JPH04103718A - Production of ultrahigh tensile strength resistance welded tube - Google Patents

Abstract

PURPOSE:To produce an ultrahigh tensile strength resistance welded tube by subjecting a slab of a steel with a specific composition for tube making to hot rolling under specific temp. conditions and to coiling, producing a resistance welded tube by the use of the resulting coiled hot rolled steel plate, and then performing heat treatment at specific temp. CONSTITUTION:A slab of a steel having a composition in which 0.005-0.30%, by weight, C, 0.05-1.5% Si, 1.0-3.0% Mn, <0.02% P, <0.006 S, and either or both of 0.7-2.0% Cu and < 1.5% Mo or further one or two kinds among <1.5% Ni, <2.0% Cr, <0.1% Nb, and <0.10% V are incorporated or, instead of Ni, Cr, Nb, and V, 0.01-0.15% Ti, 0.0003-0.003% B, and <0.005% N are added is hot-rolled and finish rolling is completed at a temp. between the Ar3 point and 950 deg.C, and the resulting hot rolled plate is coiled at 300-500 deg.C. After a resistance welded tube is produced by using this hot rolled plate as a stock, annealing is applied to this tube at 500-650 deg.C. Successively, the above tube is worked into round tube, square tube, tube of special form, etc., by means of cold tube drawing, followed by annealing. By this method, the ultrahigh tensile strength resistance welded tube can stably, be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a manufacturing method for ultra-high tensile resistance welded steel pipes used for structural members of automobiles and the like.

[Conventional technology]

Thorough weight reduction is being considered for structural members of automobiles, etc. in order to improve fuel efficiency and protect the environment, and as one measure to achieve both safety and safety, some parts have been reduced in weight by 100 kgf/
Ultra-high tensile strength steel pipes exceeding - are being adopted.

In general, the method of increasing the strength of ERW steel pipes is
2-114519, etc. to increase the strength of the hot rolled sheet material, and Nisshin Steel Technical Report No. 48, p. 88, etc. There is a method of pipe-making and tempering, that is, quenching or quenching and tempering.

[Problem to be solved by the invention]

There are two types of conventional techniques as described in the section on conventional techniques. First, JP-A-52-114519
The method of increasing the strength of the hot-rolled sheet material as described in the above publication has two problems: (1) the strength of the hot-rolled sheet cannot be sufficiently increased and an ultra-high-tensile resistance-welded needle tube cannot be obtained; ) Even if the strength of the hot-rolled sheet is sufficient, there are problems such as cracks occurring during ERW pipe manufacturing due to poor ductility, and this method is not industrially viable as a manufacturing method for ultra-high tensile ERW mesh pipes.

Next, there is a method of performing quenching or quenching and tempering after forming the ERW pipe. The manufacturing process in this case is shown in FIG.

This method not only requires dedicated heat treatment equipment and requires special attention to ensure the dimensions, shape, and materials.
This is a major obstacle to the widespread use of ultra-high tensile resistance welded steel pipes, which inevitably leads to extremely high costs in terms of capital investment and productivity. Furthermore, it is completely inappropriate as a manufacturing method for square steel pipes and deformed steel pipes, which are attracting attention as structural members with higher rigidity.

The present invention aims to solve the problems in the manufacturing method of ultra-high tensile resistance welded steel pipes.

[Means to solve the problem]

The gist of the present invention is as follows.

(1) C: 0.005-0.30% by weight, Si: 0
．． 05-1.5%, Mn: 1.0-3.0%, P
: 0.02% or less, S: 0.006% or less, ^l
: In addition to 0.01~0.08%, Cu:0.7~
2.0%, Mo: 1.5% or less of one kind or two kinds, the balance consisting of Fe and unavoidable elements is hot rolled to a thickness of 950 ° C. or less A r 3 transformation point or more A method for manufacturing ultra-high tensile resistance welded steel pipes, which comprises finishing finish rolling, then winding at 300 to 500°C, and heat-treating at 500 to 650°C after forming the electric resistance welded pipe.

(2) The pipe steel material described in 1 above further contains Ni: 1.5% or less, Cr: 2.0% or less, Nb: 0.1% or less, and V: 0.
．． The method for manufacturing ultra-high tensile resistance welded steel pipes according to item 1 above, which contains 10% or less of one or more types.

(3) Weight Te C: 0.005-0.30%, Si: 0
．． 05-1.5%, Mn: 1.0-3.0%, P
: 0.02% or less, S: 0.006% or less, AI:
0.01~0.08%, Ti:o, oi~0.15%
, B: 0.0003-0.003%, N: 0.0
In addition to 0.05% or less, Cu: 0.7 to 2.0%, Mo:
A pipe steel material containing 1.5% or less of one or two types, with the balance consisting of Fe and unavoidable elements is hot-rolled to a thickness of 95%.
Finish rolling is completed at 0°C or lower and Ar3 transformation point or higher, and then winding is continued at 300-500°C, and after ERW pipe forming, 500-65
A manufacturing method for ultra-high tensile resistance welded steel pipes characterized by heat treatment at 0°C.

(4) The pipe steel material described in 3 above further contains Ni: 1.5% or less, Cr: 2.0% or less, Nb: 0.1% or less, ■: 0
．． The method for manufacturing ultra-high tensile resistance welded steel pipes according to the above item 3, which contains 10% or less of one or more types.

(5) The ultra-high-tensile ERW according to any one of 1 to 4 above, characterized in that the ERW pipe is heat-treated after forming, and then subjected to cold drawing processing to form a round pipe, square pipe, or irregularly shaped pipe. Steel pipe manufacturing method.

(6) The method for manufacturing ultra-high tensile resistance welded steel pipes according to item 5 above, characterized in that the round tube, square tube, or irregularly shaped tube is annealed after cold drawing.

The present invention will be explained in detail below. Claims 1 to 4 in FIG.
FIG. 2 shows the manufacturing process according to the invention as described in claim 5, and FIG. 3 shows the manufacturing process according to the invention as claimed in claim 6.

In the conventional process, as described above, if an ultra-high tensile mesh pipe is to be manufactured, it is necessary to perform quenching or quenching and tempering after forming the ERW pipe. This method not only requires dedicated heat treatment equipment, requires special attention to ensure dimensions, shape, and material quality, but also requires significantly higher costs in terms of equipment investment and productivity. Furthermore, as a manufacturing method for square steel pipes and deformed steel pipes, which are attracting attention as structural members with higher rigidity, it is extremely difficult to ensure uniform hardening and size and shape, and this cannot be realized as an industrial production method. Furthermore, even if ultra-high-strength steel plates were made, they would not be able to be formed or welded during pipe manufacturing.

Therefore, in the present invention, we have created an ultra-high tensile type pipe without quenching, using non-temperature heat treatment after pipe making and additional cold drawing processing as needed. i! The aim is to manufacture steel pipes.

First, the reasons for limiting the components of the steel material for pipe making used in the present invention will be explained.

The lower the amount of C, the better the ductility and the better workability, but since the required strength cannot be obtained, the lower limit is set at 0.005%.
And so. In addition, if it exceeds 0.30%, cold workability such as formability during pipe making and toughness tend to decrease, and the heat affected zone hardens during pipe forming welding of ERW steel pipes, resulting in poor workability. Therefore, the upper limit was set at 0.30%.

In the case of killed steel, it is difficult to suppress Si to less than 0.05% due to steel manufacturing technology, and if it exceeds 1.5%, the surface quality deteriorates significantly due to scale formation, so the Si content is 1.5%.
The upper limit was %.

Regarding Mn, if it is less than 1.0%, strength will be insufficient, and if it exceeds 3.0%, cracks may occur due to lack of ductility during processing such as forming during pipe manufacturing.
The lower limit was 1.0% and the upper limit was 3.0%.

P is an element that is unavoidably mixed during steelmaking, but 0.02
If it exceeds 0.02%, weld cracks are likely to occur particularly during electric resistance welding of ultra-high tensile steel pipes, so the upper limit was set at 0.02%.

Like P, S is an element that is unavoidably mixed during manufacturing, and 0.
If it exceeds 0.006%, weld cracks are likely to occur during electric resistance welding, so the upper limit was set at 0.006%. In order to further suppress cracking caused by S during electric resistance welding, Ca, which is an element that controls the morphology of MnS, may be added.

In the case of killed steel, it is difficult to keep AI below 0.01% due to steel manufacturing technology, and if it exceeds 0.08%, it can cause cracks in the slab and internal defects due to the formation of giant oxide inclusions. The upper limit was set at 0.08% because it is easy to use.

Cu has the characteristic of being precipitated by aging treatment after solution treatment, and is effective in increasing the strength by heat treatment after pipe making, with almost no effect on the strength before pipe making. In this case, 0
．． If it is less than 7%, the effect is poor, and if it is added in excess of 2.0%, there is no improvement in the effect, so the lower limit was set to 0.7% and the upper limit was set to 2.0%. Next, although Ni is effective for improving strength and ductility, it is added at a limit of 1.5% to produce the effect. However, when the strength and ductility are sufficient, there is no need to add it.

MO also has the characteristic of being precipitated by aging treatment after solution treatment, and is effective in increasing the strength by heat treatment after pipe forming, without having almost any effect on the strength before pipe forming. In this case, 1
, since there is no improvement in the effect even if added in excess of 5%,
The upper limit was set at 1.5%.

Next, regarding Ni, Cr, Nb, and V, all of them are elements that increase the strength of steel materials, and their addition within a range that does not excessively impair ductility is effective in manufacturing ultra-high tensile resistance welded steel pipes. . Therefore, in order not to excessively impair ductility, Ni, C
The upper limits of r, Nb, and V are set to 1.5%, 2.0%, and 0, respectively.
．． 10% and 0.10%.

Next, the feature of the invention of claim 3 is that Ti, B, N
It is.

Ti is an important element for controlling strength, but 0.
If it is less than 0.01%, the strength will be insufficient, and if it is added in excess of 0.15%, the effect will not improve, so the lower limit is set at 0.01%.
, the upper limit was set at 0.15%.

B is an essential element in order to delay ferrite transformation in the cooling process and obtain a high-strength transformed structure, but if it is less than 0.0003% in the composition of the steel material for pipe making of the present invention, the strength will be insufficient; Boron exceeds
The lower limit is set to 0.0003% and the upper limit is set to 0.003%, as con5tituent is generated and the ductility is significantly reduced.
And so.

N is an element that is unavoidably mixed during steel manufacturing, but 0.00
If it exceeds 5%, the strength-increasing effects of Ti and B will be inhibited, resulting in insufficient strength, so the upper limit was set at 0.005%.

Next, the manufacturing process will be explained. The manufacturing conditions are as per claims 1-
4 are the same.

According to the present invention, a steel having the above components is heated to 950% during hot plate thickness rolling.
'C or below A r Finish rolling is completed at 3 transformation points or above. This is to optimize the balance of strength and ductility by performing appropriate low-temperature rolling, and if the finish rolling end temperature exceeds 950°C, there will be no rolling in the non-recrystallized region, resulting in deterioration of strength and ductility. , A r Below the 3 transformation point, the strength increases by rolling in the two-phase region, but the ductility significantly decreases. Therefore, by finishing the finish rolling of the steel having the above composition at a temperature of 950°C or below and above the A r 3 transformation point during hot plate thickness rolling, and then winding it under the conditions of the present invention, a material with an excellent balance of strength and ductility can be obtained. be able to.

The coiling temperature is 300 to 500°C, and the lower limit prevents deterioration of ductility due to martensite formation, and the upper limit suppresses precipitation of Cu and MO before pipe forming, softens the plate, and facilitates pipe forming. Also, it was limited in order to prevent cracks from forming.

After making the ERW pipe, heat treatment is applied at 500 to 650°C to produce Cu,
Mo is precipitated to increase strength through age hardening. If the heat treatment temperature is less than 500"C, Cu/Mo precipitation will be insufficient, and if it exceeds 650"C, over-aging precipitation will occur, both of which are not suitable for fully utilizing the precipitation hardening of Cu-Mo.

As described above, the present invention is characterized in that, while taking into account ductility and toughness, hot-rolled sheets have low strength by high-temperature winding to make them easier to form into pipes, and a predetermined strength is obtained by heat treatment after forming the pipes.

Although the methods according to claims 1 to 4 have been described above, methods according to claims 5 and 6 may also be used. FIG. 2 shows the process according to the method according to claim 5, and FIG. 3 shows the process according to the method according to claim 6, but by adding cold pipe drawing according to the method according to claim 5, Furthermore, it is possible to achieve ultra-high tensile strength and to manufacture square steel pipes and deformed steel pipes. If it is desired to obtain a steel pipe with higher ductility, annealing may be added according to the method described in claim 6.

〔Example〕

Table 1 shows the results of making electric resistance welded steel pipes of size φ34.0×t2.1 by the method of the present invention and by the conventional method as a comparative example.

As shown in Table 1, according to the present invention, a material steel plate with an excellent balance of strength and ductility can be manufactured by appropriately controlling the chemical composition, finish rolling temperature during hot plate thickness rolling, and coiling temperature. By making pipe making possible and further adding heat treatment after pipe making, it is possible to obtain ultra-high tensile resistance welded steel pipes with an excellent balance of strength and ductility in both the base metal and welded parts. By adding cold pipe drawing processing after heat treatment,
Furthermore, it is also possible to achieve ultra-high tensile strength.

〔Effect of the invention〕

If you try to manufacture ultra-high-strength steel pipes using conventional processes, it is necessary to quench or quench-temperate them after making the ERW pipes, which requires dedicated heat treatment equipment and requires special measures to ensure the dimensions, shape, and materials. Not only did this require careful attention, but it also resulted in extremely high costs in terms of capital investment and productivity. Furthermore, the method of manufacturing square steel pipes and deformed steel pipes, which are attracting attention as structural members with higher rigidity, is extremely difficult to harden uniformly and ensure the same dimensions and shape, making it unfeasible as an industrial production method. Ta. According to the present invention, it is possible to manufacture ultra-high-strength electric resistance welded steel pipes without such problems in industrial productivity and economy, and therefore the present invention makes an extremely large contribution to industry.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the manufacturing steps of the method according to claims 1 to 4,
FIG. 2 is a diagram showing the manufacturing process of the method according to claim 5, and FIG.
The figure shows the manufacturing process of the method according to claim 6, and FIG. 4 shows the conventional manufacturing process. (Kitori) 300 ~ 5α Ishiji (den)
Creation) Ea F Shin-Po F1 [“Sho-Kadan” hit

Claims (6)

[Claims] (1) C: 0.005-0.30% by weight, Si: 0.
05-1.5%, Mn: 1.0-3.0%, P: 0.0
2% or less, S: 0.006% or less, Al: 0.01-0
．． In addition to 0.08%, Cu: 0.7-2.0%, Mo: 1
．． A pipe steel material containing 5% or less of one or two types, with the balance consisting of Fe and other unavoidable elements is hot-rolled to a thickness of 950.
Finish rolling is completed at Ar_3 transformation point or higher below ℃, then winding is continued at 300 to 500℃, and after ERW pipe forming, 500 to 65
A manufacturing method for ultra-high tensile resistance welded steel pipes characterized by heat treatment at 0°C. (2) The pipe steel material according to claim 1 further contains 1.5% Ni.
Below, Cr: 2.0% or less, Nb: 0.1% or less, V:
The method for producing an ultra-high-strength electric resistance welded steel pipe according to claim 1, which contains one or more kinds in an amount of 0.10% or less. (3) C: 0.005-0.30% by weight, Si: 0.
05-1.5%, Mn: 1.0-3.0%, P: 0.0
2% or less, S: 0.006% or less, Al: 0.01-0
．． 08%, Ti: 0.01-0.15%, B: 0.00
In addition to 03 to 0.003%, N: 0.005% or less,
A pipe steel material containing Cu: 0.7 to 2.0%, Mo: 1.5% or less, and the balance consisting of Fe and unavoidable elements is hot rolled to a thickness of 950°C or less Ar_3 A method for manufacturing an ultra-high-strength electric resistance welded steel pipe, which comprises completing finish rolling at a temperature above the transformation point, then winding at 300 to 500°C, and heat-treating at 500 to 650°C after forming the electric resistance welded pipe. (4) The pipe steel material according to claim 3 further contains 1.5% Ni.
Below, Cr: 2.0% or less, Nb: 0.1% or less, V:
4. The method for producing an ultra-high-strength electric resistance welded steel pipe according to claim 3, which contains one or more kinds in an amount of 0.10% or less. (5) The ultra-high tensile electric wire according to any one of claims 1 to 4, characterized in that the electric resistance welded pipe is heat-treated after forming, and then cold drawing processing is added to form a round pipe, square pipe, or irregularly shaped pipe. Manufacturing method of sewn steel pipe. (6) The method for manufacturing an ultra-high tensile resistance welded steel pipe according to claim 5, characterized in that the round tube, square tube, or irregularly shaped tube is annealed after cold drawing.