WO2011149098A1 - 耐ねじり疲労特性に優れた電縫鋼管及びその製造方法 - Google Patents
耐ねじり疲労特性に優れた電縫鋼管及びその製造方法 Download PDFInfo
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- WO2011149098A1 WO2011149098A1 PCT/JP2011/062304 JP2011062304W WO2011149098A1 WO 2011149098 A1 WO2011149098 A1 WO 2011149098A1 JP 2011062304 W JP2011062304 W JP 2011062304W WO 2011149098 A1 WO2011149098 A1 WO 2011149098A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/08—Seam welding not restricted to one of the preceding subgroups
- B23K11/087—Seam welding not restricted to one of the preceding subgroups for rectilinear seams
- B23K11/0873—Seam welding not restricted to one of the preceding subgroups for rectilinear seams of the longitudinal seam of tubes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
- F16L9/00—Rigid pipes
- F16L9/02—Rigid pipes of metal
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
Definitions
- the present invention relates to an electric resistance welded steel pipe excellent in torsion fatigue resistance and a method for producing the same.
- Patent Document 1 discloses an excellent cold workability (cold ⁇ ) in which a seamless steel pipe whose steel composition is controlled within a desired range is used, and the austenitic grain size number after quenching is 9 or more.
- a hollow drive shaft that combines a workability, hardenability, toughness, and torsional fatigue strength and exhibits a stable fatigue life is described.
- a problem with seamless steel pipes is that the surface must be ground and ground in order to obtain sufficient fatigue resistance due to large surface decarburizing and surface flaws due to its manufacturing method.
- Patent Document 2 an electric-welded steel pipe whose steel composition is controlled within a desired range is used as a raw material, and this is subjected to quenching and tempering treatment, whereby the prior austenite grain size (prior austenite grain) With a delayed fracture resistance characterized by having a steel structure in which a hardened area with a thickness of 10 ⁇ m or less has a steel structure formed with 30% or more of the C cross section (cross section orthogonal to the pipe length direction) of the steel pipe An excellent high strength steel pipe is described.
- the present invention provides an electric resistance welded pipe made of a steel plate, and an oxide, an inclusion, and an inclusion of an electric resistance welded portion (a joint surface formed by electric-welding welding of welded end portions). By detecting and controlling defects such as these, it is possible to ensure the fatigue resistance required for drive shafts after quenching or further tempering as necessary. It is an object to provide a sewn steel pipe together with its preferred manufacturing method.
- the inventors examined the defect near the ERW weld, which is a problem when the ERW steel pipe is applied to the drive shaft.
- the one side end surface (position corresponding to the welded portion) of the steel strip was processed with a drill having different sizes and then subjected to electric resistance welding. Thereafter, after quenching and tempering the ERW steel pipe, a torsional fatigue test was performed, and the relationship between the defect size of the ERW weld and the torsional fatigue strength is shown in FIG.
- the defect size of the electric-welded welded part was expressed by a welding defect area described later.
- the defect size of the ERW weld was determined as follows. -About the sample which fractured
- a sample 3 of a welded portion sliced at a predetermined distance (in this case, 8 mm) from the seam (electrically welded portion) 2 of the electric resistance welded steel pipe 1 The seam portion was detected by performing a C scan (scanning along a scanning direction 5) with a spot focus type ultrasonic probe 4 and measuring the signal strength.
- the welding conditions of the electric resistance welded pipe are the normal electric resistance welding conditions, the welding heat input and the upset amount (amount of minute defect) so as to minimize the amount of minute defects (amount of minute defect). various conditions, including conditions for adjusting upset value).
- a point-focusing type ultrasonic probe having a frequency of 10 MHz and a beam size of 1.2 mm ⁇ 1.2 mm is used, and a ⁇ 1.6 mm drill hole is used.
- the detection range was adjusted so that the echo height was 80%, and then flaw detection was performed with a gain increase of 10 times.
- the relationship between the signal intensity (echo height) and the defect diameter in this sensitivity setting is as shown in FIG. -About the micro defect which cannot be detected by C-scan method, the defect size (defect size) was measured by observing the L cross section (tube length direction cross section) with an optical microscope (optical microscope).
- the defect size by the C-scan method and the optical microscope of the L cross section of the detection unit Investigating the correlation of defect size measurement results by observation (observation magnification x400) and confirming that there is sufficient correlation between the two and that there is sufficient accuracy for defect size measurement using the C-scan method .
- the weld defect that becomes a problem in the torsional fatigue of the drive shaft has a projected area of 40000 ⁇ m 2 or more on the ERW weld regardless of its shape. became.
- the defect size was detected by the C-scan method, but the same measurement can also be performed by tandem flaw inspection using an ultrasonic beam focused on an appropriate size with a steel pipe. .
- a point-focusing type ultrasonic probe similar to the C-scan may be used, or, as shown in FIG. 5, an array probe arranged in the circumferential direction is used. Also good.
- the welding defect here is not only an actual defect that is a void such as an oxide, inclusion, or shrinkage of welding, but also a plurality of actual defects as shown in FIG. (Actual defect) also includes an aggregation (cluster state defect) formed by gathering together at a mutual interval within 50 ⁇ m of the nearest neighbor distance (nearest-neighbor interval).
- the projection area of the weld defect on the ERW weld is 40000 ⁇ m 2 or more, and the ultrasonic beam is focused with an ultrasonic beam focused to a beam area of 5 mm 2 or less. This can be detected by scanning the sewing weld.
- the projected area of the weld defect on the electric-welded weld here (that is, the weld defect area) is the nearest neighbor in the projection plane with the electric-welded weld as the projection plane.
- Individual areas of actual defects whose distance exceeds 50 ⁇ m, or the outermost tangent line of a cluster (cluster-like defect) in which a plurality of actual defects are gathered within the nearest neighbor distance of 50 ⁇ m within the projection plane In the present invention, this region is also regarded as one weld defect).
- the summary structure is as follows. (1) The composition of the base material part is mass%, C: 0.25 to 0.55%, Si: 0.01 to 1.0%, Mn: 0.2 to 3.0%, Al: 0.00.
- N 0.0010 to 0.0100% in balance Fe and unavoidable impurities are electric resistance welded steel pipes, and the weld defect area that is the projected area of the weld defects on the electric resistance weld is 40000 ⁇ m 2 ERW steel pipe with excellent torsional fatigue resistance, characterized by being less than (2) Ti: 0.005 to 0.1%, B: 0.0003 to 0.0050%, and N / 14 ⁇ Ti / 47.9 . (3) Cr: 2% or less, Mo: 2% or less, W: 2% or less, Nb: 0.1% or less, V: 0.1% or less, or one or more of the above (1) Or the electric resistance welded steel pipe as described in (2).
- the component concentration (component content) of the composition is abbreviated as% in units of mass%.
- Si 0.01 to 1.0% Si may be added for deoxidation, and if it is less than 0.01%, a sufficient deoxidation effect cannot be obtained. At the same time, Si is a solid solution strengthening element, and in order to obtain the effect, addition of 0.01% or more is necessary. On the other hand, if it exceeds 1.0%, the hardenability of the steel pipe decreases.
- the content is preferably 0.1 to 0.4%.
- Mn 0.2 to 3.0%
- Mn is an element improving the hardenability, and 0.2% or more of addition is necessary to obtain the effect.
- it is 0.5 to 2.0%.
- Al 0.1% or less Al is an element effective for deoxidation, and is necessary for securing the strength after quenching by suppressing the growth of austenite grains during quenching.
- addition of 0.001% or more is preferable.
- Al is added in excess of 0.1%, the effect is not only saturated, but Al-based inclusions increase, and fatigue strength may be reduced.
- it is 0.01 to 0.08%.
- N 0.0010 to 0.0100%
- N is an element that combines with Al to refine crystal grains.
- N needs to be contained in an amount of 0.0010% or more. However, if it exceeds 0.0100%, N combines with B to form BN.
- the amount of free B is made short by forming, and the hardenability improvement effect by B will be inhibited.
- the content is 0.0010 to 0.005%.
- the composition further contains one or more of the following groups (A) to (D).
- Ti 0.005 to 0.1%
- B 0.0003 to 0.0050%
- B Cr: 2% or less
- Mo 2% or less
- W 2% or less
- Nb 0.1% or less
- V One or more of 0.1% or less
- C Ni: 2% or less
- Cu 2% or less
- D Ca: 0.02% or less
- REM Including 1 or 2 types out of 0.02 or less.
- Ti: 0.005 to 0.1% Ti has an action of fixing N in steel as TiN. However, if it is less than 0.005%, the ability to fix N is not sufficiently exhibited, while if it exceeds 0.1%, the workability and toughness of the steel deteriorate. More preferably, the content is 0.01 to 0.04%.
- B 0.0003 to 0.0050% B is an element that improves hardenability. If it is less than 0.0003%, the effect of improving hardenability is not sufficiently exhibited. On the other hand, even if added over 0.0050%, the effect is saturated and segregates at the grain boundary to promote grain boundary fracture and deteriorate fatigue resistance. More preferably, the content is 0.0010 to 0.0040%.
- Mo 2% or less Mo is an element that improves hardenability, and is effective in increasing the strength of steel and improving fatigue strength. In order to obtain the effect, addition of 0.001% or more is preferable. However, if Mo is added in excess of 2%, the workability is significantly reduced. More preferably, the content is 0.001 to 0.5%. W: 2% or less W is effective in improving the strength of steel by forming carbides. In order to obtain the effect, addition of 0.001% or more is preferable. However, if W is added in excess of 2%, unnecessary carbides are precipitated, reducing the fatigue resistance and reducing the workability. More preferably, the content is 0.001 to 0.5%.
- Nb 0.1% or less Nb is an element that improves hardenability, and also forms carbides and contributes to an increase in strength. In order to obtain the effect, addition of 0.001% or more is preferable. However, even if Nb is added in excess of 0.1%, the effect is saturated and workability is lowered. More preferably, the content is 0.001 to 0.04%. V: 0.1% or less V is an element that forms carbides and is effective in increasing the strength of steel and has resistance to temper softening. In order to obtain the effect, addition of 0.001% or more is preferable. However, if added over 0.1%, the effect is saturated and workability is reduced. More preferably, the content is 0.001 to 0.5%.
- Ni 2% or less Ni is an element that improves hardenability, and is effective in increasing the strength of steel and improving fatigue strength. In order to obtain the effect, addition of 0.001% or more is preferable. However, when it exceeds 2%, workability is remarkably lowered. More preferably, the content is 0.001 to 0.5%.
- Cu 2% or less Cu is an element that improves hardenability, and is effective for increasing the strength of steel and improving fatigue strength. In order to obtain the effect, addition of 0.001% or more is preferable. However, when it exceeds 2%, workability is remarkably lowered. More preferably, the content is 0.001 to 0.5%.
- Ca 0.02% or less
- REM 0.02% or less
- Each of Ca and REM has a non-metallic inclusion shape in a spherical shape, and cracks at the time of fatigue failure in a usage environment in which repeated stress is applied. It is an element effective in reducing the starting point, and can be selected and contained as necessary. Such an effect is recognized when both Ca and REM contain 0.0020% or more. On the other hand, when the content exceeds 0.02%, the amount of inclusions increases so that the cleanliness is reduced. For this reason, it is preferable to limit both Ca and REM to 0.02% or less. When both Ca and REM are used in combination, the total amount is preferably 0.03% or less.
- the welding defects referred to in the present invention include not only actual defects that are voids such as oxides, inclusions, or shrinkage of welding, but also a plurality of actual defects as shown in FIG. Include clusters (cluster-like defects) that are gathered together at a mutual interval within 50 ⁇ m of the nearest neighbor distance. Only a weld defect having a projected area of the weld defect on the ERW weld portion (ie, weld defect area) of 40000 ⁇ m 2 or more has an adverse effect on the torsional fatigue resistance (eg, as shown in FIG.
- the weld defect area is less than 40000 ⁇ m 2 (that is, there is no weld defect having a weld defect area of 40000 ⁇ m 2 or more in the ERW weld).
- an assembly of a plurality of actual defects whose nearest neighbor distance exceeds 50 ⁇ m is torsional fatigue resistance if the projected area of each actual defect in the assembly to the ERW weld is less than 40000 ⁇ m 2. Since the adverse effect on is negligible, it does not belong to the welding defect referred to in the present invention.
- a steel plate having the composition according to any one of the above (1) to (4) is formed into a pipe by electric resistance welding, and then the electric resistance welding portion of the pipe is mainly used.
- the range of ⁇ 1 mm in the circumferential direction is scanned with an ultrasonic beam in which an ultrasonic beam is focused to a beam area of 5 mm 2 or less, and the weld defect area that is the projected area of the weld defect on the ERW weld is 40000 ⁇ m 2 or more. It is possible to detect a welding defect that is, and to exclude a pipe length direction portion specified by the detection as a defective portion. According to this manufacturing method, since the obtained ERW steel pipe does not contain any weld defects having a weld defect area of 40000 ⁇ m 2 or more, the ERW steel pipe having excellent torsional fatigue resistance is reliably and stably provided. can get.
- the electric resistance welded steel pipe is hardened or further tempered for use in the drive shaft, so that the fatigue resistance required for the drive shaft can be reliably ensured.
- FIG. 7 shows the result of examining the S / N of a defect of 40000 ⁇ m 2 . Since the defect can be detected if S / N ⁇ 2, the preferable range of the ultrasonic beam area is 5 mm 2 or less. More desirably, it is 3.3 mm 2 or less where S / N ⁇ 3.
- the lower limit is preferably set to 0.01 mm 2 which is a limit from the ultrasonic frequency applicable to the steel pipe and the geometrical dimensional relationship of the steel pipe and the probe.
- Table 1 shows a steel strip obtained by hot rolling a steel slab having a steel composition (mass%).
- the welding heat input and upset amount Adjust the combination in two ways: normal conditions where oxides and inclusions are unlikely to remain (Electric seam welding conditions A in Table 2) and conditions where they are likely to remain (Electric seam welding conditions B in Table 2).
- the weld defect size in the ERW welded portion of the manufactured ERW steel pipe was measured by the C-scan method (see FIG. 2) or the array UT method (see FIG. 5) to determine the weld defect area.
- a part of the sample was tempered at 180 ° C. for 1 hour after quenching.
- the diameter reduction rolling conditions shown in Table 2 (the heating temperature in Table 2 is the reheating temperature by induction heating).
- the diameter reduction rolled steel pipe (stretch reduced steel pipe) is used hereinafter.
- the drive shaft from the ERW steel pipe or the reduced diameter rolled steel pipe of the present invention example has a longer fatigue life than that of the comparative example, and has superior torsional fatigue resistance, Compared with the drive shaft (conventional product) from the seamless steel pipe of the comparative example, the fatigue life is longer and it has more excellent torsional fatigue resistance.
- the pipe material of the ERW steel pipe is a hot-rolled steel sheet.
- the present invention is not limited to this, and a cold-rolled steel strip may be used as the pipe material. .
- the defect size present in the forged portion satisfies the size specified in the present invention, the fatigue resistance characteristics required as a drive shaft are obtained. Realization of a forged steel pipe that can be reliably guaranteed can be expected.
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Abstract
Description
本発明は上記の課題を解決すべく、鋼板を素材とした電縫鋼管において、電縫溶接部(被溶接端部を電縫溶接結合してなる結合面)の酸化物(oxide)、介在物等の欠陥を検出し、これを管理することで、焼入れ、あるいはさらに必要に応じ焼戻し処理を施した後にドライブシャフトとして必要とされる耐疲労特性を保証された、耐ねじり疲労特性に優れた電縫鋼管を、その好ましい製造方法と共に提供することを目的とする。
・ねじり疲労試験で電縫溶接部の欠陥を割れ起点として破断したサンプルについては、破面を走査型電子顕微鏡(scanning electron microscope)(SEM)により直接観察することにより欠陥サイズを求めた。
・電縫溶接部の欠陥部で割れずに、それ以外の部分で割れてしまったものについては、電縫溶接部の欠陥部をシームスライス材(C scan method for seam slice material)Cスキャン法(略してCスキャン法)により調査することで欠陥サイズを求めた。
ここで、電縫鋼管の溶接条件(welding condition)は、通常の電縫溶接条件と、微小欠陥量(amont of minute defect)が極力少なくなるように溶接入熱(welding heat input)とアプセット量(upset value)を調整する条件とを含み、種々変化させた。また、点集束型超音波探触子には周波数が、10MHzで、ビームサイズ(beam size)が、1.2mm×1.2mmのものを使用し、φ1.6mmのドリルホール(drill hole)からのエコー高さ(echo height)が80%となるように感度(detection range)を調整し、その後、10倍にゲインアップ(gain up)して探傷を行った。この感度設定における信号強度(エコー高さ)と欠陥径(diameter of defect)の関係は図3に示すとおりである。
・Cスキャン法で検出できない微小な欠陥については、L断面(管長さ方向断面)を光学顕微鏡(optical microscope)により観察することで欠陥サイズ(defect size)を測定した。
また、発明者らの知見では、電縫溶接部への溶接欠陥の投影面積が40000μm2以上であるものは、超音波ビームをビーム面積(beam area)5mm2以下に集束させた超音波で電縫溶接部を走査することにより検出することができる。
本発明は、上述した知見に基づきなされたものであって、その要旨構成は以下の通りである。
(1) 母材部の組成が質量%で、C:0.25~0.55%、Si:0.01~1.0%、Mn:0.2~3.0%、Al:0.1%以下、N:0.0010~0.0100%を含み残部Fe及び不可避的不純物である電縫鋼管であって、電縫溶接部への溶接欠陥の投影面積である溶接欠陥面積が40000μm2未満であることを特徴とする耐ねじり疲労特性に優れた電縫鋼管。
(2) Ti:0.005~0.1%、B:0.0003~0.0050%を含み、かつ、N/14<Ti/47.9である上記(1)に記載の電縫鋼管。
(3) Cr:2%以下、Mo:2%以下、W:2%以下、Nb:0.1%以下、V:0.1%以下のうち1種または2種以上を含む上記(1)又は(2)に記載の電縫鋼管。
(4) Ni:2%以下、Cu:2%以下のうち1種又は2種を含む上記(1)~(3)のいずれか1つに記載の電縫鋼管。
(5) Ca:0.02%以下、REM:0.02以下のうち1種又は2種を含む上記(1)~(4)のいずれか1つに記載の電縫鋼管。
(6) ドライブシャフト用である上記(1)~(5)のいずれか1つに記載の電縫鋼管。
(7) 上記(1)~(6)のいずれか1つに記載の組成を有する鋼板を電縫溶接により管となした後、該管の電縫溶接部を中心とした円周方向±1mmの範囲を、超音波ビームをビーム面積5mm2以下に集束させた超音波で走査して、電縫溶接部への溶接欠陥の投影面積である溶接欠陥面積が40000μm2以上である溶接欠陥を検出し、該検出によって特定した管長さ方向部分を不良部分として排除することを特徴とする耐ねじり疲労特性に優れた電縫鋼管の製造方法。
(8) 上記(7)において、前記不良部分を排除した後、管に焼入れ或いは更に焼戻し処理を施してドライブシャフト用とすることを特徴とする電縫鋼管の製造方法。
(必須に含有する成分)
C:0.25~0.55%
Cが0.25%未満では、焼入れしても十分な硬度が得られず、要求される耐疲労特性が得られない。一方で、0.55%を超えると、溶接性が悪くなる為、安定した電縫溶接品質が得られない。なお、好ましくは0.30~0.40%である。
Siは脱酸のために添加する場合もあり、0.01%未満では十分な脱酸効果が得られない。同時に、Siは固溶強化元素(solid solution hardening element)でもあり、その効果を得るためには0.01%以上の添加が必要である。一方で、1.0%を超えると、鋼管の焼入れ性(hardenability)が低下する。なお、好ましくは0.1~0.4%である。
Mnは焼入れ性を向上させる元素であり、その効果を得るには0.2%以上の添加が必要である。一方で、3.0%を超えると電縫溶接品質(electric resistance weld quality)を低下させ、さらに残留オーステナイト量(retained austenite)が増加し耐疲労特性が低下する。なお、好ましくは0.5~2.0%である。
Al:0.1%以下
Alは脱酸に有効な元素であり、また、焼入れ時のオーステナイト粒の成長を抑制することで焼入れ後の強度を確保するために必要である。その効果を得るためには、0.001%以上の添加が好ましい。しかし、Alが、0.1%を超えて添加するとその効果は飽和するだけでなく、Al系の介在物が増え、疲労強度(fatigue strength)を低下する場合がある。なお、好ましくは0.01~0.08%である。
Nは、Alと結合し結晶粒を微細化する元素であり、このためには0.0010%以上含有する必要があるが、0.0100%を超えて過剰に含有すると、Bと結合しBNを形成することでフリーB量を不足せしめ、Bによる焼入れ性向上効果を阻害してしまう。なお、好ましくは0.0010~0.005%である。
(任意選択的に含有できる成分)
すなわち、具体的には、上記成分組成に加えて、さらに、下記のグループ(A)~(D)の一種または、二種以上を含有する。
(A) Ti:0.005~0.1%、B:0.0003~0.0050%を含み、かつ、N/14<Ti/47.9である
(B) Cr:2%以下、Mo:2%以下、W:2%以下、Nb:0.1%以下、V:0.1%以下のうち1種または2種以上
(C) Ni:2%以下、Cu:2%以下のうち1種又は2種を含む
(D) Ca:0.02%以下、REM:0.02以下のうち1種又は2種を含む
以下、個々の元素について、規定理由を述べる。
Ti:0.005~0.1%
Tiは鋼中のNをTiNとして固定する作用を有する。しかし、0.005%未満ではNを固定する能力が十分に発揮されず、一方で0.1%を超えると鋼の加工性、靭性が低下する。なお、より好ましくは0.01~0.04%である。
Bは焼入れ性を向上させる元素である。0.0003%未満では焼入れ性向上効果が十分に発揮されない。一方で0.0050%を超えて添加しても、その効果は飽和し、粒界に偏析して粒界破壊を促進し耐疲労特性を劣化させる。なお、より好ましくは0.0010~0.0040%である。
フリーBを確保するためには、Nを確実にTiで固定する必要があり、そのためにはN原子%(=N質量%/N原子量14)がTi原子%(=Ti質量%/Ti原子量47.9)より小さい必要がある。
Cr:2%以下
Crは焼入れ性の向上に有効である。その効果を得るためには、0.01%以上の添加が好ましい。しかし、Crが、2%を超えて添加すると、酸化物を形成しやすくなり、電縫溶接部にCr酸化物が残存し電縫溶接品質が低下する。なお、より好ましくは0.001~0.5%である。
Moは焼入れ性を向上させる元素であり、鋼の強度を高め疲労強度の向上に有効である。その効果を得るためには、0.001%以上の添加が好ましい。しかし、Moが、2%を超えて添加すると加工性が著しく低下する。なお、より好ましくは0.001~0.5%である。
W:2%以下
Wは炭化物を形成することで鋼の強度を向上させるのに有効である。その効果を得るためには、0.001%以上の添加が好ましい。しかし、Wが、2%を超えて添加すると不必要な炭化物が析出し、耐疲労特性を低下させ加工性を低下させることになる。なお、より好ましくは0.001~0.5%である。
Nbは焼入れ性を向上させる元素であるほか、炭化物を形成し強度上昇に寄与する。その効果を得るためには、0.001%以上の添加が好ましい。しかし、Nbが0.1%を超えて添加してもその効果は飽和し、加工性が低下する。なお、より好ましくは0.001~0.04%である。
V:0.1%以下
Vは炭化物を形成し、鋼の強度を上昇させるのに有効でかつ焼戻し軟化抵抗を有する元素である。その効果を得るためには、0.001%以上の添加が好ましい。しかしながら0.1%を超えて添加するとその効果は飽和し、加工性が低下する。なお、より好ましくは0.001~0.5%である。
Niは焼入れ性を向上させる元素であり、鋼の強度を高め疲労強度の向上に有効である。その効果を得るためには、0.001%以上の添加が好ましい。しかし、2%を超えて添加すると加工性が著しく低下する。なお、より好ましくは0.001~0.5%である。
Cu:2%以下
Cuは焼入れ性を向上させる元素であり、鋼の強度を高め疲労強度の向上に有効である。その効果を得るためには、0.001%以上の添加が好ましい。しかし、2%を超えて添加すると加工性が著しく低下する。なお、より好ましくは0.001~0.5%である。
Ca、REMは、いずれも非金属介在物の形態を球状とし、繰り返し応力が付与されるような使用環境下での疲労破壊時の割れ起点の低減に有効な元素であり、必要に応じて選択して含有できる。このような効果は、Ca、REMともに0.0020%以上の含有で認められる。一方で、0.02%を超えて含有すると、介在物量が多くなりすぎて清浄度が低減する。このためCa、REMともに0.02%以下に限定することが好ましい。Ca、REMの両者を併用する場合には、合計量で0.03%以下とすることが好ましい。
次に、溶接欠陥面積の限定理由について述べる。前述の通り、本発明にいう溶接欠陥には、溶接起因の酸化物、介在物、又は溶接の引け巣等の空隙である実欠陥のみならず、図6に示したように、複数の実欠陥が最隣接距離50μm以内の相互間隔で寄り集まってなる集合体(クラスタ状欠陥)をも含まれる。かかる溶接欠陥の、電縫溶接部への投影面積(すなわち溶接欠陥面積)が40000μm2以上である溶接欠陥のみが、耐ねじり疲労特性に悪影響を及ぼす(例えば図1に示した通り)。よって本発明では、溶接欠陥面積が40000μm2未満であること(すなわち、電縫溶接部には溶接欠陥面積が40000μm2以上である溶接欠陥が全く存在しないこと)を必須とした。
次に、好ましい製造方法としては、上記(1)~(4)のいずれか1つに記載の組成を有する鋼板を電縫溶接により管となした後、該管の電縫溶接部を中心とした円周方向±1mmの範囲を、超音波ビームをビーム面積5mm2以下に集束させた超音波で走査して、電縫溶接部への溶接欠陥の投影面積である溶接欠陥面積が40000μm2以上である溶接欠陥を検出し、該検出によって特定した管長さ方向部分を不良部分として排除することが挙げられる。この製造方法によれば、得られる電縫鋼管は溶接欠陥面積が40000μm2以上である溶接欠陥を全く含まないものとなるから、耐ねじり疲労特性に優れた電縫鋼管が確実にかつ安定的に得られる。そして、この電縫鋼管に焼入れ或いは更に焼戻し処理などを施してドライブシャフト用とすることで、ドライブシャフトに必要な耐疲労特性を確実に保証することができる。
製造した電縫鋼管の電縫溶接部における溶接欠陥サイズをCスキャン法(図2参照)又はアレイUT法(図5参照)で測定し、溶接欠陥面積を求めた。また、電縫溶接部を真横にして扁平試験(flattening test)を行い、扁平値(flattening Value)(割れ発生時の管高さH/扁平前の管外径D)を求めて扁平値が0.5以下のものを溶接品質良好と判断した。その後、電縫鋼管に対し、冷牽加工(冷間引き抜き加工)を行い、その後、焼準(950℃×10分)を行った後に、成形加工を加えて、中空ドライブシャフト形状とし、その後、高周波加熱(high−frequency heating)により焼入れを施してドライブシャフトとした。
また、一部のものについては、熱延鋼帯(hot rolled steel sheet)を電縫鋼管とした後に、表2に示す縮径圧延条件(表2中の加熱温度は誘導加熱による再加熱温度の意)にて縮径圧延(diameter−reduction rolling)行い、電縫鋼管(縮径圧延を行わない電縫鋼管と区別するために、以降は縮径圧延鋼管(stretch reduced steel pipe)
と称す)を得た後、同上の溶接欠陥サイズ測定→冷牽加工(cold drawing)→焼準(normalizing)→成形加工(forming)→焼入れ(→あるいはさらに焼戻し)、を行ったものを作製した。
焼入れ後あるいはさらに焼戻し後のドライブシャフトは、焼入れ部から軸方向に引張試験片(ASTM比例試験片(ASTM proportional test piece))を採取し、引張強度を測定した。その後、これらのドライブシャフトに対し、外面でのせん断応力(shear stress)τが350MPaとなる条件で両振りねじり疲労試験(torsional fatigue test under completely reversed stress)を行い、疲労寿命(fatigue−life time)の比較を行った。これら特性評価結果を表2に示す。
なお、この実施例では電縫鋼管の管素材を熱延鋼板としたが、本発明はこれに限定されるものではなく、管素材として冷延鋼帯を使用する形態のものであってもよい。
Claims (8)
- 母材部の組成が質量%で、C:0.25~0.55%、Si:0.01~1.0%、Mn:0.2~3.0%、Al:0.1%以下、N:0.0010~0.0100%を含み残部Fe及び不可避的不純物である電縫鋼管であって、電縫溶接部への溶接欠陥の投影面積である溶接欠陥面積が40000μm2未満である電縫鋼管。
- Ti:0.005~0.1%、B:0.0003~0.0050%を含み、かつ、N/14<Ti/47.9である請求項1に記載の電縫鋼管。
- Cr:2%以下、Mo:2%以下、W:2%以下、Nb:0.1%以下、V:0.1%以下のうち1種または2種以上を含む請求項1又は2に記載の電縫鋼管。
- Ni:2%以下、Cu:2%以下のうち1種又は2種を含む請求項1~3のいずれか1項に記載の電縫鋼管。
- Ca:0.02%以下、REM:0.02以下のうち1種又は2種を含む請求項1~4のいずれか1項に記載の電縫鋼管。
- ドライブシャフト用である請求項1~5のいずれか1項に記載の電縫鋼管。
- 請求項1~6のいずれか1項に記載の組成を有する鋼板を電縫溶接により管となした後、該管の電縫溶接部を中心とした円周方向±1mmの範囲を、超音波ビームをビーム面積5mm2以下に集束させた超音波で走査して、電縫溶接部への溶接欠陥の投影面積である溶接欠陥面積が40000μm2以上である溶接欠陥を検出し、該検出によって特定した管長さ方向部分を不良部分として排除する電縫鋼管の製造方法。
- 請求項7において、前記不良部分を排除した後、管に焼入れ或いは更に焼戻し処理を施してドライブシャフト用とする電縫鋼管の製造方法。
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CN201180026243.7A CN102906293B (zh) | 2010-05-27 | 2011-05-23 | 耐扭转疲劳特性优异的电阻焊钢管及其制造方法 |
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JP2016074004A (ja) * | 2014-10-07 | 2016-05-12 | Jfeスチール株式会社 | 電縫溶接部の中温域のクリープ特性に優れた高強度電縫鋼管の製造方法 |
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JP6070617B2 (ja) * | 2014-04-03 | 2017-02-01 | Jfeスチール株式会社 | 耐内圧疲労特性に優れた燃料噴射管用継目無鋼管 |
KR102390423B1 (ko) * | 2017-12-27 | 2022-04-22 | 제이에프이 스틸 가부시키가이샤 | 전봉 용접 강관 및 전봉 용접 강관의 제조 방법 |
CN109763063B (zh) * | 2018-12-19 | 2020-08-21 | 钢铁研究总院 | 一种适合用作高强度传动轴的合金结构钢 |
CN111101069A (zh) * | 2020-02-17 | 2020-05-05 | 本钢板材股份有限公司 | 汽车、发动机传动零件用钢材及其制备方法 |
KR20220136428A (ko) | 2020-03-18 | 2022-10-07 | 제이에프이 스틸 가부시키가이샤 | 전봉 강관, 그 제조 방법 및 자동차용 구조 부재 |
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