JP3581801B2 - Ferritic stainless steel sheet excellent in workability and surface properties and method for producing the same - Google Patents

Description

【００３１】
【表２】

【００３２】
【表３】

【００３３】
【発明の効果】
本発明鋼板は、代表的なフェライト系ステンレス鋼板として、家庭用、業務用、工業用の各種用途に広く採用されているＳＵＳ４３０系について、成分的にきめ細かな限定を行ったものであり、リジングが発生し難く、プレス加工などの一般の加工性が良好で、かつ表面光沢に優れ、ローピングやチリメン皺の発生を抑制した表面性状の優れた薄板製品が得られる。
また本発明法は、本発明鋼板を製造するにあたり、熱延条件、熱延板の焼鈍および酸洗条件を限定したものであり、通常の製造設備により、安定した製造ができる。
【図面の簡単な説明】
【図１】本発明におけるγｐの限定理由を説明するためのグラフである。
【図２】本発明におけるＮ含有量とＮ^＊ の関係を説明するためのグラフである。
【図３】本発明法における硝弗酸酸洗の酸濃度限定理由を説明するためのグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ferritic stainless steel sheet which has good workability such as press working, has excellent surface gloss, and has excellent surface properties in which roping and generation of wrinkles are suppressed, and a method for producing the same.
[0002]
[Prior art]
A sheet product of a ferritic stainless steel sheet represented by SUS430 is subjected to descaling to remove oxide scale on the surface after hot rolling and annealing the slab, and then to cold rolling, annealing and pickling, It is manufactured by temper rolling. This is called a 2B product. In addition, there is also a BA product which is subjected to temper rolling after annealing in a reducing atmosphere furnace after cold rolling.
Annealing after hot rolling may be performed in a coil state in a box furnace, or may be performed by passing a strip through a continuous annealing furnace. The descaling after hot-rolled sheet annealing is performed in a continuous pickling line that combines mechanical treatment such as shot blasting and pickling. In the case of annealing in a continuous annealing furnace, a continuous annealing pickling line (AP line) is used. Done.
[0003]
Conventional problems of ferritic stainless steel sheets are to suppress the occurrence of ridging and to improve workability such as press working, and many proposals have been made regarding the component composition and production method.
For example, Japanese Patent Publication No. Hei 6-94574 discloses that Al and N are positively added to steel, AlN precipitates are made to satisfy Al / N ≧ 2, and an unrecrystallized structure is formed by hot-rolled sheet annealing. A method of producing excellent ridging resistance and a high average r value by cold rolling and finish annealing has been proposed.
[0004]
[Problems to be solved by the invention]
Ferritic stainless steel sheets have problems in the formability evaluated by the ridging and r-value as described above, as well as the surface properties of the steel sheets generated in the manufacturing process. The present inventors conducted research based on the recognition that products with excellent surface properties having a high market reputation can be obtained by maintaining surface gloss at a high level and suppressing roping and occurrence of wrinkles. went.
Here, roping is a concavo-convex pattern similar to ridging generated in cold rolling. Crimson wrinkles are wrinkle-like patterns generated due to the yield phenomenon of the material in temper rolling.
[0005]
The problem to be solved by the present invention is that a ferritic material which hardly generates ridging, has good general workability such as press working, and has excellent surface gloss, and has excellent surface properties which suppresses the occurrence of roping and wrinkles. To produce stainless steel plates using ordinary production equipment.
[0006]
[Means for Solving the Problems]
The steel sheet of the present invention for solving the above-described problems is, in mass %,
C: 0.01 to 0.10%, Si: 0.05 to 0.50%,
Mn: 0.05-1.00%, Ni: 0.01-0.50%,
Cr: 10 to 20%, Mo: 0.005 to 0.50%,
Cu: 0.01 to 0.50%, V: 0.001 to 0.50%,
Ti: 0.001 to 0.50%, Al: 0.01 to 0.20%,
Nb: 0.001 to 0.50%, N: 0.005 to 0.050%,
B: 0.00010 to 0.00500%,
The balance consists of Fe and unavoidable impurities, γp represented by the following formula (1) is 40% or more, and N content is N ^* or less represented by the following formula (2). A ferritic stainless steel sheet with excellent workability and surface properties.
[0007]
γp = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-11.5Si-12Mo-23V-47Nb-49Ti-52Al + 189 (1)
N ^* = Al (14/27) + V (14/51) + Ti (14/48)
+ Nb (14/93) + B (14/11) …………………… (2)
In the formulas (1) and (2), C, N, Cu, Mn, Cr, Si, Mo, V, Nb, Ti, Al, and B are mass % of each.
[0008]
Further, the method of the present invention for solving the above-mentioned problems, a slab comprising the composition of the above-mentioned invention steel sheet, hot-rolled at a rolling end temperature of 900 ° C. or lower, after annealing in the α single phase region, and shot blasting, without performing sulfuric acid cleaning, HF: 10~100g / l, HNO 3: perform pickling in nitric-hydrofluoric acid solution containing 40~200g / l, cold rolling, annealing, to perform temper rolling This is a method for producing a ferritic stainless steel sheet excellent in characteristic workability and surface properties.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the reasons for limiting the components of the steel sheet of the present invention will be described.
If C exceeds 0.10%, the material becomes hard and the workability deteriorates, and if it is less than 0.01%, refining costs increase due to high purification. Therefore, the range of C is set to 0.01 to 0.10%. Further, in consideration of economic efficiency and material properties, the content is desirably 0.01 to 0.08%.
[0010]
Si is added at the time of refining as a deoxidizing element. When the content in steel exceeds 0.50%, corrosion resistance and workability deteriorate, and when it is less than 0.05%, refining cost increases. Therefore, the range of Si is set to 0.05 to 0.50%. Further, in consideration of the material properties, the content is preferably set to 0.05 to 0.40%.
If Mn exceeds 1.00%, corrosion resistance and workability deteriorate, and if it is less than 0.05%, refining costs increase. Therefore, the range of Mn is set to 0.05 to 1.00%. Further, considering the material properties, it is desirable to set the content to 0.10 to 0.80%.
[0011]
Ni is added in an amount of 0.01% or more in order to improve corrosion resistance. However, if it exceeds 0.50%, the cost of raw materials increases. Therefore, the range of Ni is set to 0.01 to 0.50%. Further, in consideration of economy, it is preferable to set the content to 0.01 to 0.30%.
Cr needs to be added in an amount of 10% or more to improve corrosion resistance and high-temperature oxidation resistance. However, if it exceeds 20%, workability is deteriorated. Therefore, the range of Cr is set to 10 to 20%. Further, from the viewpoint of ensuring corrosion resistance and workability, 15 to 18% is desirable.
[0012]
Mo is added in an amount of 0.005% or more to improve corrosion resistance. However, if it exceeds 0.50%, workability is reduced. Therefore, the range of Mo is set to 0.005 to 0.50%. Further, in consideration of economy, 0.005 to 0.10% is desirable. Cu is added in an amount of 0.01% or more to improve corrosion resistance. However, if it exceeds 0.50%, workability is reduced. Therefore, the range of Cu is set to 0.01 to 0.50%. Further, in consideration of economy, 0.01 to 0.30% is desirable.
[0013]
V has an effect of reducing solid solution C and N similarly to Ti and Nb, and the range of V is set to 0.001 to 0.50% for the same reason as in the case of Ti described later. From the viewpoint of surface flaws caused by V precipitates and economy, 0.001 to 0.20% is desirable.
Ti combines with C and N at the time of solidification and precipitates as TiC and TiN, respectively, to form nuclei of equiaxed crystals during solidification. At the same time, it reduces the amount of solute C and N to soften the product, thereby improving workability. Improve. These effects occur when the content of Ti is 0.001% or more, but when the content exceeds 0.50%, hardening due to an increase in solid solution Ti and surface defects due to Ti-based inclusions are caused. Therefore, the range of Ti is set to 0.001 to 0.50%. Furthermore, 0.001 to 0.20% is desirable from the viewpoint of economy and surface properties.
[0014]
Al combines with N during annealing and precipitates as AlN, thereby reducing solid solution N to soften the product and improve workability. These effects occur when Al is 0.01% or more, but when it exceeds 0.20%, Al ₂ O ₃ -based inclusions increase to deteriorate rust resistance and workability. Therefore, the range of Al is set to 0.01 to 0.20%.
Nb has an effect of reducing solid solution C and N like Ti, and the range of Nb is set to 0.001 to 0.50% for the same reason as in the case of Ti. 0.001 to 0.20% is desirable from the viewpoint of surface flaws caused by Nb precipitates and economy.
[0015]
If N exceeds 0.050%, the effect of reducing the amount of solute N due to the precipitation of nitrides with Ti, Nb, Al, etc. becomes insufficient, so that N becomes hard. On the other hand, if the content is less than 0.005%, refining costs will increase due to high purification. Therefore, the range of N is set to 0.005 to 0.050%. Further, in consideration of economy and material properties, 0.008 to 0.030% is desirable.
[0016]
B has an effect of reducing solid solution C and N like Ti, Nb and V, and has an effect of finely precipitating an austenite phase precipitated during solidification and hot rolling in ferrite grains. This is conceivably because B segregates at the ferrite grain boundaries and the grain boundary precipitation energy of the austenite phase is reduced, so that preferential precipitation occurs in the grains, and that boron carbide forms the austenite precipitation site.
In any case, since the austenite phase precipitates in the ferrite grains, the effect of separating the ferrite phase that expands during hot rolling is enhanced. These effects occur when B is 0.00010% or more. However, when B exceeds 0.00500%, the weldability deteriorates. Therefore, the range of B is set to 0.00010 to 0.00500%. Further, considering productivity and economy, 0.00010 to 0.00300% is desirable.
[0017]
Further, γp in the formula (1) indicates that the higher this value, the easier the austenite phase is formed. By setting γp to 40% or more, as shown in FIG. 1, the roping height is reduced to 0.02 μm or less. Can be suppressed. Roping is an uneven pattern similar to the ridging generated by cold rolling as described above. If the roping height is 0.02 μm or less, the surface properties of the product sheet will not be a problem by temper rolling after annealing. Can be held down.
[0018]
Further, the N content is set to be equal to or less than N ^{* represented by the} equation (2). That is, by setting N ≦ N ^* , as shown in FIG. In FIG. 2, the degree of occurrence of wrinkles is ranked from A to D. A rank shows almost no wrinkles, B rank shows slight wrinkles but does not impair the aesthetic appearance, and C shows The rank impairs the aesthetic appearance, and the D rank remarkably impairs the aesthetic appearance. In appearance, A and B ranks passed, and C and D ranks failed.
N ^* represented by the formula (2) corresponds to the amount of N required to precipitate as a nitride, and by setting N ≦ N ^* , the formation of nitrides such as AlN, VN, TiN, NbN, and BN Since the amount of solute nitrogen in the steel decreases and the yield stress decreases, wrinkles hardly occur. Note that N has a large coefficient in the equation (1) and is an effective element for increasing γp, so that N ^* is increased by adding Al, V, Ti, Nb, and B as described above, Secure the amount in the above range.
[0019]
Such a steel sheet of the present invention can be manufactured by a conventional manufacturing method as described above using ordinary manufacturing equipment in addition to the method of the present invention. And the obtained thin plate product is hard to generate ridging, has good general workability such as press working, and is excellent in surface gloss, in which the occurrence of roping and creaking is suppressed, and the surface properties are excellent. .
[0020]
Next, the method of the present invention is a method of hot-rolling a slab of ferritic stainless steel, performing hot-rolled sheet annealing, descaling, cold rolling, cold-rolled sheet annealing, and temper rolling to form a thin sheet product. In the above, the steel composition is the above-mentioned composition of the steel sheet of the present invention, and the hot rolling conditions, hot rolled sheet annealing conditions, and hot rolled sheet descaling conditions are limited.
[0021]
The hot rolling conditions are such that the finish temperature of the finish rolling is 900 ° C. or less. When the slab of the above component is hot-rolled under these conditions, the roping height when cold-rolled after annealing in the α single phase region becomes 0.02 μm or less as shown in FIG. The subsequent average r value is improved. As described above, when the roping height of the cold-rolled sheet is 0.02 μm or less, the product sheet can be pressed by temper rolling after annealing to such an extent that the surface properties of the product sheet do not cause any problem. In addition, deep drawing workability of a thin sheet product is improved by improving the average r value.
[0022]
The hot rolled sheet annealing condition is performed in a temperature range of α single phase lower than the Ac1 point. The annealing furnace may be a box furnace or a continuous furnace of the AP line. The annealing of the hot-rolled sheet changes the recrystallization structure into an α-single phase and reduces Cr negative segregation at grain boundaries. If the γ phase remains, it causes the deterioration of workability of the sheet product.If there is Cr negative segregation at the grain boundary, intergranular corrosion occurs by nitric hydrofluoric acid pickling in the subsequent descaling process, and the gloss is improved by cold rolling. It becomes difficult.
The descaling conditions after the hot-rolled sheet annealing are such that after performing mechanical treatment such as shot blasting, nitric hydrofluoric acid washing is performed without performing sulfuric acid pickling. The concentration of the nitric-hydrofluoric _{acid, HF: 10~100g / l, HNO} 3: a 40~200g / l.
[0023]
The conventional descaling method employs a method of washing with a sulfuric acid after a mechanical treatment, followed by a washing with a nitric hydrofluoric acid. However, as a result of investigations by the present inventors, the sulfuric acid washes resulted in an impurity element, particularly P particles. It has been found that the grain boundaries are eroded due to the extremely sensitive action of field segregation, which causes the surface gloss to be hardly produced by cold rolling.
Therefore, conditions for descaling by nitric hydrofluoric acid washing without performing sulfuric acid washing were examined. As a result, when the HF was less than 10 g / l, descaling could not be performed irrespective of the HNO ₃ concentration. When the HF was 10 g / l or more, as shown in FIG. 3, the HF concentration and the HNO ₃ concentration were appropriate in the above ranges. In FIG. 3, when the HNO ₃ concentration was more than 200 g / l, the skin became rough due to peracid washing, and the gloss of the cold rolled sheet was poor. The results in FIG. 3 were obtained at a liquid temperature of 70 ° C., but similar results were obtained in a liquid temperature range of 30 to 90 ° C.
[0024]
After descaling the hot-rolled sheet, normal cold rolling, cold-rolled sheet annealing and temper rolling are performed to obtain a thin sheet product. The cold-rolled sheet annealing can be performed in a continuous annealing furnace of the AP line or the BA line. In the former case, pickling is continuously performed in the pickling tank of the AP line. In the case of the latter, pickling is unnecessary because annealing is performed in a reducing atmosphere.
[0025]
【Example】
(1) From a continuous cast slab of ferritic stainless steel composed of the components shown in Tables 1 and 2, hot rolling and cold rolling were performed to produce a thin sheet product. The thickness of the hot rolled sheet is 3.5 mm, the finish rolling end temperature of hot rolling is 800 ° C, and the winding temperature is 600 ° C. The hot-rolled sheet annealing was performed at 830 ° C. in a box furnace, and descaling was performed by shot blasting and nitric hydrofluoric acid washing. Subsequently, it was cold-rolled to 0.5 mm, annealed and pickled with an AP line, and temper-rolled with an elongation of 1.4%.
[0026]
Table 2 shows the results of evaluation of wrinkles and roping on the obtained thin plate product. Chirimen evaluation of wrinkles was visually evaluated on the criteria previously described, it was evaluated by the evaluation of the roping is also visually observed. In both the wrinkles and the roping, rank A is hardly recognized, rank B is slightly recognized but does not impair the appearance, rank C impairs the appearance, and rank D impairs the appearance significantly. The appearance of both the wrinkles and the roping was acceptable for ranks A and B, and failed for ranks C and D.
[0027]
In all of the examples of the present invention, both wrinkles and roping were ranked A or B.
No. of the comparative example. 17, No. 18 and No. In No. 26, since N> N ^* , the wrinkles were C rank or D rank. No. of the comparative example. 21, no. 22, no. 23 and no. In No. 25, since γp <40%, the roping was D rank. No. of the comparative example. 19, No. 20 and no. In No. 24, since N> N ^* and γp <40%, the wrinkles were D rank and the roping was C rank or D rank.
[0028]
(2) Examples of the present invention in Tables 1 and 2 The slab No. 1 was hot-rolled to a thickness of 3.5 mm under the conditions shown in Table 3, rolled up at 600 ° C, annealed at 830 ° C in a box furnace, shot blasted, and pickled. The pickling conditions are as shown in Table 3. Thereafter, the sheet was cold-rolled to 0.5 mm, annealed and pickled in an AP line, and temper-rolled to an elongation of 1.4% to obtain a thin sheet product. Table 3 shows the surface gloss evaluation results and the average r values of the products.
The surface gloss was evaluated by visual observation and gloss, and indicated by gloss rank. A rank has no scale residue and gloss of 850% or more, B rank has no scale residue and has a gloss of 800% or more and less than 850%, and C rank has no scale residue and has a gloss of 750% or more and less than 800%. , D rank is the one with scale remaining. The glossiness is based on the value of 45-degree specular gloss according to JIS Z8741.
[0029]
In each of the examples of the present invention, both the surface gloss and the average r value are good. When the average r value is 1.1 or more, normal press workability is good.
No. of the comparative example. 11, No. 14, No. 15 and no. Sample No. 16 had a low average r value and was unsuitable for press working because the finish rolling end temperature of hot rolling exceeded 900 ° C. No. of the comparative example. 11 and No. In No. 13, the grain boundaries were eroded due to sulfuric acid pickling in the pickling of the hot-rolled sheet, and the surface roughness of the product was conspicuous and the gloss became C rank.
No. of the comparative example. 9 and No. 9 In No. 15, since the concentration of hydrofluoric acid was too high in the pickling of nitric acid and hydrofluoric acid on the hot-rolled sheet, the scale was descaled, but the surface was roughened, and the gloss became C rank. No. of the comparative example. 10 and No. In No. 12, gloss was ranked D due to poor descaling because the concentration of hydrofluoric acid was too high in the nitric acid hydrofluoric acid washing of the hot rolled sheet.
[0030]
[Table 1]

[0031]
[Table 2]

[0032]
[Table 3]

[0033]
【The invention's effect】
The steel sheet of the present invention is a typical ferritic stainless steel sheet, which is a SUS430 series widely used in various applications for home use, business use, and industrial use, and is a component in which fine adjustment is made in terms of components. A thin sheet product that is hardly generated, has good workability such as press working, has excellent surface gloss, and has excellent surface properties in which roping and generation of wrinkles is suppressed.
In the method of the present invention, the conditions of hot rolling, annealing of hot rolled sheet and pickling are limited in producing the steel sheet of the present invention, and stable production can be performed by ordinary production equipment.
[Brief description of the drawings]
FIG. 1 is a graph for explaining the reason for limiting γp in the present invention.
FIG. 2 is a graph for explaining the relationship between N content and N ^* in the present invention.
FIG. 3 is a graph for explaining the reason for limiting the acid concentration of nitric acid hydrofluoric acid in the method of the present invention.

Claims (2)

In mass %,
C: 0.01 to 0.10%, Si: 0.05 to 0.50%,
Mn: 0.05-1.00%, Ni: 0.01-0.50%,
Cr: 10 to 20%, Mo: 0.005 to 0.50%,
Cu: 0.01 to 0.50%, V: 0.001 to 0.50%,
Ti: 0.001 to 0.50%, Al: 0.01 to 0.20%,
Nb: 0.001 to 0.50%, N: 0.005 to 0.050%,
B: 0.00010 to 0.00500%,
The balance consists of Fe and unavoidable impurities, γp represented by the following formula (1) is 40% or more, and N content is N ^* or less represented by the following formula (2). Ferritic stainless steel sheet with excellent workability and surface properties.
γp = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-11.5Si-12Mo-23V-47Nb-49Ti-52Al + 189 (1)
N ^* = Al (14/27) + V (14/51) + Ti (14/48)
+ Nb (14/93) + B (14/11) …………………… (2)
In the formulas (1) and (2), C, N, Cu, Mn, Cr, Si, Mo, V, Nb, Ti, Al, and B are mass % of each. In mass %,
C: 0.01 to 0.10%, Si: 0.05 to 0.50%,
Mn: 0.05-1.00%, Ni: 0.01-0.50%,
Cr: 10 to 20%, Mo: 0.005 to 0.50%,
Cu: 0.01 to 0.50%, V: 0.001 to 0.50%,
Ti: 0.001 to 0.50%, Al: 0.01 to 0.20%,
Nb: 0.001 to 0.50%, N: 0.005 to 0.050%,
B: 0.00010 to 0.00500%,
The balance is made of a ferritic stainless steel having a composition of Fe and unavoidable impurities, γp represented by the following formula (1) of 40% or more, and N content of N ^* or less represented by the following formula (2) The slab is hot-rolled at a rolling end temperature of 900 ° C. or lower, annealed in the α single phase region, subjected to shot blasting, without sulfuric acid pickling, HF: 10 to 100 g / l, HNO ₃ : 40 to A method for producing a ferritic stainless steel sheet having excellent workability and surface properties, comprising pickling with a nitric hydrofluoric acid solution containing 200 g / l and performing cold rolling, annealing, and temper rolling.
γp = 420C + 470N + 23Ni + 9Cu + 7Mn-11.5Cr-11.5Si-12Mo-23V-47Nb-49Ti-52Al + 189 (1)
N ^* = Al (14/27) + V (14/51) + Ti (14/48)
+ Nb (14/93) + B (14/11) …………………… (2)
In the formulas (1) and (2), C, N, Cu, Mn, Cr, Si, Mo, V, Nb, Ti, Al, and B are mass % of each.

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