JP2002003941A - Method for producing high strength and high toughness electric resistance welded tube for cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength and high toughness electric resistance welded tube for a cylinder free from breakage even in the case that high pressure is repeatedly applied thereto. SOLUTION: In this method for producing a high strength and high toughness electric resistance welded tube for a cylinder, the tube is produced by using a hot rolled coil obtained by subjecting a slab having a composition containing 0.01 to 0.10% C, <=0.3% Si, 1.0 to 2.5$ Mn, <=0.015% P, <=0.005% S, <=0.1% sol.Al, 0.01 to 0.05% Nb and 0.005 to 0.03% Ti and, if required, further containing one or more metals selected from 0.05 to 0.50% Mo and 0.0002 to 0.002% B, wherein a condition of Nb+Ti<=0.055% is satisfied, and the balance Fe with inevitable impurities to hot rolling and coiling the same at a coiling temperature of <=700 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing a steel sheet having a tensile strength of 500 N /
High strength of ² mm or more and ductile fracture surface ratio in ERW weld 5
The present invention relates to a method for manufacturing an electric resistance welded steel pipe for a cylinder, which is a machine structural part requiring high toughness corresponding to a transition temperature of 0% or less of 5 ° C. or less.

[0002]

2. Description of the Related Art Conventionally, a cylinder tube used for a hydraulic cylinder or a pneumatic cylinder is JIS G 3473.
As described in the above, it is manufactured by performing various manufacturing methods or heat treatments, and is generally manufactured by cold drawing a seamless steel pipe or an electric resistance welded steel pipe. In particular,
When manufacturing cylinder tubes with high internal pressure, seamless steel tubes have been used in most cases.

[0003] In recent years, ERW steel pipes are being used instead of seamless steel pipes from the viewpoint of reducing manufacturing costs. Furthermore, there have been cases in which an EG pipe (an electric resistance welded steel pipe other than the hot finish and the cold finish) in which normalizing heat treatment and cold drawing are omitted has been used. In connection with these electric resistance welded steel pipes, the present applicant has proposed a steel pipe having improved toughness while maintaining the strength required for the steel pipe or a method for manufacturing the same (Japanese Patent Application Laid-Open No. 10-212549 and Japanese Patent Application Laid-Open No. H10-212549). See Japanese Unexamined Patent Publication No. Hei 11-199929).

[0004] These steel pipes are electric resistance welded steel pipes in which the toughness of the entire steel pipe is increased mainly by reducing the content of C in the steel and increasing the content of Mn. However, when a cylinder tube manufactured using such an ERW steel pipe is used in an environment where a high internal pressure is applied, cracks may occur in the ERW welded portion and the weld heat affected zone.

More specifically, a cylinder tube manufactured using an ERW steel pipe in which impurities such as inclusions are present in an ERW weld portion, a weld heat affected zone, or in the vicinity thereof has a high internal pressure that causes repeated load. When exposed to such an environment, there is a problem that the electric resistance welded portion is cracked starting from the above impurities. This problem was particularly remarkable in a high-strength ERW steel pipe, since the toughness and fatigue strength in the ERW welded part decreased as the strength of the ERW pipe increased.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an electric resistance welded steel pipe for a cylinder which can be manufactured at a lower cost than a seamless steel pipe.
More specifically, high strength that the ERW weld and the weld heat affected zone are not damaged even when high pressure is repeatedly applied,
An object of the present invention is to provide an electric resistance welded steel pipe having high toughness.

[0007]

Means for Solving the Problems The present inventor has conducted research on the occurrence of cracks in the ERW welded portion and the heat affected zone of the ERW steel pipe, and has completed the present invention.

The gist of the present invention is an electric resistance welded steel pipe for a cylinder shown in the following (1) and (2). (1) In mass%, C: 0.01 to 0.10%, Si: 0.3% or less, Mn:
1.0 to 2.5%, P: 0.015% or less, S: 0.005% or less, sol.
Al: 0.1% or less, Nb: 0.01-0.05%, Ti: 0.005-0.03%
And Nb + Ti ≦ 0.055%, with the balance being Fe
Manufacture of high strength, high toughness electric resistance welded steel tubes for cylinders, characterized in that steel slabs consisting of unavoidable impurities are hot rolled and manufactured using hot rolled coils wound at a winding temperature of 700 ° C or less. Method. (2) In mass%, C: 0.01 to 0.10%, Si: 0.3% or less, Mn:
1.0 to 2.5%, P: 0.015% or less, S: 0.005% or less, sol.
Al: 0.1% or less, Nb: 0.01-0.05%, Ti: 0.005-0.03%
And Nb + Ti ≦ 0.055% is satisfied, and Mo:
Hot-rolled steel slab containing at least one of 0.05 to 0.50% and B: 0.0002 to 0.002%, the balance being Fe and unavoidable impurities, and hot-rolled at a winding temperature of 700 ° C or less. A method for producing an electric resistance welded steel pipe for a high-strength, high-toughness cylinder, characterized by producing using a coil.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the chemical components of the steel used in the present invention are described below. Note that “%” of the chemical component amount is “% by mass”.

C: 0.01 to 0.10% C is an element necessary for securing the strength of steel. If the content is less than 0.01%, sufficient tensile strength cannot be obtained, and if it exceeds 0.10%, the toughness of the ERW weld and the heat affected zone decreases, and welding defects occur in the ERW weld. It will be easier. Therefore, its content is 0.01-0.
10%.

Si: 0.3% or less Si is an element necessary for deoxidizing steel and ensuring the strength of steel. However, if the content exceeds 0.3%, the toughness of the base metal, the ERW welded part and the weld heat affected zone is reduced, and welding defects in the ERW welded part are liable to occur, resulting in reduced workability. Therefore, its content
0.3% or less. Note that Si has the above-mentioned effects even when added in a small amount, and thus its content may be substantially at the impurity level.

Mn: 1.0-2.5% Mn is an element necessary for securing the strength of steel, and has the effect of refining the structure of steel and improving the toughness. If the content is less than 1.0%, sufficient strength and toughness cannot be obtained, and if it exceeds 2.5%, MnO precipitates during ERW and penetrator defects are likely to occur. Therefore, the content was set to 1.0 to 2.5%.

Al: 0.1% or less Al is an element effective for deoxidizing steel and refining the structure of steel. However, if the content exceeds 0.1%, the toughness of the electric resistance welded joint decreases. Therefore, its content
0.1% or less. In addition, since Al has the above-mentioned effect even when added in a small amount, its content may be 0.05% or less.

P: 0.015% or less Since P segregates in steel and lowers the toughness of the base metal, the electric resistance welded portion and the weld heat affected zone, its content is made 0.015% or less.

S: 0.005% or less S combines with Mn, Fe, etc. to form non-metallic inclusions, and lowers the toughness of the base metal, the electric resistance welded portion, and the weld heat affected zone. 0.005% or less.

Nb: 0.01-0.05% Nb has an effect of increasing the strength of steel by forming precipitates, and is also an element effective for refining the structure of steel and particularly improving the toughness of the base metal. It is. In order to secure these effects, it is necessary to contain 0.01% or more.
However, if it exceeds 0.05%, the toughness of the electric resistance welded portion is reduced, so the content was made 0.01 to 0.05%.

Ti: 0.005% to 0.03% Ti is an element effective for promoting the refinement of the structure of steel, and particularly for improving the toughness of an electric resistance welded portion. In order to secure this effect, it is necessary to contain 0.005% or more. However, if the content exceeds 0.03%, the toughness is rather reduced. Therefore, the content is set to 0.005 to 0.03%.

Nb + Ti: 0.055% or less If the total content of Nb and Ti exceeds 0.055%, sufficient toughness cannot be ensured even if their contents are below the respective upper limits. Therefore, the total content of Nb and Ti is set to 0.055% or less. In addition, although the toughness cannot be sufficiently secured when the total content of Nb and Ti is too small, in the present invention, the total of the lower limit values of Nb and Ti,
That is, if it is 0.015% or more, toughness can be secured.

When it is desired to further improve the strength and toughness of the steel, it is preferable to include one or more of Mo and B in addition to the above chemical components. When these elements are added, the reasons for limiting the contents are shown below.

Mo: 0.05-0.50% Mo enhances the strength of steel by solid solution strengthening,
It is an element effective for improving hardenability. In order to obtain this effect, it is necessary to contain 0.05% or more.
However, if it exceeds 0.50%, the toughness decreases,
The content was set to 0.05 to 0.50%.

B: 0.0002-0.002% B is an effective element for increasing the strength of steel. In order to obtain this effect, the content needs to be 0.0002% or more. However, if the content exceeds 0.002%, the toughness of the base metal, the electric resistance welded portion, and the weld heat affected zone decreases, so the content was made 0.0002 to 0.002%.

The production method of the present invention is characterized in that a steel slab having the above chemical composition is hot-rolled and wound at a winding temperature of 700 ° C. or less. Here, the reason why the winding temperature during hot rolling is specified is that if the winding temperature during hot rolling exceeds 700 ° C., the crystals become coarse and sufficient toughness cannot be obtained. The lower limit of the winding temperature during hot rolling is not particularly limited, but may be 300 ° C. or higher from the viewpoint of roll formability.

In the present invention, in order to stabilize the strength and the toughness, an electric resistance welded steel pipe is manufactured using the above-mentioned hot rolled coil wound at a winding temperature of 700 ° C. or less, and then the stress is removed as required. Annealing, annealing, normalizing, quenching, and tempering can be performed, and any of processing such as cold drawing and stress relief annealing after cold drawing can be performed.

[0024]

(Example 1) A steel slab obtained by melting and casting steel having the chemical composition shown in Table 1 was hot-rolled to a winding temperature of 550 ° C.
To produce a hot steel plate having a thickness of 10.7 mm.

[0025]

[Table 1] Next, an ERW welded steel pipe having an outer diameter of 139.8 mm was manufactured by the normal ERW manufacturing process using the above hot steel sheet. Table 2 shows the results of stress annealing of the steel pipe at 600 ° C. and various property tests.

The "tensile strength" in Tables 2 and 3
Shows the results of a tensile test performed using a 12B test piece specified in JIS Z2201. "VTs temperature" is JIS Z2202
The results of the Charpy test in the circumferential direction of the electric resistance welded portion using the V-notch test specimen specified in the above are shown as transition temperatures (° C) at a ductile fracture rate of 50%. Furthermore, "internal pressure fatigue"
With a 500 mm long steel pipe sealed at both ends, a maximum internal pressure of 6
9000kPa hydraulic pressure is repeatedly applied and the number of repetitions is 30
The symbol x indicates that the sample was broken less than 10,000 times, and the symbol ○ indicates that the sample was not damaged even after 300,000 times.

[0027]

[Table 2] As shown in Table 2, Comparative Examples 1 to 8 had a tensile strength of 500 N /
Although keeping the mm ² or more, VTS temperature as high as 20 to 65 ° C., sufficient for toughness is not obtained, damage the electric-resistance welded portion or the welding heat affected zone from the time of loading 100,000 about pressure Began to occur. On the other hand, all of Examples 1 to 13 of the present invention have sufficient strength and toughness with a tensile strength of 600 N / mm ² or more and a vTs temperature of 5 ° C. or less, and no internal pressure fatigue was observed. From the above results, the winding temperature during hot rolling was
Even when the temperature is 700 ° C. or less, an ERW steel pipe manufactured from a steel slab having a chemical composition not in the range specified in the present invention is unsuitable as an ERW steel pipe for a cylinder.

(Example 2) Of the steels having the chemical compositions shown in Table 1 above, steels Nos. 6 to 10, 14 and 15 were smelted and cast, and a steel slab was hot-rolled to a winding temperature. It was wound at 750 ° C. to produce a hot steel plate having a thickness of 10.7 mm. Next, by using the above-mentioned hot steel sheet and performing a normal electric resistance welding manufacturing process,
Table 3 shows the results of producing a 139.8 mm ERW welded steel pipe and performing various property tests.

[0029]

[Table 3] As shown in Table 3, Comparative Examples 9 to 15 had a tensile strength of 500 N /
Although keeping the mm ² or more, VTS temperature as high as 23 to 70 ° C., sufficient for toughness is not obtained, damage the electric-resistance welded portion or the welding heat affected zone from the time of loading 100,000 about pressure Began to occur. From the above results, even if the steel slab having the chemical composition specified in the present invention, the winding temperature is 70
ERW steel pipes made from hot rolled steel sheets above 0 ° C are not suitable as ERW pipes for cylinders.

[0030]

According to the production method of the present invention, the tensile strength is
500 N / mm ² or more high strength, and vTs in electric resistance welding unit
A high-toughness electric resistance welded steel tube for a cylinder having a temperature of 5 ° C. or less can be manufactured. Further, the ERW steel pipe for a cylinder manufactured by the manufacturing method of the present invention has a high pressure of up to 69000 kPa.
Even if the load is repeatedly applied 300,000 times or more, no breakage occurs in the ERW and the heat affected zone.

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4E028 CB04 CB06 4K032 AA01 AA04 AA16 AA17 AA22 AA27 AA29 AA31 AA35 BA03 CE01 CE02

Claims (2)

[Claims] C .: 0.01 to 0.10%, Si: 0.3% by mass%
Mn: 1.0 to 2.5%, P: 0.015% or less, S: 0.005%
Below, sol.Al: 0.1% or less, Nb: 0.01-0.05%, Ti: 0.0
A hot-rolled coil containing a steel slab containing 0.05 to 0.03% and satisfying Nb + Ti ≤ 0.055%, with the balance being Fe and unavoidable impurities, hot rolled and rolled at a winding temperature of 700 ° C or less A method for producing an electric resistance welded steel pipe for a high-strength, high-toughness cylinder, the method comprising: 2. C: 0.01 to 0.10%, Si: 0.3% by mass%
Mn: 1.0 to 2.5%, P: 0.015% or less, S: 0.005%
Below, sol.Al: 0.1% or less, Nb: 0.01-0.05%, Ti: 0.0
Including 05-0.03%, and satisfying Nb + Ti ≦ 0.055%,
Further, a steel slab containing at least one of Mo: 0.05 to 0.50% and B: 0.0002 to 0.002%, the balance being Fe and unavoidable impurities is hot-rolled and wound at a winding temperature of 700 ° C. or less. A method for producing an electric resistance welded steel pipe for a high-strength, high-toughness cylinder, which is produced using the hot-rolled coil taken.