WO1988002032A1 - Ferritic-austenitic stainless steel and a heat treatment process for precipitation hardening of the steel - Google Patents
Ferritic-austenitic stainless steel and a heat treatment process for precipitation hardening of the steel Download PDFInfo
- Publication number
- WO1988002032A1 WO1988002032A1 PCT/SE1987/000387 SE8700387W WO8802032A1 WO 1988002032 A1 WO1988002032 A1 WO 1988002032A1 SE 8700387 W SE8700387 W SE 8700387W WO 8802032 A1 WO8802032 A1 WO 8802032A1
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- atom
- max
- steel
- ageing
- impurities
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Classifications
-
- 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
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/02—Hardening by precipitation
Definitions
- Ferritic-austenitic stainless steeland a heat treatment process for precipitation hardening of the steel
- the present invention relates to a precipitation hardening ferriticaustenitic stainless steel with very high strength, good ductility and impact strength, as well as good resistance to general and intercrystalline corrosion.
- Grade SIS 2324 which contains about 0.1 % C , 26 % Cr, 5 % Ni and 1.5 % Mo , is an example of this type of steels. This steel' is used for many applications where high demands upon corrosion resistance are raised, and in comparison with conventional austenitic stainless steel this steel grade also has a high strength. Often, however, there is a strong demand for a steel with even higher strength than that of Grade SIS 2324 in combination with good ductility and impact strength as well as good corrosion resistance.
- Precipitation hardening is a frequently used method for providing such increased strength.
- the steel has a suitable alloy composition and that a suitable ageing treatment is performed.
- the ageing treatment which conventionally is performed at a rather low temperature, usually follows after a solution heat treatment at a high temperature.
- ferritic-austenitic steels of the type: appr. 20 % Cr, appr. 6 % Ni, appr. 2 % Mo, etc., if the content of Si is increased to appr. 2%, and if Nb or Ti is added to the steel to bind C and N, and if the steel is solution treated at 1050-1150°C and subsequently aged at 500-700°C.
- the hot working characteristics can be favourable if the composition of the steel in other respects is properly balanced and if the content of impurities is kept at a relatively low level.
- the present steel therefore represents something novel and is considered to satisfy an important need on the market concerning castings as well as forged products.
- the present invention thus could be defined as a method of providing a corrosion resistant ferritic-austenitic steel with hight strength and toughness as well as good production features, characterized therein, that the steel has the following composition expressed in weight percent:
- Mn max 5.0 preferably max 2.5, however, suitably max 2.0 Cr 18.0-26.0, preferably 18.0-24.0, however, suitably 18.0-22.0
- Mo 1.0-4.0 preferably 1.5-3.5, however, suitably 1.5-3.0
- Ti max 1.5 preferably max 1.0, however, suitably max 0.5 balance iron and impurities and accessory components normal for this type of steel and wherein (atom % Nb + atom % Ti) ⁇ atom % C, preferably ⁇ (atom % C + atom % N).
- the steel of the invention shall be solution heat treated at 1000-1200°C and aged at 400-700°C.
- the ageing treatment advantageously may be divided into a pre-ageing at 400-500°C and a final ageing at 500-700°C.
- Tables 1 and 2 relate to investigations concerning a number of steels referred to as 1-4, which were studied in their as cast conditions.
- the tables show examples of a high Si-content ( > 1 %) as defined by the composition limits of the claims as well as defined above, and the examples also illustrate the precondition that the steel should be stabilized by Nb or Ti.
- steels 3 and 4 fall within the ranges as defined for the invention.
- This steel had excellent hot working characteristics and could readily be forged to desired dimensions without any tendencies to cracking.
- the steel was examined in a series of different conditions of heat treatment and thicknesses of the test specimens. For a thickness of 60 mm the following characteristics were obtained:
- KU impact strengths in joules using U-specimen according to Charpy method.
- the precipitation hardening effect could be increased with appr. 50 MPa.
- the steel has in the above mentioned conditions of heat treatments been found to have a good resistance to intercrystalline corrosion during tests in boiling NaCl-solution saturated with AgCl and Ca(OH) 2 . Also other corrosion features were good.
- the steel has a comparatively simple composition, is easy to manufacture and can be heat treated, in conventional heat treatment ovens.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
Stainless ferritic-austenitic steel with very high strength, good ductility and impact strength as well as good resistance to general and intercrystalline corrosion. The steel has the following composition expressed as weight percent: C max 0.04; Si 1.5-2.5; Mn max 2.0; Cr 18.0-22.0; Ni 4.0-8.0; Mo 1.5-3.0; Nb max 1.0; Ti max 0.5; balance iron and impurities and accessory components normal for this type of steel and wherein (atom % Nb + atom % Ti) atom % C, preferably (atom % C + atom % N). The steel is precipitation hardened through solution heat treatment at 1000-1200° C and ageing at 500-700° C, preferably subsequent to pre-ageing at 400-500° C prior to final ageing at 500-700° C.
Description
Ferritic-austenitic stainless steeland a heat treatment process for precipitation hardening of the steel.
The present invention relates to a precipitation hardening ferriticaustenitic stainless steel with very high strength, good ductility and impact strength, as well as good resistance to general and intercrystalline corrosion.
it is a characteristic feature of ferritic-austenitic high chromium steels that they have very good corrosion resistance also in aggressive environments. Grade SIS 2324, which contains about 0.1 % C , 26 % Cr, 5 % Ni and 1.5 % Mo , is an example of this type of steels. This steel' is used for many applications where high demands upon corrosion resistance are raised, and in comparison with conventional austenitic stainless steel this steel grade also has a high strength. Often, however, there is a strong demand for a steel with even higher strength than that of Grade SIS 2324 in combination with good ductility and impact strength as well as good corrosion resistance.
Precipitation hardening is a frequently used method for providing such increased strength. In order to achieve the finely dispersed precipitation which is necessary for the desired increase of strength it is a prerequisite that the steel has a suitable alloy composition and that a suitable ageing treatment is performed. The ageing treatment, which conventionally is performed at a rather low temperature, usually follows after a solution heat treatment at a high temperature.
As far as the above mentioned high chromium ferritic-austenitic steels of type SIS 2324 are concerned, it has, however, turned out to be difficult to perform the precipitation hardening with satisfactory results. If the ageing treatment is performed at a temperature between about 400°C and 525°C the well-known, so called 475°C-embrittlement will occur, and if the ageing treatment is performed between 700°C and 850°C embrittlement will also occur through precipitation of σ -phase.
Therefore, it is difficult in practice to perform the ageing treatment in the above mentioned temperature ranges without avoiding an unacceptable reduction of the impact strength. Also, ageing treatments between the temperatures 525°C and 700°C are inconvenient because of the fact that ageing treatments between 500°C and 750°C very quickly cause that the susceptibility to intercrystalline corrosion will be unacceptably high.
During the recent 15 years, however, various precipitation hardening ferritic-hardening stainless steels have been suggested in the technical literature and in patent applications. By way of example it has turned out to be possible to some extent to make use of the 475°C- embrittlement for precipitation hardening if the content of austenite is maintained sufficiently high. Precipitation hardening with Cu and Al is also possible as well as with Be. For articles exposed to wear it ha,s even Been possible to utilize σ -phase for the purpose of precipitation hardening. Presipitation hardening with austenite or ferrite has also been suggested, e.g. in the U.S. patent No. 4 353 755. So far, however, any commercially feasible steel has not been launched as a result from these works. The primary reason for this is an unfavourable combination of features of the steel, or susceptibility to cracking during forging, or will the steels require a solution heat treatment temperature which from a practical point of view is unrealistic ( > 1200°C).
During the search for a high strength ferritic austenitic steel with good corrosion characteristics it has now, however, quite surprisingly been found possible to achieve these features by ferritic-austenitic steels of the type: appr. 20 % Cr, appr. 6 % Ni, appr. 2 % Mo, etc., if the content of Si is increased to appr. 2%, and if Nb or Ti is added to the steel to bind C and N, and if the steel is solution treated at 1050-1150°C and subsequently aged at 500-700°C. Further, the hot working characteristics can be favourable if the composition of the steel in other respects is properly balanced and if the content of impurities is kept at a relatively low level. The present steel
therefore represents something novel and is considered to satisfy an important need on the market concerning castings as well as forged products.
The present invention thus could be defined as a method of providing a corrosion resistant ferritic-austenitic steel with hight strength and toughness as well as good production features, characterized therein, that the steel has the following composition expressed in weight percent:
C as low as possible, however, max 0.10, preferably max 0.06, suitably max 0.04
Si 1.0-3.0, preferably between 1.5 and 2.5
Mn max 5.0, preferably max 2.5, however, suitably max 2.0 Cr 18.0-26.0, preferably 18.0-24.0, however, suitably 18.0-22.0
Ni 4.0-10.0, preferably 4.0-8.0
Mo 1.0-4.0, preferably 1.5-3.5, however, suitably 1.5-3.0
Nb max 2.0, preferably max 1.5, however, suitably max 1.0
Ti max 1.5, preferably max 1.0, however, suitably max 0.5 balance iron and impurities and accessory components normal for this type of steel and wherein (atom % Nb + atom % Ti) ≥ atom % C, preferably ≥ (atom % C + atom % N).
Further the steel of the invention shall be solution heat treated at 1000-1200°C and aged at 400-700°C. The ageing treatment advantageously may be divided into a pre-ageing at 400-500°C and a final ageing at 500-700°C.
The invention has been defined in the accompanying claims and will now be further illustrated through the following examples.
EXAMPLE 1
Tables 1 and 2 relate to investigations concerning a number of steels referred to as 1-4, which were studied in their as cast conditions. The tables show examples of a high Si-content ( > 1 %) as defined by
the composition limits of the claims as well as defined above, and the examples also illustrate the precondition that the steel should be stabilized by Nb or Ti. Thus steels 3 and 4 fall within the ranges as defined for the invention.
Solution heat treatment from 1200°C gave appr. 5-15 Brinell units higher hardness, while solution heat treatment from 1000°C or lower gave relatively unsignificant precipitation hardening effect in all the steels. A pre-ageing at appr. 475°C followed by a final ageing at 600°C was found to be very favourable from precipitation hardening point of view. For steels 3 and 4 hardnesses up to 350 Brinell could be achieved by such double-ageing.
EXAMPLE 2
In order more carefully to investigate the features of a steel according to the present concept there was manufactured a steel having the following composition:
c Si Mn Cr Ni Mo Ti N
0.03 2.0 0.6 19.5 6.0 2.0 0.37 0.04
This steel had excellent hot working characteristics and could readily be forged to desired dimensions without any tendencies to cracking. The steel was examined in a series of different conditions of heat treatment and thicknesses of the test specimens. For a thickness of 60 mm the following characteristics were obtained:
Heat Treatment KU
Rp0.2 A5 MPa % J
1125°C, water + 550°C 750 19 49 " + 575°C 720 20 32 " + 600°C 690 20 25
1050°C, water + 550°C 720 22 45 " + 600°C 660 28 41
Rp0.2 = 0.2 proof stress
A5 = elongation, (fracture bending) in tensile test with gauge length L = 5d for circular cross section or general gauge length of L = 5.65 A. Both diameter d and cross sectional area A refer to original dimensions.
KU = impact strengths in joules using U-specimen according to Charpy method.
By pre-ageing at by way of example 475°C prior to final ageing at 550-600°C the precipitation hardening effect could be increased with appr. 50 MPa.
For a thickness of 25 mm of the test specimen there was measured 20-50 MPa higher yield strength than above mentioned, while the yield strength for a 200 mm thickness of the test specimen was estimated to lie 20-50 MPa below the above mentioned values with reference to simulated heat treatment experiments.
The steel has in the above mentioned conditions of heat treatments been found to have a good resistance to intercrystalline corrosion during tests in boiling NaCl-solution saturated with AgCl and Ca(OH)2. Also other corrosion features were good.
Through the present invention it has thus been provided a steel with very interesting features for the future. The steel has a comparatively simple composition, is easy to manufacture and can be heat treated, in conventional heat treatment ovens.
Claims
1. Method for providing a corrosion resistant ferritic-austenitic steel with high strength and toughness as well as good manufacturing characteristics, c h a r a c t e r i z e d in that the steel has the following composition expressed in weight percent:
C max 0.10
Si 1.0- 3.0
Mn max 5.0
Cr 18.0-26.0
Ni 4.0-10.0
Mo 1.0- 4.0
Nb max 2.0
Ti max 1.5
balance iron and impurities and accessory components normal for this type of steel arid wherein (atom % Nb + atom % Ti) ≥ atom % C, preferably ≥ (atom % C + atom % N) .
2. Method according to claim 1, c h a r a c t e r i z e d in that the steel is solution heat treated at 1000-1200°C and aged at 500-700°C.
3. Method according to claim 1 and 2, c h a r a c t e r i z e d in that it is pre-aged at 400-500°C prior to final ageing at 500-700°C.
4. Method according to claim 1, c h a r a c t e r i z e d in that the composition of the steel expressed in weight percent is
c max 0.06
Si 1.5- 2.5
Mn max 2.5
Cr 18.0-24.0
Ni 4.0- 8.0
Mo 1.5- 3.5
Nb max 1.5
Ti max 1.0
balance iron and impurities and accessory components normal for this type of steel and wherein (atom % Nb + atom % Ti) ≥ atom % C, preferably ≥ (atom % C + atom % N) .
5. Method according to claims 1-4, c h ar a c t e r i z e d in that the composition of the steel expressed in weight percent is
c max 0.04
Si 1.5- 2.5
Mn max 2.0
Cr 18.0-22.0
Ni 4.0- 8.0
Mo 1.5- 3.0
Nb max 1.0
Ti max 0.5
balance iron and impurities and accessory components normal for this type of steel and wherein (atom % Nb + atom % Ti) ≥ atom % C, preferably ≥ (atom % C + atom % N).
6. Stainless ferritic-austenitic steel with very high strength, good ductility and impact strength as well as good resistance to general as well as intercrystalline corrosion, c h a r a c t e r i z e d in that it has the following composition expressed in weight percent
C max 0.04
Si 1.5- 2.5
Mn max 2.0
Cr 18.0-22.0
Ni 4.0- 8.0
Mo 1.5- 3.0
Nb max 1.0
Ti max 0.5
balance iron and impurities and accessory components normal for this
type of steel and wherein (atom % Nb + atom % Ti) ≥ atom % C, preferably ≥ (atom % C + atom % N).
7. Steel according to claim 6, c h a r a c t e r i z e d in that it contains max 0.1 N.
8. Steel according to claim 6 or 7, c h a r a c t e r i z e d in that it has a structure obtained through precipitation hardening through solution heat treatment at 1000-1200°C and ageing at 500-700°C.
9. Steel according to claim 8, c h a r a c t e r i z e d in that it has been pre-aged at 400-500°C prior to final ageing at 500-700°C.
10. Steel according to claim 8 or 9, c h a r a c t e r i z e d in that it has the following nominal composition:
C 0. .01 - 0.03
Si 2.0
Mn max 2.0
Cr 20
Ni 6
Mo 2
(Ti + 0.3 - 0.5
N max 0.1
balance iron, impurities and accessory components in normal amounts.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19873790573 DE3790573T1 (en) | 1986-09-12 | 1987-09-01 | CORROSION-FREE FERRITIC-AUSTENITIC STEEL AND HEAT TREATMENT METHOD FOR HARDENING THE STEEL |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE8603811-4 | 1986-09-12 | ||
| SE8603811A SE453837B (en) | 1986-09-12 | 1986-09-12 | PROCEDURE FOR EXCELLENCE CURE OF A FERRIT-AUSTENITIC STAINLESS STEEL |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO1988002032A1 true WO1988002032A1 (en) | 1988-03-24 |
Family
ID=20365553
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/SE1987/000387 WO1988002032A1 (en) | 1986-09-12 | 1987-09-01 | Ferritic-austenitic stainless steel and a heat treatment process for precipitation hardening of the steel |
Country Status (4)
| Country | Link |
|---|---|
| AT (1) | AT395018B (en) |
| AU (1) | AU7913587A (en) |
| SE (1) | SE453837B (en) |
| WO (1) | WO1988002032A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0576802A1 (en) * | 1992-07-01 | 1994-01-05 | SHINKO WIRE COMPANY, LTD., also known as SHINKO KOSEN KOGYO KABUSHIKI KAISHA | Two-phase stainless steel wire rope having high fatigue resistance and corrosion resistance |
| WO1994004714A1 (en) * | 1992-08-24 | 1994-03-03 | Crs Holdings, Incorporated | Corrosion resistant austenitic stainless steel with improved galling resistance |
| EP0659896A1 (en) * | 1993-12-20 | 1995-06-28 | Shinko Kosen Kogyo Kabushiki Kaisha | Stainless steel wire product |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1089824A (en) * | 1964-01-29 | 1967-11-08 | Sandvikens Jernverks Ab | Corrosion-resistant steel alloys |
| US3929520A (en) * | 1971-12-23 | 1975-12-30 | Lars Ivar Hellner | Corrosion-resistant austenitic-ferritic stainless steel |
| SE399914B (en) * | 1972-11-14 | 1978-03-06 | Suedwestfalen Ag Stahlwerke | USE OF A CORROSION-RESISTANT OSTABILIZED FERRITIC-AUSTENITIC CHROM-NICKEL-MOLYBDEN-NITROGEN STALL ALLOY FOR THE MANUFACTURE OF WELDED FOREMALS WITHOUT HEAT TREATMENT |
-
1986
- 1986-09-12 SE SE8603811A patent/SE453837B/en not_active IP Right Cessation
-
1987
- 1987-09-01 AT AT905187A patent/AT395018B/en not_active IP Right Cessation
- 1987-09-01 AU AU79135/87A patent/AU7913587A/en not_active Abandoned
- 1987-09-01 WO PCT/SE1987/000387 patent/WO1988002032A1/en active Application Filing
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1089824A (en) * | 1964-01-29 | 1967-11-08 | Sandvikens Jernverks Ab | Corrosion-resistant steel alloys |
| US3929520A (en) * | 1971-12-23 | 1975-12-30 | Lars Ivar Hellner | Corrosion-resistant austenitic-ferritic stainless steel |
| SE399914B (en) * | 1972-11-14 | 1978-03-06 | Suedwestfalen Ag Stahlwerke | USE OF A CORROSION-RESISTANT OSTABILIZED FERRITIC-AUSTENITIC CHROM-NICKEL-MOLYBDEN-NITROGEN STALL ALLOY FOR THE MANUFACTURE OF WELDED FOREMALS WITHOUT HEAT TREATMENT |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0576802A1 (en) * | 1992-07-01 | 1994-01-05 | SHINKO WIRE COMPANY, LTD., also known as SHINKO KOSEN KOGYO KABUSHIKI KAISHA | Two-phase stainless steel wire rope having high fatigue resistance and corrosion resistance |
| WO1994004714A1 (en) * | 1992-08-24 | 1994-03-03 | Crs Holdings, Incorporated | Corrosion resistant austenitic stainless steel with improved galling resistance |
| US5340534A (en) * | 1992-08-24 | 1994-08-23 | Crs Holdings, Inc. | Corrosion resistant austenitic stainless steel with improved galling resistance |
| EP0659896A1 (en) * | 1993-12-20 | 1995-06-28 | Shinko Kosen Kogyo Kabushiki Kaisha | Stainless steel wire product |
Also Published As
| Publication number | Publication date |
|---|---|
| AU7913587A (en) | 1988-04-07 |
| SE453837B (en) | 1988-03-07 |
| SE8603811D0 (en) | 1986-09-12 |
| AT395018B (en) | 1992-08-25 |
| ATA905187A (en) | 1992-01-15 |
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