mm thickness × 10 mm width × 55 mm length) in a test temperature range of −60 to 100 ° C. In the pitting corrosion test, a φ15 disk specimen was polished with sandpaper # 600 and then left in the air for 5 hours or longer to form a passive film. As a solution, 800 ml of 3.5% NaCl was used.

  Table 5 shows the results of evaluating the impact characteristics of the welds for the five types of test materials. When Examples 13 to 15 which are examples of the present invention are compared with the Ca and Zr additive-free material and the Ca single additive material of Examples 11 to 12, when Ca and Zr are added in combination, Hardness decreased, and the DBTT characteristics and impact energy variation of the welded part improved. In particular, when Ca and Zr are added in combination, even if the content of C and N is about 180 ppm, the low temperature impact characteristics of the weld and the corrosion resistance of the steel material can be ensured, and the operating time of the refining process It has been determined that the effect of shortening can be obtained.

Claims (14)

  % By weight: C: 0.01% or less, N: 0.01% or less, Si: 1.0% or less, Mn: 1.0% or less, Cr: 10.0 to 20.0%, Al: 0 .15% or less, Ca: 0.0005 to 0.002%, Zr: 0.0018 to 0.01%, O: 0.004 to 0.008%, and the balance Fe and other inevitable impurities Including ferritic stainless steel.   The ferritic stainless steel according to claim 1, wherein the stainless steel includes a Ca—Zr-based oxide and a Ti-based precipitate.   The ferritic stainless steel according to claim 2, wherein the stainless steel includes a Ca—Zr—Ti oxide. The stainless steel contains 3 to 10 μm of Ca—Zr or Ca—Zr—Ti oxide at a density of 5 to 10 / mm ² , and 39000 Ti precipitates having a size of 1 μm or less. pieces / mm comprising at least ^two density, ferritic stainless steel according to claim 2.   2. The ferritic stainless steel according to claim 1, wherein, when welding is applied, the stainless steel has a crystal grain of a welded portion of 300 μm or less and a hardness of the welded portion of 145 Hv or less.   % By weight: C: 0.01% or less, N: 0.01% or less, Si: 1.0% or less, Mn: 1.0% or less, Cr: 10.0 to 20.0%, Al: 0 .15% or less, Ca: 0.0005 to 0.002%, Zr: 0.0018 to 0.01%, O: 0.004 to 0.008%, Nb: 0.01 to 0.5% And Ti: Ferritic stainless steel containing at least one component selected from the group consisting of 0.01 to 0.5% and the balance Fe and other inevitable impurities.   The ferritic stainless steel according to claim 6, wherein the stainless steel includes a Ca—Zr-based oxide and a Ti-based precipitate.   The ferritic stainless steel according to claim 7, wherein the stainless steel includes a Ca—Zr—Ti oxide.   The ferritic stainless steel according to claim 6, wherein, when welding is applied, the stainless steel has a crystal grain of a welded portion of 300 μm or less and a hardness of the welded portion of 155 Hv or less. % By weight: C: 0.01% or less, N: 0.01% or less, Si: 1.0% or less, Mn: 1.0% or less, Cr: 10.0 to 20.0%, Al: 0 .15% or less, Ca: 0.0005 to 0.002%, Zr: 0.0018 to 0.01%, O: 0.004 to 0.008%, and the balance Fe and other inevitable impurities A manufacturing method for manufacturing ferritic stainless steel containing
Producing a molten stainless steel in an electric furnace;
Refining the produced stainless steel melt,
Continuously casting the refined molten metal to obtain a steel ingot;
Rolling the cast steel ingot;
Annealing the rolled rolled steel material,
The refining step includes a step of controlling oxygen to 0.01% or less, and a step of adding Ca after adding Zr to the molten metal, and a method for producing ferritic stainless steel. When the welding is applied, the stainless steel includes a Ca—Zr-based or Ca—Zr—Ti-based oxide having a size of 1 to 3 μm in a welded portion at a density of 5 pieces / mm ² or more and 1 μm or less. The manufacturing method of the ferritic stainless steel of Claim 10 which contains the Ti-type deposit of the magnitude | size of 39000 piece / mm < ² > or more.   11. The method for producing a ferritic stainless steel according to claim 10, wherein, when welding is applied, the stainless steel has a crystal grain of a welded portion of 300 μm or less and a hardness of the welded portion of 145 Hv or less. % By weight: C: 0.01% or less, N: 0.01% or less, Si: 1.0% or less, Mn: 1.0% or less, Cr: 10.0 to 20.0%, Al: 0 .15% or less, Ca: 0.0005 to 0.002%, Zr: 0.0018 to 0.01%, O: 0.004 to 0.008%, Nb: 0.01 to 0.5% And at least one component selected from the group consisting of 0.01 to 0.5%, and a method for producing a ferritic stainless steel containing the balance Fe and other inevitable impurities,
Producing a molten stainless steel in an electric furnace;
Refining the produced stainless steel melt,
Continuously casting the refined molten metal to obtain a steel ingot;
Rolling the cast steel ingot;
Annealing the rolled rolled steel material,
The refining step includes a step of adding Ca to Zr after adding Zr to the molten metal, and a method for producing ferritic stainless steel.   The ferritic stainless steel manufacturing method according to claim 13, wherein when the welding is applied, the stainless steel has a crystal grain of a welded portion of 300 μm or less and a hardness of the welded portion of 155 Hv or less.