CN101163808A - Low alloy steel - Google Patents

Low alloy steel Download PDF

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Publication number
CN101163808A
CN101163808A CNA2006800129779A CN200680012977A CN101163808A CN 101163808 A CN101163808 A CN 101163808A CN A2006800129779 A CNA2006800129779 A CN A2006800129779A CN 200680012977 A CN200680012977 A CN 200680012977A CN 101163808 A CN101163808 A CN 101163808A
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steel
content
quality
low alloy
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五十岚正晃
河野佳织
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Nippon Steel Corp
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Sumitomo Metal Industries Ltd
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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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

A low alloy steel for a heat-resisting structural member being improved in long time creep ductility at high temperatures and temper softening resistance, characterized by comprising, 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: <in-line-formulae description=''In-line Formulae'' end=''lead''>BSO=B-(11/14)N-(11/32)S-(11/16)O (1), <in-line-formulae description=''In-line Formulae'' end=''tail''> wherein each element symbol in the formula ( 1 ) represents the content (by mass %) of the element concerned. The steel may further contain one or more element selected from among W, Cu, Ni, Co, Mg, Ca, La, Ce, Y, Sm and Pr.

Description

Low alloy steel
Technical field
The present invention relates to the outstanding low alloy steel of high temperature creep characteristic and toughness.Low alloy steel of the present invention mainly is suitable for the equipment that at high temperature uses with device etc. with boiler, turbine, atomic energy generating equipment, chemical industry as generating or the heat resistant structure member of machine.
Background technology
Generating is used under high temperature, high pressure with device etc. for a long time with boiler, turbine, atomic energy generating equipment, chemical industry.Therefore, it is outstanding usually to require to be used in intensity at high temperature, erosion resistance, oxidation-resistance and the toughness at normal temperatures etc. of the heat-stable material in these devices.In such use, in the past, (for example use austenite stainless steel always, the SUS321H of JIS, the steel of SUS347H), low alloy steel (for example, the steel of the STBA24 of JIS, promptly, 2.25Cr-1Mo the high Cr ferritic steel that steel), also has 9～12Cr system (for example, the steel of the STBA26 of JIS, that is, and the 9Cr-1Mo steel; The steel of STBA28, that is, and improvement 9Cr-1Mo steel) etc.
In recent years, in steam power plant, to reduce CO in order to prevent global warming 2Deng discharge capacity.Therefore, must improve thermo-efficiency, in boiler, build the novel appts that the steam condition High Temperature High Pressureization (for example, has been surpassed temperature, 300 normal atmosphere of 600 ℃).On the other hand, the many construction in the existing equipment of high development phase welcome planned life in succession, be to upgrade novel appts, still by sectional repair to seek prolongs life, become bigger social concern gradually.This also relates to the problem of Japan Energy policy.
On the other hand, be subjected to the request from deregulation regulation both domestic and external, electric utility is further liberalization also, can pass in and out this field from the enterprise beyond the electric power relation.Consequently, cause the price competition fierceness, aspect generating set, also more more paid attention to economy gradually.
Under background as described above, as a kind of method that reduces the generating set cost, pointed to by making the further high strength of heat resistant structure member that in equipment, uses reduce the steel usage quantity, the high-strength material that meets above-mentioned requirements is just under development.
Under the last lower temperature scope that is limited to about 500 ℃, be extensive use of steel (1Cr-0.5Mo steel), the steel (1.25Cr-0.5Mo steel) of STBA23 and the steel Cr-Mo series low-alloy steel such as (2.25Cr-1Mo steel) of above-mentioned STBA24 of the STBA22 of JIS in the past always.The steel of having replaced a part of Mo in order further to improve hot strength with W is for example also disclosed in the patent documentation 1.In addition, the steel that adds Co and improved hardenability is disclosed in the patent documentation 2.
In new steel as described above, utilize W, Co to improve softening opposing at high temperature, particularly tremendous raising has been arranged at the Primary Steel more in the past of the creep strength more than 500 ℃.But, because high strength, such problem significantly descends toughness variation and long-time creep ductility (elongation, section shrink) therefore to have occurred.
As the steel that prevents from the toughness variation and improved the anti-steel of thermal destruction again, disclose in patent documentation 3 and the patent documentation 4 in the Cr-Mo steel, to add the Ti of denier and nitrogen content is controlled to be denier.In this steel, though improved toughness, fail to realize high creep strength and creep ductility and deposit.And, after welding procedure, carry out the position that SR handles sometimes repeatedly, owing to thermal destruction is again added thermal softening again creep strength is significantly descended.
Low, the middle Cr series heat-resistant steel that has density that is characterized as the precipitate that has limited specific size is disclosed in the patent documentation 5.Though its creep strength height of this steel may not be the composition design of having considered long-time creep ductility, anti-thermal softening characteristic again.
In addition, disclosing Cr content in the patent documentation 6 is 0.40～1.50% low alloy steel.But therefore this steel is surpassing under 500 ℃ the temperature range and may not necessarily fully resist high temperature corrosion because Cr content is very few, and use temperature is restricted.
Patent documentation 1: Japanese kokai publication hei 8-134584 communique
Patent documentation 2: Japanese kokai publication hei 9-268343 communique
Patent documentation 3: Japanese kokai publication hei 8-144010 communique
Patent documentation 4: TOHKEMY 2001-234276 communique
Patent documentation 5: TOHKEMY 2001-342549 communique
Patent documentation 6: TOHKEMY 2004-107719 communique
Summary of the invention
The objective of the invention is to, the heat resistant structure member low alloy steel that improve in the past in generating set etc., uses under the last temperature range that is limited to about 500 ℃ provides and improved the steel that the long-time creep ductility of high temperature and temper softening are resisted, also can be used greatly under the last temperature range that is limited to about 550 ℃.
The inventor is at various heat-resisting creep strain characteristics with low alloy steel, that is, at creep strength and creep ductility and thermal softening characteristic again, probe the chemical constitution of material and the relation between the metallographic structure (microtexture).As a result, obtained following new opinion.
(a) in the Cr-Mo steel, when having replaced a part of Mo, improved creep strength though stablized carbide for more time with W, toughness and creep ductility significantly descend on the contrary.In addition, carbide for example is M 3C, M 7C 3, M 23C 6, M 6The form of C.M is based on Fe and Cr, solid solution the Mo of some amounts and W etc.Along with the increase of Cr amount from M 3C becomes M 7C 3, M 23C 6, M 6C.
(b) when adding Co in the Cr-Mo steel, though hardenability improves along with the increase of Co amount tremendously, heavy addition Co also can equally with W improve creep embrittlement susceptibility.
(c) on the other hand, when in the Cr-Mo steel, adding V, Nb etc., disperse to separate out MC carbide (M with V, Nb have been the main body solid solution a part of Mo) imperceptibly, compare during with independent interpolation Mo, obtained significant precipitation strength effect and improved high temperature creep strength.But creep embrittlement susceptibility still significantly increases.
(d) adding B in the Cr-Mo steel can improve hardenability and effectively improve intensity, toughness.Though this point is known, learn according to inventor's investigation, add excessive B toughness is significantly descended.
(e) inventor found that after further study, suitably change by making B, N, S and O (oxygen) content separately, and to make the BSO value with aftermentioned formula (1) expression is 0.0001～0.010, can improve tremendously creep ductility and again thermal softening resist.In addition, also recognizing also can heavy addition W, B.
The present invention is that the basis makes with above-mentioned opinion, and it will be intended to following low alloy steel.
(1) a kind of low alloy steel, it is characterized in that, in quality %, its composition is: C:0.03～0.10%, below the Si:0.30%, below the Mn:1.0%, Cr: greater than 1.5% and smaller or equal to 2.5%, Mo:0.01%～1.0%, V:0.04～0.30%, Nb:0.001～0.10%, Ti:0.001～0.020%, B:0.0001～0.020%, Al:0.001～0.01%, Nd:0.0001～0.050%, all the other compositions are made of Fe and impurity, P in the impurity is below 0.020%, S is below 0.003%, N is less than 0.0050%, O (oxygen) is below 0.0050%, and the BSO value of representing with following formula (1) is 0.0001～0.010.
BSO＝B-(11/14)N-(11/32)S-(11/16)O ……(1)
Wherein, the symbol of element of formula (1) is the content (quality %) of each element.
(2) low alloy steel of above-mentioned (1) wherein, replaces the part of Fe, also contains the following W of 2.0 quality %.
(3) low alloy steel of above-mentioned (1) or (2) wherein, replaces the part of Fe, also contains 0.50 quality % following Cu, Ni and among the Co more than one respectively.
(4) any low alloy steel in above-mentioned (1)～(3), wherein, a part that replaces Fe also contains among the following Pr of following Sm of 0.005 quality % following Mg, 0.005 quality % following Ca, 0.02 quality % following La, 0.02 quality % following Ce, 0.05 quality % following Y, 0.05 quality % and 0.05 quality % more than one.
Embodiment
Below, the action effect of each composition of low alloy steel of the present invention and the qualification reason of content are described.In addition, " % " expression " quality % " of component content in following record.
C：0.03～0.10％
C is an austenite stabilizer element, can make bainite structure (bottom bainite structure) or martensitic stucture stabilization as this parent phase of Cr-Mo base steel tissue, and forms various carbide and be of value to high strength.If C content is less than 0.03%, the carbide of then separating out is few, can't obtain enough intensity.On the other hand, if C content surpasses 0.10%, then steel significantly hardens and reduces weldability, processibility.The preferred lower limit of C content and the upper limit are respectively 0.04% and 0.08%.
Below the Si:0.30%
Si is used as reductor and uses in system steel operation, can residue in the steel inevitably.In the past, in the steel that the heat resistant structure member is used, added Si energetically as guaranteeing the oxidation-resistance desirable ingredients.But, discover according to the inventor, if the Si that contains as impurity is few, then not only reduce creep embrittlement, can also obtain to reduce thermal embrittlement again and reach the effect of thermal destruction susceptibility again.If Si content is controlled to be below 0.30%, then this effect is remarkable.In addition, even, can use the Cr oxygenating, therefore can not cause negative impact to oxidation-resistance because Si content is controlled to be below 0.30% yet.Making Si content for above reason is below 0.30%.More preferably below 0.15%.
Below the Mn:1.0%
Mn is the same with C to be austenite stabilizer element, very important for the stabilization of bainite structure.But heavy addition Mn can reduce the Ac of steel 1Transformation temperature also can cause thermal embrittlement again.Therefore, making Mn content is below 1.0%.If below 0.30%, then can further improve creep ductility.In addition, the following level that is limited to common impurity of Mn content gets final product.
Cr: greater than 1.5% and smaller or equal to 2.5%
Cr is indispensable for the stabilization of low-carbon (LC) prime system bainite parent phase tissue.In order to obtain this effect, make Cr content surpass 1.5%.Be limited to 1.6% the amount that surpasses under the preferred Cr content.On the other hand, if Cr content surpasses 2.5%, then can make M 7C 3Type, M 23C 6The separating out remarkable increase of type carbide and reduce creep strength.
Mo：0.01～1.0％
Mo is the solution strengthening element, and is of value to M 3C type, M 7C 3Type, M 23C 6The stabilization of type carbide in addition, can form Mo 2C and also be of value to the stabilization of MC type carbide and improve creep strength.In order to obtain above-mentioned effect, making Mo content is more than 0.01%.But if excessive interpolation then can make bainite parent phase or martensite parent phase instability, therefore making the Mo upper content limit is 1.0%.
V：0.04％～0.30％
Because V can form MC type carbide and significantly be of value to the raising creep strength with aftermentioned Nb, therefore contain more than 0.04%.But because excessive interpolation meeting significantly reduces long-time creep ductility, therefore making the V upper content limit is 0.30%.
Nb：0.001％～0.10％
Nb is the same with V can be formed fine carbide and is of value to high strength.Making Nb content in order to obtain this effect is more than 0.001%.On the other hand, if Nb content surpasses 0.10%, then can undermine toughness because of generating excessive charcoal nitride.The lower limit of preferred Nb content and the upper limit are respectively 0.020% and 0.060%.
Ti：0.001～0.020％
Ti can form fine carbide and be of value to high strength.Therefore, contain more than 0.001%.Particularly, improve creep ductility, the embrittlement when inhibition is hot again and the effect of fracture, therefore preferably contain more than 0.010% owing to have.But excessive interpolation meeting brings negative impact to toughness, therefore makes to be limited to 0.020% on it.
B：0.0001～0.020％
B can effectively improve hardenability.Making B content is just to obtain this effect more than 0.0001%.On the other hand, because heavy addition B can bring negative impact to toughness, therefore should make the B upper content limit is 0.020%.Its upper limit is preferably 0.015%, and more preferably 0.012%.In addition, need to be adjusted to the BSO value that makes by above-mentioned formula (1) expression be 0.0001～0.010 to B content.
Nd：0.0001％～0.050％
Nd is for improving the element of long-time creep ductility.In order to obtain this effect, need make Nd content is more than 0.0001%.But because excessive N d can form and diminish the thick inclusion of flexible, therefore making the Nd upper content limit is 0.050%.Preferred Nd content is greater than 0.010% and smaller or equal to 0.050%.
Al：0.001～0.01％
Al is the important element as the reductor of steel.Need to make Al content be more than 0.001% in order to obtain deoxidation effect.On the other hand, make strength and toughness and deposit the aspect consideration from what the invention is intended to, Al content should not surpass 0.01%.
A kind of steel of low alloy steel of the present invention, except above-mentioned each composition, all the other compositions are made of Fe and impurity.But, need the P in the control impurity, S, N and O (oxygen) as following.
Below the P:0.020%, below the S:0.003%, below the O:0.0050%
These elements are the bad impurity that makes the toughness variation of steel.They are respectively below the above-mentioned higher limit, preferably make them few as far as possible.
N: less than 0.0050%
N is the solution strengthening element, and forms the charcoal nitride sometimes and be of value to hot strength, but in the present invention, particularly in order to seek to make creep strength and toughness and to deposit and improve creep ductility, and N content is controlled to be less than 0.0050%.And it is 0.0001～0.010 that N content also needs to be adjusted to the BSO value that makes by above-mentioned formula (1) expression.
BSO：0.0001～0.010
As mentioned above, BSO represents with following formula (1).For improve creep ductility and again thermal softening opposing need to make the BSO value be 0.0001～0.010.
BSO＝B-(11/14)N-(11/32)S-(11/16)O ……(1)
The technical meaning of this BSO is, guarantees that B content makes when at high temperature using steel of the present invention, effectively prevents thickization of charcoal nitride, suppresses grain circle's embrittlement.If the BSO value, then can not be guaranteed effective B amount less than 0.0001, on the other hand,, then can form and diminish the thick inclusion of flexible if greater than 0.010.Therefore, making the BSO value is 0.0001～0.010.Be limited to 0.001 under the preferred BSO.
The another kind of steel of low alloy steel of the present invention on the basis of mentioned component, also contains the composition of selecting more than a kind from W, Cu, Ni, Co, Mg, Ca, La, Ce, Y, Sm and Pr.State the action effect of these compositions and the qualification reason of content below.
Below the W:2.0%
When desiring further to improve the long-time creep strength of high temperature, add W.As mentioned above, in the past, heavy addition W can cause thermal embrittlement again and improve fracture susceptibility, still, was in the steel in 0.0001～0.010 scope making the BSO value, reached 2.0% W and also above-mentioned disadvantage can not occur even contain.In addition, W also is of value to the raising creep ductility.Make this reliable for effect, preferably contain more than 0.20%.
Cu, Ni, Co: each is below 0.50%
These elements are austenite stabilizer element, are of value to the stabilization of bainite or martensitic stucture.Make this reliable for effect, preferably respectively contain the content more than 0.01%.But,, then need carry out the softening thermal treatment of over-drastic etc. sometimes because hardness of steel is too high if respectively surpass 0.50%.Therefore, when adding these compositions, content separately should terminate in 0.50%.
Mg, Ca: each is below 0.005%, and La, Ce: each is below 0.02%, and Y, Sm, Pr: each is below 0.05%
Because these elements have the effect that prevents to solidify fracture when cast steel, therefore contain as required.If these elements surpass above-mentioned higher limit, then all can bring negative impact to toughness.In addition, make additive effect reliable, preferably make them be content more than 0.0001%.
Steel of the present invention is implemented " normalizing-tempering " thermal treatment and is used after being processed into pipe, plate etc.This heat treatment on microstructure is the tissue based on tempering bainite or tempered martensite.
Embodiment
Below, utilize embodiment to specify effect of the present invention.
With each 150kg of steel of chemical constitution shown in the vacuum induction melting stove melting table 1, ingot casting, then make the plate tensile sample of thick 25mm * wide 100mm by forge hot.Then,, carry out water-cooled after keeping 1 hour, tempering temperature is changed and to heat 1 hour laggard line space of maintenance cold in 720～760 ℃ scope at 950 ℃ as normalizing treatment.All steel have all become tempering bainite tissue or tempered martensite.
To a part of sample after the above-mentioned thermal treatment, further, estimated again the thermal softening opposing in the variation with investigation hardness in 10 hours of 730 ℃ of reheat.
Cut the Charpy bar of the band 2V breach of the creep rupture sample of diameter 6mm, GL30mm and 10mm * 10mm * 5mm from the gained sample.Under the condition of 550 ℃ of temperature, bearing strength test 200MPa, implement repture test, under-60 ℃～60 ℃ temperature range, implemented Charpy impact test.Above-mentioned test-results is shown in Table 2.
In table 2, the ◎ in " toughness " hurdle represents that vTrs is lower than-40 ℃ temperature, and zero expression vTrs be-40 ℃～-20 ℃ scopes, and △ represents that vTrs is greater than-20 ℃ and smaller or equal to 0 ℃ scope, * represent that vTrs is higher than 0 ℃ temperature.In addition, in " the anti-opposing of thermal softening again " hurdle, zero expression is through above-mentioned reheat (730 ℃ of heating 10 hours), and the decline of Vickers' hardness (Hv) is less than 20%, and the decline of * expression Vickers' hardness (Hv) is more than or equal to 20%.
Table 1
Table 1
Distinguish No. Chemical constitution (quality %, all the other compositions: Fe and impurity)
C Si Mn P S Cr Mo V Nb Ti B Ai N Nd O BSO W Cu Ni Co Other
Steel of the present invention 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 0.08 0.07 0.08 0.07 0.08 0.07 0.06 0.08 0.08 0.07 0.07 0.06 0.05 0.05 0.04 0.06 0.08 0.07 0.07 0.05 0.07 0.08 0.15 0.07 0.08 0.07 0.06 0.06 0.13 0.03 0.11 0.07 0.04 0.12 0.21 0.02 0.06 0.11 0.03 0.09 0.12 0.05 0.13 0.06 - 0.11 0.20 0.04 0.21 0.13 0.29 0.24 0.28 0.07 0.05 0.10 0.27 0.23 0.28 0.10 0.22 0.14 0.16 0.17 0.30 0.23 0.003 0.013 0.011 0.019 0.015 0.005 0.010 0.013 0.018 0.014 0.018 0.008 0.009 0.009 0.008 0.004 0.018 0.001 0.018 0.002 0.005 0.019 0.001 0.002 0.002 0.002 0.002 0.002 0.003 0.002 0.002 0.003 0.002 0.002 0.001 0.002 0.001 0.001 0.001 0.003 0.001 0.002 0.002 0.003 1.81 2.11 2.28 1.93 2.07 2.07 1.89 2.32 2.41 2.20 2.02 2.13 2.28 2.02 2.47 2.08 2.40 2.30 1.58 2.17 1.59 2.36 0.35 0.71 0.72 0.19 0.10 0.98 0.78 0.94 0.16 0.35 0.32 0.08 0.67 0.82 0.04 0.88 0.27 0.27 0.98 0.88 0.80 0.43 0.19 0.11 0.27 0.22 0.05 0.23 0.10 0.28 0.18 0.23 0.04 0.20 0.08 0.07 0.19 0.09 0.28 0.12 0.15 0.10 0.20 0.19 0.048 0.038 0.032 0.026 0.046 0.039 0.043 0.034 0.028 0.028 0.058 0.023 0.034 0.039 0.038 0.058 0.050 0.057 0.022 0.054 0.041 0.047 0.016 0.017 0.009 0.018 0.008 0.008 0.018 0.014 0.012 0.012 0.020 0.011 0.010 0.008 0.012 0.007 0.017 0.013 0.007 0.009 0.015 0.013 0.0048 0.0038 0.0060 0.0060 0.0088 0.0064 0.0071 0.0073 0.0046 0.0071 0.0096 0.0089 0.0041 0.0059 0.0072 0.0051 0.0082 0.0073 0.0082 0.0049 0.0050 0.0058 0.0018 0.0072 0.0077 0.0083 0.0037 0.0048 0.0020 0.0013 0.0040 0.0032 0.0081 0.0046 0.0053 0.0041 0.0080 0.0082 0.0056 0.0078 0.0018 0.0031 0.0048 0.0038 0.0017 0.0027 0.0002 0.0027 0.0041 0.0020 0.0019 0.0030 0.0038 0.0037 0.0028 0.0047 0.0030 0.0044 0.0032 0.0021 0.0004 0.0043 0.0010 0.0032 0.0009 0.0009 0.0481 0.0252 0.0185 0.0223 0.0188 0.0168 0.0288 0.0238 0.0488 0.0178 0.0137 0.0185 0.0342 0.0255 0.0119 0.0144 0.0124 0.0488 0.0375 0.0106 0.0136 0.0369 0.0015 0.0009 0.0010 0.0011 0.0015 0.0013 0.0019 0.0039 0.0009 0.0002 0.0031 0.0020 0.0012 0.0023 0.0028 0.0041 0.0041 0.0034 0.0016 0.0014 0.0038 0.0010 0.0021 0.0002 0.0045 0.0024 0.0018 0.0032 0.0033 0.0016 0.0003 0.0030 0.0048 0.0011 0.0008 0.0002 0.0024 0.0003 0.0047 0.0008 0.0060 0.0007 0.0010 0.0032 1.40 - - 1.63 1.55 0.86 - - - 1.42 - - - - - - 1.44 - 1.88 1.97 - 1.36 - - - - - - 0.16 - - - - - - - - - 0.37 - 0.21 - - - - - - - - - - 0.36 - - - - - - - - 0.14 - - - - 0.12 - - - - - - - - 0.44 - - - - - - - 0.25 - - - - - - - - - - - - - - - - Mg:0.0034 Ca:0.0032 La:0.0058 Co:0.0184 Y:0.0122 Sm:0.0050 Pr:0.0428 - Mg:0.0031.La:0.0026 - Mg:0.0024 Mg:0.0005 Sm:0.0441
Comparative steel 30 31 32 33 34 35 36 37 0.07 0.05 0.07 0.07 0.04 0.03 0.05 0.08 0.21 0.25 0.08 0.27 0.15 0.29 0.07 0.11 0.11 0.07 0.30 0.10 0.01 0.11 0.17 0.20 0.014 0.004 0.005 0.017 0.015 0.020 0.016 0.010 0.002 0.001 0.001 0.001 0.002 0.002 0.001 0.002 1.88 1.58 2.11 1.15 2.30 1.70 2.02 0.56 0.07 0.03 0.23 1.12 0.38 0.26 0.97 0.81 0.10 0.19 0.15 0.17 0.35 0.25 0.20 0.15 0.047 0.038 0.046 0.027 0.051 - 0.057 0.020 0.019 0.015 0.013 0.012 0.019 0.013 0.025 0.013 0.0033 0.0121 0.0078 0.0055 0.0092 0.0063 0.0053 0.0068 0.0020 0.0048 0.0058 0.0001 0.0048 0.0089 0.0012 0.0038 0.0024 0.0005 0.0029 0.0022 0.0002 0.0014 0.0008 0.0055 0.0178 0.0218 0.0583 0.0354 0.0443 0.0415 0.0304 0.0481 0.0037 0.0004 0.0041 0.0032 0.0043 0.0025 0.0048 0.0025 -0.0018 0.0111 0.0024 0.0012 0.0054 0.0028 0.0010 0.0001 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Existing steel 51 52 53 54 0.05 0.07 0.08 0.03 0.26 0.35 0.40 0.29 0.20 0.26 0.11 0.20 0.014 0.013 0.010 0.018 0.002 0.002 0.005 0.002 1.03 1.22 1.24 1.27 0.50 0.47 0.50 0.50 0.06 0.05 0.08 0.07 0.031 0.033 0.025 0.033 0.015 0.014 0.015 0.012 0.0022 0.0018 0.0015 0.0010 0.0048 0.0047 0.0035 0.0033 0.0058 0.0047 0.0043 0.0020 - - - - 0.0025 0.0026 0.0025 0.0023 -0.0048 -0.0044 -0.0053 -0.0028 - - - - - - - - - - - - - - - - - - - -
Table 2
Distinguish No. Repture test (550 ℃, 200MPa) Toughness The anti-opposing of thermal softening again
Rupture time (h) Elongation (96) Section shrinks (96)
Steel of the present invention 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 14204 12918 11934 12092 13822 11749 14280 13185 13960 13200 13238 12137 13074 13807 13724 11974 13575 13318 13923 11665 12196 13523 17.4 16 17.6 17.7 17.3 16.7 15.6 16.2 17.8 15.0 17.7 15.7 17.6 17.8 17.1 17.8 15.8 15.1 16.2 16.2 17.9 18.0 74.8 77.4 71.6 76.1 80.0 74.5 82.0 80.6 79.1 72.9 78.5 75.6 82.8 86.7 71.4 70.7 85.1 78.3 83.1 75.2 81.0 84.4 ◎ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
Comparative steel 30 31 82 33 34 35 36 37 12242 5166 7628 11879 7286 5869 11255 7325 6.3 11.1 10.1 6.3 12.2 12.8 7.8 6.1 47.8 44.8 57.1 47.8 52.6 41.1 55.3 57.3 × × × × × × × × × × × × × × × ×
Existing steel 51 52 53 54 8413 3988 5012 8139 5.3 6.7 10.2 8.5 6.7 5.3 7.3 22.7 ○ ○ ○ △ × × × ×
As shown in table 2, the creep fracture time of the steel of the present invention of No.1～22 has all surpassed 10,000 hours, has surpassed existing steel (NO.51～54).In addition, aspect toughness,, then fabulous if vTrs is below-20 ℃.
On the other hand, the comparative steel of No.30～37 or departed from the present invention fixed compositing range, or be outside 0.0001～0.010 scope with the BSO value of formula (1) expression.Their creep rupture section shrinks with anti-the thermal softening resistivity is all poor than steel of the present invention again, and toughness is also bad.
Utilizability on the industry
Steel of the present invention is used in the high temperature range that is limited to about 550 ℃, and its long-time creep ductility, thermal softening repellence and toughness are outstanding again. The structural material of the generating equipment that this steel turns round as the sensing HTHP etc. is useful.

Claims (4)

1. low alloy steel, it is characterized in that, in quality %, its composition is: C:0.03～0.10%, below the Si:0.30%, below the Mn:1.0%, Cr: greater than 1.5% and smaller or equal to 2.5%, Mo:0.01%～1.0%, V:0.04～0.30%, Nb:0.001～0.10%, Ti:0.001～0.020%, B:0.0001～0.020%, Al:0.001～0.01%, Nd:0.0001～0.050%, all the other compositions are made of Fe and impurity, P in the impurity is below 0.020%, S is below 0.003%, N is less than 0.0050%, O (oxygen) is below 0.0050%, and, BSO value with following formula (1) expression is 0.0001～0.010
BSO＝B-(11/14)N-(11/32)S-(11/16)O ……(1)
Wherein, the symbol of element of formula (1) is the content (quality %) of each element.
2. low alloy steel according to claim 1 wherein, replaces the part of Fe, also contains the following W of 2.0 quality %.
3. low alloy steel according to claim 1 and 2 wherein, replaces the part of Fe, also contains 0.50 quality % following Cu, Ni and among the Co more than one respectively.
4. according to each described low alloy steel in the claim 1～3, wherein, a part that replaces Fe also contains among the following Pr of following Sm of 0.005 quality % following Mg, 0.005 quality % following Ca, 0.02 quality % following La, 0.02 quality % following Ce, 0.05 quality % following Y, 0.05 quality % and 0.05 quality % more than one.
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