KR20090130334A - Ferrite heat resistant steel - Google Patents

Abstract

It is intended to provide a ferrite heat resistant steel excellent in solvent cracking resistance and creep strength in the HAZ.A high-Cr-containing ferrite heat resistant steel, characterized by containing (in terms of percent by mass) Si: not less than 0.1% and 1.0% or less, Mn: 2.0% or less, Co: 1 to 8%, Cr: 7 to 13%, V: 0.05 to 0.4%, Nb: 0.01 to 0.09%, either one of or the total of both of Mo and W: 0.5 to 4%, B: 0.005 to 0.025%, Al: 0.03% or less and N: 0.003 to 0.06%, and further containing C in an amount that satisfies the following formula (1), and Fe and impurities as remainders, wherein as the impurities, O, P and S are contained in an amount of 0.02% or less, 0.03% or less, and 0.02% or less, respectively. 0.005 <= C <= (-5/3) × B + 0.085 (1) In the formula, C and B represent the contents (% by mass) of the respective elements. Further, it may contain one element or two or more elements of Nd, Ta, Ca and Mg.

Description

Ferritic Heat Resistant Steel {FERRITE HEAT RESISTANT STEEL}

TECHNICAL FIELD The present invention relates to a ferritic heat resistant steel having excellent high temperature strength and weld cracking resistance used in a member used at a high temperature such as a thermal power boiler.

In recent years, in order to improve thermal efficiency in thermal power generation, high temperature and high pressure of steam conditions are advanced, and operation in the super supercritical pressure condition of 650 degreeC and 350 atmospheres is planned in the future. Ferritic heat resistant steels are widely used because they are inexpensive compared to austenitic stainless steels and have advantages as heat resistant steels having a low coefficient of thermal expansion.

In the ferritic heat resistant steel, high strength is aimed at in order to cope with future congestion of steam conditions. For example, Patent Document 1 and Patent Document 2 propose to include Co and B while optimizing the content of W and Mo. In addition, Patent Document 3 proposes a steel in which reinforcement by a fine intermetallic compound phase is added by adding W and Mo. Patent Literature 4 proposes a steel having a high strength by utilizing M ₂₃ C ₆ -based carbide and intermetallic compound phases deposited at martensite lath interface.

However, in the case where these ferritic heat resistant steels are used as the welding structure, for example, as shown in Non-Patent Document 1, the creep strength is greatly reduced in the welding heat affected part (hereinafter referred to as HAZ) that undergoes a heat cycle by welding. There is work to do. Therefore, there exists a problem that it cannot fully utilize the advantage of the steel which aimed at high strength. Therefore, proposals have been made not only for steel but also for steel for the purpose of improving the creep strength of HAZ subjected to a welding heat cycle.

For example, Patent Document 5 generates Ti, Zr, and Hf-based nitrides that are stable to welding heat input, and adds W to Patent Document 6 and finely deposits (Nb, Ta) carbonitrides. Patent Literature 7 and Patent Literature 8 disclose steels in which the long-term creep strength of the joint portion is improved by suppressing the formation of Cr carbides and increasing the long-term stability of carbonitrides such as fine V and Nb. As described above, various methods for improving the strength of HAZ utilizing carbonitrides have been proposed, but further improvement in HAZ strength is required in practical terms.

Patent Literature 9 also proposes a method of containing 0.003-0.03% of B to suppress fine graining in HAZ and to improve creep strength in HAZ. However, while B is known to be an element having such an effect, it is widely known that B is an element that enhances solidification cracking of weld metal and liquefaction cracking sensitivity of HAZ when welding. For this reason, when used as a thin member such as a main steam pipe for a boiler or a pressure vessel, there is a problem that sufficient weldability (welding cracking property) is not obtained.

[Patent Document 1: Japanese Patent Application Laid-Open No. 4-371551]

[Patent Document 2: Japanese Patent Application Laid-Open No. 4-371552]

[Patent Document 3: Japanese Patent Application Laid-Open No. 2001-152293]

[Patent Document 4: Japanese Patent Application Laid-Open No. 2002-241903]

[Patent Document 5: Japanese Patent Application Laid-open No. Hei 8-85848]

[Patent Document 6: Japanese Patent Application Laid-Open No. 9-71845]

[Patent Document 7: Japanese Patent Application Laid-Open No. 2001-279391]

[Patent Document 8: Japanese Patent Application Laid-Open No. 2002-69588]

[Patent Document 9: Japanese Patent Application Laid-Open No. 2004-300532]

[Non-Patent Document 1: Science and Technology of Welding and Joining, 1996, Vol. 1, No. 1, p. 36 to 42]

Problems to be Solved by the Invention

As described above, the ferritic heat-resistant steel has an advantage of having a low coefficient of thermal expansion in addition to being inexpensive. Therefore, it is expected that the ferritic heat-resistant steel is used as a welding structure in a thermal power generation boiler or the like in which the high temperature and high pressure of the steam condition is advanced.

As described above, various proposals have been made in order to improve the creep strength of the HAZ of the weld joint while further increasing the strength, so that it can be used even at high temperature and high pressure conditions. However, the high strength of the HAZ is still insufficient, and there is a problem that sufficient weld cracking property at the time of welding is not obtained.

In view of such a situation, it is an object of the present invention to provide a ferritic heat-resistant steel which is excellent in weld cracking resistance of HAZ and also excellent in creep strength.

Means for solving the problem

In order to improve the creep strength of HAZ, it became clear that Cr, Co, V, and Nb were regulated in a predetermined range, and that B was added. However, when the amount of B required to increase the strength of HAZ is added, it becomes clear that the crack susceptibility of the HAZ and the weld metal increases, and there is a problem in the weld cracking property.

Therefore, in order to improve creep strength in HAZ and to achieve excellent weldability, it has been found that the problem can be solved by optimizing the contents of C and B as follows. In the ferritic heat-resistant steel according to the present invention, the creep strength in the HAZ is a breaking time of three times or more, preferably five times or more of the breaking time of the general-purpose steel.

As a result of investigation and investigation, when B is contained in a ferritic steel having a composition range of Cr: 7 to 13%, Co: 1 to 8%, V: 0.05 to 0.4%, and Nb: 0.01 to 0.09%, It was confirmed that HAZ was intensified.

The decrease in the creep strength in the HAZ compared to the base metal is caused by finer grains due to heating to the temperature between Ac ₁ , the transformation point and the Ac ₃ transformation point by the welding heat cycle. Fine graining occurs when the ferrite phase (quenching martensite phase), which is the original structure, is heated to this temperature range, and the austenite phase newly nucleates and grows at the grain boundary. B is an element that tends to segregate at the grain boundary, and when heated to this temperature range, it segregates to the original ferrite grain boundary, reduces the energy of the grain boundary, and suppresses and delays the granulation by inhibiting and delaying nucleation of the austenite phase. As a result, it was thought to improve the creep strength in HAZ.

However, when it contains B more than the required amount from which the effect of improving creep strength is obtained, it was found that solidification cracking of the weld metal and liquefaction cracking susceptibility of HAZ increase.

This is one factor that B is an element which is easy to segregate at the grain boundary, and which greatly reduces the melting point. In addition, S and P, like B, are also easy to segregate grain boundaries and are elements that significantly lower the melting point. Therefore, in HAZ right next to the melting line, it was thought that grain boundary segregation of P and S overlapped with grain boundary segregation of B, grain boundary melting occurred, opening by thermal stress or external stress, and causing liquefied cracking. .

Solidification cracking of a weld metal can be prevented by adjusting the component of a welding material. On the other hand, the liquefaction crack of HAZ is a subject related to the composition of the steel to be used, and becomes a big restriction on practical use. Based on such a problem, the requirements for enabling the prevention of liquefaction cracking of the HAZ and for increasing the strength of the HAZ have been carefully investigated.

As a result of repeating the examination, new knowledge was obtained that the liquefaction cracking can be prevented only when the C content is defined in a predetermined range. And this reason was considered as follows.

That is, C acts as a melting | fusing point lowering element similarly to B, superimposes on melting | fusing point reduction effect | action by B mentioned above, and improves the liquefaction cracking sensitivity of HAZ. Therefore, it was thought that it becomes possible to reduce the fall of melting | fusing point by reducing content of C according to content of B. And solidification brittle temperature range (BTR) in the range of Cr: 7 to 13%, Co: 1 to 8%, V: 0.05 to 0.4%, and Nb: 0.01 to 0.09%, which are the basic alloy components of the present invention. In practice, the upper limit of the content (%) of C to be reduced to 100 ° C. or less, which can sufficiently prevent liquefied cracking, was identified from the thermodynamic theory calculation as (-5/3) × [% B] +0.085. . Here, [% B] represents content (mass%) of B in steel (it is the same below).

In addition, C interacts with the free energy of sulfides and phosphides. That is, at high temperatures, the solubility of sulfides or phosphides such as Cr, Nd, and the like decreases with increasing C content, and when the C content increases, these solubility tends to increase again. When the solubility of sulfide or phosphide increases, the amount of S and P segregating at the grain boundary increases due to thermal influences such as welding, thereby increasing the susceptibility of liquefied cracking. Therefore, in the case of the C content of the present invention in which the amount of C is reduced, the solubility of sulfides and phosphides becomes small, and a stable compound is formed. Thereby, it was thought that S and P in a grain boundary reduce, and the liquefaction crack of HAZ is prevented by synergistic action with suppression of melting | fusing point fall.

In addition, when the content of C is reduced after containing B, not only liquefaction cracking can be prevented, but also new knowledge has been obtained that the creep strength of the HAZ is more improved than when only B is included.

This decreases the carbide present in the grain boundary when the C content is reduced to a predetermined range. Therefore, the pinning effect is small even when heated to a temperature between the Ac ₁ transformation point and the Ac ₃ transformation point and nucleation of the austenite phase at the grain boundary makes crystal grains easily coarse. As a result, the effect of suppressing refining in HAZ becomes large by the superposition effect of nucleation suppression by B containing. In addition, the growth rate of the fine carbonitrides of V and Nb in the grains contributing to the strengthening of the ferritic steel is suppressed, and it is thought that the reinforcing band of creep strength is increased as compared with the case where only B is contained.

However, when the content of C is extremely reduced, it is considered that the amount of fine carbonitrides of V and Nb contributing to reinforcement in the grain is small, and the effect of improving strength is small because the effect of reinforcing is not sufficiently obtained. Therefore, the minimum of content of C was made into 0.005% or more.

From the results of these studies, in order to enable the prevention of liquefaction cracking of the HAZ and to improve the creep strength of the HAZ, B: 0.005 to 0.025%, and 0.005 ≦ C ≦ (−5/3) × [ It turned out that it is necessary to satisfy the conditions of% B] +0.085.

This invention is completed based on such a new knowledge, The summary of the ferritic heat-resistant steel which concerns on this invention is as showing to following (1)-(3). Hereinafter, this invention is called (1)-(4), respectively. These may be collectively referred to as the present invention.

(1) In mass%, Si: more than 0.1% and 1.0% or less, Mn: 2.0% or less, Co: 1-8%, Cr: 7-13%, V: 0.05-0.4%, Nb: 0.01-0.09%, One or both of Mo and W in total contain 0.5 to 4%, B: 0.005 to 0.025%, Al: 0.03% or less, and N: 0.003 to 0.06%, and C in an amount satisfying the following formula (1) And a remainder consisting of Fe and impurities, and O, P, and S as impurities are O: 0.02% or less, P: 0.03% or less, and S: 0.02% or less, respectively.

0.005? C? (-5/3) x B + 0.085 ... (One)

Here, C and B represent content (mass%) of each element.

(2) The high Cr ferritic heat resistant steel according to the above (1), wherein Nd: 0.08% or less is included in place of a part of Fe in mass%.

(3) The high Cr ferritic heat resistant steel according to the above (1) or (2), wherein the mass% contains 0.08% or less of Ta in place of a part of Fe.

(4) Any one of the above items (1) to (3), wherein the mass% contains one or two of Ca: 0.02% or less and Mg: 0.02% or less, in place of a part of Fe. High Cr ferritic heat resistant steel described in the above.

Effect of the Invention

The ferritic heat-resistant steel according to the present invention is excellent in weld cracking resistance of HAZ and has an excellent HAZ creep strength.

1 shows a longitudinal crack susceptibility test method.

Next, the reason for limitation of the steel of this invention is described. In addition,% display represents the mass%.

C: 0.005% or more and ｛(-5/3) x [% B] +0.085}% or less

C, together with B, is an important element in the present invention. C is an essential element because it is an effective element for forming carbide, contributing to securing high temperature strength, and obtaining martensite structure. However, when segregation occurs in the grain boundary, it overlaps with B, S, and P to promote lowering of the melting point of the grain boundary, and indirectly participates in the formation of sulfides or phosphides of the granulated HAZ, thereby affecting the liquefaction crack susceptibility. In addition, when the content of C is reduced, the fine grain HAZ has an effect of improving creep strength by promoting coarsening of crystal grains during transformation and suppressing growth of fine carbides. C It suppresses the lowering of the melting point of the grain boundary and forms stable sulfides and phosphides with the granulated HAZ, reduces the melting point caused by the grain boundary segregation of S and P, prevents liquefaction cracking, and creep strength of the fine grain HAZ. In order to improve the efficiency, as described later, the content of B is defined in a specific range, and C is made 0.005% or more, and C (-5/3) × [% B] +0.085}% or less. There is a need. The minimum with preferable C content is 0.010%.

Si: more than 0.1% and less than 1.0%

Although Si is contained in excess of 0.1% as a deoxidizer, when it contains excessively, since creep ductility and toughness fall, it sets an upper limit to 1.0%. Preferably it is 0.8% or less. More preferably, it is more than 0.2% and 0.7% or less.

Mn: 2.0% or less

Like Si, Mn is contained as a deoxidizer, but when excessively contained, it causes creep embrittlement and a decrease in toughness. Therefore, you may be 2.0% or less. Preferably it is 1.8% or less. However, excessive reduction leads to an increase in manufacturing cost while degrading the cleanliness of the steel without obtaining a sufficient deoxidation effect. For this reason, although a minimum in particular is not provided, it is preferable to contain Mn 0.01% or more.

Co: 1-8%

Co is an austenite generating element and is an element necessary for martensite formation of a matrix. In order to acquire the effect, it is necessary to contain 1% or more. However, incorporation in excess of 8% causes a significant decrease in creep ductility. Also, it is preferably more than 2% and 7% or less.

Cr: 7-13%

Cr is an essential element in order to secure oxidation resistance and high temperature corrosion resistance in a heat resistant steel and to stably obtain the martensite structure of the matrix. In order to acquire the effect, it is necessary to contain 7% or more. However, when excessively contained, the formation of a large amount of Cr decreases the stability of the carbide, leads to a decrease in the creep strength, and deteriorates the toughness. Therefore, content of Cr needs to be 13% or less. Preferably, it is 8 to 12%. More preferably, it is 8-10%.

V: 0.05 to 0.4%

V is an element which forms fine carbonitride in the grain together with Nb and contributes greatly to the improvement of creep strength. In order to acquire the effect, it is necessary to contain at least 0.05% or more. However, when excessively contained, the growth rate of carbonitride is increased, the dispersion strengthening effect is lost early, and the toughness is reduced. Therefore, the content of V needs to be 0.4% or less. . Preferably, it is 0.10 to 0.35%.

Nb: 0.01% to 0.09%

Nb is an element which, together with V, forms fine carbonitrides stable to a high temperature in the grains and contributes greatly to the improvement in creep strength. In order to acquire the effect, it is necessary to contain at least 0.01% or more. However, when it contains excessively, the growth rate of carbonitride is called the increase, the dispersion strengthening effect lose | disappears early, and since toughness is brought about, Nb content needs to be 0.09% or less. .

One or both of Mo and W: 0.5 to 4% (total)

Mo and W are elements which solidify the matrix and contribute to the improvement of creep strength. In order to acquire this effect, it is necessary to contain one or both of Mo and W in total at least 0.5%. However, when it contains excessively more than 4%, a coarse intermetallic compound is produced and the extreme fall of toughness is called. In addition, when containing W independently, it is preferable to make the minimum of content of W into 1%.

B: 0.005-0.025%

B, together with C, is an important element in the present invention. B segregates at grain boundaries in HAZ and lowers grain boundary energy, thereby delaying nucleation of the austenite phase and suppressing fine graining. In order to fully acquire the effect, it is necessary to contain at least 0.005% or more. However, in granulated HAZ, grain boundary segregation B promotes the melting | fusing point fall of a grain boundary, overlaps with segregation of S and P, and produces liquefied crack. In order to prevent this, it is necessary to define C to the above-mentioned range. However, when the content of B exceeds 0.025%, the effect of improving the creep strength of HAZ is saturated, and liquefied cracking cannot be prevented even if the content of C is defined in the above-described range. Moreover, as for the minimum of content of B, 0.007% or more is preferable. A more preferable range is more than 0.01% and 0.02% or less.

N: 0.003-0.06%

N forms fine carbonitrides containing V and Nb and is an element effective for securing creep strength. In order to acquire the effect, it is necessary to contain 0.003% or more. However, when it contains excessively, the precipitation amount of carbonitride will increase and it will cause embrittlement. Therefore, the upper limit of content of N is made into 0.06%.

Al: 0.03% or less

Although Al is contained as a deoxidizer, when it contains excessively, since creep ductility and toughness fall, the upper limit is made into 0.03%. Preferably it is 0.02% or less. However, excessive reduction leads to an increase in manufacturing cost while degrading the cleanliness of the steel without obtaining a sufficient deoxidation effect. For this reason, although a minimum in particular is not formed, it is preferable to contain Al 0.001% or more.

O: 0.02% or less

O exists as an impurity, but when it is contained in a large amount, a large amount of oxide is formed, and workability and ductility are deteriorated. Therefore, it is necessary to make content of O into 0.02% or less.

P: 0.03% or less

P is included as an impurity, but together with S and B, it segregates at grain boundaries in the granulated HAZ and lowers the melting point to cause liquefaction cracking. In order to prevent it, while defining C, Nb, S, and B in a predetermined range, it is necessary to make content of P into 0.03% or less.

S: 0.02% or less

S is included as an impurity similarly to P, segregates at grain boundaries in granulated HAZ, and lowers the melting point to cause liquefaction cracking. In order to prevent it, while defining C, Nb, S, and P in a predetermined range, it is necessary to make content of S into 0.02% or less.

Steel of this invention can contain the element shown next by a predetermined amount as needed.

Nd: 0.08% or less

Nd has strong affinity with P and S, forms a compound between S and P at the grain boundary of granulated HAZ, thereby suppressing the melting point decrease due to S and P and preventing liquefied cracking of HAZ, It is effective to reduce grain boundary embrittlement during use at high temperatures by S and P, and to improve creep ductility of HAZ. However, since the affinity with oxygen is strong, when it contains excessively, an extra oxide will produce | generate and it will cause the toughness of HAZ to fall, and therefore an upper limit shall be 0.08%. The upper limit is preferably 0.06%. In addition, in order to ensure the said effect by containing Nd, it is preferable to contain Nd 0.005% or more. More preferably, it is 0.015% or more.

Ta: O.08% or less

Ta, like V and Nb, forms stable fine carbide up to high temperature and greatly contributes to the improvement of creep strength. Therefore, Ta may be contained as necessary. However, when it contains excessively, since the growth rate of a carbide will increase, the dispersion strengthening effect will lose | disappear prematurely and will call for a fall of toughness, and therefore an upper limit shall be 0.08% or less. Moreover, in order to acquire the said effect by Ta containing, it is preferable to contain 0.005% or more.

Ca: 0.02% or less

Ca is an element which improves the hot workability of steel, and can contain it, when it is necessary to improve hot workability. However, when the content exceeds 0.02%, the coarsening of inclusions is called, and conversely, the upper limit is made 0.02% due to impairing workability and toughness. In addition, in order to acquire the said effect by Ca containing, it is preferable to contain 0.0003% or more. In addition, the range with more preferable content of Ca is 0.001 to 0.01%.

Mg: 0.02% or less

Mg is an element which improves the hot workability of steel similarly to Ca, and when it is necessary to improve hot workability, Mg can be contained together with Ca or Mg independently. However, when the content exceeds 0.02%, the coarsening of inclusions is called, and conversely, the upper limit is made 0.02% due to impairing workability and toughness. In addition, in order to acquire the said effect by Mg containing, it is preferable to contain 0.0003% or more. In addition, the range with more preferable content of Ca is 0.001 to 0.01%.

Example 1

After 16 kinds of steels having the chemical composition shown in Table 1 were melted by a vacuum melting furnace, cast and rolled, and then maintained at 1150 ° C. for 1 hour, normalized by air cooling, and held at 770 ° C. for 1.5 hours, and then cooled by air tempering. Heat treatment was performed. In addition, No. 13 is a steel equivalent to the general-purpose steel SUS410J3TB, and was used as a comparative steel regarding creep strength. By machining, a steel plate with a plate thickness of 12 mm, a width of 50 mm and a length of 300 mm and a plate thickness of 10 mm, a width of 100 to 120 mm and a length of 300 to 500 mm was produced. The steel plate of 12 mm of plate | board thickness was used for the longitudinal crack susceptibility test, and the liquefaction crack susceptibility of HAZ was evaluated.

In the longitudinal crack susceptibility test, as shown schematically in FIG. 1, bead-on-plate welding is performed in the longitudinal direction of the steel sheet by GTA welding, and a deformation due to warpage is performed by applying a force F to the end portion during the welding. It is a method of evaluating the liquefied cracking susceptibility of HAZ by adding and forcibly generating a crack in HAZ and measuring the total length. The welding conditions were 200 A x 15 V x 10 cm / min, and the amount of additional strain was 4%, and the liquefaction crack did not occur in the HAZ as the pass.

For steel grades where no liquefaction cracks occurred in the HAZ, a test material having a plate thickness of 10 mm, a width of 10 mm and a length of 100 mm was taken from a 10 mm thick steel sheet and heated for 5 seconds at a temperature of 1000 ° C. at which the drop in strength of the HAZ was particularly significant. A reproduction heat cycle was given. Thereafter, the test material was subjected to post-weld heat treatment at 740 ° C. for 30 minutes and air-cooled, and the creep test piece was taken out, and the creep test was performed under conditions of a temperature of 650 ° C. and a stress of 117.7 MPa.

In Table 2, the weld crack length (mm) in a longitudinal cracking sensitivity test and the breaking time (hr) in a creep test are shown.

As is apparent from Table 2, the materials of Nos. 3 to 6, 9 to 11, 14, and 15 in which the contents of C and B satisfy the prescribed range of the present invention and formula (1) are the same as in the longitudinal cracking sensitivity test. Also in the difficult crack test, the liquefied crack of HAZ did not generate | occur | produce, and the creep rupture time of HAZ was three times or more of the rupture time of No.13. In particular, in the materials of Nos. 3 to 5, 9, 11, 14, and 15, the creep rupture time of HAZ was 5 times or more of the rupture time of No. 13.

However, although the content of B is within the prescribed range of the present invention, in the materials of Nos. 1, 2, and 16 in which the C content exceeds the upper limit of the formula (1), the melting point decrease of the grain boundary of the granulated HAZ is remarkable, and in the longitudinal direction In the crack susceptibility test, liquefied cracks occurred in the HAZ.

On the other hand, in the material of Nos. 7, 8, and 12, liquefaction crack did not generate | occur | produce in HAZ in the longitudinal cracking susceptibility test, either, the creep rupture time of HAZ did not satisfy the target value.

That is, although the content of B is within the prescribed range of the present invention, the number 12 in which the content of C does not fall below the lower limit of the formula (1), the creep rupture time of the HAZ did not satisfy the target value. On the other hand, in the material of No. 8 whose content of B does not fall within the prescribed range of the present invention, the content of C satisfies the formula (1), but the creep rupture time of HAZ did not satisfy the target value. Moreover, in addition to the content of B not falling within the scope of the present invention, the material of No. 7 in which the content of C exceeded the upper limit of the formula (1) had a lower creep rupture time of HAZ than in No. 8.

From the above result, it turns out that the material which has a chemical component which satisfy | fills the scope of this invention has the outstanding liquefaction crack resistance and creep strength in HAZ.

Since the ferritic heat resistant steel which concerns on this invention provides the ferritic heat resistant steel excellent in the weld cracking property and creep strength of HAZ, it can be used as a welding structure in the thermal power generation boiler etc. which advanced the high temperature and high pressure of steam conditions.

Claims (4)

By mass%, Si: more than 0.1% and 1.0% or less, Mn: 2.0% or less, Co: 1 to 8%, Cr: 7 to 13%, V: 0.05 to 0.4%, Nb: 0.01 to 0.09%, Mo and W One or both of 0.5 to 4%, B: 0.005 to 0.025%, Al: 0.03% or less, and N: 0.003 to 0.06%, containing C in an amount satisfying the following formula (1), The remainder consists of Fe and an impurity, and O, P, and S as impurities are O: 0.02% or less, P: 0.03% or less, and S: 0.02% or less, respectively. 0.005

C

(-5/3) x B + 0.085... … (One) Here, C and B represent content (mass%) of each element. The method according to claim 1, A high Cr ferritic heat resistant steel comprising, in mass%, Nd: 0.08% or less in place of a part of Fe. The method according to claim 1 or 2, A high Cr ferritic heat resistant steel comprising, in mass%, Ta: 0.08% or less in place of a part of Fe. The method according to any one of claims 1 to 3, A high Cr ferritic heat resistant steel comprising, in mass%, one or two of Ca: 0.02% or less and Mg: 0.02% or less.

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