CA2604428A1 - Low alloy steel - Google Patents
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- CA2604428A1 CA2604428A1 CA002604428A CA2604428A CA2604428A1 CA 2604428 A1 CA2604428 A1 CA 2604428A1 CA 002604428 A CA002604428 A CA 002604428A CA 2604428 A CA2604428 A CA 2604428A CA 2604428 A1 CA2604428 A1 CA 2604428A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
Abstract
A low alloy steel for a heat-resistant structure member being improved in high-temperature long-time creep ductility and temper softening resistance, characterized in that it comprises 0.03 to 0.10 mass% of C, 0.30 mass% or less of Si, 1.0 mass% or less of Mn, more than 1.5 mass% and not more than 2.5 mass% of Cr, 0.01 to 1.0 mass% of Mo, 0.04 to 0.30 mass% of V, 0.001 to 0.10 mass% of Nb, 0.001 to 0.020 mass% of Ti, 0.0001 to 0.020 mass% of B, 0.001 to 0.01 mass% of Al, 0.0001 to 0.05 mass% of Nd and the balance comprising Fe and impurities, the impurities include 0.020 mass% or less of P, 0.03 mass% or less of S, less than 0.0050 mass% of N and 0.0050 mass% or less of O(oxygen), and a value of BSO represented by the following formula (1) is 0.0001 to 0.010; BSO = B - (11/14)N - (11/32)S - (11/16)O ---- (1) where the symbol of an element in the formula (1) represents the content (mass %) of the element.
The steel may further contain one or more of W, Cu, Ni, Co, Mg, Ca, La, Ce, Y, Sm and Pr.
The steel may further contain one or more of W, Cu, Ni, Co, Mg, Ca, La, Ce, Y, Sm and Pr.
Description
LOW ALLOY STEEL
TECHNICAL FIELD
[0001]
The present invention relates to a low alloy steel excellent in high temperature creep characteristics and toughness. The low alloy steel of the present invention is suitable for heat-resisting structural members such as electric power plant boilers, turbines, nuclear power plant facilities, chemical industry facilities and other facilities or apparatus, which are used at high temperatures.
BACKGROUND ART
TECHNICAL FIELD
[0001]
The present invention relates to a low alloy steel excellent in high temperature creep characteristics and toughness. The low alloy steel of the present invention is suitable for heat-resisting structural members such as electric power plant boilers, turbines, nuclear power plant facilities, chemical industry facilities and other facilities or apparatus, which are used at high temperatures.
BACKGROUND ART
[0002]
Electric power plant boilers, turbines, nuclear power plant facilities, chemical industry facilities and the like are used at high temperature and high pressure conditions for a long time. Therefore, the heat-resisting materials to be used in such facilities and the like are generally required to be excellent in strength, corrosion resistance and oxidation resistance at high temperatures as well as toughness and the like at room temperature.
In those fields of application, austenitic stainless steels (for example, JIS
SUS321H and SUS347H steels), low alloy steels (for example, JIS STBA24 steel, namely 2.25Cr-1Mo steel) and further, 9-12Cr type high-Cr ferritic steels (for example, JIS STBA26 steel, namely 9Cr-1Mo steel, and JIS
STBA28 steel, namely improved 9Cr-1Mo steel) have been used in the past.
Electric power plant boilers, turbines, nuclear power plant facilities, chemical industry facilities and the like are used at high temperature and high pressure conditions for a long time. Therefore, the heat-resisting materials to be used in such facilities and the like are generally required to be excellent in strength, corrosion resistance and oxidation resistance at high temperatures as well as toughness and the like at room temperature.
In those fields of application, austenitic stainless steels (for example, JIS
SUS321H and SUS347H steels), low alloy steels (for example, JIS STBA24 steel, namely 2.25Cr-1Mo steel) and further, 9-12Cr type high-Cr ferritic steels (for example, JIS STBA26 steel, namely 9Cr-1Mo steel, and JIS
STBA28 steel, namely improved 9Cr-1Mo steel) have been used in the past.
[0003]
Recently, in the thermal power plants, attempts have been made to reduce the discharge of CO2 and so forth for the prevention of global warming. Therefore, it is essential to improve the thermal efficiency and, regarding the boilers, new type plants have been built to be operated under high temperature and high pressure steam conditions (for example, 300 atmospheres at temperatures over 600 C). On the other hand, a number of existing plants which were built during the period of rapid economic growth, are each nearing the end of their scheduled life span one after another and it is becoming a great social problem whether they should be replaced with new advanced plants or their lives should be prolonged by partial mending. This is also a problem which involves the energy policy of Japan.
Recently, in the thermal power plants, attempts have been made to reduce the discharge of CO2 and so forth for the prevention of global warming. Therefore, it is essential to improve the thermal efficiency and, regarding the boilers, new type plants have been built to be operated under high temperature and high pressure steam conditions (for example, 300 atmospheres at temperatures over 600 C). On the other hand, a number of existing plants which were built during the period of rapid economic growth, are each nearing the end of their scheduled life span one after another and it is becoming a great social problem whether they should be replaced with new advanced plants or their lives should be prolonged by partial mending. This is also a problem which involves the energy policy of Japan.
[0004]
On the other hand, advanced liberalization in the electric power business field in compliance with the request for deregulation inside and outside the country, has now made it possible for an enterprise outside the electric power industry to go into that field. This has resulted in increased price competition and therefore economical efficiency in electric power plants has become more important as well.
On the other hand, advanced liberalization in the electric power business field in compliance with the request for deregulation inside and outside the country, has now made it possible for an enterprise outside the electric power industry to go into that field. This has resulted in increased price competition and therefore economical efficiency in electric power plants has become more important as well.
[0005]
Therefore due to a need to reduce the cost of new power plants, a trend is growing toward improving the strength of the heat-resisting structural materials used in the power plants and also reduce the steel consumption in order to meet this requirement, new high strength materials are under development.
Therefore due to a need to reduce the cost of new power plants, a trend is growing toward improving the strength of the heat-resisting structural materials used in the power plants and also reduce the steel consumption in order to meet this requirement, new high strength materials are under development.
[0006]
In the relatively low temperature region up to about 500 C, Cr-Mo type low alloy steels such as JIS STBA22 steel (lCr-0.5Mo steel), STBA23 steel (1.25Cr-0.5Mo steel) and the above-mentioned STBA24 steel (2.25Cr-1Mo steel) and the like, have so far been used. Also a steel containing W in substitution for a part of Mo in order to increase the high temperature strength more is disclosed in the Patent Document 1. Further, a steel improved in hardenability by adding Co is also disclosed in the Patent Document 2.
In the relatively low temperature region up to about 500 C, Cr-Mo type low alloy steels such as JIS STBA22 steel (lCr-0.5Mo steel), STBA23 steel (1.25Cr-0.5Mo steel) and the above-mentioned STBA24 steel (2.25Cr-1Mo steel) and the like, have so far been used. Also a steel containing W in substitution for a part of Mo in order to increase the high temperature strength more is disclosed in the Patent Document 1. Further, a steel improved in hardenability by adding Co is also disclosed in the Patent Document 2.
[0007]
In such new steels as referred to above, the high temperature softening resistance is improved by W or Co, and especially the creep strength at 500 C or above is markedly improved as compared with the conventional multipurpose steels. However, there is a problem in that increases in strength result in a deterioration in toughness and marked decreases in long time creep ductility (that is, elongation and reduction of are a) .
In such new steels as referred to above, the high temperature softening resistance is improved by W or Co, and especially the creep strength at 500 C or above is markedly improved as compared with the conventional multipurpose steels. However, there is a problem in that increases in strength result in a deterioration in toughness and marked decreases in long time creep ductility (that is, elongation and reduction of are a) .
[0008]
In the Patent Documents 3 and 4, as steels prevented from deterioration in toughness and also improved in reheat cracking resistance, steels resulting from the addition of a very small amount of Ti to the Cr-Mo steels, with a nitrogen content suppressed to a very low level, are disclosed.
The steels are definitely improved in toughness but fail to simultaneously attain high creep strength and creep ductility. Further, in regions subjected to repeated SR treatment following welding, reheat cracking may occur and, in addition, marked decreases in creep strength may be sometimes encountered due to reheat softening.
In the Patent Documents 3 and 4, as steels prevented from deterioration in toughness and also improved in reheat cracking resistance, steels resulting from the addition of a very small amount of Ti to the Cr-Mo steels, with a nitrogen content suppressed to a very low level, are disclosed.
The steels are definitely improved in toughness but fail to simultaneously attain high creep strength and creep ductility. Further, in regions subjected to repeated SR treatment following welding, reheat cracking may occur and, in addition, marked decreases in creep strength may be sometimes encountered due to reheat softening.
[0009]
In the Patent Document 5, a low and medium Cr type heat-resisting steel characterized by a regulated density of occurrence of precipitates within a specific range of size is disclosed. This steel is high in creep strength but the composition design is not always made in consideration of long time creep ductility or reheat softening resistance characteristics.
In the Patent Document 5, a low and medium Cr type heat-resisting steel characterized by a regulated density of occurrence of precipitates within a specific range of size is disclosed. This steel is high in creep strength but the composition design is not always made in consideration of long time creep ductility or reheat softening resistance characteristics.
[0010]
In the Patent Document 6, a low alloy steel with a Cr content of 0.40 to 1.50% is disclosed. However, the Cr content is too low, therefore the resistance to high temperature corrosion in the temperature range above 500 C is not always sufficient and the temperature range for its use is restricted.
Patent Document 1: ei'apanese Laid-open Patent Publication No.
08-134584, Patent Document 2: Japanese Laid-open Patent Publication No.
09-268343, Patent Document 3: Japanese Laid-open Patent Publication No.
08-144010, Patent Document 4: Japanese Laid-open Patent Publication No.
Patent Document 5: Japanese Laid-open Patent Publication No.
Patent Document 6: Japanese Laid-open Patent Publication No.
DISCLOSURE OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
In the Patent Document 6, a low alloy steel with a Cr content of 0.40 to 1.50% is disclosed. However, the Cr content is too low, therefore the resistance to high temperature corrosion in the temperature range above 500 C is not always sufficient and the temperature range for its use is restricted.
Patent Document 1: ei'apanese Laid-open Patent Publication No.
08-134584, Patent Document 2: Japanese Laid-open Patent Publication No.
09-268343, Patent Document 3: Japanese Laid-open Patent Publication No.
08-144010, Patent Document 4: Japanese Laid-open Patent Publication No.
Patent Document 5: Japanese Laid-open Patent Publication No.
Patent Document 6: Japanese Laid-open Patent Publication No.
DISCLOSURE OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0011]
The objective of the present invention is to provide a steel which is markedly improved in long time creep ductility at high temperatures and in temper softening resistance and is capable of being used even in a temperature range up to about 550 C by improving low alloy steels for heat-resisting structural members which have so far been in a temperature range of up to about 500 C in electric power plants and so forth.
MEANS FOR SOLVING THE PROBLEM
The objective of the present invention is to provide a steel which is markedly improved in long time creep ductility at high temperatures and in temper softening resistance and is capable of being used even in a temperature range up to about 550 C by improving low alloy steels for heat-resisting structural members which have so far been in a temperature range of up to about 500 C in electric power plants and so forth.
MEANS FOR SOLVING THE PROBLEM
[0012]
The present inventors made detailed investigations concerning the effects of the chemical composition of each material and the metallurgical structure (that is, microstructure) on the creep deformation properties, namely creep strength, creep ductility and reheat softening characteristics, in various heat-resisting low alloy steels. As a result, the following new findings were obtained.
[00131 (a) When, in the Cr-Mo steels, a part of Mo is substituted with W, the carbides become stable for a longer time and the creep strength increases but, contrariwise, the toughness and creep ductility markedly decrease. For example the said carbides occurred in the form of M3C, M, C3, M23C6 and M6C. M mainly comprises Fe and Cr and some quantities of Mo, W and the like are dissolved in the said M. With the increase in the amount of Cr, M3C
changes into M 7 Cs, M28C6 and M6C.
[0014]
(b) When Co is added to the Cr-Mo steels, the hardenability is markedly improved with the increase of the amount of Co. However, the addition of Co in large amounts, like W, leads to increases in susceptibility to creep embrittlement.
[0015]
(c) On the other hand, when V, Nb and the like are added to the Cr-Mo steels, MC carbides (M comprising mainly V and Nb, and a part of Mo is dissolved in the said M) precipitate out finely and dispersedly and a more significant precipitation hardening effect is obtained compared with the single addition of Mo; the high temperature creep strength is thus improved.
However, the susceptibility to creep embrittlement also increases markedly.
[0016]
(d) The addition of B to the Cr-Mo steels is effective in increasing the hardenability, and so the strength and toughness are improved. Although such a phenomenon is already known, the investigations made by the present inventors revealed that when excessive B is added, the toughness markedly decreases.
[0017]
(e) Further research works made by the present inventors revealed that the creep ductility and reheat softening resistance are both markedly improved when the contents of B, N, S and O(oxygen) are respectively optimized and the value of BSO represented by the formula (1) given below is adjusted to 0.0001 to 0.010. It was also revealed that it becomes possible to add W and B, for instance, in large amounts.
[0018]
The present invention has been accomplished on the basis of the above-mentioned findings. The gists of the present invention are the following low alloy steels.
[0019]
(1) A low alloy steel, which comprises by mass percent, C: 0.03 to 0.10%, Si: not more than 0.30%, Mn: not more than 1.0%, Cr: more than 1.5%
to not more than 2.5%, Mo: 0.01 to 1.0%, V: 0.04 to 0.30%, Nb: 0.001 to 0.10%, Ti: 0.001 to 0.020%, B: 0.0001 to 0.020%, Al: 0.001 to 0.01% and Nd: 0.0001 to 0.050%, with the balance being Fe and impurities, wherein the content of P
is not more than 0.020%, the content of S is not more than 0.003%, the content of N is less than 0.0050% and the content of O(oxygen) is not more than 0.0050% among the impurities, in which the value of BSO represented by the following formula (1) is 0.0001 to 0.010:
BSO = B - (11/14)N - (11/32)S - (11/16)0 = = = = = (1), wherein each element symbol in the formula (1) represents the content (by mass %) of the element concerned.
[0020]
(2) A low alloy steel according to the above (1), which further contains W: not more than 2.0% by mass in lieu of part of Fe.
[0021]
(3) A low alloy steel according to the above (1) or (2), which further contains one or more elements selected from among Cu, Ni and Co each at a level not more than 0.50% by mass in lieu of part of Fe.
[0022]
(4) A low alloy steel according to any one of the above (1) to (3), which further contains one or more elements selected from among Mg: not more than 0.005% by mass, Ca: not more than 0.005% by mass, La: not more than 0.02% by mass, Ce: not more than 0.02% by mass, Y. not more than 0.05% by mass, Sm: not more than 0.05% by mass and Pr: not more than 0.05% by mass.
[BEST MODE FOR CARRYING OUT THE INVENTION
[0023]
The working-effect of the each component constituting the low alloy steel of the present invention and the reasons for restricting the contents thereof will next be explained. In the following description, the symbol "%"
for the content of each component represents "% by mass".
[0024]
C: 0.03 to 0.10%
C serves as an austenite-stabilizing element and stabilizes the bainite phase (lower bainite phase) or martensite phase, which is the basic parent phase of the Cr-Mo steels. It also forms various carbides and contributes toward increasing strength. If the content of C is less than 0.03%, however, the extent of carbide precipitation is small; hence a sufficient level of strength cannot be obtained. On the other hand, if the content of C exceeds 0.10%, the steel is markedly hardened and the weldability and workability are deteriorated. A more preferable lower and the upper limit of C are 0.04% and 0.08%, respectively.
[0025]
Si: not more than 0.30%
Si is used as a deoxidizer in the steelmaking process and inevitably remains in the steel. Conventionally, Si is positively added as an element necessary for securing the oxidation resistance in the steels used for heat-resisting structural members. However, according to the study made by the present inventors, it was revealed that reductions in the amount of Si contained as an impurity can produce the effects of reducing not only the creep embrittlement but also the reheat embrittlement and the reheat cracking susceptibility. When the content of Si is suppressed to 0.30% or less, the effects become significant. Even when the content of Si is suppressed to 0.30% or below, the Cr captures oxygen and therefore causes no harmful effect on the oxidation resistance. From the reasons mentioned above, the content of Si is set to not more than 0.30%. A more preferable content of Si is not more than 0.15%.
[0026]
Mn: not more than 1.0%
Like C, Mn is an austenite-stabilizing element and important for the stabilization of the bainite phase. However, higher levels of the addition of Mn cause a lower Acl transformation point of the steel and further, cause reheat embrittlement. Therefore, the content of Mn is set to not more than 1.0%. If the content of Mn is not more than 0.30%, the creep ductility is further improved. The lower limit content of Mn may be an ordinary impurity level.
[0027]
Cr: more than 1.5% to not more than 2.5%
Cr is essential for the stabilization of the low carbon type bainitic parent phase. In order to obtain the said effect, the content of Cr is set to more than 1.5%. A more preferable lower limit content of Cr is more than 1.6%. On the other hand, if the content of Cr exceeds 2.5%, the precipitation of M7C3 and M2aC6 type carbides increases remarkably, and it causes a decrease in creep strength.
[0028]
Mo: 0.01 to 1.0%
Mo is an element which produces solid solution hardening and contributes to the stabilization of M3C, ivl, Cs and PvI2aC6 type carbides and further, it forms Mo2C and, in addition, contributes to the stabilization of MC
type carbides and improves the creep strength. In order to obtain the said effects, the content of Mo is set to not less than 0.01%. However, if there is an excessive addition of Mo, the bainitic or martensitic parent phase becomes unstable, and therefore, the upper limit content of Mo is set to 1.0%.
[0029]
V: 0.04 to 0.30%
V, together with Nb which will be mentioned later herein, forms MC
type carbides and remarkably contributes to improvement in creep strength.
In order to obtain the said effect, the content of not less than 0.04% of V is needed. Since, at excessive additional levels, it markedly reduces the long time creep ductility, the upper limit content of V is set to 0.30%.
[0030]
Nb: 0.001 to 0.10%
Like V, Nb forms fine carbides which contribute toward increasing the creep strength. In order to obtain the said effect, the content of not less than 0.001% of Nb is needed. However, if the content of Nb exceeds 0.10%, the toughness deteriorates due to the excessive formation of carbonitrides.
A more preferable lower and the upper limit of Nb are 0.020% and 0.060%, respectively.
[0031]
Ti: 0.001 to 0.020%
Ti forms fine carbides and contributes toward increasing the strength.
Therefore, the content of not less than 0.001% of Ti is needed. In particular, it is effective in improving the creep ductility and in preventing embrittlement and cracking during reheating, so that the content of not less than 0.010% of Ti is more preferable. Excessive addition, however, adversely affects the toughness; hence the upper limit content of Ti is set to 0.020%.
[0032]
B: 0.0001 to 0.020%
B is effective in increasing the hardenability. The said effect is obtained if the content of B is not less than 0.0001%. On the other hand, at excessive additional levels, it adversely affects the toughness and therefore, the upper limit content of B should be set to 0.020%. It is noted that the upper limit content of B is preferably 0.015% and more preferably 0.012%.
It is necessary that the content of B is set so that the value of BSO
represented by the formula (1) given above may fall within the range of 0.0001 to 0.010.
[0033]
Nd: 0.0001 to 0.050%
Nd is an element which improves long time creep ductility. In order to obtain the said effect, the content of not less than 0.0001% of Nd is needed.
Excessive Nd, however, forms coarse inclusions unfavorable to the toughness and therefore, the upper limit content of Nd is set to 0.050%. A more preferable content of Nd is more than 0.010% and not more than 0.050%.
[0034]
Al: 0.001 to 0.01%
Al is an element which is important as a steel deoxidizer for steels.
In order to obtain the deoxidizing effect, the content of not less than 0.001%
of Al is needed. On the other hand, the content of Al levels exceeding 0.01%
is unfavorable to simultaneously securing both the strength and toughness which is an aim of the present invention.
[0035]
One of low alloy steels according to the present invention comprises the components mentioned above with the balance being Fe and impurities.
It is necessary, however, to suppress the contents of P, S, N and 0 (oxygen) among the impurities in the following manner.
[0036]
P: not more than 0.020%, S: not more than 0.003%, 0: not more than 0.0050%
These elements are unfavorable impurities which deteriorate the toughness of the steel. The contents thereof should be not more than the respective upper limits given above and are preferably as low as possible.
[0037]
N: less than 0.0050%
N is an element which produces solid solution hardening and forms carbonitrides therefore sometimes contributes to the high temperature strength. However, in the practice of the present invention, the content of N
is suppressed to less than 0.0050% in order to obtain both the creep strength and toughness, and also to obtain the improved creep ductility. Further, it is necessary that the content of N is adjusted so that the value of BSO
represented by the formula (1) given above may fall within the range of 0.0001 to 0.010.
[0038]
BSO: 0.0001 to 0.010 As mentioned hereinabove, the BSO is expressed in terms of the formula (1) given below. In order to improve the creep ductility and the reheat softening resistance, it is necessary that the value of BSO is 0.0001 to 0.010:
BSO = B - (11/14)N - (11/32)S - (11/16)0 = = = = . (1).
[0039]
The technical meaning of the BSO is to secure an amount of B which is effective in preventing the carbonitrides from becoming coarse and also effective in preventing grain boundary embrittlement when the steel of the present invention is used at high temperatures. If the value of BSO is smaller than 0.0001, no effective amount of B is secured. Arid when it is greater than 0.010, coarse inclusions which are harmful to the toughness are formed. Therefore, the value of BSO is set to 0.0001 to 0.010. A more preferable lower limit value of BSO is 0.001.
[0040]
The low alloy steel according to the present invention also contains the components mentioned above and further one or more components selected from among W, Cu, Ni, Co, Mg, Ca, La, Ce, Y, Sm and Pr. The working-effects of these components and the reasons for restricting the contents thereof are described below.
[0041]
W: not more than 2.0%
W is added when a further improvement in the long time creep strength at high temperatures is desired. As mentioned hereinabove, high addition levels of W have so far been regarded as causing reheat embrittlement and also increase cracking susceptibility. However, in the steels having a value of BSO within the range of 0.0001 to 0.010, the content of 2.0% or less of W does not produce these above harmful effects. W also contributes to improvement in creep ductility. In order to definitely obtain these effects, a content of W of not less than 0.20% is preferable.
[0042]
Cu, Ni, Co: each not more than 0.50%
All of these elements are austenite-stabilizing elements and contribute to the stabilization of the bainite phase or martensite phase. In order to definitely obtain this effect, the content of each element is preferably not less than 0.01%. However, if the content of each element is above 0.50%, the steel sometimes becomes too high in strength, making it necessary for example to carry out excessive softening heat treatment and the like.
Therefore, when these components are added, the content of each should be suppressed to not more than 0.50%.
[0043]
Mg, Ca: each not more than 0.005%, La, Ce: each not more than 0.02%, Y, Sm, Pr: each not more than 0.05%
All of these elements have an effect of preventing solidification cracking during steel casting, and therefore they are added according to necessity. At levels exceeding the respective upper limit values described above, they adversely affect the toughness. In order to secure the effect of their addition, the content of each is preferably not less than 0.0001%.
[0044]
The steel of the present invention, after processing into pipes, plates and so forth, is subjected to "normalizing-tempering" heat treatment and then used. The microstructure after the said heat treatment is mainly composed of tempered bainite or tempered martensite.
EXAMPLES
[0045]
In the following, the effects of the present invention are explained concretely in reference to examples.
Steels having chemical compositions shown in Table 1 were melted by use of a 150 kg vacuum induction melting furnace, followed by ingot making and hot forging, to give plate-like test materials, 25 mm in thickness x 100 mm in width. Then, they were subjected to normalizing treatment, namely they were maintained at 950 C for 1 hour and water cooled, and then reheated and maintained at a tempering temperature varying within the range of 720 to 760 C for 1 hour and then air cooled. The microstructure of each steel was tempered bainite or tempered martensite.
[0046]
A portion of the said test materials after the above heat treatment, was further reheated at 730 C for 10 hours in order to examine the changes in hardness and for reheat softening resistance evaluation.
The present inventors made detailed investigations concerning the effects of the chemical composition of each material and the metallurgical structure (that is, microstructure) on the creep deformation properties, namely creep strength, creep ductility and reheat softening characteristics, in various heat-resisting low alloy steels. As a result, the following new findings were obtained.
[00131 (a) When, in the Cr-Mo steels, a part of Mo is substituted with W, the carbides become stable for a longer time and the creep strength increases but, contrariwise, the toughness and creep ductility markedly decrease. For example the said carbides occurred in the form of M3C, M, C3, M23C6 and M6C. M mainly comprises Fe and Cr and some quantities of Mo, W and the like are dissolved in the said M. With the increase in the amount of Cr, M3C
changes into M 7 Cs, M28C6 and M6C.
[0014]
(b) When Co is added to the Cr-Mo steels, the hardenability is markedly improved with the increase of the amount of Co. However, the addition of Co in large amounts, like W, leads to increases in susceptibility to creep embrittlement.
[0015]
(c) On the other hand, when V, Nb and the like are added to the Cr-Mo steels, MC carbides (M comprising mainly V and Nb, and a part of Mo is dissolved in the said M) precipitate out finely and dispersedly and a more significant precipitation hardening effect is obtained compared with the single addition of Mo; the high temperature creep strength is thus improved.
However, the susceptibility to creep embrittlement also increases markedly.
[0016]
(d) The addition of B to the Cr-Mo steels is effective in increasing the hardenability, and so the strength and toughness are improved. Although such a phenomenon is already known, the investigations made by the present inventors revealed that when excessive B is added, the toughness markedly decreases.
[0017]
(e) Further research works made by the present inventors revealed that the creep ductility and reheat softening resistance are both markedly improved when the contents of B, N, S and O(oxygen) are respectively optimized and the value of BSO represented by the formula (1) given below is adjusted to 0.0001 to 0.010. It was also revealed that it becomes possible to add W and B, for instance, in large amounts.
[0018]
The present invention has been accomplished on the basis of the above-mentioned findings. The gists of the present invention are the following low alloy steels.
[0019]
(1) A low alloy steel, which comprises by mass percent, C: 0.03 to 0.10%, Si: not more than 0.30%, Mn: not more than 1.0%, Cr: more than 1.5%
to not more than 2.5%, Mo: 0.01 to 1.0%, V: 0.04 to 0.30%, Nb: 0.001 to 0.10%, Ti: 0.001 to 0.020%, B: 0.0001 to 0.020%, Al: 0.001 to 0.01% and Nd: 0.0001 to 0.050%, with the balance being Fe and impurities, wherein the content of P
is not more than 0.020%, the content of S is not more than 0.003%, the content of N is less than 0.0050% and the content of O(oxygen) is not more than 0.0050% among the impurities, in which the value of BSO represented by the following formula (1) is 0.0001 to 0.010:
BSO = B - (11/14)N - (11/32)S - (11/16)0 = = = = = (1), wherein each element symbol in the formula (1) represents the content (by mass %) of the element concerned.
[0020]
(2) A low alloy steel according to the above (1), which further contains W: not more than 2.0% by mass in lieu of part of Fe.
[0021]
(3) A low alloy steel according to the above (1) or (2), which further contains one or more elements selected from among Cu, Ni and Co each at a level not more than 0.50% by mass in lieu of part of Fe.
[0022]
(4) A low alloy steel according to any one of the above (1) to (3), which further contains one or more elements selected from among Mg: not more than 0.005% by mass, Ca: not more than 0.005% by mass, La: not more than 0.02% by mass, Ce: not more than 0.02% by mass, Y. not more than 0.05% by mass, Sm: not more than 0.05% by mass and Pr: not more than 0.05% by mass.
[BEST MODE FOR CARRYING OUT THE INVENTION
[0023]
The working-effect of the each component constituting the low alloy steel of the present invention and the reasons for restricting the contents thereof will next be explained. In the following description, the symbol "%"
for the content of each component represents "% by mass".
[0024]
C: 0.03 to 0.10%
C serves as an austenite-stabilizing element and stabilizes the bainite phase (lower bainite phase) or martensite phase, which is the basic parent phase of the Cr-Mo steels. It also forms various carbides and contributes toward increasing strength. If the content of C is less than 0.03%, however, the extent of carbide precipitation is small; hence a sufficient level of strength cannot be obtained. On the other hand, if the content of C exceeds 0.10%, the steel is markedly hardened and the weldability and workability are deteriorated. A more preferable lower and the upper limit of C are 0.04% and 0.08%, respectively.
[0025]
Si: not more than 0.30%
Si is used as a deoxidizer in the steelmaking process and inevitably remains in the steel. Conventionally, Si is positively added as an element necessary for securing the oxidation resistance in the steels used for heat-resisting structural members. However, according to the study made by the present inventors, it was revealed that reductions in the amount of Si contained as an impurity can produce the effects of reducing not only the creep embrittlement but also the reheat embrittlement and the reheat cracking susceptibility. When the content of Si is suppressed to 0.30% or less, the effects become significant. Even when the content of Si is suppressed to 0.30% or below, the Cr captures oxygen and therefore causes no harmful effect on the oxidation resistance. From the reasons mentioned above, the content of Si is set to not more than 0.30%. A more preferable content of Si is not more than 0.15%.
[0026]
Mn: not more than 1.0%
Like C, Mn is an austenite-stabilizing element and important for the stabilization of the bainite phase. However, higher levels of the addition of Mn cause a lower Acl transformation point of the steel and further, cause reheat embrittlement. Therefore, the content of Mn is set to not more than 1.0%. If the content of Mn is not more than 0.30%, the creep ductility is further improved. The lower limit content of Mn may be an ordinary impurity level.
[0027]
Cr: more than 1.5% to not more than 2.5%
Cr is essential for the stabilization of the low carbon type bainitic parent phase. In order to obtain the said effect, the content of Cr is set to more than 1.5%. A more preferable lower limit content of Cr is more than 1.6%. On the other hand, if the content of Cr exceeds 2.5%, the precipitation of M7C3 and M2aC6 type carbides increases remarkably, and it causes a decrease in creep strength.
[0028]
Mo: 0.01 to 1.0%
Mo is an element which produces solid solution hardening and contributes to the stabilization of M3C, ivl, Cs and PvI2aC6 type carbides and further, it forms Mo2C and, in addition, contributes to the stabilization of MC
type carbides and improves the creep strength. In order to obtain the said effects, the content of Mo is set to not less than 0.01%. However, if there is an excessive addition of Mo, the bainitic or martensitic parent phase becomes unstable, and therefore, the upper limit content of Mo is set to 1.0%.
[0029]
V: 0.04 to 0.30%
V, together with Nb which will be mentioned later herein, forms MC
type carbides and remarkably contributes to improvement in creep strength.
In order to obtain the said effect, the content of not less than 0.04% of V is needed. Since, at excessive additional levels, it markedly reduces the long time creep ductility, the upper limit content of V is set to 0.30%.
[0030]
Nb: 0.001 to 0.10%
Like V, Nb forms fine carbides which contribute toward increasing the creep strength. In order to obtain the said effect, the content of not less than 0.001% of Nb is needed. However, if the content of Nb exceeds 0.10%, the toughness deteriorates due to the excessive formation of carbonitrides.
A more preferable lower and the upper limit of Nb are 0.020% and 0.060%, respectively.
[0031]
Ti: 0.001 to 0.020%
Ti forms fine carbides and contributes toward increasing the strength.
Therefore, the content of not less than 0.001% of Ti is needed. In particular, it is effective in improving the creep ductility and in preventing embrittlement and cracking during reheating, so that the content of not less than 0.010% of Ti is more preferable. Excessive addition, however, adversely affects the toughness; hence the upper limit content of Ti is set to 0.020%.
[0032]
B: 0.0001 to 0.020%
B is effective in increasing the hardenability. The said effect is obtained if the content of B is not less than 0.0001%. On the other hand, at excessive additional levels, it adversely affects the toughness and therefore, the upper limit content of B should be set to 0.020%. It is noted that the upper limit content of B is preferably 0.015% and more preferably 0.012%.
It is necessary that the content of B is set so that the value of BSO
represented by the formula (1) given above may fall within the range of 0.0001 to 0.010.
[0033]
Nd: 0.0001 to 0.050%
Nd is an element which improves long time creep ductility. In order to obtain the said effect, the content of not less than 0.0001% of Nd is needed.
Excessive Nd, however, forms coarse inclusions unfavorable to the toughness and therefore, the upper limit content of Nd is set to 0.050%. A more preferable content of Nd is more than 0.010% and not more than 0.050%.
[0034]
Al: 0.001 to 0.01%
Al is an element which is important as a steel deoxidizer for steels.
In order to obtain the deoxidizing effect, the content of not less than 0.001%
of Al is needed. On the other hand, the content of Al levels exceeding 0.01%
is unfavorable to simultaneously securing both the strength and toughness which is an aim of the present invention.
[0035]
One of low alloy steels according to the present invention comprises the components mentioned above with the balance being Fe and impurities.
It is necessary, however, to suppress the contents of P, S, N and 0 (oxygen) among the impurities in the following manner.
[0036]
P: not more than 0.020%, S: not more than 0.003%, 0: not more than 0.0050%
These elements are unfavorable impurities which deteriorate the toughness of the steel. The contents thereof should be not more than the respective upper limits given above and are preferably as low as possible.
[0037]
N: less than 0.0050%
N is an element which produces solid solution hardening and forms carbonitrides therefore sometimes contributes to the high temperature strength. However, in the practice of the present invention, the content of N
is suppressed to less than 0.0050% in order to obtain both the creep strength and toughness, and also to obtain the improved creep ductility. Further, it is necessary that the content of N is adjusted so that the value of BSO
represented by the formula (1) given above may fall within the range of 0.0001 to 0.010.
[0038]
BSO: 0.0001 to 0.010 As mentioned hereinabove, the BSO is expressed in terms of the formula (1) given below. In order to improve the creep ductility and the reheat softening resistance, it is necessary that the value of BSO is 0.0001 to 0.010:
BSO = B - (11/14)N - (11/32)S - (11/16)0 = = = = . (1).
[0039]
The technical meaning of the BSO is to secure an amount of B which is effective in preventing the carbonitrides from becoming coarse and also effective in preventing grain boundary embrittlement when the steel of the present invention is used at high temperatures. If the value of BSO is smaller than 0.0001, no effective amount of B is secured. Arid when it is greater than 0.010, coarse inclusions which are harmful to the toughness are formed. Therefore, the value of BSO is set to 0.0001 to 0.010. A more preferable lower limit value of BSO is 0.001.
[0040]
The low alloy steel according to the present invention also contains the components mentioned above and further one or more components selected from among W, Cu, Ni, Co, Mg, Ca, La, Ce, Y, Sm and Pr. The working-effects of these components and the reasons for restricting the contents thereof are described below.
[0041]
W: not more than 2.0%
W is added when a further improvement in the long time creep strength at high temperatures is desired. As mentioned hereinabove, high addition levels of W have so far been regarded as causing reheat embrittlement and also increase cracking susceptibility. However, in the steels having a value of BSO within the range of 0.0001 to 0.010, the content of 2.0% or less of W does not produce these above harmful effects. W also contributes to improvement in creep ductility. In order to definitely obtain these effects, a content of W of not less than 0.20% is preferable.
[0042]
Cu, Ni, Co: each not more than 0.50%
All of these elements are austenite-stabilizing elements and contribute to the stabilization of the bainite phase or martensite phase. In order to definitely obtain this effect, the content of each element is preferably not less than 0.01%. However, if the content of each element is above 0.50%, the steel sometimes becomes too high in strength, making it necessary for example to carry out excessive softening heat treatment and the like.
Therefore, when these components are added, the content of each should be suppressed to not more than 0.50%.
[0043]
Mg, Ca: each not more than 0.005%, La, Ce: each not more than 0.02%, Y, Sm, Pr: each not more than 0.05%
All of these elements have an effect of preventing solidification cracking during steel casting, and therefore they are added according to necessity. At levels exceeding the respective upper limit values described above, they adversely affect the toughness. In order to secure the effect of their addition, the content of each is preferably not less than 0.0001%.
[0044]
The steel of the present invention, after processing into pipes, plates and so forth, is subjected to "normalizing-tempering" heat treatment and then used. The microstructure after the said heat treatment is mainly composed of tempered bainite or tempered martensite.
EXAMPLES
[0045]
In the following, the effects of the present invention are explained concretely in reference to examples.
Steels having chemical compositions shown in Table 1 were melted by use of a 150 kg vacuum induction melting furnace, followed by ingot making and hot forging, to give plate-like test materials, 25 mm in thickness x 100 mm in width. Then, they were subjected to normalizing treatment, namely they were maintained at 950 C for 1 hour and water cooled, and then reheated and maintained at a tempering temperature varying within the range of 720 to 760 C for 1 hour and then air cooled. The microstructure of each steel was tempered bainite or tempered martensite.
[0046]
A portion of the said test materials after the above heat treatment, was further reheated at 730 C for 10 hours in order to examine the changes in hardness and for reheat softening resistance evaluation.
13 [0047]
Creep rupture test specimens, 6 mm in diameter and 30 mm in GL
and Charpy test specimens 10 mm x 10 mm x 5 mm in size, having a 2 mm V
notch were cut out from each test material obtained. The creep rupture test was carried out under the condition of a temperature of 550 C and an applied stress of 200 MPa, and the Charpy impact test was carried out within a temperature range of -60 C to 60 C. The results of these tests are shown in Table 2.
[0048]
In Table 2, in the column "toughness", the mark "oo" indicates that the vTrs was lower than -40 C; the mark "o" indicates that the vTrs was within the range of -40 C to -20 C; the mark "A" indicates that the vTrs was within the range exceeding -20 C and not higher than 0 C; and the mark "x"
indicates that the vTrs was higher than 0 C. In the column "reheat softening resistance", the mark "o" indicates that the decrease in Vickers hardness (Hv) after the reheating mentioned above (that is, 10 hours of heating at 730 C) was smaller than 20% and the mark "x" indicates 20% or larger.
[0049]
[Table 1]
Creep rupture test specimens, 6 mm in diameter and 30 mm in GL
and Charpy test specimens 10 mm x 10 mm x 5 mm in size, having a 2 mm V
notch were cut out from each test material obtained. The creep rupture test was carried out under the condition of a temperature of 550 C and an applied stress of 200 MPa, and the Charpy impact test was carried out within a temperature range of -60 C to 60 C. The results of these tests are shown in Table 2.
[0048]
In Table 2, in the column "toughness", the mark "oo" indicates that the vTrs was lower than -40 C; the mark "o" indicates that the vTrs was within the range of -40 C to -20 C; the mark "A" indicates that the vTrs was within the range exceeding -20 C and not higher than 0 C; and the mark "x"
indicates that the vTrs was higher than 0 C. In the column "reheat softening resistance", the mark "o" indicates that the decrease in Vickers hardness (Hv) after the reheating mentioned above (that is, 10 hours of heating at 730 C) was smaller than 20% and the mark "x" indicates 20% or larger.
[0049]
[Table 1]
14 'O
N
O
O O p~ C~I OS~ O O
0 r I r r t I I r t Q p O ~ O O O r t q Q~ t r t t r r. t r t r r r ~~a U}N o rnc~~
rn r r t r t t t r~ r t t r r t r N r t t r r r r r t r r r r t t r r V o 0 2 r r t t r t r(i I r I r I r I I t t r r r t r t r t i r r t r r i t r r r r~ r r r r r r r r r(i t(~J r r r r t r t r t r r r r r r ~O M h'o N 'q' r70 N. ~O
v7 cq r I r er t r r I I r~ r W o= r M t t r n r r r t r t r r N LO -O M 10 ~10 N'7 M N O ip~ _O N 00 ~~ N d' [0 O~ dJ 't M a0 O N O't N O O O O Q S S O O O S O O O S~ N ~~ N r S O~ O O
mSggSooooZ5 ooo000000000, 0 0,000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o cq Q, t.n P O r- h M P P P N~ ~~~1O N 1~ t N M~ DO ~ h 10 u) M
OO,~~oopoo,NOOO~ N oN p S g S
EO~ oSSg88$S$oM o, o,o o,o o, o,gg$(g~foo,M M~
b O O O O O O O O O O O O O O O O O O O O O O O O O O O Q p O O O O O
N u) M c0 O. 'O P'O a0 N. u~ N u') O. d' o~ u~ 'o 'o P cD o0 c=) v M y) v 41 .v ~O Y) Q. N10 10 CO M 00 0_O ~.- CO O 1~ ~p u7 'af O 00 r r t tL ~' N N N N'd M N Mv I
Z O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
ai o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C 1~ t~ N N ~ O O, O a0 f~ aD t\ O'-It N~-V' M O N OK O, ~~ O~ N N'~Y oO v) c9 r~ M O
oZ888SgSooMSoooooSoSg8S8$ooooSo 00 N h M 1~ ~O o M O N %O cM "R ~ O NO O OO 00 ~p O10 00 ~-- N P N 00 10 t~ LO
a'~
N~~p N. N. Pp Mp Qp CpV ~~ M 0 OD 0 V v) P O, h N. ~p Mp~pt M N'~t ~) sY M'~
'~ l~7 C'M
00 00, 0 00, 00, 00 00, 00, 00, a O O ~ O O O O 00, 00, 00, 00, 0 00, O, 0 0 0, 0, O O O 0 0 o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -0 C a0 -O 0 O CO v M~ o P O, N N ('') N P O'O M 00 v) N frJ M 06 N CO v) O
C V' M'o ~O 'o 'O P'O u) i, tA c0 N 0 < LO u) M NN LO o- 10 u) 10 N
o000 a o 0 0 0 o o a o 0 0 0 0 0 0 0 o 0 0 0 0 o d o a o 0 0 0 0 0 0 0 0 E~~O ~ P ap P cA O V' N N O~ O~o N N N M N O, t+7 M P*O M N O~ M w) M r+) 'd' u) N
0~-oogoSgooooooooo,ooo,oo o, o,ooooo00000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o p o 0 0 0 o O o 0 0 0 0 o O O o 0 o 0 [O O. N[O %O O. M<f a0 w oD P o0 M O N 93 ~o N h tN N
V M CM') N rM7 v cV
-O ~ c+) N V' M~' M N N~) N o'y M M t+') ul ~) ~') ~'Z O~ o O p O O O O O O O O O O O O O O O O O O O O O O O O O O O O
d O o o O O O O O O O O O 0 00 000000 0 O O O O O 0 O O O P Q
'C P~ N. N L7 M ONO 00 MV 0 a0 N P P P NLO 0 0 P O O% LO N. u7 Ln OLn 10 v7 %U
N.
V.J O N~ N O N O O O N~~~ ~-N ~ 7 ~~ M N N~ O O O O
O O O O O O O O O O O O O O O O O Q O O O O O O O O O O O O O O O O
p u] N P O'O 'O .:r 10 t17 N1D N N C 00 N h 00 OD Q M~O, O N N a N T W~ ~
~--I~ P r(h M O ~ N O c0 P P
N N w'7 M
1t ~ P
C O O b b O O 6 O C) O O O O O C) O C) O O O 0 O C) 0 O O O C) O CD CD O
~ O. M N N O. N'- O N M 00 N I, Co O 0 14 h P1O P W O O N1O M NN.
V a0 ~ N O; O O~o M'a O~ O'~Y O'~t M LO ~ h M t0 h M h OLq O N N N
CV fV N cV ~ N N[V CV N N N N N CV CV N~ CV N N~ N O- r-- ~
~ N N N N N M N N Mp N N N M N N P ' ) N p 'p-- N N N N N LO N
y O O O O O S O O O O O O O S S O O O O S O O O S O O S b O S O O O O
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M M~_ P_ t2 tr) O_ M~O ~ 00 'O P P m VO .- P N u] P~ dLr) r', u') O v) OM O a0 ~' O O O O o O O O O O O O O O O O O O O O O O O O O O O 6 O O O O O O
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
c ~ O st M P'at 00 1~ o '0 h M M O N V'O h O M~ I~ O p .-- h O O 'O =-- 0 N
O N N
N~ O O ~ N N N~ N~~~ M N O C7 ~ O -- Y- N CV ~ N
r O O O O O O C O O O O O O O O O O O O O O O O O O O O O O N 0 C) O C) 2 O O O O O M OO O N O O O O N O M O N O N~ N O N C~~) ~ CPV
O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O o ,o N 10 h~O 1" 10 rp "O N. N. O v) t,o <Y O 'O I" N. h r~ 10 htn N t~ -~t 1O
v) a0 tl') 1~ -C M
U O O O O O O O O O O O O O O O O O O O O O O O O O O O O q p O O O O
O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
- N M ~ h1O f-- w P O~ N M~ tA ~O t~ c0 P O N O N(rJ aL+7 10 h N M'-t p - ~ ~.-- ~.- .- ~.- ~ N N N M M('') M t'') m M M t+') t/7 tr') tr1 z o enIIuenui eni;eaedwoo jeuoi}uanuop .N
.' [0050]
[Table 2]
m c ~~
~gO O O O O O O O O O O O O O O O O O O O O O x x x x x x x x x x x x v ~
-Fd 0 O O O O O O O O O O O O O O O O O O O O O x x x x x x x x O O O 4 w OD ~O p i!l O~O ~ O. V) -O OD ~(h N O~; 40 O~ ~ P'O ~ Cl P'; N M f7 ~
D 10 V- CV D. 04 10 LO N-C O~O P ~r7 ~ ~' h V r~ h N h hQ vj N
~ O~ f, N OD N OO CO 1~ f~ N 1-1 00 f0 h N c0 N 00 I, aD co hLn hof) N
~ N p a S,j H o _ h d p'd; ,p 'D 1~ M h-O CO O f-~ f-% -O a0 OD ID N P O~~=- M N 130 D, .- m f~ NO
D LO O hLO N h N N Ih N i/] LO %G -C h 00 d~ O N N K C ~dO .- ~ 00 - - - - - - r- - r- .- .- - - - -be j W
U i CD~p. M Npp. N~~ O N D ~ O M C~7 np NO~ N n~m N~ a N'NV ~ NN a~O ~~ N~ G~D
N M
m< Nd' r7 M M t~ N') N M C'') e 7 ~ P M ~ N M N vl ~ P~ h N n~ M~ aD
y ~~=-- ~ ~ ~ ~.- - - - r- - - -~~.-N aM LO 'D N aD O~ OO N N ch ~LA h N M st z N N N!'') P') C") V) m P7 C=7 07 u) W) LO v) > m d ~
N C m C
> j a >
G 5 c 0 U
[0051]
As shown in Table 2, all of the inventive steels Nos. 1 to 22 showed a creep rupture time exceeding 10000 hours and were superior to the conventional steels (Nos. 51 to 54) in this respect. As regards the toughness as well, the vTrs was not higher than -20 C and was very excellent.
[0052]
On the other hand, the comparative steels Nos. 30 to 37 had a composition outside the range specified in accordance with the present invention or had a value of BSO represented by the formula (1) outside the range of 0.0001 to 0.010. These were inferior in the reduction of area in the said creep rupture test and reheat softening resistance to the inventive steels and further, they were unsatisfactory in the toughness as well.
INDUSTRIAL APPLICABILITY
[0053]
The steel of the present invention is a low alloy steel usable in a high temperature range up to about 550 C and excellent in long time creep ductility, reheat softening resistance and toughness. This steel is useful as a structural material for high temperature, high pressure operation-aimed electric power plants and the like.
N
O
O O p~ C~I OS~ O O
0 r I r r t I I r t Q p O ~ O O O r t q Q~ t r t t r r. t r t r r r ~~a U}N o rnc~~
rn r r t r t t t r~ r t t r r t r N r t t r r r r r t r r r r t t r r V o 0 2 r r t t r t r(i I r I r I r I I t t r r r t r t r t i r r t r r i t r r r r~ r r r r r r r r r(i t(~J r r r r t r t r t r r r r r r ~O M h'o N 'q' r70 N. ~O
v7 cq r I r er t r r I I r~ r W o= r M t t r n r r r t r t r r N LO -O M 10 ~10 N'7 M N O ip~ _O N 00 ~~ N d' [0 O~ dJ 't M a0 O N O't N O O O O Q S S O O O S O O O S~ N ~~ N r S O~ O O
mSggSooooZ5 ooo000000000, 0 0,000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o cq Q, t.n P O r- h M P P P N~ ~~~1O N 1~ t N M~ DO ~ h 10 u) M
OO,~~oopoo,NOOO~ N oN p S g S
EO~ oSSg88$S$oM o, o,o o,o o, o,gg$(g~foo,M M~
b O O O O O O O O O O O O O O O O O O O O O O O O O O O Q p O O O O O
N u) M c0 O. 'O P'O a0 N. u~ N u') O. d' o~ u~ 'o 'o P cD o0 c=) v M y) v 41 .v ~O Y) Q. N10 10 CO M 00 0_O ~.- CO O 1~ ~p u7 'af O 00 r r t tL ~' N N N N'd M N Mv I
Z O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
ai o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 C 1~ t~ N N ~ O O, O a0 f~ aD t\ O'-It N~-V' M O N OK O, ~~ O~ N N'~Y oO v) c9 r~ M O
oZ888SgSooMSoooooSoSg8S8$ooooSo 00 N h M 1~ ~O o M O N %O cM "R ~ O NO O OO 00 ~p O10 00 ~-- N P N 00 10 t~ LO
a'~
N~~p N. N. Pp Mp Qp CpV ~~ M 0 OD 0 V v) P O, h N. ~p Mp~pt M N'~t ~) sY M'~
'~ l~7 C'M
00 00, 0 00, 00, 00 00, 00, 00, a O O ~ O O O O 00, 00, 00, 00, 0 00, O, 0 0 0, 0, O O O 0 0 o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -0 C a0 -O 0 O CO v M~ o P O, N N ('') N P O'O M 00 v) N frJ M 06 N CO v) O
C V' M'o ~O 'o 'O P'O u) i, tA c0 N 0 < LO u) M NN LO o- 10 u) 10 N
o000 a o 0 0 0 o o a o 0 0 0 0 0 0 0 o 0 0 0 0 o d o a o 0 0 0 0 0 0 0 0 E~~O ~ P ap P cA O V' N N O~ O~o N N N M N O, t+7 M P*O M N O~ M w) M r+) 'd' u) N
0~-oogoSgooooooooo,ooo,oo o, o,ooooo00000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o p o 0 0 0 o O o 0 0 0 0 o O O o 0 o 0 [O O. N[O %O O. M<f a0 w oD P o0 M O N 93 ~o N h tN N
V M CM') N rM7 v cV
-O ~ c+) N V' M~' M N N~) N o'y M M t+') ul ~) ~') ~'Z O~ o O p O O O O O O O O O O O O O O O O O O O O O O O O O O O O
d O o o O O O O O O O O O 0 00 000000 0 O O O O O 0 O O O P Q
'C P~ N. N L7 M ONO 00 MV 0 a0 N P P P NLO 0 0 P O O% LO N. u7 Ln OLn 10 v7 %U
N.
V.J O N~ N O N O O O N~~~ ~-N ~ 7 ~~ M N N~ O O O O
O O O O O O O O O O O O O O O O O Q O O O O O O O O O O O O O O O O
p u] N P O'O 'O .:r 10 t17 N1D N N C 00 N h 00 OD Q M~O, O N N a N T W~ ~
~--I~ P r(h M O ~ N O c0 P P
N N w'7 M
1t ~ P
C O O b b O O 6 O C) O O O O O C) O C) O O O 0 O C) 0 O O O C) O CD CD O
~ O. M N N O. N'- O N M 00 N I, Co O 0 14 h P1O P W O O N1O M NN.
V a0 ~ N O; O O~o M'a O~ O'~Y O'~t M LO ~ h M t0 h M h OLq O N N N
CV fV N cV ~ N N[V CV N N N N N CV CV N~ CV N N~ N O- r-- ~
~ N N N N N M N N Mp N N N M N N P ' ) N p 'p-- N N N N N LO N
y O O O O O S O O O O O O O S S O O O O S O O O S O O S b O S O O O O
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M M~_ P_ t2 tr) O_ M~O ~ 00 'O P P m VO .- P N u] P~ dLr) r', u') O v) OM O a0 ~' O O O O o O O O O O O O O O O O O O O O O O O O O O O 6 O O O O O O
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
c ~ O st M P'at 00 1~ o '0 h M M O N V'O h O M~ I~ O p .-- h O O 'O =-- 0 N
O N N
N~ O O ~ N N N~ N~~~ M N O C7 ~ O -- Y- N CV ~ N
r O O O O O O C O O O O O O O O O O O O O O O O O O O O O O N 0 C) O C) 2 O O O O O M OO O N O O O O N O M O N O N~ N O N C~~) ~ CPV
O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O o ,o N 10 h~O 1" 10 rp "O N. N. O v) t,o <Y O 'O I" N. h r~ 10 htn N t~ -~t 1O
v) a0 tl') 1~ -C M
U O O O O O O O O O O O O O O O O O O O O O O O O O O O O q p O O O O
O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
- N M ~ h1O f-- w P O~ N M~ tA ~O t~ c0 P O N O N(rJ aL+7 10 h N M'-t p - ~ ~.-- ~.- .- ~.- ~ N N N M M('') M t'') m M M t+') t/7 tr') tr1 z o enIIuenui eni;eaedwoo jeuoi}uanuop .N
.' [0050]
[Table 2]
m c ~~
~gO O O O O O O O O O O O O O O O O O O O O O x x x x x x x x x x x x v ~
-Fd 0 O O O O O O O O O O O O O O O O O O O O O x x x x x x x x O O O 4 w OD ~O p i!l O~O ~ O. V) -O OD ~(h N O~; 40 O~ ~ P'O ~ Cl P'; N M f7 ~
D 10 V- CV D. 04 10 LO N-C O~O P ~r7 ~ ~' h V r~ h N h hQ vj N
~ O~ f, N OD N OO CO 1~ f~ N 1-1 00 f0 h N c0 N 00 I, aD co hLn hof) N
~ N p a S,j H o _ h d p'd; ,p 'D 1~ M h-O CO O f-~ f-% -O a0 OD ID N P O~~=- M N 130 D, .- m f~ NO
D LO O hLO N h N N Ih N i/] LO %G -C h 00 d~ O N N K C ~dO .- ~ 00 - - - - - - r- - r- .- .- - - - -be j W
U i CD~p. M Npp. N~~ O N D ~ O M C~7 np NO~ N n~m N~ a N'NV ~ NN a~O ~~ N~ G~D
N M
m< Nd' r7 M M t~ N') N M C'') e 7 ~ P M ~ N M N vl ~ P~ h N n~ M~ aD
y ~~=-- ~ ~ ~ ~.- - - - r- - - -~~.-N aM LO 'D N aD O~ OO N N ch ~LA h N M st z N N N!'') P') C") V) m P7 C=7 07 u) W) LO v) > m d ~
N C m C
> j a >
G 5 c 0 U
[0051]
As shown in Table 2, all of the inventive steels Nos. 1 to 22 showed a creep rupture time exceeding 10000 hours and were superior to the conventional steels (Nos. 51 to 54) in this respect. As regards the toughness as well, the vTrs was not higher than -20 C and was very excellent.
[0052]
On the other hand, the comparative steels Nos. 30 to 37 had a composition outside the range specified in accordance with the present invention or had a value of BSO represented by the formula (1) outside the range of 0.0001 to 0.010. These were inferior in the reduction of area in the said creep rupture test and reheat softening resistance to the inventive steels and further, they were unsatisfactory in the toughness as well.
INDUSTRIAL APPLICABILITY
[0053]
The steel of the present invention is a low alloy steel usable in a high temperature range up to about 550 C and excellent in long time creep ductility, reheat softening resistance and toughness. This steel is useful as a structural material for high temperature, high pressure operation-aimed electric power plants and the like.
Claims (4)
1. A low alloy steel, which comprises by mass percent, C: 0.03 to 0.10%, Si: not more than 0.30%, Mn: not more than 1.0%, Cr: more than 1.5%
to not more than 2.5%, Mo: 0.01 to 1.0%, V: 0.04 to 0.30%, Nb: 0.001 to 0.10%, Ti: 0.001 to 0.020%, B: 0.0001 to 0.020%, Al: 0.001 to 0.01% and Nd: 0.0001 to 0.050%, with the balance being Fe and impurities, wherein the content of P
is not more than 0.020%, the content of S is not more than 0.003%, the content of N is less than 0.0050% and the content of O(oxygen) is not more than 0.0050% among the impurities, in which the value of BSO represented by the following formula (1) is 0.0001 to 0.010:
BSO = B - (11/14)N - (11/32)S - (11/16)O ~~~~~ (1), wherein each element symbol in the formula (1) represents the content (by mass %) of the element concerned.
to not more than 2.5%, Mo: 0.01 to 1.0%, V: 0.04 to 0.30%, Nb: 0.001 to 0.10%, Ti: 0.001 to 0.020%, B: 0.0001 to 0.020%, Al: 0.001 to 0.01% and Nd: 0.0001 to 0.050%, with the balance being Fe and impurities, wherein the content of P
is not more than 0.020%, the content of S is not more than 0.003%, the content of N is less than 0.0050% and the content of O(oxygen) is not more than 0.0050% among the impurities, in which the value of BSO represented by the following formula (1) is 0.0001 to 0.010:
BSO = B - (11/14)N - (11/32)S - (11/16)O ~~~~~ (1), wherein each element symbol in the formula (1) represents the content (by mass %) of the element concerned.
2. A low alloy steel according to claim 1, which further contains W:
not more than 2.0% by mass in lieu of part of Fe.
not more than 2.0% by mass in lieu of part of Fe.
3. A low alloy steel according to claim 1 or 2, which further contains one or more elements selected from among Cu, Ni and Co each at a level not more than 0.50% by mass in lieu of part of Fe.
4. A low alloy steel according to any one of claims 1 to 3, which further contains one or more elements selected from among Mg: not more than 0.005% by mass, Ca: not more than 0.005% by mass, La: not more than 0.02% by mass, Ce: not more than 0.02% by mass, Y: not more than 0.05% by mass, Sm: not more than 0.05% by mass and Pr: not more than 0.05% by mass.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2005120239 | 2005-04-18 | ||
| JP2005-120239 | 2005-04-18 | ||
| PCT/JP2006/308018 WO2006112428A1 (en) | 2005-04-18 | 2006-04-17 | Low alloy steel |
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| Publication Number | Publication Date |
|---|---|
| CA2604428A1 true CA2604428A1 (en) | 2006-10-26 |
| CA2604428C CA2604428C (en) | 2013-07-16 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2604428A Expired - Fee Related CA2604428C (en) | 2005-04-18 | 2006-04-17 | Low alloy steel |
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| Country | Link |
|---|---|
| US (1) | US20080050265A1 (en) |
| EP (1) | EP1873270B1 (en) |
| JP (1) | JP4561834B2 (en) |
| KR (1) | KR100915489B1 (en) |
| CN (1) | CN101163808A (en) |
| CA (1) | CA2604428C (en) |
| WO (1) | WO2006112428A1 (en) |
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| CN112283939A (en) * | 2020-10-14 | 2021-01-29 | 四川省登尧机械设备有限公司 | Novel steam hot air double-coil hot air furnace |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CA2621014C (en) | 2005-09-06 | 2011-11-29 | Sumitomo Metal Industries, Ltd. | Low alloy steel |
| CN102492895B (en) * | 2011-12-24 | 2013-02-13 | 王崇高 | Heat resistant steel for high temperature furnace tube |
| CN103451555A (en) * | 2013-08-02 | 2013-12-18 | 安徽三联泵业股份有限公司 | Stainless steel material for water pump impeller and preparation method thereof |
| CN103667898B (en) * | 2013-11-14 | 2016-01-20 | 安徽荣达阀门有限公司 | A kind of spool gadolinium-containing alloy steel and preparation method thereof |
| CN104195445A (en) * | 2014-09-02 | 2014-12-10 | 青岛永通电梯工程有限公司 | Alloy steel |
| CN104590064B (en) * | 2014-12-23 | 2017-05-10 | 宁波中哲汽车安全系统有限公司 | Automobile child safety seat ISOFIX system |
| CN104791041B (en) * | 2015-05-18 | 2017-11-21 | 嵊州亿源投资管理有限公司 | A kind of cylinder cover of automobile engine |
| CN104895639B (en) * | 2015-05-24 | 2018-03-16 | 新昌县勤勉贸易有限公司 | A kind of high temperature-resistant cylinder exhaust valve group |
| CN106382403A (en) * | 2016-08-30 | 2017-02-08 | 宁波长壁流体动力科技有限公司 | Main valve element of reversing valve |
| CN106286885A (en) * | 2016-08-30 | 2017-01-04 | 宁波长壁流体动力科技有限公司 | A kind of main valve plug for reversal valve |
| CN109266971B (en) * | 2018-11-30 | 2020-10-13 | 武汉大学 | Reheating crack resistant W-containing high-strength low-alloy heat-resistant steel |
| JP2021031771A (en) * | 2019-08-13 | 2021-03-01 | 日本製鉄株式会社 | Low alloy heat-resistant steel and steel pipe |
| CN110923560A (en) * | 2019-12-18 | 2020-03-27 | 陕西易莱德新材料科技有限公司 | Impeller material for enhancing corrosion resistance and preparation method thereof |
| WO2022145062A1 (en) * | 2020-12-28 | 2022-07-07 | 日本製鉄株式会社 | Steel material |
| CN116745450A (en) * | 2020-12-28 | 2023-09-12 | 日本制铁株式会社 | Steel material |
| JPWO2023276297A1 (en) * | 2021-06-28 | 2023-01-05 | ||
| CN113564470B (en) * | 2021-07-16 | 2023-01-17 | 鞍钢股份有限公司 | 1700MPa heat-resistant steel for agricultural machinery and manufacturing method thereof |
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| JP3334217B2 (en) * | 1992-03-12 | 2002-10-15 | 住友金属工業株式会社 | Low Cr ferritic heat resistant steel with excellent toughness and creep strength |
| JP2622516B2 (en) * | 1992-03-25 | 1997-06-18 | 住友金属工業株式会社 | Welding material for heat resistant steel with excellent creep strength |
| JPH09296249A (en) * | 1996-05-02 | 1997-11-18 | Nkk Corp | Chromium-molybdenum steel |
| JP3565331B2 (en) * | 1999-08-18 | 2004-09-15 | 三菱重工業株式会社 | High strength low alloy heat resistant steel |
| JP3518515B2 (en) * | 2000-03-30 | 2004-04-12 | 住友金属工業株式会社 | Low / medium Cr heat resistant steel |
| JP3733902B2 (en) * | 2001-12-27 | 2006-01-11 | 住友金属工業株式会社 | Low alloy ferritic heat resistant steel |
| JP3775371B2 (en) * | 2002-09-18 | 2006-05-17 | 住友金属工業株式会社 | Low alloy steel |
| WO2004111291A1 (en) * | 2003-06-10 | 2004-12-23 | Sumitomo Metal Industries, Ltd. | Steel for hydrogen gas environment, structural hardware member and method for producing same |
-
2006
- 2006-04-17 WO PCT/JP2006/308018 patent/WO2006112428A1/en active Application Filing
- 2006-04-17 KR KR1020077023015A patent/KR100915489B1/en active IP Right Grant
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| CN112283939A (en) * | 2020-10-14 | 2021-01-29 | 四川省登尧机械设备有限公司 | Novel steam hot air double-coil hot air furnace |
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| Publication number | Publication date |
|---|---|
| US20080050265A1 (en) | 2008-02-28 |
| EP1873270A4 (en) | 2009-12-02 |
| JPWO2006112428A1 (en) | 2008-12-11 |
| JP4561834B2 (en) | 2010-10-13 |
| KR100915489B1 (en) | 2009-09-03 |
| CN101163808A (en) | 2008-04-16 |
| EP1873270A1 (en) | 2008-01-02 |
| KR20070110139A (en) | 2007-11-15 |
| CA2604428C (en) | 2013-07-16 |
| WO2006112428A1 (en) | 2006-10-26 |
| EP1873270B1 (en) | 2012-05-30 |
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