JP3420373B2 - Chrome steel sheet with excellent formability - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chrome steel sheet having formability, particularly excellent deep drawability, secondary work embrittlement resistance and low yield ratio.

[0002]

2. Description of the Related Art Ferritic stainless steel sheets, which are a representative steel type among chrome steel sheets, are usually manufactured by heating a continuously cast slab and then performing hot rolling, hot rolling annealing, cold rolling and finish annealing. Manufactured. The ferritic stainless steel produced in this manner is generally excellent in stress corrosion cracking resistance and inexpensive, and therefore various kitchen appliances,
Widely used in fields such as automobile parts. However, particularly in applications such as automobile fuel filter cases, severe deep drawing is performed, and therefore, there has been a problem that cracking often occurs due to brittleness in secondary processing. Further, ferritic stainless steels generally have a higher yield ratio than austenitic stainless steels and are poor in shape fixability after press forming, often causing problems such as springback.

By the way, many attempts have been made so far in order to improve the deep drawing formability or the secondary work brittleness resistance of ferritic stainless steel sheets. For example,
Japanese Patent Publication No. 54-11770 discloses a technology for producing a ferritic stainless steel sheet aiming at high cold workability by adding Ti, and Japanese Patent Publication No. 57-55787 discloses a Rankford value (hereinafter , Abbreviated as “r value”), and manufacturing techniques of ferritic stainless steel sheets have been proposed. Further, Japanese Patent Publication No. 2-7391 proposes 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.

However, each of these techniques has the following problems. That is, Japanese Examined Japanese Patent Publication 54-1
In the technique disclosed in Japanese Patent No. 1770, brittle cracks were occasionally found during secondary processing after severe deep drawing. Also,
The technique disclosed in Japanese Examined Patent Publication No. 57-55787 is not suitable for severe deep drawing because the deep drawing property is not sufficient. Further, in the technique disclosed in Japanese Examined Patent Publication No. 2-7391, although Ti and B are added, either the deep drawability or the secondary work brittleness is inferior, and both properties are not satisfied at the same time. It was In addition, each of the above techniques has a problem that the in-plane anisotropy of the r value (hereinafter, simply referred to as “Δr”) has not been sufficiently improved. Further, none of these techniques is aimed at the shape fixability after forming, and in fact, the steel sheet manufactured by the above technique has a high yield ratio, and therefore the shape fixability after forming is not satisfactory. There wasn't.

[0005]

As described above, all of the above-mentioned known techniques improve the characteristics of either deep drawability or secondary work brittleness, but they do not satisfy both of these characteristics at the same time. They had common problems. For this reason, when severe deep drawing is performed, subsequent secondary processing brittle cracking is feared. Moreover, since the yield ratio is high, there is a problem that the shape fixability after molding is insufficient.

Therefore, a main object of the present invention is to provide a manufacturing technique of a chromium steel sheet having a good forming workability by solving the above-mentioned problems of the known technique, namely,
It is an object of the present invention to provide a chromium steel sheet which is excellent in both deep drawability and secondary work embrittlement resistance and has good shape fixability after forming (low yield ratio). Another object of this invention is that the r value is 1.
5 or more, Δr is 0.3 or less, brittle crack initiation temperature is -50 ℃
The purpose of the present invention is to provide a chromium steel sheet having a yield ratio of 0.5 or less.

[0007]

[Means for Solving the Problems] As a result of earnest research aimed at realizing the above-mentioned objects, the inventors have found that the above characteristics can be simultaneously achieved by controlling the chemical composition of a chromium steel sheet in an appropriate range. Find that it is possible to be satisfied,
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%, V: 0.
Chrome steel sheet containing 01 to 0.5 wt% with the balance Fe and unavoidable impurities and excellent formability.

(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
A chromium steel sheet that contains wt%, V: 0.01 to 0.5 wt%, Mo: 0.1 to 5.0 wt%, and the balance is Fe and inevitable impurities, and is excellent in formability.

(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
A chromium steel sheet that contains wt%, V: 0.01 to 0.5 wt%, Ca: 0.0005 to 0.01 wt%, and the balance is Fe and inevitable impurities, and is excellent in formability.

(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%, V: 0.01 to 0.5 wt%, Mo: 0.1 to 5.0 wt%,
A chromium steel plate containing Ca: 0.0005 to 0.01 wt% and the balance being Fe and unavoidable impurities and having excellent formability.

[0012]

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 effective element 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 hot workability. Especially 0.05wt
%, The effect will be significant, so 0.05 wt% or less,
It is 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. In particular, 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 to 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- (0.02-0.03) wt% P- (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- (0.000
8 shows the effect of Nb on Δr of a chromium steel sheet containing 8 to 0.0010) wt% B. From Figure 1, Δr is 0.00
It can be seen that the addition of 3 wt% or more of Nb significantly improves, and thus the ear shape after deep drawing is significantly improved.

Further, FIG. 2 shows (0.007 to 0.009) wt% C-
(0.3-0.4) wt% Si- (0.3-0.4) wt% Mn- (0.02-0.03)
wt% P- (0.005-0.007) wt% S- (0.0070-0.0090) wt
% N- (16-18) wt% Cr- (0.02-0.03) wt% Al- (0.1
5 to 0.17) wt% Ti- (0.001 to 0.018) wt% Nb- (0.0008 to
The effect of Nb amount on the relationship between secondary working embrittlement cracking and r value after working of a chromium cold rolled steel sheet containing 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%

V: 0.01 to 0.5 wt%, V is an important element in the present invention. In Figure 2, (0.0
10-0.016) wt% C- (0.29-0.60) wt% Si- (0.19-0.
31) wt% Mn- (0.018-0.030) wt% P- (0.004-0.008) wt
% S- (0.0030 to 0.0080) wt% N- (16.8 to 17.3) wt%
Cr- (0.001-0.043) wt% Al- (0.103-0.159) wt% Ti-
The influence of V content on the yield ratio of the chromium cold rolled steel sheet containing (0.003 to 0.016) wt% Nb- (0.0004 to 0.0011) wt% B is shown. As shown in FIG. 3, by adding an appropriate amount of V, the yield ratio can be significantly reduced without lowering the r value, Δr, and the temperature at which brittle cracks occur, and the shape fixability is greatly improved. . If the amount is less than 0.01% by weight, the effect hardly appears, and if it exceeds 0.5% by weight, the yield ratio tends to be rather high. Therefore, the addition range of V is 0.01 to 0.5.
%, and the preferable range is 0.02 to 0.30 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%.

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 depending on 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%

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, Ni, C
It is also acceptable to include elements added for other purposes such as o, Cu, W, Ce, Se and La.

[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 drawing formability (r value, Δr), secondary work embrittlement resistance and shape freezing property (yield ratio) 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. -Yield ratio Tested in accordance with JIS Z2241 using JIS No. 2, and determined from yield point / tensile strength. The results of these tests are also shown in Tables 1 and 2.

From Table 3, the steel of the present invention has an r value of 1.5 or more,
It can be seen that Δr is 0.3 or less, the crack initiation temperature indicating secondary work embrittlement resistance is -50 ° C or less, and the yield ratio is 0.5 or less, which is an extremely low value. In contrast, the comparative steel is inferior in at least one of the above properties.

[0034]

As described above, according to the present invention, it is possible to manufacture a chromium steel sheet having excellent deep drawability, secondary workability, and shape fixability. Also, according to the present invention, r
It is possible to manufacture a chromium steel sheet having a good formability of 1.5 or more, Δr of 0.3 or less, a brittle crack generation temperature of −50 ° C. or less, and a yield ratio of 0.5 or less.

[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 V content on the yield ratio.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Sato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Laboratory (56) Reference JP-A-4-232230 (JP, A) Hei 6-41696 (JP, A) 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%, V: 0.01-0.5wt% , A balance of Fe and unavoidable impurities, a chrome steel sheet with excellent formability. 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) ~ 0.5wt%, Nb: 0.003-0.020wt%, B: 0.0002-0.005wt%, V: 0.01-0.5wt%, Mo: A chromium steel sheet containing 0.1 to 5.0 wt% with the balance Fe and unavoidable impurities and excellent formability. 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) ~ 0.5wt%, Nb: 0.003-0.020wt%, B: 0.0002-0.005wt%, V: 0.01-0.5wt%, Ca: A chromium steel sheet containing 0.0005 to 0.01 wt% and the balance being Fe and inevitable impurities with excellent formability. 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%, V: 0.01-0.5wt%, Mo: A chromium steel sheet containing 0.1 to 5.0 wt% and Ca: 0.0005 to 0.01 wt%, with the balance being Fe and inevitable impurities, and excellent in formability.