JP3420371B2 - Chrome steel sheet with excellent formability and weatherability - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromium steel sheet which is excellent in formability and weatherability.

[0002]

2. Description of the Related Art Chromium steel generally has characteristics of excellent resistance to stress corrosion cracking and excellent formability such as deep drawability as compared with austenitic stainless steel. In addition, since it is possible to adjust the corrosion resistance in a wide range according to the amount of added Cr and is relatively inexpensive, it is widely used in various fields such as kitchen appliances, automobile parts and outer panels for construction.

Many attempts have been made to improve the properties of such chromium steel sheets. For example, Japanese Patent Publication No. 57-55787 discloses a technique for producing a ferritic stainless steel sheet aiming at a higher Rankford value (hereinafter simply referred to as “r value”) by adding B. The publication discloses a technique for producing a ferritic stainless steel sheet in which brittle cracking is less likely to occur during stretch forming after deep drawing by adding Ti and B.

[0004]

However, none of these techniques is aimed at the corrosion resistance in the natural environment after processing (hereinafter abbreviated as "weather resistance"), and in fact, When the steel sheet manufactured by the above-mentioned technique is used as a vehicle outer panel, for example, in a severe corrosion condition such as a coastal environment, there is a problem that rusting occurs mainly in the processed part.

Therefore, a main object of the present invention is to provide a chrome steel plate manufacturing technique that solves the above-mentioned problems that the known technique has. That is, it is to provide a manufacturing technique of a chrome steel sheet which is excellent in both formability and weatherability. Further, as specific target values thereof, the r value is 1.5 or more, the in-plane anisotropy (Δr) of the r value is 0.3 or less, and the brittle crack initiation temperature after molding is −50 ° C. or less. It is an object of the present invention to provide a manufacturing technology for a chrome steel sheet having excellent properties.

[0006]

[Means for Solving the Problems] As a result of intensive studies aimed at achieving the above-mentioned objects, the inventors have found that the formability and weatherability can be improved by controlling the chemical composition of the chromium steel sheet in an appropriate range. It has been found that it is possible to improve both the sex and the sex at the same time, and the present invention has been completed.

That is, the present invention has the following structures. (1) C: 0.03 wt% or less, Si: 1.0 wt% or less, Mn:
1.0 wt% or less, P: 0.05 wt% or less, S: 0.015 wt%
% Or less, N: 0.02 wt% or less, Cr: 5 to 60 wt%,
Al: 0.10 wt% or less, Ti: 4 (C + N) to 0.5 wt%, Nb:
0.003 to 0.020 wt%, B: 0.0002 to 0.005 wt% included,
And molding containing any one or more selected from Ni, Co, Cu and W so as to satisfy the following formula: 0.3 ≤ Ni + Co + 2Cu + W ≤ 6.0, and the balance being Fe and inevitable impurities. Chrome steel sheet with excellent workability and weather resistance.

(2) C: 0.03 wt% or less, Si: 1.0 wt
% Or less, Mn: 1.0 wt% or less, P: 0.05 wt% or less,
S: 0.015 wt% or less, N: 0.02 wt% or less, Cr: 5
60wt%, Al: 0.10wt% or less, Ti: 4 (C + N) ~ 0.5
wt%, Nb: 0.003 to 0.020 wt%, B: 0.0002 to 0.005
wt%, Mo: 0.1 to 5.0 wt% and at least one selected from Ni, Co, Cu, W is contained so as to satisfy the following formula: 0.3 ≦ Ni + Co + 2Cu + W ≦ 6.0 However, the balance is Fe and unavoidable impurities, and it is a chromium steel sheet with excellent formability and weather resistance.

(3) C: 0.03 wt% or less, Si: 1.0 wt
% Or less, Mn: 1.0 wt% or less, P: 0.05 wt% or less,
S: 0.015 wt% or less, N: 0.02 wt% or less, Cr: 5
60wt%, Al: 0.10wt% or less, Ti: 4 (C + N) ~ 0.5
wt%, Nb: 0.003 to 0.020 wt%, B: 0.0002 to 0.005
wt%, Ca: 0.003 to 0.020 wt%, and Ni, Co, Cu,
One or more selected from W are contained so as to satisfy the following formula; 0.3 ≤ Ni + Co + 2Cu + W ≤ 6.0, and the balance is Fe and inevitable impurities, and is excellent in moldability and weather resistance. Chrome steel plate.

(4) C: 0.03 wt% or less, Si: 1.0 wt
% Or less, Mn: 1.0 wt% or less, P: 0.05 wt% or less,
S: 0.015 wt% or less, N: 0.02 wt% or less, Cr: 5
60wt%, Al: 0.10wt% or less, Ti: 4 (C + N) ~ 0.5
wt%, Nb: 0.003 to 0.020 wt%, B: 0.0002 to 0.005
wt%, Mo: 0.1 to 5.0 wt%, Ca: 0.003 to 0.020 wt%, and any one or more selected from Ni, Co, Cu, W is expressed by the following formula; 0.3 ≤ Ni + Co + 2Cu + W A chromium steel sheet that is contained so as to satisfy ≦ 6.0 and that the balance is Fe and inevitable impurities, and that has excellent formability and weather resistance.

[0011]

Next, the reason why the chemical composition of the chromium steel sheet is limited to the above-mentioned essential constitution in the present invention will be explained. C: 0.03 wt% or less C is an element that deteriorates the r value and the elongation property. Especially, when the content exceeds 0.03 wt%, the effect becomes remarkable, so 0.
It should be below 03wt%. The range is preferably 0.01 wt% or less.

Si: 1.0 wt% or less Si is an element effective for deoxidation, but excessive addition causes deterioration of cold workability, so the addition range is 1.0 wt%.
Below, preferably 0.5 wt% or less.

Mn: 1.0 wt% or less Mn is an element effective for precipitating and fixing S existing in steel and maintaining hot rollability, but excessive addition causes deterioration of cold workability. Therefore, the addition range is 1.0 wt% or less, preferably 0.5 wt% or less.

P: 0.05 wt% or less P is an element harmful to the hot workability of chromium steel. 0.05
When it exceeds wt%, the effect becomes remarkable, so the content of P is
The amount is 0.05 wt% or less, preferably 0.04 wt% or less.

S: 0.015 wt% or less S is a harmful element that segregates at the crystal grain boundaries and promotes grain boundary embrittlement. If it exceeds 0.015 wt%, the effect becomes remarkable, so 0.015 wt% or less, preferably 0.008 wt% or less.

N: 0.02 wt% or less N, like C, is an element harmful to deep drawability.
Especially, if it exceeds 0.02wt%, its effect becomes remarkable.
It should be 0.02 wt% or less. The range is preferably 0.01 wt% or less.

Cr: 5-60 wt% Cr is an essential element for ensuring corrosion resistance.
If the amount is less than 5% by weight, the corrosion resistance is insufficient, while if it exceeds 60% by weight, the cold workability is deteriorated. Therefore, the addition range is 5 to 60% by weight, preferably 10 to 45% by weight.

Al: 0.10 wt% or less Al is an effective element for deoxidation, but excessive addition is not recommended.
Since the increase of Al-based inclusions causes surface defects,
It is added in a range of 0.10 wt% or less, preferably 0.07 wt% or less.

Ti: 4 (C + N) to 0.5 wt% Ti is an element useful for precipitating and fixing C and N, which are harmful to deep drawability, and ensuring high deep drawability. The effect is
If it is less than 4 (C + N) wt%, it cannot be obtained. On the other hand, addition of more than 0.5wt% not only saturates these effects but also lowers the productivity. Therefore, the addition amount of Ti is 4 (C + N) to 0.5.
wt%, preferably 4 (C + N) to 0.3 wt%.

Nb: 0.003 to 0.020 wt% Nb is an important element in the present invention that improves the deep drawing formability and the secondary work embrittlement resistance at the same time by the combined addition of Ti, B and the like. The effect is not obtained at less than 0.003 wt%, while the effect is saturated even if added at more than 0.020 wt%, which would rather increase the manufacturing cost.
The addition amount of 0.003 to 0.020 wt%, preferably 0.004 to
0.018 wt%

Here, the effect of Nb on the deep drawability and the resistance to secondary work embrittlement will be described in detail with reference to the drawings. Figure 1
Is (0.007 to 0.009) wt% C- (0.3 to 0.4) wt% Si- (0.3 to
0.4) wt% Mn- (0.005-0.007) wt% S- (0.0070-0.0090
) wt% N- (16-18) wt% Cr- (0.02-0.03) wt% Al-
It shows the effect of Nb on the Δr of the chromium steel containing (0.15 to 0.17) wt% Ti- (0.0008 to 0.0010) wt% B. From FIG. 1, it can be seen that Δr is remarkably improved by the addition of 0.003 wt% or more of Nb, and therefore the ear shape after deep drawing is greatly improved.

Further, in FIG. 2, (0.007 to 0.009) wt% C-
(0.3-0.4) wt% Si- (0.3-0.4) wt% Mn- (0.005-0.007)
wt% S- (0.0070-0.0090) wt% N- (16-18) wt% Cr
-(0.02-0.03) wt% Al- (0.15-0.17) wt% Ti- (0.0
The effect of Nb amount on the relationship between the secondary working embrittlement crack and the r value after working of a chromium steel sheet containing (008 to 0.0010) wt% B is shown. From FIG. 2, it can be seen that the steel sheet containing 0.003 wt% or more of Nb has a high r value, which is an index of forming limit during deep drawing, and has a low embrittlement cracking temperature. As explained above, 0.
It is shown that by incorporating 003 wt% or more of Nb, both deep drawability and secondary work embrittlement resistance can be balanced at a high level. The method of calculating the r value in the above experiment,
The embrittlement cracking test method was the same as the method described later.

B: 0.0002 to 0.005 wt% B is an element effective for improving the secondary work embrittlement resistance after deep drawing. The effect cannot be obtained at less than 0.0002 wt%, but excessive addition deteriorates the deep drawing formability, so the addition amount is 0.0002 to 0.005 wt%, preferably 0.0002 to 0.005 wt%.
03 to 0.003 wt%

Ni, Co, Cu, W; these elements are the above Ti, N
It is an important element that enhances the weather resistance while maintaining a high deep drawability by the combined addition of b and B. The effect is Ni +
In the formula of Co + 2Cu + W, if it is less than 0.3, it cannot be obtained. On the other hand, if it exceeds 6.0, the effect is saturated and only the economical efficiency is impaired.
0.3 ≤ Ni + Co + 2Cu + W ≤ 6.0, preferably 0.5 ≤ Ni +
Co + 2Cu + W ≦ 4.0. The preferable addition amount of each element is Ni: 0.3 to 3.0 wt%, Co: 0.3 to 3.0 wt%, respectively.
%, Cu: 0.15 to 1.5 wt%, W: 0.3 to 3.0 wt%.

In FIG. 3, (0.007-0.009) wt% C- (0.3-0.
4) wt% Si- (0.3-0.4) wt% Mn- (0.005-0.007) wt% S-
(0.0070-0.0090) wt% N- (16-18) wt% Cr- (0.02
~ 0.03) wt% Al- (0.15-0.17) wt% Ti- (0.0008-0.
[0010] Regarding a chromium steel sheet containing wt% B, after deep drawing test, 6 at a position facing south 15 m from the coast of the Gulf Industrial Zone.
The effect of Ni, Co, Cu, and W on the erosion depth after a weathering test of atmospheric exposure for a month is shown. The weather resistance method in the above experiment was the same as the method described later. From Fig. 3, the weather resistance after forming is Ni + Co + 2Cu + W is 0.3 wt.
It can be seen that the improvement is remarkably achieved when the ratio is above%.

Ca: 0.0005 to 0.01 wt% Ca is an element that has the effect of suppressing nozzle clogging due to Ti-based inclusions during steelmaking casting, and is selectively added according to the amount of Ti. However, if added in excess, Ca
Since the system inclusion has an adverse effect that it becomes a starting point of brittle fracture, the addition range of Ca is 0.0005 to 0.01 wt%, preferably 0.
0005 to 0.006 wt%

Mo: 0.1 to 5.0 wt% Mo is an element that further improves the corrosion resistance, and is selectively added. The effect can be obtained by adding 0.1 wt% or more, but addition of more than 5.0 wt% lowers the deep drawability, so the amount of Mo added is 0.1 to 5.0 wt%, preferably 0.3 to 3.
It shall be 0 wt%.

In the production process of the steel sheet of the present invention, the steel having the above-mentioned composition is melted in a usual steelmaking furnace such as a converter or an electric furnace,
Hot rolling after forming steel pieces by continuous casting method or ingot making method
(Hot rolled sheet annealing) -Pickling-Cold rolling-Cold rolled sheet annealing-Pickling
If necessary, a method of repeatedly performing cold rolling-annealing-pickling may be used. Further, the effect aimed at by the steel sheet of the present invention is exhibited regardless of the surface finish state (HL, 2B, etc.) of the steel sheet. In the steel sheet of the present invention, V, L
Incorporation of elements added for other purposes such as a, Se and Ce is also allowed.

[0029]

[Examples] Steel having the chemical composition shown in Tables 1 and 2 was melted in a vacuum melting furnace to form a slab, which was then heated to 1250 ° C and hot-rolled into a hot-rolled sheet having a thickness of 4.0 mm. . This hot-rolled sheet is annealed by hot-rolled sheet (800-950 ° C)
Cold-rolled steel sheet with a thickness of 0.7 mm was obtained by mono-pickling.

[0030]

[Table 1]

[0031]

[Table 2]

Using the steel sheet obtained by the above method as a test material, deep drawability (r value, Δr), secondary work embrittlement resistance and weather resistance were investigated by the following methods.・ R value, Δr JIS No. 5 test piece was sampled from the rolling direction of steel plate, the direction of 45 ° with respect to the rolling direction, and the direction of 90 ° with respect to the rolling direction. The Rankford value in each direction was measured from the ratio of the lateral strain and the plate thickness strain when a tensile prestrain was applied, and was calculated by the following formula. r = (r _L + 2r _D + r _T ) / 4 Δr = (r _L −2r _D + r _T ) / 2 where r _L , r _D, and r _T are the rolling directions,
It represents the Rankford value in the direction of 45 ° to the rolling direction and 90 ° to the rolling direction.・ Secondary processing Brittleness resistance Cup-shaped test piece deep-drawn with a drawing ratio of -100 to 20 ℃
After holding at the specified temperature, the drop weight test (weight 5 kg, drop 0.
An impact load was applied to the cup head by 8 m), and the crack initiation temperature was determined from the presence or absence of brittle cracks on the cup side wall. For each of the steels, the temperature was set to 2 at a temperature of 5 ° C., and if even one of them caused brittle cracking, the highest temperature at that time was taken as the cracking temperature. The results of these tests are shown in Table 3.・ A cup-shaped test piece that has been deep-drawn with a weathering reduction ratio of 2 is exposed to the atmosphere for 6 months southward at a position 15 m from the coast of the Gulf Industrial Zone. The depth was measured. Each of the 10 points from the maximum point was measured, and the values of the top 5 points were averaged to obtain the erosion depth. The results are shown in Table 3.

[0033]

[Table 3]

From Table 3, the steel sheets of the present invention have characteristics that the r value is 1.5 or more, the Δr is 0.3 or less, and the cracking temperature showing secondary work embrittlement resistance is -50 ° C or less. It is clear that the film has excellent moldability and excellent weatherability with an erosion depth of 40 μm or less.

[0035]

As described above, according to the present invention, the r value is 1.5 or more, the Δr is 0.3 or less, and the brittle crack initiation temperature is -50 ° C or less. It is possible to manufacture chrome steel sheets with excellent properties. Therefore, the steel sheet of the present invention, after being deep-drawn in particular, greatly contributes to prolonging the service life of a member used in an atmospheric environment under severe corrosion conditions.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of Nb content on Δr.

FIG. 2 is a graph showing the effect of Nb content on the relationship between r value and crack initiation temperature.

FIG. 3 is a graph showing the effect of Ni + Co + 2Cu + W on the erosion depth.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References Patent 2933826 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (4)

(57) [Claims] 1. C: 0.03 wt% or less, Si: 1.0 wt% or less, Mn: 1.0 wt% or less, P: 0.05 wt% or less, S: 0.015 wt% or less, N: 0.02 wt% or less, Cr: 5 〜60wt%, Al: 0.10wt% or less, Ti: 4 (C + N) 〜0.5wt%, Nb: 0.003〜0.020wt%, B: 0.0002〜0.005wt%, and Ni, Co, Cu, W Chromium containing at least one selected from the following formulas: 0.3 ≤ Ni + Co + 2Cu + W ≤ 6.0, the balance being Fe and inevitable impurities, and excellent in formability and weatherability. steel sheet. 2. C: 0.03 wt% or less, Si: 1.0 wt% or less, Mn: 1.0 wt% or less, P: 0.05 wt% or less, S: 0.015 wt% or less, N: 0.02 wt% or less, Cr: 5 -60 wt%, Al: 0.10 wt% or less, Ti: 4 (C + N) -0.5 wt%, Nb: 0.003-0.020 wt%, B: 0.0002-0.005 wt%, Mo: 0.1-5.0 wt%,
And molding containing any one or more selected from Ni, Co, Cu and W so as to satisfy the following formula: 0.3 ≤ Ni + Co + 2Cu + W ≤ 6.0, and the balance being Fe and inevitable impurities. Chrome steel sheet with excellent workability and weather resistance. 3. C: 0.03 wt% or less, Si: 1.0 wt% or less, Mn: 1.0 wt% or less, P: 0.05 wt% or less, S: 0.015 wt% or less, N: 0.02 wt% or less, Cr: 5 -60 wt%, Al: 0.10 wt% or less, Ti: 4 (C + N) -0.5 wt%, Nb: 0.003-0.020 wt%, B: 0.0002-0.005 wt%, Ca: 0.003-0.020 wt%, And molding containing any one or more selected from Ni, Co, Cu and W so as to satisfy the following formula: 0.3 ≤ Ni + Co + 2Cu + W ≤ 6.0, and the balance being Fe and inevitable impurities. Chrome steel sheet with excellent workability and weather resistance. 4. C: 0.03 wt% or less, Si: 1.0 wt% or less, Mn: 1.0 wt% or less, P: 0.05 wt% or less, S: 0.015 wt% or less, N: 0.02 wt% or less, Cr: 5 ~ 60wt%, Al: 0.10wt% or less, Ti: 4 (C + N) ~ 0.5wt%, Nb: 0.003-0.020wt%, B: 0.0002-0.005wt%, Mo: 0.1-5.0wt%, Ca: It contains 0.003 to 0.020 wt% and contains one or more selected from Ni, Co, Cu and W so as to satisfy the following formula; 0.3 ≤ Ni + Co + 2Cu + W ≤ 6.0, and the balance Fe. And a chrome steel sheet consisting of inevitable impurities and excellent in formability and weather resistance.