JP3377155B2 - Manufacturing method of steel sheet for extremely low carbon cans - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a tin-plated steel sheet, T
The present invention relates to a method for manufacturing an original plate of a steel plate for a can such as FS.

[0002]

2. Description of the Related Art As a steel sheet for ultra-low carbon cans, at least one of Ti and Nb which has a strong bonding force with the interstitial solid solution elements (C, N) in the steel and easily forms carbonitrides. So-called IF steel (Interstitial Free Stee
l) is well known. Since this steel contains no interstitial solid solution elements, no yield point elongation appears even after coating. As a result, there is no concern about the appearance defect during can making due to the presence of elongation at the yield point such as waist bending and stretcher strain.
With the progress of degassing technology, it is now easy to produce ultra-low carbon steel, and IF steel is used in large quantities as a soft steel sheet for cans.

[0003]

However, IF steel has the following problems. First, the recrystallization temperature becomes high because Ti or Nb is added. As a result, high temperature annealing at 750 ° C or higher is essential. Since the steel plate for cans has a small thickness, high-temperature annealing tends to cause operational problems such as breakage and drawing. Secondly, the material cost is high because expensive Ti and Nb are added. Third, the weld strength is weak. This is because ultra-low carbon steel has no quenching effect.

As a method for solving such a problem of the IF steel for cans, for example, Japanese Patent Application Laid-Open No. 5-263143 discloses a technique of adding a trace amount of B instead of Ti and Nb.

However, in the technique disclosed in Japanese Patent Laid-Open No. 263143/1993, although the first and second problems are solved, the C content has to be extremely low, and therefore, the current problem is solved. Gas technology raises new problems of high cost and uncertain achievement. Also,
The third problem is also insufficient.

The present invention has been made to solve such problems, and is a method for producing a steel sheet for cans which does not require addition of expensive Nb or Ti, is easy to produce, and has excellent weldability. The purpose is to provide.

[0007]

[Means for Solving the Problems] The above problems are as follows: C: 0.0016-0.0025%, Mn: 0.05-2.0%, Al: 0.
025 to 0.13%, N: 0.0030% or less, B: 0.0005 to 0.0024
%, With the balance consisting essentially of Fe and unavoidable impurities, and having a composition with a B / N (weight ratio) of 0.5-0.8, a coiling temperature in hot rolling of 400- 650 ℃, radiant tube heating
A method for producing a steel plate for an ultra-low carbon can having excellent weldability, characterized in that the annealing temperature in continuous annealing is 650 to 690 ° C, and the elongation in temper rolling is 0.8 to 4%. Will be solved by.

Further, the elongation ratio in temper rolling is 1.8 to
If it is 4%, the characteristics of the steel sheet for ultra-low carbon cans are further improved.

The reasons for limiting the manufacturing conditions of the present invention will be described below. C: In the painting process, paint baking treatment (210 ° C x 10 minutes)
Is done. At this time, if solid solution C is present, it precipitates as extremely fine metastable precipitates on the dislocations and hinders the movement of the dislocations. As a result, yield point elongation occurs. The yield strength elongation increases as the amount of dissolved C increases. If this value is large, waist bending and stretcher strain occur during can forming. In order to avoid such poor appearance, the yield point elongation must be 5% or less. In the steel of the present application, Ti, N
Since no carbide forming element such as b is added, the solid solution C content is proportional to the total C content in the steel. If the C content exceeds 0.0025%, the yield point elongation after coating cannot be reduced to 5% or less. If it is less than 0.0016%, the manufacturing cost in steelmaking becomes very high.

Mn: To prevent red hot embrittlement, addition of 0.05% or more is necessary. The hardness is adjusted by adjusting the amount of Mn added. The upper limit is determined from the upper limit of required hardness.

Al: Al is added as a deoxidizer,
In the present invention, it also acts to fix the solid solution N 2 as AlN.
Solid solution N is first fixed as BN by B, and the remaining portion becomes AlN. If it is less than 0.025%, the amount of solid solution N remaining after the precipitation of BN is small, so the precipitation of AlN during annealing becomes unstable. The solid solution N, which has not completely turned into AlN, is involved in the generation of yield point elongation due to N aging during coating. Increasing the amount of Al, which is a strong deoxidizer, is not preferable for the surface properties of the slab. It also leads to higher costs. Is the upper limit
0.130% considers this point.

N: N is an impurity which is inevitably mixed. As the amount of N increases, the amount of B added to fix the N must be increased. This is costly because B is very expensive. The upper limit of 0.0030% is set in consideration of this point.

B: The purpose of addition is the following three. The first is to control the elongation at the yield point during coating by refining the hot-rolled sheet structure and the cold-rolled sheet structure. This is because grain refining increases the number of grain boundaries that are the segregation points of solute C during the cooling process of annealing, and the solute carbon segregated at grain boundaries does not contribute to the occurrence of yield point elongation.

The second is to reduce the adverse effect of solute N. N
Is fixed as BN to suppress the occurrence of a yield point due to N aging during painting.

The third is strengthening of the weld heat affected zone. The decrease in the hardenability of the weld heat affected zone due to the extremely low C is compensated by B. If less than 0.0005%, these three effects cannot be obtained. If it exceeds 0.0024%, due to the relationship with the above N content, there may be a case where B is contained in excess of the amount precipitated as BN.
Although N aging decreases, the amount of solute C increases, as will be described later, which is not preferable. Adding a large amount of B is costly,
It is also not preferable for the surface quality of the slab.

B / N: An important factor for keeping the yield point elongation after coating to 5% or less. If B / N is less than 0.5, the effect of adding B cannot be obtained.

When B / N exceeds 0.8, B becomes larger than N in terms of the number of atoms. Excess B segregates at the grain boundaries before C and interferes with the segregation of solid solution C at the grain boundaries. That is, the existence of surplus B is
The solid solution C in the grains is increased, and the yield point elongation after coating is 5% or more.

Winding temperature after hot rolling: If it is less than 400 ° C., stable winding work cannot be performed. If the temperature exceeds 650 ° C, the crystal grains of the hot rolled sheet become coarse. When the crystal grains of the hot-rolled sheet become large, the crystal grains after cold rolling-annealing also become large, and the segregation points of solid solution C in the cooling process of annealing decrease.

Annealing temperature in continuous annealing: When the temperature is less than 650 ° C., unrecrystallized parts remain. If the temperature exceeds 690 ° C, the yield point elongation after coating will exceed 5%. This is because C that has precipitated or segregated in the grain boundaries of the hot rolled sheet is re-dissolved in the crystal grains as the temperature rises during annealing, but the amount exceeding C of 690 ° C becomes too large. Further, as the annealing temperature becomes higher, the crystal grains become larger and the number of segregation points decrease, which also leads to an increase in the yield point elongation.

Elongation ratio in temper rolling: the normal range of 0.
Although the purpose of the present invention is to achieve the yield point elongation of 5% or less at 8 to 4%, 1.8 to 4% is particularly desirable within this range. The yield point elongation after coating becomes smaller with the increase of the elongation rate, and the yield point elongation can be made 3.5% or less at 1.8% or more. A stretch ratio of more than 4% cannot be achieved due to the capacity of the temper rolling mill.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The slab may be directly hot-rolled without being reheated after continuous casting, or may be hot-rolled after reheating in a heating furnace. The heating temperature for heating in the heating furnace may be a usual temperature range of 1000 to 1250 ° C.

The finishing temperature in hot rolling is a normal condition, Ar3
It should be more than a point. The cold rolling rate may be in the usual range of 80 to 95%.

Even if continuous annealing is carried out by using a so-called can steel plate-dedicated type equipment for heating, soaking, and cooling, heating, soaking,
It may be carried out by using equipment for quenching / overaging treatment / cooling cold-rolled steel sheet for drawing. The object of the present invention can be achieved even if the heating and holding time, the cooling rate, etc. are arbitrarily selected.

[0024]

【Example】

(Example 1) Steels A to J having the chemical components shown in Table 1 were melted by a degasser. Then, a slab was manufactured by continuous casting, the slab was heated to 1200 ° C, and then hot-rolled under the conditions of a finishing temperature of 870 ° C and a winding temperature of 560 ° C to obtain a hot-rolled steel sheet having a finished sheet thickness of 2.3 mm. Then, this hot-rolled steel sheet was cold-rolled to manufacture a cold-rolled steel sheet having a finished thickness of 0.23 mm. This cold rolled steel sheet was continuously annealed at a heating temperature of 670 ° C. in a radiant tube heating / cooling tube and gas jet cooling type continuous annealing furnace. After that, temper rolling with an elongation of 1.5% was performed, and the surface was plated with tin.

The yield point elongation and the welding strength were measured after heat treatment (210 ° C. × 10 minutes) equivalent to the baking condition for coating. The tensile test for measuring the yield point elongation was performed according to JIS 2241. Spot welding condition is tip; CF of 6mmφ
Mold, load: 50kgf, nugget diameter: 2.8mm, current: 3.7kA
10 cycles, the strength test is a cross tension test based on JIS Z3137.

The results are shown in Table 2. In addition, steel plates A to Table 2
J is manufactured from each of the steels A to J shown in Table 1.

Steel plates A, B, C, D and E show the effects of B / N. Steel plates A and B whose B / N is out of the upper limit
The yield elongation after coating exceeds the allowable limit of 5%. The steel plate E having a B / N that is out of the lower limit has an elongation at yield exceeding the allowable limit and also has a too low welding strength.

Steel plates F, G, and H show the effect of the amount of C. The higher the C content, the greater the yield point elongation. The yield point elongation of the steel plate H in which the amount of C is outside the upper limit exceeds the allowable limit.

The steel sheets I and J are hardened, so that the amount of Mn is increased within the limited range of the present invention. The effect of the present application is exhibited even if the amount of Mn is increased.

[0030]

[Table 1]

[0031]

[Table 2]

(Example 2) Using Steel C in Table 1, the coiling temperature in hot rolling was changed in four stages in the range of 450 ° C to 680 ° C, and the effect of coiling temperature was investigated. Other manufacturing conditions are: slab heating temperature; 1240 ° C, hot rolling; finishing plate thickness 2.3 mm, finishing temperature 87
0 ℃, cold rolling; finished sheet thickness 0.23 mm, continuous annealing; radiant tube heating / overaging treatment type continuous annealing furnace, heating temperature 670
℃, temper rolling; elongation 2.0%, surface treatment; TFS treatment,
Met.

The results are shown in Table 3. The influence of the winding temperature mainly appears on the yield point elongation after painting. The lower the coiling temperature, the smaller the yield point elongation. For steel plate C-4, which is outside the upper limit of the present application, the yield point elongation is 6.1%, which is the allowable limit.
% Is exceeded.

[0034]

[Table 3]

(Example 3) Using the steel G in Table 1, the annealing temperature was changed in four steps in the range of 640 to 700 ° C, and the influence on the annealing temperature was examined. Other manufacturing conditions are: slab heating temperature; 1180 ° C, hot rolling; finishing plate thickness 2.3 mm, finishing temperature 890 ° C,
Winding temperature 540 ° C, cold rolling; finished sheet thickness 0.23 mm, continuous annealing; radiant tube heating gas jet cooling type continuous annealing furnace,
The heating temperature was 640 to 700 ° C., temper rolling; elongation rate 1.8%, surface treatment; TFS treatment.

Table 4 shows the results. The effect of annealing temperature appears in hardness and elongation at yield. Steel plate G-1 whose annealing temperature is out of the lower limit of the present application has unusually high hardness. This is because recrystallization has not been completed. Steel plate G that is out of the upper limit
-4 has a yield point elongation of 6.4%, which exceeds the allowable limit of 5%. This is because the amount of redissolved solid solution C is large and the crystal grains are too large.

[0037]

[Table 4]

(Example 4) Using Steel I in Table 1, the elongation ratio in temper rolling was changed in four stages within the range of 0.6 to 3.0%, and the effect of the elongation ratio was investigated. Other manufacturing conditions are slab heating temperature; 1200 ° C, hot rolling; finishing plate thickness 2.3 mm, finishing temperature
It was 900 ° C., winding temperature 590 ° C., cold rolling; finished sheet thickness 0.23 mm, continuous annealing; radiant tube heating / gas jet cooling type continuous annealing furnace, heating temperature 670 ° C., surface treatment; tin plating.

The results are shown in Table 5. The higher the amount of Mn, the higher the hardness. The influence of the elongation rate mainly appears in the yield point elongation. The higher it is, the smaller the yield point elongation. In steel sheet I-1 having an elongation of 0.6%, which is lower than the lower limit of 0.8% of the present invention, the yield point elongation exceeds the allowable limit of 5%. The range of extension ratio is I-, which is within the range of claim 2.
In No. 3 and I-4, the yield point elongation is 3.5% or less, which is in a more preferable range.

[0040]

[Table 5]

[0041]

Since the present application is constituted as described above, it is possible to provide a method for producing a can steel sheet which is easy to produce and has excellent weldability without adding expensive Nb or Ti. .

─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Hisanori Enno 1-2 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Katsumi Kojima 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe (56) References JP-A-5-295427 (JP, A) JP-A-6-192745 (JP, A) JP-A-6-207222 (JP, A) JP-A-5-345926 (JP, A) A) JP-A 2-118024 (JP, A) JP-A 63-109121 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21D 9/46-9/48 C21D 8 / 00-8/04 C22C 38/00-38/60

Claims (2)

(57) [Claims] 1. C: 0.0016 to 0.0025% by weight, Mn:
0.05 to 2.0%, Al: 0.025 to 0.13%, N: 0.0030% or less, B: 0.0005 to 0.0024%, and the balance substantially F
e) and inevitable impurities, and using a steel having a composition having a B / N (weight ratio) of 0.5 to 0.8,
The coiling temperature in hot rolling is 400 to 650 ° C, the annealing temperature in continuous annealing with radiant tube heating is 650 to 690 ° C, and the elongation in temper rolling is 0.8 to 4%. A method for producing a steel sheet for an ultra-low carbon can having excellent weldability, which is characterized by the following. 2. The elongation in temper rolling is 1.8 to 4.0%.
The method for producing a steel plate for an ultra-low carbon can having excellent weldability according to claim 1.