JP3258704B2 - Hot-rolled steel sheet for enameling which has high strength after enamel firing and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled steel sheet for enamel which has good toe-jumping resistance after forming and which has high strength after enamel firing.

[0002]

2. Description of the Related Art An enamel is a non-combustible material obtained by baking glass on the surface of a steel sheet and has various properties such as heat resistance, weather resistance, chemical resistance, water resistance and stain resistance. There are various features. With respect to the base material for the enamel related to this, press moldability is required depending on the use in addition to firing distortion characteristics, anti-sticking property, adhesion, and foam / black spot resistance. In general, a cold rolled steel sheet is used as a base material that requires press formability, while a hot rolled steel sheet having a large thickness is used for an enamel silo, a hot water tank, and the like. However, in hot-rolled steel sheets for these uses, a high-strength steel sheet which is thinner and lighter in weight than a soft and good-forming steel sheet has been desired.

[0003] Such a high-strength hot-rolled steel sheet is:
JP-B-58-1170, JP-B-59-6894, JP-A-sho
No. 61-117246 is disclosed, but Ti is added to any steel sheet having a chemical composition having a C content of 0.005% or more,
The purpose is to increase the strength by precipitating C finely in steel during hot rolling or enamel firing.

[0004]

However, in general, Ti-added steel is disclosed in Japanese Unexamined Patent Publication No.
When the enamel treatment is performed as disclosed in Japanese Patent No. 93046, there is a problem that surface defects such as bubbles and black spots are easily generated. Further, when solid solution C is present in the steel before the enamel firing as in JP-A-61-117246, (1) the Ac ₃ transformation point decreases as is well known in the Fe-C phase diagram, Α-γ transformation occurs during firing, resulting in a shape defect called firing strain. (2) During sintering, C on the surface of the steel sheet combines with oxygen in the air to generate CO ₂ gas, which causes more bubbles and black spot defects. (3) There is a problem in that TiC is not sufficiently generated by a short-time heat treatment such as firing, and a jump defect is likely to occur.

Accordingly, an object of the present invention is to provide a hot-rolled steel sheet for enamel which is hard to generate bubbles and black spot defects, has good anti-sticking property, and has a high strength after enamel firing, and a method for producing the same. Is what you do.

[0006]

SUMMARY OF THE INVENTION The present invention provides a weight ratio
And C: 0.002 to 0.020%, Si: 0.01 to 0.10%, Mn:
0.05-3.0%, Al: 0.010% or less, N: 0.0050-0.02
00%, B: 0.0050-0.0200%, Cu: 0.01-0.4%,
Ni: 0.01 to 0.1%, Nb: 0.01 to 0.10%, O: 0.01 to
0.10%, P: 0.02 to 0.10% and S: 0.02 to 0.10%
And, if necessary, 0.001 to 0.050 Se.% Included
And (P + S) / Cu: 0.02-2.0, B / N ≧ 1, Nb
/ C ≧ 7, {precipitated Nb (%)} / {Total Nb (%)} ≧ 0.
5 are satisfied, and the balance is iron and unavoidable impurities?
Strengthen after enamel firing
It is a hot-rolled steel sheet for enamel, and C:
0.002 to 0.020%, Si: 0.01 to 0.10%, Mn: 0.05 to 3.0
%, Al: 0.010% or less, N: 0.0050 to 0.0200%, B:
 0.0050 to 0.0200%, Cu: 0.01 to 0.4%, Ni: 0.01
~ 0.1%, Nb: 0.01 ~ 0.10%, O: 0.01 ~ 0.10%,
P: 0.02 to 0.10% and S: 0.02 to 0.10%,
0.001 to 0.050 Se if necessary% IncludedMikatsu,
(P + S) / Cu: 0.02-2.0, B / N ≧ 1, Nb / C ≧ 7
Respectively, the balance is from iron and inevitable impurities
Hot-rolled into a continuous rolled slab
And then winding at 600 ℃ or more
Manufacturing method of hot-rolled steel sheet for enamel to increase the strength after brazing
Is the law.

[0007]

The main feature of the present invention is that Nb is added, solute C is precipitated as NbC during the hot rolling step to soften, and then molded, NbC is re-dissolved during enamel firing, and solid solution in steel is obtained. The point is to increase the amount of carbon and to increase the strength of the material of the steel sheet base after firing. Thus, even if the sheet thickness is reduced, a tensile rigidity can be obtained, and advantageous properties such as anti-jumping property, firing distortion resistance, foam resistance and black spots can be made advantageous.

Next, the reasons for limiting the components in the present invention will be described. C: C is an interstitial solid solution element, and is an element that is advantageous for increasing the strength of the material. However, when the content is more than 0.020%, the Ac ₃ transformation point is lowered, and firing enamel is easily generated. Therefore, the upper limit was made 0.020%. The lower limit is at the stage of hot rolling.
In order to form NbC and re-dissolve it at the time of firing the enamel to obtain a high-strength steel sheet by solid solution C, the content must be at least 0.002% or more. Therefore, the range of the content of C is 0.002 to
The range was 0.020%.

Si: Si is a solid solution strengthening element, and its content is preferably 0.01% or more. However, an excessively large content significantly deteriorates the adhesion of the enamel, so the upper limit was set to 0.10%. Mn: Mn is a solid solution strengthening element like Si, but in a component system containing a large amount of S and oxygen as in the present invention, Mn forms oxides and sulfides and deteriorates the material. It is an element that hardly causes hydrogen, but rather can trap hydrogen that causes a jump-off defect, and can improve the material and the jump-proof resistance. For this purpose, the content is required to be at least 0.05% or more. However
Since the addition of more than 3.0% increases the cost of molten steel, the upper limit is set to 3.0%.

Al: Al is usually used as a deoxidizing agent in the steelmaking stage. In the present invention, oxygen is controlled to a specific range for the purpose of improving the anti-sticking property and adhesion. Therefore, Al is sufficient if it has a necessary amount, and a content of more than 0.01% removes oxygen, which is an important element in the present invention, as Al ₂ O _3. Limited to.

N: N is an element effective in forming BN together with B in the present invention to secure the anti-sticking property, and it needs to be contained at least 0.0050%. However,
If the content exceeds 0.0200%, B must be added in a large amount, and there is a risk of cracking during hot rolling. Therefore, the upper limit of the N content is set to 0.0200%.

B: In the present invention, B forms B ₂ O ₃ and BN;
In addition to ensuring the jumping resistance, it has the effect of preventing aging deterioration due to solid solution N, and at least 0.0050% is necessary because it is an effective element. However, 0.0200
%, The range of B is set to 0.0050% to 0.0200%, since cracking tends to occur during hot rolling.

[0013] Cu: Cu is an element added for the purpose of controlling the pickling rate during the enamel pretreatment and for the purpose of improving the adhesiveness.
A content of 0.01% or more is required. However, 0.40
% Increases the segregation of the steel sheet surface and makes it difficult to pickle during the enamel pretreatment.
0.40%.

Ni: Ni has the effect of preventing surface defects called "scabs" generated when a large amount of Cu is added.
It is an effective element to improve the adhesion of the enamel, but 0.01
The addition of less than 0.1% has no effect, and the addition of more than 0.1% increases the cost of molten steel.
01 to 0.1%.

Nb: Nb is an effective element added for the purpose of forming NbC in the hot-rolled sheet stage, re-dissolving NbC during enamel firing, increasing the amount of solid solution C, and increasing the strength. is there. At least 0 to get these effects.
01% is required. However, if the content exceeds 0.10%, the effect is saturated and the cost increases, so the upper limit is set to 0.
10%.

O: O is an effective element for the purpose of improving the anti-sticking property and adhesion, but its effect cannot be obtained with a content of less than 0.01%. If the content exceeds 0.10%, the surface properties of the continuously cast slab are severe, the cost of slab surface care is increased, and the product yield is deteriorated. Therefore, the content range is set to 0.01 to 0.10%.

P: P is an element effective for increasing the strength, and it must be contained at least 0.02% or more. However, the content of more than 0.10% significantly increases the pickling rate, so that the content is limited to 0.10% or less. S: S forms sulfides with Mn and disperses in the steel to improve the jump-resistant property, and since these precipitates are also effective elements for improving the enamel adhesion, Its content must be at least 0.01%. However, if the content exceeds 0.10%, the pickling rate during the pretreatment of the enamel is remarkably increased, and the formation of a smut that causes bubbles and black spot defects is promoted. Therefore, the S content is set to 0.01 to 0.10%.

(P + S) / Cu: 0.02 to (P + S) / Cu
The reason for limiting to 2.0 is to stabilize the weight loss of pickling against fluctuations in the enamel pretreatment conditions (temperature and time).
In the present invention, 0.02 or less than 2.0
Within the range of 2.0. Nb / C: The reason for setting Nb / C ≧ 7 is that it is difficult to form NbC in the hot-rolled sheet stage when the value is less than 7, and when solid solution C remains, it causes Since firing distortion occurs, at least 7 or more must be contained in order to prevent these adverse effects.

B / N: The reason why B / N ≧ 1 is that at least B / N ≧ 1 must be satisfied in order to fix N which causes aging deterioration as BN. {Precipitated Nb (%)} / {Total Nb (%)} ≥0.5: In the present invention, the amount of NbC precipitates in the hot-rolled sheet before the enamel firing is calculated as {precipitated Nb (%)} / {Total Nb (%). ) It is necessary to satisfy｝ ≧ 0.5. If the content is less than 0.5%, it is difficult to increase the strength after firing, which is a feature of the present invention.

Se: Se is added mainly for the purpose of improving the weldability, but 0.001%
The above addition is necessary, and addition of more than 0.050% deteriorates the surface properties.
50%. In addition, inevitable impurities need to be reduced as much as possible, but the present invention does not particularly limit them.

Hot-rolling winding temperature: The reason for setting the hot-rolling winding temperature to 600 ° C. or higher is that if the temperature is lower than 600 ° C., precipitation occurs in the hot rolling stage.
It is difficult to satisfy Nb (%)｝ / {Total Nb (%)} ≧ 0.5. In order to bring out the effect of NbC, which is a feature of the present invention, it is necessary to set the hot-rolling winding temperature to 600 ° C. or higher. is there. Although there is no particular upper limit, 750 ° C
If the winding temperature is too high, the thickness of the scale increases and the product yield deteriorates.

[0022]

EXAMPLE A continuous cast slab having a chemical composition as shown in Table 1 was inserted into a heating furnace at 1200 ° C. for 3 hours, and after three passes of rough rolling, the finishing temperature was 860 ° C. and the sheet thickness was 2.5 mm with a finishing mill. Hot-rolled, cooled at a cooling rate of 20 ° C / s,
The film was wound at a temperature in the range of 700700 ° C.

After the steel sheets were subjected to shot blasting and descaling, they were subjected to two times of enamelling as shown in Table 2 and a corresponding heat treatment without the enamelling treatment. Then, processed into JIS No. 5 tensile test specimen,
The materials before and after the enamel firing were investigated. ASTM-C313
The enamel adhesion was investigated by -59. In addition, the occurrence of bubble defects and toe defects was visually observed. Further Procee
Vol. 55, p. 431 (1955), the firing strain was measured. Weldability is welding current 100
A, TIG welding was performed at a speed of 50 cm / min, and evaluation was made based on whether or not a hole was formed. Table 3 shows the results.

As a result, the steel sheet of the present invention manufactured at the chemical composition and hot-rolling temperature has high strength, has no firing distortion, no skipping defects, and has no puncture even during welding. However, the material and the enamel properties were satisfied. On the other hand, the steel sheet outside of the present invention showed a small change in strength before and after firing, and furthermore, firing distortion occurred, and skipping defects and the like occurred.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

Since the steel sheet according to the present invention has high strength, there is no problem in strength even if the steel sheet is made thinner than the conventional steel sheet. Since this leads to a reduction in the weight of the product, it is also advantageous in handling such as transportation and mounting work on a building.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-10048 (JP, A) JP-A-63-277742 (JP, A) JP-A-2-34793 (JP, A) (58) Field (Int. Cl. ⁷ , DB name) C22C 38/00 301

Claims (4)

(57) [Claims] [Claim 1] In terms of weight ratio, C: 0.002 to 0.020%, Si: 0.01 to 0.10%, Mn: 0.05 to 3.0%, Al: 0.010% or less, N: 0.0050 to 0.0200%, B: 0.0050 to 0.0200% , Cu: 0.01 to 0.4%, Ni: 0.01 to 0.1%, Nb: 0.01 to 0.10%, O: 0.01 to 0.10%, P: 0.02 to 0.10%, and S: 0.02 to 0.10%, and (P + S) / Cu: 0.
02-2.0, B / N ≧ 1, Nb / C ≧ 7, {precipitated Nb (%)}
/ {Total Nb (%)} ≧ 0.5, and the balance consists of iron and inevitable impurities. 2. The method of claim 1, wherein the weight ratio of Se is 0.001 to 0.05.
0% containing Mukoto after enamel baking of claim 1, wherein, enameling for hot rolled steel sheet for high strength. 3. Weight ratio: C: 0.002 to 0.020%, Si: 0.01 to 0.10%, Mn: 0.05 to 3.0%, Al: 0.010% or less, N: 0.0050 to 0.0200%, B: 0.0050 to 0.0200% , Cu: 0.01 to 0.4%, Ni: 0.01 to 0.1%, Nb: 0.01 to 0.10%, O: 0.01 to 0.10%, P: 0.02 to 0.10%, and S: 0.02 to 0.10%, and (P + S) / Cu: 0.
02-2.0, B / N ≧ 1, Nb / C ≧ 7, respectively.
A continuous cast slab consisting of iron and unavoidable impurities with the remainder being subjected to normal hot rolling to form a hot-rolled sheet and then wound at a temperature of 600 ° C or higher. Manufacturing method of hot rolled steel sheet. 4. The method according to claim 1, wherein the weight ratio of Se is 0.001 to 0.05.
4. The method for producing a hot-rolled steel sheet for enamel according to claim 3, wherein the strength is increased after firing the enamel.