JP2013006207A - Method for manufacturing high-strength thick electric resistance welded steel pipe excellent in sour resistant property of electric resistance welded part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a high-strength thick electric resistance welded steel pipe excellent in a sour resistant property of an electric resistance welded part, wherein hydrogen induced cracking does not occur in the electric resistance welded part in HIC (Hydrogen Induced Cracking) test of the NACE regulation.SOLUTION: In the electric resistance welded part, by plastically deforming a welded end face, a welded end part shape just before electric resistance welding is formed in a groove shape having a taper-like pipe inner face side groove part 6 wherein a groove width is (1/7)t to (3/7)t from a parallel part 5 of the middle in a t direction to the pipe inner face side, with respect to a plate thickness t direction and wherein a groove angle is 15-45°, and a taper-like pipe outer face side groove part 7 wherein a groove width is (1/7)t to (3/7)t from the parallel part to the pipe outer side and wherein a groove angle is 15-45°, the equal circle diameter of each of oxides 1 in the electric resistance welded part is 20 μm or below, and the equal circle diameter of a cluster 2 that is a group wherein a plurality of oxides gather together at the nearest neighbor interval of 100 μm or below is 300 μm or below.

Description

  The present invention relates to a method for producing a high-strength thick-walled electric resistance welded steel pipe excellent in sour resistance of an electric resistance welded portion, and more specifically, by optimizing the welded end face shape of the electric resistance welded pipe material, High-strength thick-walled electric stitching with excellent sour resistance in ERW welds that limits the equivalent circle diameter of the oxide alone and in the weld seam and suppresses hydrogen-induced cracking (HIC) starting from the seam The present invention relates to a method for manufacturing a steel pipe.

  Here, “excellent sour resistance” means that a specimen including an ERW welded part is subjected to a HIC test that is immersed in a solution A solution specified by NACE at 25 ° C. for 96 hours. It means that the plate thickness direction crack ratio (CTR) measured by ultrasonic flaw detection perpendicular to the weld seam surface is less than 1.5%. “High strength” means strength of API (American Petroleum Institute) standard grade X65 or higher, and “thick” means that the thickness is 10 mm or more.

  Conventionally, ERW steel pipes for high-strength, thick-line pipes have been subjected to heat input adjustment and V-shape angle adjustment depending on experience from the viewpoint of improving welded part quality. Qualitatively, the weld quality has been improved qualitatively by high heat input and proper V-shape angle (approximately 2 to 3 degrees). However, the adjustment based on such experience does not always guarantee 100% sour resistance performance, and sometimes significant HIC (hydrogen induced cracking) occurs and cannot be suppressed. .

  On the other hand, the molten steel produced by melting in the converter is vacuum degassed and / or Mn, Si deoxidized so that the oxygen in the molten steel is 250 ppm or less, then the alloy composition is Ti: 10 to 70 wt%, the balance: Fe , Mn, Si, one or more types and alloys that are inevitable impurities are added to molten steel, and steel with a specific steel composition is continuously cast with high toughness for ERW steel pipes with excellent sour resistance Is known (see Patent Document 1). Thereby, it is said that only the oxide inclusions having a Ti oxide as a main component and a particle size of 200 μm or less are contained in the steel, so that the sour resistance of the ERW welded portion can be improved.

Japanese Patent No. 3293024

The conventional ERW steel pipe manufacturing method based on the qualitative welding condition management described above has not yet achieved a product that exhibits stable and excellent sour resistance properties. Moreover, there is a concern that the method of Patent Document 1 is limited to Ti-containing steel and its application range is narrow. These points were problems.
The present invention solves the above-mentioned problems, and does not generate hydrogen-induced cracks in the ERW welds in the NACE stipulated HIC test, regardless of whether or not Ti is contained. An object of the present invention is to provide a method for producing a meat-electrically welded steel pipe.

  The inventors have various heat input conditions for welded end faces and groove shape conditions for welded end faces of Ti-containing and non-Ti-containing materials of ERW steel pipes for high-strength thick line pipes of API standard X65 and X70 grades. Conduct a modified ERW welding experiment and investigate in detail the relationship between the form of oxide remaining in the ERW weld (by SEM observation) and the sour resistance of the ERW weld (HIC test results stipulated by the NACE) did.

  As a result, regardless of the presence or absence of Ti, as shown in FIG. 2, the individual equivalent circular diameters of the oxide 1 are 20 μm or less, and a plurality of oxides have a spacing of 100 μm or less. It was found that hydrogen-induced cracking does not occur only when the equivalent circular diameter of cluster 2 which is a cluster gathered together (however, it is over 0 μm) is 300 μm or less. Here, the equivalent circular diameter is a diameter of a circle having the same area as the target figure in the cross-sectional view. When the object is the cluster, the cluster figure is a figure surrounded by the outermost tangent line 3 of the group of oxides as shown in FIG.

  In order to achieve the oxide form as described above, the tube material whose initial shape is a strip shape is dispensed, and then formed into a tubular shape, and the edge of the V shape formed (to be welded corresponding to the band width end) 1), the welded end faces are plastically deformed until they are brought into contact with each other, and the welded end shape of the tube blank 10 immediately before ERW welding is changed to the groove shape shown in FIG. With respect to the plate thickness t direction, a taper having a groove width b = (1/7) t to (3/7) t and a groove angle a = 15 to 45 ° from the parallel portion 5 in the middle of the t direction to the inner surface of the tube. The inner pipe-side groove portion 6 and the parallel portion 5 to the outer side of the pipe have a groove width d = (1/7) t to (3/7) t and a groove angle c = 15 to 45 °. The present invention has been made by obtaining the knowledge that it is extremely important to make the groove shape having the outer surface side groove portion 7 of the tube.

That is, the present invention is as follows.
(1) After the tube material having an initial shape of a strip plate is dispensed, the welded end surfaces are plastically deformed after being formed into a tubular shape and joining the welded end surfaces that are the edges of the formed V shape. In this case, the shape of the welded end immediately before the ERW welding has a groove width of (1/7) t to (3/7) t from the parallel part in the middle of the t direction to the inner surface of the pipe with respect to the thickness t direction. , A taper-shaped inner surface side groove portion with a groove angle of 15 to 45 °, a groove width from the parallel portion to the tube outer side is (1/7) t to (3/7) t, and the groove angle is As a groove shape having a taper tube outer surface side groove portion of 15 to 45 °, each equivalent circular diameter of the oxide in the ERW weld portion is 20 μm or less, and a plurality of the oxides are the largest. An electro-welded welded portion having an equivalent circular diameter of 300 μm or less, which is a cluster of clusters gathered at an adjacent interval of 100 μm or less, is obtained. Method of producing a high strength thick electric resistance welded steel pipe with excellent properties.
(2) The said pipe | tube raw material is the mass%, C: 0.01-0.15%, Si: 0.005-0.9%, Mn: 0.2-1.3%, P: 0.01 %, S: 0.01% or less, Al: 0.1% or less, the balance being Fe and inevitable impurities, sour resistance of the ERW weld as described in (1) above A manufacturing method for high strength thick-walled ERW steel pipes with excellent characteristics.
(3) In the above (2), the pipe material contains, by mass%, one or two kinds selected from Cu: 0.5% or less and Ni: 0.5% or less. The manufacturing method of the high intensity | strength thick-walled ERW steel pipe excellent in the sour-proof characteristic of the described ERW welding part.
(4) The above tube material (2) or (2), wherein the pipe material contains one or two kinds selected from Cr: 3.0% or less and Mo: 2.0% or less in mass%. The method for producing a high-strength thick-walled ERW steel pipe excellent in sour resistance of the ERW weld as described in (3).
(5) The tube material contains, by mass%, one or more selected from Nb: 0.1% or less, V: 0.1% or less, Ti: 0.1% or less. The method for producing a high-strength thick-walled electric-welded steel pipe excellent in sour-resistance characteristics of the ERW weld according to any one of (2) to (4) above.
(6) The tube material contains, by mass%, Ca: 0.005% or less, sour resistance of the ERW weld according to any one of (2) to (5) above A manufacturing method for high strength thick-walled ERW steel pipes with excellent characteristics.

  According to the present invention, an ERW steel pipe for high-strength thick-walled line pipes with excellent sour resistance in an ERW welded part that does not generate hydrogen-induced cracks in an ERW welded part in a NACE-defined HIC test in a wide composition range. Can provide.

It is sectional drawing which shows the to-be-welded end face groove shape requirement of this invention. It is explanatory drawing of the oxide form requirements of this invention.

[Oxide morphology requirements]
First, the oxide form requirements of the present invention will be described.
According to the knowledge of the inventors, the end face to be welded is oxidized and an oxide is generated at the time of ERW welding, but the generated oxide is discharged along the flow of molten steel pushed out by abutting pressure welding. At this time, it is difficult for all the oxides to be discharged, and some of the oxides remain in the ERW weld, but when the equivalent circular diameter of the remaining oxides exceeds 20 μm, It can be the starting point of HIC. Therefore, it was limited that each equivalent circular diameter of the oxide in the ERW welded portion was 20 μm or less.

  In addition, the oxide remaining in the electric resistance welded portion is dispersed in an unspecified range. A group in which a plurality of dispersed oxides gather together at a re-adjacent interval of 100 μm or less behaves as if it is one oxide, and may become a starting point of HIC. This group is defined as a cluster, and the conditions under which the cluster becomes the starting point of HIC were determined by the above-mentioned ERW welding experiment. As shown in FIG. 2, the outermost tangent line 3 of the group of oxides 1 forming cluster 2 is obtained. It was found that if the equivalent circular diameter of the enclosed region (that is, the equivalent circular diameter of the cluster) was 300 μm or less, the cluster would not be the starting point of HIC. Therefore, the equivalent circular diameter of the cluster is limited to 300 μm or less.

By the way, the reason why the thickness of 10 mm or more is defined as “thick” is that the influence of HIC is small when the thickness is less than 10 mm. However, if the thickness is less than 11.9 mm, the HIC sensitivity is relatively small and the HIC suppressing effect of the present invention is not noticeable. Therefore, in the present invention, the thickness is preferably 11.9 mm or more.
The reason why the API standard grade X65 or higher is defined as “high strength” is that the low grade of less than X65 has a low HIC cracking susceptibility, and a sour-resistant material can be produced without any practical problems.

[Manufacturing process]
In the present invention, basically, a tube material whose initial shape is a band plate shape is formed into a tubular shape, and the edges of the formed V shape (corresponding to the end portions of the band width) are brought into contact with each other and electro-welded. However, in the prior art, an oxide having an equivalent circular diameter of more than 20 μm or a cluster having an equivalent circular diameter of more than 300 μm exists at any part in the pipe length direction of the ERW weld. .

  On the other hand, according to the manufacturing method of the present invention, the adoption of the groove shape shown in FIG. 1 allows the molten steel to smoothly discharge the oxide during the electric resistance welding, and the oxide in the electric resistance welding portion. Can meet the form requirements. The numerical range of any one of the four factors of the groove angle a on the tube inner surface side, the groove width b on the same side, the groove angle c on the tube outer surface side, and the groove width d on the same side is the actual value range. If it deviates from the scope of the invention, the oxide form requirement is not satisfied, and the effect of improving sour resistance cannot be obtained.

  The groove processing of the welded end is performed by plastic deformation. The groove processing is preferably performed at the end of the roll forming step for forming into a tubular shape from the viewpoint of avoiding the disturbance of the groove shape due to roll forming after the groove processing. In that case, a method other than plastic deformation (Cutting, grinding, etc.) incurs the disadvantage of adding equipment to the pipe making line. The plastic deformation process does not cause such a disadvantage because an existing roll forming roll can be used. Most preferably, in fin pass forming, which is the final stage of roll forming, a fin roll whose fin shape is adjusted to a groove-shaped female die equivalent shape is used.

[Chemical composition]
In the method for manufacturing an electric resistance welded steel pipe according to the present invention, the chemical composition (abbreviated composition) is taken into consideration by a customer who places importance on lowering the transportation cost of the steel pipe, considering the overall cost reduction when laying the line pipe. In consideration of requirements, it was designed based on a composition that can achieve high strength (API standard X65 grade or higher). The reasons for limiting the preferred ranges for the individual components will be described below. Each component content unit of the composition is mass% and is abbreviated as%. The composition of the base material part is adjusted at the melting stage of the tube material. The composition of the welded portion is almost the same as the composition of the base metal part because the electro-welding process does not involve the addition of alloying elements.
(C: 0.01 to 0.15%) C is an element that contributes to precipitation strengthening as a carbide, but if it is less than 0.01%, sufficient strength cannot be secured, while if it exceeds 0.15%, pearlite. In addition, the second-phase structure fraction such as martensite increases, making it difficult to ensure the required sour resistance. For this reason, C: 0.01 to 0.15%. In addition, More preferably, it is C: 0.02-0.07%.
(Si: 0.005 to 0.9%) Si is added for deoxidation, but if it is less than 0.005%, the deoxidation effect is not sufficient. Si: 0.005 to 0.9% is used for significant deterioration.
(Mn: 0.2 to 1.3%) Mn is added to ensure strength and toughness, but if it is less than 0.2%, the effect is not sufficient. Since the fraction increases and it is difficult to ensure excellent sour resistance, Mn: 0.2 to 1.3%.
(P: 0.01% or less) P is an element that deteriorates the electric resistance weldability, but if it is 0.01% or less, there is no problem, so P: 0.01% or less.
(S: 0.01% or less) In general, S is a MnS inclusion in steel, and it is better as it is smaller because it becomes the starting point of HIC. If it is 0.01% or less, there is no problem, so S: 0.01% or less.
(Al: 0.1% or less) Al is added as a deoxidizer, but if it exceeds 0.1%, the cleanliness of the steel decreases and the toughness deteriorates, so Al: 0.1% or less .

For the purpose of further improving the strength, sour resistance, etc. of the electric resistance welded steel pipe, in addition to the above components, one or two selected from Cu: 0.5% or less and Ni: 0.5% or less Species, Cr: 3.0% or less, Mo: One or two selected from 2.0% or less, Nb: 0.1% or less, V: 0.1% or less, Ti: 0.1% One or more selected from the following, Ca: 0.005% or less can be selected and contained.
(Cu: 0.5% or less) Cu is effective in improving the sour resistance by generating a surface layer coating, but if it exceeds 0.5%, a problem arises in the manufacturability of the tube material, so Cu: 0.5% The following.
(Ni: 0.5% or less) Ni is an element effective for improving toughness and increasing strength, but if it exceeds 0.5%, a hardened second phase is likely to be formed, leading to deterioration of HIC characteristics. Ni: 0.5% or less.
(Cr: 3.0% or less) Similar to Mn, Cr is an effective element for obtaining sufficient strength even at low C. However, if it exceeds 3.0%, the second phase is likely to be formed, and HIC characteristics Therefore, Cr: 3.0% or less.
(Mo: 2.0% or less) Mo is an element effective for obtaining sufficient strength even at low C as in Mn and Cr. However, if it exceeds 2.0%, the second phase is likely to be formed. In order to deteriorate the HIC characteristics, Mo: 2.0% or less.
(Nb: 0.1% or less) Nb improves strength and toughness by fine precipitation of carbonitride and fine graining of the structure, but when it exceeds 0.1%, the cured second phase tends to increase, In order to significantly deteriorate the HIC characteristics, Nb: 0.1% or less.
(V: 0.1% or less) V also contributes to an increase in strength by fine precipitation of carbonitrides in the same manner as Nb. However, if it exceeds 0.1%, the cured second phase fraction increases in the same manner as Nb. V: 0.1% or less because the HIC characteristics deteriorate significantly.
(Ti: 0.1% or less) Ti, like Nb and V, contributes to strength increase by fine precipitation of carbonitride, but if it exceeds 0.1%, the second phase fraction cured in the same manner as Nb Since it increases and the HIC characteristics are remarkably deteriorated, Ti: 0.1% or less.
(Ca: 0.005% or less) Ca is an element necessary for controlling the morphology of elongated MnS, which tends to be the starting point of HIC, but when added over 0.005%, excessive Ca oxide and sulfide are generated. And Ca: 0.005% or less because it leads to toughness deterioration.

  The balance excluding the above components is Fe and inevitable impurities. It is preferable that inevitable impurities (O and others) be as small as possible.

Table 1 uses steel strips (A to I) showing the composition, plate thickness, YS, and TS as pipe materials, and various conditions are changed as shown in Table 2 for welded end groove conditions. 3 produced an ERW steel pipe having an outer diameter and a strength grade. Each of the steel strips was manufactured by a method in which a steel slab was rolled to a predetermined plate thickness by hot rolling and then wound into a hot coil.
The groove processing of the welded end portion was performed by plastic deformation processing using a fin roll at the fin pass forming stage immediately before the ERW welding.

Evaluate the sour resistance of the ERW welded part of the manufactured ERW steel pipe by the thickness direction crack rate (CTR) measured by the following HIC test. If the CTR of the welded part is less than 1.5%, sour resistance The characteristic was determined to be acceptable (◯), otherwise it was rejected (x).
[HIC test]
(Test piece) A full-thickness test piece having a width of 20 mm and a length (pipe length direction) of 100 mm, with the center position of the ERW welded portion (position of the weld seam surface) at the center of the test piece width direction.
(Test method) A solution A solution defined by NACE was used and immersed for 96 hours at 25 ° C, and then ultrasonic flaw detection was performed perpendicularly to the weld seam surface to measure CTR.

Moreover, the oxide form in the ERW weld was investigated by the following method.
[Oxide morphology survey method]
Using the welding seam surface as the surface to be observed, SEM (scanning electron microscope) is used to observe magnifications of 100 to 1000 times and the number of fields of view of 10 or more. Was measured.

These measurement results are shown in Table 3. The value of the equivalent circle diameter of the oxide and cluster for each steel pipe in Table 3 is the maximum value of the measured data.
From Table 3, the examples of the present invention all show excellent sour resistance characteristics and pass, while the comparative examples show that the equivalent circular diameters of oxides and / or clusters deviate from the scope of the present invention and fail. is there.

DESCRIPTION OF SYMBOLS 1 Oxide 2 Cluster 3 Outermost tangent 5 Parallel part 6 Pipe inner surface side groove part 7 Pipe outer surface side groove part

Claims (6)

  After discharging the tube material whose initial shape is a strip shape, forming the tube shape and plastically deforming the welded end surfaces between the welded end surfaces that are the edges of the formed V shape, With respect to the thickness t direction, the shape of the welded end immediately before the electric-welding welding has a groove width of (1/7) t to (3/7) t from the parallel portion in the middle of the t direction to the pipe inner surface side. Tapered tube inner surface side groove portion with an angle of 15 to 45 °, groove width from the parallel portion to the tube outer side is (1/7) t to (3/7) t, and groove angle is 15 to 45 As a groove shape having a tapered outer tube side groove portion of °, each equivalent circular diameter of the oxide in the electric resistance welded portion is 20 μm or less, and a plurality of the oxides are 100 μm closest to each other. The sour resistance characteristic of ERW welds is obtained by obtaining ERW welds in which the cluster equivalent circle diameter is 300 μm or less. Method of manufacturing the excellent high-strength thick electric resistance welded steel pipe.   The tube material is mass%, C: 0.01 to 0.15%, Si: 0.005 to 0.9%, Mn: 0.2 to 1.3%, P: 0.01% or less, S: 0.01% or less, Al: 0.1% or less, with the balance being Fe and inevitable impurities, excellent sour resistance of the ERW weld according to claim 1 Manufacturing method of high strength thick wall ERW steel pipe.   3. The electric sewing according to claim 2, wherein the pipe material contains one or two kinds selected from Cu: 0.5% or less and Ni: 0.5% or less by mass%. A method for manufacturing high-strength thick-walled ERW steel pipes with excellent sour-resistance characteristics at welds.   The said pipe | tube raw material contains the 1 type (s) or 2 types chosen from Cr: 3.0% or less and Mo: 2.0% or less by mass%. A method for manufacturing high-strength thick-walled ERW steel pipes with excellent sour-resistance characteristics for ERW welds   The tube material contains, by mass%, one or more selected from Nb: 0.1% or less, V: 0.1% or less, and Ti: 0.1% or less. The manufacturing method of the high intensity | strength thick wall ERW steel pipe excellent in the sour-proof characteristic of the ERW weld part as described in any one of Claims 2-4.   The said pipe | tube raw material contains the 0.005% or less of Ca by mass%, The high intensity | strength excellent in the sour-proof characteristic of the electric-welded welding part as described in any one of Claims 2-5 characterized by the above-mentioned. A method for manufacturing thick-walled electric resistance welded steel pipes.

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