Classifications

• • 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
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/10—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
• • 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
  • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
• • 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
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • 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
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • 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 the production of high Cr seamless steel pipes used for oil wells, gas wells, various plants, construction materials, and the like. More specifically, the present invention relates to a pipe material containing 10 to 20% Cr (a billet). The present invention relates to a method for producing a high Cr seamless steel pipe with less occurrence of inner surface flaws even when producing a seamless steel pipe. Background art
• seamless steel pipes containing 10 to 20% Cr, which are used for oil wells, various plants, or construction structures, have been used.
• seamless steel pipes are manufactured from round steel slabs by mannesmann drilling, press drilling, etc. to produce hollow shells, which are then expanded by a rolling mill such as a mandrel mill or Bragg mill to reduce the wall thickness. It is manufactured by reducing the outside diameter with a drawing rolling machine such as a stretch reducer and finishing it into a steel pipe with the target dimensions.
• round steel slabs obtained by rolling flakes manufactured by continuous slab or ingot ingot ingot casting method are used as pipe material (billets).
• the steel slab used as the material is generally made by forming a slab (plume) having a rectangular cross section by continuous sintering or ingot ingot slabging method, heating it to a uniform temperature, and then performing slab rolling, bulging. It is manufactured by hot rolling into a round shape with a mining mill or the like, or by directly forming into round pieces by continuous forming.
• high Cr steels are inferior in hot workability compared to general steels, and may cause internal surface defects in steel pipes after pipe making.
• internal flaws such as internal flaws on steel pipes (hereinafter referred to as “internal flaws”) not only reduces the yield of products, but also results in piercing rolling mills, elongation rolling mills, and rolling mills. In some cases, the entire pipe mill must be stopped, in which case production efficiency will be significantly impaired.
• the present invention has been made in view of the above-mentioned problems, and is not accompanied by a decrease in productivity when manufacturing a seamless steel pipe using a high Cr steel slab or a steel slab as a material for pipe making. It is an object of the present invention to provide a method for producing a high Cr seamless steel pipe that can effectively prevent the occurrence of internal flaws.
• the brittle part of the high Cr steel in hot working is the grain boundary between austenite grains, which are the main structure of the steel type in a high-temperature state, and five grains that are included in a small amount with the formation of 5-ferrite.
• measures to reduce the internal surface flaws generated during hot working are as follows: (1)-Reduce the amount of generated fluoride and reduce the parts that are vulnerable to the structure, or (2) Grain boundary strength between y grains and (5 grains) As a countermeasure for the above (1), it is effective to reduce impurity elements (S, P) that weaken grain boundaries, but excessive reduction will increase manufacturing costs.
• (2) JP-A-4-224659 mentioned above
• JP-A-4-224659 JP-A-4-224659
• the present inventors conducted a more detailed study to accurately determine the degree of influence of the contained Cr and other added alloy elements on the formation of 6-ferrite. It was confirmed that the thermal history at the manufacturing stage of the material or at the stage before material pipe production affected the amount of 5-ferrite, and the degree of these effects could also be indexed. By verifying the results of these examinations in an actual production line, it is possible to efficiently improve the pipe production conditions, etc., without excessively reducing impurity elements (S, P). We have found that it is possible to manufacture seamless steel pipes that are inexpensive and have excellent inner surface quality with productivity.
• the present invention has been completed based on the above findings, and has a gist of the following (1) and (2) methods for producing a high Cr-based seamless steel pipe.
• the Cr content is 10 to 20%
• the content of impurities S and P is 0.050% or less, respectively
• C, Mn, Ni, N, Cu, Si, Mo, Ti ⁇ , Nb and V and one or more slabs or steel slabs containing a total of ⁇ 1 (hours) of time soaked at 1100 ° C or higher, 1 After soaking the total time of soaking at 100 ° C or more as ⁇ t 2 (hour), and then heating to 1200 ° C to make a tube, soak or soak as to satisfy the following equation (b). And a high-Cr seamless steel pipe characterized by heating.
• the element symbols in the formula indicate the content (% by mass) of each component element.
• the Cr content should be 10-20%, the content of impurities S and P should be 0.050% or less, and C, Mn, Ni, N, Cu, Si, Mo, A piece or a piece of steel containing one or more of Ti, Nb and V and having a total time of soaking at 1100 ° C or more of ⁇ tl (hours) The material is soaked at noo ° c or more for a total time of ⁇ t 2 (hours) and then soaked, and then 1100-1300 ° C (excluding 1200 ° C)
• This is a method for producing a high Cr seamless steel pipe, characterized in that when producing a pipe by heating at a temperature equal to or / and so as to satisfy the following equation (C).
• FIG. 1 is a diagram showing the relationship between the F value of a high Cr seamless steel pipe based on the example and the incidence rate (%) of inner surface flaws.
• the production method of the present invention is characterized in that a high Cr steel having a composition in which the content of Cr is 10 to 20% by mass% and the content of impurities S and P is 0.050% or less is used as a material for pipe making. And In the following description, “%” means “% by mass”.
• Cr is an essential component element for improving the corrosion resistance
• the content is 10% non Mitsurude the desired corrosion resistance, for example resistance C0 2 corrosion resistance can not be ensured.
• the Cr content exceeds 20%, a ⁇ -fluorite phase is liable to be generated at the time of high-temperature heating, and the corrosion resistance (SSC resistance) and the hot workability are deteriorated. Increases production costs.
• the content of P is set to 0.050% or less.
• S is an unavoidable element in steel as an impurity element and adversely affects hot workability
• the lower the content the better. If the content exceeds 0.050%, the strength of the ferrite / a grain boundary is reduced and the hot workability is remarkably reduced, so the S content is set to 0.050% or less.
• the prescribed S content is effective for the machinability and weldability of steel, so to achieve that effect, the content should be 0.004% or more. desirable.
• C 0.30% or less, Si: 1.00% or less,: 2.0% or less, Mo: 3.00% or less, Cu: 0.50% % Or less, Ni: 11.00% or less, Ti: 0.200% or less, A1: 0.100% or less, N: 0.150% or less, B: 0.0050% or less, Nb: 0.150% or less, V: 0.20% or less and Ca :
• elements such as 0.0050% or less can be appropriately contained. Hereinafter, the operation when these elements are contained will be described.
• the upper limit of the C content is set to 0.30%.
• Si is added as a deoxidizer during the steelmaking process, but if it is contained excessively, the toughness deteriorates, so its content should be 1.00% or less.
• Mn is a component that improves the hardenability of steel and is effective in ensuring the strength of steel. It also suppresses the formation of S-ferrite, which affects hot workability, and also has the effect of fixing S in steel. However, an excessive content lowers the toughness, so the Mn content should be 2.0% or less.
• Mo is extremely effective in strengthening the corrosion resistant film in environments containing carbon dioxide and hydrogen sulfide. Therefore, from the viewpoint of corrosion resistance, the more the element is added, the more it is improved. However, if a large amount of Mo is added, it becomes easy to generate S-ferrite, and accordingly, a large amount of austenite forming element cannot be added. And the cost of soup is increasing. Therefore, the upper limit of the Mo content is set to 3.00%.
• Is an austenite-forming element (It suppresses the formation of ferrite and is effective for stabilizing the structure. However, excessive addition lowers the ductility during use at high temperatures and for a long time. The amount should not exceed 0.50%.
• Ni is an austenite-forming element that suppresses the formation of d-ferrite, stabilizes the structure, secures necessary strength, improves corrosion resistance, and improves hot workability. It is an effective element. However, adding too much will only saturate their effect and increase the cost of addition, reducing ductility during use at high temperatures. Therefore,
• Ni content should be 11.00% or less.
• Ti is an element effective in improving strength and toughness in accordance with improvement in corrosion resistance. However, if the content exceeds 0.200%, the toughness deteriorates.
• A1 is an element added as a steel deoxidizer. Excessive addition lowers the cleanliness of the steel, impairs workability and lowers the high-temperature strength, so its content should be 0.100% or less.
• N is effective in ensuring the strength of the steel, but if added excessively, it deteriorates the toughness, so its content should be 0.150% or less.
• Nb is an element that forms fine carbides or carbonitrides in steel to increase creep strength. However, excessive addition promotes coarsening of carbides and lowers toughness, so the Nb content should be 0.150% or less.
• V is an element that forms fine carbides or carbonitrides in steel to increase strength, toughness and creep strength. However, excessive addition promotes coarsening of carbides and lowers toughness, so the V content should be 0.20% or less.
• Ca is an element effective in improving the shape of sulfides in steel and improving hot workability. However, if added excessively, the toughness and corrosion resistance deteriorate, so the Ca content should be 0.0050% or less.
• the material for pipe making of the present invention is 13% Cr steel and its component elements are Ni: 1.5% or less and Mo: 1.0% or less
• Cu is not added (for example, the content is less than 0.2%). It is desirable that the F value shown in the equation (b) described later be less than 19.4.
• Cu is an austenite-forming element, but it is also a low-melting-point metal and an element that degrades the hot workability at grain boundaries.
• ⁇ (austenite) grains This is because the number of fields increases and inner surface flaws easily occur.
• S-ferrite refers to ferrite that precipitates during solidification or ferrite that forms during high-temperature heating.
• the f-value defined by the above equation (a) facilitates the ease with which this 5-ferrite is formed. It is indexed so that it can be judged. In other words, in the formula, the austenite-forming element is classified as “+” and the ferrite-forming element is classified as “1”. Due to the composition of the steel material, the temperature in a high temperature heating state (1000 to 1300 ° C) in hot working is considered. (5—Difficulty of ferrite formation is indicated by the product of the influence coefficient and the content of the constituent elements. In other words, the f value is also grasped as an index indicating the ease with which the austenite phase is generated. be able to.
• the manufacturing process employed in the present invention may be a conventional seamless steel pipe manufacturing process.As described above, a hollow shell is manufactured from a round steel piece by Mannesmann drilling, press drilling, or the like. Any method may be used in which the raw pipe is rolled and then rolled to finish it into a steel pipe.
• the Mannesmann-mandrel mill method or the Mannesmann-plug mill method is applied because it is advantageous in terms of dimensional accuracy and productivity.
• the raw material for pipe production manufactured by continuous casting is heated to ⁇ 00 ⁇ : 1300 ° C, then pierced to form a hollow shell by piercing and then drawn and rolled by a mandrel mill for finish rolling.
• the raw tube for finish rolling is stretched and rolled, or after being reheated to 850 to 1100 ° C, passed through a stretcher or a sizer to be finished into a seamless steel tube of a predetermined size.
• the heat history of the steel pipe produced affects the formation of the filament structure in the pipe production process.
• the soaking time at high temperature (1100 ° C or more) at the stage of slabs or billets up to pipe rolling and at the stage of material (bill) is long, biased diffusion spreads, —Ferrite formation is suppressed. Therefore, as a slab or a billet at 1100 ° C or more It is necessary to manage the sum of the soaking time as ⁇ tl (hour) and the sum of the time that the material soaks at 1100 ° C or more as ⁇ t 2 (hour).
• the soaking time for the slab or billet stage is the time during which the steel material is soaked at 1100 ° C or higher in a heating furnace or soaking furnace in the slab rolling process. ⁇ This is the soaking time for one piece, and for two heat rolling, it is the soaking time for one piece and one piece.
• the reason why the soaking at 1100 ° C or higher is targeted is to target the treatment at which the diffusion speed of the paradox is increased, and by performing the soaking at 1100 ° C or longer for a long time.
• localized high concentration of P and S can be avoided. It is not necessary to specify the upper limit temperature for soaking, but usually a temperature range of 1100 ⁇ : L300 ° C is adopted.
• the heating temperature during pipe production affects the formation of S-ferrite, and the lower the heating temperature T, the more the formation of ferrite is suppressed.
• the heating temperature T mentioned here is the material temperature in piercing and piercing and rolling, and can be grasped as the temperature of the furnace after the material (billet) is heated to 1100 to 1300 ° C.
• the above technical idea of the present invention is quantified by the following equation (b).
• the diffusion effect of the impurity (S, P) bias is determined, and the soaking time at the slab or billet stage, the material stage
• the F value has been introduced to confirm the effect of the soaking time on heating and the effect of the heating temperature during pipe production.
• the segregation improvement allowance due to the soaking time varies depending on the slab rolling process or the pipe making process, but in any process, the segregation improvement allowance is approximately expressed as an exponential function of the soaking time.
• the segregation improvement allowance 1 fi m ⁇ .
• the above equation (b) shows the conditions when the tube is manufactured with the heating temperature T set to 1200 ° C. If the heating temperature T deviates from 1200 ° C, the KT expressed by the following equation (:) Correction is required. At this time, the correction was made in accordance with the parabolic law, while considering the case where the value was negative.
• Sample Nos. 1 to 28 are 13% Cr steel
• Sample Nos. 29 to 33 are SUS304 steel
• Sample Nos. 34 to 38 are SUS316 steel
• Sample Nos. 39 to 42 are SUS321 steel
• Sample Nos. 44 to 48 correspond to SUS347 steel, respectively.
• the above steel slab is used as a raw material for pipe making, heated in a heating furnace at a temperature in the range of 1100 to 1300 ° C, and then pierced with a piercer " ⁇ " to form a hollow shell.
• the raw tube for finish rolling was heated to 1100 ° C, passed through a storage user, and seamlessly with an outer diameter of 88.9, an inner diameter of 70, and a length of 1000 thighs. Steel pipes were manufactured.
• Tables 4 to 6 show the soaking time ⁇ t l of the slab, the soaking time ⁇ t 2 of the raw material, and the heating temperature T during the tube making as the production and tube making conditions at this time. Further, the f-value according to the above equation (a) and the F-value according to the equations (b) and (c) are calculated, and the values are shown in Tables 4 to 6.
• FIG. 1 is a diagram showing the relationship between the F value of a high Cr seamless steel pipe based on the present embodiment and the incidence rate (%) of inner surface flaws.
• the occurrence rate (%) of inner surface flaws shown in Fig. 1 is indicated by the ratio of the number of material-covered flaws and hedging flaws that were confirmed in the inspection after pipe making.
• the production method of the present invention even when high Cr steel is used as a material for pipe making, generation of 5-ferrite in the hot pipe making process can be sufficiently suppressed, so that generation of inner surface flaws is reduced. It is possible to manufacture seamless high Cr Cr steel pipes. In addition, there is no need to excessively reduce impurities in the material composition, and a predetermined productivity can be secured at the time of pipe production, so that high Cr seamless steel pipes with excellent inner surface quality can be efficiently manufactured at low production cost. Can be manufactured. Thereby, it can be widely used for seamless steel pipe applications.

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• 2001
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