JP2009120875A - High alloy seamless tube and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a seamless tube excellent in the quality of a tube outer surface after tube-making since a crack and a flaw are not caused on a billet surface when carrying out rolling after blooming or forging, and a manufacturing method therefor. <P>SOLUTION: The high alloy seamless tube has chemical composition composed of, by mass, 0.005-0.250% C, 0.05-2.00% Si, 0.05-3.00% Mn, ≤0.04% P, ≤0.004% S, 0.01-3.0% Cu, 10-35% Cr, 10-80% Ni, 0.01-7.0% Mo, 0.001-0.200% Al, 0.001-0.300% N and the balance Fe with impurities, and Zn and Pb in the impurities, are ≤0.004% Zn and ≤0.0025% Pb. A manufacturing method for the seamless tube is also provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a high alloy seamless pipe excellent in outer surface quality and a method for producing the same. More specifically, the present invention relates to a high-alloy seamless pipe excellent in outer surface quality suitable for oil well pipes and line pipes, and also suitable as various structural members in nuclear power plants and chemical industrial plants, and a method for producing the same.

  Since the first oil shock, the development of oil and gas wells on a global scale has progressed. However, as energy demand in developing countries increases, deep wells and corrosiveness of oil wells and gas wells have become more severe. Drilling of wells has been forced. In addition, from the viewpoint of efficient use of energy and the like, the use conditions of high temperature and high pressure are being promoted in nuclear power plants and chemical industrial plants. With such severe oil / gas well environment and plant operating conditions, various high Cr-high Ni alloys with higher strength, high corrosion resistance and high temperature resistance have been developed. It is used practically as a non-tube.

  For example, Patent Document 1 and Patent Document 2 disclose various high Cr-high Ni alloys that have higher strength and better corrosion resistance than conventional ones. Patent Document 3 includes a high Cr-high Ni alloy in which the content of Mo is reduced and the economy is improved in an alloy containing 20 to 35% and 25 to 50% by weight of Cr and Ni, respectively. Seamless pipes are disclosed.

  However, after the end of the East-West Cold War and the EU integration, price competition among companies has become more and more intense with the globalization of the economy, such as corporate integration and reorganization that has rapidly progressed on a global scale. As a result, in the development of oil wells and gas wells, in addition to ensuring safety, further higher efficiency and lower cost have been demanded.

  However, it contains not only high alloys with high Cr and Ni contents proposed in Patent Documents 1 and 2, but also 20 to 35% Cr and 25 to 50% Ni proposed in Patent Document 3. As for the high Cr-high Ni alloy, there is a problem that the outer surface of the seamless tube is liable to be cracked or wrinkled, resulting in poor outer surface quality.

JP 54-107828 A JP 54-1227831 A Japanese Patent Laid-Open No. 11-302801

  This invention is made | formed in view of the said present condition, The objective is to provide the high alloy seamless pipe excellent in outer surface quality, and its manufacturing method.

  In order to achieve the above-mentioned object, the present inventors have made a mechanism for generating cracks and flaws generated on the outer surface of a seamless tube made of a high alloy of high Cr-high Ni system with extremely low hot workability. As a result of various examinations and experiments, the following findings (a) to (d) were obtained.

  (a) The seamless pipe is a Eugene Sejurune method after a slab having a predetermined chemical composition obtained by ingot or continuous casting is made into a billet having a predetermined cross-sectional shape by a rolling process such as ingot or forging. It is manufactured by making a pipe by a hot extrusion method such as Mannesmann's pipe making method by piercing and rolling with a piercer. Note that the cross-sectional shape of the billet is not particularly limited, and may be round or square, but a round shape is preferable.

  However, since the high Cr-high Ni alloy has extremely low hot workability, cracks and flaws are likely to occur on the surface of the obtained billet when the slab is rolled by ingot or forging. The cracks and wrinkles generated in the rolling process are amplified in the subsequent pipe making process, and as a result, cracks and wrinkles are formed on the outer surface of the obtained tube, resulting in a seamless pipe having inferior outer surface quality.

  Therefore, if cracks or wrinkles occur on the billet surface after rolling in a rolling process such as this lump or forging, the billet surface is cut off with a grinder before sending it to the pipe making process, and the cracks and wrinkles are maintained. It is necessary to keep it. The care process becomes a factor of cost increase. In addition, the presence of billets that cannot remove cracks and wrinkles even by such care, and even if it seems that cracks and wrinkles could be removed by care from the appearance at the billet stage, The existence of pipe products that must be discarded as defective products due to cracks and wrinkles also increases costs.

  (b) In high-Cr-high-Ni high alloy slabs, especially when the Cr and Ni contents are Cr: 10% or more and Ni: 10% or more, the ingots, forgings, etc. Cracks and wrinkles are likely to occur on the billet surface after rolling in the rolling process. As a cause, it was confirmed that Zn and Pb contained as impurities in the cast slab of high alloy were concentrated at the grain boundaries, thereby causing grain boundary embrittlement. Conventionally, it has been known that P and S contained as impurities in the slab of alloy concentrate at the grain boundary, thereby causing embrittlement at the grain boundary. However, Zn and Pb also have the same reason. The present inventors have found for the first time that grain boundary embrittlement occurs.

  (c) Such grain boundary embrittlement due to Zn and Pb was confirmed both in the slab (ingot material) produced by the casting method and in the slab (continuous cast material) produced by the continuous casting method. In either case, cracks and wrinkles are generated on the billet surface after a subsequent rolling step such as ingot or forging, thereby deteriorating the outer surface quality of the pipe product after pipe making. When comparing the ingot material and the continuous cast material, the continuous cast material is intermittently pulled out from the mold by the oscillation during continuous casting, so that an oscillation mark part (valley part) is formed on the outer surface of the slab. At the time of rolling, stress concentrates on the oscillation mark portion, so that the continuous cast material is more likely to crack or wrinkle on the billet surface after rolling.

  (d) When forming the billet by rolling the slab by ingot or forging, if the total rolling ratio at 800-1300 ° C. is too large, cracks and wrinkles occur on the surface of the billet after rolling. It becomes easy. Therefore, the total rolling ratio is preferably 12.0 or less. The total rolling ratio is more preferably 7.0 or less.

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

  The gist of the present invention resides in a high alloy seamless pipe shown in the following (1) and a manufacturing method thereof shown in (2) to (3). Hereinafter, they are referred to as “present invention 1” to “present invention 3”, respectively. In addition, it may be referred to as “the present invention”.

  (1) By mass%, C: 0.005 to 0.250%, Si: 0.05 to 2.00%, Mn: 0.05 to 3.00%, P: 0.04% or less, S: 0.004% or less, Cu: 0.01-3.0%, Cr: 10-35%, Ni: 10-80%, Mo: 0.01-7.0%, Al: 0.001-0. 200% and N: 0.001 to 0.300% included, the balance has chemical composition of Fe and impurities, Zn and Pb in the impurities are Zn: 0.004% or less and Pb: 0.0025% A high-alloy seamless pipe characterized by:

  (2) A method of producing a high alloy seamless pipe by forming a billet by rolling a slab made of a high alloy having the chemical composition of (1) above, and thereafter producing the high alloy seamless pipe, A method for producing a high alloy seamless pipe, characterized in that a rolling temperature is set to 800 to 1300 ° C. and a total rolling ratio therebetween is set to 12.0 or less when forming into a billet.

  (3) A method for producing a high alloy seamless pipe by forming a billet by rolling a slab made of a high alloy having the chemical composition of the above (1), and thereafter producing a high alloy seamless pipe. A method for producing a high alloy seamless pipe, characterized in that a rolling temperature is set to 800 to 1300 ° C. and a total rolling ratio therebetween is set to 7.0 or less when forming into a billet.

  The high alloy seamless pipe according to the present invention is made of a high Ni-high Cr alloy of Cr: 10 to 35% and Ni: 10 to 80%. Since the surface of the billet obtained by rolling is not easily cracked or wrinkled, it is possible to provide a high alloy seamless pipe excellent in the outer surface quality of the product after pipe making.

  Hereinafter, each requirement of the present invention will be described in detail.

(A) Chemical composition of high alloy seamless pipe In the following explanation, “%” indication of the content of each element means “mass%”.

C: 0.005 to 0.250%
C is an element necessary for obtaining the strength of the pipe product, and it is necessary to contain at least 0.005%. However, if the content exceeds 0.250%, the amount of M ₂₃ C ₆ type carbide is remarkably increased, and the ductility and toughness of the pipe product are lowered. Therefore, the C content is specified to be 0.005 to 0.250%. In addition, when content of C shall be 0.006-0.030%, since it is excellent in a strength, ductility, and toughness, and corrosion resistance improves, it is preferable. Here, M in the “M ₂₃ C ₆ type carbide” means that a metal element such as Mo, Fe and Cr is contained in combination.

Si: 0.05-2.00%
Si has a deoxidizing action. In order to express this deoxidation effect, it is necessary to contain at least 0.05%. However, when the content exceeds 2.00%, the ductility and toughness of the pipe product are lowered. Therefore, the Si content is defined as 0.05 to 2.00%. In addition, when content of Si shall be 0.20 to 0.50%, since it is excellent in the ductility and toughness of a pipe product and corrosion resistance improves, it is preferable.

Mn: 0.05 to 3.00%
Mn has a deoxidizing action. In order to express this deoxidation effect, it is necessary to contain at least 0.05%. However, when the content exceeds 3.00%, ductility and toughness of the pipe product are lowered, and cracks on the inner surface of the pipe and covering on the inner and outer surfaces of the pipe are likely to occur. Therefore, the Mn content is defined as 0.05 to 3.00%. The Mn content is preferably 0.20 to 1.00%.

P: 0.04% or less P is an impurity mixed in from raw materials and scrap. Generally, when a large amount is present in an alloy, hot workability is deteriorated and corrosion resistance is also deteriorated. In particular, when the P content exceeds 0.04%, the hot workability decreases and the corrosion resistance deteriorates remarkably. Therefore, the allowable P content is set to 0.04% or less. The P content is preferably 0.03% or less.

S: 0.004% or less S is also an impurity mixed in from raw materials and scraps. Generally, when a large amount is present in an alloy, hot workability is lowered and corrosion resistance is also deteriorated. In particular, when the S content exceeds 0.004%, the hot workability is deteriorated and the corrosion resistance is remarkably deteriorated. Therefore, the allowable S content is set to 0.004% or less. More preferably, the S content is 0.003% or less. In addition, it is more preferable that the content of S is 0.0015% or less because particularly excellent hot workability is exhibited.

Cu: 0.01 to 3.0%
Cu is an element effective for improving corrosion resistance, and the effect is obtained when the Cu content is 0.01% or more. However, if the Cu content exceeds 3.0%, the ductility and toughness may decrease. Therefore, the Cu content is set to 0.01 to 3.0%. Note that the Cu content is preferably 0.02 to 1.5%.

Cr: 10 to 35%
Cr, together with Mo and N, has the effect of improving the corrosion resistance and strength of the alloy. The above effect is obtained when the Cr content is 10% or more. However, when the Cr content exceeds 35%, the hot workability of the alloy is lowered. Therefore, the Cr content is set to 10 to 35%. The Cr content is preferably 21 to 27%.

Ni: 10-80%
Ni has an effect of stabilizing the austenite base together with N, and is an essential element for containing a large amount of elements having a strengthening action and corrosion resistance such as Cr and Mo in the high alloy. These effects are obtained when the Ni content is 10% or more. On the other hand, the addition of a large amount of Ni causes an excessive increase in the alloy cost. In particular, when the Ni content exceeds 80%, the increase in cost becomes extremely large. Therefore, the Ni content is 10 to 80%. Note that the Ni content is preferably 20 to 70%.

Mo: 0.01-7.0%
Mo has the effect of increasing the strength of the alloy in the presence of Cr. This effect is obtained when the Mo content is 0.01% or more. However, if the Mo content exceeds 7.0%, mechanical properties such as ductility and toughness are deteriorated. Therefore, the Mo content is set to 0.01 to 7.0%. Note that the Mo content is preferably 2.80 to 7.0%.

Al: 0.001 to 0.200%
Al has a deoxidizing action. In order to exhibit this effect, it is necessary to contain at least 0.001%. On the other hand, when Al is added excessively, the cleanliness of the alloy is deteriorated and defects starting from inclusions are generated. Therefore, the Al content is specified to be 0.001 to 0.200%. The Al content is preferably 0.001 to 0.150%.

N: N: 0.001 to 0.300%
N has the effect of stabilizing the austenite substrate together with Ni. In order to ensure the action, it is necessary to contain at least 0.001%. On the other hand, if N is added excessively, the toughness of the pipe product may be lowered, and if it exceeds 0.300%, the toughness may be significantly lowered. Therefore, the N content is specified to be 0.001 to 0.300%. The N content is preferably 0.0040 to 0.270%.

Fe: balance Fe has the effect of reducing the alloy cost by ensuring the strength of the tube product and enabling the Ni content to be reduced. For this reason, in the alloy used as the material of the seamless pipe according to the present invention, the balance element is Fe.

Zn: 0.004% or less Although Zn is contained as an impurity, it segregates at the grain boundary and generates cracks and flaws on the billet surface after rolling a cast slab made of a high alloy such as ingot or forging. Therefore, the Zn content is 0.004% or less. Note that the Zn content is preferably 0.003% or less.

Pb: not more than 0.0025% Pb is contained as an impurity, but segregates at the grain boundaries and causes cracks and wrinkles to occur on the billet surface after rolling a cast slab made of a high alloy such as ingot or forging. Therefore, the Pb content is 0.0025% or less. The Pb content is preferably 0.0020% or less.

  High alloy seamless pipes having the chemical composition described so far are excellent in mechanical properties such as strength and ductility and also in corrosion resistance, so various structures in oil well pipes and line pipes as well as in nuclear power plants and chemical industrial plants. It can be used as a member.

(B) Manufacturing method of seamless pipe After preparing a high alloy molten metal having the above chemical composition, a slab can be produced by adopting any of the ingot method and the continuous casting method. In the continuous casting method, the slab is intermittently pulled out from the mold by oscillation, so that an oscillation mark (valley) is formed on the outer surface of the slab. Therefore, since continuous stress is concentrated on this oscillation mark in the next rolling process, cracks and wrinkles are likely to occur on the billet surface after rolling, so that the total rolling rate should not be severely reduced. Is preferably kept low.

  Also, a high alloy slab produced by an ingot method or a continuous casting method is first heated to a temperature of 1300 ° C. or lower and rolled several tens of times before the slab temperature falls below 800 ° C. To form a billet.

  Before the slab is rolled into a billet, it may be heated only once to a temperature of 1300 ° C. or lower, or may be heated twice or more. Usually, when rolling several dozen times (usually about 20 reciprocations) is completed based on one heating (this is referred to as “one heat rolling”), and after one heat rolling, the temperature is further reduced to 1300 ° C. or less. Two methods of heating to a temperature and rolling again several tens of times (usually about 20 reciprocations) before the temperature of the material to be rolled falls below 800 ° C. (this is referred to as “two-heat rolling”). Is adopted.

  In this way, when a slab made of a high alloy is formed into a billet by 1-heat rolling or 2-heat rolling, if the total rolling ratio at 800 to 1300 ° C. is too large, the billet surface after rolling is cracked. Since wrinkles are likely to occur, the total rolling ratio is preferably 12.0 or less. The total rolling ratio is more preferably 7.0 or less.

  As described above, when a slab made of a high alloy is formed into a billet, when rolling is performed based on heating only once as in 1-heat rolling, or twice or more as in 2-heat rolling. In some cases, the rolling is performed based on the heating, but the total rolling ratio in the present invention refers to the rolling ratio after each heating.

  That is, the total rolling ratio in the present invention refers to the total rolling ratio in a plurality of rollings performed immediately after each heating, and is calculated by the following equation (1).

Total rolling ratio = (Cross sectional area before rolling) / (Cross sectional area after rolling) (1) And, by making a billet made of the high alloy thus obtained, Get a seamless tube. As a pipe making method, either a hot extrusion method such as the Eugene Sejurune method or a Mannesmann pipe making method by piercing and rolling with a piercer may be adopted, and any of them may be performed by a usual method.

  The piercing and rolling by Piercer may be performed under the same conditions as in the case of martensitic stainless steel such as carbon steel, low alloy steel, and so-called “13% Cr steel”. Specifically, for example, piercing and rolling may be performed with a billet heating temperature of 1200 to 1300 ° C., a roll crossing angle of 0 to 10 °, and a roll inclination angle of 7 to 14 °.

  Then, after drawing and rolling with a mandrel mill, plug mill, assel mill, push bench, etc., it can be finished into a seamless tube having a desired cross-sectional dimension by rolling with a constant diameter rolling machine such as a stretch reducer or sizer.

  Hereinafter, the present invention will be described in more detail with reference to examples.

  Various alloys having the chemical composition shown in Table 1 were melted by an EF (electric furnace) -AOD-VOD process, and then a slab was obtained by an ingot method or a continuous casting method. In Table 1, alloy no. 1 to 10 are examples of the present invention in which the chemical composition is within the range defined by the present invention. It is a comparative example in which Zn and / or Pb out of 11 to 18 impurities deviate from the content range defined in the present invention. The cross-sectional dimensions of each slab are as shown in Table 2.

  Next, each slab was soaked at 1250 to 1300 ° C. for 2 to 8 hours, and then one slab was hot-forged by one-heat rolling (the number of passes per heating was 20 reciprocations). The ratio is shown in Table 2.), and the other slab is heated by two heat rolling (the number of passes per heating is 20 reciprocations. The rolling ratio per heating is shown in Table 2). A round billet was produced by performing forging. Note that the forging finishing temperature was 800 ° C. or higher.

  About each of the round billets obtained in this way, the surface is cut off by a lathe with a depth of about 2 to 3 mm, and the surface after the cutting is subjected to a color check inspection by a penetrant flaw detection method, resulting in grain boundary cracking. The outer surface quality of the round billet was evaluated by examining the degree of occurrence of outer surface defects (cracking and covering flaws). The results are shown in Table 3. Here, the evaluation criteria are as follows.

(Double-circle): There is no external surface defect resulting from a grain boundary crack.
○: Outer surface defect occurrence rate due to grain boundary cracking: less than 10%.
X: Occurrence rate of external defects due to intergranular cracking: 10% or more.

  Furthermore, round billets with an outer surface defect occurrence rate of less than 10% due to grain boundary cracking are extracted, and the outer surface defect portions are removed by grinding, and seamless pipes are manufactured by the Eugene tube method or Mannesmann tube method. did. In the Eugene tube manufacturing method, the round billet was heated in the range of 1150 to 1230 ° C. to produce a seamless tube having an outer diameter of 55 mm to 227 mm and a wall thickness of 7 mm to 16 mm. On the other hand, in the Mannesmann tube manufacturing method, a round billet was heated at 1250 ° C. to produce a seamless tube having an outer diameter of 244.5 mm and a wall thickness of 15 mm. Next, the outer surface of each tube was inspected by an ultrasonic flaw detection method and evaluated by investigating the degree of occurrence of external surface defects (cracking and covering defects) caused by grain boundary cracking. The results are shown in Table 4. Here, the evaluation criteria are as follows.

(Double-circle): There is no external surface defect resulting from a grain boundary crack.
○: Outer surface defect occurrence rate due to grain boundary cracking is less than 5%.

  As shown in Table 4, when pipes were produced using a round billet having a chemical composition within the scope of the present invention, a seamless pipe having a low external defect rate was obtained.

  Since the high alloy seamless pipe according to the present invention is a billet obtained by rolling the slab by ingot or forging, the surface of the pipe is less likely to be cracked or wrinkled. A high alloy seamless pipe excellent in quality can be provided.

Claims (3)

  In mass%, C: 0.005 to 0.250%, Si: 0.05 to 2.00%, Mn: 0.05 to 3.00%, P: 0.04% or less, S: 0.004 %: Cu: 0.01 to 3.0%, Cr: 10 to 35%, Ni: 10 to 80%, Mo: 0.01 to 7.0%, Al: 0.001 to 0.200% or less And N: 0.001 to 0.300%, the balance having the chemical composition of Fe and impurities, Zn and Pb in the impurities are Zn: 0.004% or less and Pb: 0.0025% or less A high alloy seamless pipe characterized by being.   A method for producing a high alloy seamless pipe by forming a billet by rolling a slab made of a high alloy having the chemical composition according to claim 1, and thereafter producing the high alloy seamless pipe. A method for producing a high-alloy seamless pipe, wherein the rolling temperature is 800 to 1300 ° C. and the total rolling ratio is 12.0 or less during molding.   A method for producing a high alloy seamless pipe by forming a billet by rolling a slab made of a high alloy having the chemical composition according to claim 1, and thereafter producing the high alloy seamless pipe. A method for producing a high-alloy seamless pipe, wherein a rolling temperature is set to 800 to 1300 ° C. during forming and a total rolling ratio therebetween is set to 7.0 or less.