JPS59136425A - Preparation of cold rolled steel plate for press work - Google Patents

Abstract

PURPOSE:To inexpensively prepare steel having good press workability, by forming steel respectively containing C, Si, Mn, N and one or more of Ti, Nb and Zr in a predetermined ratio under a specific condition into a plate shaped cast piece by continuous casting while applying hot rolling and re-crystallization annealing to the cast piece. CONSTITUTION:Steel containing 0.001-0.020% C, 2.0% or less Si, 1.20% or less Mn, and 0.0080% or less N and further containing one or more of 0.20% or less Ti, 0.20% or less Nb and 0.20% or less Zr and satisfing the next condition is prepared. That is, it is necessary that the relation of the Ti-equivalent (a) of the formula I and the C-equivalent (b) of the formula II satisfies the formula III. In the next step, steel is formed into a plate shaped piece by continuous casting and hot rolling at 100-450 deg.C and recrystallization annealing are applied to said cast piece. As a result, a cold rolled steel plate excellent in press workability can be prepared in good efficiency and low cost without applying the conventionally performed hot rolling of the cast piece.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a steel plate with good press formability at low cost.

Conventionally, to produce cold-rolled steel sheets for press forming, completely solidified continuously cast slabs are cut, cooled, subjected to surface inspection and flaw removal, and then placed in a heating furnace maintained at 1100 to 1300°C. It was common practice to hot-roll the coil after soaking it for 30 minutes to 1 hour, and then cold-roll the resulting hot-rolled coil and annealing it.

However, in recent years, continuous casting methods with extremely good slab surface properties have been developed, but at the same time energy-saving ideas have become increasingly widespread and established, continuous casting slabs have become increasingly popular. A method of cold-rolling a steel sheet as it is without hot rolling to obtain a desired thickness, and then recrystallization annealing has been considered.

By the way, in this case, from the viewpoint of energy saving, the process of cooling the continuously cast slab to room temperature for cold rolling,
Furthermore, it is most desirable to save as much energy as possible in the step of heating the cold-rolled steel sheet for recrystallization, and to roll the slab while it is still hot.

However, even if such a method is attempted, in the case of steel with normal composition, the slab used for rolling has a solidified structure and contains many solid solution C and N atoms, so it is difficult to heat the slab. The texture developed by inter-rolling is insufficient, and as a result, the texture after recrystallization annealing is not desirable, and the drawability of the product is significantly inferior to that of steel sheets produced by conventional cold rolling of hot-rolled coils. There was a problem with it being put away.

From the above-mentioned viewpoint, the inventors of the present invention have realized that by warm rolling continuously cast plate slabs as they are without soaking or hot rolling the slabs, the present inventors have achieved the same results as those achieved by conventional methods. As a result of conducting research to find a method for manufacturing cold-rolled steel sheets with good press formability, the following findings were obtained.

(a) In general, steel sheets with a cast structure have many crystal grains with (100) axes in the normal direction of the sheet surface, but as in the case of manufacturing conventional cold-rolled steel sheets, As a result of the hot rolling step, this (100) texture is destroyed, and the steel plate after hot rolling has a random crystal orientation with almost no texture. Therefore, this is cold-rolled to increase the number of crystals with (111) axes in the normal direction of the sheet surface, and then during recrystallization, the precipitation of AQ and H is used to create such (11,1) crystals. If the texture is further increased, the deep drawability shown by the r value of the annealed sheet will be good and the press formability will be improved, but if the hot rolling process is omitted, the (100) texture will be increased. When steel with a . Even in annealed plates, the (111) texture is weak < (10
0) The texture becomes strong and only products with poor deep drawability can be obtained.

(bl If the hot rolling process is omitted, AU, H
Due to the inability to perform appropriate solution treatment for C and the inability to perform C precipitation treatment, (
Since 1'1) does not promote the development of texture, the (111') texture further decreases.

(C) However, if the steel material satisfies the above formula (3), plastic deformation will be extremely easy during warm rolling, and even if the (100) texture is strong in the steel sheet before warm rolling, the rolling At times, the (111) texture develops, and even during annealing, the (111) texture develops sufficiently without the aid of AAN precipitates or carbides.

This invention was made based on the findings (a) to (C) above, and 5C: 0.001 to 0.020%.

Si: 2.0% or less.

Mn: 1.20% or less.

N: 0.0080% or less.

including, Ti: 0.20% or less.

Nb: 0.20% or less.

Zr: 0.20% or less.

contains one or more of the following, and the relationship between the T1 equivalent calculated by the above formula (1) and the C equivalent calculated by the above formula (2) satisfies the above formula (3),
Furthermore, if necessary, REM: 0.03 to 0.20%.

B: 0.0003 to O, OO50%.

one or more of the following: P: 0.12% or less.

5o4Ap: 0.01-0.10%.

A steel containing one or two of the following, with the remainder consisting of Fe and unavoidable impurities, is made into a plate slab by continuous casting, which is then warm rolled at 100 to 450°C and recrystallized. It is characterized by the ability to efficiently produce cold-rolled steel sheets with excellent press formability at low cost by applying annealing, without the conventional hot rolling of slabs. It is.

Next, the reason why the chemical composition of the steel is limited as described above in the method of the present invention will be explained.

■ C The smaller the C component is, the better the press formability of the cold-rolled steel sheet product will be, so it is preferable; however, if the C content is less than 0.0001%, it will be extremely difficult to melt.
．． If the content exceeds 0.020%, not only will a large amount of carbonitride-forming elements be required, but also the amount of carbonitride precipitation will increase, deteriorating the press formability of the final product. The content was set to 0.001 to 0.020%.

■ 5I S1 component has the effect of strengthening steel, and is added in the required amount depending on the desired strength, but the amount added is 2.0%.
If the
Its content was set to 2.0% or less.

■ Mn The Mn component has the effect of improving the toughness of steel sheets, but 1
．． If the content exceeds 20%, melting becomes difficult and costs increase, so the content should be reduced to 1.
．． It was set to 20% or less.

■ P The P component has the effect of strengthening steel, so it is added as necessary, but if it is added in excess of 0.12%, recrystallization becomes difficult and good ductility cannot be obtained. The content was set to 0.12% or less.

■ sot, AQ sot-Aε is added as necessary to perform sufficient deoxidation and improve the yield of carbonitride-forming elements.
．． Even if it is added in excess of 10%, no further deoxidizing effect can be obtained and the cost will be high, so the content should be reduced to 0.1%.
It was set to 0% or less.

(2) N The smaller the N content, the less the Ti equivalent, ie, the added content of carbonitride-forming elements, is preferable.

If the N content exceeds 80% of O, OO, the press formability of the final product will deteriorate, so the content is set to 0% or less.

■ Ti, Nb, and Zr These components form fine carbonitrides in the plate slab to increase the mobile dislocation density in the plate slab.
It has the effect of forming a (111) texture in the final warm-rolled plate product, improving the deep drawability represented by the r value, and improving the press formability, but if it exceeds 0.20% Even if Ti is contained, no further improvement effect can be seen and the cost will be high, so the content of each Ti: 0.2
0% or less, Nb2: 0.20% or less and Zr: 0.20
% or less.

In addition, the above equations (1) to (3) show the relational expressions for setting the amount of solid solution (C0N) to 0.0010 (%) or less and precipitating the remaining C0N as carbonitrides. It is something.

In addition, the upper limit of (C equivalent) - 7 (Tl equivalent) is 0.00
The reason why we chose UO (%) is that when this upper limit is exceeded, solid solution [
This is because the amount of carbon (C+N) increases and the press formability of the product cold-rolled steel sheet after warm rolling of the plate slab deteriorates.

Furthermore, it is necessary to uniformly distribute the above-mentioned components, which can be achieved by applying a continuous casting rapid solidification method with less segregation.

(2) B and REM These components have the effect of improving the secondary processing brittleness of the steel sheet, so they are added as necessary, but each component is REM: less than 0.03%.

If the content of B2O, 0O0 is less than 3%, the desired improvement effect cannot be obtained; on the other hand, REM: 0.20%.

B: If the content exceeds 0.0050%, the weldability and surface quality of the steel plate will deteriorate.
:0.0O03 to 0.0050%.

The method of this invention involves continuously casting steel having the above-mentioned composition into a plate shape, and then subjecting it to warm rolling and recrystallization annealing. Naturally, the surface condition is adjusted as necessary by removing surface flaws or scale, and then warm rolling is performed, or the surface condition is adjusted after warm rolling or recrystallization annealing.

It is most effective to adjust the surface roughness and flatness after annealing.

The temperature of warm rolling is preferably 100 to 450°C. That is, at temperatures below 100° C., processing heat cannot be used for recrystallization annealing, so the advantage in terms of thermal energy is small, and the load for warm rolling becomes large, making it difficult to perform warm rolling at a high rolling reduction rate, which will be described later.

Further, if the temperature exceeds 450°C, a good texture is not formed during warm rolling and the drawability of the steel sheet decreases (Table 1), so the warm rolling temperature was set to 00 to 4501°C.

Further, the reduction ratio in warm rolling is preferably 50% or more, and the larger the reduction ratio, the better the press formability of the product cold-rolled steel sheet.

Further, the subsequent recrystallization annealing is preferably performed by box annealing, continuous annealing, continuous hot-dip plating, etc. at a temperature of 660° C. or higher.

In order to improve the efficiency of continuous casting and modify the shape of the slab, it is possible to perform light hot working or rolling on the slab during solidification or immediately after solidification. When combined into two lines.

Since the heat from warm rolling can be used for recrystallization annealing, the energy saving effect is further improved.

Next, the method of the present invention will be explained using examples and comparing with comparative examples.

Example 1 C2 0.006%, Si: 0.
0.01%, Mn: 0.08%.

P: 0.010%, S: 0.0 0
1% + 5ol-AQ: 0.05 salary, N: 0
．． Vacuum melting various steels containing 0.004%, varying Ti in the range of 0 to 0.20%, and the remainder Fe,
Thickness: lOm/m, Width: 110m/m, Length: 00m
/m, and immediately cooled to room temperature.

Next, this plate-shaped slab was pickled, heated to 300°C, and warm-rolled at a reduction rate of 92% to form a cold-rolled plate of 0.8 mm. Continuous annealing was performed under conditions of holding the temperature at 800°C for 90 seconds.

Then, the r value and elongation were determined for the JI No. 65 tensile test piece taken from the annealed cold-rolled steel sheet, and the results were used as the amount of solid solute C in the cold-rolled steel sheet, that is, the C The relationship between the equivalent weight and (Ti equivalent weight) is shown in FIG.

As is clear from Figure 1, the value of equation (3) above is 0.00.
It can be seen that when the content is 10% or less, it is possible to produce a cold-rolled steel sheet that exhibits a high r value and also exhibits good elongation.

Example 2 C: 0.0040%, Si: 0.0 1 0
%, Mn: 0.28%, P: 0.012%,
S: O, OO'7%, soA, AA: 0.08%, N
: 0.0030%, Nb: 0.055
A steel consisting of % + Fe: remainder, C: 0.045
%, Si: 0.010%, Mn: 0.22%,
P: 0.011%, S: O,OO'i'%,
sot, M: 0. 0 5 1%
, N2 0.0032%, Fe: After melting B steel consisting of the remainder, it was continuously rapidly cooled and solidified to a thickness of 8 m.
A plate-shaped slab with a width of 220 m/m and a width of 220 m/m was immediately cooled to 400°C.

Steel A has a Ti equivalent of 0.028% and a C equivalent of O, OO66.
Although it is a steamed rice cake and satisfies the above formula (3), steel B
is a comparative conventional steel that falls outside this range.

These two types of plate slabs were heated as they were in the temperature range of 300 to 400°C for 1. It was warm rolled to a thickness of Qm/ya at a vehicle weight of 87%, and then continuously annealed at a temperature of 850° C. for 230 seconds.

Next, these annealed plates were temper-rolled at an elongation car weight of 0.6%, and then JI No. 35 tensile test pieces were taken and their mechanical properties were measured.

The results are shown in Table 1.

Table 1 As shown in Table 1, cold-rolled steel sheets manufactured by the method of the present invention using steel A have a higher r value and better elongation than those using steel B. It is clear that the press formability is excellent.

Example 3 Steel having the composition shown in Table 2 was vacuum melted to a thickness of 40 m.
/m, width: zzom/m+length 1440 m/m, and immediately cooled to room temperature.

After cutting and removing the scale, these slabs were heated at 4.0 to 1.2 m/min at various temperatures shown in Table 2.
A cold-rolled steel sheet according to methods 1 to 28 of the present invention is produced by warm rolling at a rolling reduction of near 0% and continuous annealing at 2,800° C. for 90 seconds to a thickness of Cold-rolled steel sheets were manufactured by Comparative Methods 29 to 33, respectively.

In addition, the cold rolled steel sheets obtained by Comparative Methods 29 to 33 are all out of the scope of the present invention in terms of composition or warm rolling temperature, and the relevant ones are marked with * in Table 2. .

Next, the tensile properties and r-values of the cold-rolled steel sheets obtained by the method 1 to 2 of the present invention and the cold-rolled steel sheets obtained by the comparative methods 29-33 were measured, and these results were used in the second test.
It is also shown in the table.

As shown in Table 2, the cold rolled steel sheets prepared by methods 1 to 28 of the present invention all have good elongation and high r value, that is, good press formability, whereas the cold rolled steel sheets obtained by the comparative method 29
The cold-rolled steel sheet according to
i equivalent) are respectively high beyond the scope of this invention, the characteristic values of the product are low r value and elongation, indicating poor press formability.

In the cold-rolled steel sheet prepared by Comparative Method 31, the amount of C was increased by Comparative Method 33.
Since the warm rolling temperature of the cold-rolled steel sheet according to the invention is higher than the range of the present invention, the r value is inferior.

Furthermore, since the cold-rolled steel sheet produced by Comparative Method 30 is a normal AP, killed steel sheet that does not contain carbonitride-forming elements, the r value of the product is extremely low.

As described above, according to the method of the present invention, cold-rolled steel sheets with good press formability can be produced at low cost and high efficiency by minimizing energy consumption and omitting hot rolling equipment. It brings about industrially useful effects such as being able to be manufactured.

[Brief explanation of drawings]

Figure 1 shows (C equivalent) -- (Ti equivalent) in cold rolled steel sheet.
FIG. 2 is a diagram showing the influence of the value on the elongation of the product and the r value. Applicant: Sumitomo Metal Industries, Ltd.

Claims (1)

[Claims] (1) C: 0.001 to 0.020%. Si: 2.0% or less. Mn: 1.20% or less. N: 0.0080% or less. Contains Ti: 0.20% or less. Nb: 0.20% or less. Zr: 0.20% or less. and the relationship between the T1 equivalent calculated by the above formula (1) and the C equivalent calculated by the above formula (2) satisfies the above formula (3), and the remaining 9 is a composition consisting of Fe and unavoidable impurities (more than % by weight)
1. A method for producing a cold-rolled steel sheet for press forming, characterized in that the steel is made into a plate-shaped slab by continuous casting, and then subjected to warm rolling at 100 to 450°C and recrystallization annealing. (2) C: O, OO 1-0.020%. 2.0% or less in S. Mn: 1.20% or less. N: 0.0080% or less. Contains Ti: 0.20% or less. Nb: 0.20% or less. Zr: 0.20% or less. Contains one or more of the following, and 48 48 T1 equivalent - Ti (%) + - Nb (%) 10 - Z r (
%)-=-(1)93 91 The relationship between the T1 equivalent calculated by the above formula (1) and the C equivalent calculated by the above formula (2) satisfies the above formula (3), and further, sob, AQ: A steel having a composition (more than 1% by weight) containing 0.10% or less of F'e and the remainder consisting of 10 unavoidable impurities is made into a plate slab by continuous casting, and then 1.
A method for producing a cold-rolled steel sheet for press forming, which comprises performing warm rolling at 00 to 450°C and recrystallization annealing. (3) C: 0.001-0.020%. Si: 2.0% or less. Mn: 1.20% or less. N: 0.00080% or less. Contains Ti: 0.20% or less. Nl): 0.20% or less. Zr: 0.20% or less. contains one or more of the following, and the relationship between the Ti equivalent calculated by the above formula (1) and the C equivalent calculated by the above formula (2) satisfies the above formula (3), and A steel containing 0.12% or less of P and the remainder consisting of Fe and unavoidable impurities (more than 10% by weight) is made into a plate slab by continuous casting, and then cast into a slab of 100 to 50% by weight.
With warm rolling at °C. A method for producing a cold-rolled steel sheet for press forming, characterized by subjecting it to recrystallization annealing. (4) C: 0.001-0.20%. 2.0% or less in S. Mn: 1.20% or less. N: 0.0080% or less. Contains Ti: 0.20% or less. Nb: 0.20% or less. Zr: 0.20% or less. contains one or more of the following, and the relationship between the Ti equivalent calculated by equation (1) and the C equivalent calculated by equation (2) above satisfies equation (3). ,
Furthermore, REM: 0.03-0.20%. B: O, 0O03 to 0.0050%. A composition containing one or more of the following, and the remainder consisting of Fe and inevitable impurities (more than
1.) A method for producing a cold-rolled steel sheet for press forming, characterized in that steel is continuously cast into a plate-shaped slab, which is then subjected to warm rolling at 100 to 450°C and recrystallization annealing. (5) C: O, OO1-0.020%. Si: 2.0% or less. Mn: 1.20% or less. N: 0.0080% or less. Contains Ti: 0.2.0% or less. Nt): 0.20% or less. Zr: 0.20% or less. Contains one or more of the following, and T1 equivalent -Ti (%) + -Nb (%) + -Z
r (%) ...-(1)93 91 2 C per t-Ci%) + -N (%) -・-・-(
2) 4 (C equivalent) --(Ti equivalent) ≦0.0010 (%)
......(3) The relationship between the T1 equivalent calculated by the above formula (1) and the C equivalent calculated by the above formula (2) is the above (3)
) formula, and P: 0.12% or less. sot, AA: 0.10% or less, with the remainder consisting of Fe and unavoidable impurities (more than 10% by weight) is made into a plate-shaped slab by continuous casting, and then 10%
A method for producing a cold-rolled steel sheet for press forming, which comprises performing warm rolling at 0 to 450°C and recrystallization annealing. (6) C: 0.001-0.020%. Si: 2.0% or less. Mn: 1.20% or less. N: 0.0080% or less. Contains T'i 20, 20% or less. Nb: 0.20% or less. Zr: 0.20% or less. The relationship between the amount of Tii calculated by formula (1) and the C equivalent calculated by formula (2) above is expressed by formula (3) above. Satisfied and further REM: 0.03-0.20%. B: 0.0003 to 0.0050. Contains one or more of the following, and P: 0.12 or less. The remainder consists of Fe and unavoidable impurities (more than 1% by weight)
Press forming (7) characterized in that the steel of ) is made into a plate-shaped slab by continuous casting, and then subjected to warm rolling at 100 to 450°C and recrystallization annealing (7) C: 0.0
01-0.020%. Si: 2.0% or less. Mn: 1.20%. N: 0.0080% or less. Contains Ti: 0.20% or less 1 Nb: 0.20% or less. Zr: 0.20% or less. The relationship between the T1 equivalent calculated by the above formula (1) and the C equivalent calculated by the above formula (2) satisfies the above formula (3). , and further REM: 0.03 to 0.20%. B: O,0O03~0.00!50%. Contains one or more of the following: sot, AM: 0.10%, and the remainder is F.
A steel with a composition (more than 1% by weight) consisting of e + unavoidable impurities is made into a plate slab by continuous casting, and then this is
A method for producing a cold-rolled steel sheet for press forming, which comprises performing warm rolling at 50°C and recrystallization annealing. (8) C: 0. OO1~0020%. Sl, 260% or less. Mn: 1.20% or less. N: 0.0080% or less. Contains 'l'i: 0.20% or less. Nb: 0.20% or less. Zr: 0.20% or less. contains one or more of the following, and the relationship between the T1 equivalent calculated by the above formula (1) and the C equivalent calculated by the above 1. (2) formula satisfies the above formula (3). ,
Furthermore, REM: 0.03-0.20%. B: 0.0O03~O, OO50%. 1 loading dock and 2, P: 0.12% or less. sol, A (1: 0.10% or less), with the remainder consisting of Fe and unavoidable impurities (
% by weight or more) into plate-shaped slabs by continuous casting,
A method for producing a cold-rolled steel sheet for press forming, which is then subjected to warm rolling at OO to 450°C and recrystallization annealing.