JP6520892B2 - Seamless steel pipe manufacturing method and seamless steel pipe manufacturing equipment - Google Patents

Description

  The present invention relates to a method of manufacturing a seamless steel pipe and a seamless steel pipe manufacturing facility, in which variation in mechanical characteristics is small in the longitudinal direction of the steel pipe.

Seamless steel pipes are used as oil fields, gas field development and heat exchangers, piping for chemical plants, and structural members. In recent years, a variety of products, from thin-walled products to thick-walled products, have been required, such as thin-walled products by increasing the strength of steel pipe materials for the purpose of weight reduction of steel pipes and extremely thick products for expanding use in environments exposed to severe external forces. ing. For example, in Patent Document 1, C: 0.005 to 0.050%, Si: 0.05 to 0.50%, Mn: 0.20 to 1.80%, Cr: 15.5 by mass%. -18%, Ni: 1.5 to 5%, Mo: 1 to 3.5%, V: 0.02 to 0.20%, N: 0.01 to 0.15%, O: 0.006% Containing the following, Cr + 0.65 Ni + 0.6 Mo + 0.55 Cu-20 C 1 19.5 and Cr + Mo + 0.3 Si-43.5 C-0.4 Mn-Ni-0.3 Cu-9 N 1 11.5 Steel material having a component composition satisfying the content (% by mass of element) is heated, pipe-formed by hot working, pipe-formed, and cooled to room temperature at a cooling rate of air cooling or more. Make a seamless steel pipe of a specified size, and then reheat the seamless steel pipe to a temperature of 850 ° C or more to cool it by air cooling or more. By cooling to 100 ° C. or less at a speed and then heating to 700 ° C. or less, a structure containing 10 to 60% of a ferrite phase by volume ratio and having a remainder of a martensite phase is provided. And a technology capable of obtaining a high strength stainless steel pipe for oil wells having a yield strength of 654 MPa or more is disclosed. As a result, in Patent Document 1, the steel pipe has high strength and has sufficient corrosion resistance even under severe corrosive environments at high temperatures up to 230 ° C., including CO ₂ and Cl ⁻ .

  On the other hand, in order to reduce the number of pipe end joints at the time of construction as much as possible, the demand for long products is increasing. As a rolling technology and shape control technology for forming a seamless steel pipe into a desired shape with high efficiency, Patent Document 2 discloses that a steel block heated to a rolling temperature is drilled in a hollow shell by an inclined roll drilling machine. Then, in a method for producing a seamless steel pipe of the type which is then extended into a blank and then rolled into a finished tube, the stretching is carried out immediately after the drilling, in the same inclined roll drilling machine, opposite to the drilling operation. A technique is disclosed that can be made into a desired shape while extending in the pass direction while minimizing the investment in the number of facilities and the ancillary facilities required for transportation between the facilities. Further, according to Patent Document 3, the outer surface temperature and the inner surface temperature of the blank are measured during stretching and rolling performed after piercing and rolling, and the longitudinal variation of the processing temperature increase value is obtained using a relational expression corresponding to the steel type and size. A method of controlling the rolling speed so as not to occur is disclosed.

JP 2005-336595 A JP-A-63-26209 Unexamined-Japanese-Patent No. 6-54402

  When the seamless steel pipe becomes long, the material temperature at the front end and the rear end greatly changes, and if the difference becomes extreme, it becomes impossible to manufacture, so the temperature of the raw pipe is in a predetermined temperature range over the entire length of the pipe It is important to control and achieve uniform temperature.

  However, in a material having a large amount of Cr as described in Patent Document 1, since a large amount of Cr, which is a ferrite stabilizing element, is contained, coarsening of ferrite grains is easily caused when rolling at a high temperature, and the toughness is lowered. It's easy to do. On the other hand, when the rolling temperature is lowered, the processability is reduced and cracking is likely to occur. For this reason, in the material which increased Cr as described in patent document 1, when lengthening, there exists a problem that the temperature which can be manufactured stably is restricted.

  Further, in the method described in Patent Document 2, since rolling is performed by reciprocating with one device, the cycle time is extended and it is not suitable for mass production. Further, although the method described in Patent Document 3 can reduce the temperature difference that may occur in the longitudinal direction of the hollow shell to some extent, it is not possible to expect the effect of canceling the temperature difference in the longitudinal direction that has already occurred in the piercing rolling in the previous step. Therefore, it can not be said for materials that require strict temperature uniformity.

  In view of the state of the prior art, in the present invention, a method of manufacturing a seamless steel pipe with less variation in mechanical characteristics in the thickness direction and the longitudinal direction of the steel pipe with respect to a thin and long seamless steel pipe and a seamless steel pipe manufacturing facility Intended to provide. In addition, thin thickness here shall show 20 mm or less, and a long shall mean the product length of 8 m or more.

  The present inventors first investigated the temperature difference in the longitudinal direction (front and rear end) of the steel pipe after piercing and rolling in order to achieve the above-described purpose. As a result, in the steel pipe immediately after rolling, it is found that the front end / end temperature difference of the inner surface of the steel pipe is larger than the front / rear end temperature difference of the outer surface of the steel pipe. I thought it was important.

  That is, when the outer surface of the steel pipe contacts the rolling roll, the roll temperature is difficult to rise because the roll diameter is sufficiently large relative to the steel pipe, and there is no large difference in the heat removal from the steel pipe at the front and rear ends. On the other hand, since the inner surface of the steel pipe has to use a tool having a small volume and a small heat capacity, and can not be contact cooled, the temperature gradually rises from the front end to the rear end at the time of rolling. Decreases. Therefore, the temperature of the rear end is significantly higher than that of the front end of the steel pipe. As a result, the uniformity of the material can not be achieved, and the mechanical characteristics differ in the longitudinal direction of the steel pipe, and a desired steel pipe can not be obtained. This tendency is further amplified in hot working performed continuously in piercing and rolling, so that even when the same forming strain is applied at the front and back ends, the temperature at the time of processing is significantly different, thereby obtaining the desired material. Not only that, it is found that it has resulted in narrowing the manufacturable range.

  Therefore, to conduct further researches and simply suppress the variation in mechanical characteristics in the longitudinal direction, the steel pipe tip end after the piercing and rolling is reversed, and then hot working is performed. It was considered effective to make the steel pipe temperature uniform in the longitudinal direction by offsetting the difference in the inner surface temperature in the steel pipe longitudinal direction that occurred in the hot working of the round. In addition, after piercing and rolling, the inner surface temperature of the front and rear end of the steel pipe before hot working is grasped, and the temperature of the heating furnace is controlled so that the inner surface temperature becomes a predetermined temperature range. It has been found that it is possible to achieve the homogenization of the above, reduce the variation of mechanical properties, and obtain the desired properties.

The present invention has been completed based on the above findings, and specifically is as follows.
[1] After heating the steel material, the heated steel material is subjected to piercing rolling to obtain a hollow material, and the hollow material is subjected to hot working to form a seamless steel pipe,
After piercing and rolling, the front end and the rear end of the hollow material are inverted and then subjected to hot working,
After piercing, the prior hot working to measure a hollow material of the tip and rear end of the inner surface temperature, controls the temperature of the heating furnace so that each inner surface temperature measured is in the range of 1100 ° C. or higher [delta] _A ° C. or less A manufacturing method of a seamless steel pipe characterized by doing.
However, δ _A is a temperature at which the δ ferrite phase becomes a single phase in the temperature raising process.
[2] The when measured inner surface temperature is outside the range of 1100 ° C. or higher [delta] _A ° C. or less, method of producing a seamless steel pipe having the constitution [1] to control the temperature of the heating furnace.
[3] The seam temperature described in [2] is characterized in that the temperature of the heating furnace is controlled when it is determined that the measured inner surface temperature is out of the range of 1180 ° C. or more (δ _A −70) ° C. Method of manufacturing steel pipe.
[4] When the measured inner surface temperature is lower than 1100 ° C., the temperature of the heating furnace is increased by the difference,
When the measured inner surface temperature is higher than δ _A ° C., the temperature of the heating furnace is controlled so as to lower the temperature of the heating furnace by the difference thereof [1] or [2]. Method of manufacturing seamless steel pipe.
[5] When the measured inner surface temperature is lower than 1180 ° C., the temperature of the heating furnace is increased by the difference,
The temperature of the heating furnace is controlled to lower the temperature of the heating furnace by the difference when the measured inner surface temperature is higher than (δ _A- 70) ° C. Method of manufacturing seamless steel pipe.
[6] The above-mentioned steel material is mass%,
C: 0.050% or less Si: 1.00% or less
Mn: 0.20 to 1.80% Cr: 15.5 to 18.0%
Ni: 1.5 to 5.0%, Mo: 1.0 to 3.5%,
V: 0.02 to 0.20%, N: 0.01 to 0.15%,
O: 0.006% or less is contained and it consists of remainder Fe and an unavoidable impurity, The manufacturing method of the seamless steel pipe in any one of [1]-[5] characterized by the above-mentioned.
[7] The above-mentioned steel material is, furthermore, in mass%, next group A to group D group A: Al: 0.002 to 0.050%
Group B: Cu: 3.5% or less, W: 3.5% or less, REM: 0.3% or less One or more selected from C group: Nb: 0.2% or less, Ti One or more selected from 0.3% or less, Zr: 0.2% or less D group: Ca: 0.01% or less, B: 0.01% or less The method for producing a seamless steel pipe according to [6], which comprises one or two or more groups selected from among one or two.
[8] A heating device for heating a steel material, a piercing-rolling device for forming a hollow material by subjecting the heated steel material to piercing-rolling, and the piercing-rolling device arranged continuously with the piercing-rolling device A seamless steel pipe manufacturing facility comprising a hot working apparatus for processing to form a seamless steel pipe, comprising:
The hot working apparatus
A heating furnace,
A reversing mechanism capable of reversing the front end and the rear end of the hollow material on the inlet side of the hot working apparatus;
The inner surface temperature measured by the temperature measuring means for measuring the inner surface temperature of the front end and the rear end of the hollow material and the temperature measuring means becomes 1100 ° C. or more and δ _A ° C. or less on the inlet side of the hot working apparatus A seamless steel pipe manufacturing facility characterized by controlling a temperature of a heating furnace.
However, δ _A is a temperature at which the δ ferrite phase becomes a single phase in the temperature raising process.

  According to the present invention, a seamless steel pipe having less variation in mechanical characteristics in the longitudinal direction of the steel pipe can be easily manufactured, and an industrially significant effect is achieved. Further, according to the present invention, even when the temperature difference in the longitudinal direction of the steel pipe becomes large due to an increase in work heat generation or lengthening, it becomes possible to hot work the entire length of the steel pipe in an appropriate temperature range. It is possible to easily provide a seamless steel pipe with less variation in mechanical properties in the direction.

FIG. 1 is a view showing an example of a seamless steel pipe manufacturing facility.

  Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments.

  An example of the seamless steel pipe manufacturing equipment of the present invention is shown in FIG. The seamless steel pipe manufacturing equipment of the present invention is formed by arranging the heating device 1, the piercing and rolling device 2 and the hot working device 3 in this order. In the present invention, the steel material is heated by the heating device 1, and then the steel material heated by the piercing and rolling device 2 is subjected to piercing and rolling to form a hollow material. Next, the hollow material is hot-worked by the hot-working apparatus 3 to manufacture a seamless steel pipe of a predetermined shape.

  The heating device 1 used in the present invention may be any heating furnace capable of heating steel materials such as slabs and billets to a predetermined temperature, and is not particularly limited. For example, common heating furnaces such as rotary hearth furnaces and walking beam furnaces can be applied. Moreover, it is good also as a heating furnace of an induction heating system.

  Further, the piercing and rolling device 2 used in the present invention may be a piercing and rolling mill capable of forming a hollow material by piercing and rolling a heated steel material, for example, using a barrel type roll, a cone type roll, etc. Any of commonly known piercing and rolling mills such as Mannesmann inclined boring and hot extrusion piercing can be applied.

  The hot working apparatus 3 used in the present invention may be any apparatus capable of processing a hollow material to form a seamless steel pipe of a predetermined shape, and according to the purpose, for example, an Elongator 31 is perforated. A plug mill 32 for extending the hollow tube thin and long, a reel (not shown) for smoothing the outer surface of the tube, a rolling mill arranged in the order of a sizing mill 33 for adjusting to a predetermined size, or a steel pipe of a predetermined size A commonly known rolling mill for hot working such as a mandrel mill (not shown) to be used, a rolling mill having a reducer to adjust the outer diameter and thickness by a slight pressure, and the like are arranged. Applicable Preferably, since the steel pipe has a mechanism for moving the steel pipe relative to the fixed inner surface tool as a process after drilling, the effect of canceling the temperature difference between the front and rear ends is obtained by using a hot working apparatus provided with an elongator. large. After these hot workings, they are preferably cooled to room temperature at a cooling rate higher than that of air cooling to make a seamless steel pipe of a predetermined size and shape.

  In the present invention, after piercing and rolling, the front end and the back end of the hollow material are inverted and then hot working is performed. By hot working after reversing the front and rear end of the hollow material, the difference in the inner surface temperature in the longitudinal direction of the steel pipe that occurs in the case of piercing rolling or when performing hot working multiple times after piercing and rolling is offset by The steel pipe temperature can be homogenized.

  The reversing mechanism that reverses the front end and the rear end of the hollow material is a mechanism that switches the hot working start direction of the hollow material, and may be installed on the entrance side of the hot working device 3. Further, as shown in FIG. 1, when a plurality of rolling mills such as the Elongator 31, the plug mill 32, and the sizing mill 33 are continuously arranged, the reversing mechanism may be installed on the entrance side of each rolling mill. As the reversing mechanism, the hollow material may be rotated about the longitudinal center of the hollow material, or the leading end and the rear end of the hollow material may be reversed during conveyance.

In the present invention, the inner surface temperature of the front end and the rear end of the hollow material is further measured after piercing rolling and before hot working, and the inner surface temperature measured is in the range of 1100 ° C. or more and δ _A ° C. or less. Control the temperature. By grasping the inner surface temperature of the front and rear ends of the hollow material before hot working and controlling the temperature of the heating furnace of the hot working apparatus so that the inner surface temperature becomes a predetermined temperature range, It is possible to achieve homogenization, reduce variations in mechanical properties in the longitudinal direction, and obtain desired properties.

Note that δ _A is a temperature at which δ ferrite single phase is formed in the temperature rising process, and may be calculated by thermal equilibrium calculation, or it is generated when the thermal expansion curve during heating is measured and δ ferrite single phase is obtained. The inflection point of the thermal expansion curve may be measured.

  The measuring means for measuring the inner surface temperature of the front end and the rear end of the hollow material may be measured, for example, by a thermometer. The thermometer may be a thermometer that measures on-line, and may be either a contact type or non-contact type. In consideration of the time when both the front end and the rear end of the hollow material are hot-worked, the timing of measuring the temperature of the front end and the rear end of the hollow material leads the inner surface temperature of the front end and the rear end under the same conditions. Is preferred. In addition, the inner surface temperature of the hollow material may be measured after piercing-rolling and before being subjected to hot working. That is, the installation position of the thermometer may be on the entry side of the hot working apparatus 3. Further, as shown in FIG. 1, when the hot working apparatus 3 has a plurality of rolling mills such as the Elongator 31, plug mill 32 and sizing mill 33 continuously arranged, the thermometers are provided for each entry side of each rolling mill. It should be installed. However, if there is a restriction on the installation position, heat transfer calculation may be used to derive the inner surface temperatures of the front end and the rear end of the hollow material. In the present invention, since it is important to control the inner surface temperature of the front end and the rear end of the hollow material, at least one thermometer needs to be installed on the entrance side of the hot working apparatus after piercing and rolling. . On the other hand, it is preferable to provide thermometers at a plurality of locations from the viewpoint of grasping the relationship between the processing temperature and strain in hot working and predicting the final material.

  Moreover, about the position which measures the inner surface temperature of a hollow raw material, it is preferable to measure in the position within the range of 20-200 mm to a longitudinal direction from a front end or a back end. This is because at a position within 20 mm in the longitudinal direction from the front end or rear end of the hollow material, the amount of heat release is large and the shape is easily unstable, and temperature variations may occur.

  In addition, about the arrangement | positioning relationship between an inversion mechanism and a thermometer, since it is all necessary before hot processing is given, after inverting the front-end and back end of a hollow material by an inversion mechanism, a hollow material is measured by a thermometer. The inner surface temperature of the front end and the rear end of the hollow material may be measured, or after the inner surface temperature of the front end and the rear end of the hollow material is measured by a thermometer, the front end and the rear end of the hollow material may be reversed by an inversion mechanism.

In the present invention, front and rear ends the temperature of the inner surface of the hollow material to control the temperature of the heating furnace of the hot working apparatus so that the 1100 ° C. or higher [delta] _A ° C. or less. Since the influence of the relationship between processing temperature and strain on hot working on the material is different depending on the material component, the target of the temperature difference to be reduced is different depending on the material. Mainly, grain growth is likely to occur at high temperatures for materials containing ferrite phases at high temperatures, and temperature control during hot working becomes important. In piercing and rolling, the inner surface tool used has a small heat capacity because of its small volume. Furthermore, since contact cooling can not be performed, the temperature rises gradually from the front end to the rear end at the time of piercing and rolling. Along with this, the heat removal amount from the inner surface of the hollow material decreases, and the temperature of the rear end becomes significantly higher than that of the front end of the hollow material. Furthermore, also in the subsequent hot working, the temperature difference on the rear end side which contacts with the tip end which touches the tool first and the tool temperature rises is further enlarged. The expansion of the temperature difference is remarkable particularly when thinning and expansion rolling are performed after piercing and rolling.

As described above, since the heat removal amount to the tool is smaller at the inner surface than at the outer surface of the hollow material, the temperature tends to rise. Therefore, the temperature is highest at the inner surface side of the rear end of the hollow material. As the temperature of the tube increases, the toughness decreases significantly with respect to the tip. As a result of investigations by the present inventors, when the material is exposed to a temperature exceeding δ _A (the temperature at which the δ ferrite phase becomes a single phase in the temperature rising process), the ferrite phase is rapidly grown and coarsened, and the toughness is significantly lowered. I understood it. On the other hand, when the material is subjected to the subsequent hot rolling at less than 1100 ° C., the fraction of the second phase having higher strength than the ferrite becomes too large, and the rolling load increases, causing the rolling defects and the like. I understand.

From the above, in the present invention, the inner surface temperatures of the front end and the rear end of the hollow material are measured before hot working, and the inner surface temperature measured is in the range of 1100 ° C. or more and δ _A ° C. or less. Control the temperature. As a result, it is possible to offset the difference in inner surface temperature between the front end and the rear end in the longitudinal direction of the steel pipe, achieve homogenization of the material in the longitudinal direction, and reduce variations in mechanical characteristics in the longitudinal direction.

  The heating furnace is a heating furnace used to heat the hollow material in hot working, and may be a commonly used heating furnace that can heat the hollow material to a predetermined temperature, and it is not necessary to limit it in particular. For example, a rotary hearth furnace can be exemplified. In addition, it is good also as a heating furnace of an induction heating system.

Control of the temperature of the furnace is measured inner surface temperature may be performed at the time out of the range of 1100 ° C. or higher [delta] _A ° C. or less. By controlling the temperature of the heating furnace immediately after the measurement, it is possible to offset the difference in the inner surface temperature of the front end and the rear end in the longitudinal direction of the steel pipe during the subsequent hot working and to achieve homogenization of the material in the longitudinal direction.

With regard to temperature control of the heating furnace, when the measured inner surface temperature is lower than 1100 ° C., the temperature of the heating furnace is increased by the difference, and when the measured inner surface temperature is higher than δ _A ° C., only the difference The temperature of the heating furnace may be lowered. By controlling the temperature of the heating furnace in this manner, the inner surface temperature of the steel pipe is maintained in an appropriate range, the material homogenization in the longitudinal direction is achieved, and the variation in mechanical characteristics in the longitudinal direction is further reduced. Can be suppressed.

Further, with regard to temperature control of the heating furnace, it is preferable to control the temperature of the heating furnace such that the measured inner surface temperature is in the range of 1180 ° C. or more (δ _A- 70) ° C. It is preferable to control the temperature of the heating furnace when it is determined that the temperature is outside the range of 1180 ° C. or more and (δ _A −70) ° C. or less. By setting the measured inner surface temperature in the range of 1180 ° C. or higher (δ _A −70) ° C., the temperature of the heating furnace of the hot working apparatus can be more appropriately controlled, so the inner surface temperature of the steel pipe is 1100 ° C. it is possible to control the range of [delta] _a ° C. or higher. As a result, during the subsequent hot working, it is possible to offset the difference in the inner surface temperature of the front end and the rear end in the longitudinal direction of the steel pipe, and to homogenize the material in the longitudinal direction. When the temperature of the heating furnace is controlled so that the measured inner surface temperature is in the range of 1180 ° C. or higher (δ _A -70) ° C., when the measured inner surface temperature is lower than 1180 ° C., only the difference If the temperature of the heating furnace is raised and the measured inner surface temperature is higher than (δ _A −70) ° C., the temperature of the heating furnace may be lowered by the difference. By controlling the temperature of the heating furnace in this manner, the inner surface temperature of the steel pipe is maintained in an appropriate range, homogenization of the material is achieved in the longitudinal direction, and variations in mechanical properties in the longitudinal direction are reduced. Occurrence can be suppressed.

  Next, the reasons for limitation of the composition of the steel material of the present invention will be described. The steel material which exhibits effects by the application of the present invention is preferably a steel material having a composition in which the δ ferrite phase is single phase at a relatively low temperature and the δ ferrite phase remains at the time of the product at normal temperature. C: 0.050% or less, Si: 1.00% or less, Mn: 0.20 to 1.80%, Cr: 15.5 to 18.0%, Ni: 1.5 to 5% by mass. 0%, Mo: 1.0 to 3.5%, V: 0.02 to 0.20%, N: 0.01 to 0.15%, O: 0.006% or less, balance Fe and unavoidable It is more preferable that it is the component composition which consists of a chemical impurity.

  The reasons for limitation of the preferred composition of the steel material will be described. Incidentally, mass% is simply expressed as% unless otherwise specified.

C: 0.050% or less C is an important element that affects the formation amount of the martensite phase, and it is desirable to contain 0.005% or more. On the other hand, if the content is more than 0.050%, the sensitization at tempering due to the Ni content is increased. From the viewpoint of corrosion resistance, it is desirable that C be small. From such a thing, C was limited to 0.050% or less. In addition, Preferably it is 0.030 to 0.050%.

Si: 1.00% or less Si is an element that acts as a deoxidizer, and it is desirable to contain 0.05% or more. A content of more than 1.00% reduces the corrosion resistance and further reduces the hot workability. For this reason, Si was limited to 1.00% or less. In addition, Preferably it is 0.10 to 0.30%.

Mn: 0.20 to 1.80%
Mn is an element having the effect of increasing the austenite phase fraction, and in order to obtain such an effect, the content needs to be 0.20% or more. On the other hand, if the content exceeds 1.80%, the toughness is adversely affected. For this reason, Mn was limited to 0.20 to 1.80%. In addition, Preferably it is 0.20 to 1.00%.

Cr: 15.5 to 18.0%
Cr is a main element which forms a protective film and improves the corrosion resistance, and at the same time, is an element having an effect of increasing the phase fraction of the ferrite phase. In order to obtain such an effect, the content needs to be 15.5% or more. On the other hand, if the content is more than 18.0%, the strength is reduced. For this reason, Cr was limited to 15.5 to 18.0%. In addition, Preferably it is 16.0 to 18.0%.

Ni: 1.5 to 5.0%
Ni is an element having the function of repairing the protective film and enhancing the corrosion resistance, and at the same time, an element having the function of increasing the phase fraction of the austenite phase. It is also an element that improves toughness. Such effects are observed at a content of 1.5% or more. On the other hand, if the content exceeds 5.0%, the material cost rises and the strength is lowered. For this reason, Ni was limited to 1.5 to 5.0%. In addition, Preferably it is 2.5 to 4.5%.

Mo: 1.0 to 3.5%
Mo is an element that increases the resistance to pitting corrosion by Cl ⁻ . In order to acquire such an effect, it is desirable to contain 1.0% or more. On the other hand, when the content is more than 3.5%, the strength is lowered and the material cost is increased. For this reason, Mo was limited to 1.0 to 3.5%. In addition, Preferably it is 2.0 to 3.5%.

V: 0.02 to 0.20%
V is an element that improves the corrosion resistance as well as increasing the strength. In order to acquire such an effect, it is necessary to contain 0.02% or more. On the other hand, if the content exceeds 0.20%, the toughness is lowered. For this reason, V was limited to 0.02 to 0.20%. In addition, Preferably it is 0.02 to 0.08%.

N: 0.01 to 0.15%
N is an element that significantly improves the pitting resistance, and in order to obtain such an effect, it is necessary to contain 0.01% or more. On the other hand, if the content is more than 0.15%, various nitrides are formed to lower the toughness. For this reason, N was limited to 0.01 to 0.15%. In addition, Preferably it is 0.02 to 0.08%.

O: 0.006% or less O is present as an oxide in steel and adversely affects various properties. For this reason, it is desirable to reduce as much as possible. In particular, when O is contained in a large amount exceeding 0.006%, the hot workability, the toughness and the corrosion resistance remarkably decrease. For this reason, O was limited to 0.006% or less.

Although the above-described components are basic components, in addition to the basic components, the following groups A to D are also selected elements: Al: 0.002 to 0.050%
Group B: Cu: 3.5% or less, W: 3.5% or less, REM: 0.3% or less One or more selected from C group: Nb: 0.2% or less, Ti One or more selected from 0.3% or less, Zr: 0.2% or less D group: Ca: 0.01% or less, B: 0.01% or less It can contain one group or two or more groups selected from one or two.

Group A: Al: 0.002 to 0.050%
Group A: Al is an element acting as a deoxidizing agent, and in order to obtain such an effect, it is preferable to contain 0.002% or more, but if it is contained more than 0.050%, it is to toughness Adversely affect. For this reason, when it contains, it is preferable to limit to 0.002 to 0.050%. In the case where Al is not added, about 0.002% or less is acceptable as an unavoidable impurity.

Group B: Cu: 3.5% or less, W: 3.5% or less, REM: 0.3% or less One or more selected from B group: Cu, W, REM, protective film Strengthens, suppresses the entry of hydrogen into the steel, and increases the resistance to sulfide stress corrosion cracking. Such effects are significant when Cu: 0.5% or more, W: 0.5% or more, and REM: 0.001% or more. However, if the content of Cu: 3.5%, W: 3.5%, REM: 0.3% or more is contained, the toughness is lowered. Therefore, it is preferable to limit Cu and W to 3.5% or less and REM to 0.3% or less. More preferably, Cu: 0.8 to 1.2%, W: 0.8 to 1.2%, and REM: 0.001 to 0.010.

C group: Nb: 0.2% or less, Ti: 0.3% or less, Zr: 0.2% or less selected from one or more selected from C group: Nb, Ti, Zr all It is an element that improves strength and hot workability, and can be selected and contained as necessary. Such effects are observed when Nb: 0.03% or more, Ti: 0.03% or more, and Zr: 0.03% or more. On the other hand, the contents exceeding Nb: 0.2%, Ti: 0.3%, and Zr: 0.2%, respectively, lower the toughness. Therefore, when it is contained, it is preferable to limit each to Nb: 0.2% or less, Ti: 0.3% or less, and Zr: 0.2% or less.

Group D: Ca: 0.01% or less, B: 0.01% or less One or two selected from Group D: Ca, B improve the hot workability during multiphase rolling Has an effect of suppressing product wrinkles, and may contain one or two if necessary. Such effects are significant when Ca: 0.0005% or more and B: 0.0005% or more. However, when Ca: 0.01% and B: 0.01% or more, corrosion resistance is descend. For this reason, when it contains, it is preferable to limit to Ca: 0.01% or less and B: 0.01% or less.

  The balance other than the above components is Fe and unavoidable impurities. As unavoidable impurities, P: 0.03% or less and S: 0.005% or less are acceptable.

  The method for producing the steel material having the composition described above is not particularly limited. A molten steel of the above composition is melted using a conventional melting furnace such as a converter or an electric furnace, and a slab (round slab) is formed by ordinary casting method such as continuous casting. It is preferable to use a material. In addition, it is good also as a steel material as a steel piece of a predetermined dimension by hot-rolling a cast piece. Moreover, it is made into a billet by the ingot-slab rolling method, and there is no problem as a steel material at all.

  A molten steel having the composition shown in Table 1 was melted and subjected to a degassing treatment, and then a billet of 230φ × 6000 length was produced by the ingot method and air-cooled to room temperature. Next, the billet was heated in a heating furnace and then pierced and rolled in a piercer.

In addition, as shown in Table 2, in the invention example, after piercing and rolling, the front end and the rear end in the longitudinal direction of the steel pipe were reversed, and then transported to the hot working process. In addition, as a hot working process after drilling, thickness reduction and tube expansion rolling with an Elongator were performed, followed by drawing rolling with a plug mill, polishing with a reel, and fixed form rolling with a sizing mill. Alternatively, after drawing rolling with a mandrel mill, fixed rolling with a reducer was performed. After the fixed form rolling, it was allowed to cool, and a seamless steel pipe having an outer diameter of 248.8 mm, a thickness of 13.91 mm and a length of 15 m was obtained. In addition, about the inner surface temperature of the front end and back end of the steel pipe (hollow material) after piercing-rolling, it measured with the radiation thermometer. After drilling and rolling with a radiation thermometer, the inner surface temperatures of the front and rear ends of the steel pipe are measured, and for the invention example, the temperature of the heating furnace is appropriately controlled to reach the inner surface temperature shown in Table 2, and then hot working is performed. gave. In addition, for the temperature (δ _A ) at which the δ ferrite single phase is obtained, the thermal expansion curve in the heating process was measured in advance, and the transformation to δ ferrite was completed, and the point at which the curvature of the expansion curve changed was used.

  Thereafter, quenching was performed by cooling the seamless steel pipe heated to a predetermined quenching temperature to 100 ° C. or less at a cooling rate higher than air cooling. The quenching and heating conditions were 20 minutes at 960 ° C. for all steel pipes. After quenching, the seamless steel pipe was subjected to tempering to cool to room temperature at a cooling rate higher than air cooling after heating. The tempering heating conditions were 40 minutes at 600 ° C. for all steel pipes.

  In addition, test pieces were collected from the leading end position and the trailing end position of the obtained seamless steel pipe, and the tensile properties and toughness were examined. The survey method is as follows.

(A) Tensile properties From the thickness center of the hardened and tempered seamless steel pipe, an API arc-shaped tensile test specimen is taken so that the tensile direction is in the axial direction according to the API-5CT standard, and further API A tensile test was conducted in accordance with the standard, and as tensile properties, yield strength YS (MPa) and tensile strength TS (MPa) were measured.

(B) Toughness From V-notch test piece (10 mm thickness) is taken from the thickness center of the hardened and tempered seamless steel pipe in accordance with the ISO-11960 standard so that the circumferential direction becomes the test piece length. Further, a Charpy impact test was performed at a test temperature of -10 ° C to measure the absorbed energy vE _-10 (J). Three test pieces were used, and their arithmetic mean value was used as the absorbed energy of the steel pipe.

(C) Rolling Stock The inner surface and the outer surface of the obtained seamless steel pipe were visually observed to evaluate hot workability. Those with cracks of 5 mm or more in length of the seamless steel pipe are regarded as "presence: x", and those other than that are shown as "no: ○".

  The obtained results are shown in Table 2.

As is clear from Table 2, each of the inventive examples has high strength of 758 MPa (= 110 ksi) or more for YS and high toughness of 40 J or more for vE- ₁₀ , and mechanical at the front and rear ends There is no variation in the characteristics. On the other hand, in the comparative example, since inversion of the front and rear ends was not performed or the furnace temperature was not controlled, rolling defects were generated or toughness was lowered at the rear end, and the machine in the longitudinal direction Characteristics have been different. It is considered that this is because the temperature of the steel pipe rises on the inner surface at the rear end during tube expansion rolling or fixed form rolling, and the ferrite grains become coarse.

Further, if the inner surface temperature to control the temperature of the furnace to be in the range of 1100 ° C. or higher [delta] _A ° C. or less, the steel pipe outside the range of 1100 ° C. or higher [delta] _A ° C. or less, four (manufacturing number: 110 present )Met. On the other hand, when the heating furnace is controlled so that the inner surface temperature is in the range of 1180 ° C. or more (δ _A- 70) ° C., there are 0 steel pipes out of the range of 1100 ° C. or more and δ _A ° C. The

Reference Signs List 1 heating device 2 piercing and rolling device 3 hot working device 31 Elongator 32 plug mill 33 sizing mill

Claims (8)

After heating the steel material, the heated steel material is subjected to piercing rolling to obtain a hollow material, and the hollow material is subjected to hot working to form a seamless steel pipe,
After piercing and rolling, the front end and the rear end of the hollow material are inverted and then subjected to hot working,
After piercing, the prior hot working to measure a hollow material of the tip and rear end of the inner surface temperature, controls the temperature of the heating furnace so that each inner surface temperature measured is in the range of 1100 ° C. or higher [delta] _A ° C. or less A manufacturing method of a seamless steel pipe characterized by doing.
However, δ _A is a temperature at which the δ ferrite phase becomes a single phase in the temperature raising process. Wherein when the measured inner surface temperature is outside the range of 1100 ° C. or higher [delta] _A ° C. or less, method of producing a seamless steel pipe according to claim 1, characterized in that to control the temperature of the heating furnace. The temperature of the heating furnace is controlled when it is determined that the measured inner surface temperature is out of the range of 1180 ° C. or more (δ _A -70) ° C. or less, and the seamless steel pipe is manufactured according to claim 2. Method. When the measured inner surface temperature is lower than 1100 ° C., the temperature of the heating furnace is increased by the difference,
The seam temperature according to claim 1 or 2, wherein the temperature of the heating furnace is controlled to lower the temperature of the heating furnace by the difference when the measured inner surface temperature is higher than δ _A ° C. Method of manufacturing steel pipe. When the measured inner surface temperature is lower than 1180 ° C., the temperature of the heating furnace is increased by the difference,
The temperature of the heating furnace is controlled to lower the temperature of the heating furnace by the difference when the measured inner surface temperature is higher than (δ _A- 70) ° C. Method of manufacturing seamless steel pipe. The steel material is in mass%,
C: 0.050% or less Si: 1.00% or less
Mn: 0.20 to 1.80% Cr: 15.5 to 18.0%
Ni: 1.5 to 5.0%, Mo: 1.0 to 3.5%,
V: 0.02 to 0.20%, N: 0.01 to 0.15%,
O: 0.006% or less is contained and it consists of remainder Fe and an unavoidable impurity, The manufacturing method of the seamless steel pipe in any one of the Claims 1-5 characterized by the above-mentioned. The above-mentioned steel material is, furthermore, in mass%, next group A to group D group A: Al: 0.002 to 0.050%
Group B: Cu: 3.5% or less, W: 3.5% or less, REM: 0.3% or less One or more selected from C group: Nb: 0.2% or less, Ti One or more selected from 0.3% or less, Zr: 0.2% or less D group: Ca: 0.01% or less, B: 0.01% or less The method for producing a seamless steel pipe according to claim 6, characterized in that it contains one group or two or more groups selected from among one type or two types. A heating device for heating a steel material, a piercing-rolling device for forming a hollow material by subjecting the heated steel material to piercing-rolling, and the piercing-rolling device are disposed continuously to perform hot working on the hollow material A seamless steel pipe manufacturing facility equipped with a hot working apparatus for forming a seamless steel pipe,
The hot working apparatus
A heating furnace,
A reversing mechanism capable of reversing the front end and the rear end of the hollow material on the inlet side of the hot working apparatus;
The inner surface temperature measured by the temperature measuring means for measuring the inner surface temperature of the front end and the rear end of the hollow material and the temperature measuring means becomes 1100 ° C. or more and δ _A ° C. or less on the inlet side of the hot working apparatus A seamless steel pipe manufacturing facility characterized by controlling a temperature of a heating furnace.
However, δ _A is a temperature at which the δ ferrite phase becomes a single phase in the temperature raising process.

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