JP3314834B2 - Method for producing ferritic stainless steel sheet with excellent living properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ferritic stainless steel sheet which is excellent in living (striated undulation parallel to the rolling direction on the surface of a ferritic stainless steel sheet after cold rolling).

[0002]

2. Description of the Related Art Ridging is a streak-like undulation defect parallel to the rolling direction that appears on the surface of a cold-rolled ferritic stainless steel sheet when processed. As a method for improving the ridging property of a ferritic stainless steel sheet, Japanese Patent Publication No. 59-576 has been proposed.
JP, JP-B-59-37334, JP-B-60-
No. 9088, Japanese Patent Publication No. 61-19686, and the like are disclosed. These techniques aim to improve ridging properties by incorporating Al and appropriately combining the annealing conditions and the cold rolling conditions of the hot-rolled sheet.

[0003]

However, these prior arts cannot completely eliminate living that occurs on the surface after cold rolling. When living occurs on the surface of the plate, the image looks distorted when, for example, a fluorescent lamp is photographed. An object of the present invention is to reduce the waviness pattern to such an extent that it is not observed with the naked eye by destroying the cast structure that is the cause of the living, and by reducing the crystal grains of the product plate to fine grains of 10 μm or less. To provide a beautiful ferritic stainless steel sheet.

[0004]

Means for Solving the Problems Important surface properties of a ferritic stainless steel sheet include surface gloss and living.
The living is attributable to the cast structure, and despite the fact that many improvements have been studied, the swell height is 0.1-
At present, 0.3 μm living remains on the product plate. The present invention has been accomplished by finding the component composition, hot rolling conditions, and cold rolling conditions necessary to make this living almost completely free. That is, the present invention provides a gamma potential (γ′p
), The cast structure is randomized by hot rolling and the strain is accumulated, and the strain in hot rolling is transferred to the cold rolling process without annealing the hot rolled sheet, and the total draft is reduced even in cold rolling. Larger values further increase the accumulation of distortion. In the final annealing, recrystallization is performed to randomize the crystal orientation and refine the crystal grains, and finally, temper rolling is performed so that the living space is almost eliminated.

That is, according to the present invention, C: 0.
04 to 0.10%, Si: 1.0% or less, Mn: 1.0
%, P: 0.040% or less, S: 0.030% or less, Cr: 13.0 to 18.0%, N: 0.03 to 0.3%.
Gamma potential (γ ′) defined by the equation (1).
A slab of ferritic stainless steel having a component composition satisfying p) is heated to a temperature of 1100 ° C. or more and 1220 ° C. or less, followed by hot rolling at a finish rolling temperature of 950 ° C. or more and 1050 ° C. or less, and Winding is performed at a temperature of not less than 800 ° C. and not more than 800 ° C., then descaling is performed, and then cold rolling is performed at a total reduction of 70% or more, and then final air annealing and descaling or bright annealing are performed. The present invention provides a method for producing a ferritic stainless steel sheet having excellent living properties, which is characterized by performing tempering and subsequent temper rolling. γ'p = 420C% + 470N% + 7Mn% -11.5Cr% -11.5Si% + 179 ≧ 30.0 (1) Hereinafter, the present invention will be described in detail.

[0006]

First, the reasons for limiting the chemical components of steel in the present invention will be described. C has a large effect on γ'p, and (1)
If it is less than 0.04% to satisfy the formula, the amount of other austenite-forming elements must be increased, and from the viewpoint of cost and manufacturability, 0.04% or more is required to achieve an appropriate balance. On the other hand, C has an adverse effect on the workability of steel, so the upper limit was made 0.10%. Since Si and Mn are effective as deoxidizing agents for steel, each of them contains 1.0% or less. If it exceeds 1.0%, mechanical properties deteriorate.

Since P and S are impurity elements and deteriorate toughness and corrosion resistance, P and S are desirably 0.04% or less and 0.030% or less, respectively. Cr must be added at least 13.0% in order to improve corrosion resistance and high temperature oxidation resistance.
If it exceeds 0%, γ'p decreases, the toughness deteriorates, and the production becomes difficult. Therefore, the content is set to 13.0 to 18.0%. N is C
In the same way as above, the effect on γ'p is great. To satisfy the expression (1), if it is less than 0.03%, the other austenite forming elements must be increased, and a proper balance is obtained from the viewpoint of cost and productivity. For this purpose, 0.03% or more is required. On the other hand, the upper limit is set to 0.06 because it adversely affects the workability of steel.
%.

Next, the gamma potential will be described. C: 0.01 to 0.08%, Si: 0.1 to 0.7
%, Mn: 0.1 to 1.0%, P: 0.02 to 0.03
%, S: 0.002 to 0.010% or less, Cr: 13.
0-17.0%, N: 0.007-0.060%, the balance being substantially composed of Fe.gamma.'p = 20-60%.
Of ferritic stainless steel in a converter
Thick slabs were cast. After heating this slab to 1220 ° C., it was formed into a hot-rolled sheet having a thickness of 3 mm at a finish rolling temperature of 1050 ° C. and wound up at 800 ° C. Subsequently, descaling is performed without annealing, and a rolling reduction of 70% is performed by a single cold rolling to produce a cold-rolled sheet having a product sheet thickness of 0.9 mm. Final annealing, pickling, and temper rolling are performed. The living height on the surface was measured with a roughness meter. The results are shown in FIG. In order to reduce the height of the living room of the product board to 0.1 μm or less, which is invisible to the naked eye, from FIG.
The gamma potential must be at least 30%. This is considered to be an effect that the austenite phase destroys the cast structure during hot rolling to make the structure finer.

Next, the heating temperature of the slab will be described. C: 0.050%, Si: 0.25%, Mn: 0.1%
61%, P: 0.022%, S: 0.003%, Cr:
A ferritic stainless steel containing 16.45%, N: 0.0402%, γ'p of the formula (1): 31.11%, and the remainder substantially consisting of Fe in a converter, having a thickness of 250 mm Cast slabs. This slab is 1050-1250
After heating to ° C., a hot-rolled steel sheet having a thickness of 3 mm was formed by hot rolling. FIG. 2 shows the depth of scale flaws generated on the hot-rolled sheet surface at this time. 10 μm depth at which scale flaw depth is practically harmless
In order to keep the temperature below, the slab heating temperature must be 1100 ° C. or higher. If the temperature is lower than 1100 ° C., the scale flaw is rapidly deteriorated due to the steel composition, the scale composition, the lubricity of the scale, the lubrication between the roll and the material, and the deformation resistance of hot rolling.

Also, the same slab as above is used for 1050 to 12
After heating to 90 ° C., finish rolling temperature of hot rolling 1050
℃, plate thickness 3mm, winding temperature 800 ℃ to make a hot rolled sheet, cold rolling once without annealing, a total draft of 70%,
A cold-rolled sheet having a product thickness of 0.9 mm was used. Subsequently, 840
The final annealing at 60 ° C. × 60 sec, pickling, and temper rolling at an elongation of 1.0% were performed. FIG. 3 shows the result of measuring the living height on the surface of the product plate with the roughness meter. In order to make the living height of the product board invisible to the naked eye, it must be 0.1 μm or less. For this purpose, the slab heating temperature is 1220 ° C.
Must be: If the temperature exceeds 1220 ° C., it is considered that the crystal grains are coarsened and the austenite phase is reduced, so that fracture of the cast structure is reduced by hot rolling. Therefore, the slab heating temperature that satisfies both scale flaw prevention and living suppression is 1100 to 1220 ° C.

Next, the finish rolling temperature of hot rolling will be described. Using the same slab as above, with a slab heating temperature of 122
0 ° C, adjust the finish rolling temperature to 920-1090 ° C,
A hot-rolled sheet with a thickness of 3 mm and a winding temperature of 800 ° C, annealing was omitted, and one-time cold rolling was performed to reduce the total draft by 70% and 840 ° C x 60.
sec. annealing and pickling, temper rolling at 1.0% elongation 0.9%
A product plate having a thickness of mm was used, and the living height was measured. The results are shown in FIG. 4. In order to reduce the living height to 0.1 μm or less, the finishing temperature must be 1050 ° C. or less. 105
If the temperature exceeds 0 ° C., the accumulation of strain in hot rolling becomes small, and the recrystallized grains at the time of final annealing exceed 10 μm, so that the living exceeds 0.1 μm. However, when the finish rolling temperature is lower than 950 ° C., the deformation resistance of the finished hot rolling increases, and scale flaws increase. Therefore, the finish rolling temperature of hot rolling is 950 to 1050 ° C.

Next, the winding temperature of hot rolling will be described.
Using the same slab as above, slab heating temperature 1220 ° C,
Finished rolling temperature is 1050 ° C, hot rolled sheet with thickness of 3mm, winding temperature is adjusted to 450 ~ 890 ° C, annealing is omitted, single rolling is 70% in total reduction, annealing at 840 ° C x 60sec and pickling. A product plate having a thickness of 0.9 mm was formed by temper rolling at an elongation of 1.0%, and the living height was measured. The results are shown in FIG. 5. The winding temperature must be 800 ° C. or less in order to make the living height 0.1 μm or less. If the temperature exceeds 800 ° C., the tempered martensite of the hot-rolled sheet is decomposed into ferrite and chromium carbide, and partly recrystallized to release the strain caused by hot rolling. Can be On the other hand, when the winding temperature is lowered, the strength of the material is increased, and it becomes difficult to wind the coil. Therefore, the lower limit is set to 450 ° C. Therefore, the winding temperature is set at 450 ° C to 800 ° C. In the next step, the hot-rolled sheet is often annealed.However, in the present invention, the main purpose is to increase the strain accumulation of the material. Do.

Next, the total draft in cold rolling will be described. Using the same slab as above, with a slab heating temperature of 12
A hot rolled sheet having a temperature of 20 ° C., a finish rolling temperature of 1050 ° C., a thickness of 3 mm, and a winding temperature of 800 ° C., omitting annealing, and adjusting the total draft of single cold rolling to 55 to 95%, 840 ° C. × 60 sec.
After annealing, pickling, and temper rolling at an elongation of 1.0%, the living height was measured. The results are shown in FIG. 6. In order to reduce the living height to 0.1 μm or less, the cold rolling reduction is required to be 70% or more. If it is less than 70%, it is considered that the amount of strain introduced is insufficient and the effect of destroying the cast structure is reduced, and fine recrystallized grains having a size of 10 μm or less cannot be obtained.

[0014]

【Example】

Example 1 A ferritic stainless steel having the chemical composition shown in Table 1 was melted in a converter to obtain a continuous cast slab having a thickness of 250 mm. This was heated at a slab heating temperature of 1220 ° C., a finish rolling temperature of 1050 ° C., a thickness of 3.0 mm, and a winding temperature of 800.
It was made into a hot rolled sheet at ℃. Equation (1) was used to calculate γ'p. However, since there is a steel containing Al in the comparative example, γ ″ p = 420C% + 470N% + 7Mn% -11.5Cr% -11.5Si%
It was calculated by the formula of -52Al% + 179. The hot-rolled sheet was subjected to a single cold-rolling process without annealing, and a rolling reduction of 70% was applied to obtain a cold-rolled sheet having a product sheet thickness of 0.9 mm. Subsequently, final annealing at 840 ° C. × 60 sec, pickling, and temper rolling at an elongation of 1.0% were performed in the air, and the living height of the product plate surface was measured. Table 1 shows the results.
The living heights of the steels of the present invention are all 0.10 μm or less, while the comparative examples all exceed 0.10 μm.

[0015]

[Table 1]

[Example 2] Table 1, No. 250 of the two components
Using a slab having a thickness of mm, a cold-rolled sheet was produced under the production conditions shown in Table 2. The thickness of the hot-rolled sheet was 3.0 mm, and the one subjected to the hot-rolled sheet annealing was subjected to box annealing at 850 ° C. × 4 hours. Subsequently,
After cold rolling once or twice, final annealing and pickling in air at 840 ° C x 60 sec, temper rolling with elongation of 1.0% were performed, and the living height of the product plate surface was measured. 2 is shown. The living height of each of the examples of the present invention is 0.10 μm or less, whereas the height of each of the comparative examples exceeds 0.10 μm.

[0017]

[Table 2]

[0018]

As described in detail above, the ferritic stainless steel obtained according to the present invention is excellent in living properties and has a great industrial effect.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a gamma potential (γ′p) and a living height of a product plate.

FIG. 2 is a diagram showing the relationship between the slab heating temperature of ferritic stainless steel and the depth of scale flaws in a hot-rolled sheet.

FIG. 3 is a diagram showing a relationship between a slab heating temperature of ferritic stainless steel and a living height of a product plate.

FIG. 4 is a diagram showing a relationship between a hot rolling finish rolling temperature of ferritic stainless steel and a living height of a product sheet.

FIG. 5 is a diagram showing the relationship between the hot rolling winding temperature of ferritic stainless steel and the living height of a product plate.

FIG. 6 is a diagram showing the relationship between the cold rolling reduction of ferritic stainless steel and the living height of a product plate.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C21D 9/46-9/48 C21D 8/00-8/04 C22C 38/00-38/60

Claims (1)

(57) [Claims] C: 0.04 to 0.10%, Si: 1.0% or less, Mn: 1.0% or less, P: 0.040% or less, S: 0.030% by weight% Hereinafter, a ferrite-based alloy containing Cr: 13.0 to 18.0%, N: 0.03 to 0.06%, the balance being Fe and unavoidable impurities, and having a component composition satisfying the expression (1). The stainless steel slab is heated to a temperature of 1100 ° C. or more and 1220 ° C. or less, followed by hot rolling at a finish rolling temperature of 950 ° C. or more and 1050 ° C. or less, and subsequently 450 ° C. or more to 800 ° C.
C. or less, followed by descaling, followed by cold rolling at a total reduction of 70% or more, followed by final atmospheric annealing and descaling, or bright annealing. A method for producing a ferritic stainless steel sheet having excellent living properties, wherein temper rolling is performed. γ'p = 420C% + 470N% + 7Mn% -11.5Cr% -11.5Si% + 179 ≧ 30.0 ... (1)