JPH0756052B2 - Manufacturing method of cold rolled steel sheet for processing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a method for producing a cold rolled steel sheet which is soft and excellent in workability by a thin cast piece.

<Prior art> Conventionally, cold-rolled steel sheet for processing uses a continuous cast slab or a slab of slab with a thickness of 200 to 250 mm, and is 2 to 6 mm by hot rolling.
It is manufactured by rolling it to the thickness of No. 1, pickling, cold rolling and annealing. In this case, hot rolling ratio (slab thickness / hot rolled thickness)
Since it is as large as 40-100, it requires a powerful hot rolling machine train,
A large amount of energy is required for hot rolling. Recently, attempts have been made to reduce the energy required for processing by making the slab size closer to the product shape. For strip products, there is a strip continuous casting method for thinning a cast piece.
However, when a cold-rolled steel sheet is manufactured using this thin slab, the obtained product is generally hard and inferior in workability, and therefore cannot be used in applications requiring workability. In addition, roughening may occur during press working.

<Problems to be Solved by the Invention> The object of the present invention is to solve the above-mentioned problems of the prior art, good workability with a thin slab as a starting material, and a cold-rolled steel sheet in which roughening does not occur during processing. The provision of a manufacturing method.

<Means for Solving Problems> The gist of the present invention is as follows.

(1) C: 0.0010 to 0.070%, Mn: 0.05 to 0.50% by weight%,
S: Less than 0.013%, Al: 0.005 to 0.090%, with the balance being iron and inevitable impurities, a thin cast piece, the cooling rate of the cast piece: V (average cooling rate between 1350 and 1000 ° C / min. ) And hot rolling reduction ratio: R (thickness of slab / thickness of hot rolling) is V ≦ 10 ³ ℃ / mi
In n, 4.5 ≧ R ≧ {− (5/6) logV + 3.5} is satisfied, and V>
A method for producing a cold-rolled steel sheet for working, comprising performing hot rolling under conditions satisfying 4.5 ≧ R> 1.0 at 10 ³ ° C./min, followed by cold rolling and then annealing.

(2) C: 0.0010 to 0.070%, Mn: 0.05 to 0.50% by weight%
S: 0.015% or less, Al: 0.005 to 0.090%, 50p
pm or less Ca, REM / S ≦ 2.0 REM, 50ppm or less Mg, Zr / S ≦ 10
Zr, 0.3 ≤ B / N ≤ 1.5, one or more of B, with the balance being iron and unavoidable impurities, the thin cast slab being cooled at a cooling rate of V (between 1350 and 1000 ℃ Average cold speed of ℃ / m
in) and hot rolling reduction ratio: R (thickness of slab / thickness of hot rolling) is V ≧ 10 ³ ℃ / min 4.5 ≧ R ≧ {− (5/6) logV + 3.5}
And V> 10 ³ ° C / min, hot rolling is performed under the condition of 4.5 ≧ R> 1.0, followed by cold rolling, and then annealing. Manufacturing method.

Hereinafter, the present invention will be described in more detail.

As mentioned above, if thin cast pieces of continuous casting are simply hot-rolled, cold-rolled and annealed, they are hard and inferior in workability.
In addition, even though the crystal grains of the product are fine grains, a layered surface roughness is generated during processing, and the surface properties of the product are significantly deteriorated. The inventors of the present invention have various workability, have good workability, and do not have rough surface even after pressing, and as a result of various studies on a method for producing a cold rolled steel sheet by a thin cast piece, control the cooling rate of the cast piece after casting. At the same time, by controlling the relationship between the cooling rate and the reduction ratio in hot rolling, energy consumption in hot rolling can be minimized, and workability is good,
The present invention has been completed by finding that a cold-rolled steel sheet that does not cause rough skin can be manufactured.

The component limitation of the cold rolled steel sheet for processing of the present invention will be described.

It is well known that C is an element that becomes hard when the added amount is large and deteriorates the workability. If C exceeds 0.070%, the workability is deteriorated even by the method of the present invention, so the upper limit is set to 0.070%. did. The lower the C content, the better the workability, so the lower limit of the C content is 0.0010 which is industrially practicable.
%. A preferred range is C: 0.0010 to 0.050%.

In order to prevent hot brittleness due to S at the time of hot rolling, Mn is 0.
05% or more is necessary. If the amount of Mn exceeds 0.50%, the workability is deteriorated as in the case of C and the characteristics of the present invention are impaired.
Therefore, the amount of Mn was limited to 0.05 to 0.50%. A preferred range is 0.10 to 0.30%.

The limitation of S is particularly important in the present invention. Since S is an element that induces cracking during hot working, not only is it preferable that it be low, but it is a component that greatly affects workability in the present invention. If the S content is 0.013% or more, the steel hardens and the workability deteriorates, so the S content is specified to be less than 0.013%.
However, as in the invention of claim 2, as a selective element
When containing one or more of Ca, REM, Mg, B,
Even if the S content is increased to 0.015%, the workability is not deteriorated and the effect of the present invention is not impaired. Therefore, in the invention of claim 2, the S content is defined as 0.015% or less.
A preferred range is 0.009% or less. The lower limit of the S content is preferably lower from the viewpoint of workability, and the industrially achievable value is
It is 0.0005%.

Since Al is a killed steel, at least 0.005% is required. On the other hand, when the amount of Al exceeds 0.090%, the steel plate becomes hard, surface defects increase, and the cost increases. A preferred range is Al: 0.010 to 0.060%. Other impurities such as P, Si and O are not particularly limited, but it is preferable that they are as small as possible.

Although the reasons for limiting the basic components of C, Mn, S, and Al constituting the present invention have been described above, in the present invention Ca ≦ 50 ppm, preferably 5 ppm ≦ Ca ≦ 50 ppm, REM / S ≦ 2.0, preferably 0.5. ≤RE
REM of M / S ≦ 2.0, Mg ≦ 50ppm, preferably 5ppm ≦ Mg ≦ 50p
pm, Zr / S ≦ 10, preferably 5 ≦ Zr / S ≦ 10 Zr, 0.3 ≦ B / N
The effect of the present invention is further manifested by including one or more of B of ≦ 1.5. If the upper limits of these elements are exceeded, the effect will be saturated and the cost will be high. Particularly regarding the addition of B, the feature of the present invention is further exhibited by adding B which is a nitride forming element to the basic component of the first aspect of the invention. If the B / N is less than 0.3, the workability will not be improved by adding B, and if the B / N exceeds 1.5, the workability will be decreased.

The addition of carbonitride forming elements such as Ti and Nb does not impair the characteristics of the present invention. When adding, Ti ≧ 4C ＋ 3.42N ＋ 1.5
It is preferable to satisfy the condition of S, Nb ≧ 3C.

The components specified as above are melt-cast into thin slabs and immediately hot-rolled (including those without hot-rolling).
In the present invention, the cooling rate of the slab and the specification of the hot rolling ratio,
This is an extremely important constituent element, which will be described below.

In the laboratory, C: 0.030%, Mn: 0.25%, S: 0.007%, Al:
For 0.035%, Si: 0.01%, P: 0.008%, N: 0.0025% steel, casting temperature can be changed by variously changing the cooling rate (between 1350 and 1000 ℃) of the slab immediately after solidification and by varying the slab thickness. The hot rolling reduction ratio of the piece was changed to obtain a 3.7 mm hot-rolled sheet and an as-cast piece (without rolling). This was cold-rolled at a cold rolling rate of 78.4% to 0.80 mm, and annealed at 750 ° C x 1 min + 400 ° C x 3 min to obtain 1.0
Material properties were investigated after a skin pass of%.

FIG. 1 shows the elongation, FIG. 2 shows the r value, and FIG. 3 shows the relationship between the surface roughness after press working and the cooling rate / hot rolling reduction ratio of the slab. The contour lines in FIGS. 1 to 3 are created by the average value of a large number of experimental results. The skin is scored on a scale of 1 to 5, with a score of 5 being extremely large, a score of 4 being large, and a score having 3 being 2
Indicates slight skin roughness, and 1 indicates no skin roughness.
A score of 2 or less is a pass in practical use.

It can be seen from FIG. 1 that there is a region of good elongation due to the combination of the cooling rate of the slab and the reduction ratio. That is, in the cross section at a certain cooling rate, it can be seen that the elongation decreases if the hot rolling reduction ratio is too small or too large.

It can be seen from FIG. 2 that the value increases as the hot rolling reduction ratio increases. However, when the cooling rate is high, a high value can be obtained with a low hot rolling reduction ratio.

Roughness is a hot rolling reduction ratio of 1.0 when the cooling rate exceeds 10 ³ ° C / min.
If it is super, there will be no rough skin. However, cooling rate ≤ 10 ³
If the reduction ratio is small at ° C / min, roughening of the skin occurs, and in order to suppress the roughening, a reduction ratio of a predetermined amount or more is required.

The above knowledge, that is, as a region in which the workability of value and elongation is excellent and the surface roughness does not occur, the relationship between the cooling rate of the slab and the hot rolling reduction ratio is 4.5 ≧ R ≧ {-(V ≦ 10 ³ ℃ / min 5/6) logV
+3.5}, and V> 10 ³ ° C / min, 4.5 ≧ R> 1.0.
(R: hot rolling reduction ratio (thickness of slab / thickness of hot rolling), V: cooling rate of slab ℃ / min (between 1350 and 1000 ℃)). The upper limit of R was determined by the conditions that a good elongation was obtained and the hot rolling mill could be made compact. R ≦ 4.0 is preferable in order to make the hot rolling machine compact and to obtain stable elongation. On the other hand, the lower limit of R is skin roughness, elongation, and R ≧ (−5 /
6logV + 3.5) was determined. From the workability of the steel sheet and the accuracy of the thickness of the steel sheet, it is preferable that R ≧ 1.2.

When there is hot rolling, it is preferable that the hot rolling finish temperature is Ar ₃ points or more from the viewpoints of the steel sheet passing property, cold rolling, and workability after annealing. Also, steel strips are
It is wound up at 500-800 ℃.

The cooling rate of the slab was represented by only the average rate from 1350 to 1000 ° C, because the measurement and control are easy.

The steel sheet manufactured by the above process is cold-rolled after descaling. Cold reduction is carried out in the range of 60 to 90% as in the usual case.

The annealing may be continuous annealing or box annealing. The annealed plate is skin-passed as required and is used as a finished product.

The cold-rolled steel sheets produced in this way are Zn, Zn-Al, Zn-Fe, S
The characteristics of the present invention are exhibited even when applied as a surface-treated steel sheet such as n.

<Example> A cold-rolled steel sheet was manufactured under the chemical composition and manufacturing conditions shown in Table 1, and the material properties thereof are shown in the table. That is, by changing the plate thickness and cooling rate of the slab, changing the hot rolling reduction ratio to obtain a hot rolled plate, pickling, cold rolling, annealing under the conditions shown in Table 1, and temper rolling at 1.5%. Then, the material characteristics were investigated. The skin roughness was classified into 1 to 5 according to the degree of skin roughness by a bulge test. A score of 1 indicates no rough skin, a slight roughness of 2 is recognized, a rough skin of 3 occurs, a rough texture of 4 is large, and a rough texture of 5 is extremely large.

From the results shown in Table 1, those manufactured by the method of the present invention have higher ductility and higher value than those manufactured by the methods other than the present invention, and the skin roughening score is 1 which is a good characteristic. I understand. Coil Nos. 11, 12, and 13 are componentally manufactured outside the scope of the present invention, but have poor workability. Coil Nos. 14 and 15 are out of the scope of the present invention on the side where the cold speed of the slab and the rolling ratio of the hot rolling are small, but the skin is rough. On the other hand, coil No. 16 is outside the scope of the present invention on the side with a large reduction ratio. In this case, the ductility is poor.

<Effects of the Invention> According to the present invention, as is clear from the above examples, molten steel having a limited component is not subjected to hot rolling under a cumulative large reduction by a powerful hot rolling mill train as in the prior art, By controlling the relationship between the cold speed after casting and the hot rolling reduction ratio without performing small hot rolling or hot rolling, it becomes possible to manufacture a good workable cold rolled steel sheet. Thus, energy saving and cost reduction can be achieved with labor saving in the process, and the present invention is an industrially extremely useful invention.

[Brief description of drawings]

Fig. 1 shows the relationship between the cooling rate of the slab (135 to 1000 ℃) and the hot rolling reduction ratio, and the elongation of the steel sheet after cold rolling annealing (the numbers in the figure are% elongation), and Fig. 2 is the slab. Showing the relationship between the cooling rate and reduction ratio of the steel sheet and the value of the steel sheet after cold rolling and annealing (the numbers in the figure are values), and FIG. 3 is the cooling rate and reduction ratio of the slab and the surface of the steel sheet after cold rolling and annealing. It is a figure (the number in the figure is a rough skin score) which shows the relationship of that nature.

Claims (2)

[Claims] 1. C: 0.0010 to 0.070% by weight%, Mn: 0.05 to 0.5
0%, S: less than 0.013%, Al: 0.005 to 0.090%, with the balance being iron and unavoidable impurities, the thin cast piece has a cooling rate: V (average cooling rate between 1350 and 1000 ℃). (° C / min) and hot rolling reduction ratio: R (thickness of slab / thickness of hot rolling) is V ≦ 10 ³
At ℃ / min, 4.5 ≧ R ≧ {-(5/6) logV + 3.5} is satisfied, and at V> 10 ³ ℃ / min, 4.5 ≧ R> 1.0 is satisfied. A method for producing a cold rolled steel sheet for working, which comprises cold rolling and then annealing. 2. C: 0.0010 to 0.070% by weight%, Mn: 0.05 to 0.5
0%, S: 0.015% or less, Al: 0.005 to 0.090%, 50 ppm or less of Ca, REM / S ≤ 2.0 REM, 50 ppm or less of Mg, Zr / S
A thin cast slab containing Zr of ≦ 10, B of 0.3 ≦ B / N ≦ 1.5, and the balance of iron and unavoidable impurities, and the cooling rate of the slab: V (135 to 1000 Average cold speed between ℃ ℃ / m
in) and hot rolling reduction ratio: R (thickness of slab / thickness of hot rolling) is V ≧ 10 ³ ℃ / min 4.5 ≧ R ≧ {− (5/6) logV + 3.5}
And V> 10 ³ ° C / min, hot rolling is performed under the condition of 4.5 ≧ R> 1.0, followed by cold rolling, and then annealing. Manufacturing method.