JPH0617542B2 - High strength ERW steel pipe with good pipe expandability - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high-strength electric resistance welded steel pipe (electric suture welded steel pipe) having good pipe expandability, which is usually manufactured by low frequency and high frequency welding.

(Prior Art) In recent years, significant improvements have been made in improving the fuel consumption rate of automobiles.
As one of the countermeasures, various studies have been made to reduce the weight of the vehicle body. Among them, research on hollowing parts that have been manufactured from steel bars has been remarkable, and the replacement of steel bars with electric resistance welded pipes is being actively promoted. When such electric resistance welded pipe parts are used as they are after processing, they have a tensile strength of 45 kgf.
When the component has a high strength of not less than / mm ² or requires a higher strength, it is required to subject the component to heat treatment such as quenching and tempering and induction hardening to further increase the strength.

(Problems to be solved by the invention) The electric resistance welded steel pipe having a tensile strength of less than 45 kgf / mm ² has a low C content and does not contain alloy elements such as Cr and Mo which increase hardenability, and has a heat effect after welding. The degree of curing of the part is low and the ductility is good. Therefore, the pipe expandability is excellent, and the influence of inclusions contained in the metal flow portion of the weld is small, so there are few problems. However, the above high-strength electric resistance welded steel pipe is used in order to secure pipe strength or hardenability. Pipe (eg JI
S G 3445 Carbon steel pipe STM1 for machine structure)
In many cases, the amount of carbon is piped depending on the material.

Therefore, the bead after welding has a structure close to the quenched structure and has a higher hardness than the base metal, and post-annealing (annealing of the welded part) in the pipe forming line alone limits the softening of the welded part. The hardness of the base material cannot be softened.

On the other hand, on the manufacturing side of ERW pipes, the bead on the outer surface is removed by cutting because the rising of the metal flow occurs at the welded part due to the upset during welding, but one end of the metal flow is exposed on the outer surface and the ductility is the most. The bad thickness surface will be exposed.

Therefore, a high-strength electric resistance welded steel pipe having a tensile strength of 45 kgf / mm ² or more causes cracks along the metal flow during pipe expansion due to the above two causes.

Therefore, in order to reduce the hardness of the heat-affected zone of welding, it is the current situation that the structure is homogenized by heat treatment such as annealing or normalizing.

(Means for Solving the Problem) In view of such a situation as described above, the present inventors have studied in detail the factors affecting the pipe expandability of the electric resistance welded steel pipe after the pipe making, and found that the tensile strength was 45 kgf / mm ² or more. The expandability of high strength ERW steel pipe is
It has been found that the above problems can be solved by limiting the rising angle of the metal flow and the amount of sulfur (S) in the steel during pipe making to a certain value or less.

In addition, a small amount of Cr and / or Nb, Ti,
Any one or more of B and Al, in addition to them, a trace amount of C
It has been found that the addition of a is effective in solving the above problems.

According to the present invention, C: 0.05-0.60%, Si:
0.01-1.0%, Mn: 0.30-2.0%, P: 0.03% or less, balance consisting essentially of Fe, and having a tensile strength of 45 kgf / mm ² or more. It is an electric resistance welded steel pipe, and the S content of the steel is the following formula: S ≦ [22−σ / 6−25 (t / D)] × 10 ⁻³ (S in the formula: S content in the steel (wt /% ) Σ: tensile strength of the electric resistance welded steel pipe (kgf / mm ² t: thickness of the electric resistance welded steel pipe (mm) D: outer diameter of the electric resistance welded steel pipe (mm)) Provided is an electric resistance welded steel pipe having a metal flow rising angle of 45 ° or more and 75 ° or less and having good pipe expanding workability.

Further, according to the present invention, the above-mentioned electric resistance welded steel pipe further containing Cr: 0.03 to 1.0%, said Cr and C
a: containing 5 to 100 ppm, Nb: 0.02 to 0.20%, Ti: 0.01 to 0.2
0%, B: 5 to 100 ppm, Al: 0.01 to 0.1
Any one of 0% Cr: 0.03 to 1.0% and any one of the above, Cr in the above amount and any one of the following Nb or less and Ca
Is provided.

In these electric resistance welded steel pipes, by adding 70 g / ton or more of Ca as a pure Ca content at the time of melting the steel, it is possible to have 5 to 100 ppm of Ca as a residual content in the steel.

The present invention solves the problem of the electric resistance welded steel pipe having a tensile strength of 45 kgf / mm ² or more as described above.

C, Si and Mn are tensile strength of ERW steel pipe 45kgf / mm
It is a component necessary to obtain ² or more, and for that purpose, C: 0.05% or more, Si: 0.01% or more, Mn:
It is necessary to add 0.30% or more.

However, C: 0.60%, Si: 1.0%, M
If each of n: 2.0% is exceeded, martensite is likely to be generated in the welded portion after welding and the risk of cracking in the welded portion increases, so the content is set to the above amount or less.

P is 0.03 to secure the toughness of the welded portion of the electric resistance welded steel pipe.
% Or less.

Further, Cr is effective in increasing the strength of the welded portion of the electric resistance welded steel pipe, but if it is less than 0.03%, it has no effect, while if it exceeds 1.0%, martensite is likely to be generated in the welded portion, Since the risk of cracking of the part increases, 1.0% is made the upper limit.

In steels with a tensile strength of 45 kgf / mm ² or more, the amount of S in the steel has a great effect on its pipe expandability, and the sulfide inclusion cutoff is related to the tensile strength and the wall pressure ratio (t / D). The chipping effect is different. It was found that when the amount of S in the steel corresponding to the sulfide-based inclusions exceeds the amount shown by the above formula, cracking occurs during pipe expansion processing.

This formula is an empirical formula derived from the experimental results.

The rise angle of the metal flow of not less than 45 ° and not more than 75 ° can be achieved by controlling the pressure of the squeeze roll.

On the other hand, in order to prevent the deterioration of pipe expandability due to strain age hardening during the manufacture of ERW steel pipe, in order to fix the solid solution N, Nb, T
It is effective to add at least one of i, B, and Al. For that purpose, it is necessary to add at least 0.02%, 0.01%, 5 ppm, 0.01% or more of these elements, respectively. Is. However, these elements are 0.20%, 100ppm, 0.01%, respectively.
Above these values, the effects will be saturated and will rather impair the cleanliness of the steel, so the above amounts are limited. These elements are equivalent in the present invention. However, Al is also an inevitable mixed element, and Al less than the limited amount is an inevitable impurity.

When Al is added alone, nitride (AlN)
Is dependent on the coiling temperature, and hot rolling must be carried out at a coiling temperature of 600 ° C. or higher in order to generate sufficient AlN to control the decrease in ductility due to strain age hardening.

In addition, Ca is added to control the morphology of non-metallic inclusions to be spherical. In this case, the amount of Ca must be at least 5 ppm as a residual amount, but if it exceeds 100 ppm, the cleanliness of the steel will be impaired. It is disadvantageous to be played.

If the rising angle of the metal flow exceeds 75 °, cracks occur along the metal flow, so this angle is limited.

(Examples) Hereinafter, the present invention will be described in detail by examples with reference to the drawings.

Fig. 1 is a diagram showing an example of the hardness distribution in the weld heat affected zone after the seam portion of an electric resistance welded steel pipe equivalent to STKM type 15 is annealed in the pipe making line with a seam annealer. It can be seen that the annealing is not enough to soften the weld.

Figure 2 is a photograph of the steel structure showing the metal flow of the welded part of the electric resistance welded steel pipe. The cut surface of the outer bead exposes the thickest surface with the worst ductility.

(Α is the rising angle in the figure.) These problems are solved by the present invention.

The steels shown in Table 1 were melted by a conventional method in a converter, continuously cast into slabs, hot-rolled at a coiling temperature of 630 ° C., pickled, slitted, and then subjected to pipe forming. When Ca is added (Samples 9, 10, and 14), the Ca content is 2% in the form of Ca-Al alloy.
It was added to the molten steel at a rate of 10 g / ton. Sample 11,
In Nos. 12, 13, and 14 (STKM17 type), annealing was performed after hot rolling pickling. The pipes were manufactured by ordinary high frequency welding into electric resistance welded pipes of various diameters.

The electric resistance welded tube manufactured in this way is expanded with a conical punch having a cone angle of 60 °, and the outer diameter of the raw tube is D _o (m
m), and the outer diameter at the time of crack occurrence was D (mm), and D / D _o was used as an index of pipe expandability.

The test results are the first, along with the chemical composition of the sample, pipe forming conditions, etc.
Shown in the table.

Fig. 3 shows the STK with a tensile strength of 60 to 65 kgf / mm ^{2 in which} the S content is 0.009% or less ([22-σ / 6-25 (t / D)] × 10 ^-3 or less).
M15 class ERW steel pipe (22.2mm diameter x 2.6mm
The relationship between the rising angle of the metal flow and the pipe expandability is shown.

From Table 1 and Fig. 3, the following can be found. (1) In the case of electric resistance welded steel pipe of STKM11 type with a tensile strength of less than 45 kgf / mm ² , even if the strain aging effect is controlled by adding Al (Sample 2) , No improvement in pipe expandability is observed.

(2) On the other hand, the effect of the present invention is recognized in the electric resistance welded steel pipe having a tensile strength of 45 kgf / mm ² or more. That is, in the STKM type 15 steels (Samples 3, 4, 5, and 6), the pipe expandability is improved in Samples 5 and 6 in which the S content and the metal flow rising angle are limited.

(3) In STKM15 type steel, even if Cr is contained, T
Improvement of pipe expandability is recognized by addition of i, Al, B and Ca treatment (addition of Ca).

(4) STKM17 type steel has a large tensile strength of 7 / t.
Although it is a 0 kgf / mm ² class ERW steel pipe, pipe expandability is improved by adding Al or Ca and limiting the metal flow rise angle of S content.

(5) In the high-strength electric resistance welded tube of STKM20 type, the pipe expandability is improved by adding Al and Nb and / or Ti and limiting the S content and the metal flow rising angle.

(Effects of the Invention) As described above, according to the present invention, in any of the steel types, the improvement of the pipe expanding property is recognized, and the pipe expanding can be performed without performing the heat treatment such as the normalizing or the annealing, and It is clear that the simplification of the manufacturing process can contribute to the manufacture of inexpensive steel pipes.

[Brief description of drawings]

FIG. 1 is a diagram showing a hardness distribution of a heat-affected zone of an electric resistance welded steel pipe of STKM 15 grade steel after seam annealing. FIG. 2 is a sketch corresponding to the photograph showing the metal structure showing the metal flow of the welded portion. Fig. 3 shows the STK with a tensile strength of 60 to 65 kgf / mm ^{2 in which} the S content is 0.009% or less ([22-σ / 6-25 (t / D)] × 10 ^-3 or less).
M15 class ERW steel pipe (22.2mm diameter x 2.6mm
The relationship between the rising angle of the metal flow and the pipe expandability is shown.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-53-1673 (JP, A) JP-A-58-123858 (JP, A) JP-A-60-13025 (JP, A) JP-A-58- 174550 (JP, A) JP 56-35751 (JP, A) JP 52-14567 (JP, A)

Claims (6)

[Claims] 1. C: 0.05 to 0.60%, Si: 0.0
1 to 1.0%, including Mn: 0.30 to 2.0%, P:
If less than 0.03%, the balance consists essentially of Fe, 45k
An electric resistance welded steel pipe having a tensile strength of gf / mm ² or more, in which the S content of steel is expressed by the following formula: S ≦ [22−σ / 6-25 (t / D)] × 10 ⁻³ (where S : S content in steel (wt /%) σ: Tensile strength of electric resistance welded steel pipe (kgf / mm ² ) t: Thickness of electric resistance welded steel pipe (mm) D: Outer diameter of electric resistance welded steel pipe (mm)) The electric resistance welded steel pipe with good expandability, which is the amount shown by and the metal flow rising angle of the weld is 45 ° or more and 75 ° or less. 2. C: 0.05 to 0.60%, Si: 0.0
1 to 1.0%, Mn: 0.30 to 2.0%, Cr: 0.
An electric resistance welded steel pipe containing 03 to 1.0%, P: 0.03% or less, the balance being substantially Fe, and having a tensile strength of 45 kgf / mm ² or more, in which the S content of steel is The following equation S ≦ [22−σ / 6-25 (t / D)] × 10 ⁻³ (wherein S: S content in steel (wt /%) σ: tensile strength of the electric resistance welded steel pipe (kgf / mm ² ) t: wall thickness of ERW steel pipe (mm) D: outer diameter of ERW steel pipe (mm)), and the metal flow rising angle of the weld is 45 ° or more and 75 ° or less ERW steel pipe with good pipe expanding workability. 3. C: 0.05 to 0.60%, Si: 0.0
1 to 1.0%, Mn: 0.30 to 2.0%, Cr: 0.
03-1.0%, including Ca: 5-100 ppm, P:
If less than 0.03%, the balance consists essentially of Fe, 45k
An electric resistance welded steel pipe having a tensile strength of gf / mm ² or more, in which the S content of steel is expressed by the following formula: S ≦ [22−σ / 6-25 (t / D)] × 10 ⁻³ (where S : S content in steel (wt /%) σ: Tensile strength of electric resistance welded steel pipe (kgf / mm ² ) t: Thickness of electric resistance welded steel pipe (mm) D: Outer diameter of electric resistance welded steel pipe (mm)) The electric resistance welded steel pipe with good expandability, which is the amount shown by and the metal flow rising angle of the weld is 45 ° or more and 75 ° or less. 4. C: 0.05-0.60%, Si: 0.0
1 to 1.0%, Mn: 0.30 to 2.0% and N
b: 0.02 to 0.20%, Ti: 0.01 to 0.20
%, B: 5 to 100 ppm, Al: 0.01 to 0.10.
%, Including one of the following, P: 0.03% or less,
The balance is substantially Fe and is an electric resistance welded steel pipe having a tensile strength of 45 kgf / mm ² or more, and the S content of the steel is S <= 22-σ / 6-25 (t / D)] × 10 ^-3 (S in the formula: S content in steel (wt /%) σ: Tensile strength of the electric resistance welded steel pipe (kgf / mm ² ) t: Thickness of the electric resistance welded steel pipe (mm) D: Electric resistance welding An electric resistance welded steel pipe with good expandability that is the amount indicated by the outer diameter (mm) of the steel pipe and the rising angle of the metal flow at the weld is 45 ° or more and 75 ° or less. 5. C: 0.05 to 0.60%, Si: 0.0
1 to 1.0%, Mn: 0.30 to 2.0%, Cr: 0.
03-1.0% and Nb: 0.02-0.20%,
Ti: 0.01 to 0.20%, B: 5 to 100 ppm,
E: Electric resistance sewing containing Al: 0.01 to 0.10%, P: 0.03% or less, the balance being substantially Fe, and having a tensile strength of 45 kgf / mm ² or more. In a steel pipe, the S content of steel is expressed by the following formula: S ≦ [22−σ / 6−25 (t / D)] × 10 ⁻³ (S in the formula: S content in steel (wt /%) σ : Tensile strength of ERW steel pipe (kgf / mm ² ) t: Thickness of ERW steel pipe (mm) D: Outer diameter of ERW steel pipe (mm)) ERW steel pipe with a good flow-expansion workability with a flow rising angle of 45 ° or more and 75 ° or less. 6. C: 0.05 to 0.60%, Si: 0.0
1 to 1.0%, Mn: 0.30 to 2.0%, Cr: 0.
03-1.0%, Ca: 5-100 ppm and Nb:
0.02 to 0.20%, Ti: 0.01 to 0.20%,
B: 5 to 100 ppm, Al: 0.01 to 0.10%, and P: 0.03% or less, the balance consisting essentially of Fe, and tensile of 45 kgf / mm ² or more An electric resistance welded steel pipe having strength, in which the S content of steel is expressed by the following formula: S ≦ [22−σ / 6−25 (t / D)] × 10 ⁻³ (S in the formula: S content in steel) (Wt /%) σ: Tensile strength of the electric resistance welded steel pipe (kgf / mm ² ) t: Thickness of the electric resistance welded steel pipe (mm) D: The amount indicated by the outer diameter (mm) of the electric resistance welded steel pipe, Also, an electric resistance welded steel pipe with good pipe expansion workability, in which the metal flow rising angle of the welded portion is 45 ° or more and 75 ° or less.