JPWO2006106802A1 - Seamless pipe manufacturing method - Google Patents

Abstract

A seamless pipe manufacturing method including a piercing and rolling process, wherein the billet diameter is R (m), the billet axial crack length is r (m), and after the billet contacts the rolling roll, the piercing plug Production of seamless pipe with reduced inner surface flaws for piercing and rolling so that the relationship of the following formulas (1) to (3) is satisfied at the same time, where N is twice the amount of billet rotation until Is the method. 0 ≦ r / R ≦ 0.13 ・ ・ (1), r / R ≧ −0.13N + 0.13 ・ ・ (2), r / R ≦ −0.065N + 0.39 (3) Even if it is a wide slab, a high quality seamless pipe can be manufactured at low cost without causing piercing and rolling defects and inner surface flaws of the pipe.

Description

  The present invention relates to a method for manufacturing a seamless pipe including a piercing and rolling process, and more particularly, to a method for manufacturing a seamless pipe that does not generate internal flaws using a piercing and rolling method.

  Oil and gas wells have been actively developed in response to rising energy demand for crude oil and natural gas. Moreover, in recent years, both oil wells and gas wells have shifted from onshore to the seabed, and the environment in which oil wells and gas wells exist as well as in oil wells and gas well environments has become severe.

  Line pipes that transport crude oil and natural gas from oil wells and gas wells are designed for larger diameters and thicker walls in consideration of the installation environment including operability for mass transport and pressure resistance in the deep sea Tend to be performed. From the standpoint of steel material properties, not only strength but also toughness at low temperatures is required, and from the standpoint of layability, weldability is required.

  Of the above characteristics, in order to ensure weldability, it is effective to reduce the C content, and based on this, other alloy elements are combined to optimize the strength. Moreover, in order to ensure toughness, the steel component composition and the steel structure are adjusted by controlling the form of inclusions by reducing impurity elements such as P and S and adding Ca.

  On the other hand, as the manufacturing process, a billet is manufactured by continuous casting, and a process of piercing and rolling the billet is often employed. In the above continuous casting, since solidification proceeds from the outer peripheral portion of the slab toward the center, defects such as center porosity, axial center cracks, and center segregation are likely to occur near the center of the slab. In addition, since the C content is decreased in order to ensure weldability as described above, cracks due to volume shrinkage due to phase transformation from the δ ferrite phase to the γ austenite phase in the initial stage of solidification further increase.

  The amount of the billet axial center crack can be easily grasped by collecting, investigating and measuring a billet cross-section sample. In addition, when the axial center crack is large, wrinkles are likely to occur on the inner surface of the product pipe, so that the inner surface of the pipe is prevented from generating wrinkles by suppressing the axial center crack of the billet. Many have been reported.

  For example, Japanese Patent Application Laid-Open No. 2002-327234 discloses a temperature difference (DF) between a transformation temperature from a liquid phase calculated from a steel component composition to δ ferrite and a transformation temperature from δ ferrite to γ austenite (hereinafter referred to as “DF”). By setting the “ferrite temperature range (DF)” to 150 ° C. or less, the occurrence of defects such as porosity in the center of the billet is suppressed, and there are few inner surface defects even if piercing and rolling is performed while continuously casting. A round billet capable of producing a tubeless tube at low cost and a method for producing the same are disclosed.

  However, in order to satisfy all of the various mechanical characteristic values required by customers, for example, pipes must be formed using a slab having a component composition in which the value of the DF exceeds 150 ° C. There are cases where it cannot be obtained. Furthermore, a round billet having a center porosity must be pierced and rolled while continuously cast.

  As described above, even in the case of a slab having a steel composition in which the ferrite temperature range (DF) exceeds 150 ° C., in order to eliminate the occurrence of inner surface defects due to piercing and rolling, and to produce a high quality seamless pipe There are still problems that must be resolved.

  The present invention has been made in view of the above problems, and the problem is that even in the case of a slab having a steel composition in which the ferrite temperature range becomes higher than 150 ° C., the inner surface of the pipe is defective due to piercing and rolling. It is an object of the present invention to provide a method of manufacturing a seamless pipe that can manufacture a high quality seamless pipe at a low cost without causing any problems.

  In order to solve the above-mentioned problems, the present inventors can prevent the occurrence of piercing and rolling defects and internal flaws in advance by appropriately combining billet casting conditions and piercing and rolling conditions in view of conventional problems. At the same time, the production of a seamless pipe capable of improving the production yield was studied, and the following findings (a) to (e) were obtained to complete the present invention.

  (A) As the billet receives the number of rotation forgings from the time when the billet comes into contact with the rolling roll until it reaches the piercing plug (in the case of a two-roll type piercing and rolling machine, the billet is pierced more). Deformation until reaching the plug is large and wrinkles (inner rashes) easily occur on the inner surface of the tube.

  (B) The smaller the amount of rotation of the billet from when the billet comes into contact with the rolling roll until it reaches the perforated plug, the more the occurrence of internal surface irritation can be suppressed, but on the other hand, the bite biting into the rolling roll is reduced. There is a possibility that the problem of poor biting due to the occurrence of the problem.

  (C) If the billet axial crack ratio is large, the billet has a sufficient starting point for piercing and rolling, so even if the number of rotation forgings in the piercing and rolling mill is set low, the billet The biting property is good. Conversely, if the number of rotation forgings is set to be large, internal rashes are likely to occur.

  (D) If the billet shaft center crack rate is small, there will be no sufficient starting point for piercing and rolling in the billet. . On the contrary, even if the number of rotation forgings is set to be large, internal rashes are unlikely to occur.

(E) Considering the above (a) to (d), the number of rotation forgings to ensure biting into a piercing rolling mill and to produce a seamless pipe without generating internal rashes The appropriate range of the relationship between (N) and the billet axial crack ratio (r / R) (the billet axial crack length r (m) divided by the billet diameter by R (m)). If it calculates | requires, it will become the range which satisfy | fills following (1)-(3) Formula simultaneously.
0 ≦ r / R ≦ 0.13 (1)
r / R ≧ −0.13N + 0.13 (2)
r / R ≦ −0.065N + 0.39 (3)

  This invention is completed based on said knowledge, The summary exists in the manufacturing method of the seamless pipe shown to following (1)-(3).

  (1) A seamless pipe manufacturing method including a piercing and rolling step, wherein the billet has a diameter of R (m), the billet's axial center crack length is r (m), and the billet is in contact with the rolling roll. Piercing and rolling so that the relationship expressed by the following formulas (1) to (3) is satisfied at the same time, where N is 2 times the amount of rotation of the billet during the period from when it reaches the piercing plug. A method of manufacturing a seamless pipe with reduced inner surface flaws.

0 ≦ r / R ≦ 0.13 (1)
r / R ≧ −0.13N + 0.13 (2)
r / R ≦ −0.065N + 0.39 (3)

  (2) The said seamless pipe is mass%, C: 0.02-0.15%, Si: 0.05-0.4%, Mn: 0.3-2.0%, and P as an impurity : 0.03% or less and S: 0.03% or less, further Cu: 0.05-0.4%, Cr: 0.05-0.6%, Ni: 0.05-0. 8% and Mo: one or more of 0.03 to 0.5%, the balance being made of Fe and impurities, the seamless pipe with reduced internal flaws according to (1) above Production method.

(3) The ratio (r / R) of the billet axial length crack length r to the billet diameter R is expressed by the following equation (4), and after the billet contacts the rolling roll, the perforated plug The method for producing a seamless pipe according to the above (1) or (2), wherein N which is twice the amount of billet rotation until the value reaches is estimated by the following equation (5).
r / R = {(8 + W) × (DF × Vc × R ² ) − (16 / R)} / 1000 (4)
N = 2 × L / (Vs / EL) × Brps (5)
Here, W is the specific water amount during casting of the billet (L / kg-steel), Vc is the billet casting speed (m / min), DF is the ferrite temperature range (° C.), and L is in contact with the mill roll. The distance from the position to the tip of the perforated plug (m), Vs is the longitudinal travel speed (m / s) of the perforated shell, EL is the perforation ratio (-), and Brps is the number of rotations of the billet (times / s) Respectively.

  FIG. 1 is a diagram showing an appropriate range of the relationship between the crack rate of the billet shaft center due to casting and the number of times the billet is rotated and forged during piercing and rolling.

  As described above, the method of the present invention is a method of manufacturing a seamless pipe including a piercing-rolling step, and the axial center crack rate (r / R) obtained from the billet diameter and the billet axial crack length. And the number of rotation forgings (N) received from when the billet contacts the rolling roll until reaching the piercing plug, is adjusted within a range that simultaneously satisfies the relationship expressed by the above formulas (1) to (3). This is a method of manufacturing a seamless pipe. Below, the manufacturing method of the seamless pipe of this invention is demonstrated in more detail.

1) Billet axial crack ratio The billet axial crack ratio, as described above, is the value obtained by dividing the billet axial crack length (r) by the billet diameter (R) (r / R). Define. Here, when a plurality of axial center part cracks exist in the axial center part of the billet, the maximum crack length among them is used as the axial center part crack length.

  The axial crack rate may be obtained by cutting the billet each time and dividing the axial crack length measured in the cross section by the billet diameter. It is convenient to use the estimation formula described according to the operating conditions.

  The present inventors have collected samples from a large number of billets and investigated the relationship between the billet casting conditions and the axial center crack rate, and the axial center crack rate (r / R) is expressed by the following equation (4). I found out that

r / R = {(8 + W) × (DF × Vc × R ² ) − (16 / R)} / 1000 (4)
Here, r / R is the axial center crack rate (−), r is the billet axial crack length (m), R is the billet diameter (m), and W is the specific water amount during casting of the billet (L / Kg-steel), Vc represents the billet casting speed (m / min), and DF represents the ferrite temperature range (° C.).

  As described above, the ferrite temperature range (DF) means the temperature difference between the transformation temperature from the liquid phase to δ ferrite and the transformation temperature from δ ferrite to γ austenite. For example, JP 2002-327234 A Can be calculated using the following formulas (6) to (8).

DF = TLδ−Tδγ (6)
TLδ = 100000 / (55.25 + 2.35C + 0.37Si + 0.16Mn + 1.01P + 1.15S + 0.18Cu + 0.04Cr + 0.13Ni + 0.12Mo) (7)
Tδγ = 100000 / (60.06−4.51C + 3.84Si−0.19Mn + 0.98P + 0.25S−1.49Cu + 1.01Cr−1.34Ni + 0.55Mo) (8)
Here, the element symbols in the above formulas (7) and (8) represent the content (mass%) of each element in the steel.

  According to the above formulas (4) and (6) to (8), in order to reduce the axial center crack ratio (r / R), within the range where the casting operation is not hindered and the outer surface flaws of the billet are not generated. It is understood that it is effective to select the operation specifications by reducing the specific water amount during casting or by reducing the casting speed. It is also effective to reduce the ferrite temperature range by increasing the content of steel components such as C, Mn, Cu and Ni within a range that does not harm the steel quality other than the ferrite temperature range.

2) Number of rotational forgings The number of rotational forgings (N) is the number of rotational forgings that the billet receives from the time the billet contacts the rolling roll until it reaches the piercing plug as described above, and two inclined rolls around the pass line. In the case of a two-roll piercing and rolling mill equipped with, the amount of rotation of the billet is twice. Although the value actually measured each time may be used, it is practical to estimate by the following equation (5).

N = 2 × L / (Vs / EL) × Brps (5)
Here, N is the number of rotation forgings (times), L is the distance (m) from the position where the billet contacts the rolling roll to the tip of the drilled plug, and Vs is the traveling speed in the longitudinal direction of the drilled shell (m / s) ( = Roll peripheral speed x sin (β) x η), β is the roll roll inclination angle (degrees), η is the average drilling efficiency (-), EL is the drilling ratio (-), and Brps is the billet speed (Times / s).

  From the above equation (5), in order to reduce the number of rotation forging (N), the distance from the position where the billet contacts the rolling roll to the tip of the drilling plug is reduced, or the inclination angle of the rolling roll is increased. It can be seen that such a method is effective.

3) Appropriate range of the relationship between the number of rotation forgings and the cracking ratio of the shaft center part The effects of the number of rotation forgings and the cracking ratio of the shaft center part on the occurrence of inner surface flaws and the biting property of the billet into the piercing rolling mill are As described in the findings of a) to (d). Considering these, the relationship between the number of rotation forgings and the crack rate of the billet's shaft center part to ensure seamless biting into the piercing and rolling mill and produce seamless pipes without causing internal fraying The appropriate range was determined by a casting test and a piercing and rolling test described later.

  FIG. 1 is a diagram showing the proper range of the relationship between the billet axial cracking ratio of the billet due to casting and the number of rotation forging of the billet during piercing and rolling based on the results of the casting test and piercing and rolling test described later. is there. In the figure, a straight line AB is a straight line represented by r / R = 0.13, a straight line AD is a straight line represented by r / R = −0.13N + 0.13, and a straight line BC is r The straight lines represented by /R=−0.065N+0.39 are respectively represented.

  According to the results shown in the figure, in the case of a condition that does not satisfy the relationship of the above formula (1) or the relationship of the above formula (3), there is no defect in piercing and rolling due to poor biting into the piercing and rolling mill. However, as indicated by the ■ marks in the figure, internal rashes have occurred on the tube. Further, in the case of a condition that does not satisfy the relationship of the expression (2), as shown by a cross in the figure, a piercing and rolling defect occurs. On the other hand, in the case of the conditions satisfying all the relationships expressed by the above formulas (1) to (3), as shown by the circles in the figure, both the piercing and rolling defects and the inner surface rashes on the pipe occurred. No good product has been obtained.

4) Preferred range of steel component composition The preferred range of steel component composition in the present invention and the reason thereof will be described below.

C: 0.02-0.15%
C is contained for the purpose of securing the strength of the seamless pipe. If the content is less than 0.02%, it is difficult to ensure the required strength. On the other hand, if the content rate exceeds 0.15%, cracks are likely to occur during welding. For the above reason, the C content is preferably in the range of 0.02 to 0.15%. In addition, the more preferable range of C content is 0.03 to 0.10%.

Si: 0.05-0.4%
Si is an element having a deoxidizing action of molten steel and an action of improving the strength. In order to obtain the effect, the content is preferably 0.05% or more. However, when the content is higher than 0.4%, the amount of inclusions increases, and the cleanliness of the steel decreases and the toughness may decrease. Therefore, the Si content is preferably in the range of 0.05 to 0.4%.

Mn: 0.3 to 2.0%
Mn is an element having a deoxidizing action and an action of improving the strength without degrading the toughness of the steel. To obtain the effect, Mn is preferably contained in an amount of 0.3% or more. However, when the content exceeds 2.0%, the amount of inclusions increases, and the cleanliness of the steel may decrease. For the above reasons, the Mn content is preferably in the range of 0.3 to 2.0%. In addition, the more preferable range of Mn content is 0.5 to 1.8%.

P: 0.030% or less P is an impurity element in steel, segregates at the grain boundary to cause toughness reduction, and adversely affects hot workability. Therefore, its content is 0.030% or less. It is preferable to do. The lower the P content, the better.

S: 0.030% or less S is also an impurity element in the steel, segregates at the grain boundary to cause toughness reduction and adversely affects hot workability, so its content is 0.030% or less. It is preferable to do. In addition, the lower the S content, the better.

Cu: 0.05 to 0.4%
Cu is an element having an effect of increasing the strength of steel. Although it is not necessary to make it contain, the effect can be acquired by making it contain 0.05% or more. However, when the content rate exceeds 0.4%, the occurrence of flaws on the outer surface of the tube during Mannesmann drilling increases. For the above reason, the range of the content when Cu is contained is set to 0.05 to 0.4%.

Cr: 0.05-0.6%
Cr is an element having an effect of increasing the strength of steel. Although it is not necessary to make it contain, the effect can be acquired by making it contain 0.05% or more. However, since Cr improves the hardenability of the steel, if its content exceeds 0.6%, cracking occurs during welding. For the above reason, the range of the content when Cr is contained is set to 0.05 to 0.6%.

Ni: 0.05-0.8%
Ni is an element having an effect of increasing the strength of steel. Although it is not necessary to make it contain, the effect can be acquired by making a content rate into 0.05% or more. However, when the content exceeds 0.8%, the hot workability of steel deteriorates and the cost also increases. For the above reasons, the range of the content when Ni is included is set to 0.05 to 0.8%.

Mo: 0.03-0.5%
Mo is an element having an effect of increasing the strength of steel. Although it is not necessary to make it contain, the effect can be acquired by making it contain 0.03% or more. However, since Mo has the effect of improving the hardenability of steel, cracks during welding work occur when the content exceeds 0.5%. For the above reasons, the range of the content when Mo is contained is set to 0.03 to 0.5%.

(Example)
In order to confirm the effect of the method for producing a seamless pipe of the present invention, the following test was conducted and the result was evaluated.
Using test steels having the chemical composition and ferrite temperature range shown in Table 1, continuous casting was performed under the casting conditions shown in Table 2 to produce round billets.

  Further, using the billet obtained as described above, a pipe making test was performed under the piercing and rolling conditions shown in Table 2.

  In the table, (r / R) is the billet axial crack rate (−) as described above, and N is the number of rotation forgings (times). Also, in the overall evaluation column, as in the case of the evaluation of the test results in FIG. 1, the case where the inner surface rash was generated on the pipe by ◯ mark when the piercing and rolling defect did not occur and the inner surface rash occurred. Were evaluated by distinguishing each by a mark ■, and when a piercing and rolling defect occurred by a mark x.

  In addition, the presence or absence of the occurrence of internal rash was determined as follows. That is, when the inner surface of the pipe is visually inspected and one or more rashes are detected per billet, it is determined as “occurrence of rashes”, and below that, it is determined that “no rashes occur”. did.

  In addition, regarding the presence or absence of piercing and rolling defects, if the piercing and rolling fails without being caught in the piercing and rolling mill, it is determined that `` piercing and rolling defects have occurred '', otherwise `` no piercing and rolling defects have occurred '' Judged.

  Test Nos. 1, 2, 4, 6, 8, 9, 11, 13 and 16 to 18 are tests on examples of the present invention that satisfy the scope of the present invention, and test Nos. 3, 5, 7, 10, 14 , 15 and 19 are tests on comparative examples that do not satisfy the scope of the present invention.

  In test numbers 1, 2, 4, 6, 8, 9, 11-13, and 16-18, neither piercing and rolling defects nor internal surface irritation of pipes occurred, and the internal surface quality was good. Seamless pipes could be manufactured with high yield. In the above examples of the present invention, one or more of Cu, Cr, Ni and Mo may be contained, and a high-strength seamless pipe having a tensile strength of 531 MPa or more was obtained.

  On the other hand, in the test numbers 7 and 15, which have a large billet axial center crack ratio and do not satisfy the relationship of the above formula (1), no piercing and rolling defects occurred, but the inner surface fraying of the pipe occurred. The internal quality was poor. In addition, test numbers 5, 10, 14, and 19 that do not satisfy the relationship of the above expression (3) with a large number of rotational forgings relative to the value of the billet shaft center part crack rate, did not cause piercing and rolling defects. The inner surface irritation of the tube occurred and the inner surface quality was poor.

  And in the test number 3 in which the number of rotation forgings is small with respect to the value of the crack rate of the billet shaft center part and does not satisfy the relationship of the above formula (2), the piercing and rolling failure due to the failure of biting of the billet into the piercing and rolling mill. Occurred.

  According to the seamless pipe manufacturing method of the present invention, the billet is pierced and rolled by optimizing the combination of the billet shaft center crack size depending on the billet casting conditions and the piercing and rolling conditions in the piercing and rolling process. The occurrence of defects and the occurrence of internal flaws on the pipe can be prevented, and the production yield of the pipe product can be greatly improved. Therefore, the present invention is a technique that can be widely applied in the field of seamless pipe manufacturing where optimum manufacturing conditions are required from both sides of billet continuous casting conditions and billet piercing and rolling conditions.

Claims (3)

A seamless pipe manufacturing method including a piercing and rolling process, wherein a billet diameter is R (m), a billet axial crack length is r (m), and the billet is in contact with a rolling roll before the piercing plug. The seamless is characterized by piercing and rolling so that the relationship represented by the following formulas (1) to (3) is satisfied simultaneously, where N is twice the amount of billet rotation until reaching A method of manufacturing a tube.
0 ≦ r / R ≦ 0.13 (1)
r / R ≧ −0.13N + 0.13 (2)
r / R ≦ −0.065N + 0.39 (3)   The seamless pipe is, by mass%, C: 0.02 to 0.15%, Si: 0.05 to 0.4%, Mn: 0.3 to 2.0%, and P: 0.005 as impurities. Containing 0.3% or less and S: 0.03% or less, and further Cu: 0.05-0.4%, Cr: 0.05-0.6%, Ni: 0.05-0.8% and Mo: One or more of 0.03 to 0.5% are contained, and the balance consists of Fe and impurities, The manufacturing method of the seamless pipe according to claim 1 characterized by things. The ratio (r / R) of the billet axial crack length r to the billet diameter R is expressed by the following equation (4), and from when the billet contacts the rolling roll until it reaches the perforated plug. The method for producing a seamless pipe according to claim 1 or 2, wherein N which is twice the amount of rotation of the billet is estimated by the following equation (5).
r / R = {(8 + W) × (DF × Vc × R ² ) − (16 / R)} / 1000 (4)
N = 2 × L / (Vs / EL) × Brps (5)
Here, W is the specific water amount during casting of the billet (L / kg-steel), Vc is the billet casting speed (m / min), DF is the ferrite temperature range (° C.), and L is in contact with the mill roll. The distance from the position to the tip of the perforated plug (m), Vs is the longitudinal travel speed (m / s) of the perforated shell, EL is the perforation ratio (-), and Brps is the number of rotations of the billet (times / s) Respectively.

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