JPS61199054A - Non-ageing galvanized sheet for deep drawing and its production - Google Patents

Abstract

PURPOSE:To obtain non-ageing galvanized sheet having high ductility and super deep drawability by limiting the additive quantities of Cr, Ti and Nb and also specifying cold rolling and annealing conditions. CONSTITUTION:A composition consists of, 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, and the balance Fe with inevitable impurities, and further contains Ti so that (available Ti quantity) represented by an equation is 4XC%-0.15% and also contains Nb so that Nb quantity is <=0.05% and simultaneously satisfies (available Ti quantity)+Nb<=0.20%. A steel slab with the above composition is hot-rolled and then cold-rolled at >=40% draft, and the obtained steel strip is passed through an inline annealing type continuous zinc hot dipping apparatus, where the steel strip is subjected to continuous annealing at the temp. between the recrystallization temp. and 900 deg.C and then to zinc hot dipping treatment.

Description

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

[Prior Art] For example, automobile quarter panels, fenders, oil pans, etc. must be formed by extremely severe press working. Attempts have been made to apply galvanized steel sheets to such molded products. This requires high ductility and ultra-deep drawability, as well as non-aging properties. In order to meet these demands, it is necessary to improve the material properties of the steel sheet itself, which is the base material of galvanized steel sheets. Charcoal annealed cold rolled steel sheet or.

By adding carbonitride-forming elements such as Ti, Nb, and Cr singly or in combination, C and N in the steel are fixed, increasing ductility and ensuring non-aging properties.
(b) is effective in improving deep drawability due to the action of carbonitride (
Non-aging cold-rolled steel sheets for deep drawing that have developed a recrystallized texture in the 111) orientation are known.

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.; Nb
Additive steels are disclosed, such as in Japanese Patent Publication No. 50-30572 and Japanese Patent Application Laid-open No. 58-185752.
Additive steel is disclosed, and JP-A-59-67319 discloses TiNb-added steel, and JP-A-59-1 discloses TiNb-added steel.
No. 23720 discloses TiNbCr added steel.

On the other hand, it is a galvanized steel that uses carbonitride-forming element added steel as a base material and galvanizes it.

Japanese Patent Publication No. 46-20563 discloses a galvanized steel sheet using Ti-added steel as a base material, and Japanese Patent Publication No. 55-7382
No. 5 and Japanese Unexamined Patent Publication No. 55-7382f+ disclose galvanized steel sheets using Ti-Cr added steel as a base material.

And, Special Publication No. 58-737, Special Publication No. 58-22
No. 48 and Japanese Unexamined Patent Publication No. 59-74231 disclose galvanized steel sheets using Ti--Nb added steel as a base material.

[Problem that the invention seeks to solve]

Even if an attempt is made to satisfy the above-mentioned requirements, decarburized annealed steel has a problem in that the grain size tends to increase and roughness such as orange peel tends to occur during press forming. T
, i-added steel and Ti Cr1l, Ti is O,
Because it has a strong bond with S and forms oxides and sulfides,
In order to ensure non-aging properties by fixing C and N, Ti should be added in an amount more than several times the stoichiometric equivalent to C and N.
, it is necessary to add the amount. 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-(1"o" +
r9G"-2r45°)/2] becomes larger,
The Y"min r4s° decreases, leaving problems with press workability. In Nb-added steel, with the recent progress in steel degassing technology, C can be relatively easily reduced to a range of C < 50 ppm. Since it has become possible to reduce the amount of C and N
A method for manufacturing Nb-added steel with a very small amount of b has been proposed, but unless Nb-added steel is coiled at a high temperature of 700°C or higher after hot rolling, the recrystallization temperature is high at normal coiling temperatures. Therefore, during annealing, particularly in the case of continuous annealing, it is necessary to make the annealing temperature higher than that of Ti-added steel. Also,
Even after high-temperature winding, both longitudinal ends of the hot-rolled coil remain intact.

There is a problem that a uniform material cannot be obtained because the cooling rate is faster than that in the central part.

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.
As stated in Japanese Patent Application Laid-open No. 59-123720, this manufacturing method adopts a high cold rolling rate of 70 to 80%, although this may be because the Nb content is too low. Even if
Since r4s°, which is rmin, becomes too small, there is still a problem in press formability.

In addition, by setting the cold rolling rate to 80% or more, rmin
It is possible to improve the in-plane anisotropy of the r value by increasing the r value, but for cold-rolled steel products with a large thickness, the thickness of the hot-rolled sheet should be thicker than the routine thickness. This necessitates a problem in actual operation and also a problem in the capacity of the cold rolling mill.

Such problems also occur in the case of galvanized steel sheets using such steel sheets as the base material.

[Means for solving problems]

The present invention is a galvanized steel sheet that solves the above-mentioned problems.

In weight%.

C: 0.001-0.01%.

Si: 0.1% or less.

Mn: 0.5% or less.

Sol, 8/i 0.01-0.10%.

Cr; 0.06-0o20%.

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%×(4B/32) +O%X (48/12)
X %) ...(11) is used as a base material, and the surface of this base material is galvanized to provide a non-aging galvanized steel sheet for deep drawing.

In weight%.

Ci　O,OOL~0.01%.

5iH0.1% or less1 Mn: 0.5% or less.

Sol, Al; 0.01-0.10%.

Cr; 0.06-0.20%.

Pio, 03% or less.

s: 0.015% or less.

N: 0.007% or less.

0, 0.0.1% or less.

TX; [effective Ti amount] according to the following formula (1) is 4XC% or more and this [effective Ti amount] is 0.15% or less 1Nb i
A range that satisfies [effective Ti amount] + NbS2.20% in relation to [effective Ti amount].

Remainder: Fe and unavoidable impurities.

[Effective Ti amount] = Total Ti amount - [N%X (4B/14
) + S%x (48/32) +Q%x (48/
12) X %) ... After hot rolling the steel slab consisting of (1), cold rolling at a reduction rate of 40% or more,
The obtained steel strip is passed through an in-line annealing type continuous hot-dip galvanizing device, and in this device, the temperature is 9
The present invention provides a method for producing a non-aging hot-dip galvanized steel sheet for deep drawing, which comprises continuous annealing at a temperature of 00° C. or lower and then hot-dip galvanizing.

The present invention uses Ti as a base material for galvanized steel sheets.
Although Nb Cr added steel is used.

At this time, the ductility is increased by reducing the amount of C and Ti to below a predetermined value, and the γ value is increased by adding Nb in a combination of a predetermined amount or more and an amount related to the [effective Ti amount]. Significantly improves in-plane anisotropy (Δγ),
rmin which is r4. The basic feature is that the temperature is increased, and by this, a non-aging galvanized steel sheet for deep drawing, which solves the above-mentioned problems, has been obtained.

The excellent properties of the galvanized steel sheet according to the present invention will be specifically shown in the examples below, but the reasons for limiting the chemical composition values of the base material S4 will be summarized as follows.

The lower the C content, the better in terms of improving the ductility of the steel sheet, and if the amount exceeds 0.01%, a large amount of carbonitride-forming elements are required and the amount of carbonitride precipitation increases. Press formability deteriorates. On the other hand, in a practical-scale steelmaking furnace, the C content is reduced to 0.
It is difficult to reduce it to less than 0.001%. For these reasons, the C content is set to 0.001 to 0.01%.

Mn is added for the purpose of preventing hot embrittlement of steel, but if added in too large a quantity, the ductility and deep drawability are reduced, so the content is limited to 0.5% or less.

Si is added for the purpose of deoxidizing molten steel, but adding too much will not only reduce ductility but also cause non-plating during hot-dip galvanizing, so the amount added should be 0.
．． 1% or less.

1M is added for the purpose of deoxidizing /8 steel, but the amount is 0.01 in terms of Sol and A 12 (acid soluble l) in the steel.
If the amount is less than %, the purpose cannot be fully achieved. Sol, J/ again! If the amount exceeds 0.10%, the effect will be saturated and it will even increase non-metallic inclusions, causing surface defects.
! The amount is set to 0.01 to 0.10%.

If Cr is used alone, it will not be possible to obtain the desired results aimed at by the present invention, but when it is added together with Ti and Nb, it exhibits the effect of improving deep drawability and stretchability. However, the Cr content is 0.0
If it is less than 6%, there is no such effect, and if it is less than 0.20
%, this effect not only becomes saturated but also increases manufacturing costs.

Therefore, Cr is contained in a range of 0.06 to 0.20%, and this Cr plays an important role in 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 the grain boundaries and cause secondary work cracking, so the upper limit of its content should be set to 0. .03%.

The smaller the amount of N, the smaller the amount of Ti added. However, if it is too large, it reduces the [effective amount of Ti] and deteriorates the press formability of the final product, so the allowable limit is N≦0.007%. shall be.

Both S and O decrease [effective Ti amount].

If these amounts increase, the total Ti amount to ensure [effective Ti amount] increases, and the surface quality deteriorates, so the allowable limits for S and O are set to S ≦ 0.0, respectively.
15%, O50.01%.

Ti secures non-aging property by fixing C and N, and the generated TiC serves to consolidate the recrystallization aggregation of the C111) orientation, which is effective for improving deep drawability. For this purpose, the equation (1) described above is used.
Effective Ti amount] is required to be 4×c% or more. but,
When it exceeds 0.15%, the amount of Ti dissolved in solid solution in ferrite increases, resulting in an increase in yield strength and a decrease in ductility. This also increases manufacturing costs. Therefore, as for Ti, [effective Ti amount] should be 4XC% or more and 0.15% or less. In addition, in the nine invention steels,
By adding Nb in addition to Ti, the in-plane anisotropy of the r value can be improved even with a small amount of Ti added, and there is an upper limit for the [effective Ti amount] in relation to Nb. The total amount of Ti content) + Nb is up to 0.20% as described later.

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 produced when the amount of Nb is (0.2% - [effective Ti1t
) ) is achieved with the following amounts; adding more Nbi leads to an increase in recrystallization temperature and a decrease in ductility.

Therefore, [effective Ti amount]+Nb≦0.2% or less. However, if the amount of Nb is less than O, OS%, 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. A non-aging cold-rolled steel sheet for deep drawing is then galvanized. It is preferable to manufacture this galvanized 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. This makes it possible to advantageously lower C1o in H4 as described above and adjust it to the aforementioned component range with a high yield. When performing this vacuum degassing treatment, AA can also be added for deoxidation treatment. c,
After adjusting o and adjusting the composition to the above-mentioned range by adding ferroalloy, a slab is manufactured by ingot-forming, 9-blanking rolling or continuous casting, and after performing slab maintenance as necessary, hot rolling is carried out. conduct.

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, the obtained steel strip is passed through an in-line annealing type continuous hot-dip galvanizing machine, and in this machine, it is continuously annealed at a temperature above the recrystallization temperature (preferably above 750 °C) and below 900 °C. By performing the hot-dip galvanizing treatment, a hot-dip galvanized steel sheet that achieves the above-mentioned objectives can be obtained.

〔Example〕

Example ■ 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 ℃ to obtain a hot-rolled plate having a thickness of 3.2 Ilm.

After pickling, the sheets were cold rolled to a thickness of 0.81, and each cold rolled sheet was continuously annealed at 900°C for 1 minute at approximately 10°C/s.
450 air-cooled with EC and added with 0.15% Aj2
A hot-dip galvanizing process was performed by immersing the sample in a zinc bath at ±5° C. for about 3 seconds. The mechanical property values of the obtained galvanized steel sheet are shown in Table 2.

As shown in Tables 1 and 2, the steels 11hl to -7 all had a high total elongation of 47.0% or more.

And not only does it have a high r value of 1.71-1.95.

By adding 0.05% or more of Nb, the in-plane anisotropy of r value (Δr) was significantly improved, and rmin, r4. ° is 1.60 or more. therefore.

It can be seen that the galvanized steel sheet of the present invention is a non-aging galvanized steel sheet with high ductility and ultra-deep drawability.

On the other hand, comparative steel fish 8 to 12 (Nb is less than 0.05% as specified in the present invention) have a total elongation of 48
．． Although it is high at 0% or more, Δr is thick at 0.78 to 1.08 (and rna° which is Yn+in is a low value at 1.36 or less, and there is a problem in deep drawability.

In addition, Arashi 13 steel with a high Ti content ([effective Ti content] exceeds 0.15%) has Y of 1.73 and r
Since min is high at 1.70 and Δr is small at 0.06, the deep drawability is sufficient, but the total elongation is 45.2, which is lower than the steel of the present invention.

And Cr-free case 14 and 0.013%
The steels of Fish 15, which have a large amount of C, all have low total elongation, similar to N113.

Example 2 The composition of 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 1.
250~1280℃, finishing temperature 900~930℃, one coiling temperature 700~730℃, one plate thickness 3.2mm0 hot rolled coil, after pickling, cold rolling to plate thickness 0.8mm,
This coil was passed through an in-line annealing-type continuous hot-dip galvanizing device, and continuous annealing and hot-dip galvanizing were performed at 900° C. for 1 minute to produce hot-dip galvanized steel sheets on an actual line. The conditions for the hot-dip galvanizing treatment were the same as in Example 1.

Table 4 shows the mechanical property values of the obtained hot-dip galvanized steel sheets.

As seen in the results in Table 4, the total elongation of the steel according to the present invention is as high as 48.1%, and r is also 1.90.
flin(r45°) is as large as 1.70, and Δ
Since r is as small as 0.40, it can be seen that this is a galvanized steel sheet with high ductility and ultra-deep drawability.

The l1hB steel, in which the amount of Nb is less than the range specified in the present invention, has a high total elongation of 4866%, but has an rmin of 1.2.
5, which is too low, and Δr is also high, 0.76. Therefore, there is a problem with deep drawability.

For N11C steel with Ti and Cr added and no Nb added, 7ha 1.94. rmin (r4s”
) Ha1.817! : Relatively high and Δr is also 0.26
Although it can be said that the deep drawability is good because of the small amount of Ti, the total elongation is 45.5, which is lower than the steel of the present invention because of the large amount of Ti.

[
The galvanized steel sheet of the present invention, which is made by galvanizing a base material of a steel sheet with appropriate composite addition in the range of + Nb≦2.0%, has a particularly high It has succeeded in significantly improving the in-plane anisotropy of r value and increasing ra+in while maintaining ductility, and is therefore a non-aging galvanized 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 galvanized steel sheet for deep drawing, which uses a cold-rolled steel sheet consisting of (1) as a base material, and has the surface of this base material galvanized. (2) 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, 0; 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]+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),
The steel strip obtained by cold rolling at a reduction ratio of 40% or more is passed through an in-line annealing type continuous hot-dip galvanizing device, and in this device, it is continuously annealed at a temperature above the recrystallization temperature and below 900°C. A method for manufacturing a non-aging hot-dip galvanized steel sheet for deep drawing, which comprises applying hot-dip galvanizing treatment to the steel sheet.