JP4137517B2 - Method for producing stainless steel sheet having good surface properties - Google Patents

Description

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【表２】

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【表３】

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【表４】

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【発明の効果】
本発明によって、従来技術では達成できなかった、最終製品表面にマクロ模様のない鋼帯を製造することが出来る。
【図面の簡単な説明】
【図１】成分の異なる熱延鋼帯を製造し、熱延後の熱処理を付与したり省略して、メカニカルデスケーリングし、酸洗し、冷間圧延し、弱酸化性雰囲気中で焼鈍し、電解酸洗した場合に、成分条件をγｐとして纏め、このγｐと、熱延鋼帯の熱処理有無と、筋状の模様との関係を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique related to a method of manufacturing a steel strip having no macro pattern on the surface of a final product when manufacturing a cold rolled steel strip of stainless steel.
[0002]
[Prior art]
Regarding the production of a stainless steel cold-rolled steel strip, a hot coil after hot rolling is descaled and then cold-rolled, annealed, pickled, and manufactured as a product. Such a steel plate is often used on the surface of various devices, and the finished surface is required to be beautiful.
[0003]
Regarding the pickling performed before the product of the manufacturing method of this cold-rolled steel strip, JP-A-61-276999 discloses a Cr-containing steel plate in a sulfuric acid aqueous solution having a specific concentration, fluorosilicate or fluoroborate, and A method of obtaining a steel sheet having a beautiful finish surface by electrolytic pickling with a solution to which nitrate or sulfate is added is shown.
[0004]
Moreover, regarding annealing and pickling performed before the product of the manufacturing method of this cold-rolled steel strip, in JP-A-3-90600, the dew point of the Cr-containing cold-rolled steel sheet is −15 to −40 ° C. in a slightly oxidizing atmosphere. And high-speed mass production of steel plates with smooth appearance by annealing in the range of the recrystallization start temperature of the steel plate to the recrystallization completion temperature + 50 ° C. and electrolytic pickling with an aqueous sulfuric acid solution containing fluorosilicate or the like It is shown.
[0005]
[Problems to be solved by the invention]
As a result of further detailed studies on this production method, the following was found.
When a cold-rolled steel strip is manufactured by the method disclosed in Japanese Patent Application Laid-Open Nos. 61-276999 and 3-90600, a width of 0. 0 in the L direction is formed on the surface of the steel sheet after cold rolling, annealing and pickling. It was found that many streak patterns with a length of about 5 to 2 mm and a length of about 30 to 70 mm may occur.
An object of the present invention is to produce a steel strip without a macro pattern on the surface of a final product that cannot be achieved by the prior art.
[0006]
[Means for Solving the Problems]
In order to solve this problem, the gist of the present invention is as follows.
(1) By mass
C: 0.12% or less, Si: 1.00% or less,
Mn: 1.00% or less, P: 0.1% or less,
S: 0.030% or less, Cr: 10-20%,
Ni: 0.75% or less, Cu: 0.005 to 0.20%,
Ti: 0.001 to 0.30 %, Al: 0.001 to 0.30 %,
N: 0.06% or less, the balance being Fe and inevitable impurities, producing a hot-rolled steel strip controlled to the composition shown in the following formula (1), and as a heat treatment after hot-rolling, after hot-rolling When annealing after cooling the coil, the annealing temperature is 700 to 880 ° C. , the annealing temperature is 1 to 6 hours , mechanical descaling, pickling, cold rolling, dew point −15 to −40 ° C., hydrogen After annealing in a temperature range from the recrystallization start temperature of the steel sheet to the recrystallization completion temperature + 60 ° C. in a weakly oxidizing atmosphere with a concentration of 1 to 20% , a fluorosilicate or fluoroboric acid is added in a 20 to 400 g / L sulfuric acid aqueous solution. one or two of salt added 1~50g per sulfate aqueous solution 1L (liter), further nitrate, in pickling solution mixed 50~400g per aqueous sulfuric 1L one or sulfates, current density 20 ~ 60 Method for producing a good stainless steel surface texture, characterized in that to produce electrolytically pickled / Dm ^2.
γp (%) = 420 * [C] + 470 * [N] + 23 * [Ni] + 9 * [Cu] + 7 * [Mn] -11.5 * [Cr] -11.5 * [Si] -12 *
[Mo] -23 * [V] -47 * [Nb] -49 * [Ti] -52 * [Al] +189 ≧ 30 ・ ・ ・ ・ Formula (1)
(2) As a heat treatment after hot rolling, the steel strip winding temperature after hot rolling is kept at 700 ° C. or higher, and annealing is performed after coil cooling, and the stainless steel with good surface properties according to (1) above A method of manufacturing a steel sheet .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
As a result of various detailed studies for solving the problems, the present inventors, as a method for producing a steel strip having no macro pattern on the surface of the final product, have performed hot rolling in which components are controlled so that γp becomes a certain value or more. It has been found that it is most effective to produce a steel strip, annealed, mechanically descaled, pickled, cold-rolled, annealed in a weakly oxidizing atmosphere, and electrolytically pickled. Hereinafter, it demonstrates according to an experimental result.
[0008]
As described above, when a cold-rolled steel strip is manufactured by the method disclosed in JP-A-61-276999 and JP-A-3-90600, L is applied to the steel plate surface after cold-rolling, annealing and pickling. It was found that a large number of streak patterns having a width of about 0.5 to 2 mm and a length of about 30 to 70 mm may occur in the direction.
[0009]
Therefore, the present inventors examined the heat treatment conditions after hot rolling that can reduce the occurrence of such patterns by the following experiments.
Using a SUS430 hot rolled steel strip 3-5 mm thick, annealing is omitted at a coiling temperature of 600 ° C. or annealing at 700-880 ° C. for 2 hours, mechanical descaling, pickling, 0.6- Cold rolled to a thickness of 1.2 mm, annealed at 880 ° C. for 20 seconds in a weakly oxidizing atmosphere with a dew point of −20 ° C. containing 8% hydrogen in nitrogen, and in a 100 g / L (liter) sulfuric acid aqueous solution, Electrolytic pickling was performed for 10 seconds at 80 ° C. at a current density of 40 A / Dm ² with an aqueous solution in which 20 g / L Na ₂ SiF ₆ , 50 g / L NaNO ₃ and 50 g / L Na ₂ SO ₄ were mixed.
[0010]
FIG. 1 shows the results of summarizing the relationship between the occurrence of the streak pattern produced in this manner and the calculation of the component condition γp and the presence or absence of heat treatment of the hot-rolled steel strip.
As is apparent from FIG. 1, when the heat treatment of the hot-rolled steel strip is omitted, a lot of streak patterns are generated and become slightly better as γp increases. Further, when annealing is performed at 700 to 880 ° C. for 2 hours, a great improvement is observed, and when γp is 30% or more, there are no streak patterns.
[0011]
As described above, the reason why it is effective to increase γp and to provide annealing is that the γp is small and the generation of γ phase in the hot-rolled steel strip is small, and the hot-rolled steel strip is not sufficiently annealed. In some cases, micro unevenness along the rolling L direction is likely to occur during cold rolling. This is because when the recesses and the projections are annealed in a weakly oxidizing atmosphere, a difference occurs in the generation of oxide scale, and a pattern is formed after electrolytic pickling. For this reason, it is considered that increasing γp for reducing minute irregularities after cold rolling and annealing are effective.
[0012]
Next, the reason for limiting the present invention will be described.
The reasons for limiting the components are as follows. The unit is mass%.
C is preferably lower in terms of pitting corrosion resistance and corrosion resistance, but the upper limit is set to 0.12% in consideration of manufacturability.
[0013]
Si is a useful component having a deoxidizing action, but if it exceeds 1.00%, hot workability deteriorates, and surface flaws during hot rolling frequently occur. It was 1.00% or less.
[0014]
Mn contributes effectively to the maintenance of mechanical strength and deoxidation, but if it exceeds 1.00%, it causes a disadvantage of toughness deterioration, and surface flaws occur frequently in hot rolling, so 1.00% It is necessary to do the following.
[0015]
P is a harmful element that concentrates at the grain boundaries as the solid solubility of P decreases and causes segregation at the grain boundaries, and creates intergranular corrosion grooves when combined with sulfuric acid. The lower the value, the better. And 0.1% or less.
S is desirably as low as possible for improving corrosion resistance, and is 0.030% or less.
[0016]
Cr is an important element as stainless steel for improving corrosion resistance and oxidation resistance. For this purpose, at least 10% is necessary. On the other hand, if it exceeds 20%, toughness is deteriorated. % Range.
[0017]
Ni has an effect of imparting excellent corrosion resistance and acid resistance, and also has an effect of improving pitting corrosion resistance and crevice corrosion resistance. However, since addition exceeding 0.75% impairs economic efficiency, it was made 0.75% or less.
[0018]
Cu is an element useful for improving corrosion resistance and mechanical strength. However, if it is less than 0.005%, a desired effect cannot be obtained. On the other hand, if it exceeds 0.20%, hot workability decreases. Therefore, the content is limited to 0.005 to 0.20%.
[0019]
Ti is an element useful for improving corrosion resistance and mechanical properties. However, if it is less than 0.001%, a desired effect cannot be obtained. On the other hand, if it exceeds 0.30%, hot workability decreases. Therefore, the content is limited to 0.001 to 0.30%.
[0020]
Al is a component that has a deoxidizing action and is useful for the material, but if less than 0.001%, the desired effect cannot be obtained, and if it exceeds 0.30%, hot workability deteriorates. Since surface flaws frequently occur during hot rolling, the content is set to 0.30% or less.
[0021]
N is an element useful for improving corrosion resistance and mechanical strength. However, if it exceeds 0.06%, it is not preferable in terms of a decrease in hot workability, so it is limited to a range of 0.06% or less.
[0022]
These components are represented by the above formula (1), that is, γp (%) = 420 * [C] + 470 * [N] + 23 * [Ni] + 9 * [Cu] + 7 * [Mn] -11.5 * [Cr] −11.5 * [Si] −12 * [Mo] −23 * [V] −47 * [Nb] −49 * [Ti] −52 * [Al] + 189 ≧ 30 is there.
When γp is 30% or more, the streak pattern disappears in combination with annealing of the hot-rolled steel strip. On the other hand, if less than 30%, improvement is difficult even when combined with annealing.
[0023]
In the heat treatment of the steel strip after hot rolling, it is effective to reduce the streak pattern by setting the annealing temperature to 700 to 880 ° C. when annealing after cooling the coil. If the heating temperature is less than 700 ° C., there is no effect, and if the heating temperature is 700 ° C. or higher, the effect is further increased. However, if a γ phase appears above 880 ° C., ear cracks occur during cold rolling and the rolling load increases, so the temperature was set to 880 ° C. or lower.
[0024]
The heat treatment of the steel strip after hot rolling also works effectively by maintaining the winding of the steel strip after the hot rolling at a temperature of 700 ° C. or higher. Below 700 ° C. there is no effect and above 700 ° C. there is an effect .
[0025]
These steel strips after heat treatment are mechanically descaled and pickled to completely remove the oxide scale, and then cold-rolled and annealed in a weakly oxidizing atmosphere. About the annealing conditions of a cold-rolled steel strip, let a dew point be in -15--40 degreeC weakly oxidizing atmosphere. In the range of −15 to −40 ° C., an oxide scale that is easy to electrolytically pickle is formed. On the other hand, an oxide scale having a thickness that cannot be removed by electrolytic pickling at temperatures higher than −15 ° C. is generated. The lower the dew point, the better, but the equipment cost increases to obtain a dew point lower than −40 ° C. It is because it ends.
[0026]
This weakly oxidizing atmosphere is obtained by adding 1-20% of hydrogen in nitrogen. If the hydrogen concentration is less than 1%, the thickness of the oxide scale becomes extremely thick, and the pickling operation to be performed later becomes complicated. Further, if the hydrogen concentration exceeds 20%, the cost of the gas to be supplied increases, which causes problems in safety management in terms of operation.
[0027]
Moreover, in order to make a product steel strip into a soft steel strip which is easy to process, it anneals in the range of the recrystallization start temperature of a steel plate-recrystallization completion temperature +60 degreeC. Softening is not stable at a recrystallization completion temperature of less than + 20 ° C., but is stable at + 20 ° C. or higher. This is because if the temperature exceeds + 60 ° C., the grains are likely to grow and the structure cannot be made constant.
[0028]
As an electrolytic pickling solution, a fluorosilicate such as Na ₂ SiF ₆ or a fluoroborate such as NaBF ₄ is added to a 20 to 400 g / L (liter) sulfuric acid aqueous solution, and NaNO ₃ and Na ₂ SO ₄ are added. A pickling solution in which one or two of nitrate and sulfate are mixed. 20 to 400 g / L is in enabling stable electrolytic pickling sulfate, pickling ability is extremely small at less than 20 g / L, it is hardly properly controlling the pickling capacity exceeds 400 g / L.
[0029]
A fluorosilicate such as Na ₂ SiF ₆ or a fluoroborate such as NaBF ₄ is added to greatly improve the removal rate of the oxide scale. The amount added is preferably 1 to 50 g per liter (liter) of aqueous sulfuric acid solution. When the amount is less than 1 g per liter of sulfuric acid aqueous solution, the effect is hardly observed, while when the amount exceeds 50 g, the effect is saturated.
[0030]
Nitrate such as NaNO ₃ promotes dissolution of the base when the steel strip becomes a cathode during electrolytic pickling, and sulfate such as Na ₂ SO ₄ suppresses over pickling in electrolytic pickling. Added. The amount added is preferably 50 to 400 g per liter of sulfuric acid aqueous solution. When the amount is less than 50 g per liter of sulfuric acid aqueous solution, the effect is hardly observed, while when the amount exceeds 400 g, the effect is saturated.
In the electrolytic pickling, indirect energization pickling is performed by providing a set of two anode plates and a cathode plate facing both surfaces of a steel strip passing through a pickling bath.
[0031]
【Example】
As shown in Table 1, SUS430 steel is a hot rolled steel strip having a γp of 30% or more, and annealing at 700 to 880 ° C. shown in Table 2 is performed, or the steel strip winding temperature after hot rolling is 700 ° C. or higher, Mechanical descaling, pickling, 40-90% cold rolling, annealing under the conditions in Table 3, and electrolytic pickling under the conditions in Table 4. The final product steel strip manufactured under these conditions did not have a streak pattern as shown in Table 2. On the other hand, streaky patterns were clearly observed in the steel strips manufactured under other conditions.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
[Table 3]

[0035]
[Table 4]

[0036]
【The invention's effect】
According to the present invention, it is possible to produce a steel strip having no macro pattern on the surface of the final product, which can not be achieved by the prior art.
[Brief description of the drawings]
[Fig. 1] Manufacturing hot-rolled steel strips with different components, applying or omitting heat treatment after hot rolling, mechanical descaling, pickling, cold rolling, annealing in a weakly oxidizing atmosphere The figure which summarizes component conditions as (gamma) p when electrolytically pickling, and shows the relationship between this (gamma) p, the heat processing presence or absence of a hot-rolled steel strip, and a streaky pattern.

Claims (2)

By mass
C: 0.12% or less,
Si: 1.00% or less,
Mn: 1.00% or less,
P: 0.1% or less,
S: 0.030% or less,
Cr: 10 to 20%,
Ni: 0.75% or less,
Cu: 0.005 to 0.20%,
Ti: 0.001 to 0.30%,
Al: 0.001 to 0.30%,
N: 0.06% or less, the balance being Fe and inevitable impurities, producing a hot-rolled steel strip controlled to the composition shown in the following formula (1), and as a heat treatment after hot-rolling, after hot-rolling When the coil is cooled and then annealed, the annealing temperature is 700 to 880 ° C , the annealing temperature is 1 to 6 hours , mechanical descaling, pickling, cold rolling, dew point -15 to -40 ° C, hydrogen After annealing in a temperature range from the recrystallization start temperature of the steel sheet to the recrystallization completion temperature + 60 ° C. in a weakly oxidizing atmosphere having a concentration of 1 to 20% , a fluorosilicate or fluoroboric acid is added in a 20 to 400 g / L sulfuric acid aqueous solution. one or two of salt added 1~50g per sulfate aqueous solution 1L (liter), further nitrate, in pickling solution mixed 50~400g per aqueous sulfuric 1L one or sulfates, current density 20 ~ 60 Method for producing a good stainless steel surface texture, characterized in that to produce electrolytically pickled / Dm ^2.
γp (%) = 420 * [C] + 470 * [N] + 23 * [Ni] + 9 * [Cu] + 7 * [Mn] -11.5 * [Cr] -11.5 * [Si] -12 *
[Mo] -23 * [V] -47 * [Nb] -49 * [Ti] -52 * [Al] +189 ≧ 30 ・ ・ ・ ・ Formula (1) The method for producing a stainless steel plate with good surface properties according to claim 1, characterized in that, as the heat treatment after hot rolling, the steel strip winding temperature after hot rolling is maintained at 700 ° C or higher and annealing is performed after coil cooling. .

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