WO2016024370A1 - フェライト系ステンレス鋼板 - Google Patents
フェライト系ステンレス鋼板 Download PDFInfo
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- WO2016024370A1 WO2016024370A1 PCT/JP2015/001030 JP2015001030W WO2016024370A1 WO 2016024370 A1 WO2016024370 A1 WO 2016024370A1 JP 2015001030 W JP2015001030 W JP 2015001030W WO 2016024370 A1 WO2016024370 A1 WO 2016024370A1
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- corrosion resistance
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
Definitions
- the present invention relates to a ferritic stainless steel sheet having excellent corrosion resistance and workability equivalent to or higher than SUH409L.
- Ferritic stainless steel has excellent corrosion resistance and is resource-saving, so it is used in various applications including automobile exhaust system parts, building materials, kitchen appliances, and home appliance parts.
- the most important alloying element contained in ferritic stainless steel is Cr.
- increasing the Cr content improves the corrosion resistance but lowers the workability.
- low Cr steel grades with excellent workability but poor corrosion resistance typically are SUH409L (Japanese Industrial Standard JIS G 4312: 2011, 11 mass% Cr-0.3 mass% Ti)
- a medium Cr steel type typically type is SUS430 (Japanese Industrial Standards JIS G 4305: 2012, 16 mass% Cr)), which has excellent corrosion resistance, is often used depending on the application.
- Patent Document 1 discloses high-purity ferritic stainless steel having excellent surface characteristics and corrosion resistance.
- the corrosion resistance is improved by controlling the form of the Ti-based precipitate.
- Patent Document 2 discloses a ferritic stainless steel sheet having excellent ductility.
- the improvement of elongation is implement
- Patent Document 1 pitting potential, which is an index of corrosion resistance, is examined, but workability such as total elongation and r value is not examined.
- Patent Document 2 product elongation (breaking elongation), which is an index of workability, is examined, but corrosion resistance is not studied. As shown in these figures, in past studies of ferritic stainless steel, there are very few examples focusing on both corrosion resistance and workability.
- the present invention provides a ferritic stainless steel having excellent corrosion resistance and excellent workability equivalent to or better than SUH409L in ferritic stainless steel.
- the inventors of the present invention have made a comprehensive study to satisfy both the corrosion resistance and the workability with respect to the above problems.
- Nb content of 0.010% or more and 0.100% or less is effective in improving workability.
- the added Nb has the effect of forming a solid solution in the steel and reducing the crystal grains. Since a ⁇ 111 ⁇ ⁇ 001> -oriented crystal grain is likely to be generated from a locally inhomogeneous portion in the vicinity of the crystal grain boundary, the ⁇ 111 ⁇ plane in the recrystallization process as the crystal grain is refined by the addition of Nb described above. The generation frequency of recrystallized grains increases.
- the present invention is based on the above findings, and the gist configuration is as follows.
- V 0.01 to 0.25% by mass
- Ti content and Nb content satisfy the following formula (1)
- Ti content, Nb content, and V content are The ferritic stainless steel sheet according to any one of [1] to [5], wherein the following formula (2) is satisfied. 0.10 ⁇ Nb / Ti ⁇ 0.30 (1) 0.20 ⁇ V / (Ti + Nb) ⁇ 1.00 (2)
- the element symbols in the formulas (1) and (2) mean the content of each element.
- the ferritic stainless steel sheet of the present invention is excellent in corrosion resistance and workability. Specifically, according to the present invention, a ferritic stainless steel having excellent corrosion resistance and workability equivalent to or higher than SUH409L can be obtained.
- FIG. 1 is a diagram showing the influence of Ti content and Nb content on corrosion resistance.
- FIG. 2 is a diagram showing the influence of Ti content, Nb content and V content on corrosion resistance.
- the ferritic stainless steel sheet of the present invention is, by mass%, C: 0.025% or less, Si: 0.01 to 1.00%, Mn: 0.05 to 1.00%, P: 0.020 to 0 0.040%, S: 0.030% or less, Al: 0.001 to 0.100%, Cr: 12.5 to 14.4%, Ni: 0.01 to 0.80%, Ti: 0.11 To 0.40%, Nb: 0.010 to 0.100%, and N: 0.020% or less.
- % indicating a component of a ferritic stainless steel sheet means “% by mass” unless otherwise specified.
- C 0.025% or less C is an element effective for increasing the strength of steel. From the viewpoint of obtaining the effect, the C content is preferably 0.001% or more. However, if the C content exceeds 0.025%, the corrosion resistance and workability are significantly reduced. Therefore, the C content is 0.025% or less. More preferably, it is 0.015% or less. More desirably, it is 0.010% or less.
- Si 0.01 to 1.00% Si is an element useful as a deoxidizer. This effect can be obtained by making the Si content 0.01% or more. On the other hand, if the Si content exceeds 1.00%, the steel becomes hard and the workability decreases. Therefore, the Si content is limited to a range of 0.01 to 1.00%. More preferably, it is 0.03 to 0.50% of range. More preferably, it is 0.06 to 0.20% of range.
- Mn 0.05 to 1.00% Mn has a deoxidizing effect. From the viewpoint of obtaining this effect, the Mn content is set to 0.05% or more. On the other hand, when the Mn content exceeds 1.00%, precipitation and coarsening of MnS are promoted and the corrosion resistance is lowered. Therefore, the Mn content is limited to the range of 0.05 to 1.00%. More preferably, it is in the range of 0.10 to 0.40%. More preferably, it is in the range of 0.20 to 0.30%.
- P 0.020 to 0.040%
- P is an element that decreases the corrosion resistance. Moreover, hot workability falls because P segregates at the crystal grain boundary. Therefore, the P content is desirably as low as possible, and is set to 0.040% or less. However, excessive reduction of the P content to less than 0.020% leads to an increase in steelmaking costs. Therefore, the P content is limited to the range of 0.020 to 0.040%. More preferably, it is in the range of 0.020 to 0.030%.
- S 0.030% or less S forms Mn and precipitate MnS.
- the interface between the MnS and the stainless steel base material becomes a starting point of pitting corrosion, and reduces the corrosion resistance of the ferritic stainless steel. Therefore, the lower S content is desirable, and it is 0.030% or less. Preferably it is 0.020% or less. More preferably, it is 0.010% or less.
- Al 0.001 to 0.100%
- Al is an effective element for deoxidation. This effect can be obtained by making the Al content 0.001% or more.
- the Al content is limited to a range of 0.001 to 0.100%. More preferably, it is in the range of 0.01 to 0.08%. More preferably, it is 0.02 to 0.06% of range.
- Cr 12.5 to 14.4% Cr is an important element that determines the corrosion resistance and workability of ferritic stainless steel.
- the corrosion resistance of ferritic stainless steel is obtained by forming a passive film on the steel surface by Cr. Therefore, the corrosion resistance improves as the Cr content increases.
- the corrosion resistance of the steel is improved by adjusting the Cr content to a specific range and adjusting the Ti content and Nb content described below to a specific range.
- the workability of ferritic stainless steel decreases as the Cr content increases. In the present invention, the workability is improved by adding Nb described later.
- Cr in order to obtain the workability equivalent to or higher than SUH409L, Cr can be contained up to 14.4% or less. Therefore, the Cr content is limited to the range of 12.5 to 14.4%. More preferably, it is in the range of 13.0 to 13.8%.
- Ni 0.01 to 0.80%
- Ni is an element that suppresses the anodic reaction due to acid and enables the passive state to be maintained even at a lower pH.
- Ni has an effect of increasing crevice corrosion resistance, remarkably suppresses the progress of corrosion in the active dissolution state, and improves the corrosion resistance of ferritic stainless steel.
- the Ni content is 0.01% or more.
- the Ni content is limited to the range of 0.01 to 0.80%. More preferably, it is in the range of 0.10 to 0.40%.
- Ti 0.11 to 0.40% Ti is an element that fixes C and N, prevents sensitization by Cr carbonitride, and improves corrosion resistance. Furthermore, Ti further improves the corrosion resistance due to the combined effect with Nb described later.
- the Ti content is 0.11% or more.
- the Ti content exceeds 0.40%, the stainless steel plate becomes hard and the workability decreases. Furthermore, Ti-based inclusions are generated on the surface and the surface quality is deteriorated. Therefore, the Ti content is in the range of 0.11 to 0.40%. More preferably, it is in the range of 0.20 to 0.35%.
- Nb 0.010 to 0.100% Nb has the effect of forming a solid solution in the steel and reducing the crystal grains. Since crystal grains with ⁇ 111 ⁇ ⁇ 001> orientation are likely to be generated near the grain boundaries, the proportion of recrystallized grains on the ⁇ 111 ⁇ plane increases in the recrystallization process as the crystal grains are refined by adding Nb. . Thereby, the generation of crystal grains of Goss orientation ( ⁇ 110 ⁇ ⁇ 001>) that increases the in-plane anisotropy and lowers the workability is suppressed, and the in-plane anisotropy of the structure is reduced.
- Nb further improves the corrosion resistance due to the combined effect with Ti described later. The effect is obtained when the Nb content is 0.010% or more. On the other hand, if the Nb content exceeds 0.100%, the ferritic stainless steel is hardened and the workability is lowered. Accordingly, the Nb content is in the range of 0.010 to 0.100%. More preferably, it is in the range of 0.030 to 0.070%.
- the corrosion resistance can be improved by adding Ti and Nb in a composite manner.
- the mechanism is considered as follows. It is known that the corrosion of stainless steel is caused by local destruction of the passive film called pitting corrosion. The cause of pitting corrosion is a local gap in the gap formed near the surface of the precipitate-steel base metal interface due to the difference in strain applied to the precipitate and the steel base metal during processing such as rolling. There is corrosion. MnS and Ti carbonitride are representative of precipitates that form this gap. Furthermore, since Ti carbonitride is coarse and has a linear interface, the anode reaction is concentrated in the gap formed at the interface, and the corrosion resistance of the steel is reduced.
- Nb to Ti takes the form of precipitation of Ti—Nb composite carbonitride in which Nb carbonitride adheres around Ti carbonitride.
- the interface between the Ti—Nb composite carbonitride and the stainless steel base material thus obtained is not linear. That is, since the total length of the interface is increased and the anode reaction is dispersed, pitting corrosion hardly occurs and the corrosion resistance is improved.
- the contents of Ti and Nb are in the above-described ranges. More preferably, the ratio of Nb content to Ti content (Nb / Ti) is 0.10 or more and 0.30 or less. This further improves the corrosion resistance. By setting the ratio (Nb / Ti) to 0.10 or more, the precipitation of Nb carbonitride around the Ti carbonitride becomes sufficient. Further, by setting the ratio (Nb / Ti) to 0.30 or less, it becomes difficult for Nb alone carbonitride to precipitate, and Ti—Nb composite carbonitride is easily formed.
- N 0.020% or less N is an element inevitably mixed in steel. However, if the N content exceeds 0.020%, the corrosion resistance and workability are significantly reduced. Therefore, the N content is 0.020% or less. More preferably, it is 0.015% or less.
- Mo 0.01-0.30%
- Mo has the effect of improving the crevice corrosion resistance of ferritic stainless steel.
- the effect is acquired by making Mo content 0.01% or more.
- Mo content exceeds 0.30%, the effect is not only saturated, but the workability is lowered. Therefore, when Mo is added, the Mo content is set to 0.01 to 0.30%. More preferably, it is 0.03 to 0.10%.
- Cu 0.01 to 0.50%
- Cu has the effect of improving the toughness of steel. The effect is obtained when the Cu content is 0.01% or more. On the other hand, if the Cu content exceeds 0.50%, the toughness of the steel is lowered and the workability is further lowered. Therefore, when Cu is added, the Cu content is set to 0.01 to 0.50%. More preferably, it is 0.01% to less than 0.10%. More preferably, it is 0.03 to 0.06%.
- Co 0.01 to 0.50%
- Co is an element that improves the crevice corrosion resistance of stainless steel. This effect can be obtained by setting the Co content to 0.01% or more. However, if the Co content exceeds 0.50%, the effect is saturated and the workability is further deteriorated. Therefore, when Co is added, the Co content is set to 0.01 to 0.50%. More preferably, it is 0.03 to 0.30% of range. More preferably, it is in the range of 0.05 to 0.10%.
- W 0.01 to 0.50%
- W is an element that improves the crevice corrosion resistance of ferritic stainless steel.
- the W content is preferably 0.01% or more.
- the W content is set to 0.01 to 0.50%. More preferably, it is 0.03 to 0.30% of range. More preferably, it is in the range of 0.05 to 0.10%.
- V 0.01 to 0.25%
- V is an element that improves the crevice corrosion resistance of ferritic stainless steel. This effect is obtained by making the V content 0.01% or more. On the other hand, when the V content exceeds 0.25%, the effect is saturated and the workability is deteriorated. Therefore, V is limited to a range of 0.01 to 0.25%. More preferably, it is 0.03 to 0.20% of range. More preferably, it is 0.05 to 0.10% or less.
- Ti and Nb carbonitrides By containing V in steel, Ti and Nb carbonitrides contain V, and Ti and V composite carbonitrides ((Ti, V) (C, N)) and Nb and V Composite carbonitride ((Nb, V) (C, N)), and further, composite carbonitride ((Ti, Nb, V) (C, N)) is formed.
- the temperature at which precipitation is most promoted which is the precipitation peak temperature, is lower than when V is not included. As a result, grain growth also occurs at lower temperatures.
- Ti—Nb composite carbonitrides Since diffusion is slow at low temperatures, coarsening of each grain is suppressed, and Ti or Nb carbonitrides containing V and their composite carbonitrides (generally referred to as Ti—Nb composite carbonitrides). .), Each carbonitride containing V (generally referred to as Ti—Nb—V composite carbonitride) has a relatively small size and takes a more dispersed precipitate form. As a result of the reduced size of each composite carbonitride, the gap formed between the carbonitride and the steel base material during processing such as rolling is reduced. Therefore, local crevice corrosion is less likely to occur, and the occurrence of pitting corrosion is suppressed, thereby improving the corrosion resistance.
- the contents of Ti, Nb, and V are adjusted so as to be within the above-described ranges, and at the same time, Ti
- the ratio of Nb content to content (Nb / Ti) is 0.10 to 0.30, and the ratio of V content to the total of Ti content and Nb content (V / (Ti + Nb)) Is set to 0.20 or more and 1.00 or less.
- the corrosion resistance is further improved.
- the ratio (V / (Ti + Nb)) to 0.20 or more, the precipitation temperature of (Ti, V) (C, N) or (Nb, V) (C, N) is significantly reduced.
- the ratio (V / (Ti + Nb)) to 1.00 or less, it becomes difficult for V-specific carbonitrides to precipitate, and Ti-Nb-V composite carbonitrides are easily formed.
- Zr 0.01 to 0.30%
- Zr has the effect of fixing C and N like Ti and Nb, preventing sensitization by Cr carbonitride, and improving corrosion resistance. The effect is obtained when the Zr content is 0.01% or more. However, if the Zr content exceeds 0.30%, ZrO 2 and the like are generated and surface scratches occur. Therefore, when Zr is added, the Zr content is set to 0.01 to 0.30%. More preferably, the content is 0.01 to 0.20%.
- B 0.0003 to 0.0030%
- B is an element that improves hot workability and secondary workability.
- B is known to be effective for addition to Ti-added steel. This effect can be obtained by setting the B content to 0.0003% or more.
- the B content exceeds 0.0030%, the workability decreases. Therefore, when B is added, the B content is set in the range of 0.0003 to 0.0030%. More preferably, it is in the range of 0.0010 to 0.0025%. More preferably, it is in the range of 0.0015 to 0.0020%.
- Mg forms Mg oxide together with Al in molten steel and acts as a deoxidizer. This effect can be obtained by setting the Mg content to 0.0005% or more. On the other hand, if the Mg content exceeds 0.0030%, the toughness of the steel is lowered and the productivity is lowered. Therefore, when adding Mg, the Mg content is limited to the range of 0.0005 to 0.0030%.
- Ca 0.0003 to 0.0030%
- Ca is an effective component for preventing nozzle clogging due to crystallization of Ti-based inclusions that are likely to occur during continuous casting. This effect is obtained when the Ca content is 0.0003% or more.
- the Ca content exceeds 0.0030%, the toughness of the steel is lowered and the productivity is lowered.
- the Ca content exceeds 0.0030% the corrosion resistance decreases due to the precipitation of CaS. Therefore, when Ca is added, the Ca content is limited to a range of 0.0003 to 0.0030%. More preferably, it is in the range of 0.0010 to 0.0020%.
- Y 0.001 to 0.20%
- Y is an element that decreases the viscosity of molten steel and improves cleanliness. This effect is obtained when the Y content is 0.001% or more. On the other hand, when the Y content exceeds 0.20%, the effect is saturated and the workability is further deteriorated. Therefore, when Y is added, the Y content is limited to a range of 0.001 to 0.20%. More preferably, it is in the range of 0.001 to 0.10%.
- REM rare earth metal
- REM rare earth metal: elements having atomic numbers 57 to 71 such as La, Ce, and Nd
- REM is an element that improves high-temperature oxidation resistance. This effect is obtained when the REM content is 0.001% or more.
- the REM content exceeds 0.10%, not only the effect is saturated, but also surface defects occur during hot rolling. Therefore, when REM is added, the REM content is limited to a range of 0.001 to 0.10%. More preferably, it is in the range of 0.005 to 0.05%.
- Sn, Sb 0.001 to 0.50%
- These elements are effective in improving ridging resistance by promoting the formation of deformation bands during rolling. This effect is obtained when the content of any of these elements is 0.001% or more. However, when the content of these elements exceeds 0.50%, not only the effect is saturated but also the workability is further lowered. Therefore, when adding Sn or Sb, the respective contents are made 0.001 to 0.50%. More preferably, the respective contents are in the range of 0.003 to 0.20%.
- the balance other than the above components is Fe and inevitable impurities.
- the steel having the above component composition is melted by a known method such as a converter, electric furnace, vacuum melting furnace or the like, and is made into a steel material (slab) by a continuous casting method or an ingot-bundling method.
- This steel material is heated to 1000 ° C. to 1200 ° C. and then hot-rolled to a plate thickness of 2.0 mm to 5.0 mm under a finishing temperature of 700 ° C. to 1000 ° C.
- the hot-rolled steel sheet thus produced is annealed at a temperature of 800 ° C. to 1100 ° C.
- cold-rolled and cold-rolled sheet annealed at a temperature of 700 ° C. to 1000 ° C.
- pickling is performed to remove scale.
- the cold-rolled steel sheet from which the scale has been removed may be subjected to skin pass rolling.
- Table 1 No. in Table 1 (Table 1-1, Table 1-2, and Table 1-3 are combined into Table 1).
- a steel having a composition shown in 1 to 82 was melted in a vacuum melting furnace, and then cast into a 30 kg steel ingot. After heating the steel ingot to a temperature of 1050 ° C., hot rolling was performed at a finishing temperature of 900 ° C. to obtain a hot rolled steel plate having a plate thickness of 5 mm. Thereafter, annealing was performed in an Ar atmosphere at 1000 to 1050 ° C. for 1 minute, dipped in sulfuric acid and pickled, and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1.0 mm. The obtained cold-rolled steel sheet was annealed at 900 ° C. for 1 minute in an Ar atmosphere, and pickled by neutral salt electrolysis, nitric hydrofluoric acid immersion, and nitrate electrolysis to obtain a cold-rolled annealed pickled steel sheet.
- No. 1 in Table 1 Ferritic stainless steel having the compositions shown in 83 and 84 was melted in a vacuum melting furnace, and then cast into a 30 kg steel ingot. After heating the steel ingot to a temperature of 1050 ° C., hot rolling was performed at a finishing temperature of 900 ° C. to obtain a hot rolled steel plate having a plate thickness of 5 mm. Thereafter, annealing was performed in the air at 800 to 850 ° C. for 12 hours, dipping in sulfuric acid and pickling, and then cold rolling to obtain a cold rolled sheet having a sheet thickness of 1.0 mm. The obtained cold-rolled steel sheet was annealed in an Ar atmosphere at 800 ° C. for 1 minute, and was pickled by neutral salt electrolysis, nitric hydrofluoric acid immersion, and nitrate electrolysis to obtain a cold-rolled annealed pickled steel sheet.
- test No. in Table 1 82 and 83 are SUH409L equivalent steel and SUS430 equivalent steel, respectively.
- the ferritic stainless steel cold-rolled annealed pickled steel sheet obtained under the above production conditions was cut to 80 ⁇ 60 mm by shearing. After cutting, it was polished up to 320 with emery polishing paper and degreased with acetone. The end and back of the obtained steel plate were sealed and placed on a cyclic corrosion tester at an inclination of 60 °.
- Corrosion weight loss was 1.0 g / m 2 or less “ ⁇ ”(pass: very good), and 1.0 g / m 2 to 5.0 g / m 2 or less“ ⁇ ” ”(Pass: excellent), what was 5.0 g / m 2 to 8.0 g / m 2 or less“ ⁇ ”(pass: excellent), 8.0 g / m 2 to 16 Those that were 0.0 g / m 2 or less were evaluated as “ ⁇ ” (passed), and those that were larger than 16.0 g / m 2 were evaluated as “ ⁇ ” (failed).
- the 13B test piece specified in JIS Z 2201 was sampled in the rolling direction, the 45 ° direction with respect to the rolling direction, and the direction perpendicular to the rolling direction, and subjected to a tensile test at room temperature to evaluate workability. did. El min 33% or more and those r min is 1.1 or more " ⁇ " (pass), those el min 33% less than or r min is less than 1.1 " ⁇ " (fail) It was.
- Test No. of invention steel In Nos. 1 to 65, the evaluation of corrosion resistance is “ ⁇ ”, “ ⁇ ”, or “ ⁇ ”, and the evaluation of workability is “ ⁇ ”, which indicates that the corrosion resistance and workability are excellent.
- test No. of invention steel satisfying the ratio (V / (Ti + Nb)) of 0.20 or more and 1.00 or less.
- the evaluation of corrosion resistance and workability was “ ⁇ ”.
- FIG. 1 is a graph summarizing the results of the inventive examples, the results of comparative examples in which the Ti content is outside the scope of the present invention, and the results of comparative examples in which the Nb content is outside the scope of the present invention. As shown in FIG. 1, it can be seen that the Ti and Nb contents have better corrosion resistance when the formula (1) is satisfied.
- FIG. 2 is a graph summarizing the results of corrosion resistance in terms of the sum of the V content and the Ti and Nb contents for the inventive examples in which the Ti and Nb contents satisfy the formula (1). As shown in FIG. 2, it can be seen that when the contents of Ti, Nb, and V satisfy the formula (2), they have better corrosion resistance.
- Test steel No. in which the ratio (V / (Ti + Nb)) satisfies 0.20 or more and 1.00 or less. For 34 to 47 and 55 to 65, the evaluation of corrosion resistance and workability was “ ⁇ ”.
- Test No. The comparative examples of 66, 68, 70, and 71 are inferior in corrosion resistance because the contents of Cr, Ni, and Ti are lower than the component ranges of the present invention, respectively.
- Test No. The comparative examples of 67, 69, 72, 73, 76, 77, 78, 79, 80 are inferior in workability because the Cr, Ni, Ti, Nb, V content is higher than the component range of the present invention, respectively. Yes.
- Test No. In Comparative Examples 74 and 75, since the Nb content is lower than the component range of the present invention, both corrosion resistance and workability are inferior.
- the comparative example of 82 does not contain Nb and the Cr content is lower than the range of the present invention, it is inferior in corrosion resistance.
- Test No. The comparative examples 83 and 84 do not contain Nb, and are inferior in workability because the C content, N content and Cr content are higher than the range of the present invention.
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Abstract
Description
0.10≦Nb/Ti≦0.30 (1)
式(1)における元素記号は、各元素の含有量を意味する。
0.10≦Nb/Ti≦0.30 (1)
0.20≦V/(Ti+Nb)≦1.00 (2)
式(1)、(2)における元素記号は、各元素の含有量を意味する。
Cは、鋼の強度を高めるのに有効な元素である。その効果を得る観点からは、C含有量を0.001%以上にすることが好ましい。しかし、C含有量が0.025%を超えると、耐食性および加工性が著しく低下する。よって、C含有量は0.025%以下とする。より好ましくは0.015%以下とする。さらに望ましくは0.010%以下である。
Siは脱酸剤として有用な元素である。この効果はSi含有量を0.01%以上にすることで得られる。一方、Si含有量が1.00%を超えると鋼が硬質化して加工性が低下する。従って、Si含有量は0.01~1.00%の範囲に限定する。より好ましくは、0.03~0.50%の範囲である。さらに好ましくは0.06~0.20%の範囲である。
Mnには脱酸効果がある。この効果を得る観点から、Mn含有量を0.05%以上にする。一方、Mn含有量が1.00%を超えると、MnSの析出および粗大化を促して耐食性が低下する。従って、Mn含有量は0.05~1.00%の範囲に限定する。より好ましくは、0.10~0.40%の範囲である。さらに好ましくは0.20~0.30%の範囲である。
Pは耐食性を低下させる元素である。また、Pが結晶粒界に偏析することで熱間加工性が低下する。そのため、P含有量は可能な限り低いほうが望ましく、0.040%以下とする。しかしながら、0.020%未満への過度なP含有量の低減は製鋼コストの上昇を招く。従って、P含有量は0.020~0.040%の範囲に限定する。より好ましくは0.020~0.030%の範囲である。
SはMnと析出物MnSを形成する。このMnSとステンレス鋼母材の界面は孔食の起点となり、フェライト系ステンレス鋼の耐食性を低下させる。よって、S含有量は低いほうが望ましく、0.030%以下とする。好ましくは0.020%以下である。さらに好ましくは0.010%以下とする。
Alは脱酸のために有効な元素である。この効果はAl含有量を0.001%以上にすることで得られる。一方、Al含有量が0.100%を超えるとAl系の非金属介在物による表面傷の増加により表面品質が低下する。従って、Al含有量は0.001~0.100%の範囲に限定する。より好ましくは0.01~0.08%の範囲である。さらに好ましくは0.02~0.06%の範囲である。
Crはフェライト系ステンレス鋼の耐食性と加工性を決定する重要な元素である。フェライト系ステンレス鋼の耐食性は、Crが鋼表面に不動態皮膜を形成することによって得られる。そのため、Cr含有量を増加させるほど耐食性は向上する。本発明では、Cr含有量を特定の範囲に調整するとともに、後述するTi含有量及びNb含有量も特定の範囲に調整することで、鋼の耐食性を向上させている。本発明において、優れた耐食性を得るためには12.5%以上のCrの含有が必要である。一方、Cr含有量が増加するに従って、フェライト系ステンレス鋼の加工性は低下する。本発明では、後述するNb添加により加工性を向上させており、本発明においては、SUH409Lと同等以上の加工性を得るために、14.4%以下までCrを含有できる。従って、Cr含有量は12.5~14.4%の範囲に限定する。より好ましくは、13.0~13.8%の範囲である。
Niは酸によるアノード反応を抑制し、より低いpHでも不動態の維持を可能にする元素である。すなわちNiは、耐隙間腐食性を高める効果があり、活性溶解状態における腐食の進行を顕著に抑制して、フェライト系ステンレス鋼の耐食性を向上させる。
Tiは、C、Nを固定してCr炭窒化物による鋭敏化を防ぎ、耐食性を向上させる元素である。さらに、Tiは後述するNbとの複合効果により、耐食性をさらに向上させる。
Nbは鋼中に固溶し、結晶粒を細粒化する効果を有する。結晶粒界近傍からは、{111}〈001〉方位の結晶粒が生成されやすいため、Nb添加による結晶粒微細化にともない、再結晶過程において{111}面の再結晶粒の割合が増加する。これにより、面内異方性を増大させて、加工性を低下させるGoss方位({110}〈001〉)の結晶粒の生成が抑制され組織の面内異方性が低減する。この結果、Elmin(圧延方向、圧延方向に対して45度方向、圧延方向に直角方向をそれぞれL方向、D方向、C方向として、各方向の伸びの中での最小値)およびrmin(L、D、C各方向のr値の中での最小値)が増加して加工性が向上する。さらにNbは、後述するTiとの複合効果により、耐食性をさらに向上させる。その効果はNb含有量が0.010%以上で得られる。一方、Nb含有量が0.100%を超えると、フェライト系ステンレス鋼が硬質化して、加工性が低下する。従って、Nb含有量は0.010~0.100%の範囲とする。より好ましくは0.030~0.070%の範囲である。
Nは、鋼中に不可避的に混入する元素である。しかし、N含有量が0.020%を超えると耐食性と加工性が著しく低下する。従って、N含有量は0.020%以下とする。より好ましくは0.015%以下である。
Moには、フェライト系ステンレス鋼の耐隙間腐食性を向上させる効果がある。その効果はMo含有量を0.01%以上にすることで得られる。しかし、Mo含有量が0.30%を超えるとその効果は飽和するだけでなく、加工性が低下する。そこで、Moを添加する場合はMo含有量を0.01~0.30%とする。より好ましくは0.03~0.10%である。
Cuには、鋼の靱性を向上させる効果がある。その効果はCu含有量が0.01%以上で得られる。一方、Cu含有量が0.50%を超えると鋼の靱性は低下し、さらに加工性が低下する。そこで、Cuを添加する場合はCu含有量を0.01~0.50%とする。より好ましくは0.01%~0.10%未満である。さらに好ましくは0.03~0.06%である。
Coは、ステンレス鋼の耐隙間腐食性を向上させる元素である。この効果はCo含有量を0.01%以上にすることで得られる。しかし、Co含有量が0.50%を超えるとその効果は飽和し、さらに、加工性が低下する。そのため、Coを添加する場合は、Co含有量を0.01~0.50%とする。より好ましくは0.03~0.30%の範囲である。さらに好ましくは0.05~0.10%の範囲である。
Wは、フェライト系ステンレス鋼の耐隙間腐食性を向上させる元素である。この効果をえるためにはW含有量は0.01%以上が好ましい。しかし、その含有量が0.50%を超えるとその効果は飽和し、さらに、加工性が低下する。そのため、Wを添加する場合はW含有量を0.01~0.50%とする。より好ましくは0.03~0.30%の範囲である。さらに好ましくは0.05~0.10%の範囲である。
Vは、フェライト系ステンレス鋼の耐隙間腐食性を向上させる元素である。この効果は、V含有量を0.01%以上にすることにより得られる。一方、V含有量が0.25%を超えると、その効果は飽和し、加工性の悪化を招く。従って、Vは0.01~0.25%の範囲に限定する。より好ましくは、0.03~0.20%の範囲である。さらに好ましくは0.05~0.10%以下の範囲である。
ZrにはTiやNbと同様にC、Nを固定して、Cr炭窒化物による鋭敏化を防ぎ、耐食性を向上させる効果がある。その効果はZr含有量が0.01%以上で得られる。しかし、Zr含有量が0.30%を超えるとZrO2等が生成して表面傷が生じる。そこで、Zrを添加する場合はZr含有量を0.01~0.30%とする。より好ましくは0.01~0.20%である。
Bは、熱間加工性や2次加工性を向上させる元素である。Bは、Ti添加鋼への添加が有効であることで知られている。この効果はB含有量を0.0003%以上にすることで得られる。一方、B含有量が0.0030%を超えると加工性が低下する。従って、Bを添加する場合はB含有量を0.0003~0.0030%の範囲にする。より好ましくは、0.0010~0.0025%の範囲である。さらに好ましくは、0.0015~0.0020%の範囲である。
Mgは、溶鋼中でAlとともにMg酸化物を形成し脱酸剤として作用する。この効果はMg含有量を0.0005%以上にすることで得られる。一方、Mg含有量が0.0030%を超えると鋼の靱性が低下して製造性が低下する。従って、Mgを添加する場合はMg含有量を0.0005~0.0030%の範囲に限定する。
Caは、連続鋳造の際に発生しやすいTi系介在物の晶出によるノズルの閉塞を防止するのに有効な成分である。この効果はCa含有量が0.0003%以上で得られる。一方、Ca含有量が0.0030%を超えると、鋼の靱性が低下して製造性が低下する。また、Ca含有量が0.0030%を超えると、CaSの析出により耐食性が低下する。従って、Caを添加する場合は、Ca含有量は0.0003~0.0030%の範囲に限定する。より好ましくは0.0010~0.0020%の範囲である。
Yは、溶鋼の粘度を減少させ、清浄度を向上させる元素である。この効果はY含有量が0.001%以上で得られる。一方、Y含有量が0.20%を超えるとその効果は飽和し、さらに、加工性が低下する。そこで、Yを添加する場合は、Y含有量は0.001~0.20%の範囲に限定する。より好ましくは0.001~0.10%の範囲である。
REM(希土類金属:La、Ce、Ndなどの原子番号57~71の元素)は、耐高温酸化性を向上させる元素である。この効果はREM含有量が0.001%以上で得られる。一方、REM含有量が0.10%を超えるとその効果が飽和するだけでなく、熱間圧延の際に表面欠陥が生じる。そこで、REMを添加する場合はREM含有量を0.001~0.10%の範囲に限定する。より好ましくは0.005~0.05%の範囲である。
これらの元素は、圧延時における変形帯の生成の促進による耐リジング性の向上に効果的である。この効果はこれらの元素のいずれかの含有量が0.001%以上で得られる。しかし、これらの元素の含有量がそれぞれ0.50%を超えるとその効果が飽和するだけでなく、さらに加工性が低下する。そこで、SnやSbを添加する場合はそれぞれの含有量を0.001~0.50%とする。より好ましくは、それぞれの含有量が0.003~0.20%の範囲である。
Claims (6)
- 質量%で、C:0.025%以下、Si:0.01~1.00%、Mn:0.05~1.00%、P:0.020~0.040%、S:0.030%以下、Al:0.001~0.100%、Cr:12.5~14.4%、Ni:0.01~0.80%、Ti:0.11~0.40%、Nb:0.010~0.100%およびN:0.020%以下を含有し、残部がFeおよび不可避的不純物からなることを特徴とするフェライト系ステンレス鋼板。
- Ti含有量およびNb含有量が下記式(1)を満たすことを特徴とする請求項1記載のフェライト系ステンレス鋼板。
0.10≦Nb/Ti≦0.30 (1)
式(1)における元素記号は、各元素の含有量を意味する。 - さらに、質量%で、Mo:0.01~0.30%、Cu:0.01~0.50%、Co:0.01~0.50%、およびW:0.01~0.50%のうちから選んだ1種または2種以上を含有することを特徴とする請求項1または2に記載のフェライト系ステンレス鋼板。
- さらに、質量%でV:0.01~0.25%、Zr:0.01~0.30%、B:0.0003~0.0030%、Mg:0.0005~0.0030%、Ca:0.0003~0.0030%、Y:0.001~0.20%、およびREM(希土類金属):0.001~0.10%のうちから選んだ1種または2種以上を含有することを特徴とする請求項1~3のいずれかに記載のフェライト系ステンレス鋼板。
- さらに、質量%でSn:0.001~0.50%およびSb:0.001~0.50%のうちから選んだ1種または2種を含有することを特徴とする請求項1~4のいずれかに記載のフェライト系ステンレス鋼板。
- 質量%でV:0.01~0.25%を含み、
Ti含有量およびNb含有量が下記式(1)を満たし、
さらに、Ti含有量、Nb含有量、およびV含有量が下記式(2)を満たすことを特徴とする請求項1~5のいずれかに記載のフェライト系ステンレス鋼板。
0.10≦Nb/Ti≦0.30 (1)
0.20≦V/(Ti+Nb)≦1.00 (2)
式(1)、(2)における元素記号は、各元素の含有量を意味する。
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JP2010031315A (ja) * | 2008-07-28 | 2010-02-12 | Nippon Steel & Sumikin Stainless Steel Corp | 加熱後耐食性に優れた自動車排気系部材用省合金型フェライト系ステンレス鋼 |
JP2013100596A (ja) * | 2011-10-14 | 2013-05-23 | Jfe Steel Corp | フェライト系ステンレス鋼 |
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JP2010031315A (ja) * | 2008-07-28 | 2010-02-12 | Nippon Steel & Sumikin Stainless Steel Corp | 加熱後耐食性に優れた自動車排気系部材用省合金型フェライト系ステンレス鋼 |
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