JP4322726B2 - Manufacturing method of stainless steel sheet with excellent surface gloss - Google Patents
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- 229910001220 stainless steel Inorganic materials 0.000 title claims description 32
- 239000010935 stainless steel Substances 0.000 title claims description 31
- 238000004519 manufacturing process Methods 0.000 title claims description 19
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 99
- 238000000137 annealing Methods 0.000 claims description 40
- 229910000831 Steel Inorganic materials 0.000 claims description 37
- 239000010959 steel Substances 0.000 claims description 37
- 150000001447 alkali salts Chemical class 0.000 claims description 36
- 238000007654 immersion Methods 0.000 claims description 34
- 238000005554 pickling Methods 0.000 claims description 24
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 14
- 238000001816 cooling Methods 0.000 claims description 14
- 229910017604 nitric acid Inorganic materials 0.000 claims description 14
- 230000001590 oxidative effect Effects 0.000 claims description 14
- 229910052760 oxygen Inorganic materials 0.000 claims description 10
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 9
- 239000001301 oxygen Substances 0.000 claims description 9
- 229910052938 sodium sulfate Inorganic materials 0.000 claims description 9
- 235000011152 sodium sulphate Nutrition 0.000 claims description 9
- 238000005868 electrolysis reaction Methods 0.000 claims description 7
- 239000000243 solution Substances 0.000 claims description 2
- 239000007864 aqueous solution Substances 0.000 claims 2
- 238000000034 method Methods 0.000 description 15
- 239000002253 acid Substances 0.000 description 11
- 239000000463 material Substances 0.000 description 10
- 238000010438 heat treatment Methods 0.000 description 8
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 238000005097 cold rolling Methods 0.000 description 5
- 230000003628 erosive effect Effects 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 229910052748 manganese Inorganic materials 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 238000004383 yellowing Methods 0.000 description 4
- 239000002585 base Substances 0.000 description 3
- 238000005260 corrosion Methods 0.000 description 3
- 230000007797 corrosion Effects 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000000758 substrate Substances 0.000 description 3
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 239000003513 alkali Substances 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 238000007598 dipping method Methods 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000012266 salt solution Substances 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 1
- 150000001342 alkaline earth metals Chemical class 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000002932 luster Substances 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000033116 oxidation-reduction process Effects 0.000 description 1
- 238000002161 passivation Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 229910052596 spinel Inorganic materials 0.000 description 1
- 239000011029 spinel Substances 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
Description
本発明は、酸化雰囲気焼鈍、溶融アルカリ塩処理によるスケール改質、硝弗酸浸漬によるスケール除去を行うステンレス鋼板の製造方法に関し、特に表面光沢に優れるステンレス鋼板の製造方法に関するものである。 The present invention relates to a method for manufacturing a stainless steel plate that performs annealing in an oxidizing atmosphere, scale modification by molten alkali salt treatment, and scale removal by immersion in nitric hydrofluoric acid, and particularly relates to a method for manufacturing a stainless steel plate having excellent surface gloss.
ステンレス鋼は、化学工業や産業装置分野だけではなく、美しい金属光沢と耐食性を備えた素材として、家電製品、建築建材、各種装飾品、厨房器具、食品関連機器・容器、日用品などにも広く使用されている。ところで、ステンレス鋼は冷間圧延後に、燃焼性ガス雰囲気などの酸化性雰囲気で焼鈍(酸化焼鈍)すると表面に酸化スケールが生成するため、焼鈍後にスケール除去処理を行うのが一般的である。 Stainless steel is widely used not only in the chemical industry and industrial equipment field, but also as a material with beautiful metallic luster and corrosion resistance, for home appliances, building materials, various decorative items, kitchen utensils, food-related equipment / containers, daily necessities, etc. Has been. By the way, when stainless steel is annealed (oxidation annealing) in an oxidizing atmosphere such as a combustible gas atmosphere after cold rolling, an oxide scale is generated on the surface. Therefore, the scale removal treatment is generally performed after annealing.
こうした工程の中で実施される酸洗は、その前工程である焼鈍時に表面に生成した酸化スケールを除去することを目的とするものであるが、スケール除去が完全でない場合には、結果としてステンレス鋼板の表面美観を損ねるのみならず、耐食性を低下させることとなる。従って、酸洗工程では確実にデスケーリングを完了させるために、例えば特許文献1に酸濃度を分析して酸を補給したり酸の消費量に応じて酸を補給する方法が開示されている。また、その処理時間を長く取ったり、使用する酸の組成範囲や使用回数、温度等の管理に厳しい規制を加えたりするなどの格別な配慮が必要である。
The pickling performed in such a process is intended to remove the oxidized scale formed on the surface during annealing, which is the previous process, but if the scale removal is not complete, the result is stainless steel. This not only impairs the surface aesthetics of the steel sheet, but also reduces the corrosion resistance. Therefore, in order to reliably complete descaling in the pickling step, for example,
この酸洗工程でのデスケーリング技術をより有効に実施する上で、焼鈍中に形成する酸化スケール性状をよりデスケールし易いものに制御することが重要である。こうした中で、特許文献2には酸洗でスケールを除去し易いスケール厚みを0.15μm以下または0.25μm以上となるように焼鈍条件を設定し、脱スケール性を向上させる手法が開示されている。また、特許文献3には所定加熱温度領域を700〜900℃とし、この所定加熱温度領域における昇温速度を50〜200℃/secで急速加熱させることによりスケール生成を抑えスケール除去の酸洗時間を短縮する方法が開示されている。さらに、特許文献4には焼鈍時の雰囲気中の残留酸素濃度を2vol.%以上とし、750℃までを毎秒50℃以上で加熱すると共に750℃を超える温度域に750℃までに要した加熱時間の0.8倍以上滞在させることによりスケール中のCr濃度を増大させ中性塩溶液による電解デスケールがより容易となる技術が開示されている。
In order to more effectively implement the descaling technique in the pickling process, it is important to control the oxide scale property formed during annealing to be more easily descaled. Under these circumstances,
ところで、ステンレス鋼の表面品質に対する要求は近年益々厳しくなっている。従来のスケールが除去できていれば良いというレベルから、光学機器で計測される白色度を高位に保ち、しかも製造ロット間で均一に揃えることや、高い光沢度と白色度を共に有するなどという高い品質が求められている。この際、酸洗デスケールにおいて、過度に下地侵食を行うと、光沢度が低下し好ましくない。しかし、光沢を高めようとデスケールを弱めると軽微なスケール残りに起因する黄ばみが生じ、白色度を高めることができなくなる。また、高い光沢と白さを両立するためには、粒内は平坦で粒界のみが酸で侵食された表面形態とする必要がある。 By the way, the demand for the surface quality of stainless steel has become increasingly severe in recent years. From the level that the conventional scale can be removed, the whiteness measured by the optical equipment is kept high, and it is evenly uniform between production lots, and it has both high glossiness and whiteness. Quality is required. At this time, if the base erosion is excessively performed in the pickling descale, the glossiness is lowered, which is not preferable. However, if the descaling is weakened to increase the gloss, yellowing due to a slight scale residue occurs, and the whiteness cannot be increased. In order to achieve both high gloss and whiteness, it is necessary to have a surface form in which grains are flat and only grain boundaries are eroded by acid.
そこで、発明者らは、焼鈍条件と酸洗条件を共に適切に管理することで、デスケールが容易なスケールを形成させ、下地を過度に侵食することなくデスケールを完遂することで、高い白色度と高い光沢度を両立できるステンレス鋼の焼鈍酸洗条件を見出すことを試み成功した。 Therefore, the inventors appropriately controlled both the annealing condition and the pickling condition, thereby forming a scale that can be easily descaled, and by completing the descaling without excessively eroding the ground, high whiteness and We succeeded in finding an annealing pickling condition for stainless steel that can achieve both high glossiness.
即ち、本発明の要旨とするところは以下の通りである。
(1)ステンレス鋼板を冷間圧延し、その後に酸化性雰囲気中で900℃以上の温度で焼鈍し、引き続き焼鈍後の鋼板を溶融アルカリ塩処理してスケール改質を行い、硝弗酸浸漬にてスケール除去を行うステンレス鋼板の製造方法において、
Y≦0.7X+75.3
但し,Y:酸化雰囲気中での焼鈍処理において、900℃以上の温度域に滞在する時間(sec)、
X:硝弗酸浸漬時間(sec)
なる関係を満足する条件を用いて焼鈍酸洗することを特徴とする表面光沢に優れるステンレス鋼板の製造方法。
(2)鋼板を酸化性雰囲気中で900℃以上に焼鈍するまでの各温度域での酸素濃度が、500℃未満で3%未満、500℃以上900℃未満で5%未満、900℃以上で5%以上10%未満であることを特徴とする上記(1)に記載の表面光沢に優れるステンレス鋼板の製造方法。
(3)鋼板を900℃以上に焼鈍した後の冷却において、500℃以下までの鋼板の平均冷却速度が5℃/sec以上20℃/sec以下であることを特徴とする上記(1)又は(2)に記載の表面光沢に優れるステンレス鋼板の製造方法。
(4)焼鈍後の鋼板を溶融アルカリ塩処理する時の溶融アルカリ塩の温度が440℃以上480℃以下、およびその時の鋼板の温度が420℃以上450℃以下であることを特徴とする上記(1)乃至(3)のいずれかに記載の表面光沢に優れるステンレス鋼板の製造方法。
(5)溶融アルカリ処理と硝弗酸浸漬の間に、電解酸洗を実施することを特徴とする上記(1)乃至(4)のいずれかに記載の表面光沢に優れるステンレス鋼板の製造方法。
(6)上記(5)に記載の電解酸洗において、濃度が100g/L以上150g/L以下の硝酸と、100g/L以下の硫酸ナトリウムの混合液を用い、電流密度が20mA/cm2以上100mA/cm2以下であることを特徴とする表面光沢に優れるステンレス鋼板の製造方法。
That is, the gist of the present invention is as follows.
(1) Cold-rolling a stainless steel plate, and then annealing in an oxidizing atmosphere at a temperature of 900 ° C. or higher . Subsequently, the steel plate after annealing is treated with molten alkali salt to modify the scale, and immersed in nitric hydrofluoric acid. In the method of manufacturing a stainless steel plate for descaling,
Y ≦ 0.7X + 75.3
However, Y: Time for staying in a temperature range of 900 ° C. or higher (sec) in the annealing treatment in an oxidizing atmosphere,
X: Nitrofluoric acid immersion time (sec)
A method for producing a stainless steel sheet having excellent surface gloss, characterized by annealing and pickling using conditions that satisfy the following relationship:
(2) The oxygen concentration in each temperature range until the steel sheet is annealed to 900 ° C. or higher in an oxidizing atmosphere is less than 3% at less than 500 ° C., less than 5% at 500 ° C. to less than 900 ° C., and more than 900 ° C. It is 5% or more and less than 10%, The manufacturing method of the stainless steel plate excellent in surface gloss as described in said (1) characterized by the above-mentioned.
(3) In cooling after annealing the steel plate to 900 ° C. or higher, the average cooling rate of the steel plate up to 500 ° C. or lower is 5 ° C./sec or more and 20 ° C./sec or less (1) or ( A method for producing a stainless steel sheet having excellent surface gloss as described in 2).
(4) The above, wherein the temperature of the molten alkali salt when the molten steel sheet is treated with the molten alkali salt is 440 ° C. or higher and 480 ° C. or lower, and the temperature of the steel plate at that time is 420 ° C. or higher and 450 ° C. or lower ( The manufacturing method of the stainless steel plate which is excellent in the surface gloss in any one of 1) thru | or (3).
(5) The method for producing a stainless steel plate having excellent surface gloss according to any one of (1) to (4), wherein electrolytic pickling is performed between the molten alkali treatment and the nitric hydrofluoric acid immersion.
(6) In the electrolytic pickling described in (5) above, a mixed solution of nitric acid having a concentration of 100 g / L or more and 150 g / L or less and sodium sulfate of 100 g / L or less is used, and the current density is 20 mA / cm 2 or more. A method for producing a stainless steel plate excellent in surface gloss, characterized by being 100 mA / cm 2 or less.
本発明は、ステンレス鋼板を冷間圧延し、その後に酸化性雰囲気中で焼鈍し、引き続き焼鈍後の鋼板を溶融アルカリ塩処理してスケール改質を行い、硝弗酸浸漬にてスケール除去を行うステンレス鋼板の製造方法において、焼鈍温度が900℃以上の時間(Y)と硝弗酸浸漬時間(X)の関係をY≦0.7X+75.3、溶融アルカリ塩処理時の溶融アルカリ塩の温度を440℃以上480℃以下、溶融アルカリ塩処理時の鋼板表面温度が420℃以上450℃以下、硝弗酸浸漬時の温度を55℃以上60℃以上、電解酸洗時に濃度が100g/L以上150g/L以下の硝酸と100g/L以下の硫酸ナトリウムの混合液を用い、電流密度を20mA/cm2以上100mA/cm2 以下とすることにより、表面光沢に優れたステンレス鋼板を製造することができる。 In the present invention, a stainless steel plate is cold-rolled, and then annealed in an oxidizing atmosphere. Subsequently, the annealed steel plate is treated with molten alkali salt to modify the scale, and the scale is removed by immersion in nitric hydrofluoric acid. In the method for producing a stainless steel sheet, the relationship between the time when the annealing temperature is 900 ° C. or higher (Y) and the nitric hydrofluoric acid immersion time (X) is Y ≦ 0.7X + 75.3, and the temperature of the molten alkali salt during the molten alkali salt treatment is 440 ° C. or higher and 480 ° C. or lower, steel plate surface temperature during molten alkali salt treatment is 420 ° C. or higher and 450 ° C. or lower, temperature during nitric hydrofluoric acid immersion is 55 ° C. or higher and 60 ° C. or higher, and concentration is 100 g / L or higher and 150 g when electrolytic pickling. A stainless steel plate with excellent surface gloss by using a mixed solution of nitric acid of / L or less and sodium sulfate of 100 g / L or less and having a current density of 20 mA / cm 2 or more and 100 mA / cm 2 or less. Can be manufactured.
以下に、本発明の範囲の限定理由について述べる。 The reasons for limiting the scope of the present invention will be described below.
酸化性雰囲気での焼鈍の後に、溶融アルカリ塩処理を行い、その後に硝弗酸浸漬を行うのは、低コストで高効率にスケール除去を実施すると共に材質造り込みを行うためである。すなわち、冷間圧延後のステンレス鋼は加工硬化しており、これを軟質化するために焼鈍が必要である。焼鈍には酸化性雰囲気で行うものと還元性雰囲気で行うものとがあるが、後者に比べ前者は設備費・操業費用共に低コスト化が可能である。酸化性雰囲気での焼鈍では、ステンレス鋼の基本成分であるFeとCrの酸化物が濃縮したスケールが生成する。Cr酸化物は酸類には溶解しにくいため溶融アルカリ塩に浸漬し除去することが好適である。その後、残存物であるFe酸化物の溶解と下地金属/スケール界面に生じたCr欠乏層の溶解のためには、硝弗酸浸漬が好適である。以上より、本発明では、冷間圧延後に酸化性雰囲気で焼鈍し、引き続き溶融アルカリ塩処理を行い、更に硝弗酸浸漬を行うものとした。 The reason why the molten alkali salt treatment is performed after the annealing in the oxidizing atmosphere and the nitrohydrofluoric acid immersion is performed thereafter is to perform scale removal at low cost and to build up the material. That is, the stainless steel after cold rolling is work hardened, and annealing is necessary to soften it. Although annealing is performed in an oxidizing atmosphere and in a reducing atmosphere, the former can reduce both the equipment cost and the operating cost compared to the latter. Annealing in an oxidizing atmosphere produces a scale in which oxides of Fe and Cr, which are basic components of stainless steel, are concentrated. Since Cr oxides are hardly dissolved in acids, it is preferable to remove them by immersing them in a molten alkali salt. Thereafter, immersion in nitric hydrofluoric acid is suitable for dissolving the residual Fe oxide and the Cr-deficient layer formed at the base metal / scale interface. As described above, in the present invention, after cold rolling, annealing is performed in an oxidizing atmosphere, followed by molten alkali salt treatment, and further immersion in nitric hydrofluoric acid.
尚、溶融アルカリ塩の組成は特に限定しないが、NaOHやKOHなどのアルカリおよびアルカリ土類金属の水酸化物を主成分として、これにNaNO3やKMnO4などのCr3+/Cr6+の酸化還元電位よりも貴な平衡電位を有する物質を添加したものが好適である。 The composition of the molten alkali salt is not particularly limited, but the main component is an alkali such as NaOH or KOH and a hydroxide of an alkaline earth metal, and this includes Cr 3+ / Cr 6+ such as NaNO 3 and KMnO 4 . What added the substance which has an equilibrium potential nobler than oxidation-reduction potential is suitable.
次いで、900℃以上の焼鈍時間と硝弗酸浸漬時間の限定理由について述べる。硝弗酸浸漬時間に関しては、焼鈍で生じたスケールがデスケール処理で容易に除去可能で、過度に下地侵食を行わない程度に長いことが好適であるが、焼鈍炉の加熱能力や鋼材の板厚などで通板速度が決定されるため、硝弗酸槽長からおのずと浸漬時間が決められてしまう。また、焼鈍時間に関しては、スケール抑制の観点から短いほど好ましいが、材質確保のためにも、極端に短くすることは不可能である。尚、表面の高い光沢と白さを両立させるためには、高温での長時間保定は特に好ましくない。900℃以上の滞留時間が長いと、急速にCr、Mnスピネル酸化物とSiO2が発達し、溶融アルカリ塩処理した後、硝弗酸浸漬を行っても残留するため、軽微なスケール残りに起因する黄ばみが生じ、白色度を高めることができなくなる。このため、可能な限り900℃以上の温度域での焼鈍時間を短くし、Mn、Siを酸化させずに硝弗酸浸漬で除去可能なCr2O3のみを生成させる事が好ましい。具体的には、硝弗酸浸漬時間(X)と900℃以上の温度域での焼鈍時間(Y)の関係を、Y≦0.7X+75.3にする。 Next, the reasons for limiting the annealing time at 900 ° C. or higher and the nitric hydrofluoric acid immersion time will be described. Regarding the nitric hydrofluoric acid immersion time, it is preferable that the scale generated by annealing can be easily removed by the descaling process and is long enough not to cause excessive base erosion. Therefore, the immersion time is naturally determined from the length of the nitric hydrofluoric acid tank. Further, the annealing time is preferably as short as possible from the viewpoint of scale suppression, but it is impossible to make it extremely short in order to secure the material. In order to achieve both high gloss and whiteness on the surface, holding at high temperature for a long time is not particularly preferable. When the residence time of 900 ° C or higher is long, Cr, Mn spinel oxide and SiO 2 rapidly develop and remain even after immersion in nitric hydrofluoric acid after treatment with molten alkali salt, resulting in slight scale residue Yellowing occurs and whiteness cannot be increased. For this reason, it is preferable to shorten the annealing time in a temperature range of 900 ° C. or more as much as possible, and to produce only Cr 2 O 3 that can be removed by immersion in nitric hydrofluoric acid without oxidizing Mn and Si. Specifically, the relationship between the nitric hydrofluoric acid immersion time (X) and the annealing time (Y) in the temperature range of 900 ° C. or higher is set to Y ≦ 0.7X + 75.3.
ところで、ステンレス鋼を酸化性雰囲気中で900℃以上に焼鈍する場合において、焼鈍スケールの成長を促進させるものは、高温域での保定時間だけでなく各温度域での酸素濃度を特に規定する必要がある。したがって、特に高い表面性状を必要とする場合には温度500℃未満で酸素濃度3%未満、500℃以上900℃未満で5%未満、900℃以上で10%未満にすることが好適である。更に、焼鈍後の冷却も5℃/sec以上で急速冷却することで、900℃以上の滞留時間を短くしてやることも望ましい。しかし、焼鈍設備の制約から冷却速度は、20℃/sec以下とする。 By the way, when stainless steel is annealed at 900 ° C. or higher in an oxidizing atmosphere, what promotes the growth of the annealing scale is required to specify not only the holding time in the high temperature range but also the oxygen concentration in each temperature range. There is. Therefore, when particularly high surface properties are required, it is preferable that the temperature is less than 500 ° C. and the oxygen concentration is less than 3%, 500 ° C. or more and less than 900 ° C. is less than 5%, and 900 ° C. or more and less than 10%. Furthermore, it is also desirable to shorten the residence time of 900 ° C. or more by rapidly cooling the substrate after annealing at 5 ° C./sec or more. However, the cooling rate is set to 20 ° C./sec or less because of restrictions on the annealing equipment.
次に、溶融アルカリ塩処理に関した事項に関して述べる。溶融アルカリ塩にステンレス鋼の酸化スケールを浸漬すると、Crなどの酸化物は酸化溶解され、硝弗酸浸漬にて除去可能なFe酸化物が残存することになる。しかし、溶融アルカリ塩の温度が低すぎるとMn、Si酸化物は溶解できない。Mn、Si酸化物を溶解するためには、溶融アルカリ塩の温度を440℃以上にすると好ましい。しかし、工業生産に使用されている溶融アルカリ塩の最高温度は500℃であり、これ以上高温化すると、溶融アルカリ塩バス本体の耐久性に問題が生じる可能性があるため、480℃以下とすると好ましい。また、ソルト温度が過度に高い場合には、デスケール反応に加え鋼材の溶解が過度に進行し、製品の表面品質を低下させるという問題点もある。そこで、本発明では、溶融アルカリ塩の温度を440℃以上480℃以下とした。 Next, matters relating to the molten alkali salt treatment will be described. When a stainless steel oxide scale is immersed in molten alkali salt, oxides such as Cr are oxidized and dissolved, and Fe oxide that can be removed by immersion in nitric hydrofluoric acid remains. However, if the temperature of the molten alkali salt is too low, Mn and Si oxides cannot be dissolved. In order to dissolve Mn and Si oxides, the temperature of the molten alkali salt is preferably set to 440 ° C. or higher. However, the maximum temperature of the molten alkali salt used for industrial production is 500 ° C, and if the temperature is further increased, there may be a problem in durability of the molten alkali salt bath body. preferable. In addition, when the salt temperature is excessively high, the steel material is excessively dissolved in addition to the descaling reaction, and there is a problem that the surface quality of the product is deteriorated. Therefore, in the present invention, the temperature of the molten alkali salt is set to 440 ° C. or higher and 480 ° C. or lower.
また、鋼材が溶融アルカリ塩に浸漬される際の板温も、高いほどスケール改質が促進されることから、420℃以上にすることが好適である。しかし、溶融アルカリ塩バス本体のロールなど鋼材と接する設備の耐久性に問題が生じる可能性があるため、450℃以下とする必要がある。 In addition, the plate temperature when the steel material is immersed in the molten alkali salt is preferably set to 420 ° C. or higher because scale modification is promoted as the steel plate temperature increases. However, there is a possibility that a problem may occur in the durability of equipment in contact with the steel material such as a roll of a molten alkali salt bath main body, so it is necessary to set the temperature to 450 ° C. or less.
次に、硝弗酸浸漬に関する事項について述べる。硝弗酸浸漬では、溶融アルカリ塩処理により生じたFe酸化物を溶解除去することが目的である。酸液の濃度および温度が高いほどFe酸化物の除去が容易に行われる。この際、酸洗デスケールにおいて、過度に下地侵食を行うと、光沢度が低下し好ましくない。しかし、光沢を高めようとデスケールを弱めると軽微なスケール残りに起因する黄ばみが生じ、白色度を高めることができなくなる。また、高い光沢と白さを両立するためには、粒内は平坦で粒界のみが酸で侵食された表面形態とする必要がある。下地侵食を行うことなく軽微なスケール残りに起因する黄ばみを防止するためには、濃度が30g/L以上50g/L以下の弗酸と80g/L以上120g/L以下の硝酸を使用し、酸液の温度を55℃以上60℃以上にすることが望ましい。 Next, the matter regarding the nitric hydrofluoric acid immersion is described. The purpose of the nitric hydrofluoric acid immersion is to dissolve and remove the Fe oxide generated by the molten alkali salt treatment. The higher the concentration and temperature of the acid solution, the easier the removal of Fe oxide. At this time, if the base erosion is excessively performed in the pickling descale, the glossiness is lowered, which is not preferable. However, if the descaling is weakened to increase the gloss, yellowing due to a slight scale residue occurs, and the whiteness cannot be increased. In order to achieve both high gloss and whiteness, it is necessary to have a surface form in which grains are flat and only grain boundaries are eroded by acid. In order to prevent yellowing due to a slight scale residue without eroding the substrate, hydrofluoric acid having a concentration of 30 g / L to 50 g / L and nitric acid having a concentration of 80 g / L to 120 g / L are used. It is desirable that the temperature of the liquid be 55 ° C. or higher and 60 ° C. or higher.
次に、溶融アルカリ塩処理と硝弗酸浸漬の間に行う電解酸洗に関する事項について述べる。ところで、焼鈍材を溶融アルカリ塩処理した後に、硝弗酸浸漬のみでデスケールを実施する場合、硝弗酸が過度にステンレス鋼母地を侵食し表面性状を低下させることがある。これを防止し高い光沢と白色度を両立させる際には、硝弗酸浸漬の前に予備デスケールとして電解処理を実施し、硝弗酸浸漬時間の短縮や温度・濃度低減などを行うことが望ましい。その際の電解液としては、硝酸、リン酸、硫酸、中性塩水溶液など種々の物が適用可能であるが、望ましくは硝酸と硫酸ナトリウムの混合液が好適である。その際、硝酸濃度は100g/L以上とすることが望ましい。これは硝酸濃度が低いと、鋼材の自己不働態化作用が失われ金属素地の溶解が起こり光沢が低下するためである。また、硝酸濃度を150g/L超にすると設備に腐食が発生するため、硝酸濃度は100g/Lから150g/Lにする必要がある。硫酸ナトリウムは電解処理時に触媒作用的に働き、スケールのみの溶解を促進する効果を有する。溶解限である100g/L程度まで添加しても構わないが、コストと製品特性とのバランスを考慮すると15〜25g/Lの添加が最適である。また、電解電流密度であるが、電流値が低いとスケール溶解効果が弱く表面性状向上効果を期待できない。硝弗酸への浸漬時間を短縮し、表面性状向上効果を得るには、20mA/cm2以上の電解電流が不可欠である。電流は大きくても問題がないため上限は規定しないが、電流効率の点から概ね100mA/cm2以下が好適である。過度の電流は水の電気分解に電流を消費するのみで、スケール溶解速度は電流増加に見合うほど向上しないためである。 Next, matters relating to the electrolytic pickling performed between the molten alkali salt treatment and the nitric hydrofluoric acid immersion will be described. By the way, when descaling is performed only by immersion in nitric hydrofluoric acid after the annealed material is treated with molten alkali salt, the nitric hydrofluoric acid excessively erodes the stainless steel matrix and may deteriorate the surface properties. In order to prevent this and achieve both high gloss and whiteness, it is desirable to perform electrolytic treatment as a preliminary descaling before dipping in nitric hydrofluoric acid to shorten the dipping time of nitric hydrofluoric acid and reduce temperature and concentration. . As the electrolytic solution at that time, various substances such as nitric acid, phosphoric acid, sulfuric acid, and an aqueous neutral salt solution can be applied, but a mixed liquid of nitric acid and sodium sulfate is preferable. At that time, the nitric acid concentration is desirably 100 g / L or more. This is because when the nitric acid concentration is low, the self-passivation action of the steel material is lost, the metal substrate is dissolved, and the gloss is lowered. Further, if the nitric acid concentration exceeds 150 g / L, corrosion occurs in the equipment, so the nitric acid concentration needs to be changed from 100 g / L to 150 g / L. Sodium sulfate works catalytically during electrolytic treatment and has the effect of promoting dissolution of scale alone. Although it may be added up to about 100 g / L which is the solubility limit, the addition of 15 to 25 g / L is optimal in consideration of the balance between cost and product characteristics. Moreover, although it is an electrolysis current density, when a current value is low, the effect of improving surface properties cannot be expected because the effect of dissolving the scale is weak. In order to shorten the immersion time in nitric hydrofluoric acid and obtain the effect of improving the surface properties, an electrolytic current of 20 mA / cm 2 or more is indispensable. Although there is no problem even if the current is large, the upper limit is not specified, but approximately 100 mA / cm 2 or less is preferable from the viewpoint of current efficiency. This is because excessive current only consumes current for electrolysis of water, and the dissolution rate of scale does not increase as much as the increase in current.
以下、下記の実施例1〜8に基づいて本発明を詳細に説明する。 Hereinafter, the present invention will be described in detail based on the following Examples 1 to 8.
表1に示す化学組成が異なるステンレス鋼を真空溶解にて製造し、2.0mm厚さまで冷間圧延−焼鈍処理−溶融アルカリ塩処理−硝弗酸浸漬の工程を用いて焼鈍とスケール除去を行った。尚、実施例7、8では硝弗酸浸漬前に電解酸洗を施した。焼鈍は実施例2を除いて焼鈍条件を模擬した18vol%O2+11vol%H2O+12vol%CO2+残部N2の雰囲気内で赤外線加熱方式で加熱した。熱処理温度は1080℃とし、900℃以上の滞留時間は実施例1を除いて120secとした。1080℃から500℃以下までの鋼板の冷却速度は、実施例3を除いて5℃/secとした。溶融アルカリ塩処理には30wt%NaNO3+2.5%KOH+2.5%NaCl+残部NaOHという混合塩を使用し、浸漬した後、水冷・乾燥した。硝弗酸浸漬は実施例5を除いて30g/Lの弗酸と80g/Lの硝酸を使用し、浸漬した後、水冷・乾燥した。そして、鋼板の表面品質は、光沢度と白色度の機器測定で評価した。 Stainless steels with different chemical compositions shown in Table 1 are manufactured by vacuum melting, and annealing and descaling are performed using the steps of cold rolling, annealing treatment, molten alkali salt treatment, and nitric hydrofluoric acid immersion to a thickness of 2.0 mm. It was. In Examples 7 and 8, electrolytic pickling was performed before immersion in nitric hydrofluoric acid. Annealing was performed by an infrared heating method in an atmosphere of 18 vol% O 2 +11 vol% H 2 O +12 vol% CO 2 + balance N 2 simulating annealing conditions except in Example 2. The heat treatment temperature was 1080 ° C., and the residence time of 900 ° C. or more was 120 sec except for Example 1. Except for Example 3, the cooling rate of the steel sheet from 1080 ° C. to 500 ° C. or lower was 5 ° C./sec. For the molten alkali salt treatment, a mixed salt of 30 wt% NaNO 3 + 2.5% KOH + 2.5% NaCl + remainder NaOH was used, dipped, then water-cooled and dried. Nitrofluoric acid immersion was carried out using 30 g / L hydrofluoric acid and 80 g / L nitric acid except in Example 5, and after immersion, water-cooled and dried. And the surface quality of the steel plate was evaluated by instrument measurement of glossiness and whiteness.
光沢度は、JIS Z 8741に基づく鏡面光沢度Gs45°で、鋼板の白色度b*はJIS Z 8715に基づいて計測した。表面品質としては、b*値がゼロに近いほど優れている。これに加え、Gs45°が240以上310以下であるものは、特に極めて良好と判断した。 The glossiness was a specular glossiness Gs of 45 ° based on JIS Z8741, and the whiteness b * of the steel plate was measured based on JISZ8715. As the surface quality, the closer the b * value is to zero, the better. In addition to this, those having Gs45 ° of 240 or more and 310 or less were judged to be extremely good.
(実施例1)
表2に示すように、900℃以上の滞留時間、溶融アルカリ塩処理時間、硝弗酸浸漬時間を変化させて処理を行った。
Example 1
As shown in Table 2, the treatment was performed by changing the residence time of 900 ° C. or higher, the molten alkali salt treatment time, and the nitric hydrofluoric acid immersion time.
図1に硝弗酸浸漬時間と900℃以上の滞留時間を変化させた時の、処理条件とb*値との関係を整理した。図中の印は、「×」はb*値が2.4以上、「△」は、2.4未満1.7越、「○」は1.7以下1.0越、「◎」は1.0以下であることを示している。 FIG. 1 shows the relationship between treatment conditions and b * values when the hydrofluoric acid immersion time and the residence time of 900 ° C. or more were changed. In the figure, “x” indicates a b * value of 2.4 or more, “Δ” indicates less than 2.4, over 1.7, “◯” indicates less than 1.7, exceeds 1.0, and “◎” indicates It shows that it is 1.0 or less.
「○」と「◎」が本発明の範囲であり、「×」と「△」は比較例である。この図より、900℃以上の滞留時間(sec)をY、硝弗酸浸漬時間(sec)をXとした時、Y≦0.7X+75.3の関係をみたすことで良好な表面品質の鋼板を得ることができることが分かる。さらに、必要に応じてはY≦0.7X+31.0の関係を満たすことでより優れた表面品質の鋼材を得ることができる。 “◯” and “◎” are the scope of the present invention, and “×” and “Δ” are comparative examples. From this figure, assuming that the residence time (sec) above 900 ° C. is Y and the nitric hydrofluoric acid immersion time (sec) is X, a steel sheet with good surface quality can be obtained by satisfying the relationship of Y ≦ 0.7X + 75.3. It can be seen that it can be obtained. Furthermore, if necessary, a steel material with better surface quality can be obtained by satisfying the relationship of Y ≦ 0.7X + 31.0.
(実施例2)
表2に示すように900℃以上の滞留時間を120secとし、500℃未満、500℃以上900℃未満、900℃以上の時の酸素濃度を変化させて処理を行った。
(Example 2)
As shown in Table 2, the residence time of 900 ° C. or higher was 120 seconds, and the treatment was performed by changing the oxygen concentration when the temperature was lower than 500 ° C., 500 ° C. or higher and lower than 900 ° C., or 900 ° C. or higher.
図2に各温度域での酸素濃度と表面評価の関係を示す。この図より、各温度域での酸素濃度を500℃未満で3%未満、500℃以上900℃未満で5%未満、900℃以上で5%以上10%未満を満たすことで、良好な表面品質の鋼板を得ることができることが分かる。 FIG. 2 shows the relationship between the oxygen concentration and the surface evaluation in each temperature range. From this figure, the oxygen concentration in each temperature range is less than 3% at less than 500 ° C, less than 5% at 500 ° C or more and less than 900 ° C, and good surface quality by satisfying 5% or more and less than 10% at 900 ° C or more. It can be seen that a steel sheet can be obtained.
(実施例3)
表3に示すように900℃以上の滞留時間を120secとし、500℃以下に冷却するまでの冷却速度を変化させて処理を行った。
(Example 3)
As shown in Table 3, the residence time of 900 ° C. or higher was 120 seconds, and the cooling rate until cooling to 500 ° C. or lower was changed.
図3に1080℃から500℃以下に冷却するまでの冷却速度と白色度(b*)の関係を示す。この図より、冷却速度を5℃/sec以上を満たすことで、良好な表面品質の鋼板を得ることができることが分かる。さらに、必要に応じては冷却速度を10℃/sec以上を満たすことでより優れた表面品質の鋼材を得ることができる。 FIG. 3 shows the relationship between the cooling rate until cooling from 1080 ° C. to 500 ° C. or less and the whiteness (b *). From this figure, it can be seen that a steel plate with good surface quality can be obtained by satisfying the cooling rate of 5 ° C./sec or more. Furthermore, if necessary, a steel material with a superior surface quality can be obtained by satisfying the cooling rate of 10 ° C./sec or more.
(実施例4)
表3に示すように900℃以上の滞留時間を120secとし、溶融アルカリ塩処理時の鋼板の温度と浴温度を変化させて処理を行った。
(Example 4)
As shown in Table 3, the residence time of 900 ° C. or more was 120 seconds, and the treatment was performed by changing the temperature of the steel sheet and the bath temperature during the molten alkali salt treatment.
図4に溶融アルカリ塩処理時の浴温度と白色度の関係を、図5には溶融アルカリ塩処理時の鋼板の温度と白色度の関係を示す。この図より、浴温度が440℃以上、鋼板の温度420℃以上を満たすことで、白色度(b*)が1.7以下となる良好な表面品質の鋼板を得ることができることが分かる。さらに表2に示すように、この範囲ではGs45°についても、特に極めて良好と判断できる。 FIG. 4 shows the relationship between the bath temperature and the whiteness during the molten alkali salt treatment, and FIG. 5 shows the relationship between the temperature of the steel sheet and the whiteness during the molten alkali salt treatment. From this figure, it can be seen that by satisfying the bath temperature of 440 ° C. or higher and the temperature of the steel plate of 420 ° C. or higher, a steel plate with good surface quality having a whiteness (b *) of 1.7 or less can be obtained. Furthermore, as shown in Table 2, it can be judged that Gs45 ° is particularly excellent in this range.
(実施例5)
表4に示すように900℃以上の滞留時間を120secとし、弗酸濃度を変化させて処理を行った。硝酸濃度は80g/Lとし、硝弗酸の温度は50℃とした。
(Example 5)
As shown in Table 4, the residence time of 900 ° C. or more was 120 sec, and the treatment was performed by changing the concentration of hydrofluoric acid. The nitric acid concentration was 80 g / L, and the temperature of nitric hydrofluoric acid was 50 ° C.
図6に硝弗酸浸漬時の弗酸濃度と白色度の関係を示す。この図より、鋼Aは請求項1を満たしていれば硝弗酸濃度に関係なく白色度(b*)で△(2.4未満1.7越)になる。しかし、鋼Bは弗酸濃度30g/L以上を満たすことで、白色度(b*)で△を得ることができることが分かる。 FIG. 6 shows the relationship between hydrofluoric acid concentration and whiteness when immersed in nitric hydrofluoric acid. From this figure, if the steel A satisfies the first claim, the whiteness (b *) becomes Δ (less than 2.4 and over 1.7) regardless of the concentration of nitric hydrofluoric acid. However, it can be seen that steel B can obtain Δ in whiteness (b *) by satisfying a hydrofluoric acid concentration of 30 g / L or more.
(実施例6)
表4に示すように900℃以上の滞留時間を120sec、硝弗酸浸漬時間を33.7secとし、硝弗酸の温度を変化させて処理を行った。弗酸濃度は30g/Lとし,硝酸濃度は80g/Lとした。また,試験片は表1の鋼B(Mn量:1.46mass%)とした。
(Example 6)
As shown in Table 4, the residence time of 900 ° C. or higher was 120 sec, the nitric hydrofluoric acid immersion time was 33.7 sec, and the treatment was performed by changing the temperature of nitric hydrofluoric acid. The hydrofluoric acid concentration was 30 g / L and the nitric acid concentration was 80 g / L. The test piece was steel B in Table 1 (Mn content: 1.46 mass%).
図7に硝弗酸浸漬時の硝弗酸の温度と白色度の関係を示す。この図より、硝弗酸温度55℃以上を満たすことで、良好な表面品質の鋼板を得ることができることが分かる。 FIG. 7 shows the relationship between the temperature of nitric hydrofluoric acid and the degree of whiteness when immersed in nitric hydrofluoric acid. From this figure, it can be seen that a steel sheet with good surface quality can be obtained by satisfying the nitric hydrofluoric acid temperature of 55 ° C. or higher.
(実施例7)
表1の鋼B(Mn量:1.46mass%)について、表5に示すように電解酸洗の条件を変化させて処理を行った。電解酸洗時間は、SUS304鋼を対極として、試験片を8sec間カソード電解を施した後、自然浸漬電位に4sec間保持し、その後直ちに8sec間アノード電解を実施した。カソードとアノード電解時の電流密度は、共に20mA/cm2とした。表5に示すように電解酸洗処理を施すことで、良好な表面品質の鋼板を得ることができた。
(Example 7)
Steel B (Mn amount: 1.46 mass%) in Table 1 was processed by changing the conditions of electrolytic pickling as shown in Table 5. As for electrolytic pickling time, SUS304 steel was used as a counter electrode, and the test piece was subjected to cathode electrolysis for 8 sec, then held at a natural immersion potential for 4 sec, and thereafter anode electrolysis was immediately performed for 8 sec. The current density during cathode and anode electrolysis was both 20 mA / cm 2 . As shown in Table 5, a steel sheet with good surface quality could be obtained by performing electrolytic pickling treatment.
(実施例8)
表1の鋼B(Mn量:1.46mass%)について、表6に示すように、硫酸ナトリウムの濃度を変化させて処理を行った。硝酸濃度は100g/L、温度を50℃とし,電解電流密度は20mA/cm2とした。
(Example 8)
Steel B (Mn amount: 1.46 mass%) in Table 1 was processed by changing the concentration of sodium sulfate as shown in Table 6. The nitric acid concentration was 100 g / L, the temperature was 50 ° C., and the electrolysis current density was 20 mA / cm 2 .
図8に電解酸洗処理時の硫酸ナトリウムの濃度と白色度の関係を示す。この図より、硫酸ナトリウム濃度が1g/L以上を満たすことで、良好な表面品質の鋼板を得ることができることが分かる。さらに表6から、この範囲ではGs45°についても、特に極めて良好と判断できる。 FIG. 8 shows the relationship between the concentration of sodium sulfate and the whiteness during the electrolytic pickling process. From this figure, it can be seen that a steel sheet with good surface quality can be obtained when the sodium sulfate concentration satisfies 1 g / L or more. Furthermore, from Table 6, it can be judged that Gs45 ° is particularly excellent in this range.
Claims (6)
900℃以上での焼鈍処理および酸洗処理を1式を満足する条件で行うことを特徴とする表面光沢に優れるステンレス鋼板の製造方法。
Y≦0.7X+75.3 1式
但し、Y:酸化雰囲気中での焼鈍処理において、900℃以上の温度域に滞在する時間(sec)
X:硝弗酸水溶液での酸洗時間(sec) In a manufacturing method in which a stainless steel sheet is cold-rolled, subsequently annealed in an oxidizing atmosphere, subsequently treated with a molten alkali salt, and subsequently pickled with an aqueous nitric hydrofluoric acid solution to remove the scale,
A method for producing a stainless steel plate excellent in surface gloss, characterized in that annealing treatment and pickling treatment at 900 ° C. or higher are performed under conditions satisfying one set.
Y ≦ 0.7X + 75.3 Formula 1 However, Y: Time for staying in a temperature range of 900 ° C. or higher (sec) during annealing in an oxidizing atmosphere
X: Pickling time in nitric hydrofluoric acid aqueous solution (sec)
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