EP0225425B1 - Acier faiblement allié présentant une bonne résistance à la corrosion fissurante sous tension - Google Patents

Acier faiblement allié présentant une bonne résistance à la corrosion fissurante sous tension Download PDF

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Publication number
EP0225425B1
EP0225425B1 EP86108534A EP86108534A EP0225425B1 EP 0225425 B1 EP0225425 B1 EP 0225425B1 EP 86108534 A EP86108534 A EP 86108534A EP 86108534 A EP86108534 A EP 86108534A EP 0225425 B1 EP0225425 B1 EP 0225425B1
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Prior art keywords
stress corrosion
corrosion cracking
low alloy
alloy steel
crystal grain
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EP86108534A
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German (de)
English (en)
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EP0225425A2 (fr
EP0225425A3 (en
Inventor
Kazutoshi Shimogori
Kazuo Fujiwara
Kiyoshi Sugie
Kikuo Morita
Takenori Nakayama
Mutsuhiro Miyakawa
Yasushi Torii
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Kobe Steel Ltd
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Kobe Steel 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium

Definitions

  • the invention relates to low alloy steel and more specifically to nickel-chrome-molybdenum steel having good stress corrosion cracking resistance, which material is used for steam turbines or the like.
  • a nickel-chrome-molybdenum steel containing vanadium i.e. a high strength steel
  • a nickel-chrome-molybdenum steel containing vanadium i.e. a high strength steel
  • Such a steel is obtained by adding molybdenum or vanadium which is a fine carbide deposited element to nickel-chrome high strength steel sensitive to temper embrittlement as is known whereby increasing a restraint of softening, that is, a tempering resistance at a high tempering temperature.
  • This steel is well suitable for the above-described use.
  • the GB-PS 1 009 924 describes steel alloys containing C, Cr, Ni, Mo, Nb, V, Mn, Si, Al, P, S, H, N and balance Fe. It is said that this material has good yield strength and tensile strength, ductility, toughness and impact resistance. However, it does not suffice with respect to the a.m. requirements with turbines. It is generally known that intergranular stress corrosion cracking occurs in carbon steels which are subjected to tensile stress and to an environment containing OH.
  • the object of the invention is to provide a nickel-chrome-molybdenum steel which meets the requirements of high stress corrosion cracking resistance even under severe application condition.
  • the low alloy steel of claim 1 i.e. a low alloy steel having good stress corrosion cracking resistance containing
  • S is an element which greatly deteriorates hot processing characteristics, and in view of preventing cracking during hot forging, the upper limit is set to 0.030 % in claims.
  • Ni and Cr are elements indispensable to an increase in strength, improvement of hardenability an enhancement in toughness. Both the elements have each to be added in the amount in excess of 0.50 %. Preferably, Ni and Cr should be added in the amount in excess of 3.25 % and 1.25 %, respectively, in order to win further improvement of hardenability and toughness.
  • the contents of said elements exceed 4.00 % and 2.50 %, respectively, the transformation characteristics are greately varied, and it takes a long time for heat treatment to obtain an excellent toughness, which is therefore impractical.
  • the Ni content and Cr content are limited to the range of 0.50 to 4.00 % and 0.50 to 2.50 %, respectively and 3.25 to 4.00 % and 1.25 to 2.00 %, respectively, in claims 6 and 7.
  • Mo enhances the corrosion resistance of the prior y grain boundary to materially reduce the sensitivity of intergranular stress corrosion cracking, as deposited in grains as a fine carbide during the tempering and greatly contributes to prevention of temper embrittlement and increase in strength.
  • more than 0.25 % of Mo must be added; but when the content thereof exceeds 4.00 %, the aforesaid effects are saturated and the toughness begins to deteriorate.
  • higher addition of Mo as necessary is uneconomical.
  • the Mo content is limited to the range of 0,25 % to 4.00 %.
  • V is an effective element which increases the strength of steel by formation of fine crystals and precipitation hardening .
  • V is added as necessary but when the content thereof exceeds 0.30 %, the effect thereof is saturated, and therefore, in the claims, the upper limit is set to 0.30 %.
  • Si, P and Mn are greatly concerned in the sensitivity of intergranular stress corrosion cracking. They are important elements which should be complementarily limited in relation to the size of crystal grain and a small addition of Ti, At, Nb, W, B Ce and Sn.
  • Si is an element necessary for deoxidation during refining.
  • the content of Si exceeds 0.15 %, the corrosion resistance of the prior y grain boundary deteriorates and the sensitivity or intergranular stress corrosion cracking materially increases. Therefore, in the claims, the upper limit of Si is set to 0.15 %.
  • P is an impurity element which is segregated in the prior y grain boundary to deteriorate the corrosion resistance and to increase the sensitivity of intergranular stress corrosion cracking and to promote temper embrittlement.
  • chrome-molybdenum steel and nickel-chrome-molybdenum steel according to JIS Standards the content thereof is limited to 0.030 % or less in view of temper embrittlement .
  • said content is necessary to be further limited, thus in the claims 1 to 5 the content of P is set to 0.010 % or less.
  • Mn is added for deoxidation and desulfurization during refining.
  • the content of Mn exceeds 0.20 %, the a.m. segregation of grain boundary is promoted and the sensitivity of stress corrosion cracking materially increased; furthermore Si and P compositely act on the stress corrosion cracking, and the range of application thereof is greatly concerned in the size of crystal grains and the small addition of Ti, At, Nb, W, B, Ce and Sn, as is demonstrated by the invention.
  • the sensitivity of stress corrosion cracking also depends on the prior austenite crystal grain size, and sufficient reliability cannot be obtained even if the a.m. alloy composition should be satisfied when the ASTM crystal grain size number is smaller than 3. Accordingly in the present claim 1 the prior austenite crystal grain size number is limited to above 4 in addition to the limitation of the a.m. alloy elements.
  • At, Ti, Nb, Ce, W, B and Sn are addition elements indispensable for enhancement of corrosion resistance of the prior y grain boundary and for great contribution to reduce the sensitivity of stress corrosion cracking of the grain boundary type.
  • these six elements i.e., At, Ti, Nb, Ce, W and B
  • more than one kind of these elements need be added in the amount of 0.001 % or more in total.
  • the Nb addition set to 0.005 % or more is the most effective to reduce the stress corrosion cracking, relating to the limitations of Si + Mn + 20 P 5 0.50 %.
  • the toughness is materially deteriorated.
  • the total amount of addition of these elements is limited to the range of 0.001 to 0.50 %.
  • similar effect to the addition of the aforesaid six elements may be obtained by addition of more than 0.003 % of Sn but when the content thereof exceeds 0.015 %, the temper embrittlement is increased to materially deteriorate the toughness.
  • the content of Sn is limited to the range of 0.003 to 0.015 %.
  • limitation of Mn content and/or range of Si + Mn + 20 P or limitation of size of crystal grains are necessary.
  • NiCrMo steel according to the present invention contains optimum alloy elements having the excellent stress corrosion cracking resistance in the range of an optimum composition ratio and or has an appropriate microstructure (crystal grain size); and therefore, even if said steel is used for members subjected to a high load stress under the corrosion environment such as NaOH, OH- or the like, there is less possibility in producing stress corrosion cracking.
  • Table 1 gives chemical compositions of sample steel used for stress corrosion cracking test and the prior y crystal grain size. These steels were produced by adjusting compositions and melting them in a high frequency induction electric furnace, thereafter making ingots, hot forging them into 25 mm thickness, heating them to a temperature for forming austenite and water quenching them, thereafter heating them up to 620 C and holding them for one hour and then cooling them at a speed of 4°C/min. The crystal grain size was variously varied by adjusting the heating temperature and its holding time. The sample steel thus produced was machined to produce a strip of testpiece of 1.5 mm thickness x 15 mm width x 65 mm length.
  • Table 3 gives chemical composition of sample steel used for stress corrosion cracking test and the prior ⁇ crystal grain size.
  • these steels were produced by adjusting compositions and melting them in a high frequency induction electric furnace, thereafter making ingots, hot forging them into 25 mm thickness, heating them to a temperature for forming austenite and water quenching them, thereafter heating them up to 620° C and holding them for one hour and then cooling them at a speed of 4 0 C/min.
  • the crystal grain size was variously varied by adjusting the heating temperature and its holding time.
  • the sample steel thus produced was machined to produce a strip of testpiece of 1.5 mm thickness x 15 mm width x 65 mm length.
  • the corresponding testpiece was attached to a four-point bending constant load testing apparatus, bending stress corresponding to 60 % or 100 % of 0.2 % proof stress of the steel was applied thereto, the testpiece was immersed in 30 % NaOH aqueous solution at 150°C for one week or three weeks, and thereafter the presence of cracking and the depth of cracking of the testpiece were measured by observation with an optical microscope.
  • Test III which has the most severe testing conditions, only steels corresponding to Nos. 85 to 94, that is, those which are fulfilled with Si + Mn + 20 P ⁇ 0.50 and ASTM crystal grain size number in excess of 4 have no stress corrosion cracking. Thus it is evident that this condition is the most effective embodiment to limit the prevention of stress corrosion craking.

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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)
  • Turbine Rotor Nozzle Sealing (AREA)

Claims (8)

1. Acier faiblement allié possédant une bonne résistance à la corrosion fissurante sous tension contenant les éléments qui suivent :
C : ≦ 0,40%,
Si : ≦ 0,15%,
Mn : ≦ 0,20%,
P : ≦ 0,010%,
S : ≦ 0,030%,
Ni : 0,50 à 4,00%,
Cr : 0,50 à 2,50%,
Mo : 0,25 à 4,00% et
V : ≦ 0,30%,
lesdits Si, Mn et P étant soumis à la relation Si + Mn + 20 P ≦ 0,30%, le reste étant constitué de Fe et d'impuretés inévitables, le calibre du grain de cristal du type austénite préalable étant supérieur de 4 à l'indice du calibre de grain de cristal ASTM.
2. Acier faiblement allié possédant une bonne résistance à la corrosion fissurante sous tension contenant les éléments qui suivent :
C : ≦ 0,40%,
Si : ≦ 0,15%,
Mn : ≦ 0,60%,
P : ≦ 0,010%,
S : ≦ 0,030%,
Ni : ≦ 0,50 à 4,00%,
Cr : 0,50 à 2,50%,
Mo : 0,25 à 4,00% et
V : ≦ 0,30%

et contenant, en outre, au moins l'un des éléments choisis parmi les groupes (i) et (ii) suivants :
(i) au moins un élément choisi parmi AI, Ti, Nb, W, B et Ce : 0,00 1 à 0,50% au total,
(ii) Sn : 0,003 à 0,015%,
lesdits Si, Mn et P étant soumis à la relation Si + Mn + 20 P ≦ 0,75%, le reste étant constitué de Fe et d'impuretés inévitables.
3. Acier faiblement allié possédant une bonne résistance à la corrosion fissurante sous tension contenant les éléments qui suivent
C : ≦ 0,40%,
Si : ≦ 0,15%,
Mn : ≦ 0,60%,
P : ≦ 0,010%,
S : ≦ 0,0 30%,
Ni : 0,50 à 4,00%,
Cr : 0,50 à 2,50%,
Mo : 0,25 à 4,00% et
V : ≦ 0,30%

et contenant, en outre, au moins l'un des éléments choisis parmi les groupes (i) et (ii) suivants :
(i) au moins l'un des éléments choisis parmi AI, Ti, Nb, W, B et Ce : 0,001 à 0,50% au total,
(ii) Sn : 0,003 à 0,015%,
le reste étant constitué de Fe et d'impuretés inévitables, le calibre du grain de cristal du type austénite préalable étant supérieur de 4 à l'indice du calibre de grain de cristal ASTM.
4. Acier faiblement allié possédant une bonne résistance à la corrosion fissurante sous tension contenant les éléments qui suivent
C : ≦ 0,40%,
Si : ≦ 0,15%,
Mn : ≦ 0,60%,
P : ≦ 0,010%,
S : ≦ 0,030%,
Ni : 0,50 à 4,00%,
Cr : 0,50 à 2,50%,
Mo : 0,25 à 4,00% et
V : ≦ 0,30%

et contenant, en outre, au moins l'un des éléments choisis parmi les groupes (i) et (ii) suivants :
(i) au moins l'un des éléments choisi parmi AI, Ti, Nb, W, B et Ce : 0,001 à 0,50% au total,
(ii) Sn : 0,003 à 0,015%,
lesdits Si, Mn et P étant soumis à la relation Si + Mn + 20 P ≦ 0,75%, le reste étant constitué de Fe et d'impuretés inévitables, le calibre du grain de cristal du type austénite préalable étant supérieur de 4 à l'indice du calibre de grain de cristal ASTM.
5. Acier faiblement allié suivant la revendication 2 ou 4, caractérisé en ce que Si, Mn et P sont soumis à la relation Si + Mn + 20 P ≦ 0,50%.
6. Acier faiblement allié suivant les revendication 1 à 5, caractérisé en ce que Ni : 3,25 à 4,00% et Cr : 1,25 à 2,00%.
7. Acier faiblement allié possédant une bonne résistance à la corrosion fissurante sous tension contenant les éléments qui suivent
C : ≦ 0,40%,
Si : ≦ 0,15%,
Mn : ≦ 0,60%,
P : ≦ 0,010%,
S : ≦ 0,030%,
Ni 3,25 à 4,00%,
Cr : 1,25 à 2,00%,
Mo : 0,25 à 4,00%,
V : ≦ 0,30% et
Nb : 0,005 à 0,50%,
lesdits Si, Mn et P étant soumis à la relation Si + Mn + 20 P ≦ 0,50%, le reste étant constitué de Fe et d'impuretés inévitables.
8. Utilisation de l'acier suivant les revendications précédentes pour la confection de turbines à vapeur et analogues.
EP86108534A 1985-11-06 1986-06-23 Acier faiblement allié présentant une bonne résistance à la corrosion fissurante sous tension Expired - Lifetime EP0225425B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP249707/85 1985-11-06
JP60249707A JPS62109949A (ja) 1985-11-06 1985-11-06 耐応力腐食割れ性に優れたＮｉＣｒＭｏ鋼

Publications (3)

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EP0225425A2 EP0225425A2 (fr) 1987-06-16
EP0225425A3 EP0225425A3 (en) 1988-10-05
EP0225425B1 true EP0225425B1 (fr) 1991-08-21

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DE (1) DE3680995D1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102014016073A1 (de) * 2014-10-23 2016-04-28 Vladimir Volchkov Stahl

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63255344A (ja) * 1987-04-13 1988-10-21 Japan Steel Works Ltd:The 超高純度タ−ビンロ−タ軸材
US5383768A (en) 1989-02-03 1995-01-24 Hitachi, Ltd. Steam turbine, rotor shaft thereof, and heat resisting steel
DE69034106T2 (de) * 1989-02-03 2004-06-17 Hitachi, Ltd. Hitzebeständiger Stahl- und Rotorwelle einer Dampfturbine
EP0505085B2 (fr) * 1991-03-20 2003-07-09 Hitachi, Ltd. Acier pour arbre d'induit de machines électriques
JPH04362155A (ja) * 1991-06-10 1992-12-15 Japan Steel Works Ltd:The 高低圧一体型タービンロータ用高純度鋼
FR2748036B1 (fr) * 1996-04-29 1998-05-22 Creusot Loire Acier faiblement allie pour la fabrication de moules pour matieres plastiques
ES2576453T3 (es) * 2007-04-13 2016-07-07 Sidenor Investigación Y Desarrollo, S.A. Acero endurecido y revenido y procedimiento de obtención de piezas de dicho acero
US20130323075A1 (en) * 2012-06-04 2013-12-05 General Electric Company Nickel-chromium-molybdenum-vanadium alloy and turbine component
DE102016005532A1 (de) 2016-05-02 2017-11-02 Vladimir Volchkov Stahl
EP4008801A1 (fr) * 2020-12-01 2022-06-08 CRS Holdings, LLC Alliage d'acier à haute résistance et ayant une forte ténacité à l'impact, article fabriqué à partir de cet alliage et procédé de fabrication associé

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3254991A (en) * 1962-06-29 1966-06-07 Republic Steel Corp Steel alloy and method of making same
US3438822A (en) * 1966-10-31 1969-04-15 United States Steel Corp Method of making fine-grained steel
DE2754524B2 (de) * 1977-12-07 1980-07-03 Jurij Fedorovitsch Leningrad Balandin Stahl
SE442024B (sv) * 1980-08-05 1985-11-25 N Proizv Ob T Mas Proizv Ob Iz Stal

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102014016073A1 (de) * 2014-10-23 2016-04-28 Vladimir Volchkov Stahl

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JPS62109949A (ja) 1987-05-21
DE3680995D1 (de) 1991-09-26
EP0225425A2 (fr) 1987-06-16
EP0225425A3 (en) 1988-10-05

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