Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B23/00—Tube-rolling not restricted to methods provided for in only one of groups B21B17/00, B21B19/00, B21B21/00, e.g. combined processes planetary tube rolling, auxiliary arrangements, e.g. lubricating, special tube blanks, continuous casting combined with tube rolling
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B19/00—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work
  • B21B19/02—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work the axes of the rollers being arranged essentially diagonally to the axis of the work, e.g. "cross" tube-rolling ; Diescher mills, Stiefel disc piercers or Stiefel rotary piercers
  • B21B19/04—Rolling basic material of solid, i.e. non-hollow, structure; Piercing, e.g. rotary piercing mills
• • 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
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
  • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
• • 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
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B25/00—Mandrels for metal tube rolling mills, e.g. mandrels of the types used in the methods covered by group B21B17/00; Accessories or auxiliary means therefor ; Construction of, or alloys for, mandrels or plugs
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
  • B21B3/02—Rolling special iron alloys, e.g. stainless steel
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
  • B21B45/004—Heating the product

Definitions

• the present invention relates to a method for producing a high-Cr seamless pipe or tube used for oil or gas wells, for various industrial plants, for building structures, and so on.
• the present invention relates in particular to a method for producing a high-Cr seamless pipe or tube containing, by mass%, 8.0 to 16.0% of Cr.
• High-Cr seamless pipes or tubes containing, by mass%, 8.0 to 16.0% of Cr have been widely used for oil or gas wells, for various industrial plants and for building structures.
• an inclined roll type piercing mill (hereinafter often referred to as a "piercing mill”) in the piercing and rolling process.
• a hollow pipe or tube stock is produced from a solid steel stock with a round section (hereinafter referred to as a "billet") by use of a piercing mill.
• the pierced pipe or tube stock is elongated and rolled by an elongator such as a mandrel mill, a plug mill, an Assel mill, or a push bench, and the outer diameter thereof is then narrowed by use of a stretch reducing mill or a sizing mill.
• the Patent Document 1 discloses a technique for enhancing the hot workability of a steel stock in the piercing and rolling process by a piercing mill while minimizing the contents of P and S that are impurity elements in a steel, thereby suppressing internal fracture flaws.
• the Patent Document 2 discloses a technique for suppressing the production of ⁇ -ferrite by reducing the heating temperature of a billet and also by suppressing the work heat generation through reducing the average strain rate in the piercing and rolling process by a piercing mill.
• the Patent Document 3 discloses a method for producing a martensitic seamless steel pipe or tube, capable of improving the microstructure which is formed in the hot working process, by regulating the contents of the specified alloy components and also by controlling the annealing heating time and setting the billet heating temperature to lower.
• the Patent Document 4 discloses a technique for performing piercing and rolling while adjusting, in the piercing and rolling process by a piercing mill with disk roll-type guide shoes, the diameter of a steel stock, the clearance between guide shoes, the inclined roll gap, and so on.
• the Patent Document 5 discloses a method for producing a high-Cr seamless steel pipe or tube, capable of improving the microstructure which is formed in the hot working process, by regulating the content of Cr, the contents of S and P as impurity elements, the contents of elements to be added, and also by adjusting the heating or soaking time of the billet, thereby preventing internal surface defects.
• the Patent Document 6 discloses a method for producing a martensitic stainless seamless steel pipe or tube, capable of improving the microstructure which is formed in the hot working process, by regulating the contents of specified alloy components and adjusting the cross angle and the feed angle at the time of piercing and rolling, thereby preventing internal surface defects.
• Patent document 7 discloses a method for producing a seamless pipe or tube with an inclined roll type piercing mill and a mandrel mill, by using a billet whose rear end part is processed into a depression prior to piercing and rolling process, thereby avoiding occurrence of flaws on pulling out the mandrel bar in the elongating and rolling process.
• the present inventors observed internal fracture flaws on the high-Cr seamless pipes or tubes in detail in order to examine the causal relationship between occurring the flaws and the various conditions, such as the billet heating condition, preliminary work condition on the billet prior to piercing and rolling, or various conditions of the piercing and rolling.
• the gist of the present invention is a method for producing a high-Cr seamless pipe or tube described in the following:
• the internal fracture flaws among the internal surface defects, which are caused in the piercing and rolling process by a piercing mill, can be suppressed.
• the billet containing 8.0 to 16.0% of Cr and having a value of Cr* represented by the said formula (1) of not more than 9.0% is heated in a heating furnace at a soaking temperature of 1100 to 1300°C for an in-furnace time which satisfies the said formula (2), whereby the occurrence of ⁇ -ferrite can be suppressed by the soaking effect. Therefore, the major factor in causing internal fracture flaws which occur in the piercing and rolling process by a piercing mill can be suppressed.
• the "piercing efficiency" can be improved by setting a punching angle of a centering machine to a specified range in the process of forming a center hole, since the interval between the time the rolls bite the billet and the time when piercing and rolling stabilizes is shortened.
• the stable piercing and rolling of the billet can be achieved by making the center hole diameter equal to or larger than a specified value determined relative to the billet diameter, even in the case of a low "plug tip draft rate" without the occurrence of defective biting of a billet to piercing rolls.
• the present invention has been accomplished on the basis of the above findings.
• a billet, that is a steel stock for a high-Cr seamless pipe or tube, according to the present invention needs to be made of high-Cr steel which has a chemical composition containing 8.0 to 16.0% of Cr, with a value of Cr* represented by the above-mentioned formula (1) of not more than 9.0%.
• the content of Cr In order to obtain corrosion resistance, the content of Cr must be set to 8.0% or more. However, if the content of Cr be a large amount, ⁇ -ferrite is easily occurred at the time of high-temperature working since Cr is a ferrite forming element, and the hot workability is impaired. Particularly, if the content of Cr exceeds 16.0%, the hot workability is impaired remarkably. Moreover, an excessive addition of Cr leads to an increase in manufacturing cost of seamless pipes or tubes. Therefore, the content of Cr is set to 8.0 to 16.0%.
• Value of Cr* not more than 9.0%
• the value of Cr* represented by the above-mentioned formula (1) exceeds 9.0%, ⁇ -ferrite is easily occurred even if the content of Cr is within the above range of 8.0 to 16.0%, and so, the sulfide stress cracking resistance and hot workability are deteriorated. Therefore, the value of Cr* represented by the above-mentioned formula (1) is set to not more than 9.0%.
• a high-Cr steel which has a chemical composition containing 18.0 to 16.0% of Cr and having a value of Cr* represented by the above-mentioned formula (1) of not more than 9.0% is used as a billet in the present invention.
• a high-Cr steel which contains C: 0.15 to 0.22%, Si: 0.1 to 1.0%, Mn: 0.10 to 1.00%, Cr: 12.0 to 14.0%, P: not more than 0.020%, S: not more than 0.010%, N: not more than 0.05%, O (oxygen): not more than 0.0060%, one or more elements selected from 0.005 to 0.200% each of V, Nb and Ti and 0.0005 to 0.0100% of B (a total of 0.005 to 0.200% in combination of two or more thereof), Al: 0 to 0.1%, Ni: 0 to 0.5%, Cu: 0 to 0.25%, Ca: 0 to 0.0050% and the balance being Fe and impurities, with a value of Cr* represented by the formula (1) of not more than 9% can be recommended.
• the billet that is the steel stock for a high-Cr seamless pipe or tube of the present invention for example, a high-Cr steel which contains C: 0.003 to 0.050%, Si: 0.05 to 1.0%, Mn: 0.10 to 1.50%, Cr: 10.5 to 14.0%, P: not more than 0.035%, S: not more than 0.010%, N: not more than 0.070%, O (oxygen): not more than 0.0060%, V: 0 to 0.200%, Ti: 0 to 0,300%, Mo: 0.2 to 3.0%, Ni: 0 to 7.0%, Zr: 0 to 0.580% and the balance being Fe and impurities, with a value of Cr* represented by the formula (1) of not more than 9% can also be recommended.
• a high-Cr steel which contains C: 0.003 to 0.050%, Si: 0.05 to 1.0%, Mn: 0.10 to 1.50%, Cr: 10.5 to 14.0%, P: not more than 0.035%, S: not more than 0.010%, N: not more
• the billet that is the steel stock for a high-Cr seamless pipe or tube, which has the above chemical composition described in the above section (A)
• a heating furnace at a soaking temperature 1100 to 1300°C so that the in-furnace time from the charging of the billet into the heating furnace to the discharging therefrom can satisfy the above-mentioned formula (2).
• a soaking temperature is below 1100 °C
• the temperature in the piercing and rolling process by a piercing mill, or the temperature in the elongating and rolling process by a mandrel mill or a plug mill is reduced. Therefore, in that case, the deformation resistance of the material to be rolled increases, and the piercing and rolling or the elongating and rolling becomes unstable and seizure flaws are easily caused.
• the billet that is the steel stock to be pierced and rolled by the piercing mill, is heated at a soaking temperature of 1100 to 1250°C so that the in-furnace time from charging of the billet into the heating furnace to the discharging therefrom satisfies the above-mentioned formula (2).
• the above-mentioned in-furnace time in the heating furnace is desirably set to less than "1.5 ⁇ diameter of the billet (mm)".
• the plug does not be pressed back in the center of the billet end face in the piercing and rolling process.
• the billet can be pierced and rolled quickly and stably even at a low plug tip draft rate, that is to say, even at a low roll forging frequency N represented by the above-mentioned formula (5), thereby shortening the time needed for piercing and rolling.
• N represented by the above-mentioned formula (5)
• the punching angle of the centering machine is set to 60 to 110°.
• the diameter of the center hole should satisfy the above-mentioned formula (3), that is to say, should be "0.34 ⁇ billet diameter (mm)" or more.
• the billet having a center hole formed under the conditions described in the above section (C) must be pierced and rolled at a plug tip draft rate of not more than 8.0%.
• a plug tip draft rate exceeding 8.0% means that the value of "L" in the above-mentioned formula (5), that is to say, the distance from the position where the rolls bite the billet to the tip of the plug is geometrically large. Since the roll forging frequency N, represented by the above-mentioned formula (5), is increased in this case, so-called “Mannesmann fractures” are excessively caused, which leads to an easy occurrence of internal fracture flaws. Therefore, the plug tip draft rate is set to not more than 8.0%. A more preferable plug tip draft rate is not more than 6.0%. The lower limit of the plug tip draft rate, which depends on the conditions of the center hole described in the above section (C), is about 3.0% at which the billet can be geometrically bitten into the rolls of piercing mill.
• the round billet that is the steel stock for a high-Cr seamless pipe or tube, having the chemical composition described in the above section (A)
• the round billet is heated under the conditions described in the above section (B), formed the center hole under the conditions described in the above section (C), and pierced and rolled at a plug tip draft rate of the piercing mill of not more than 8.0%.
• the piercing efficiency of the piercing mill is not necessarily regulated.
• the roll forging frequency N represented by the above-mentioned formula (5) is increased, the said so-called "Mannesmann fractures" are excessively caused, which facilitates the occurrence of the internal fracture flaws. Consequently, the preferable piercing efficiency of the piercing mill is not less than 50%.
• the upper limit of the piercing efficiency of the piercing mill is empirically about 60 to 70% in barrel type rolls (cross angles 0°), or about 75 to 95% in cone type rolls (cross angle: 5 to 30°).
• the steel ingots which have chemical compositions shown in Table 1 were hot rolled in a blooming mill by a general method and made into round billets of 191 mm or 225 mm in diameter.
• the steel A1 and B1 in Table 1 are the steels related to the examples with chemical compositions within the range regulated by the present invention.
• the each round billet of the above-mentioned size was next charged into a heating furnace and heated at a soaking temperature of 1200°C for an in-furnace time of 240 minutes, and then formed a center hole by means of a centering machine at one end face, pierced and rolled by a piercing mill, under conditions shown in Table 2, to produce a pipe stock with an outer diameter of 228.0 mm (in case of the round billet of 225 mm diameter) or with an outer diameter of 196.0 mm (in case of the round billet of 191 mm diameter).
• the in-furnace time represented by the above-mentioned formula (2) is "0.5 ⁇ 191 (mm)” minutes or longer, that is to say, 95.5 minutes or longer for the billet of 191 mm diameter, and "0.5 ⁇ 225 (mm)” minutes or longer, that is to say, 112.5 minutes or longer for the billet of 225 mm diameter. Therefore, the above 240 minute in-furnace time satisfies the in-furnace time condition regulated by the present invention.
• each of the pipe stocks of Test Nos. 7 to 11 and 13 to 17 obtained by the method of the present invention that is to say, by forming a center hole having a diameter represented by the above formula (3), at one end face of the round billet where piercing starts, by means of a centering machine which has a punch with a punching angle of 60 to 110°, after heating the said round billet of the high-Cr steel having the components shown in Table 1 under the conditions regulated by the present invention, and then, by piercing and rolling, within the effective biting of the billet to rolls, at a plug tip draft rate regulated by the present invention, shows a excellent internal surface properties. No defective rolling properties such as the uneven wall thickness were observed in any of these pipe stocks.
• the punching angle of 50° was lower than the regulated lower limit of 60°. This required deep punching to secure the required hole diameter, 105.5 mm for the pipe stock of the Test No. 1 and 91.1 mm for the pipe stocks of the Test Nos. 2 and 3, resulting in punching flaws (internal surface defects).
• a high-Cr seamless pipe or tube with minimized internal surface defects can be produced. Further, since it is not necessary to excessively reduce the impurities in the chemical composition of the steel, and predetermined productivity can be ensured in pipe or tube making, a high-Cr seamless pipe or tube, excellent in internal surface properties, can be efficiently produced.

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• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
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• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
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• Crystallography & Structural Chemistry (AREA)
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• Heat Treatment Of Steel (AREA)

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• 2007
  • 2007-03-01 EP EP07737596A patent/EP1990107A4/fr not_active Withdrawn
  • 2007-03-01 WO PCT/JP2007/053916 patent/WO2007100042A1/fr active Application Filing
  • 2007-03-01 CN CN2007800072046A patent/CN101394943B/zh not_active Expired - Fee Related
  • 2007-03-01 JP JP2008502840A patent/JPWO2007100042A1/ja active Pending
• 2008
  • 2008-08-29 US US12/230,497 patent/US20090000709A1/en not_active Abandoned

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