JPH0261033A - Cold rolled steel sheet for deep drawing - Google Patents

Abstract

PURPOSE:To obtain a cold rolled steel sheet for deep drawing excellent in formability as well as in corrosion resistance by specifying a composition consisting of C, Si, Mn, P, S, N, Al, Nb, Ti, Cr, and Fe and also a compositional relationship in the above composition, respectively. CONSTITUTION:The title steel sheet is a cold rolled steel sheet for deep drawing having a composition which consists of, by weight, <=0.01% C, <=0.5% Si, <=0.5% Mn, <=0.05% P, <=0.02% S, <=0.01% N, 0.02-0.2% Al, 0.001-0.05% Nb, 0.01-0.10% Ti, 3-10% Cr, and the balance Fe with inevitable impurities and further contains, if necessary, 0.0001-0.002% B and in which relations in (C/12+N/14+S/32)<(Ti/48+Nb/93) are satisfied and also having superior corrosion resistance. In the above steel sheet, formability and corrosion resistance are improved by adding Ti and Nb together with Cr as mentioned above. Moreover, by further adding the prescribed amount of B, resistance to secondary working brittleness can be improved and high-degree press working is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a deep-drawing cold-rolled steel sheet with excellent corrosion resistance, which is used for can manufacturing, automobile steel sheets, and the like.

[Conventional technology]

In the field of thin steel sheets used for automobile steel sheets, etc.
In order to improve its corrosion resistance, there is an increasing demand for surface-treated steel sheets that have been subjected to various surface treatments.

Examples of the surface-treated steel sheets include hot-dip galvanized steel sheets and electrogalvanized steel sheets, each of which has excellent corrosion resistance.

By the way, since these surface-treated steel sheets are also used as members for deep drawing, they are inevitably subjected to strength processing. Therefore, peeling and damage to the surface coating during processing may occur.
There is a disadvantage that the base metal is easily exposed and the base metal rusts. In addition, powder exfoliated during press molding causes surface defects called stars, which often pose a problem.

Furthermore, the end faces formed by shearing and punching after press forming have a disadvantage in that they easily rust because there is no surface coating. In order to prevent such rust from forming on the end faces, the current situation is to newly perform surface treatment on the end faces, and the labor and cost required for this process are enormous.

Therefore, several corrosion-resistant steel sheets that have excellent formability even without surface treatment have been disclosed. for example,
In Japanese Patent Application Laid-Open No. 61-IL7249, C: 0
．． 0048% by weight, S i :0.01% by weight M
n: 0.32% by weight, P: 0.019% by weight
, S: 0.012% by weight, Cr: 9.50% by weight, A
A: 0.029 heavy view l. Ti: 0.07
After hot rolling and cold rolling, a steel with a composition of 2% by weight, N: 0.0069%L6 was annealed at a temperature of 750°C in a reducing atmosphere of 75% H2 + 25% NZ (dew point -50°C).
By holding at for 60 seconds and cooling in the furnace to room temperature,
r value (Lankford value) and elongation rate (EA) are r
=1.78. A cold-rolled steel sheet with E 6 =36.8% and excellent corrosion resistance is disclosed.

[Problem to be solved by the invention]

In the conventional corrosion-resistant steel sheet described in JP-A-61-117249 mentioned above, a large amount of Ti is added in order to improve press formability and ensure corrosion resistance. However, when a large amount of Ti is added to -C, a problem arises in that the surface properties of the steel sheet deteriorate. Furthermore, although Ti-added steel has a high level of r value, its anisotropy (Δr
) is large, and the moldability is not necessarily sufficient.

Furthermore, with regard to cold rolled steel sheets for deep drawing which are subjected to intense press working, it is an important issue how to prevent secondary work brittleness.

In order to solve the conventional problems, the first object of the present invention is to provide a cold-rolled steel sheet for deep drawing that has both excellent corrosion resistance and formability, and further has the following object: A second object of the present invention is to provide a cold-rolled steel sheet for deep drawing that has excellent resistance to secondary work brittleness.

[Means to solve the problem]

The present inventors conducted various studies on cold-rolled steel sheets with excellent corrosion resistance and deep drawability, and found that they added Cr to improve corrosion resistance to low carbon steel with excellent deep drawability, and added Cr to improve corrosion resistance and deep drawability. By adding Ti and Nb, which improve the properties of the steel, a cold-rolled steel sheet that does not corrode in various corrosive environments and has excellent deep drawability has been obtained.

Furthermore, B is added to this cold rolled steel sheet to improve secondary work brittleness resistance.
By adding this, we were able to obtain a cold-rolled steel sheet that can be press-formed with higher strength.

That is, the invention according to claim (1) which achieves the above first object has c: o, ot weight % or less, Si: 0.5 weight % or less, Mn: 0.5 weight % or less, p: o , o5% by weight
Below, S: 0.02% by weight or less, N: 0.01% by weight or less, A#: 0.02 to 0.2% by weight, Nb: 0
．． 001 to 0.05% by weight, T i : 0.01 to
0.10% by weight, Cr: 3 to 10% by weight, and (C/12+N/14+S/32)<(Ti/4B+
It is a cold-rolled steel sheet for deep drawing that has excellent corrosion resistance and deep drawability.

Further, the present invention according to claim (2) which achieves the second object is characterized in that C: 0.01% by weight or less, Si: 0.5% by weight or less.
Below, Mn: 0.5% by weight or less, P: 0.05% by weight or less, S: 0.02% by weight or less, N: 0.001% by weight or less, A, 1: 0.02-0.2 Weight%, N
b: 0.001 to 0.05%, Ti: 0
．． 01~0.10 heavy view, B:0.0001~0.00
2% by weight, Cr: 3-10% by weight, and (C
/12+N/14+S/32)<(Ti/48+Nb/
93), and the remainder consists of iron and unavoidable impurities, making it a cold-rolled steel sheet for deep drawing that has excellent not only corrosion resistance and deep drawability, but also resistance to secondary work brittleness. .

[Effect]

Next, the effects of the various components of the steel sheet according to the present invention and the reason why the amounts of these various components added are limited to the above ranges will be explained.

(a) C: 0.01% by weight or less The less C there is, the better the deep drawability is, so it is preferable. Furthermore, C forms carbides with Cr, but if Cl is small, Cr carbides are difficult to form, and as a result,
The content is limited to 0.01% by weight or less because it effectively works on corrosion resistance (as the amount of Cr increases and the corrosion resistance also improves.If the content is 0.01% by weight or less, it does not have a very negative effect on deep drawability and corrosion resistance. The content was limited to 0.01% by weight or less.

(b) Si: 0.5% by weight or less Si has the effect of reinforcing the steel and is added in the necessary amount depending on the desired strength, but if the amount added exceeds 0.5% by weight, the deep drawability will deteriorate. Since it has an adverse effect on

(c) Mn: 0.5% by weight or less Mn has the effect of strengthening steel, and is added in the necessary amount depending on the desired strength, but if the amount added exceeds 0.5% by weight, deep drawability will deteriorate. Since it has an adverse effect, it is limited to 0.5% by weight or less.

(dlP: less than 0.05% by weight) has the effect of strengthening the steel, and is added in the necessary amount depending on the desired strength, but if the amount added exceeds 0.05% by weight, the deep drawability and corrosion resistance Since it has an adverse effect on

(e) S: 0.02% by weight or less The smaller the amount of S, the better for improving deep drawability and corrosion resistance, but if its content is 0.02% by weight or less, it does not have a significant negative effect on deep drawability and corrosion resistance. Therefore, the content was limited to 0.02% by weight or less.

ff) N: 0.01% by weight or less The smaller the N content, the better the deep drawability is, so it is preferable, but if the content is 0.01% by weight or less, it does not have a significant negative effect on the deep drawability and corrosion resistance. Therefore, the content was limited to 0.01% by weight or less.

fgl A # 70.02 to 0.2% by weight AN is added as necessary for deoxidizing, but if the amount added is less than 0.02% by weight, there is no effect of addition;
Even if it is added in an amount exceeding 2% by weight, the deoxidizing effect will not be increased, so it is limited to 0.02 to 0.2% by weight.

(h) Cr: 3 to 10% by weight Cr needs to be added to improve corrosion resistance,
In order to ensure excellent corrosion resistance in various corrosive environments, it is necessary to add 3% by weight or more.

On the other hand, in order to ensure excellent deep drawability, the amount of Cr added must be 10% by weight or less. Therefore, 3 to 10% by weight is required to satisfy both the characteristics of corrosion resistance and deep drawability.
limited to.

FIG. 1 shows the relationship between the r value and corrosion resistance of the cold rolled steel sheet according to the present invention after annealing and the amount of Cr added.

The r value and corrosion resistance depend on the amount of Cr added, and as shown in Figure 1, when the Cr content is less than 3.0% by weight,
Corrosion loss is large, corrosion resistance is deteriorated, and Cr content is 10.0
It can be seen that when the weight percentage is exceeded, the average value of the r value decreases and the deep drawability deteriorates.

(1) Nb: 0.001 to 0.05% by weight Nb is a carbide-forming element that reduces solid solution C in steel and preferentially forms the (111) orientation, which is advantageous for deep drawability. Prevents the formation of Cr carbides and has an advantageous effect on corrosion resistance (C
It is added to improve the corrosion resistance of cold-rolled steel sheets for deep drawing by increasing rl.

Furthermore, Nb is added to improve the anisotropy of r value (Δr). In other words, adding a small amount of Nb is effective in refining the grains of a hot-rolled sheet, and when a hot-rolled sheet with such fine grains is cold-rolled and annealed, the anisotropy of the r value is A small steel plate is obtained. If the amount added is less than o or ooi weight %, the desired effect cannot be obtained, while if it is added in excess of 0.05 weight %, further improvement of the effect cannot be obtained and the recrystallization temperature increases. Since it is only 0.001 to 0.
The amount was limited to 0.05% by weight.

(J) Ti: 0.010 to 0.10% by weight Ti
is a carbide-, sulfide-, and nitride-forming element that reduces solid solution (C, N,) in steel and is advantageous for deep drawability (111
) orientation, prevents the formation of Cr carbides, and has an advantageous effect on corrosion resistance (by increasing the amount of Cr, it is added to improve the corrosion resistance of cold-rolled steel sheets for deep drawing. If the amount added is 0.010% by weight, the desired effect cannot be obtained, while if it is added in an amount exceeding 0.10% by weight, no further improvement in the effect can be obtained, and on the contrary, the steel plate surface 0.010 to 0.0 because it leads to deterioration of properties.
It was limited to 10% by weight.

(k) B: 0.0001 to 0.002% by weight B is added in a very small amount to improve grain boundary strength and improve the secondary work brittleness resistance of cold rolled steel sheets for deep drawing. . If the amount added is less than 0.0001% by weight, the desired effect cannot be obtained, and on the other hand, even if it is added in excess of 0.002% by weight, further improvement in the effect cannot be obtained.
0.002 heavy view heavy view limited.

(11(C/12+N/14+S/32)<(Ti/4
8+Nb/93) As mentioned above, Ti and Nb are dissolved in solid solution (C) in steel.

N,) is added to reduce the By the way, Ti forms Tic, TiN, and TiS in steel, while Nb forms NbC. Therefore, solid solution in steel (C
, N,) is completely precipitated and fixed by Ti and Nb, it is necessary to form a solid solution (C) in the steel.

It is necessary that the number of Ti and Nb atoms present is greater than that of N,). Therefore, as above <(C/12+N/14+S
/32)<(Ti/48+Nb/93).

Figure 2 shows the lower value and corrosion resistance of the cold rolled steel sheet according to the present invention after annealing and (C/12+N/14+S/32)-(Ti/4
The relationship with 8+Nb/9'3)I is shown.

As shown in Figure 2, the lower value and corrosion resistance are as follows (C
/12+N/14+S/32) (Ti/4 a+N
b, /93) depending on the amount, (C/12+N/14+S/
32) (Ti/48+Nb/93)〈O, r
It can be seen that the average value is low and the deep drawability is poor. Furthermore, it can be seen that the corrosion loss is high and the corrosion resistance is also deteriorated.

In addition, in the cold-rolled steel sheet of the present invention, at least one of the group consisting of Cu, Ni, Sb, and In can be added as an additive element in an amount of o, oi to 0.51XM%, if necessary. If the amount of these additives is less than 0.01% by weight, the effect of improving rust resistance will not be sufficient, while if it is added in excess of 0.5% by weight, the deep drawability will be deteriorated, so 0.01~0.5 Weight percent is preferred.

The cold-rolled steel sheet according to the present invention is manufactured by a normal smelting-ingot or continuous casting-hot rolling-annealing process, and the desirable conditions for hot rolling, cold rolling, and annealing are as follows.

Hot Rolling Process The hot rolling process may be the same as a conventional method. That is, after the continuous casting or ingot-forming/disassembly rolling slab is roughly rolled, finish rolling is performed. Slab heating temperature is 1000-1250
1150°C or less is suitable for improving material quality and saving energy. The hot rolling finishing temperature is Ar, and a temperature higher than the transformation point is preferable for improving deep drawability.
If the transformation point is within the range of -100°C, the deterioration of deep drawability will be small. Winding temperature is 500-750'C
600°C or higher is suitable for improving deep drawability.

Cold rolling-annealing process The cold rolling process is necessary to ensure deep drawability, and the cold rolling reduction ratio needs to be 50 to 95% in order to obtain excellent deep drawability. Cold rolling reduction ratio is less than 50% or 95
%, it is not possible to obtain excellent deep drawability.

The cold rolled steel sheet is subsequently subjected to recrystallization annealing.

The annealing method may be either a continuous annealing method or a batch annealing method. A suitable annealing temperature is 700 to 900°C. Note that when a large amount of Cr is added to the steel of the present invention, a thin scale often called temper color may be formed on the surface of the steel plate during annealing. -30' dew point
It is preferable to make it C or less.

〔Example〕

Next, an example of a cold-rolled steel sheet for deep drawing with excellent corrosion resistance according to the present invention will be described.

Steels shown in Table 1 below were melted and made into steel ingots. After heating and soaking these steel ingots at 1250°C, rough rolling was performed to obtain a plate with a thickness of 30.
After forming a sheet bar of mm, it was heated again at 1250°C.
After soaking, finish rolling was performed to hot-roll a hot-rolled sheet with a thickness of 3.2 mm. Subsequently, this hot rolled sheet was pickled, cold rolled at a rolling reduction of 75%, and then recrystallized annealed at 800°C-403.

In Table 1, steel (1) is a cold-rolled steel sheet with excellent corrosion resistance and deep drawability as described in claim (1), and steel (21, (5
1°(6), (8) to αΦ are cold-rolled steel sheets having excellent corrosion resistance, deep drawability, and resistance to secondary work brittleness as described in claim (2), and among these, steel (3) is a Nb-based cold rolled steel sheet. Comparative example steel plate tliil (4) has a C content outside the range of the present invention, and the number of Ti and Nb atoms contained is C,N.

Less than S (X<O, X= (Ti/48+Nb/9
3) −(C/12+N/14+S/32)] Comparative Steel Plate Steel (7) is a comparative steel plate in which the Cr content is outside the range of the present invention.

The material properties, corrosion resistance, and secondary work brittleness resistance of the steel shown in Table 1 above were investigated. The results are shown in Table 2 below.

In Table 2, the tensile properties were measured using a JIS No. 5 tensile test piece. In addition, the r value was measured using a three-point method after applying 15% tensile prestrain.
45° direction in the rolling direction) and C direction (90° direction in the rolling direction)
° direction) and anisotropy as r−(rt+2r(,+rc)/4Δr
It was calculated as = (rL-2r,,+rc)/2.

In addition, as an evaluation of secondary work brittleness resistance, the critical drawing ratio was set to 3.
．． After cooling the cylindrical sample processed in step 8 to -50°C, a crush test was performed, and the presence or absence of brittle cracking was determined.
The subsequent processing brittleness was evaluated.

Furthermore, as a method for evaluating corrosion resistance, 0.5% NaCl.

The corrosion loss of the steel plate before and after the corrosion test was measured by carrying out a corrosion cycle in which the steel plate was immersed in a 0.5% CaC1z, 0.125% NatSz05 corrosive solution for 8 hours and then dried for 16 hours.

(Hereinafter, blank space) In the table, Note 2 indicates the evaluation result of secondary processing brittleness resistance, and ☆ indicates a comparative example.

It can be seen that the steel sheets manufactured within the scope of the present invention exhibit superior corrosion resistance and deep drawability compared to the comparative example steel sheets.

That is, it can be seen that steel (3) containing no Nb has a low r value and a large anisotropy (Δr). On the other hand, the steels within the range of the present invention have a high r value and a small anisotropy (Δr), which indicates that the deep drawability is improved.

On the other hand, it can be seen that steel (7) with a Cr content outside the range of the present invention has a large corrosion loss due to poor corrosion resistance and a low average r value.

In addition, in steel (4) in which the C content exceeds the range of the present invention, Cr carbides are formed and work effectively for corrosion resistance.
(X-(T i/4 B+Nb/93)(C/12+N
/14+S/32)] is negative. and steel (4
) has a low content of Ti and Nb in the steel, and it is not possible to reduce the solid solution (C, N,) in the steel, so the corrosion loss is large and the corrosion resistance is deteriorated. It can be seen that the average value is low and the deep drawability is also deteriorated.

And, compared to steel (1) to which B is not added, B
Example steels (21, (5), (6),
It can be seen that samples (8) to 00) have excellent resistance to secondary work brittleness.

Next, in order to investigate the effect of the amount of Cr added on the r value and corrosion resistance, C: 0.001 to 0.01 wt% Si
: 0.01-0.5% by weight, Mn: 0.1-0
．． 5% by weight, P: o, oos ~ 0.05% by weight
, S: 0.002-0.02% by weight, N:
0.001-0.01% by weight, AI! :0.02~0
．． 2% by weight, Nb: 0.001~0°05% by weight, Ti: o, oto ~ o, io weight%, Cr: 0
~12% by weight, and (C/12+N/14+3/32
) < (T i/48+Nb/93) was melted and made into a steel ingot. After heating and scorching these steel ingots at 1250°C, rough rolling was performed to form a sheet bar with a thickness of 30 mm, and after heating and scorching at 1250°C again, the plate thickness was 3.
It was hot rolled into a 2 mm hot rolled sheet. After pickling this hot-rolled plate, 75
After cold rolling at a rolling reduction of 100%, annealing was performed at 830°C-4O3.

The r value and corrosion resistance of this annealed sample were evaluated based on the method described in this example above.

This result is as shown in Fig. 1 mentioned above.
As shown in the figure, when the Cr content is less than 3.0% by weight, the corrosion resistance is deteriorated due to a large amount of corrosion loss, and when the Cr content is less than 10% by weight,
．． It can be seen that when it exceeds 0% by weight, the average value of the r value becomes small and the deep drawability deteriorates.

Next, in order to investigate the influence of the value of X on the r value and corrosion resistance, C: 0.002% by weight, Si: 0.01%
~0.5% by weight, Mn: 0.1-0.5% by weight
P: 0.008-0.05% by weight, S: 0
．． 002-0.02% by weight, N: 0.001-0
．． 01% by weight, /l: 0.02-0゜20% by weight,
Nb: 0.001-0.05% by weight, Cr: 45
Weight %, T i : 0.010 to 0.10 weight %
Steel with the following composition was melted and made into a steel ingot. After heating and scorching these steel ingots at 1250°C, rough rolling was performed, and the plate thickness was 30
After forming the sheet bar into a sheet bar with a thickness of 3.2 mm, the sheet bar was heated and scorched again at 1250'C, and then hot-rolled into a hot-rolled sheet with a thickness of 3.2 mm.

After pickling this hot-rolled sheet and cold-rolling it at a rolling reduction of 75%,
Annealing was performed at 30°C-405. Regarding this annealed plate, the r value and corrosion resistance were evaluated based on the method described in the above-mentioned example. The results are as shown in the above-mentioned FIG. 2. As shown in FIG. 2, it can be seen that when the value of X is negative, the average r value is small and the corrosion loss is large.

In addition, steel sheets within the composition range of the present invention listed in Table 1 above do not require surface coating even if the end faces are exposed due to shearing and punching after press forming, so product costs can be significantly reduced. Can be done.

〔Effect of the invention〕

As explained above, according to the present invention as set forth in claim 11, it is possible to provide a cold-rolled steel sheet for deep drawing that has corrosion resistance equal to or higher than that of a surface-treated steel sheet and also has excellent deep drawability. This effect is achieved.

According to the present invention as set forth in claim (2), in addition to the above-mentioned effects, it is possible to provide a cold-rolled steel sheet for deep drawing that has excellent resistance to secondary work brittleness.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the effect of the amount of Cr added on the r value and corrosion resistance of an annealed plate, and Figure 2 is a characteristic diagram showing the effect of (Ti/48+Nb/93)-(C) on the r value and corrosion resistance of an annealed plate. /1
2+N/14+S/32) is a characteristic diagram showing the influence of the amount.

Claims (2)

[Claims] (1) C: 0.01% by weight or less, Si: 0.5% by weight or less, Mn: 0.5% by weight or less, P: 0.05% by weight or less, S: 0.02% by weight or less, N: 0.01% by weight or less,
Al: 0.02-0.2% by weight, Nb: 0.001-0
．． 05% by weight, Ti: 0.01-0.10% by weight, Cr
:3 to 10% by weight, and (C/12+N/1
4+S/32)<(Ti/48+Nb/93), and the remainder is iron and unavoidable impurities. A cold-rolled steel sheet for deep drawing with excellent corrosion resistance. (2) C: 0.01% by weight or less, Si: 0.5% by weight or less, Mn: 0.5% by weight or less, P: 0.05% by weight or less, S: 0.02% by weight or less, N: 0.01% by weight or less,
Al: 0.02-0.2% by weight, Nb: 0.001-0
．． 05% by weight, Ti: 0.01-0.10% by weight, B:
Contains 0.0001 to 0.002% by weight, Cr: 3 to 10% by weight, and (C/12+N/14+S/32)
A cold-rolled steel sheet for deep drawing with excellent corrosion resistance, which has the following relationship:<(Ti/48+Nb/93), and the remainder consists of iron and unavoidable impurities.