JPS62270726A - Manufacture of cold rolled steel sheet having superior workability - Google Patents

Abstract

PURPOSE:To obtain a cold rolled steel sheet having superior workability and satisfactory ageability without causing cracking during hot rolling by continuously casting a steel having a specified composition into a thin slab and by controlling the heat history of the slab after solidification. CONSTITUTION:A molten steel consisting of, by weight, <=0.070% C, 0.07-0.50% Mn, <=0.015% S, 0.005-0.100% Al and the balance Fe with inevitable impurities is cast into a slab of 20-80mm thickness. The slab is held in the temp. range of 1,150-950 deg.C for 3-60min immediately after solidification and then it is hot rolled, cold rolled and annealed. The steel may further contain B in 0.3-1.5 ratio of B/N. Thus, a rough rolling stage during hot rolling can be eliminated, so the consumption of energy can be considerably reduced.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a cold-rolled steel sheet with excellent workability.

[Conventional technology]

Cold-rolled steel sheets with excellent workability are made by converting steel with conventionally limited steel components into continuous casting slabs or blooming slabs with a thickness of 200 to 250 m, rolling them to a thickness of 2 to 611 I, pickling and processing.
Manufactured through cold rolling and annealing processes. in this case,
Since hot rolling is performed from 200 to 2501 mm thick to 2 to 61 mm thick, a powerful rolling mill is required, and its energy consumption is also large. Recently, attempts have been made to make the slab thickness as close as possible to the finished product thickness as a way to overcome the above-mentioned drawbacks. Specifically, there are two methods: one is to directly produce a cold-rolled material by continuous casting without hot rolling, and the other is to produce slabs with an intermediate thickness during the hot rolling process to simplify the hot rolling process. It is considered.

Cold-rolled steel sheets manufactured by the former method are hard and have poor workability, and in addition, roughness occurs during processing, so they cannot be used for processing. On the other hand, if manufactured by the latter method,
There is no rough skin during processing, but it is still hard and has poor workability. In addition, when the slab after solidification is directly hot rolled, there is a drawback that cracks occur in the steel plate during rolling.

[Problem that the invention seeks to solve]

The present invention has been made with the object of providing a method for manufacturing a cold-rolled steel sheet with excellent workability, which solves the problems in the prior art described above.

[Means for solving problems]

As a result of examining various slab thicknesses and thermal history after solidification, the present inventors have determined that by limiting the steel composition and controlling the thermal history after solidification, it is possible to omit the rough rolling process during hot rolling. The present invention was completed based on the discovery that it is possible to produce a cold-rolled steel sheet that is free from cracks and has excellent workability.

The gist of the present invention is that C:0.070 in weight%
% or less, Mn: 0.05-0.50%, S: 0.0
Less than 15%, AJ! : 0.005 to 0.100%, and if necessary, molten steel containing B in the range of 0.3≦B/N≦1.5, with the balance consisting of iron and inevitable impurities.
When hot rolling the slab immediately after solidification, the slab is 80 mm thick.
The present invention provides a method for producing a cold-rolled steel sheet with excellent workability, which is characterized by hot rolling after being held for a minute, followed by cold rolling and annealing.

First, the component limitations of the cold-rolled steel sheet for processing of the present invention will be explained.

It is well known that C becomes hard and deteriorates workability when added in a large amount, and C! t is 0.
If it exceeds 0.070%, the processability deteriorates even with the method of the present invention, so the upper limit was set at 0.070%. The preferred range is 0.05% or less. The lower the C9, the better the processability, so the lower limit of cl was set at 0.0010%, which is industrially practicable.

Mn is required to be 0.07% or more in the method of the present invention in order to prevent hot embrittlement induced by S during hot working.

When the amount of Mn exceeds 0.50%, processability deteriorates,
This would detract from the features of the invention. Therefore, the amount of Mn is 0.07~0
．． Limited to 50%. The preferred range is 0.10-0.3
It is 0%.

Since S is an element that induces cracking during hot working, a lower value is preferable. In the present invention, S is a component that greatly affects processability. If Si exceeds 0.015%, the steel becomes hard and workability deteriorates.

The preferred range is 0.010% or less. Although the lower limit of sl is preferably lower from the viewpoint of processability, it is set to 0.0005%, which is industrially achievable.

A and l are killed steel, so they are small (both 0.005%
is necessary. On the other hand, the amount of Al is 0.1-. If it exceeds 00%, the steel plate becomes hard and at the same time the surface flaws of the steel plate increase, and furthermore, the cost increases. Therefore, the amount of Al is 0.0
It was limited to 0.05 to 0.100%. The preferred range is 0.0
10~o, oso%.

The reasons for limiting the basic components of the present invention have been described above. By adding B, which is a nitride-forming element, to this basic component, the features of the present invention are further exhibited. When B is added, the range is 0.3≦B/N≦Soil5. B/N is 0
．． If it is less than 3, there is no effect of improving workability by adding B, and
When N exceeds 16.5, workability deteriorates.

Other impurity elements such as P, Si, and O are not particularly limited, but keeping them as small as possible improves the workability of the steel sheet.7! Rira is preferable.

Next, a method for manufacturing a cold-rolled steel sheet with excellent workability using the above-mentioned limiting components will be explained.

In the laboratory: c: o, o3%, Mn: 0.20%, S: 0
．． 006%, A1: 0.040%, N: 0.002
1%, P: 0.008%, Si: 0.010% molten steel is made into a slab with a thickness of 4Qmm, and the cooling rate after solidification of the slab.

3. Various cooling patterns followed by hot rolling.
A 71 m hot rolled steel plate was used. After descaling this, 0.8
Cold rolled to 0 mm, 725℃ x 1 minute + 350"C
, X3 minutes, and the material properties were investigated after 1.0% temper rolling. The degree of edge cracking in the hot rolled sheets was also investigated before cold rolling.

Figure 1 shows the thermal history of the slab up to the start of rolling, at 50°C intervals, where the residence time is 5 minutes or more (50°C).
(including all temperature ranges with a residence time of 1 minute or more) and the elongation of cold-rolled steel sheets. As can be seen from Figure 1,
It can be seen that those which were hot rolled after staying in the temperature range of 1150 to 950°C for 5 minutes or more had excellent elongation. 11
Those with a thermal history of 5 minutes or more in a temperature range of more than 50°C or less than 950°C have large variations in elongation. Therefore, thermal history materials that stay in a temperature range of 1150 to 950°C at intervals of 50°C for 5 minutes or more are plotted in this temperature range, and the results excluding other temperature ranges are shown by the dotted line in the figure. This figure shows that the residence time in the temperature range of 1150 to 950°C is important. Therefore, from the same experiment, 11
FIG. 2 shows the relationship between the residence time until the start of hot rolling, elongation of the cold rolled steel sheet, and f value in the temperature range of 50 to 950°C.

Similarly, FIG. 3 shows the relationship between the aging index and the residence time in the temperature range of 1150 to 950°C. From FIG. 2, it can be seen that the properties correlated with workability, such as f value and elongation, become good when the residence time is 3 minutes or more in the temperature range of 1150 to 950°C.

On the other hand, the aging index increases when the residence time in the temperature range of 1150 to 950° C. exceeds 60 minutes, indicating that the aging properties of the steel sheet deteriorate.

FIG. 4 shows the relationship between the degree of edge cracking in a hot rolled sheet and the residence time at 1100 to 950°C. The cracking was evaluated on a three-level scale, with 1 being no cracking, 2 being slightly cracked, and 3 being cracking. From FIG. 4, it can be seen that cracks occur within 3 minutes of residence time at 1100 to 950°C, and that there are almost no cracks in the rolled products after 3 minutes or more.

Based on the above experimental facts, when hot rolling a slab after solidification, it is necessary to heat it in a temperature range of 1150 to 950°C for 3 minutes to 60°C.
The conditions for hot rolling after staying for a minute were limited to those that provide excellent workability, excellent aging properties, and do not cause cracking in the hot rolled sheet. By setting the residence time in this temperature range to 5 minutes or more, the object of the present invention can be stably achieved.

FIG. 5 shows the relationship between slab thickness and f-value of cold-rolled steel sheets. Conditions other than slab thickness are as follows.

C: 0.025%, Mn: 0.20%, Att:
0.036%, S: 0.005%, N: 0.0
A slab was produced from molten steel of 0.020%, and the thermal history of the slab was 15 minutes at 1100 to 950°C.
．． Hot rolled to a thickness of 7. After descaling, cold rolled to a thickness of 0.80 mm, annealed at 750°C x 1 minute + 350°C x 3 minutes, 1.
5% skin pass rolling was performed. As can be seen from Fig. 5, the 〒 value is low when the slab thickness is less than 20 mm. Based on this fact, the minimum thickness of the slab was determined. The preferred range is 30i
It is greater than or equal to n. The upper limit of the thickness of the slab is up to 801 m from the viewpoint of simplifying hot rolling equipment and reducing hot rolling energy consumption, which are the objectives of the present invention.

The hot rolling finishing temperature is preferably carried out at an Ar point or higher, similar to the normal process. After hot rolling, as usual,
Controlled cooling is preferably carried out, and continuous annealing material is preferably rolled at a temperature of 600 to 780°C, and box annealing material is rolled at a temperature of 500 to 710°C.

The hot rolled sheet is cold rolled by 60 to 90% after descaling. Both continuous annealing and box annealing exhibit the features of the present invention. The annealed plate is subjected to skin pass rolling as required, and then used as a finished product.

Even if the steel sheet manufactured by the method of the present invention is used as a surface-treated steel sheet, the characteristics of the present invention will not be impaired.

〔Example〕

A cold-rolled steel sheet is manufactured using the ingredients and manufacturing conditions shown in Table 1,
Evaluate the material properties and the degree of edge cracking in hot rolled sheets,
Shown in the same table. The edge cracking of the hot-rolled sheet was evaluated in three grades: (1) No cracking, (2) Slight cracking, and (3) Severe cracking.

From the results in Table 1, it can be seen that the products produced by the method of the present invention exhibit higher ductility, higher T value, and superior aging properties than those produced by methods other than the present invention. . In addition, no edge cracking occurred in the hot-rolled sheet.

coil! Although 1hlo, 11, and 12.13 are outside the scope of the present invention in terms of their components, they all have low elongation and f-value, which are correlated with workability. Coil Flh14 has a slab thickness of 151@
Out of the scope of the present invention, coil failure 15 is 115 until the start of hot rolling.
The JP-A patents with a temperature range of 0°C to 950°C were manufactured outside the range of the present invention, and both have poor processability.

coil! l&l16 is a case where the residence time at 1150 to 950°C is too long, and the T value is excellent, but the aging index becomes large and there is aging property.

〔Effect of the invention〕

According to the present invention, as is clear from the above embodiments, steel with a limited composition is continuously cast into thin slabs, and by controlling the cooling process of the slabs, a powerful hot rolling machine can be used as in the conventional process. Even without hot rolling with a large cumulative reduction in rows,
It becomes possible to produce a cold-rolled steel sheet with excellent workability and good aging resistance. In this way, energy is saved due to labor saving in the process.

The present invention is an industrially extremely useful invention because it enables a significant reduction in costs.

[Brief explanation of the drawings] Figure 1 is a diagram showing the relationship between the elongation of a cold-rolled steel plate and the temperature range in which the slab stays for 5 minutes or more at intervals of 50°C in the thermal history up to the start of rolling. Figure 2 shows the relationship between f and El and the residence time of the slab at 1150 to 950°C until the start of hot rolling.
A diagram showing the relationship between residence time at 50 to 950°C and aging index.
Figure 5 showing the relationship between residence time at °C and edge cracking of hot rolled sheet.
The figure shows the relationship between the slab thickness and the f value of a cold-rolled steel sheet. Patent applicant: Nippon Steel Corporation Temperature range (0C) //θa 'C-kai4υte' Ri no Kasate number; side) Fig. 5 θ 20 # u J
Fusamaubon 4yo (m 晟) Procedural amendment (spontaneous) June 10, 1985 Commissioner of the Patent Office Kuro 1) Akio Yu 1, Indication of the case 1986 Patent Application No. 90053 2, Processing of the name of the invention Manufacturing method for cold-rolled steel sheets with excellent properties 3 and its relationship with the amended case Patent applicant 2-6-3 Otemachi, Chiyoda-ku, Tokyo (665) Representative of Nippon Steel Corporation 1) Yutaka Takeshi 4. Agent Address: 2-4-1-6 Marunouchi, Chiyoda-ku, Tokyo 100 Japan, Claims column of the specification subject to amendment and Detailed Description of the Invention column 7, Contents of amendment, <--- /,;
-,,,. (1) Amend the claims as shown in the attached sheet. (2) Bottom line of page 3 of the specification r Mn: 0.05-0.
50%" is corrected to "Mn: 0.07 to 0.50%." (3) Table 1 on page 12 shall be amended as shown in the attached sheet. Claims (C: 0.070% or less at 11% by weight, Mn: 0.07
~0.50%, S: 0.015% or less, An:
0.005~0.100%, the balance being iron and unavoidable impurities, and when making a slab of 20~80mm thick, and hot rolling this slab immediately after solidification, a rolling steel of 1150~9
A method for producing a cold-rolled steel sheet with excellent workability, which comprises staying in a temperature range of 50° C. for 3 to 60 minutes, followed by hot rolling, followed by cold rolling and annealing. (2) C: 0.070% or less, Mn: 0 in weight%
．． 07-0.50%, S: 0.015% or less, A
l 70.005~0, 100% plus B 0.3
Molten steel containing ≦B/N≦1.5 with the remainder consisting of iron and inevitable impurities is made into a slab with a thickness of 20 to 80 nm,
When hot rolling this slab immediately after solidification, 1150~
A method for producing a cold-rolled steel sheet with excellent workability, which comprises staying in a temperature range of 950° C. for 3 to 60 minutes, followed by hot rolling, followed by cold rolling and annealing.

Claims (2)

[Claims] (1) C: 0.070% or less, Mn: 0.05 in weight%
~0.50%, S: 0.015% or less, Al: 0.00
Molten steel consisting of 5% to 0.100%, the balance being iron and unavoidable impurities is made into a slab with a thickness of 20 to 80mm, and when hot rolling the slab immediately after solidification, it is heated in a temperature range of 1150 to 950°C for 3 minutes. A method for producing a cold-rolled steel sheet with excellent workability, which comprises hot rolling after staying for ~60 minutes, followed by cold rolling and annealing. (2) C: 0.070% or less, Mn: 0.05 in weight%
~0.50%, S: 0.015% or less, Al: 0.00
In addition to 5 to 0.100%, B is 0.3≦B/N≦1.
The molten steel is made into a slab with a thickness of 20 to 80 mm, and when hot rolling the slab immediately after solidification, it is heated in a temperature range of 1150 to 950°C for 3 minutes. A method for producing a cold-rolled steel sheet with excellent workability, which comprises hot rolling after staying for ~60 minutes, followed by cold rolling and annealing.