JPS61157660A - Nonageable cold rolled steel sheet for deep drawing and its manufacture - Google Patents

Abstract

PURPOSE:To develop the titled steel sheet having high ductility and super deep drawability, by decreasing quantities of C and Ti in steel contg. Ti, Nb, Cr, and hot, cold rolling the steel slab incorporated with a specified quantity of Nb in relation to an effective Ti quantity, and annealing said sheet. CONSTITUTION:The steel slab contg. by weight 0.001-0.01% C, <0.1% Si, <0.5% Mn, 0.01-0.10% Sol, Al, 0.06-0.20% Cr, <0.03% P <0.015% S, 0.007% N, <0.01% O, 4 times of C%-0.15% Ti as effective Ti quantity expressed by a formula (1) and Nb quantity satisfying 0.05% [effective Ti quantity] + Nb<=0.20% is cast. The slab is hot rolled to plate of 5mm thickness, then said plate is pickled, cold rolled to sheet material of 1.2mm thickness by >=40% draft and said sheet is batch annealed at 800 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a non-aging cold rolled steel sheet having high ductility and ultra-deep drawability, and a method for producing the same.

[Conventional technology]

For example, automobile quarter panels, fenders, oil pans, etc. must be formed by extremely severe press working. Therefore, cold-rolled steel sheets used for such molded products are required to have high ductility and ultra-deep drawability. It also needs to be non-prescription. In response to these demands, conventionally, cold rolled steel sheets that have been decarburized by batch open coil annealing have been applied, or Ti, which is a carbonitride forming element, has been applied.
By adding Nb, Cr, etc. alone or in combination, C and N in the steel are fixed, increasing ductility and ensuring anti-aging properties, and the action of carbonitrides of Ti and Nb improves deep drawability. It has been proposed to use a non-aging cold-rolled steel sheet for deep drawing that has developed an effective (1111-oriented recrystallization texture).

Regarding the latter carbonitride-forming element-added steel, for example, Ti-added steel is disclosed in Japanese Patent Publication No. 44-18066, Japanese Patent Application Laid-Open No. 59-67322, and Japanese Patent Application Laid-Open No. 59-89727, etc. -1245 Publication, Japanese Patent Publication No. 59-34778, and Japanese Patent Application Publication No. 58-81952
Nb-added steel was disclosed in the Japanese Patent Publication No. 50-3.
0572 and Japanese Unexamined Patent Publication No. 185752/1985 disclose Ti/Cr added steel, and Japanese Patent Application Laid-Open No. 59-6
No. 7319 discloses T1Nb-added steel, and JP-A-59-123720 discloses TiNb C steel.
An r-added steel is disclosed.

[Problem that the invention seeks to solve]

Even if an attempt is made to meet the above requirements, decarburized annealed steel has the problem that the grain size tends to increase (and roughness such as orange peel occurs easily during press forming).T
In i-added steel and Ti-Cr steel, Ti has a strong bond with O and S and forms oxides and sulfides, so in order to ensure non-aging properties by fixing C and N, C
, H must be added in an amount that is several times the stoichiometric equivalent of Ti. In order to lower manufacturing costs and increase ductility, it is desirable that the Ti content be as low as possible within the range that ensures non-aging properties.

For this purpose, the amount of C and the amount of solid solution Ti (from the effective amount of Ti to the amount of T
However, if the amount of C and the amount of solid solute Ti are reduced too much, the in-plane anisotropy of the r value [Δr=(ro'' + T
90” 2 rq5°)/2] becomes larger,
r4S°, which is rmin, decreases, leaving a problem in press workability. In Nb-added steel, with the recent progress in steel degassing technology, it has become possible to relatively easily reduce C to a range of C < 50 ppm. C and Nb such as
A method for manufacturing Nb-added steel with a very small amount has been proposed, but unless Nb-added steel is coiled at a high temperature of 700°C or higher, the recrystallization temperature will be high at normal coiling temperatures, and it will be difficult to process the Nb-added steel, especially during continuous annealing. It is necessary to make the annealing temperature during annealing higher than that of Ti-added steel. Further, even if the hot-rolled coil is coiled at a high temperature, there is a problem that a homogeneous material cannot be obtained at the longitudinal ends of the hot-rolled coil because the cooling rate is fast.

In addition, the in-plane anisotropy of the r value is improved by reducing the amount of Ti to increase ductility and adding Nb Cr in addition to Ti in the aforementioned JP-A-59-67319.
Although it is stated in Japanese Patent Publication No. 59-123720, actual investigation and research shows that in such a manufacturing method, the Nb content is too low, but Even if a high cold rolling reduction of 80% is adopted, the in-plane anisotropy of the r value appears significantly, and r15°, which is +rmin, becomes too small, which still causes problems in press formability.

In addition, by setting the cold rolling rate to 80% or more, rmin
Although it is possible to improve the in-plane anisotropy of the r value by increasing the This becomes necessary and causes problems in actual operation, as well as problems in the capacity of the cold rolling mill.

[Means for solving problems]

The present invention aims to solve the above-mentioned problems by reducing the C and Ti amounts to below predetermined values in T1NbCr-added steel, while increasing the Nb to a predetermined amount or more and [effective Ti amount]. The solution is to add in relevant amounts. That is, 1 the present invention is at 1% by weight.

Ci　O, 001-0.01%.

Si: 0.1% or less.

Mn: 0.5% or less.

Sol, AI! ;0.01-0.10%.

Cr; 0.06-0.20%.

P: 0.03% or less.

S: 0.015% or less.

N, 0.007% or less.

0; 0.01% or less.

Ti; [effective Ti amount] according to the following formula (11) is 4XC% or more and this [effective Ti amount] is 0.15% or less.

Nb: 0.05% or more, and in relation to [effective Ti amount], a range that satisfies [effective Ti amount] + NbS 2.20%.

Remainder: Fe and unavoidable impurities.

[Effective Ti amount] - Total Ti amount - [N%X (48/14)
+S%×(48/32) +O%X (48/12)
X%] ...(1) provides a non-aging cold rolled steel sheet for deep drawing, and.

In weight%.

C: 0.001-0.01%.

Si: 0.1% or less.

Mn: 0.5% or less.

Sol, AI! ;0.01-0.10%.

Cr: 0.06-0.20%.

P: 0.03% or less.

S: 0.015% or less.

N: 0.007% or less.

0; 0.01% or less.

Ti; [effective Ti amount] according to the following formula (1) is 4XC% or more and this [effective Ti amount] is 0.15% or less.

Nb is 0.05% or more, and in relation to [effective Ti amount], the range satisfies [effective Ti amount] + NbS 2.20%.

Remainder: Fe and unavoidable impurities.

[Effective Ti amount] = Total Ti amount - [N%X (48/14)
+S%×(48/32) +O%X (4B/12・
) × z〕 After hot rolling a steel slab consisting of
Provided is a method for producing a non-aging cold rolled steel sheet for deep drawing, which comprises cold rolling at a rolling reduction of 40% or more, followed by annealing at a temperature of not less than the recrystallization temperature and not more than 900°C.

The excellent properties of the steel of the present invention will be specifically shown in Examples below, but the reasons for limiting the chemical composition values will be explained as follows.

The lower the content of C, the better it is in terms of increasing the ductility of the cold-rolled steel sheet, and if the amount exceeds 0.01%, a large amount of carbonitride-forming elements is required and the amount of carbonitride precipitation decreases. This increase causes deterioration of press formability. On the other hand, practical scale 1i! ! It is difficult to reduce the C content to less than 0.001% in a steel furnace. For these reasons, the C content is 0.001 to 0.0
1%.

St is added mainly to deoxidize molten steel, and Mn is added mainly to prevent hot embrittlement, but if too large amounts of both Si and Mn are added, they reduce ductility. In this case, the amount of Si contained in ordinary cold-rolled steel sheet is ≦0.1%.
, MnS up to 2.5% is allowed.

If the amount is in the range of

Al is added for the purpose of deoxidizing molten steel, but if the amount is less than 0.01% of Sol, 8L (acid soluble) in steel, this purpose is fully achieved. Not. Also Sol
, A 7! When Sol, Aj! exceeds 0.10%, its effect is saturated and it even increases the number of metal inclusions, causing surface defects. 0.0 as the amount of
1 to 0.10%.

When Cr is used alone, it is not possible to obtain the favorable results aimed at by the present invention, but when added in combination with Ti and Nb, it exhibits the effect of improving deep drawability and overhang. Only 1. If the Cr content is less than 0.06%, this effect 1 is not present, and if the Cr content exceeds 0.20%, this effect is saturated and the manufacturing cost only increases.

Therefore, Cr is contained in the range of 0.06 to 0.20%, and this Cr plays an important role in the steel of the present invention.

If too much P is added, it will increase the yield strength and tensile strength, and in ultra-low C steel, it will segregate to one grain boundary and cause secondary work cracking, so the content should be adjusted accordingly. The upper limit is set to 0.03%.

The smaller the amount of N, the more desirable it is because the amount of Ti added can be reduced, and if the amount of N is too large, [effective Ti
amount] and deteriorate the press formability of the final product, the allowable limit is set to N≦0.007%.

Both S and 0 decrease [effective Ti amount].

If these amounts increase, the total Ti amount to ensure [effective Ti amount] will increase, and the surface quality will deteriorate.
5%, 0≦0.01%.

Ti secures the non-aging properties of the cold-rolled steel sheet by fixing C and N, and also provides the effect of making the generated Ti a recrystallized texture with a C111) orientation, which is effective for improving deep drawability. For this purpose, the [effective Ti amount] expressed by the fl1 formula described above must be 4×C% or more. However, when the Ti amount exceeds 0.15%, the amount of Ti dissolved in the ferrite increases, resulting in an increase in yield strength and a decrease in ductility. This also increases manufacturing costs. Therefore, + Ti is [effective Ti
amount] is 4×C% or more and 0.15% or less. In addition, in the steel of the present invention, the in-plane anisotropy of the r value is improved even with a small amount of Ti by adding Nb in addition to Ti.
There is an upper limit of effective Ti1l), [effective Ti amount]+N
The total amount of b is up to 0.20% as described below.

By adding Nb in combination with Ti, even if the C content and Ti content are reduced as in the present invention, the in-plane anisotropy of the r value can be significantly improved. Such an effect is achieved when Nbi is added in an amount of (0.2% - [effective Ti amount]) or less, and adding more than this amount causes an increase in recrystallization temperature and a decrease in ductility. Therefore,
[Effective Ti amount] +Nb≦0.2% or less. but,
If the amount of Nb is less than 0.05%, the effect of improving the in-plane anisotropy of the r value cannot be obtained.

In this way, one aspect of the present invention is to reduce the amount of C and Ti to a predetermined value or less in TiNbCr-added steel.
By adding Nb in a predetermined amount or more and in an amount related to the [effective Ti amount], it is possible to ensure non-aging properties without reducing ductility, and to have a high r value with little in-plane anisotropy. This cold rolled steel sheet is intended to be a non-aging cold rolled steel sheet for deep drawing, and it is preferable to manufacture this cold rolled steel sheet under the following conditions.

First, it is desirable to melt steel in a steel-making furnace and perform vacuum degassing treatment before ingot-forming or continuous casting. As a result, it is possible to advantageously reduce the C2O content in the steel as described above and adjust it to the composition range as described above with a high yield. When performing this vacuum degassing treatment,
Eight for deoxidation treatment! can also be added. C2o
and after adjusting the composition to the above-mentioned range by adding ferroalloy, manufacture a slab by ingot-forming, bi-blowing, rolling or continuous casting, and after performing slab maintenance as necessary,
Perform hot rolling.

When carrying out this hot rolling, it is desirable to set the hot rolling finishing temperature to Ar3 or higher from the viewpoint of improving deep drawability.

Further, the hot rolling coiling temperature is preferably in the range of 650 to 750°C. Next, after pickling, cold rolling is performed, and in this cold rolling, the cold rolling ratio should be 40% or more in order to develop a (111) orientation texture that is advantageous for deep drawability. good.

Next, annealing is performed, and this annealing may be either punch type annealing or continuous annealing, and excellent press formability can be obtained by performing the annealing at a temperature range from the recrystallization temperature to 900°C. More specifically, in batch annealing, the annealing temperature is 700°C or higher and 850°C or lower.

Further, in continuous annealing, the annealing temperature may be 750°C or more and 900°C or less.

In this way, according to the present invention, it is possible to maintain a high r value while at the same time having a high rmin and low in-plane anisotropy. Provided is an economical non-aging cold rolled steel sheet for deep drawing that can withstand more severe press forming than Cr steel.

〔Example〕

Example 1 30 kg of each steel having the chemical composition shown in Table 1 was melted in a vacuum melting furnace, hot-forged at a heating temperature of 1250°C, and then finished at a finishing temperature of 880-940°C and a coiling temperature of 700-720°C.
It was hot-rolled at °C to obtain a hot-rolled plate with a thickness of 5 mm. After pickling, the sheets were cold rolled to a thickness of 1.2 n++a, and each cold rolled sheet was subjected to hatch annealing at 800° C. for 4 hours. Table 2 shows the mechanical property values of the obtained cold rolled product.

As shown in Tables 1 to 2, 1lhl to N117
All steels have high total elongation of 52.5% or more.

And not only is the Y value as high as 1.87-2.20.

The in-plane anisotropy (Δr) of r value is significantly improved,
rmin (45° is 1.70 or more. Therefore, it can be seen that the steel of the present invention is a non-aging cold-rolled steel sheet having high ductility and ultra-deep drawability.

On the other hand, comparative steels 1IIIL8 to 12 (Nb is less than 0005% as defined in the present invention) have a high total elongation of 5462% or more, but Δr of 0.98 to 1.
29 (and rmin, r45°, is a low value of 1.52 or less, and there is a problem in deep drawability.

Also, for the steel with circle 13, which has a lot of Tii, y is 1.94.

Since rmin is high at 1.86 and Δr is small at 0.32, the deep drawability is sufficient, but the total elongation is 50.8, which is lower than the steel of the present invention.

Then, Cr-free Kan 14, and No. with a high amount of C,
All steels No. 15 have low total elongation like No. 13.

Example 2 The composition of the steel was adjusted using a 180T converter and degassing equipment to have the chemical composition values shown in Table 3, and each molten steel was continuously cast to form a slab, and from this slab, the heating temperature was 1250 to 1280°C. A hot-rolled coil with a plate thickness of 5.0 mm is prepared at a finishing temperature of 900 to 930°C and a winding temperature of 700 to 730°C. After pickling, the coil is cold-rolled to a plate thickness of 1° and 2 mm, and this coil is heated to 800°C for 4 A cold-rolled steel sheet was manufactured on an actual line by performing batch annealing with holding for a certain period of time. Table 4 shows the mechanical property values of the obtained cold rolled steel sheets.

As seen in the results in Table 4, the total elongation of A of the steel according to the present invention is as high as 53.6%, Y is also 2.14%, and rm
in (TLso) is as large as 1.85, and Δ
Since r is as small as 0.58, it can be seen that this is a cold-rolled steel sheet with high ductility and ultra-deep drawability.

N[LB steel with Nbi less than the range specified in the present invention has a high total elongation of 54.0%, but rmin is 1.
40, which is too low, and Δr is also high, 0.96. Therefore, there is a problem with deep drawability.

In N[LC steel with Ti and Cr added and no Nb added, Y is 2.1B, rmin is relatively large at 1.96, and Δr is small at 0.44, so deep drawability is good. However, since there are many 1TiiE ([effective Ti
2), the total elongation is 50
．． 2, which is lower than that of the steel of the present invention.

Example 3 A cold rolled steel sheet was produced on an actual line in the same manner as in Example 2, except that the cold rolled coil was annealed continuously at 850'c x 1 minute soaking time. Table 5 shows the mechanical property values of the obtained cold rolled steel sheets.

As seen in the results in Table 5, the total elongation of the invention steel 9A is as high as 52.8%, Y is 1.86, and r
min (r45”) is relatively large at 1.60.

It can be seen that the cold-rolled steel sheet has high ductility and ultra-deep drawability even after continuous annealing.

The kB steel with a lower Nb content than the range specified in the present invention has a high total elongation of 53.9%, but has a very low Y of 1.19 and a large Δr of 0.85, resulting in poor deep drawability. There's a problem.

In steel with Ti and Cr added, NbfFl, and magnetic carbon added, the total elongation is as low as 49.1, and there is a problem in ductility.

[
The steel of the present invention with appropriate composite addition in the range of effective Ti content) + NbS of 2.0% significantly improves the in-plane anisotropy of r value while maintaining high ductility, especially due to the reduction in C and Ti content. It can be seen that the steel sheet has succeeded in increasing r min and is therefore a non-aging cold-rolled steel sheet with high ductility and ultra-deep drawability.

Claims (2)

[Claims] (1), in weight%, C: 0.001 to 0.01%, Si: 0.1% or less, Mn: 0.5% or less, Sol. Al; 0.01 to 0.10%, Cr; 0.06 to 0.20%, P; 0.03% or less, S; 0.015% or less, N; 0.007% or less, O; 0. 01% or less, Ti: [effective Ti amount] according to the following formula (1) is 4 × C% or more and this [effective Ti amount] is 0.15% or less, Nb: 0
．． 05% or more and in relation to the [effective Ti amount], [effective T
i amount] + range satisfying Nb≦0.20%, remainder: Fe and unavoidable impurities, [effective Ti amount] = total Ti amount - [N% x (48/14) +
S% x (48/32) + O% x (48/12) x 1/2
]...A non-aging cold rolled steel sheet for deep drawing consisting of (1). (2) In weight%, C: 0.001 to 0.01%, Si: 0.1% or less, Mn: 0.5% or less, Sol. Al: 0.01-0.10%, Cr: 0.06-0020%, P: 0.03% or less, S: 0.015% or less, N: 0.007% or less, O: 0.01% Hereinafter, Ti: [effective Ti amount] according to the following formula (1) is 4 × C% or more and this [effective Ti amount] is 0.15% or less, Nb: 0
．． 05% or more and in relation to the [effective Ti amount], [effective T
i amount]+Nb≦0.20%, balance; Fe
and unavoidable impurities, [effective Ti amount] = total Ti amount - [N% x (48/14) +
S% x (48/32) + O% x (48/12) x 1/2
]...After hot rolling the steel slab made of (1),
A method for producing a non-aging cold-rolled steel sheet for deep drawing, which comprises cold rolling at a rolling reduction of 40% or more, and then annealing at a temperature of not less than the recrystallization temperature and not more than 900°C.