JPS59166650A - Steel for cold rolled steel plate - Google Patents

Abstract

PURPOSE:To provide the titled steel having good processability characterized in an Fe-ultra-low C-low N-O component system, constituted by specifying a composition consisting of C, Mn, P, N, O and Fe. CONSTITUTION:This steel for a cold rolled steel plate enabled in low temp. annealing and having good processability contains 0.0050% or less C, 0.5% or less Mn, 0.1% or less P, 0.0050% or less N, 0.016-0.035% O and, if necessary, further contains one or more of 0.0001-0.0050% B, 0.003-0.08% Nb and 0.005-0.1% V and comprises the remainder of Fe and inevitable impurities. In the above mentioned components, C is harmful in processability and reduced as low as possible. Mn forms MnS along with S among impurities in steel to prevent hot embrittleness and P is necessary in order to obtain a high strength cold rolled steel plate. N is suppressed at low value because it deteriorates the quality of steel. O promotes recrystallization in recrystallization annealing and improves processability. B, Nb and V fix solid solution C, N and prevent ageing deterioration.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel for cold-rolled steel sheets with good workability and low-temperature annealing, which is characterized by a Fe-very low C-low N-0 component system.

Cold-rolled steel sheets with good workability include low C-At killed steel produced by box annealing method and IF steel (Intergtltial Free steel).
steel). Additionally, there are rimmed and capped steels that are slightly less workable than these.

In the case of low C-At killed steel, AtN is made into a solution during hot rolling and quenched to prevent precipitation. Then, during slow heating during box annealing, ktN is precipitated to develop grains with crystal orientation favorable for workability. As a result, a high Lankford value (i value) of 1.5 to 1.8 can be given.

However, such AtN retards recrystallization and is usually 7
High temperature and long-time annealing is performed at 00°C for about 12 hours.

In addition, rapid heating such as continuous annealing does not result in sufficient AtH precipitation, which can be harmful, so in continuous annealing, a thorough AtN precipitation treatment is usually performed by high-temperature coiling at the hot rolling stage. . However, high-temperature winding causes thick scales and poor pickling. Furthermore, since the inner and outer peripheries of the hot-rolled coil cool quickly after winding, AtN is not sufficiently precipitated and the material quality after annealing is poor.

In this way, low C-At killed steel is box annealed at high temperatures.

Continuous annealing has the economical disadvantage of long-time annealing, and quality defects due to high-temperature winding.

Next, IF steel is produced by vacuum degassing of molten steel! This steel has a low 1llc and also has elements such as Ti that have a strong affinity with C and N, so that solid solution C and N are virtually zero, and a high 7 value can be obtained regardless of the temperature increase rate during annealing. Furthermore, since it does not suffer from strain aging deterioration due to solid solution C and N, it is widely used as a high-grade cold rolled steel sheet material regardless of whether it is box annealed or continuous annealed. However, IF steel uses expensive elements such as Ti, and
In order to make effective use of l, it is necessary to add At and perform scleral acid. Furthermore, titanium carbonitride and the like require high-temperature annealing to significantly raise the recrystallization temperature of the steel, making it a very high-grade steel in terms of cost.

In addition, rimmed steel and cagged steel have a large amount of large oxide inclusions, so they have low elongation values as cold-rolled steel sheets.
Moreover, since these inclusions inhibit the development of good texture, the V value is not so high.

As a result of various studies under these circumstances, the gist of the present invention is as follows.

(1) C: 0.0050% or less, Mn: 0.5%
A cold-rolled steel sheet with good workability that can be annealed at a low temperature, characterized by the following: P: 0.1% or less, N: 0.0050% or less, O: 0016-0.035%, the balance being Fe and unavoidable impurities. Steel for use.

(2) C: 0.0050% or less, Mn: 0.
5% or less, P: 0.1% or less, N: 0.0050
% or less, O: 0.016 to 0.035%, and further B
: 0.0001 to 0.0050%, Nb: 0.003
~0.080% and Zr: 0.005~0.1%
1. A low-flow annealing, good-formability steel for cold-rolled steel sheets, characterized in that it contains one or more of the following, and the remainder consists of Fe and unavoidable impurities.

The present invention aims to thoroughly reduce the amount of C, which is often harmful to cold-rolled steel sheets, and actively utilize 〇, which was conventionally thought to be harmful, within a specific range. It controls recrystallization behavior in a dispersed state and maintains overall processability.

Next, the reason for limiting the numerical value of the chemical composition of the steel of the present invention will be described.

C is harmful to workability and must be thoroughly reduced. In particular, in the present invention, in order to effectively utilize the oxide, the degree of harmfulness of C must be set to be less than 0.0050. Furthermore, if C is 0.0020% or less, C aging will not occur even without adding Nbi, so if decarburization can be easily performed, C is preferably 0.0020% or less. ``The lower limit of C is approximately 0 based on current steelmaking technology.
．． It is 0010%.

Mn (l″j: ntI is necessary to prevent hot embrittlement by combining in the form of impurity S and MnS,
．． If it exceeds 5%, the ductility of the steel will deteriorate significantly. S to 0.00
Setting the Mn content to 5% or less and the total Mn content to 0.25% or less are preferable conditions for further improving processability.

Next, P is necessary when manufacturing high-strength cold-rolled steel sheets with a tensile strength of 35 to 40 kgf/rnm2 class. P strengthens the steel without significantly deteriorating its workability. Addition of more than 0.1 inch embrittles the steel and deteriorates spot weldability.

When producing a soft cold-rolled steel sheet, P should be 0.020% or less. Particularly when aiming at improving workability and preventing embrittlement, P is preferably less than 0.01%.

N causes N aging and deteriorates the steel material, so O
, OO must be 50% or less. Also, N with B and Zr
f. Even when fixing, if there is a large amount of N, a large amount of B or Zr is required, which is economically disadvantageous, and too much of these nitrides deteriorates workability, so O, OO 50%.
Must be as follows. In this way, basically N is also a harmful element, and if better workability is desired, N is 0.
It is preferable to set it to 0.025% or less.

O becomes a fine oxide with Mn, etc., promotes recrystallization in the recrystallization annealing process, and works effectively for the development of orientation useful for workability. Therefore, 0.016% is necessary. However, when the amount of 0 exceeds 0.035%, large oxide inclusions increase and processability deteriorates. This large inclusion has an O content of 0.
If the O content exceeds 0.030%, the O content is sometimes found, so if workability is important, the O content is preferably 0.030% or less.

Next, if aging deterioration due to solid solution C and N becomes a problem, B
, Nb, and V are added. The addition of B is to fix the solid solution N and is 0,0001
If it is less than 0.0050%, there will be no effect, and if it exceeds 0.0050%, defects such as slab cracks will occur. Nb is added in an amount of 0.003% to 0.080% to fix solid solution C. O,OO
If it is less than 34%, the addition has no effect, and if it exceeds 0.08%, the effect not only becomes saturated, but it is also economically disadvantageous. Also, V is O, OO 5% to 0.0% to fix C and N.
Add 1%.

If it is less than 0.005%, there is no effect, and if it exceeds 0.1%, workability will deteriorate due to precipitates.

The above is the reason for limiting the chemical composition of the steel of the present invention,
Since bubbles do not form in molten steel in the C and Q ranges of the steel of the present invention,
It is preferable to use a continuous casting method, which provides a beautiful slab surface and high productivity, to form the slab. In addition, the degassing method of molten steel is RH, D
Any method such as H may be used. The slab may be heated and hot rolled in a conventional manner, or may be heated from a hot piece slab or hot rolled directly from a hot piece slab. When heating, the heating temperature is not a problem, but low-temperature heating of 1150° C. or lower is preferable when energy saving and economical efficiency are sought. It is preferable that the final rolling finish temperature be at least the Ar3 transformation point, but even if the rolling is done at a temperature somewhat below the transformation point, the deterioration of the material after cold rolling annealing will not be so great. Next, regarding the coiling temperature, one of the characteristics of the steel of the present invention is that there is no need to limit the coiling temperature to a particularly high or low temperature.
The temperature may be 00 to 700°C. This feature is also one of the major effects of the steel of the present invention, since high-temperature coiling causes poor pickling properties, and low-temperature coiling causes deterioration of productivity in hot rolling from the viewpoint of cooling ability.

The steel of the invention is subsequently pickled, cold rolled, and then annealed.

The cold rolling rate may be the usual 50 to 85 inches. Annealing may be box annealing or continuous annealing, but in order to take advantage of the characteristics of the steel of the present invention, annealing at a low temperature is desirable. The conditions are 550 to 6 for box annealing.
80°C, and 600 to 770°C for continuous annealing. In addition, in continuous annealing, normally in the case of low C steel, precipitation treatment of supersaturated C is carried out during or after cooling during or after annealing, which is called over-aging treatment, while maintaining the temperature at 300 to 500°C. One of the features is that the equipment cost for continuous annealing can be kept low because no special treatment is required.

Furthermore, when box annealing a low C-At killed steel, a low At steel is used as a steel for continuous casting, but when the At becomes low, abnormal grain growth called roughening occurs in the portion of the annealed outer winding exposed to high temperatures. However, since such abnormal grain growth does not occur in the steel of the present invention, there are great expectations that it will be used as a steel for continuous casting in place of the low C-low At A7 killed steel for continuous casting.

The steel of the present invention is temper-rolled after annealing and is used as a steel strip or cut plate. Further, the plated steel sheet may be electroplated after this and provided as a plated steel sheet. Alternatively, after cold rolling, the steel sheet may be passed through a continuous hot-dip galvanizing line to provide a hot-dip galvanized steel sheet.

Next, examples of the present invention will be described.

Example 1 (Example using continuous annealing) Steel having the chemical components shown in Table 1 was tapped in a converter. Steels A-H and Steel J were melted in a converter, then C9O was removed by RH vacuum degassing, and the oxygen level was adjusted by adding At. Then B, Nb.

Zr and Tif were added as appropriate to obtain steel with predetermined components. After these steels are made into slabs by continuous casting, the heating temperature is 1100℃ and the finishing temperature is 910℃.
℃, the winding temperature is 620℃, and the finishing thickness is within 4 degrees.
After pickling, it was cold rolled to 0.8 ran. On the other hand, as for steel weight and steel, conventional low C-At killed and capped steels were cast into ingots and then bloomed into slabs. Although many blowhole defects were observed on the surface of the steel H slab, the surfaces of the other steel slabs were beautiful. Heat this to a temperature of 12
00℃.

Hot rolling was carried out under the conditions of a finishing temperature of 890°C, a winding temperature of 750°C (steel weight) and 700°C (steel K), and a finishing thickness of 4 (steel weight) and 3 ha (steel K), and after pickling, the temperature was 0. It was cold rolled at 8 Tat. These steels were annealed under the continuous annealing conditions shown in Table 2.1.
After temper rolling at an elongation rate of 0%, it was subjected to a test. A JI No. 85 test piece was used as the tensile test piece.

In Table 2, flats 1 to 7 are the steels of the present invention. A3 is a 35 kg f/++" grade high-strength cold-rolled steel plate.
2.14 and 15 are made by the conventional method and are low C-At killed steel, TI-IF steel and capped steel, respectively. Also, Bian 10, 11, 13, and 16 are comparative methods,
A8.9 is a comparison steel.

The steel plates of No. 1 and No. 2 are steels that do not have solid solution C and N'i fixed, but are annealed at 750°C and temper-rolled to a capacity of 20 kl? f
Yield point strength of less than /mm2, elongation of more than 45 inches and 1.3
It has a T value of about 5, and is softer and has better workability than low C-At killed steel (11) and capped steel (A15) at the same annealing temperature. Haruka 3 steel plate also has good ductility and T value as a 35 kgf/mm'' class high strength cold rolled steel plate.

Furthermore, the mechanical test values hardly change depending on the presence or absence of over-aging treatment (comparison of steel plates of Flat 1 and Flat 2). This shows a good contrast compared to the case of low C-At killed steel (steel plates of cups 10 and 11).

Steel fixed with solid solution C or N-1Nb, B, etc. (A4゜5
) becomes even softer than A1 to A39, and in particular, the softening after aging is significantly lower.
2).

Furthermore, steel plates A6 and 7, in which both C and N are fixed by the combined addition of Nb and H, are extremely soft, have a high r value, and show almost no aging deterioration (high temperature annealed material of Ti-IF steel (A14)).
) has good mechanical test values comparable to

In addition, A8 and A9 steel plates have 0 levels outside the scope of the present invention, and both exhibit mechanical properties that are considerably inferior to the present invention steel at the same annealing temperature. There were many surface defects on the steel plate.

Example 2 (Example by box annealing) In Example 2, among the steel slabs used in Example 1, steels with codes B, C, E, G, H, I, and J shown in Table 1 were used.

Among these, codes B, C, E, G, H.

Steel J was hot rolled and cold rolled under the same conditions as in Example 1. For forging and K, heating temperature 1270℃, finishing temperature 890℃ 1 winding temperature 550℃ (steel ■) and 62
0℃ (Steel K), finishing thickness 4mm (Steel I) and 3mm (Steel K)
), and after pickling, it was cold rolled to a thickness of 0.8 m.

Table 3 shows the box annealing conditions and the resulting mechanical test values.

Note that annealing was performed in a tight coil, and after cooling, skin pass rolling was performed at an elongation rate of 1%.

The steel plates of &17, 18, and 19, which are the steels of the present invention, are 66
It is clear from the comparison with JL20.21, 22.24 and 26 steel sheets that were annealed under the same conditions that the steel is soft, has high elongation, and has a high 7 value despite being annealed at a low temperature and short time of 6 hours at 0°C. It is.

As is clear from the above examples, the steel of the present invention does not require restrictions such as restrictions on the coiling temperature of hot rolling or over-aging treatment during continuous annealing, and is soft, has high elongation, and has a high 7 value through the energy-saving treatment of low-temperature annealing. It shows good workability.

Note that cold-rolled steel sheets may be used for shearing and quenching to increase strength after processing, but in the case of the steel of the present invention, At
Since it does not contain any substances such as substances and has high purity, it has excellent charcoal-grindability and is suitable for use in toiletries. When using the steel of the present invention for such uses, it is preferable not to add Nb.

Procedural amendment (voluntary) August 10, 1980 Director of the Patent Office Kazuo Wakasugi1, Indication of the case 1982 Patent Application No. 0394412, Name of the invention Steel for cold rolled steel plates3, Person making the amendment Relationship to the case Patent applicant 2-6-3 Otemachi, Chiyoda-ku, Tokyo (665) Representative Takeshi of Nippon Steel Corporation 1) Toyota 4 agent/person 2-4-1 Marunouchi, Chiyoda-ku, Tokyo 100 No. 6 Claims column of the specification subject to amendment and detailed description of the invention 1)
Amend the claims in a separate document.

2) Correct page 4, line 12 of the specification 'i-Zr J to rVJ.

3) Same page 6 line 6 “NiZ is also used when fixing N with B or Zr.
If there are many, B or ZrJ may be changed to ``N'' even when fixing N' with B or ■.
If there are many, it is corrected to B or V.

4) Page 10, line 2 “Correct zrJ to 1-VJ.

5) Notes to the patent claim characterized by "with combined addition of Nb and B" on page 14, line 2 (1) C: 0.0050% or less, Mn:
0.5% or less P: 0.1 inch or less, N: 0.00
50% or less, O: 0.016 to 0.035%, balance Fe and unavoidable impurities 75) A low-temperature anneaable steel for cold-rolled steel sheets.

7 (2) c; 0.0050 chi or less, Mn:
0.5% or less, P: 0.1 inch or less, N: 0.0
050% or less, O: 0.016 to 0.035%, and B: 0.0001 to 0.0050%.

Nb: 0.003-0.080% O and V: 0.
1. A steel for cold-rolled steel sheets that can be annealed at 100 degrees Fahrenheit and is characterized by containing one or more of 005 to 0.1% of 111Fe and unavoidable impurities.

Claims (2)

[Claims] (1) C: 0.0050% or less, Mn: 0.
5% or less, P: 0.1% or less, N: 0.0050% or less, O: 0.016 to 0.035%, and the balance is Fe and unavoidable impurities. Steel for processable cold-rolled steel sheets. (2) C: 0.0050% or less, Mn: 0.5%
Hereinafter, P: 0.1% or less, N: 0.0050% or less, O: 0.016 to 0.035%, and B: 0
．． 0001-0.0050, Nb: 0.003-o,
Steel for cold-rolled steel sheets that can be annealed at low temperatures and has good workability and is characterized by containing one or more of oso% and Zr: 0.005 to 0.1%, and the balance being Fe and unavoidable impurities. .