JP2005068490A - Solid round billet and its manufacturing method, method for manufacturing martensite stainless seamless steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid round billet having favorable biting property and anti-slipping property for a tilted roll type piercer, to provide its manufacturing method, and to provide an efficient method for manufacturing a martensite stainless seamless steel pipe by which the above billet as a raw material can be pierced with a low draft rate of the plug top, the pipe has no inner fracture flaw and the plug has a long life. <P>SOLUTION: The solid round billet comprises 0.01 to 0.08% C, 0.05 to 1.00% Si, 0.05 to 1.50% Mn, 9.0 to 15.0% Cr, 0.05 to 5.00% Mo, 0.0005 to 0.05% Al, ≤0.1% N, 0.3 to 4.0% Ni, 0 to 4.0% Cu and the balance Fe and impurities and has a two-layer structure of oxide scales produced by heating and having 1×10<SP>4</SP>to 2×10<SP>5</SP>particles/mm<SP>2</SP>dispersion density of metal particles of Ni or Ni and a Ni-Cu compound in the inner layer scales having ≥0.1 μm particle size. The billet is obtained in an oxidative atmosphere with 5 to 30 vol% steam concentration in a temperature range of 1,100 to 1,300°C for 1.5 to 6.0 hours, and after the outer layer scale is removed, the billet is subjected to pierce rolling. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a martensitic stainless steel seamless steel pipe mainly used for oil and natural gas production and transportation, and includes a hot rolling pipe including a piercing and rolling process by a piercing and rolling machine represented by Mannesmann Piercer. Solid round billets suitable for manufacturing by the method, particularly high piercing efficiency is obtained during piercing and rolling with an inclined roll type piercing and rolling machine, the piercing and rolling machine has a long plug life, and inner and outer surface defects, particularly inner and outer surface defects. The present invention relates to a solid round billet from which a hollow shell having a small amount of particles can be easily obtained, a method for producing the same, and a method for producing a highly efficient martensitic stainless steel seamless steel tube.

  Due to the recent deterioration of the oil well environment, the demand for martensitic stainless steel seamless steel well pipes represented by 13% Cr steel suitable for oil wells and gas well environments containing carbon dioxide and hydrogen sulfide is increasing.

  These seamless steel pipes are usually manufactured from a solid round billet using a piercing and rolling machine represented by Mannesmann Piercer, and the hollow elementary pipe is drawn by a plug mill or a mandrel mill. It is manufactured by forming into a blank for finishing with a rolling mill and then finishing into a pipe product of a predetermined size with a constant diameter rolling mill represented by a sizer or stretch reducer.

  However, in martensitic stainless steel represented by 13% Cr steel, the hardness of the oxide scale formed on the surface by heating is high, and a solid round billet (hereinafter also referred to as a material to be rolled) during piercing rolling by a piercing rolling mill. ) And the roll of the piercing mill. For this reason, the forward speed of the material to be rolled is reduced, and a hole formed by rotary forging is formed in the center of the solid round billet before being drilled at the tip of the plug, and this remains as an inner surface flaw in the hollow shell after piercing and rolling. . In addition, the lowering of the forward speed of the material to be rolled increases the drilling time, the plug tip becomes hot and melts, and not only the plug life is shortened, but also the pipe forming efficiency is deteriorated.

  The following method has been proposed as a method for preventing slippage between the roll of the piercing mill and the material to be rolled.

  a) A method in which a knurling process or a knurling process is performed at the time of refurbishing an inclined roll to make the roll surface a rough surface having a depression (Patent Document 1).

  b) A method in which an inclined roll during rolling is processed by the same processing method described in Patent Document 1 and the surface thereof is made rough with a depression (Patent Document 2).

  c) A method of setting the opening of the inclined roll to a specific range with respect to the diameter of the solid round billet (Patent Document 3).

  d) A method of changing the inclination angle, the crossing angle, the plug lead amount, and the like in addition to the opening degree of the inclination roll (Patent Document 4).

  e) Water-dispersed lubricants of high hardness particles such as metal particles, metal carbides, metal oxides, metal nitrides, metal carbonitrides and silicon compounds and polymer polymers during rolling A method of performing piercing and rolling while spraying and feeding the contact portion between the material to be rolled and the inclined roll (Patent Document 5).

  However, each of the above methods has the following problems.

  In the methods a) and b), the recess contributing to the advancement speed of the material to be rolled is too deep, and the trace remains on the outer surface of the hollow shell, which may become an outer surface flaw. In addition, the processing device b) is too large to be installed in the piercing and rolling mill, which increases the size of the piercing and rolling mill and increases costs, and when applied to an existing piercing and rolling mill, the cost of remodeling increases. There is also.

  In the methods c) and d), since the rolling conditions are changed, it is difficult to obtain a hollow shell having a predetermined size.

  The method e) is expensive because it requires a special lubricant and a special apparatus for stably supplying it.

  On the other hand, with so-called stainless steel seamless steel pipe inclined roll type piercing and rolling mills including martensitic stainless steel seamless steel pipes suitable for use as oil well pipes for carbon oil and hydrogen sulfide and gas well environments As a manufacturing method, a method has been proposed in which the oxidized scale thickness on the surface of the material to be rolled is 10 to 100 μm, and rolling is performed by each rolling mill including an inclined roll type piercing rolling mill (Patent Document 6).

  In addition, martensitic stainless steels suitable for use as oil wells containing carbon dioxide or hydrogen sulfide or as wells for gas well environments have also been proposed (Patent Documents 7 to 9).

  However, the method disclosed in Patent Document 6 is only an invention in which outer surface streaks caused by entanglement of oxide scales peculiar to so-called stainless steel including martensitic stainless steel is eliminated, and an inclined roll type piercing rolling machine It is not intended at all to improve the forward speed of the material to be rolled.

  In addition, the martensitic stainless steels disclosed in Patent Documents 7 to 9 are mainly intended to improve corrosion resistance such as sulfide stress corrosion cracking resistance and carbon dioxide gas corrosion resistance. In the same way, it is not intended to improve the forward speed of the material to be rolled when the solid round billet made of steel is pierced and rolled by an inclined roll type piercing and rolling mill, and there is no means for its means. Neither listed nor suggested.

JP-A-2-251305 JP-A-3-77708 JP-A 61-180603 JP-A-63-49308 Japanese Patent Laid-Open No. 5-57307 JP-A-5-269507 JP-A-2-247360 Japanese Patent Laid-Open No. 3-120337 JP-A-9-111345

  In the present invention, when a solid round billet made of martensitic stainless steel is pierced and rolled by an inclined roll type piercing and rolling machine, a special lubricant and the like can be used without using a special lubricant. It is possible to reduce the slip and improve the forward speed of the material to be rolled, in other words, the drilling efficiency, and there is no hole in the center of the solid round billet before drilling at the plug tip. A solid round billet with a so-called drilling efficiency, which can obtain a hollow shell with less outer surface defects as well as inner surface defects due to it, and can prevent melting of the plug tip and improve plug life. An object of the present invention is to provide a method for producing the same and a method for producing a highly efficient martensitic stainless steel seamless steel pipe.

  The gist of the present invention is the solid round billet of the following (1) and (2), the manufacturing method of the following (3) and (4), and the manufacturing method of the martensitic stainless steel seamless steel pipe of the following (5) It is in.

(1) By mass%, C: 0.01 to 0.08%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.50%, Cr: 9.0 to 15.0% Mo: 0.05-5.00%, Al: 0.0005-0.05%, N: 0.1% or less, Ni: 0.3-4.0%, balance: Fe and impurities This is a solid round billet of site-based stainless steel, and the density of Ni metal particles with a particle size of 0.1 μm or more contained in the inner scale layer among the two-layered oxide scale consisting of the inner layer and outer layer on the surface Is a solid round billet of 1 × 10 ^{4 to} 2 × 10 ⁵ pieces / mm ² .

(2) By mass%, C: 0.01 to 0.08%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.50%, Cr: 9.0 to 15.0% Mo: 0.05-5.00%, Al: 0.0005-0.05%, N: 0.1% or less, Ni: 0.3-4.0%, Cu: 4.0% or less, Remaining part: Martensitic stainless steel solid round billet composed of Fe and impurities, particle size of 0.1 μm included in inner scale layer among two-layered oxide scale composed of inner layer and outer layer on the surface A solid round billet in which the density of the metal particles of Ni or Ni—Cu compound is 1 × 10 ⁴ to 2 × 10 ⁵ particles / mm ² .

(3) A solid round billet having the chemical composition described in (1) or (2) above is used at 1100 ° C. or higher and 1300 ° C. or lower in an oxidizing atmosphere having a water vapor concentration of 5% by volume to 30% by volume. A method for producing a solid round billet that is heated for 1.5 hours or more and 6.0 hours or less.

(4) The manufacturing method of the solid round billet as described in said (3) which removes an outer layer scale after a heating.

(5) A method for producing a martensitic stainless steel seamless steel pipe in which the solid round billet described in (1) or (2) above is pierced and rolled into a hollow shell using an inclined roll type piercing and rolling machine.

  In order to achieve the above-mentioned problems, the present inventor has set a biting characteristic for a piercing and rolling machine represented by Mannesmann Piercer for a solid round billet made of many stainless steels including martensitic stainless steel. The present invention was completed by investigating the anti-slip characteristics and finding the following.

  Solid round billet made of martensitic stainless steel with basic components C, Si, Mn, Cr, Mo, Al and N content within a specific range and containing Ni or Ni and Cu as essential components, The outer scale layer is removed from the oxide scale consisting of a two-layer structure consisting of a dense inner layer scale that is unique to stainless steel produced during heating and good adhesion to the base material, and a porous outer layer scale that is relatively easy to peel off. It was confirmed that the biting characteristics and the slip resistance characteristics tend to be better than those not removing the outer scale layer and other solid round billets made of stainless steel.

  Therefore, the content of the basic component is the value shown in Table 1, and the Ni content is 0% (no addition), 0.7%, 1.2%, 1.7%, 3.0% and 6. Of 30 types of combinations of 6 types of 0% and 5 types of Cu content of 0% (no addition), 1.0%, 2.0%, 4.0% and 5.0%, Cu content A solid round billet made of 27 types of martensitic stainless steel, excluding 3 types of combinations of 5.0%, Ni content 0% (no addition), 0.7% and 6.0% These solid round billets, which were manufactured and removed the outer scale layer after heating, were tested under the conditions shown in Table 2 to check the biting efficiency and the drilling efficiency (%) in an inclined roll type piercing mill. .

The above piercing efficiency (%) is defined by the following equation (1), where V _{MX is} the forward speed of the material to be rolled and V _RX is the forward direction component of the material to be rolled of the peripheral speed of the inclined roll. The larger the value, the smaller the slip between the inclined roll and the material to be rolled.

Drilling efficiency (%) = (V _MX / V _RX ) x 100 (1)
The plug tip draft rate (%) shown in Table 2 is the following (2), where A is the cross-sectional area of the solid round billet and B is the cross-sectional area of the solid round billet at the plug tip position. The value defined by the equation, the smaller the value, the more the internal fracture due to rotary forging at the shaft center of the solid round billet is suppressed, and the occurrence of inner surface flaws (inner covering) is suppressed.

Plug tip draft ratio (%) = {1- (B / A)} × 100 (2)
The results of the experiment are as shown in Table 3 and FIGS. 1 and 2, and are limited to steels with a Ni content of 0.3% or more and a Cu content of 0% (no addition) or 4% or less. It was confirmed that the piercing efficiency required for piercing and rolling, that is, the piercing efficiency was 60% or more.

  Therefore, in order to know the cause, a steel having Ni content of 0.3% or more and Cu content of 0% (no addition) or 4% or less (hereinafter referred to as “steel 1”), Ni and Cu Steel having a content of 0% (no addition) (hereinafter referred to as “steel 2”) and steel having a Ni content of 0.7% or more and a Cu content of 5% (hereinafter referred to as “steel 3”) )) After heating, and particularly the inner layer scale was examined in detail.

  As a result, in the inner scale of “Steel 1”, Ni or Ni and a Ni—Cu compound having a particle size (the diameter in the case of a circle, the average diameter of a major axis and a minor axis in the case of a non-circular shape) of 0.1 μm or more. In contrast, a large amount of the metal particles were dispersed, whereas the inner scale layers of “Steel 2” and “Steel 3” had no or very little metal particles. As a result, it has been found that the metal particles increase the gripping force against the inclined roll to prevent slippage between the inclined roll and the material to be rolled, and as a result, the biting property and the drilling efficiency are improved.

  FIG. 3 shows the inner scale of the two-layered oxide scale after heating of “Steel 1” with Ni and Cu contents of 1.0% and “Steel 2” with 0% (no addition). In the microphotograph (1000 times) showing an example, FIG. 4A shows “steel 1” and FIG. 2B shows “steel 2”.

  FIG. 4 shows the state of the oxidized scale immediately after the heating of the above “steel 1” and “steel 2”, the state of the inner layer scale when the outer layer scale is removed and rolling is disclosed, and the state of the inner layer scale during piercing and rolling. FIG. 4A is “steel 1” and FIG. 2B is “steel 2”.

  However, even with the “steel 1”, the drilling efficiency may not be 60% or more, and it has also been found that the metal particles in the inner scale layer in this case are few.

Therefore, as a result of further performing the above-described experiment with various heating conditions, the result shown in FIG. 5 was obtained. That is, the resulting 60% or more perforations efficiency when the metal particles of a particle size of 1μm or more Ni or Ni and Ni-Cu compound in the inner layer scale is present 1 mm ² per 1 × 10 ⁴ or more This is the fact that seizure occurs when the number exceeds 2 × 10 ⁵ .

Moreover, the total thickness of the oxide scale having an inner scale in which 1 × 10 ⁴ to 2 × 10 ⁵ metal particles are present per 1 mm ² is about 100 to 600 μm, and such an oxide scale has a chemical composition described later. It is also found that a solid round billet having a water content can be obtained by heating and holding in a temperature range of 1100 to 1300 ° C. for 1.5 to 6.0 hours in an oxidizing atmosphere having a water vapor concentration of 5 to 30% by volume. It was.

  The solid round billet of the present invention is excellent in biting property and slip resistance with respect to a piercing mill, particularly an inclined roll type piercing mill. Moreover, the manufacturing method can be manufactured at low cost because it can be obtained simply by heating a solid round billet made of martensitic stainless steel having a predetermined chemical composition under predetermined conditions and then subjecting the outer layer scale to high-pressure water descaling. Furthermore, in the manufacturing method of the present invention using the solid round billet of the present invention as a raw material, since it is possible to perform piercing and rolling with a reduced plug tip draft ratio, it is possible to manufacture a hollow shell tube with a small inner cover with high efficiency. In addition, the plug life is improved.

  Hereinafter, the solid round billet of the present invention, the manufacturing method thereof, and the manufacturing method of the martensitic stainless steel seamless steel pipe will be described in detail.

1. About chemical composition C: 0.01 to 0.08%
C is an austenite-forming element at high temperature and is an important component that determines the strength of martensitic stainless steel. If the content is less than 0.01%, the amount of retained austenite produced is insufficient, and sufficient toughness is obtained. I can't. On the other hand, if it exceeds 0.08%, the strength becomes too high, leading to a decrease in toughness and a deterioration in corrosion resistance.

Si: 0.05-1.00%
Si is necessary as a deoxidizing agent, and if the content is less than 0.05%, the amount of Al added later increases, and the ground and the like increase, leading to deterioration of the steel quality. On the other hand, if it exceeds 1.00%, the toughness decreases.

Mn: 0.05 to 1.50%
Mn is effective as a deoxidizer and fixes hot impurities S to improve hot workability. Further, Mn stabilizes the austenite phase at a high temperature and facilitates the formation of a martensite phase. However, if the content is less than 0.05%, these effects are insufficient. On the other hand, excessive Mn causes a decrease in corrosion resistance, so the upper limit is made 1.50%.

Cr: 9.0 to 15.0%
Cr is the most important basic component of martensitic stainless steel, and if its content is less than 9%, corrosion resistance as stainless steel cannot be ensured. On the other hand, if it exceeds 15.0%, a large amount of δ ferrite is generated during billet heating, and the required strength cannot be obtained.

Mo: 0.05-5.00%
Mo has an action of preventing local corrosion in an environment containing carbon dioxide gas, but if the content is less than 0.05%, the effect is not sufficient. On the other hand, if it exceeds 5.00%, a large amount of δ ferrite is produced and the required strength cannot be obtained.

Al: 0.0005 to 0.05%
Al is added as a deoxidizer, but if its content is less than 0.0005%, deoxidation is insufficient and the soundness of steel may be inferior. On the other hand, if it exceeds 0.05%, the toughness is reduced.

N: 0.1% or less N is an impurity inevitably mixed when Cr is high, and has an effect of facilitating the formation of the martensite phase by expanding the austenite region. However, excessive N deteriorates the resistance to sulfide stress corrosion cracking, so the effect is not more significant 0.1% or less. The smaller the N content, the better.

Ni: 0.3-4.0%
Ni is one of the most important components for the present invention, and in order to disperse and deposit 1 × 10 ⁴ or more Ni metal particles per mm ^{2 in the} inner scale, the content is at least 0.3% or more. is required. On the other hand, if it exceeds 4.0%, the number of Ni metal particles dispersed per 1 mm ² exceeds 2 × 10 ⁵ and seizure occurs, so the Ni content is 0.3 to 4.0%. did.

Cu: 4.0% or less Cu need not be added. If added, the above Ni and compound (Ni-Cu) are formed and dispersed and precipitated as metal particles in the inner layer scale, and the biting property and slip resistance of the material to be rolled with respect to the inclined roll are improved. The effect can be obtained even with the impurity content level as can be seen from the experimental results shown in FIG. However, if the content exceeds 4.0%, as can be seen from the experimental results shown in FIG. 2, not only the effect of Ni is lost, but also the hot workability is lowered. For this reason, when added, the Cu content is preferably 4.0% or less. The details of why the addition of a large amount of Cu loses the effect of Ni is unclear, but because the amount of Cu in the Ni particles increases and the melting point of the metal particles decreases, seizure occurs. Presumed.

  Other than the above components, it is substantially Fe, in other words, the balance is impurities other than Fe and the above N, and if P as an impurity is up to 0.04% and S is up to 0.03%, there is a particular problem. None, but the lower the content of P and S, the better.

2. Regarding Dispersion Density of Metal Particles The inner scale after heating the solid round billet according to the present invention has a dispersion density of Ni or Ni and Ni—Cu compound metal particles having a particle diameter of 0.1 μm or more of 1 × 10 ⁴ to 2. It must be dispersed and precipitated at × 10 ⁵ pieces / mm ² . The reason for this is that, as described above, if the dispersion density is less than 1 × 10 ⁴ pieces / mm ² , the biting property is insufficient, and the gripping force due to the metal particles is insufficient, resulting in slipping and 60% or more. This is because the drilling efficiency cannot be obtained, and conversely, if it exceeds 2 × 10 ⁵ pieces / mm ² , the biting property is sufficient, but the gripping force by the metal particles becomes excessive and seizure occurs. The reason why the size of the metal particles to be counted is 0.1 m or more in terms of particle size is that metal particles smaller than this have little influence on the effect of the present invention and can be ignored.

3. Regarding heating conditions for solid round billets Ni or Ni-Ni-Cu compound metal particles having a particle size of 0.1 μm or more are dispersed and precipitated at a density of 1 × 10 ⁴ to 2 × 10 ⁵ particles / mm ² . In order to obtain a solid round billet according to the present invention having an inner layer scale, a solid round billet made of steel having the above-described chemical composition is used in an oxidizing atmosphere having a water vapor concentration of 5 to 15% by volume in a 1100- It is necessary to heat and hold in a temperature range of 1300 ° C. for 1.5 to 6.0 hours. When the water vapor concentration is less than 5% by volume, the heating temperature is less than 1100 ° C., and the holding time is less than 1.5 hours, 1 × 10 ⁴ Ni / mm ² or more in the inner layer scale or This is because the metal particles of Ni and Ni—Cu compound are not dispersed and deposited. Conversely, the water vapor concentration exceeds 30% by volume, the heating temperature exceeds 1300 ° C., and the retention time exceeds 6.0 hours. In any case, this is because Ni or Ni and Ni—Cu compound metal particles exceeding 2 × 10 ⁵ particles / mm ² are dispersed and precipitated in the inner layer scale. The above is also clear from examples described later.

4). About the manufacturing method of the martensitic stainless steel seamless steel pipe In the manufacturing method of the martensitic stainless steel seamless steel pipe of the present invention using the solid round billet after the heating according to the present invention described above as a raw material, it is generated by heating. It is necessary to perform piercing and rolling by a piercing and rolling machine after removing at least the outer layer scale of the oxide scale having a two-layer structure. This is due to the following reason.

  The metal particles that improve the biting property and slip resistance are not present in the outer layer scale, but are present only in the inner layer scale. On the other hand, the oxide scale of the two-layer structure formed on the surface of the solid round billet of the present invention containing Ni as an essential component, as shown in FIGS. 1 and 2 described above, contains Ni or Ni and Cu as essential components. There is almost no porosity in the scale as compared to those not contained. For this reason, the oxide scale not only has high adhesion to the base material, but also has high adhesion between the inner layer scale and the outer layer scale, and the outer layer scale does not contain Ni as an essential component, but the outer layer scale is almost peeled off during handling before piercing and rolling. This is because the outer layer scale of the solid round billet of the present invention hardly peels off during handling before piercing and rolling.

  The outer scale can be removed by, for example, subjecting the solid round billet after heating to a high-pressure water descaling process under the following conditions. Pressure: 490-1960 MPa, flow rate: 30-60 liters / minute, transport speed of solid round billet: 10-30 m / second. That is, when the pressure is less than 490 MPa, the flow rate is less than 30 liters / minute, or the conveyance speed exceeds 30 m / second, the removal of the outer scale may be insufficient. Conversely, if the pressure exceeds 1960 MPa, the inner scale may be removed, and if the flow rate exceeds 60 liters / minute or the conveyance speed is less than 10 m / second, the temperature drop of the solid round billet is large. Thus, piercing and rolling itself may be difficult. However, within the above range, only the outer layer scale can be removed almost reliably and stably, and a significant temperature drop can be avoided, and piercing and rolling itself does not become difficult.

  The high-pressure water descaling process as described above can be handled by remodeling only the pressurizing pump of the equipment that constitutes the high-pressure water descaler apparatus that is normally provided in this kind of piercing and rolling mill. It will not be significantly higher.

  When the piercing and rolling is performed after removing the outer layer scale as described above, the biting property of the solid round billet with respect to the piercing and rolling mill is improved, so that the piercing and rolling can be performed with the above-described plug tip draft rate being further reduced. In other words, it is possible to perform piercing and rolling with a plug before a crack due to rotary forging occurs in the shaft center portion of a solid round billet, so that a hollow shell tube with less inner covering flaws can be obtained. .

  In addition, even after biting, the slip effect is reduced by the grip effect of the metal particles in the inner layer scale, so the drilling efficiency is improved, in other words, the time that the plug is exposed to high temperature is shortened as the drilling time is shortened, Plug life is also improved.

  Four types of martensitic stainless steel having the chemical composition shown in Table 4 were melted. Then, for a solid round billet made of these steels having an outer diameter of 191 mm and a length of 2130 mm, a heating furnace using LNG as a fuel is used and heated under various conditions shown in Table 5 and formed on the surface. In addition, the density of Ni and Ni—Cu compound metal particles having a particle size of 0.1 μm or more in the inner scale was examined, and the scale thickness of the inner and outer layers was measured. In addition, the identification of the metal particle was performed using the electron microscope and EDX of the cross section of a scale 500 times.

The results are as shown together in Table 5. By heating under the conditions specified in the present invention, 1 × 10 ⁴ metal particles of Ni and Ni—Cu compound having a particle size of 0.1 μm or more are contained in the inner scale. Precipitate at a dispersion density of 1 piece / mm ² . On the other hand, when any one of the water vapor concentration in the atmosphere, the heating temperature, and the holding time is out of the range defined in the present invention, Ni and Ni—Cu present in the inner layer scale and having a particle diameter of 0.1 μm or more. It can be seen that the metal particles of the compound do not fall within the range of 1 × 10 ⁴ to 2 × 10 ⁵ particles / mm ² .

  A solid round billet made of the four types of steel shown in Table 4 and having an outer diameter of 191 mm and a length of 2130 mm was heated under the conditions shown in Table 6. The billet after the heating was subjected to high-pressure water descaling treatment under the conditions of a pressure of 980 MPa, a flow rate of 45 liters / minute, and a conveying speed of 22 m / second, and only the outer scale was removed.

  Then, these solid round billets were subjected to an inclined roll type piercing rolling mill equipped with a plug of 0.5% Cr-0.5% Mn-1.0% Ni-Fe, and the piercing setup shown in Table 6 was performed. Then, piercing and rolling were carried out, and the piercing efficiency, the middle coverage defect rate (number ratio) and the plug life (number of passes / piece) were investigated.

The dispersion density (number / mm ² ) of metal particles of Ni and Ni—Cu compound with a particle size of 0.1 μm or more in the inner scale formed on the billet surface after heating is 3000 to 3000. 4000, code B had 50000-60000, code C had 100,000-150,000, and code D had 250,000-300000.

  The results of the above investigation are summarized in Table 7, and FIG. 6 shows the relationship between the plug tip draft rate and the drilling efficiency for each steel, and FIG. 7 shows the plug tip draft rate and medium coverage defect rate for each steel. FIG. 8 shows the relationship between the plug tip draft ratio and the plug life for each steel.

  As can be seen from the results shown in Table 7 and FIGS. 6 to 8, Ni and Ni— with a Ni or Ni and Cu content within the range defined by the present invention and a particle size of 0.1 μm or more in the inner layer scale are included. In the case of a solid round billet made of steels of symbols B and C in which the dispersion density of the metal particles of the Cu compound is within the range specified in the present invention, a drilling efficiency of 60% or more is obtained at any plug tip draft rate. In addition, the inside-coverage failure rate is as low as 4% or less, and the plug life is as long as 3.3 passes / piece or more on average.

  On the other hand, the Ni content is less than the lower limit specified in the present invention, and the dispersion density of Ni metal particles having a particle size of 0.1 μm or more in the inner scale is lower than the lower limit specified in the present invention. With a solid round billet made of a small number of steel A, a drilling efficiency of 60% or more cannot be obtained unless the plug tip draft rate is increased. In this case, the coverage ratio is only as high as about 10%. In addition, the average plug life is as short as 2.5 passes / piece. Further, if the plug tip draft rate is reduced to reduce the cover loss rate and extend the plug life, a drilling efficiency of 60% or more cannot be obtained.

  In addition, a solid round billet made of steel with a sign D having an excessively high Ni content has good drilling efficiency, defective coverage, and plug life, but there are too many metal particles in the inner layer scale. Along with frequent sticking, the wear of the inclined roll was remarkable.

  The solid round billet of the present invention can be applied to a piercing and rolling machine of a press piercing mill in which the material billet is, in principle, a solid square billet.

It is a figure which shows the experimental result performed beforehand, and is a figure which arranges and shows the influence which Ni content and Cu content exert on drilling efficiency by Ni content. It is a figure which shows the experimental result performed beforehand, and is a figure which arranges and shows the influence which Ni content and Cu content exert on drilling efficiency by Cu content. It is a figure which shows the experimental result performed beforehand, and shows an example of the oxide scale after the heating of "steel 1" whose content of both Ni and Cu is 1.0% and 0% (no addition). It is a microphotograph, the same figure (a) is the case of "steel 1", and the same figure (b) is the case of "steel 2". FIG. 5 is a schematic diagram showing the state of the oxide scale immediately after heating of the above “steel 1” and “steel 2”, the state of the inner layer scale when the outer layer scale is removed and piercing is started, and the state of the inner layer scale during piercing and rolling. The figure (a) is a figure in the case of "steel 1", and the figure (b) is a figure in the case of "steel 2". It is a figure which shows the experimental result performed beforehand, and is a figure which shows the relationship between the dispersion density of the metal particle of Ni or Ni and Ni-Cu compound with a particle size of 0.1 micrometer or more which exists in an inner layer scale, and perforation efficiency. It is a figure which shows the result of an Example, and is a figure which shows the relationship between the plug tip draft rate and drilling efficiency for every used steel. It is a figure which shows the result of an Example, and is a figure which shows the relationship between the plug front-end | tip draft rate for each used steel, and a middle covering defect rate. It is a figure which shows the result of an Example, and is a figure which shows the relationship between the plug tip draft rate for every used steel, and a plug lifetime.

Claims (5)

In mass%, C: 0.01 to 0.08%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.50%, Cr: 9.0 to 15.0%, Mo: Martensitic stainless steel comprising 0.05 to 5.00%, Al: 0.0005 to 0.05%, N: 0.1% or less, Ni: 0.3 to 4.0%, balance: Fe and impurities It is a solid round billet of steel, and the density of Ni metal particles with a particle size of 0.1 μm or more contained in the inner scale layer of the oxide scale of the two-layer structure consisting of the inner layer and the outer layer on the surface is 1 × Solid round billet characterized by 10 ^{4 to} 2 × 10 ⁵ pieces / mm ² . In mass%, C: 0.01 to 0.08%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.50%, Cr: 9.0 to 15.0%, Mo: 0.05 to 5.00%, Al: 0.0005 to 0.05%, N: 0.1% or less, Ni: 0.3 to 4.0%, Cu: 4.0% or less, balance: Fe And a solid round billet of martensitic stainless steel made of impurities, and a nickel oxide having a particle size of 0.1 μm or more contained in the inner scale layer among the two-layered oxide scale consisting of an inner layer and an outer layer on the surface. Or the density of the metal particle of a Ni-Cu compound is 1 * 10 < ⁴ > -2 * 10 < ⁵ > piece / mm < ² >, The solid round billet characterized by the above-mentioned.   3. A solid round billet having the chemical composition according to claim 1 or 2 in an oxidizing atmosphere having a water vapor concentration of 5% by volume to 30% by volume at 1100 ° C. to 1300 ° C. for 1.5 hours to 6 A method for producing a solid round billet, characterized by heating for 0 hour or less.   The method for producing a solid round billet according to claim 3, wherein the outer layer scale is removed after the heating. A method for producing a martensitic stainless steel seamless steel pipe, wherein the solid round billet according to claim 1 or 2 is pierced and rolled into a hollow shell using an inclined roll type piercing and rolling mill.

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