WO2007100042A1

WO2007100042A1 - PROCESS FOR PRODUCING HIGH-Cr SEAMLESS PIPE

Info

Publication number: WO2007100042A1
Application number: PCT/JP2007/053916
Authority: WO
Inventors: Taro Ohe; Koji Nakaike
Original assignee: Sumitomo Metal Industries, Ltd.
Priority date: 2006-03-01
Filing date: 2007-03-01
Publication date: 2007-09-07
Also published as: CN101394943B; US20090000709A1; EP1990107A1; CN101394943A; JPWO2007100042A1; EP1990107A4

Abstract

A billet containing, by mass, 8.0 to 16.0% Cr whose value of the formula: Cr+4Si-(22C+0.5Mn+1.5Ni+30N) wherein the atomic symbols represent the mass% contents of respective constituent elements in steel is 9.0% or less is heated by means of a heating furnace conditioned so as to have the soaking temperature ranging from 1100° to 1300°C and allow the in-furnace time (min) to satisfy the relationship: 0.5 × billet diameter (mm) or more. Thereafter, by means of a centering machine capable of making a center hole of diameter of 0.34 × billet diameter (mm) or more at the piercing-starting-side end face of the billet by punch of 60° to 110° punching angle, a center hole is made at the piercing-starting-side end face of the billet, followed by piercing rolling by an inclined roll piercing machine of 8.0% or below plug distal-end draft ratio. The thus produced high-Cr seamless pipe realizes reduction of internal-surface defects and ensures excellent internal-surface properties.

Description

Specification

High Cr seamless pipe manufacturing method

Technical field

TECHNICAL FIELD [0001] The present invention relates to a method for producing a high Cr seamless pipe used for oil wells, gas wells, various plants or construction structural materials. In particular, the present invention relates to a method for producing a high Cr seamless pipe containing 8.0 to 16.0% Cr in mass%.

Background art

[0002] High Cr seamless steel pipes containing 8.0 to 16.0% Cr by mass% for oil or gas wells or various plants or construction structures are often used.

[0003] In order to efficiently produce this high Cr seamless pipe, it is desirable to employ an inclined roll type drill (hereinafter also referred to as "piercer") in the piercing and rolling process. Specifically, a hollow blank tube is manufactured by a piercer from a solid material with a round cross section (hereinafter referred to as “billette”), and the drilled blank tube is a mandrel mill, plug mill, assel mill, push bench, etc. Then, the outer diameter is reduced with a stretch reducer or a sizer.

[0004] However, the hot workability of high Cr steel is lower than that of so-called “regular steel”! Therefore, when piercing and rolling is performed with a piercer, defects are likely to occur on the inner surface of the drilled base tube. A typical example of this defect is a so-called inner cover,

Sometimes called “wrap ¾¾”.

[0005] In order to remove the inner surface defects of the pipe, it is necessary to cut or delete the wrinkled portion in a process separate from the manufacturing process of the pipe. This work requires a lot of man-hours and significantly reduces the production efficiency. In addition, if the defect is deep inside, the tube must be discarded. This makes the yield worse.

[0006] By the way, Patent Documents 1 to 6 propose techniques for suppressing the occurrence of internal defects at the stage of piercing and rolling.

[0007] Patent Document 1 discloses that the hot workability of a material is improved by suppressing the contents of P and S, which are impurity elements in steel, to a very low level, and the inner cover during piercing and rolling by a piercer is reduced. Suppressing technology is disclosed. [0008] Patent Document 2 discloses a technique for suppressing the generation of δ ferrite by lowering the billet heating temperature and further reducing the average strain rate during piercing and rolling by a piercer to suppress heat generation during processing. Yes.

[0009] Patent Document 3 specifies the content of a specific alloy component and improves the structure generated in the hot working process by controlling the heating time of the annealing process and the heating temperature of the billet at a low temperature. A method for producing a martensitic seamless steel pipe is disclosed.

[0010] Patent Document 4 discloses a technique for piercing and rolling by managing conditions such as a material diameter, a guide shoe interval, and an inclined roll interval when piercing and rolling with a piercer having a disc roll type guide shoe.

[0011] In Patent Document 5, the content of Cr, S and P as impurity elements, and the element to be added is specified, and the heating and soaking time of the billet are adjusted to adjust the hotness. A method for producing a high Cr seamless pipe that improves the structure produced in the machining process and prevents the occurrence of internal defects is disclosed.

[0012] Patent Document 6 specifies the content of a specific alloy component, and improves the structure generated in the hot working process by adjusting the crossing angle and the inclination angle during piercing and rolling. A method of manufacturing a martensitic stainless steel seamless pipe that prevents the occurrence of internal defects has been disclosed.

[0013] Patent Document 7 uses a billet that has been previously processed so that a billet rear end becomes a recess before piercing and rolling in the manufacturing process of a seamless steel pipe composed of an inclined piercing rolling mill and a mandrel mill. Thus, a method for producing a seamless pipe that avoids the generation of wrinkles when the mandrel bar is drawn in the drawing and rolling process is disclosed.

Patent Document 1: Japanese Patent Application Laid-Open No. 59-208055

Patent Document 2: JP-A 63-281705

Patent Document 3: Japanese Patent Laid-Open No. 4-224659

Patent Document 4: JP-A-5-69011

Patent Document 5: Japanese Unexamined Patent Publication No. 2003-3212

Patent Document 6: Japanese Unexamined Patent Application Publication No. 2004-43935

Patent Document 7: Japanese Unexamined Patent Application Publication No. 2004-82174 Disclosure of the invention

Problems to be solved by the invention

[0015] Even if the techniques proposed in the above-mentioned Patent Documents 1 to 7 are applied, the high content of Cr is 8.0 to 16.0%.

Internal defects that occur in the Cr steel perforated tube are not sufficiently suppressed.

[0016] Therefore, the present inventors have observed in detail the inner covering flaws generated in the high Cr seamless pipe, and the heating conditions of the billet, the pre-processing conditions for the billet before piercing and rolling, and the piercing and rolling settings. The causal relationship with various conditions such as conditions was investigated in detail.

[0017] As a result, it has been found that, before the piercing and rolling, the center cover is caulked on the billet end surface on the side where the piercing and rolling is started under specific conditions, so that the inner covering is greatly suppressed. .

[0018] The present invention has been made in view of the above-described contents, and its object is to achieve a high C that can particularly suppress the occurrence of medium-coverage flaws among inner surface defects generated in the piercing and rolling process by a piercer. It is an object of the present invention to provide a method for producing a seamless steel pipe, in particular, a method for producing a high Cr seamless pipe containing 8.0 to 16.0% Cr by mass%.

Means for solving the problem

[0019] The gist of the present invention is a method for producing a high Cr seamless pipe as shown below,

“A high Cr joint that includes the process of heating the billet in a heating furnace, the process of providing a center hole with a centering machine on the end face of the heated billet on the piercing start side, and the process of piercing and rolling the billet with an inclined roll type piercing machine. A method of manufacturing a steel-free pipe,

The billet is in mass% and contains 8.0 to 16.0% of Cr, and the value of Cr * represented by the following formula (1) is 9.0% or less,

In the heating process, the soaking temperature is 1100-1300 ° C, and the in-furnace time from when the billet enters the heating furnace until it exits is set so as to satisfy the following equation (2):

In the step of providing the center hole, a center hole having a diameter represented by the following formula (3) is provided on the piercing start side end surface of the billet by a punch having a punch angle of 60 to 110 °, and in the piercing and rolling step, A method for producing a high Cr seamless pipe, characterized in that the plug tip draft ratio represented by the following formula (4) is set to be 8.0% or less.

Cr * = Cr + 4Si- (22C + 0.5Mn + l .5Ni + 30N) '' (1), Furnace time (min) ≥0.5 X Round billet diameter (mm) · · '(2),

Center hole diameter (mm) ≥ 0.34 X round billet diameter (mm) · '(3),

Plug tip draft rate (%) = {(Round billet diameter (mm) Roll spacing at the tip of plug (mm)) Z round billet diameter (mm)} X 100 · · · (4).

In addition, the element symbol in (1) Formula shows content in the mass%. "

It is in.

The invention's effect

[0020] According to the method of the present invention, during the production of a high Cr seamless pipe containing 8.0 to 16.0% of Cr, generation of intermediate covering defects among inner surface defects generated in a piercing and rolling process by a piercer. Can be suppressed.

BEST MODE FOR CARRYING OUT THE INVENTION

[0021] The findings of the results of the investigation of the occurrence of mid-covers generated in the piercing and rolling process by the piercer performed by the present inventors as described above will be shown.

[0022] As shown in the following (a) to (c), the occurrence of inner covering flaws is controlled by controlling the soaking condition of the billet to suppress the formation of δ ferrite in the billet, It has become clear that by reducing the number of rotary forgings in the piercing and rolling process by

[0023] (a) Before the piercing and rolling process in the piercer, Cr contains 8.0 to 16.0%, and the value of Cr * represented by the formula (1) is 9.0% or less If a billet is heated in a heating furnace so that the soaking temperature is 1100-1300 ° C and the in-furnace time satisfies the above equation (2), the generation of δ ferrite can be suppressed by the soaking effect, and the piercer The main factor of the inner covering generated in the piercing and rolling process is suppressed.

[0024] (b) By reducing the number of rotational forgings expressed by the following formula (5), it is possible to suppress the occurrence of medium covering defects that occur during piercing and rolling by a piercer.

N = (2L X Brps) / {(Rolling speed X sin X drilling efficiency of roll gorge part) ΖPunching ratio} ··· (5).

In the above equation (5),

L: The positional force with which the roll swallows the billet is also the distance to the plug tip, Brps: Billet rotation speed, that is, “Rotational speed component of the roll peripheral speed at the position where the billet is squeezed Z perimeter of the billet”,

Perforation ratio: “Perforated tube length Z billet length”

β: roll inclination angle (°),

Drilling efficiency: Advance efficiency (%) of piercing and rolling,

Point to.

[0025] (c) As apparent from the equation (5), if the force for reducing the value of “L” and the value of the drilling efficiency are increased, the number of rotary forging “N” of the billet can be reduced. The value of “L” can be easily reduced by reducing the “plug tip draft ratio”. Although a method of increasing the roll inclination angle “| 8” is also conceivable, this method may cause the piercer roll to cause a billet stagnation failure.

[0026] Therefore, next, the conditions for improving the "piercing efficiency" of the piercing rolling by the piercer were investigated in more detail. As a result, the following findings (d) and (e) were obtained.

[0027] In the step of providing the center hole in (d), by setting the punch angle of the centering machine within a specific range, the time from when the billet is swallowed into the piercer roll until the piercing and rolling is stabilized is shortened. Therefore, the “perforation efficiency” is improved.

[0028] (e) By making the diameter of the center hole equal to or greater than a specific value determined in relation to the billet diameter, even when the billet is pierced and rolled under a condition where the “plug tip draft ratio” is small, The piercer roll can stably pierce and roll the billet without causing a stagnation failure of the billet.

The present invention has been completed based on the above findings.

[0030] Each requirement of the present invention will be described in detail below. In the following description, “%” for the content of each element means “mass%”.

[0031] (A) Chemical composition of billet

The billet, which is the material of the high Cr seamless pipe according to the present invention, contains 8.0 to 16.0% of Cr, and the value of Cr * represented by the above formula (1) is 9.0%. It must be high Cr steel with the following chemical composition.

[0032] Cr: 8.0 to 16.0% Cr must be contained in an amount of 8.0% or more to ensure corrosion resistance. On the other hand, since Cr is a ferrite forming element, if its content increases, δ-ferrite is easily formed when the material is processed at high temperature, and hot workability is reduced. In particular, when the Cr content exceeds 16.0%, the hot workability is significantly reduced. If too much Cr is added, the production cost of seamless pipes will increase. Therefore, the Cr content is set to 8.0 to 16.0%.

[0033] Value of Cr *: 9.0% or less

Even when the Cr content is 8.0-16.0%, if the value of Cr * represented by the above formula (1) exceeds 9.0%, δ ferrite is likely to be formed, and Physical stress Cracking and hot workability decrease. Therefore, the value of Cr * represented by the formula (1) is set to 9.0% or less.

[0034] From the above, in the present invention, the billet contains Cr in an amount of 8.0 to 16.0%, and the value of Cr * represented by the formula (1) is 9.0% or less. We decided to use Cr steel.

[0035] The billet that is the material of the high Cr seamless pipe according to the present invention only needs to specify the Cr content and the value of Cr * represented by the above formula (1) as its chemical composition.

[0036] In addition, as an example of the preferred billet as a raw material and the chemical composition, for example, C: 0.15-0.

22%, Si: 0.1-1.0%, Mn: 0.10-: L 00%, Cr: 12.0-14.0%, P: 0.020% or less, S: 0.010% or less, N: 0.05% or less, 0 (oxygen) : 0.0060% or less, further, their respective 0.005 to 0.200 ^_0/0 of V, Nb and Ti, as well as 0.0005 to 0.0100 ^_0/0 B power et select one or more I (provided that when two or more species In total 0.005-0.200%), A1: 0 to 0.1%, Ni: 0 to 0.5%, Cu: 0 to 0.25%, and Ca: 0 to 0.0050%. Examples include high Cr steel in which the value of Cr * represented by the formula (1) is 9% or less.

[0037] Further, as another example of the chemical composition of the billet that is a material of the high Cr seamless pipe according to the present invention, for example, C: 0.003 to 0.050%, Si: 0.05 to 1.0%, Mn: 0.10 to : L 50%, Cr: 10.5 to 14.0%, P: 0.035% or less, S: 0.010% or less, N: 0.070% or less, 0 (oxygen): 0.0060% or less, V: 0 to 0.200%, Ti: 0 to 0.300%, Mo: 0.2-3.0%, Ni: 0-7.0% and Zr: 0-0.580%, comprising the remaining force SFe and impurities, High Cr steel with Cr * value of 9% or less represented by the formula

[0038] (B) Billet heating conditions

In the present invention, a billet that is a material of a high Cr seamless pipe having the chemical composition described in the above section (A) is soaked at a soaking temperature of 1100 to 1300 ° C and the billet enters a heating furnace. It is necessary to heat in the heating furnace so that the in-furnace time until exiting can satisfy the above equation (2).

[0039] When the soaking temperature is lower than 1100 ° C, the temperature in the piercing and rolling process at the piercer and the temperature in the drawing and rolling process such as a mandrel mill and a plug mill are lowered and the deformation resistance of the rolling material is reduced. Therefore, piercing and stretching are unstable and seizure flaws are likely to occur.

[0040] When the soaking temperature exceeds 1300 ° C, δ-ferrite is generated and grows in the billet, so that it becomes easy to generate mid-coverage.

[0041] Even if the soaking temperature is 1100 to 1300 ° C, if the in-furnace time of the billet in the heating furnace does not satisfy the formula (2), the billet center is not sufficiently soaked, Stable piercing and rolling becomes difficult by the piercer. As a result, the uneven thickness rate is deteriorated.

[0042] Therefore, in the present invention, the billet, which is a material for piercing and rolling by Piercer, has a soaking temperature of 1100 to 1300 ° C and the in-furnace time from when the billet enters the heating furnace until it exits (2 It was decided to heat so as to satisfy the formula.

[0043] The in-furnace time in the heating furnace is preferably less than "1.5 X billet diameter (mm)" in order to prevent a decrease in yield due to scale loss.

[0044] (C) Billet centering

According to the present invention, there is provided a centering machine including a punch having a punch angle of 60 to L 10 ° on a drilling start side end face of a billet piercer heated under the conditions described in the above section (B). Therefore, it is necessary to be able to provide a center hole having a diameter represented by the formula (3).

[0045] In the step of providing the center hole, if the center hole is provided in the billet using a centering machine having a punch angle of 110 ° or less, the plug is not pushed back at the center of the billet end face in the piercing and rolling step. Also, the drilling pressure should be low under conditions where the plug tip draft In other words, in other words, the billet can be stably pierced and rolled immediately even if the rotational forging number N expressed by the above equation (5) is small, resulting in a shorter piercing and rolling time. In other words, the number of times that the billet is rotationally forged can be reduced, and the occurrence of intermediate covering flaws can be sufficiently suppressed. However, if the punch angle is less than 60 °, the punch must be driven deeply in order to secure a predetermined hole diameter in the billet, and an internal defect may occur in that portion, resulting in a decrease in yield. . On the other hand, when the punch angle exceeds 110 °, it is difficult to pierce and roll the billet under the condition that the draft rate of the plug tip is small, and it is difficult to ensure sufficient piercing efficiency when the roll squeezes the billet. . For this reason, it is not possible to sufficiently suppress the occurrence of crusting, and in some cases, the roll may cause a stagnation failure of the billet. Therefore, the centering machine punch angle should be 60-110 °.

[0046] Even if the punch angle of the centering machine is 60 to 110 °, if the diameter of the center hole is less than "0.34 X billet diameter (mm)", use a thin punch. Must. Therefore, it may not be possible to increase the “drilling efficiency” because the punch is damaged or the required center hole depth cannot be secured. For this reason, the diameter of the center hole needs to satisfy the above formula (3), that is, to be equal to or larger than “0.34 X billet diameter (mm)”.

[0047] (D) Piercing and rolling at piercer

In the present invention, the billet centered under the condition described in the above section (C) needs to be pierced and rolled under the condition that the draft at the tip of the plug is 8.0% or less.

[0048] When the plug tip draft ratio exceeds 8.0%, the value of “L” in the above equation (5), that is, the positional force with which the mouth bites the billet, Means scientifically big. In this case, since the rotational forging number N expressed by the above equation (5) is increased, so-called “Mannesmann fracture” occurs excessively, and the intermediate covering flaws are likely to occur. Therefore, the plug tip draft rate was set to 8.0% or less. The plug tip draft rate is preferably 6.0% or less. On the other hand, the lower limit of the plug tip draft rate is approximately 3.0%, which allows the billet to stagnate into the piercer roll geometrically due to the force of the center hole described in the above section (C). [0049] From the above, in the present invention, the round billet, which is a high Cr seamless tube material having the chemical composition described in (A) above, is heated under the conditions described in the above). Thus, after centering under the conditions described in the above section (C), it was defined that the piercing and rolling was performed with the plug tip draft rate of the piercer being 8.0% or less.

[0050] It should be noted that in the present invention, the value of the piercing efficiency at the piercer need not be particularly specified! / Repulsive force When the piercing efficiency is less than 50%, it is expressed by the above formula (5). The number of rotating forgings N increases, so-called `` Mannesmann fracture '' occurs excessively, and internal covering flaws are likely to occur, so the drilling efficiency at the piercer should be 50% or more. ,.

[0051] The upper limit of the piercing efficiency of a piercer is empirically about 60 to 70% for a barrel type roll (crossing angle 0 °), and a cone type roll (crossing angle 5 to 30 °). In the case of, it is about 75-95%.

[0052] Hereinafter, the present invention will be described in more detail by way of examples.

Example

[0053] A steel ingot having the chemical composition shown in Table 1 was subjected to ingot rolling by a conventional method to obtain a round billet having a diameter of 191 mm or 225 mm. In Table 1, both Steel A and Steel B are steels according to the present invention examples whose chemical compositions are within the range specified by the present invention.

[0054] [Table 1]

Next, the round billet of the above size was charged into a heating furnace, heated so that the soaking temperature was 1200 ° C and the in-furnace time was 240 minutes, and then drilled with centering and piercing under the conditions shown in Table 2. Hole-rolled tube with outer diameter of 228.0mm (when round billet diameter is 225mm) and outer diameter Manufactured a 196.0 mm blank (when the diameter of the round billet is 191 mm).

[0056] The in-furnace time represented by the formula (2) is required to be not less than “0.5 X 191 (mm)” when the diameter of the round billet is 191 mm, that is, not less than 95.5 minutes. In addition, when the diameter of the round billet is 225 mm, “0.5 X 225 (mm)” or more, that is, 112.5 minutes or more is required. Therefore, the in-furnace time of 240 minutes described above satisfies the conditions specified in the present invention.

[0057] In the case of Test Nos. 4 to 6 in Table 2, punching and rolling were stopped because punch breakage occurred.

[0058] [Table 2]

Table 2

With respect to each of the elementary tubes of Test Nos. 1 to 3 and Test Nos. 7 to 22 in Table 2 thus obtained, the presence or absence of the occurrence of intermediate covering wrinkles was investigated. In other words, the location of the occurrence of internal defects was first identified and marked by ultrasonic flaw detection, and the portion was cut and evaluated by visual inspection. Further, the occurrence of rolling defects such as uneven thickness was examined by visual inspection and ultrasonic flaw detection. did. [0060] Table 2 also shows the results of the investigation of the properties of the tube. In Table 2 “Roller tube properties” column, “◯” indicates that no inner cover flaws were observed on the inner surface of the tube, and “XI” indicates a punch flaw (inner surface defect) on the inner surface of the tube. In addition, “X 2” indicates that the inner cover was recognized. “I” indicates that the punch was broken and the piercing and rolling process was stopped, so no investigation was conducted (test numbers 4 to 6).

[0061] From Table 2, after heating the high Cr steel round billet containing the components shown in Table 1 under the heating conditions specified in the present invention, the punch bill has a punch angle of 60- A centering hole having a diameter represented by the above equation (3) is provided by a centering machine having an angle of 110 °, and then pierced and rolled at a plug tip draft rate under the conditions specified in the present invention within the range of the penetration limit. In the case of the test tubes 7-11 and 13-17 obtained in this way, it is clear that the inner surface properties are good. In addition, no rolling defects such as uneven thickness were found in each of the above-mentioned elementary tubes.

[0062] On the other hand, even when a steel billet having a chemical composition within the range defined by the present invention is heated under the heating conditions defined by the present invention, the centering condition or punching of the round billet is perforated. When the rolling conditions were test numbers 1 to 3, test number 12 and test numbers 18 to 22 that deviated from the provisions of the present invention, bonfire flaws (inner surface defects) or inner cover flaws were observed in the raw pipes.

[0063] That is, in the case of test numbers 1 to 3, the punch angle is 50 °, which is less than the specified 60 °, and in order to secure a predetermined hole diameter, in the case of test number 1, 105.5 mm, In the case of 2-3, it was 91.1 mm, and it was necessary to drive the punch deeply, so a punch punch (inner surface defect) occurred.

[0064] In the case of test number 12, the ratio of the center hole diameter to the round billet diameter is less than 0.34, and the force of the plug is more than 8.0% as specified in the plug tip draft rate. Covering occurred.

[0065] Further, in the case of test numbers 18 to 22, the punch angle exceeds 115 °, which is 115 °, and it is difficult to set the plug tip draft ratio to be small. It is specified as 8.2 to 8.8. Exceeded 8.0%. Also, the roll caused the billet to squeeze in and the inside cover wrinkles occurred.

[0066] In addition, as already mentioned, the test angles 4 to 6 where the punch angle is 50 ° and falls below the specified 60 °. In some cases, breakage of the punch occurred, and it was strong that the piercing and rolling had to be stopped.

[0067] While the present invention has been specifically described with reference to the examples, the present invention is not limited to these examples. Those not disclosed as examples are also included in the present invention as long as they satisfy the requirements of the present invention.

Industrial applicability

[0068] According to the production method of the present invention, it is possible to produce a high Cr seamless pipe with less occurrence of internal flaws. In addition, it is not necessary to excessively reduce impurities as the chemical composition of the steel, and since a predetermined productivity can be ensured at the time of pipe production, a high Cr seamless pipe excellent in inner surface quality can be efficiently produced.

Claims

The scope of the claims

[1] A process including heating a billet in a heating furnace, providing a center hole by a centering machine on the end face on the piercing start side of the heated billet, and piercing and rolling the billet with an inclined roll type piercing machine. A method for producing a Cr seamless steel pipe,

The billet is in mass% and contains 8.0 to 16.0% Cr and Cr represented by the following formula (1)

The value of * is 9.0% or less,

Cr * = Cr + 4Si- (22C + 0.5Mn + l .5Ni + 30N) '' (1),

Furnace time (min) ≥0.5 X Round billet diameter (mm) · · '(2),

Center hole diameter (mm) ≥ 0.34 X round billet diameter (mm) · '(3),

Plug tip draft rate (%) = {(Round billet diameter (mm) —roll interval (mm) at the tip of the plug) Z round billet diameter (mm)} X 100 ··· (4).

In addition, the element symbol in (1) Formula shows content in the mass%.