JPH08225852A - Production of ferritic stainless steel sheet excellent in ribbing characteristic - Google Patents

Abstract

PURPOSE: To produce a ferritic stainless steel sheet having a beautiful surface and excellent in ribbing characteristic by subjecting a ferritic stainless steel slab to hot rolling and annealing under specified temp. conditions, thereafter subjecting the same to cold rolling and bright annealing and finally executing skinpass rolling. CONSTITUTION: The slab of a ferritic stainless steel having a compsn. contg., by weight, 0.01 to 0.10% C, <1.0% Si, <1.0% Mn, <0.040% P, <0.030% S, <0.80% Ni, 13.0 to 18.0% Cr, 0.01 to 1.0% Al, 0.005 to 0.06% N, and the balance Fe and in which γp (gamma potential) expressed by the formula I satisfies 27<=γp<=40 is heated at 1100 to 1220 deg.C and is subjected to hot rolling so as to regulate the finish rolling temp. to 750 to 950 deg.C to work into a sheet material, which is coiled at 450 to 750 deg.C. This hot rolled steel sheet subjected to annealing by holding at a temp. T4 satisfying the inequality II for a time (t) (hr) satisfying the relationships expressed by the formula III and inequality IV, is subjected to atmospheric annealing and descaling or bright annealing and is thereafter subjected to skinpass rolling.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Surface gloss and living are important surface properties of ferritic stainless steel sheets. The present invention
The present invention relates to a method for producing a ferritic stainless steel sheet having excellent living properties (striated undulations parallel to the rolling direction, which are seen on the surface of a ferritic stainless steel sheet after cold rolling).

[0002]

2. Description of the Related Art When cold-rolled ferritic stainless steel sheets are processed, ridges appear on the surface and have ridge-like undulation defects parallel to the rolling direction. A method for improving the ridging property of a ferritic stainless steel sheet is disclosed in JP-B-59-576, JP-B-59-37332, and JP-B-60-90.
No. 88, Japanese Patent Publication No. 61-19685, and the like. These techniques are intended to improve the ridging property by containing a large amount of Al and appropriately combining annealing and cold rolling conditions of the hot rolled sheet.

[0003]

However, these conventional techniques cannot completely eliminate the living room that occurs on the surface after cold rolling. When a living room is generated on the surface of the plate, the image appears distorted when a fluorescent lamp is taken, for example, which is a serious defect in product quality. The object of the present invention is to destroy the coarse casting structure that is the cause of living and to set the major axis of crystal grains after hot-rolled sheet annealing to 1 mm or less,
To provide a method for producing a ferritic stainless steel sheet having a beautiful living surface, by reducing the height of the waviness pattern after cold rolling and reducing the waviness pattern in the product plate to an extent that is not observed with the naked eye. is there.

[0004]

[Means for Solving the Problems] Since the living room is caused by the cast structure, the living room having the undulation height of 0.1 to 0.3 μm is formed on the product plate, although many improvement studies have been conducted. The current situation is that it remains. By setting this living room to a waviness height of approximately 0.1 μm or less,
The present invention has been accomplished by finding the component composition, hot rolling conditions, and hot rolled sheet annealing conditions necessary for making them substantially harmless so that they cannot be visually recognized.

That is, according to the present invention, the gamma potential (γ
p) is increased and the austenite (γ) phase is densely precipitated during hot rolling to finely randomize the cast structure in hot rolling, and the rolling temperature required to accumulate strain under hot rolling conditions is set to Under the annealing conditions for rolled sheet, the Larson mirror parameter (LMP) is set to a certain value or more to sufficiently recrystallize and randomize the crystal orientation and refine the crystal grains. The hot-rolled annealed plate having crystal grains adjusted in this way is rolled, then annealed, and then temper-rolled to obtain a product plate.

That is, the present invention, in% by weight, is C: 0.01.
~ 0.10%, Si: 1.0% or less, Mn: 1.0% or less, P: 0.040% or less, S: 0.030% or less, N
i: 0.80% or less, Cr: 13.0 to 18.0%, A
1: 0.01-1.0%, N: 0.005-0.06%
A slab of ferritic stainless steel containing Fe, the balance consisting of Fe and unavoidable impurities, and having a composition that satisfies the formula (1) is heated to a slab heating temperature T1 (° C.) of 1100 ° C. or higher and 1220 ° C. or lower, Then 750 ℃ or more 9
Hot rolling is performed at a finish rolling temperature T2 (° C.) of 00 ° C. or lower, and then a winding temperature T3 of 450 ° C. or higher and 750 ° C. or lower.
Winding is performed at (° C.), and subsequently, an annealing temperature T4 (° C.) and a holding time t (H that satisfy the expressions (2) and (3) are satisfied.
Living property characterized by annealing in r), followed by descaling, followed by cold rolling, followed by atmospheric annealing and descaling, or bright annealing, followed by temper rolling. The gist is a method of manufacturing a ferritic stainless steel sheet excellent in heat resistance. γp = 420C% + 470N% + 7Mn% + 23Ni% -11.5Cr% -11.5Si% -52Al% + 189 27 ≦ γp ≦ 40 (1) T4 ≦ -5 · γp + 1100 (2) LMP = (T + 273) · (20 + logt) LMP ≧ 22500 (3) Hereinafter, the present invention will be described in detail.

[0007]

In the present invention, the reason for limiting the chemical composition of steel will be explained. C has a large influence on γp, and if it is less than 0.01% to satisfy the formula (1), other austenite-forming elements have to be increased, and in view of cost and manufacturability, a proper balance is required. Is required to be 0.01% or more. On the other hand, C adversely affects the workability of steel, so the upper limit was made 0.10%.

Since Si, Mn and Al are effective as deoxidizing agents for steel, Si, Mn are contained in 1.0% or less and Al is contained in 1.0% or less. When the content of each component exceeds the upper limit, mechanical properties such as ductility and toughness deteriorate. Further, Al is an element that lowers γp and is effective as a component for adjusting the formula (1) in a proper balance. Therefore, since it is necessary to contain 0.01% or more, the Al amount is set to 0.01 to 1.0%.

Since P and S are impurity elements and deteriorate in toughness and corrosion resistance, they are 0.040% or less and 0.030%, respectively.
% Or less. Ni also has an effect on γp, and (1)
It is effective as a component that adjusts the formula to a proper balance,
Since Ni is an expensive element, it is not preferable to add a large amount from the viewpoint of cost, so Ni was set to 0.80% or less.

Cr is required to be added in a minimum amount of 13.0% in order to improve corrosion resistance and high temperature oxidation resistance.
If it exceeds 8.0%, γp becomes small, the toughness deteriorates, and the manufacturing becomes difficult, so the content is made 13.0 to 18.0%. Like C, N has a large effect on γp, and if it is less than 0.005% to satisfy the formula (1), other austenite-forming elements must be increased, and the cost and manufacturability are adequately balanced. To achieve this, 0.005% or more is required.
On the other hand, since the workability of steel is adversely affected, the upper limit is 0.0
6%.

Next, the gamma potential γp will be described. C: 0.01 to 0.08%, Si: 0.1
0.7%, Mn: 0.1 to 1.0%, P: 0.020 to
0.040%, S: 0.001 to 0.010%, Ni:
0.05-0.80%, Cr: 13.0-20.0%,
Al: 0.007 to 0.13%, N: 0.003 to 0.
Γp = 1 with 060% included and the balance consisting essentially of Fe
Ferritic stainless steel adjusted to each level of 0 to 60% was melted in a converter to cast a slab having a thickness of 250 mm. After heating this slab to a slab heating temperature T1: 1200 ° C., a hot-rolled plate having a plate thickness of 3 mm at a finishing rolling temperature T2: 820 ° C., a winding temperature T3: 700 ° C., and subsequently 860 ° C. (T4) × After annealing for 5 hours (t), descaling is performed, and a single cold rolling is applied with a total reduction rate of 60% to obtain a cold rolled sheet having a product sheet thickness of 1.2 mm, and final bright annealing,
After temper rolling, the living height R of the product plate surface was measured with a roughness meter.

The results are shown in FIG. In order to make the living room of the product plate invisible to the naked eye at 0.1 μm or less, the gamma potential γp must be 27% or more from FIG. It is considered that this is because the austenite phase in the hot rolling has the effect of destroying the cast structure and making it finer.

On the other hand, if the gamma potential γp becomes too high, the austenite phase precipitation temperature in annealing will decrease, so it is necessary to lower the annealing temperature T4 in order to prevent austenite phase precipitation. When the annealing temperature T4 is low, the recrystallization is delayed and the annealing time t is required to be long, so that the production efficiency in the annealing process is reduced. Therefore,
The gamma potential was 40% or less.

Next, the heating temperature of the slab will be described. C: 0.062%, Si: 0.27%, Mn: 0.
59%, P: 0.027%, S: 0.004%, Ni:
0.14%, Cr: 16.5%, Al: 0.06%,
Including N: 0.011%, γp of the formula (1): 31.4%,
The balance was made by melting ferritic stainless steel consisting essentially of Fe in a converter and casting a slab with a thickness of 250 mm.
This slab was hot-rolled at each heating temperature of 1050 to 1250 ° C to obtain a hot rolled steel sheet having a thickness of 3 mm.

FIG. 2 shows the scale flaw depth generated on the surface of the hot-rolled steel sheet at this time. The slab heating temperature T1 must be 1100 ° C. or higher in order to reduce the scale flaw depth to a practically harmless depth of 10 μm or less. 1100
If the temperature is less than ℃, scale flaws are rapidly deteriorated due to the composition of steel, scale composition, lubricity of scale, lubrication between roll and material, and deformation resistance of hot rolling.

Further, the same slab heating temperature T1:
After heating to each temperature of 1050 to 1290 ° C., finish rolling temperature T2: 820 ° C., plate thickness: 3 mm, winding temperature T3: 7
A hot-rolled sheet was obtained by hot-rolling at 00 ° C, annealing was performed at 860 ° C for 5 hours, and then cold-rolling at a total rolling reduction of 60% was added.
A cold rolled sheet having a product sheet thickness of 1.2 mm was used. Then 900 ° C
× 10 seconds final bright annealing, then elongation 1.0%
Was temper-rolled.

The result of measuring the living height R of the surface of the product plate with a roughness meter is shown in FIG. In order to set the living height R of the product plate to 0.1 μm or less, which is invisible to the naked eye, the slab heating temperature must be 1220 ° C. or lower. When the temperature exceeds 1220 ° C., it is considered that the crystal grains coarsen and the austenite phase decreases, so that the effect of breaking the cast structure by rolling decreases. Therefore, the slab heating temperature that satisfies both scale flaw prevention and living control is 1100 to 1220 ° C.

Next, the finish rolling temperature for hot rolling will be described. Using the same slab as above, the slab heating temperature T1 is 1200 ° C., the finish rolling temperature T2 is each temperature of 720 to 950 ° C., the plate thickness: 3 mm, the winding temperature T3: 700 ° C.
A hot rolled sheet was obtained by hot rolling. Subsequently, annealing was performed at 860 ° C. for 5 hours, and cold rolling was performed at a total reduction rate of 60% to obtain 90
Bright annealing at 0 ° C for 10 seconds, temper rolling with an elongation of 1.0% to make a product plate with a thickness of 1.2 mm, living height R
Was measured. The results are shown in FIG. 4. In order to set the living height R to 0.1 μm or less, the finish rolling temperature in hot rolling needs to be 900 ° C. or less. 900
If the temperature exceeds ℃, the accumulation of strain becomes insufficient and the major axis of the recrystallized grains after annealing the hot-rolled sheet becomes a band-like structure exceeding 1 mm, so the living height R of the final product is considered to exceed 0.1 μm. To be However, when the finish rolling temperature T2 is less than 750 ° C., the deformation resistance in the finish rolling becomes large and the scale flaw increases.

Therefore, the finish rolling temperature is 750 to 900.
℃. Next, the winding temperature T3 of hot rolling will be described. Using the same slab as above, slab heating temperature T1: 1
A hot rolled sheet having a thickness of 3 mm is obtained by hot rolling at a temperature of 200 ° C. and a finish rolling temperature T2 of 820 ° C., and a winding temperature T3 of 450 to.
Winding at each temperature of 800 ° C, annealing at 860 ° C for 5 hours, cold rolling with a total reduction of 60% in one cold rolling, 900 ° C
1. Bright annealing for 10 seconds, temper rolling with an elongation of 1.0%
A living plate R having a thickness of 2 mm was measured.
The results are shown in FIG. 5, and the winding temperature T3 must be 750 ° C. or less in order to set the living height R to 0.1 μm or less. When the temperature exceeds 750 ° C., it is considered that the living height R becomes high because some recrystallization occurs in the hot-rolled sheet and the strain imparted by hot-rolling is released.

On the other hand, when the coiling temperature is low, the strength of the material becomes too high, and coiling becomes difficult, so the lower limit is set to 450 ° C. Therefore, the winding temperature T3 is 450
˜750 ° C. Next, the conditions of the Larson mirror parameter (LMP) in the hot rolled sheet annealing will be described.

Using the same slab as described above, slab heating temperature T1: 1200 ° C., finish rolling temperature T2: 820 ° C.,
Sheet thickness: 3 mm, coiling temperature T3: hot rolled by hot rolling at 700 ° C., annealed under each condition with Larson mirror parameter (LMP) value of 20000 to 25000, and then cold rolled once for total reduction. 60% cold rolling, 900 ℃
1. Bright annealing for 10 seconds, temper rolling with an elongation of 1.0%
A living plate R having a thickness of 2 mm was measured.
The results are shown in FIG. 6, and in order to reduce the living height R to 0.1 μm or less, the Larson mirror parameter (LMP) value in hot-rolled sheet annealing must be 22,500 or more. If it is less than 22500, recrystallization after hot-rolled sheet annealing will be insufficient, and it is considered that the living room of the product becomes a band-like structure in which the major axis of recrystallization exceeds 1 mm and the product has a living length of more than 0.1 μm.

Regarding the temperature T4 of hot-rolled sheet annealing, it is desirable to anneal at a higher temperature in terms of production efficiency because the higher the temperature, the more quickly LMP ≧ 22500 is reached. However, the anneal at a high temperature causes the γ phase to precipitate. , Deteriorate product material and surface quality.
Fig. 7 shows the relationship between the gamma potential γp and the precipitation temperature of the γ phase.
As shown in FIG. 5, the higher the gamma potential γp, the lower the γ-phase precipitation temperature, and the temperature at which there is no γ-phase precipitation is in the range satisfying the expression (2).

Therefore, the annealing of the hot rolled sheet is performed at a temperature satisfying the equation (2).

[0024]

【Example】

[Example 1] Ferritic stainless steel having the chemical composition shown in Table 1 was melted in a converter to obtain a continuously cast slab having a thickness of 250 mm. Slab heating temperature: 1220 ℃,
Final rolling temperature: 820 ° C., plate thickness: 3.0 mm, winding temperature: 700 ° C., to obtain a hot rolled sheet.

Equation (1) was used to calculate γp. continue,
The hot-rolled sheet was annealed at 860 ° C. for 5 hours (LMP = 23452) and then descaled, and once cold-rolled at a total rolling reduction of 60%, final bright annealing at 900 ° C. × 10 sec, and elongation. The product sheet thickness is 1.
The living height of the product plate surface was measured using a cold rolled steel plate of 2 mm. The results are shown in Table 1.

The product plate living heights of the steels of the present invention are all 0.10 μm or less, whereas those of the comparative examples are all higher than 0.10 μm. [Example 2] Table 1, No. 2 Using a 250 mm-thick slab of component No. 4, a hot rolled annealed plate was produced under the manufacturing conditions shown in Table 2.
The hot-rolled sheet thickness is 3.0 mm.

Equation (3) was used to calculate the LMP value. Subsequently, descaling is performed, and cold rolling is performed once for 60% cold rolling, 900 ° C. × 10 sec final bright annealing, and elongation ratio is 1.
0% temper rolling was performed to make a cold rolled steel sheet with a product sheet thickness of 1.2 mm, and the living height of the product sheet surface was measured.
It was shown to. The living heights of the product sheets of the steels of the present invention are all 0.10 μm or less, whereas those of the comparative examples are all over 0.10 μm.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

As is clear from the above description, according to the present invention, it is possible to produce a ferritic stainless steel sheet having excellent surface living property. In particular, according to the present invention, since the annealing temperature is higher than that of the conventional one, the annealing time can be shortened and the industrial effect is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between gamma potential (γp) and living height R (μm) of a product plate.

[Fig. 2] Slab heating temperature T of ferritic stainless steel
It is a figure which shows the relationship of 1 (degreeC) and the depth D (micrometer) of the scale flaw of a hot rolled sheet.

[Fig. 3] Slab heating temperature T of ferritic stainless steel
It is a figure which shows the relationship between 1 (degreeC) and the living height R (micrometer) of a product board.

FIG. 4 is a diagram showing a relationship between a hot rolling finish rolling temperature T2 (° C.) of a ferritic stainless steel and a living height R (μm) of a product plate.

FIG. 5: Hot rolling coiling temperature T of ferritic stainless steel
It is a figure which shows the relationship between 3 (degreeC) and the living height R (micrometer) of a product board.

FIG. 6 is a diagram showing the relationship between the Larson-Miller parameter (LMP) value of annealing in the hot rolling annealing of ferritic stainless steel and the living height R (μm) of the product sheet.

FIG. 7 is a diagram showing a relationship between a gamma potential (γp) and a gamma phase precipitation temperature.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Masaaki Kobayashi 3434 Shimada, Koji City Shin-Nippon Steel Co., Ltd. Inside the Komatsu Steel Works (72) Inventor Kenji Hirashima 3434 Shimada, Shinjuku Nippon Steel Co., Ltd. Inside the Shoko Ironworks

Claims (1)

[Claims] 1. By weight%, C: 0.01 to 0.10%, Si: 1.0% or less, Mn: 1.0% or less, P: 0.040% or less, S: 0.030% Below, Ni: 0.80% or less, Cr: 13.0 to 18.0%, Al: 0.01 to 1.0%, N: 0.005 to 0.06% are contained, and the balance is Fe and A slab of ferritic stainless steel composed of inevitable impurities and satisfying the formula (1) is
It is heated to a slab heating temperature Tl (° C) of 0 ° C or higher and 1220 ° C or lower, followed by hot rolling at a finish rolling temperature T2 (° C) of 750 ° C or higher and 900 ° C or lower, and then 450 ° C or higher and 750 ° C or lower. Winding is performed at the winding temperature T3 (° C),
Subsequently, an annealing temperature T4 that satisfies the expressions (2) and (3)
(° C) and holding time t (Hr), followed by descaling, followed by cold rolling, followed by atmospheric annealing and descaling, or bright annealing, followed by temper rolling. A method for producing a ferritic stainless steel sheet having excellent living properties, which is characterized by carrying out. γp = 420C% + 470N% + 7Mn% + 23Ni% -11.5Cr% -11.5Si% -52Al% + 189 27 ≦ γp ≦ 40 (1) T4 ≦ -5 · γp + 1100 (2) LMP = (T + 273) · (20 + logt) LMP ≧ 22500 (3)