WO2013153819A1 - 優れた低温靭性を有する高強度厚肉電縫鋼管及びその製造方法 - Google Patents
優れた低温靭性を有する高強度厚肉電縫鋼管及びその製造方法 Download PDFInfo
- Publication number
- WO2013153819A1 WO2013153819A1 PCT/JP2013/002488 JP2013002488W WO2013153819A1 WO 2013153819 A1 WO2013153819 A1 WO 2013153819A1 JP 2013002488 W JP2013002488 W JP 2013002488W WO 2013153819 A1 WO2013153819 A1 WO 2013153819A1
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- WIPO (PCT)
- Prior art keywords
- steel pipe
- erw
- less
- welded
- electric
- Prior art date
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 189
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 8
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Images
Classifications
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- Y10T428/12972—Containing 0.01-1.7% carbon [i.e., steel]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
- Y10T428/12771—Transition metal-base component
- Y10T428/12861—Group VIII or IB metal-base component
- Y10T428/12951—Fe-base component
- Y10T428/12972—Containing 0.01-1.7% carbon [i.e., steel]
- Y10T428/12979—Containing more than 10% nonferrous elements [e.g., high alloy, stainless]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/13—Hollow or container type article [e.g., tube, vase, etc.]
Definitions
- the present invention relates to a high-strength thick-walled-electric-resistance-welded-steel pipe, and more particularly to improving the reliability of an electric-welded weld.
- “high strength” means that the yield strength is YS: 400 MPa or more
- “thick” means that the thickness is 16 to 32 mm.
- Patent Document 1 a steel sheet having a predetermined composition is electro-welded, and then the electro-welded part is heated at 790 ° C. to 1050 ° C. for 5 seconds or more, and 770 ° C. to 890 ° C.
- a method of manufacturing high-strength ERW steel pipes with excellent low-temperature toughness that is rapidly cooled from a temperature of 30 ° C at a cooling rate of 30 ° C / s to 150 ° C / s to make the ERW welds a fine acicular ferrite structure Is described.
- the plate thickness of the steel plate used in the technique described in Patent Document 1 is as thin as about 8.0 mm, and the welded portion toughness of the obtained ERW steel pipe is the fracture surface transition temperature (fracture appearance transition temperature).
- the degree of toughness improvement was small up to about -40 ° C.
- a steel sheet having a predetermined composition is electro-welded, and then the electro-welded part is heated at 790 ° C. to 1050 ° C. for 5 seconds or longer, from a temperature of 750 ° C. to 950 ° C. to 30 ° C.
- heat relief treatment stress relief heat treatment
- Patent Document 3 a steel sheet having a predetermined composition is electro-welded, and then the electro-welded weld is heated to 850 ° C. to 1000 ° C., and then from 30 ° C./s to 100 ° C. from the Ar3 transformation point or higher.
- An object of the present invention is to solve such problems of the prior art, and to provide a high-strength thick-walled electric-welded steel pipe that has excellent low-temperature toughness and also excellent HIC resistance.
- excellent in low temperature toughness refers to absorption in the circumferential direction at a test temperature of ⁇ 50 ° C. in the Charpy impact test in accordance with JIS Z 2242 for both the base metal part and the ERW weld part. The case where energy vE -50 is 150J or more.
- Excellent HIC resistance means that both the base metal part and the ERW weld part are 96 hours in the NACE Solution A solution (0.5% CH 3 COOH + 5% NaCl + saturated H 2 S) specified in NACE TM0284. This refers to the case where the crack area ratio CAR (Crack Area Ratio) is 5% or less after soaking.
- CAR Crack Area Ratio
- the present inventors have developed a microstructure and an oxidation effect particularly on the low temperature toughness and HIC resistance of the base metal part and the ERW welded part of the thick ERW steel pipe having a wall thickness of over 16 mm.
- inclusions inclusions
- the temperature and temperature of the base material part and the ERW welded part of the ERW steel pipe are controlled by relating the composition and hot rolling conditions of the steel sheet used and the heat treatment method after ERW welding to a specific range.
- a thick ERW steel pipe (outer diameter: 660.4 mm ⁇ ) having a composition containing Ca-0.005 to 0.0100% N: 16 to 32 mm was prepared.
- test pieces were taken from the ERW welds after post-heat treatment, and subjected to impact tests, HIC tests, and inclusion content measurement tests.
- the test method was as follows.
- Inclusion amount measurement test A plate-like sample (size: width 2 mm x thickness: pipe thickness x length: pipe thickness) was cut out from the ERW weld centered at the center of the ERW weld. Electrolytic extraction was performed in% AA electrolyte. After electrolytic extraction, inclusions (equivalent circle diameter of 2 ⁇ m or more) are extracted using a filter mesh with a hole diameter of 2 ⁇ m, melted with alkali, and then contained by SiP, Inductively Coupled Plasma (ICP) analysis. The Cr content was measured and the total amount was determined. The total amount of Si, Mn, Al, Ca, and Cr contained in the obtained inclusion having an equivalent circle diameter of 2 ⁇ m or more was defined as the amount of inclusion present in the ERW weld.
- ICP Inductively Coupled Plasma
- FIGS. 1 and 2 The obtained results are shown in FIGS. 1 and 2 in relation to the heating temperature of the heat treatment and the cooling rate after heating.
- FIG. 1 is for vE- 50 and FIG. 2 is for CAR.
- the cooling rate after heating was the average cooling rate between 780 and 630 ° C. at the thickness center temperature. 1 and 2, when the heating temperature of the ERW weld is in the range of 800-1150 ° C and the cooling rate after heating is in the range of 7-49 ° C / s on average between 780-630 ° C, It can be seen that vE- 50 is 150 J or more and excellent ERW weld toughness and CAR is 5% or less and excellent HIC resistance.
- FIG. 3 shows the relationship between vE ⁇ 50 , CAR and the total amount of Si, Mn, Al, Ca and Cr contained in inclusions having an equivalent circle diameter of 2 ⁇ m or more.
- the amount of inclusions having an equivalent circle diameter of 2 ⁇ m or more present in the ERW weld is a predetermined value. It has been found that the toughness and HIC resistance of the ERW welds are significantly reduced when exceeding.
- the present invention has been completed on the basis of such findings and further studies. That is, the gist of the present invention is as follows.
- Pcm C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B (1) (Here, C, Si, Mn, Cu, Ni, Cr, Mo, V, B: content of each element (mass%)) Pcm defined by the formula (1) satisfies 0.20 or less, and has a composition consisting of the balance Fe and inevitable impurities.
- both the base metal part and the ERW welded part have a structure with a pseudopolygonal ferrite with a grain size of 10 ⁇ m or less, an area ratio of 90% or more, a yield strength YS of 400 MPa or more, and a Charpy impact test of ⁇ 50 Absorption energy at ° C vE -50 : High strength thick-walled electric-welded steel pipe with excellent HIC resistance, characterized by high toughness of 150 J or more.
- B A high-strength thick-walled electric-welded steel pipe according to (1), further containing B: 0.0030% or less by mass% in addition to the above composition.
- a steel material having a composition consisting of the balance Fe and inevitable impurities satisfying Pcm of 0.20 or less is defined, and the hot rolling step heats the steel material in
- hot rolling is performed so that the hot rolling rate in the non-recrystallized austenite region is 20% or more.
- the ERW welded part of the ERW steel pipe is heated online so that the total thickness is in the range of 800 ° C to 1150 ° C, and then the temperature at the center of the thickness is 780 ° C.
- the method further comprises B: 0.0030% or less by mass%, and a method for producing a high-strength thick-walled electric-welded steel pipe.
- cooling in the heat treatment is performed by connecting a nozzle capable of injecting rod-shaped cooling water having a water density of 1 m 3 / m 2 min or more above the ERW weld.
- the cooling headers arranged in a plurality of rows are arranged such that cooling water injection is individually controllable, and the method for manufacturing a high-strength thick-walled electric-welded steel pipe .
- both the base metal part and the ERW welded part can easily and stably produce a high-strength thick-walled ERW steel pipe excellent in low-temperature toughness and also in HIC resistance, There are remarkable effects in the industry.
- the high-strength thick-walled ERW steel pipe according to the present invention is excellent in both low temperature toughness and HIC resistance of ERW welds, improved reliability of ERW welds, and excellent low temperature toughness and HIC resistance. There is also an effect that it can be applied stably to the required use.
- FIG. 6 is a graph showing the influence of the relationship between the heating temperature and the cooling rate after heating on the vE- 50 of an ERW weld. It is a graph which shows the influence of the relationship between the heating temperature and the cooling rate after a heating on the crack area ratio CAR after the NACE ⁇ Solution A solution immersion of the ERW weld. Si, Mn, Al, Ca, contained in inclusions with an equivalent circle diameter of 2 ⁇ m or more present in ERW welds on vE- 50 of ERW welds and crack area ratio CAR after immersion in NACE Solution A solution It is a graph which shows the influence of the total amount (mass ppm) of Cr.
- the high-strength thick-walled electric resistance welded steel pipe according to the present invention has a thickness of 16 to 32 mm, and both the base metal part and the electric-welded welded part have a high yield strength of YS: 400 MPa or more and a test temperature: Absorbed energy of Charpy impact test in the circumferential direction at ⁇ 50 ° C. vE ⁇ 50 : Excellent low temperature toughness of 150 J or more.
- it is an electric resistance welded steel pipe having excellent HIC resistance with a crack area ratio (CAR) of 5% or less after being immersed in a NACE Solution A solution for 96 hours.
- CAR crack area ratio
- C 0.025-0.084%
- C forms a hard phase such as perlite, quasi-perlite, cementite, bainite, martensite, and has an action of increasing the strength of the steel pipe. Further, C affects the oxide formation in the ERW weld zone through freezing point depression, CO formation reaction with O 2 in the gas phase, and the like during ERW welding. In order to ensure such an effect, the content of 0.025% or more is required. If C is less than 0.025%, the desired yield strength YS: 400 MPa or more cannot be secured.
- Si 0.10 to 0.30% Si has the effect of increasing the strength of the electric resistance welded steel pipe by solid solution strengthening. Si has a stronger affinity with O than Fe, and forms a highly viscous eutectic oxide together with Mn oxide in the ERW weld. If the Si content is less than 0.10%, the Mn concentration in the eutectic oxide increases, the melting point of the oxide exceeds the molten steel temperature, and it tends to remain in the ERW weld as an oxide. For this reason, the total of Si, Mn, and Al contained in inclusions of 2 ⁇ m or more existing in the ERW weld portion exceeds 89 mass ppm, and the toughness is lowered and the HIC resistance is also lowered. For these reasons, Si was limited to 0.10% or more.
- Si is limited to 0.30% or less. It is preferably 0.15 to 0.25%.
- Mn 0.70 to 1.80% Mn has the effect of increasing the strength of the electric resistance welded steel pipe by solid solution strengthening and transformation structure strengthening. Further, Mn has a stronger affinity with O than Fe, and forms a high-eutectic eutectic oxide together with Si oxide in the ERW weld. If the Mn content is less than 0.70%, the Si concentration in the eutectic oxide increases, the melting point of the oxide exceeds the molten steel temperature, and it tends to remain in the ERW weld as an oxide.
- the total of Si, Mn, and Al contained in inclusions of 2 ⁇ m or more existing in the ERW weld exceeds 89 ppm by mass, and the toughness is lowered and the HIC resistance is lowered. Furthermore, if the Mn content is less than 0.70%, the structure of the base metal part and the ERW welded part becomes coarse polygonal ferrite having a particle diameter d ⁇ of more than 10 ⁇ m, so that the toughness decreases. For these reasons, Mn was limited to 0.70% or more.
- Mn content exceeds 1.80%, the Mn concentration in the eutectic oxide increases, the melting point of the oxide exceeds the molten steel temperature, and it tends to remain as an oxide in the ERW. For this reason, the total amount of Si, Mn, and Al contained in the inclusion having an equivalent circle diameter of 2 ⁇ m or more present in the ERW weld exceeds 89 ppm by mass, and the absolute amount as an oxide increases.
- the Mn content exceeds 1.80%, the hard phase fraction of the base metal part and the ERW welded part increases, and the area ratio exceeds 10%. For this reason, toughness falls and HIC resistance also falls. For these reasons, Mn was limited to 0.70 to 1.80%. It is preferably 0.85 to 1.65%.
- P 0.001 to 0.018%
- P is an element that contributes to an increase in strength, but segregates at grain boundaries and reduces toughness. Further, P co-segregates with Mn, and decreases the HIC resistance of the base metal part and the ERW welded part. For this reason, it is desirable to reduce P as much as possible, but extreme reduction leads to an increase in refining costs. Moreover, when it contains exceeding 0.018%, the above-mentioned fall of toughness and HIC resistance will become remarkable. Therefore, P is limited to 0.001 to 0.018%. In addition, Preferably it is 0.013% or less.
- S 0.0001-0.0029% S precipitates as MnS in the ERW weld and the base metal, and lowers toughness and HIC resistance. For this reason, it is desirable to reduce S as much as possible, but excessive reduction leads to an increase in refining costs. On the other hand, if the content exceeds 0.0029%, the toughness and HIC resistance are remarkably lowered. For this reason, S was limited to 0.0001-0.0029%. Preferably, the content is 0.0001 to 0.0019%.
- Al 0.01-0.10%
- Al is an element that acts as a deoxidizer in the steelmaking stage.
- Al precipitates as AlN in austenite, has the effect
- Al has a stronger affinity for O than Si and Mn, and forms an oxide in the form of a solid solution in an Mn—Si eutectic oxide such as 2MnO—SiO 2 (Tephroite). In order to acquire such an effect, 0.01% or more of content is required.
- Al is less than 0.01%, the deoxidizing ability at the steelmaking stage cannot be secured, the cleanliness of the steel is lowered, and Si, Mn, contained in inclusions having an equivalent circle diameter of 2 ⁇ m or more present in the ERW welds. Total Al exceeds 89ppm. For this reason, toughness and HIC resistance are reduced.
- Al is contained in excess of 0.10%, the Al concentration in the eutectic oxide increases, the melting point of the oxide exceeds the molten steel temperature, and it tends to remain in the ERW weld as an oxide.
- Al is limited to the range of 0.01 to 0.10%. Note that the content is preferably 0.03 to 0.08%.
- Nb 0.001 to 0.065%
- Nb precipitates mainly as carbides and has the effect of increasing the strength of the ERW steel pipe.
- a content of 0.001% or more is required.
- the content exceeds 0.065%, undissolved large-sized Nb carbonitride remains, so that toughness and HIC resistance are lowered.
- Nb was limited to the range of 0.001 to 0.065%.
- the content is 0.005 to 0.050%.
- V 0.001 to 0.065%
- Nb precipitates mainly as carbides and has the effect of increasing the strength of the ERW steel pipe.
- a content of 0.001% or more is required.
- V is limited to the range of 0.001 to 0.065%.
- the content is 0.005 to 0.050%.
- Ti 0.001 to 0.033%
- Ti precipitates mainly as carbides and has the effect of increasing the strength of the ERW steel pipe.
- a content of 0.001% or more is required.
- Ti was limited to the range of 0.001 to 0.033%.
- the content is 0.005 to 0.020%.
- Ca 0.0001 to 0.0035%
- Ca is an element having an action of controlling the shape of sulfide in steel in a spherical shape, and improves toughness and HIC resistance in the vicinity of the ERW weld. In order to acquire such an effect, 0.0001% or more of content is required. On the other hand, if the content exceeds 0.0035%, Ca has strong affinity with O, so the Ca concentration in the oxide increases, the melting point of the oxide exceeds the molten steel temperature, and remains as an oxide in the ERW weld. It becomes easy.
- the total amount of Si, Mn, Al, Ca, and Cr contained in inclusions having an equivalent circle diameter of 2 ⁇ m or more present in the ERW weld exceeds 89 mass ppm, and the absolute amount as an oxide increases. For this reason, toughness and HIC resistance are reduced.
- Ca is limited to the range of 0.0001 to 0.0035%. Note that the content is preferably 0.0002 to 0.0028%.
- N 0.0050% or less N is precipitated as Ti (N, C) or remains as solute N in the ERW weld and the base metal part, and lowers toughness and HIC resistance. For this reason, it is desirable to reduce N as much as possible, but since excessive reduction raises refining cost, it is desirable to limit it to 0.0001% or more. On the other hand, when it exceeds 0.0050%, the above-mentioned deterioration of toughness and HIC resistance becomes remarkable. For this reason, N was limited to 0.0050% or less. Note that the content is preferably 0.0001 to 0.0040%.
- O 0.0030% or less O remains as an oxide-based inclusion in the ERW weld and the base metal, and lowers toughness and HIC resistance. For this reason, it is desirable to reduce as much as possible. When O exceeds 0.0030%, the toughness and the HIC resistance are remarkably lowered. For this reason, O was limited to 0.0030% or less. In addition, since excessive reduction causes the refining cost to rise, it is preferable to make it 0.0001% or more. In addition, Preferably it is 0.0020% or less.
- B 0.0030% or less and / or Cu: 0.001 to 0.350%, Ni: 0.001 to 0.350%, Mo: One or more selected from 0.001 to 0.350% and Cr: 0.001 to 0.700% may be selected and contained as necessary.
- B 0.0030% or less B contributes to an increase in the strength of the electric resistance welded steel pipe through improvement of hardenability. In order to acquire such an effect, it is desirable to contain 0.0001% or more. However, even if the content exceeds 0.0030%, the effect is saturated, and an effect commensurate with the content cannot be expected. For this reason, when it contains, it is preferable to limit B to 0.0030% or less. More preferably, it is 0.0020% or less.
- Cu 0.001 to 0.350%, Ni: 0.001 to 0.350%, Mo: 0.001 to 0.350%, Cr: 0.001 to 0.700% All of Cu, Ni, Mo and Cr It is an element that contributes to increasing the strength of the base metal part and the ERW welded part of the thick-walled electric-welded steel pipe and suppressing the formation of coarse polygonal ferrite, and it can be selected as necessary and contained in one or more kinds.
- Cu secures the desired high strength through the improvement of the hardenability of the base metal part and ERW welded part of thick-walled ERW steel pipe, and suppresses the formation of coarse polygonal ferrite with a grain size d ⁇ exceeding 10 ⁇ m
- the content is preferably 0.001% or more.
- the content is preferably limited to a range of 0.001 to 0.350%. More preferably, it is 0.05 to 0.290%.
- Ni like Cu, ensures the desired high strength by improving the hardenability of the base metal part and ERW welded part of the thick-walled ERW steel tube, and coarse polygonal ferrite with a grain size d ⁇ exceeding 10 ⁇ m It has the effect
- Mo like Ni and Cu, ensures the desired high strength through the improvement of the hardenability of the base metal part and the ERW welded part of the thick-walled ERW steel pipe, and the grain size d ⁇ is coarser than 10 ⁇ m. It has the effect of suppressing the formation of polygonal ferrite. Further, Mo has the effect of improving the HIC resistance of the ERW steel pipe. In order to ensure such an effect, it is desirable to contain 0.001% or more. On the other hand, even if the content exceeds 0.350%, the effect is saturated and an effect commensurate with the content cannot be expected. Therefore, when contained, Mo is preferably limited to a range of 0.001 to 0.350%. More preferably, it is 0.05 to 0.290%.
- Cr like Mn, contributes to increasing the strength of the electric resistance welded steel pipe through the transformation structure strengthening, and has the effect of ensuring the desired high strength and suppressing the formation of coarse polygonal ferrite. In order to ensure such an effect, it is preferable to contain 0.001% or more.
- Cr has a stronger affinity with O than Fe and has a strong tendency to form an oxide. If it exceeds 0.700%, the Cr concentration in the oxide increases and the melting point of the oxide exceeds the molten steel temperature. , It tends to remain in the ERW weld as an oxide.
- Cr is preferably limited to a range of 0.001 to 0.700%. More preferably, the content is 0.01 to 0.700%. More preferably, it is 0.02 to 0.290%.
- Pcm is a parameter related to the formation of the structure after rapid cooling of the ERW weld. If Pcm satisfies 0.20 or less, the structure of the ERW weld will be the area of the pseudopolygonal ferrite with a particle size of 10 ⁇ m or less. Rate: The organization can be 90% or more. When Pcm exceeds 0.20, the structure fraction of pseudopolygonal ferrite in the ERW weld becomes less than 90% in terms of area ratio, and the toughness decreases. There is no particular limitation on the lower limit of Pcm, but it is preferable that the yield strength is YS: 0.070 or more that can stably ensure 400 MPa or more.
- the high-strength thick-walled electric-welded steel pipe of the present invention has a structure in which both the base metal part and the electric-welded welded part have a pseudopolygonal ferrite having a particle size of 10 ⁇ m or less and an area ratio of 90% or more.
- pseudopolygonal ferrite means “steel bainite photo book-1” (Japan Steel Association Basic Joint Study Group, edited by Bainite Research Group: “steel bainite photo book-1”, No.
- ⁇ q is an amorphous structure which is formed at a temperature lower than that of polygonal ferrite ⁇ p and exceeds the austenite grain boundary before transformation, and most of transformation strain is recovered.
- the fraction of pseudopolygonal ferrite was limited to 90% or more in terms of area ratio. In addition, Preferably it is 92% or more.
- the grain size d ⁇ of the pseudopolygonal ferrite exceeds 10 ⁇ m and becomes coarse, desired high strength and high toughness cannot be ensured. For this reason, the particle size d ⁇ of the pseudo-polygonal ferrite is limited to 10 ⁇ m or less. The particle size is measured using a cutting method in accordance with the provisions of JIS G 0551 (2005).
- the second phase other than the pseudopolygonal ferrite can accept pearlite, pseudopearlite, cementite, bainite, martensite, etc. with a total area ratio of less than 10%.
- the total amount of Si, Mn, Al, Ca, Cr contained in inclusions having an equivalent circle diameter of 2 ⁇ m or more present in the ERW welded portion is 0.0089% or less. It is preferable that in addition, when there is an element which does not contain among the above-described elements, the total amount is calculated with the element as zero.
- the total amount of Si, Mn, Al, Ca, and Cr contained in inclusions having an equivalent circle diameter of 2 ⁇ m or more means the amount of inclusions that affect the properties. The larger the total amount, the larger the amount of inclusions.
- the total amount of Si, Mn, Al, Ca, and Cr contained in inclusions having an equivalent circle diameter of 2 ⁇ m or more among the inclusions present in the electric resistance welded portion is obtained as follows.
- a plate-like sample (size: width 2 mm x thickness: pipe thickness x length: pipe thickness) is cut out from the ERW welded part of the ERW steel pipe, centering on the ERW welded center, and 10% AA electrolysis is performed. Electrolytic extraction was performed in the liquid. After electrolytic extraction, inclusions of 2 ⁇ m or more are extracted using a filter mesh having a hole diameter of 2 ⁇ m, and after alkali melting, the contents of Si, Mn, Al, Ca, Cr contained are measured by ICP analysis. The total amount of each element obtained is obtained and taken as the total amount of Si, Mn, Al, Ca, and Cr contained in inclusions having an equivalent circle diameter of 2 ⁇ m or more.
- a steel material such as a slab having the above composition is subjected to a hot rolling process to form a hot rolled steel strip.
- the obtained hot-rolled steel strip is further continuously roll-formed to form a tubular formed body, and a pipe-forming step for electro-welding the tubular formed body is performed to obtain an electric-welded steel pipe.
- a steel material such as a slab is subjected to a hot rolling process to form a hot rolled steel strip.
- the steel material having the composition described above is heated to a temperature in the temperature range of 1200 to 1280 ° C and held for 90 minutes or more, and then heat in the non-recrystallized austenite region (non-recrystallization temperature region).
- Hot rolling is performed at a hot rolling rate (rolling rate) of 20% or more.
- the sheet is cooled to a cooling stop temperature of 630 ° C. or less at a cooling rate of 7 to 49 ° C./s at an average temperature in the range of 780 ° C. to 630 ° C. at the center thickness of the sheet, and the coiling temperature is 400 Winding at a temperature of °C to less than 600 °C (400 to 599 °C) to make a hot-rolled steel strip.
- Heating temperature 1200 ⁇ 1280 °C
- the heating temperature of the steel material affects the strength, low temperature toughness, and HIC resistance of the steel pipe base material.
- the heating temperature is less than 1200 ° C.
- precipitation strengthening elements such as Nb, V, and Ti do not re-dissolve but remain as coarse precipitates, and a desired high yield strength YS: 400 MPa or more cannot be secured.
- residual coarse precipitates reduce HIC resistance.
- the heating temperature is higher than 1280 ° C., the crystal grains are coarsened, and the obtained pseudopolygonal ferrite is coarsened, so that the desired grain size d ⁇ : 10 ⁇ m or less cannot be satisfied.
- the heating temperature was limited to the range of 1200 to 1280 ° C.
- the heating and holding time is 90 min or longer.
- precipitation strengthening elements such as Nb, V, and Ti do not re-dissolve particularly in the central portion of the thickness, and remain as coarse precipitates, reducing HIC resistance.
- the heating and holding time was limited to 90 min or more.
- the heated steel material is subjected to hot rolling consisting of rough rolling and finish rolling.
- the hot rolling rate (rolling rate) in the non-recrystallized austenite region (non-recrystallization temperature region) 20% or more, and the finish rolling finish temperature: 780 ° C. or more.
- Hot rolling rate (reduction rate) in non-recrystallization austenite range (non-recrystallization temperature range) is 20 If it is less than%, the structure becomes coarse and the desired toughness cannot be secured. For this reason, the hot rolling rate (rolling rate) in the non-recrystallized austenite region (non-recrystallization temperature region) is limited to 20% or more. In addition, Preferably it is 30% or more.
- Finish rolling end temperature 780 ° C. or higher
- the finish rolling end temperature 780 ° C. or higher is preferable.
- the cooling rate is an average cooling rate ranging from 7 to 49 ° C / s from 780 ° C to 630 ° C at the wall thickness center temperature, cooling to a cooling stop temperature of 630 ° C or less, and coiling temperature: 400 ° C or more Wind up below 600 ° C (400-599 ° C).
- the average cooling rate is less than 7 ° C./s, coarse polygonal ferrite is generated, and desired high toughness and high strength cannot be ensured.
- the average cooling rate exceeds 49 ° C./s, bainite and martensite are generated, the strength becomes too high, and the desired high toughness cannot be ensured. For this reason, it was decided to cool at a cooling rate in the range of 7 to 49 ° C./s on average from 780 ° C. to 630 ° C.
- the average cooling rate at which the amount of pseudopolygonal ferrite produced is 92% or more is preferably 29 ° C./s or less.
- the cooling rate at each position of the total thickness excluding the outermost layer 0.2mm is 5 ° C / s on the slow side and 20 ° C / s on the fast side as a deviation from the center of the thickness. It is desirable to be within. It cools and winds up to 630 degrees C or less with the above-mentioned cooling rate at the wall thickness temperature. Cooling stop temperature: 630 ° C. or less When the cooling stop temperature exceeds 630 ° C., the desired fine structure cannot be secured, and the desired high strength and toughness cannot be secured at the base material portion. For this reason, the cooling stop temperature is limited to a temperature of 630 ° C. or lower. The temperature is preferably 600 to 550 ° C.
- Winding temperature 400 °C or more and less than 600 °C (400 ⁇ 599 °C)
- the coiling temperature is 600 ° C. or higher, the structure becomes coarse, and a structure having pseudo-polygonal ferrite having a desired particle size and a desired fraction cannot be obtained. If it is less than 400 ° C., a large amount of bainite is formed, the strength increases, and the toughness and HIC resistance decrease. For this reason, the coiling temperature was limited to 400 ° C. or more and less than 600 ° C. (400 to 599 ° C.). The temperature is preferably 550 to 450 ° C.
- the fine pseudo-polygonal ferrite having a particle size d ⁇ of 10 ⁇ m or less is 90% or more in area ratio, and the balance is pearlite or pseudo-pearlite.
- yield strength YS high strength of 400 MPa or more
- NACE After immersing in the NACE Solution A solution defined in TM0284 for 96 hours, a steel pipe having an excellent HIC resistance base material part with a crack area ratio CAR of 5% or less can be obtained.
- the obtained hot-rolled steel strip is then cut to a predetermined width, and then subjected to a pipe making process to form an electric resistance steel pipe having a predetermined size and shape.
- a pipe forming process any of the generally known electric resistance welded pipe processes can be applied, and an electric resistance welded steel pipe having a predetermined size and shape can be formed, and the conditions are not particularly limited.
- the hot-rolled steel strip is continuously cold-rolled to form a tubular molded body having a substantially circular cross-section, and then the circumferential ends of the tubular molded body are butted together so that high-frequency resistance heating or high-frequency A step of heating the circumferential end to the melting point or higher by induction heating, press-contacting with a squeeze roll, and electro-welding the seam portion to form an electric-welded steel pipe is preferable.
- a taper groove on the end surface in the width direction of the hot-rolled steel strip in fin pass forming.
- a taper groove By providing a taper groove, discharge of oxide from the ERW weld is promoted, and an ERW weld having excellent toughness and HIC resistance can be obtained.
- the taper of the groove applied to the end in the width direction is such that the distance in the thickness direction of the steel strip between the taper start position and the surface serving as the pipe outer surface or the surface serving as the pipe inner surface is 2 to 60% of the steel strip thickness. It is preferable to make it.
- the tapered shape is not limited to a straight line, and may be an arbitrary curved shape.
- the oxygen partial pressure of the atmosphere at the time of electric resistance welding By adjusting the oxygen partial pressure of the atmosphere at the time of electric resistance welding, coarse oxides present in the electric resistance welding portion can be reduced.
- the atmospheric oxygen partial pressure of the ERW weld By setting the atmospheric oxygen partial pressure of the ERW weld to 900 / f oxy mass ppm or less, the total amount of Si, Mn, Al, Ca and Cr contained in inclusions with an equivalent circle diameter of 2 ⁇ m or more is about 20 mass ppm. Can be reduced.
- a method for reducing the atmospheric oxygen partial pressure of the ERW weld there is a method of sealing the ERW weld with a box structure and supplying a non-oxidizing gas to the ERW weld.
- the surrounding atmosphere when supplying the non-oxidizing gas, the surrounding atmosphere may be involved and the atmospheric oxygen partial pressure of the ERW weld may increase.
- the nozzle for supplying the gas has a multilayer structure such as three layers so that the supplied gas becomes a laminar flow.
- it is preferable to measure the oxygen concentration of the electric resistance welding part by bringing the probe of the oximeter close to the electric resistance welding part.
- the ERW steel pipe obtained through the pipe making process is further subjected to heat treatment at the ERW weld.
- the toughness of the ERW weld is affected by the oxide amount and matrix (base) of the ERW weld. Therefore, in the present invention, heat treatment is further performed on the ERW welded part online.
- the total thickness of the ERW weld is heated so that it falls within the range of 800 ° C to 1150 ° C, and then the average thickness in the range of 780 to 630 ° C is 7 to 49 ° C / s. Cooling is performed at a cooling rate to a cooling stop temperature of 630 ° C. or lower, and then allowed to cool.
- Heating temperature for heat treatment 800 °C ⁇ 1150 °C
- the heating temperature is less than 800 ° C.
- the structure of the electro-welded weld becomes coarse polygonal ferrite, and it becomes difficult to secure desired high strength and high toughness.
- the temperature is higher than 1150 ° C.
- the particle size d ⁇ of the pseudopolygonal ferrite to be generated exceeds 10 ⁇ m and becomes coarse, and the toughness decreases.
- the heating temperature of the heat treatment was limited to a temperature in the range of 800 ° C. to 1150 ° C.
- the temperature is preferably 850 to 1100 ° C.
- Average cooling rate after heat treatment 7 to 49 ° C / s
- the average cooling rate in the range of 780 to 630 ° C. after heating is less than 7 ° C./s, the structure becomes a coarse polygonal ferrite, and it becomes difficult to ensure desired high strength and high toughness.
- bainite is likely to be formed, the fraction of pseudopolygonal ferrite is less than 90%, the strength is increased, and the low temperature toughness and the HIC resistance are decreased.
- the cooling after heating was limited to a range of 7 to 49 ° C./s with an average cooling rate in the range of 780 to 630 ° C. It is preferably 29 ° C./s or less from the viewpoint of setting the fraction of pseudopolygonal ferrite to 93% or more.
- the cooling rate at each position of the total thickness excluding the outermost layer 0.2mm is a deviation from the center of the wall thickness, 5 ° C / s on the slow side and 20 ° on the fast side. It is desirable that the temperature be within a temperature / second. As a result, variation in characteristics in the thickness direction is reduced.
- Cooling stop temperature 630 ° C or less In cooling after heating, if the cooling stop temperature exceeds 630 ° C, the desired fine structure cannot be secured, and the desired high strength and high toughness can be secured in the ERW weld. Disappear. For this reason, the cooling stop temperature is limited to a temperature of 630 ° C. or lower. The temperature is preferably 550 to 200 ° C.
- the fine pseudopolygonal ferrite having a particle size d ⁇ of 10 ⁇ m or less is 90% or more in area ratio, and the remainder is pearlite, pseudopearlite, cementite, bainite, martensite. It can be set as the electric-welding welding part which has the structure
- the cooling headers arranged in a plurality of rows are arranged so that the cooling water injection can be individually controlled. Furthermore, the temperature of the ERW welded part is measured on the downstream side in the conveyance direction, and the water injection from each cooling header is controlled on and off based on the measured ERW welded part temperature, and the cooling rate of the ERW welded part is controlled. Was adjusted to the target cooling rate.
- the temperature controllability is improved, and it is stable to cool to 630 ° C or lower at a cooling rate of 7-49 ° C / s on average between 780 ° C and 630 ° C at the desired thickness center temperature.
- a desired tissue can be stably obtained.
- the nozzle is less than 2 rows in the direction of steel pipe conveyance, or the cooling water injection speed is less than 1 m / s, the desired cooling is caused by the influence of the boiling film, etc. I can't get the speed.
- it is also effective to install the nozzle inclined or to face the nozzle in order to ensure a cooling rate by promptly removing the boiling film.
- Example 1 A steel slab (steel material) (thickness: 250 mm) having the composition shown in Table 1 was subjected to a hot rolling process consisting of heating, finish rolling, cooling after finishing rolling, and winding of the conditions shown in Table 2, and Table 2 A hot-rolled steel strip having the thickness shown in FIG. After slitting these hot-rolled steel strips to a predetermined width, roll forming was continuously performed in a cold manner, which is a conventional tube forming process, to obtain a tubular molded body having a substantially circular cross section. Then, the circumferential ends are butted together, and the circumferential ends are heated to a melting point or higher by high-frequency resistance heating, and subjected to electro-welding by pressure welding with a squeeze roll. : 26 in. ⁇ (660.4 mm ⁇ )). In roll forming, a taper groove was not applied to the end portion of the steel strip. In addition, ERW welding was performed in the atmosphere.
- a hot rolling process consisting of heating, finish rolling, cooling after finishing
- heat treatment was applied to the ERW weld.
- the heat treatment was performed by heating and cooling the conditions shown in Table 2 on the ERW welded part online. Heating was performed using a high-frequency induction heating device arranged online.
- a cooling header connected to a nozzle capable of injecting rod-shaped cooling water having a water volume density of 2 m 3 / m 2 min is provided above the ERW weld, and the cooling header is connected to the steel pipe in the conveying direction. 10 rows were arranged.
- the cooling header was individually arranged so that cooling water injection could be turned on and off, and the rod-shaped cooling water was jetted from the nozzle at a speed of 2 m / s.
- the temperature of the ERW welded part is measured on the downstream side in the steel pipe conveyance direction, and water injection from each cooling header is controlled on and off based on the measured temperature of the ERW welded part. The cooling rate of was adjusted.
- Specimens were taken from the base metal part and the ERW welded part of the obtained ERW steel pipe, and subjected to a tensile test, an impact test, an HIC test, and an inclusion amount measurement test.
- the test method was as follows.
- the fine pseudo-polygonal ferrite having a particle size d ⁇ of 10 ⁇ m or less occupies 90% or more of the area ratio in both the base metal part and the ERW weld part, and the yield strength YS: High strength of 400MPa or higher, Charpy impact test absorbed energy at -50 ° C, and excellent low temperature toughness of -50 , 150J or higher, soaked in NACE Solution A solution specified in NACE TM0284 for 96h After that, the ERW steel pipe has excellent HIC resistance with a crack area ratio CAR of 5% or less.
- the balance other than pseudopolygonal ferrite was pearlite, pseudopearlite, cementite, bainite, and martensite with an area ratio of less than 10%.
- the base material part and the ERW welded part are not obtained with a structure mainly composed of fine pseudopolygonal ferrite, or the equivalent circle diameter of the ERW welded part is 2 ⁇ m.
- the total amount of Si, Mn, Al, Ca, and Cr contained in the above inclusions exceeds 89 mass ppm, and the amount of inclusions increases. Therefore, in the comparative example, the desired high strength cannot be ensured, the low temperature toughness is lowered, or the HIC resistance is lowered.
- Comparative examples (steel pipes No. 7, No. 11, No. 17, No. 19, No. 21) in which any of C, Mn, Nb, V, and Ti deviate from the scope of the present invention are the base material, electric sewing Both welds have a softer polygonal ferrite structure, and YS is less than 400 MPa, and the desired high strength cannot be obtained.
- comparative examples (steel pipes No. 8, No. 12, No. 18, No. 20, No. 22) in which any of C, Mn, Nb, V, and Ti deviate from the scope of the present invention are the base material, The low temperature toughness and HIC resistance of both ERW welds are reduced. Comparative examples (steel pipe No. 9, No. 10, No.
- Example 2 Using the steel materials (slabs) of steel Nos. A to F shown in Table 1, a hot-rolled steel strip having the thickness shown in Table 4 was obtained in the hot-rolling step under the conditions shown in Table 4. These hot-rolled steel strips were slitted to a predetermined width, continuously roll-formed, and made into an electric-welded steel pipe having the dimensions shown in Table 4 by a pipe making process of electric-welding welding. In some steel pipes, a tapered groove having the dimensions shown in Table 4 was applied to the end portion in the steel strip width direction during roll forming. Further, the electric resistance welding was performed in the atmosphere except for some steel pipes. In some steel pipes, non-oxidizing gas was blown into the atmosphere during ERW welding. At that time, the gas blowing nozzles were arranged in three layers, and the conditions were such that the oxygen partial pressure was reduced to 45 ppm by mass.
- heat treatment was performed on the ERW welded portion of the obtained ERW steel pipe by heating and cooling under the conditions shown in Table 4.
- the heating used the induction heating apparatus arrange
- 10 rows of cooling headers connected to nozzles capable of injecting rod-shaped cooling water with a water density of 2 m 3 / m 2 min above the ERW weld are arranged in the transport direction, and rod-shaped cooling water is discharged from the nozzles.
- the injection was performed at a speed of 2 m / s or more.
- the cooling header is arranged so that the cooling water injection can be individually controlled, and the temperature of the ERW welded portion is measured on the downstream side in the conveying direction, and each cooling header is measured based on the measured ERW weld temperature.
- the cooling rate of the ERW weld was adjusted by ON-OFF control of water injection from the header.
- test pieces were collected from the obtained electric resistance welded steel pipe and subjected to a tensile test, an impact test, an HIC test, and an inclusion amount measurement test.
- the test method was the same as in Example 1. The results obtained are shown in Table 5.
- the present invention example has a high yield strength YS: 400 MPa or more and excellent low temperature toughness with Charpy impact test absorbed energy vE ⁇ 50 at ⁇ 50 ° C. of 150 J or more, and is specified in NACE TM0284. After being immersed in NACE Solution A solution for 96 hours, it is an ERW steel pipe that retains excellent HIC resistance with a crack area ratio CAR of 5% or less.
- the balance other than pseudopolygonal ferrite was pearlite, pseudopearlite, cementite, bainite, and martensite with an area ratio of less than 10%.
- comparative examples in which the heating temperature in the heat treatment falls outside the scope of the present invention (steel pipe No. A11, No. A21)
- comparative examples in which the cooling rate after heating in the heat treatment falls outside the scope of the present invention (steel pipe No. A6, In No. A26)
- the structure of the ERW weld is coarsened, the strength is lowered, and the toughness is lowered.
- comparative examples in which the heating temperature in heat treatment deviates from the scope of the present invention (steel pipe No. A15, No. A25)
- comparative examples in which the cooling rate after heating in heat treatment deviates from the scope of the present invention (steel pipe No. A10, No. A30) has a structure different from that of a desired fine pseudopolygonal ferrite in the structure of the ERW weld, and the toughness and HIC resistance of the ERW weld are reduced.
- the present invention example (steel pipe No. A14) in which a groove at the end of the steel strip was given during electric resistance welding
- the present invention example (steel pipe No. A24) in which atmosphere control was performed during electric resistance welding.
- the total amount of Si, Mn, Al, Ca and Cr contained in inclusions with an equivalent circle diameter of 2 ⁇ m or more present in the ERW weld is as low as 20 ppm by mass or less, and the vE- 50 of the ERW weld is 400 J.
- the low temperature toughness is remarkably improved.
- the present invention example (steel pipe No. A28) in which heat treatment was further tempered at 450 ° C. for 1 min after heating and cooling similarly provided good low temperature toughness and good HIC resistance.
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Abstract
Description
電縫溶接部から、JIS Z 2242の規定に準拠して、ノッチ部が電縫溶接部の中央部に一致するように、円周方向にVノッチシャルピー試験片(10mm厚)を採取し、試験温度:-50℃でシャルピー衝撃試験を実施し、吸収エネルギーvE-50を求めた。なお、試験本数は各3本とした。
電縫溶接部から、浸漬試験片(大きさ:厚さ10mm×幅20mm×長さ160mm)を採取し、NACE TM0284に規定されるNACE Solution A溶液(0.5%CH3COOH+5%NaCl+飽和H2S)中に96h間浸漬した。浸漬後、超音波探傷法にて、各試験片の割れ面積率CARを求めた。
電縫溶接部から、電縫溶接部中央を中心として、板状サンプル(大きさ:幅2mm×厚さ:管肉厚×長さ:管肉厚)を切出し、10%AA電解液中で電解抽出を行った。電解抽出後、穴径2μmのフィルターメッシュを用いて、介在物(円相当径2μm以上)を抽出し、アルカリ融解したのち、ICP(Inductively Coupled Plasma)分析により、含まれるSi、Mn、Al、Ca、Crの含有量を測定し、その合計量を求めた。得られた円相当径2μm以上の介在物に含まれるSi、Mn、Al、Ca、Crの合計量を、電縫溶接部に存在する介在物量とした。
図1、2から、電縫溶接部の加熱温度が800~1150℃の範囲で、かつ加熱後の冷却速度が780~630℃間の平均で7~49℃/sの範囲である場合に、vE-50が150J以上と、優れた電縫溶接部靭性を示し、CARが5%以下と、優れた耐HIC性を示すことがわかる。
また、得られた結果から、vE-50、CARと、円相当径2μm以上の介在物に含まれるSi、Mn、Al、Ca、Crの合計量との関係で図3に示す。
Pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B‥(1)
(ここで、C,Si,Mn,Cu,Ni,Cr,Mo,V,B:各元素の含有量(質量%))
で定義されるPcmが0.20以下を満足し、残部Fe及び不可避的不純物よりなる組成を有する。さらに母材部および電縫溶接部がともに、粒径:10μm以下の擬ポリゴナルフェライトを面積率:90%以上有する組織を有し、降伏強さYS:400MPa以上で、シャルピー衝撃試験の-50℃における吸収エネルギーvE-50:150J以上の高靭性を有することを特徴とする耐HIC性に優れた高強度厚肉電縫鋼管。
(2)(1)において、前記組成に加えてさらに、質量%で、B:0.0030%以下を含有することを特徴とする高強度厚肉電縫鋼管。
(4)(1)ないし(3)のいずれかにおいて、前記電縫溶接部に存在する、円相当径2μm以上の介在物に含まれるSi、Mn、Al、Ca、Crの合計量が、質量%で0.0089%以下であることを特徴とする高強度厚肉電縫鋼管。
Pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B‥(1)
(ここで、C,Si,Mn,Cu,Ni,Cr,Mo,V,B:各元素の含有量(質量%))
で定義されるPcmが0.20以下を満足し、残部Fe及び不可避的不純物よりなる組成を有する鋼素材とし、前記熱延工程が、前記鋼素材を、加熱温度:1200~1280℃の温度範囲の温度に加熱し、90min以上保持したのち、未再結晶オーステナイト域での熱間圧延率を20%以上とする熱間圧延を施し、該熱間圧延終了後に、板厚中央部温度で780℃~630℃の範囲の平均で、7~49℃/sの冷却速度で冷却停止温度:630℃以下まで冷却し、巻取温度:400℃以上600℃未満で巻取り、熱延鋼帯とする工程であり、前記造管工程後に、オンラインで前記電縫鋼管の電縫溶接部を、肉厚全厚が800℃~1150℃の範囲内となるように加熱したのち、肉厚中央部温度で780℃~630℃の範囲の平均で7~49℃/sの冷却速度で630℃以下の冷却停止温度まで冷却し、その後放冷する熱処理を施し、母材部および電縫溶接部がともに、降伏強さYS:400MPa以上で、シャルピー衝撃試験の-50℃における吸収エネルギーvE-50:150J以上の高靭性を有することを特徴とする耐HIC性に優れた高強度厚肉電縫鋼管の製造方法。
foxy=Mn+10(Si+Cr)+100Al+1000Ca ‥‥(2)
(ここで、Mn、Si、Cr、Al、Ca:各元素の含有量(質量%))
で定義される溶鋼の易酸化度foxyに関連して900/foxy 質量ppm以下に調整することを特徴とする高強度厚肉電縫鋼管の製造方法。
Cは、パーライト(perlite)、擬似パーライト(quasi-perlite)、セメンタイト(cementite)、ベイナイト(bainite)、マルテンサイト(martensite)など硬質相を形成し、鋼管の強度を増加させる作用を有する。また、Cは、電縫溶接時に、凝固点降下、気相中O2とのCO形成反応などを介して、電縫溶接部の酸化物形成に影響を及ぼす。このような効果を確保するためには、0.025%以上の含有を必要とする。Cが0.025%未満では、所望の降伏強さYS:400MPa以上を確保できなくなる。一方、Cが0.084%を超えて多量に含有すると、電縫溶接部および母材部の硬質相の分率が10%を超え、低温靭性が低下し、-50℃におけるシャルピー衝撃試験吸収エネルギーが150Jを下回る。それとともに、NACE TM0284に規定されるNACE Solution A溶液中に96h間浸漬した後の割れ面積率CARが5%を超えて耐HIC性が低下する。このようなことから、Cは0.025~0.084%の範囲に限定した。なお、好ましくは0.030~0.060%である。
Siは、固溶強化により電縫鋼管の強度を増加させる作用を有する。またSiは、FeよりもOとの親和力が強く、電縫溶接部において、Mn酸化物とともに粘度の高い共晶酸化物を形成する。Si含有量が0.10%未満では、共晶酸化物中のMn濃度が上がり、酸化物の融点が溶鋼温度を超えて、酸化物として電縫溶接部に残存し易くなる。このため、電縫溶接部に存在する2μm以上の介在物に含まれるSi、Mn、Alの合計が89質量ppmを超え、靭性が低下するとともに、耐HIC性も低下する。このようなことから、Siは0.10%以上に限定した。
Mnは、固溶強化と変態組織強化により、電縫鋼管の強度を増加させる作用を有する。また、Mnは、FeよりもOとの親和力が強く、電縫溶接部においては、Si酸化物とともに粘度の高い共晶酸化物を形成する。Mn含有量が0.70%未満では、共晶酸化物中のSi濃度が上がり、酸化物の融点が溶鋼温度を超え、酸化物として電縫溶接部に残存し易くなる。このため、電縫溶接部に存在する2μm以上の介在物に含まれるSi、Mn、Alの合計が89質量ppmを超えて、靭性が低下するとともに、耐HIC性が低下する。さらに、Mn含有量が0.70%未満では、母材部および電縫溶接部の組織が、粒径dα:10μm超えの粗大なポリゴナルフェライトとなるため、靭性が低下する。このようなことから、Mnは0.70%以上に限定した。
Pは、強度増加に寄与する元素であるが、粒界等に偏析して靭性を低下させる。また、Pは、Mnと共偏析し、母材部および電縫溶接部の耐HIC性を低下させる。このため、Pはできるだけ低減することが望ましいが、極端な低減は、精錬コストの高騰を招く。また、0.018%を超えて含有すると、上記した靭性、耐HIC性の低下が著しくなる。このため、Pは0.001~0.018%に限定した。なお、好ましくは0.013%以下である。
Sは、電縫溶接部および母材部にMnSとして析出し、靭性、耐HIC性を低下させる。このため、Sはできるだけ低減することが望ましいが、過度の低減は精錬コストの高騰を招く。一方、0.0029%を超えて含有すると、靭性、耐HIC性の低下が著しくなる。このため、Sは0.0001~0.0029%に限定した。なお、好ましくは0.0001~0.0019%である。
Alは、製鋼段階での脱酸剤として作用する元素である。また、Alは、オーステナイト中にAlNとして析出し、オーステナイト加熱時の粒成長を抑制し、鋼の低温靭性を向上させる作用を有する。また、Alは、Si、MnよりもさらにOとの親和力が強く,2MnO-SiO2(Tephroite)などのMn-Si共晶酸化物に固溶する形で酸化物を形成する。このような効果を得るためには、0.01%以上の含有を必要とする。Alが0.01%未満では、製鋼段階での脱酸能が確保できず、鋼の清浄度が低下して、電縫溶接部に存在する円相当径2μm以上の介在物に含まれるSi、Mn、Alの合計が89ppmを超える。このため、靭性、耐HIC性が低下する。
Nbは、主として炭化物として析出し、電縫鋼管の強度を増加する作用を有する。このような効果を得るためには0.001%以上の含有を必要とする。一方、0.065%を超えて多量の含有は、未固溶の大型Nb炭窒化物が残存し、そのため、靭性、および耐HIC性が低下する。このため、Nbは0.001~0.065%の範囲に限定した。なお、好ましくは0.005~0.050%である。
Vは、Nbと同様、主として炭化物として析出し、電縫鋼管の強度を増加させる作用を有する。このような効果を得るためには0.001%以上の含有を必要とする。一方、0.065%を超えて多量に含有すると、未固溶の大型V炭窒化物が残存し、そのため、靭性、耐HIC性が低下する。このため、Vは0.001~0.065%の範囲に限定した。なお、好ましくは0.005~0.050%である。
Tiは、Nb、Vと同様、主として炭化物として析出し、電縫鋼管の強度を増加させる作用を有する。このような効果を得るためには0.001%以上の含有を必要とする。一方、0.033%を超えて多量に含有すると、未固溶の大型Ti炭窒化物が残存し、そのため、靭性、耐HIC性が低下する。このため、Tiは0.001~0.033%の範囲に限定した。なお、好ましくは0.005~0.020%である。
Caは、鋼中の硫化物を球状に形態制御する作用を有する元素であり、電縫溶接部近傍の靭性や耐HIC性を向上させる。このような効果を得るためには、0.0001%以上の含有を必要とする。一方、0.0035%を超えて含有すると、CaがOとの親和力が強いため、酸化物中のCa濃度が上がり、酸化物の融点が溶鋼温度を超えて、酸化物として電縫溶接部に残存し易くなる。このため、電縫溶接部に存在する円相当径2μm以上の介在物に含まれるSi、Mn、Al、Ca、Crの合計が89質量ppmを超えるとともに、酸化物としての絶対量が増える。このため、靭性、耐HIC性が低下する。このようなことから、Caは0.0001~0.0035%の範囲に限定した。なお、好ましくは0.0002~0.0028%である。
Nは、電縫溶接部および母材部においては、Ti(N,C)として析出するか、固溶Nとして残存し、靭性、耐HIC性を低下させる。このため、Nはできるだけ低減することが望ましいが、過度の低減は精錬コストを高騰させるため、0.0001%以上に限定することが望ましい。一方、0.0050%を超えると、上記した靭性、耐HIC性の低下が著しくなる。このため、Nは0.0050%以下に限定した。なお、好ましくは0.0001~0.0040%である。
Oは、電縫溶接部および母材部では、酸化物系介在物として残存し、靭性、耐HIC性を低下させる。このため、できるだけ低減することが望ましい。Oが0.0030%を超えると、靭性、耐HIC性の低下が著しくなる。このため、Oは0.0030%以下に限定した。なお、過度の低減は精錬コストの高騰を招くため、0.0001%以上とすることが好ましい。なお、好ましくは0.0020%以下である。
Bは、焼入れ性向上を介して電縫鋼管の強度増加に寄与する。このような効果を得るためには0.0001%以上含有することが望ましい。しかし、0.0030%を超えて含有しても効果が飽和し、含有量に見合う効果が期待できない。このため、含有する場合には、Bは0.0030%以下に限定することが好ましい。なお、より好ましくは0.0020%以下である。
Cu、Ni、Mo、Crはいずれも、厚肉電縫鋼管の母材部および電縫溶接部の強度増加と粗大なポリゴナルフェライトの形成抑制に寄与する元素であり、必要に応じて選択して1種または2種以上含有できる。
Pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B
(ここで、C,Si,Mn,Cu,Ni,Cr,Mo,V,B:各元素の含有量(質量%))
で定義されるPcmが0.20以下を満足するように含有する。なお、上記した元素のうち、含有しない元素は零として計算するものとする。
本発明高強度厚肉電縫鋼管は、母材部および電縫溶接部がともに、粒径:10μm以下の擬ポリゴナルフェライトを面積率:90%以上有する組織を有する。
なお、ここで「擬ポリゴナルフェライト」とは、「鋼のベイナイト写真集-1」(社団法人日本鉄鋼協会基礎共同研究会 ベイナイト調査研究部会編:「鋼のベイナイト写真集-1」、第4頁、1992.6.29発行、発行元:社団法人日本鉄鋼協会)に記載された「Quasi-polygonal ferrite」(αq)である。αqは、非定形で、polygonal ferrite αpより低温で、変態前のオーステナイト粒界を超えて形成され、変態歪の大部分が回復した組織である。
なお、本発明電縫鋼管の電縫溶接部では、電縫溶接部に存在する、円相当径2μm以上の介在物に含まれるSi、Mn、Al、Ca、Crの合計量が、0.0089%以下とすることが好ましい。なお、合計量は、上記した元素のうち、含有しない元素がある場合には当該元素を零として算出するものとする。円相当径2μm以上の介在物に含まれるSi、Mn、Al、Ca、Crの合計量は、特性に影響を及ぼす介在物量を意味し、合計量が多いほど介在物量が多いことになる。
電縫鋼管の電縫溶接部より、電縫溶接部中央を中心として、板状サンプル(大きさ:幅2mm×厚さ:管肉厚×長さ:管肉厚)を切出し、10%AA電解液中で電解抽出を行った。電解抽出後、穴径2μmのフィルターメッシュを用いて、2μm以上の介在物を抽出し、アルカリ融解したのち、ICP分析により、含まれるSi、Mn、Al、Ca、Crの含有量を測定する。得られた各元素の含有量の合計量を求め、円相当径2μm以上の介在物に含まれるSi、Mn、Al、Ca、Crの合計量とする。
上記した組成のスラブ等の鋼素材に、熱延工程を施して熱延鋼帯とする。得られた熱延鋼帯に、さらに連続的にロール成形して管状成形体とし、該管状成形体を電縫溶接する造管工程を施して、電縫鋼管とする。
なお、鋼素材の製造方法については、とくに限定する必要はない。上記した組成の溶鋼を転炉(converter)等の常用の溶製方法で溶製し、連続鋳造法(continuous casting)等の常用の鋳造方法でスラブ等の鋼素材とすることが好ましい。
熱延工程は、上記した組成の鋼素材を、加熱温度:1200~1280℃の温度範囲の温度に加熱し、90min以上保持したのち、未再結晶オーステナイト域(未再結晶温度域)での熱間圧延率(圧下率)を20%以上とする熱間圧延を施す。該熱間圧延終了後に、板厚中央部温度で780℃~630℃の範囲の平均で、7~49℃/sの冷却速度で冷却停止温度:630℃以下まで冷却し、巻取温度:400℃以上600℃未満(400~599℃)で巻取り、熱延鋼帯とする。
鋼素材の加熱温度は、鋼管母材部の強度、低温靭性、耐HIC性に影響を及ぼす。加熱温度が1200℃未満では、Nb、V、Ti等の析出強化元素が再固溶せず粗大な析出物として残存し、所望の降伏強さYS:400MPa以上の高強度を確保できなくなる。また、粗大な析出物の残留は、耐HIC性を低下させる。一方、加熱温度が1280℃を超える高温では、結晶粒が粗大化し、得られる擬ポリゴナルフェライトが粗大化し、所望の粒径dα:10μm以下を満足できなくなる。また、組織が粗大化すると、靭性が低下する。このようなことから、加熱温度は1200~1280℃の範囲の温度に限定した。なお、加熱保持時間は90min以上とする。加熱保持時間が90min未満では、とくに肉厚中心部にNb、V、Ti等の析出強化元素が再固溶せず、粗大な析出物として残存し、耐HIC性を低下させる。このため、加熱保持時間は90min以上に限定した。
未再結晶オーステナイト域(未再結晶温度域)での熱間圧延率(圧下率):20%以上
未再結晶オーステナイト域(未再結晶温度域)での熱間圧延率(圧下率)が20%未満では、組織が粗大化し、所望の靭性を確保できなくなる。このため、未再結晶オーステナイト域(未再結晶温度域)での熱間圧延率(圧下率)を20%以上に限定した。なお、好ましくは30%以上である。
仕上圧延は、仕上圧延終了温度:780℃以上とすることが好ましい。仕上圧延終了温度が780℃未満では、圧延歪が残留し、熱延鋼板の靭性が低下する。
熱間圧延終了後、熱延ランナウトテーブル上で冷却される。冷却速度は、肉厚中央部温度で780℃~630℃までの平均で7~49℃/sの範囲の冷却速度で、630℃以下の冷却停止温度まで冷却し、巻取温度:400℃以上600℃未満(400~599℃)で巻き取る。
平均冷却速度が7℃/s未満では、粗大なポリゴナルフェライトが生成し、所望の高靭性、高強度を確保できなくなる。一方、平均冷却速度が49℃/sを超えると、ベイナイト、マルテンサイトが生成し、強度が高くなりすぎて所望の高靭性を確保できなくなる。このようなことから、780℃~630℃までの平均で7~49℃/sの範囲の冷却速度で冷却することにした。なお、好ましくは擬ポリゴナルフェライトの生成量が92%以上となる平均冷却速度で29℃/s以下である。
上記した冷却速度で、肉厚中央部温度で630℃以下まで冷却し巻取る。
冷却停止温度:630℃以下
冷却停止温度が、630℃超えの温度では、所望の微細な組織を確保できず、母材部で所望の高強度、高靭性を確保できなくなる。このため、冷却停止温度は630℃以下の温度に限定した。なお、好ましくは600~550℃である。
巻取温度が600℃以上となると、組織が粗大化し、所望の粒径、所望の分率の擬ポリゴナルフェライトを有する組織とすることができない。また400℃未満では、ベイナイトが多量に形成され、強度が増加し、靭性および耐HIC性が低下する。このため、巻取温度は400℃以上600℃未満(400~599℃)に限定した。なお、好ましくは550~450℃である。
造管工程は、通常公知の電縫造管工程がいずれも適用でき、所定寸法形状の電縫鋼管を成形できればよく、その条件はとくに限定されない。
好ましくは、熱延鋼帯に、冷間で連続的にロール成形を施しほぼ円形断面の管状成形体としたのち、該管状成形体の円周方向端部同士を突合せて、高周波抵抗加熱或いは高周波誘導加熱により円周方向端部を融点以上に加熱しスクイズロールで圧接しシーム部を電縫溶接して電縫鋼管とする工程が好ましい。
foxy=Mn+10(Si+Cr)+100Al+1000Ca ‥‥(2)
(ここで、Mn、Si、Cr、Al、Ca:各元素の含有量(質量%))
で定義される溶鋼の易酸化度foxyに関連して900/foxy 質量ppm以下に調整することが好ましい。
なお、電縫溶接部の雰囲気酸素分圧を低減させる方法として、電縫溶接部を箱型構造でシーリングし、非酸化性ガスを電縫溶接部に供給する方法が挙げられる。この方法では、非酸化性ガスを供給する際に、周囲の雰囲気を巻き込み、電縫溶接部の雰囲気酸素分圧が増加する場合がある。このような弊害を防止するために、供給するガスが層流となるように、ガスを供給するノズルを3層等の多層構造とすることが好ましい。なお、電縫溶接部の酸素濃度は、酸素濃度計の探触子を電縫溶接部直近に近づけて測定することが好ましい。
電縫溶接部の靭性は、電縫溶接部の酸化物量とマトリクス(基地)の影響を受ける。そのため、本発明では、オンラインで、電縫溶接部に、さらに熱処理を施す。熱処理は、電縫溶接部の全厚を、800℃~1150℃の範囲内となるように加熱したのち、肉厚中央部温度で780~630℃の範囲の平均で7~49℃/sの冷却速度で、630℃以下の冷却停止温度まで冷却し、その後放冷する処理とする。なお、電縫溶接部の加熱は、主に、オンラインに設置された誘導加熱装置で行うことが、生産性の観点から好ましい。
加熱温度が800℃未満では、電縫溶接部の組織が粗大なポリゴナルフェライトとなり、所望の高強度、高靭性を確保することが難しくなる。一方、1150℃を超えて高温とすると、生成する擬ポリゴナルフェライトの粒径dαが10μmを超えて粗大化し、靭性が低下する。このため、熱処理の加熱温度を800℃~1150℃の範囲の温度に限定した。なお、好ましくは850~1100℃である。
加熱後の、780~630℃の範囲の平均冷却速度が7℃/s未満では、組織が粗大なポリゴナルフェライトとなり、所望の高強度、高靭性を確保することが難しくなる。一方、49℃/sを超えると、ベイナイトが生成しやすくなり、擬ポリゴナルフェライトの分率が90%を下回り、強度が上昇し、低温靭性と耐HIC性が低下する。このため、加熱後の冷却を、780~630℃の範囲の平均冷却速度で7~49℃/sの範囲に限定した。なお、好ましくは擬ポリゴナルフェライトの分率を93%以上とする観点から29℃/s以下である。
冷却停止温度:630℃以下
加熱後の冷却では、冷却停止温度が、630℃超えの温度では、所望の微細な組織を確保できず、電縫溶接部で所望の高強度、高靭性を確保できなくなる。このため、冷却停止温度は630℃以下の温度に限定した。なお、好ましくは550~200℃である。
そこで、本発明では、熱処理を行うにあたり、電縫溶接部上方に水量密度:1m3/m2min以上の棒状冷却水が噴射可能なノズルを接続した冷却ヘッダを搬送方向に少なくとも複数列配設することとした。そして、当該ノズルから棒状冷却水を1m/s以上の速度で噴射することが好ましい。また、複数列配設された冷却ヘッダーは、冷却水の注水が各々個別に制御可能に配設されることが好ましい。さらに、電縫溶接部の温度を搬送方向の下流側で測定し、測定された電縫溶接部温度に基づいて各冷却ヘッダーからの注水をON-OFF制御して、電縫溶接部の冷却速度を目標の冷却速度となるように調整することとした。これにより、温度制御性が向上し、所望の、肉厚中央部温度で780℃~630℃間の平均で、7~49℃/sの冷却速度で、630℃以下まで冷却することが安定して可能となり、所望の組織を安定的に得ることができる。
表1に示す組成の鋼スラブ(鋼素材)(肉厚:250mm)に、表2に示す条件の加熱、仕上圧延、仕上圧延終了後の冷却、巻取りからなる熱延工程を施し、表2に示す板厚の熱延鋼帯とした。これらの熱延鋼帯を所定の幅にスリッティングした後、常用の造管工程である、冷間で連続的にロール成形を施しほぼ円形断面の管状成形体とした。その後、円周方向端部同士を突合せて、高周波抵抗加熱により円周方向端部を融点以上に加熱しスクイズロールで圧接して電縫溶接する造管工程を施して、電縫鋼管(外径:26in.φ(660.4mmφ))とした。なお、ロール成形では、鋼帯端部へのテーパー開先の付与は行わなかった。また、電縫溶接は大気中で行なった。
熱処理は、オンラインで、電縫溶接部に、表2に示す条件の加熱及び冷却を施す処理とした。加熱は、オンラインに配設した高周波誘導加熱装置を用いて行った。また、加熱後の冷却は、電縫溶接部の上方に、2m3/m2minの水量密度の棒状冷却水が噴射可能なノズルを接続した冷却ヘッダを設け、該冷却ヘッダを鋼管の搬送方向に10列配列して行った。なお、冷却ヘッダは、個別に冷却水の注水がON-OFF可能に配設され、ノズルから2m/sの速度で棒状冷却水が噴射可能に配設された。また、鋼管搬送方向の下流側で電縫溶接部の温度を測定し、測定された電縫溶接部の温度に基づいて、各冷却ヘッダーからの注水をON-OFF制御して、電縫溶接部の冷却速度を調整した。
得られた電縫鋼管の母材部および電縫溶接部から、母材部では引張方向が管軸方向となるように、JIS Z 2241の規定に準拠して、JIS 12C号試験片を採取した。電縫溶接部では、引張方向が円周方向となるようにJIS Z 2241の規定に準拠して、JIS 1A号試験片を採取し引張試験を行い、引張特性(降伏強さYS、引張強さTS)を求めた。
得られた電縫鋼管の母材部および電縫溶接部から、JIS Z 2242の規定に準拠して、電縫溶接部ではノッチ部が電縫溶接部の中央部に一致するようにして、円周方向にVノッチシャルピー試験片(10mm厚)を採取し、試験温度:-50℃でシャルピー衝撃試験を実施し、吸収エネルギーvE-50を求めた。なお、試験本数は各3本とした。
得られた電縫鋼管の母材部および電縫溶接部から、浸漬試験片(大きさ:厚さ10mm×幅20mm×長さ160mm)を採取し、NACE TM0284に規定されるNACE Solution A溶液(0.5%CH3COOH+5%NaCl+飽和H2S)中に96h間浸漬した。浸漬後、超音波探傷法にて、各試験片の割れ面積率CARを求めた。
得られた電縫鋼管の電縫溶接部から、電縫溶接部中央を中心として、板状サンプル(大きさ:幅2mm×厚さ:管肉厚×長さ:管肉厚)を切出し、10%AA電解液中で電解抽出を行った。電解抽出後、穴径2μmのフィルターメッシュを用いて、2μm以上の介在物を抽出し、アルカリ融解したのち、ICP分析により、含まれるSi、Mn、Al、Ca、Crの含有量を測定し、その合計量を求めた。得られた円相当径2μm以上の介在物に含まれるSi、Mn、Al、Ca、Crの合計量を、電縫溶接部に存在する粗大な介在物量とした。 得られた結果を表3に示す。
表1に示す鋼No.A~Fの鋼素材(スラブ)を用いて、表4に示す条件の熱延工程で表4に示す板厚の熱延鋼帯とした。これら熱延鋼帯を所定幅にスリッティングし、連続的にロール成形し、電縫溶接する造管工程により、表4に示す寸法の電縫鋼管とした。なお、一部の鋼管では、ロール成形時に表4に示す寸法のテーパー開先を鋼帯幅方向端部に付与した。また、電縫溶接は、一部の鋼管を除いて大気中で行なった。一部の鋼管では、電縫溶接時に雰囲気中に非酸化性ガスを吹き込んだ。その際、ガス吹き込み用ノズルは3層に配置したものを用い、酸素分圧を45質量ppmまで低減させた条件で行った。
熱間圧延の加熱温度が本発明の範囲を高く外れる比較例(鋼管No.A2)、熱間圧延における未再結晶温度域での圧下率が本発明の範囲を低く外れる比較例(鋼管No.A5)、熱間圧延終了後の冷却速度が本発明の範囲を低く外れる比較例(鋼管No.A16)は、母材部の組織が粗大化した組織となり、母材部の靭性が低下している。また、熱間圧延における鋼素材の加熱温度が本発明の範囲を低く外れる比較例(鋼管No.A3)、熱間圧延における鋼素材の加熱保持時間が本発明の範囲を低く外れる比較例(鋼管No.A4)、熱間圧延終了後の冷却速度が本発明の範囲を高く外れる比較例(鋼管No.A20)は、母材部の耐HIC性が低下している。
Claims (11)
- 質量%で、
C:0.025~0.084%、 Si:0.10~0.30%、
Mn:0.70~1.80%、 P:0.001~0.018%
S:0.0001~0.0029%、 Al:0.01~0.10%、
Nb:0.001~0.065%、 V:0.001~0.065%
Ti:0.001~0.033%、 Ca:0.0001~0.0035%
N:0.0050%以下、 O:0.0030%以下
を含有し、かつ下記(1)式で定義されるPcmが0.20以下を満足し、残部Fe及び不可避的不純物よりなる組成を有し、さらに母材部および電縫溶接部がともに、粒径:10μm以下の擬ポリゴナルフェライトを面積率:90%以上有する組織を有し、降伏強さYS:400MPa以上で、シャルピー衝撃試験の-50℃における吸収エネルギーvE-50:150J以上の高靭性を有することを特徴とする耐HIC性に優れた高強度厚肉電縫鋼管。
記
Pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B‥‥(1)
ここで、C,Si,Mn,Cu,Ni,Cr,Mo,V,B:各元素の含有量(質量%) - 前記組成に加えてさらに、質量%で、B:0.0030%以下を含有することを特徴とする請求項1に記載の高強度厚肉電縫鋼管。
- 前記組成に加えてさらに、質量%で、Cu:0.001~0.350%、Ni:0.001~0.350%、Mo:0.001~0.350%、Cr:0.001~0.700%のうちから選ばれた1種または2種以上を含有することを特徴とする請求項1又は2に記載の高強度厚肉電縫鋼管。
- 前記電縫溶接部に存在する、円相当径2μm以上の介在物に含まれるSi、Mn、Al、Ca、Crの合計量が、質量%で0.0089%以下であることを特徴とする請求項1ないし3のいずれかに記載の高強度厚肉電縫鋼管。
- 鋼素材を、加熱し、熱間圧延を施したのち、冷却し巻取り熱延鋼帯とする熱延工程と、該熱延工程を経た前記熱延鋼帯に、冷間で連続的にロール成形を施しほぼ円形断面の管状成形体としたのち、該管状成形体の円周方向端部同士を突合せて電縫溶接し電縫鋼管とする造管工程と、を施す電縫鋼管の製造方法において、
前記鋼素材を、質量%で、
C:0.025~0.084%、 Si:0.10~0.30%、
Mn:0.70~1.80%、 P:0.001~0.018%
S:0.0001~0.0029%、 Al:0.01~0.10%、
Nb:0.001~0.065%、 V:0.001~0.065%
Ti:0.001~0.033%、 Ca:0.0001~0.0035%
N:0.0050%以下、 O:0.0030%以下
を含有し、かつ下記(1)式で定義されるPcmが0.20以下を満足し、残部Fe及び不可避的不純物よりなる組成を有する鋼素材とし、前記熱延工程が、前記鋼素材を、加熱温度:1200~1280℃の温度範囲の温度に加熱し、90min以上保持したのち、未再結晶オーステナイト域での熱間圧延率を20%以上とする熱間圧延を施し、該熱間圧延終了後に、板厚中央部温度で780℃~630℃の範囲の平均で、7~49℃/sの冷却速度で冷却停止温度:630℃以下まで冷却し、巻取温度:400℃以上600℃未満で巻取り、熱延鋼帯とする工程であり、前記造管工程後に、オンラインで前記電縫鋼管の電縫溶接部を、肉厚全厚が800℃~1150℃の範囲内となるように加熱したのち、肉厚中央部温度で780℃~630℃の範囲の平均で7~49℃/sの冷却速度で630℃以下の冷却停止温度まで冷却し、その後放冷する熱処理を施し、母材部および電縫溶接部がともに、降伏強さYS:400MPa以上で、シャルピー衝撃試験の-50℃における吸収エネルギーvE-50:150J以上の高靭性を有することを特徴とする耐HIC性に優れた高強度厚肉電縫鋼管の製造方法。
記
Pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B‥‥(1)
ここで、C,Si,Mn,Cu,Ni,Cr,Mo,V,B:各元素の含有量(質量%) - 前記造管工程における前記ロール成形のフィンパス成形において、前記熱延鋼帯の幅方向端面にテーパー開先を付与するにあたり、該テーパー開先のテーパー開始位置と管外面となる表面あるいは管内面となる表面との鋼帯肉厚方向の距離を熱延鋼帯肉厚の2~60%とすることを特徴とする請求項5に記載の高強度厚肉電縫鋼管の製造方法。
- 前記造管工程における前記電縫溶接の雰囲気酸素分圧を、下記(2)式で定義される溶鋼の易酸化度foxyに関連して900/foxy 質量ppm以下に調整することを特徴とする請求項5または6に記載の高強度厚肉電縫鋼管の製造方法。
記
foxy=Mn+10(Si+Cr)+100Al+1000Ca ‥‥(2)
ここで、Mn、Si、Cr、Al、Ca:各元素の含有量(質量%) - 前記組成に加えてさらに、質量%で、B:0.0030%以下を含有することを特徴とする請求項5ないし7のいずれかに記載の高強度厚肉電縫鋼管の製造方法。
- 前記組成に加えてさらに、質量%で、Cu:0.001~0.350%、Ni:0.001~0.350%、Mo:0.001~0.350%、Cr:0.001~0.700%のうちから選ばれた1種または2種以上を含有することを特徴とする請求項5ないし8のいずれかに記載の高強度厚肉電縫鋼管の製造方法。
- 前記熱処理における冷却を、前記電縫溶接部上方に水量密度:1m3/m2min以上の棒状冷却水が噴射可能なノズルを接続した冷却ヘッダを搬送方向に少なくとも複数列配設し、前記ノズルから前記棒状冷却水を1m/s以上の速度で噴射する冷却とすることを特徴とする請求項5ないし9のいずれかに記載の高強度厚肉電縫鋼管の製造方法。
- 前記複数列配設された前記冷却ヘッダーは、冷却水の注水が各々個別に制御可能に配設されることを特徴とする請求項10に記載の高強度厚肉電縫鋼管の製造方法。
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Also Published As
Publication number | Publication date |
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EP2837708A4 (en) | 2015-08-12 |
JPWO2013153819A1 (ja) | 2015-12-17 |
KR101641450B1 (ko) | 2016-07-20 |
JP5534111B2 (ja) | 2014-06-25 |
US20150083266A1 (en) | 2015-03-26 |
CN104220622A (zh) | 2014-12-17 |
EP2837708B1 (en) | 2019-03-06 |
IN2014MN01980A (ja) | 2015-07-10 |
EP2837708A1 (en) | 2015-02-18 |
CA2869879A1 (en) | 2013-10-17 |
CN104220622B (zh) | 2016-11-02 |
RU2613824C2 (ru) | 2017-03-21 |
CA2869879C (en) | 2017-08-29 |
US9841124B2 (en) | 2017-12-12 |
RU2014145519A (ru) | 2016-06-10 |
KR20140138942A (ko) | 2014-12-04 |
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