EP0049033B1 - Brazeable ferritic stainless steel, method of using same and article formed therefrom - Google Patents

Brazeable ferritic stainless steel, method of using same and article formed therefrom Download PDF

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Publication number
EP0049033B1
EP0049033B1 EP81303337A EP81303337A EP0049033B1 EP 0049033 B1 EP0049033 B1 EP 0049033B1 EP 81303337 A EP81303337 A EP 81303337A EP 81303337 A EP81303337 A EP 81303337A EP 0049033 B1 EP0049033 B1 EP 0049033B1
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EP
European Patent Office
Prior art keywords
brazeable
ferritic stainless
stainless steel
titanium
brazing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP81303337A
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German (de)
English (en)
French (fr)
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EP0049033A1 (en
Inventor
George Aggen
Paul Richard Borneman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Allegheny Ludlum Corp
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Allegheny Ludlum Corp
Allegheny Ludlum Steel Corp
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Application filed by Allegheny Ludlum Corp, Allegheny Ludlum Steel Corp filed Critical Allegheny Ludlum Corp
Publication of EP0049033A1 publication Critical patent/EP0049033A1/en
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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
    • 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

Definitions

  • the present invention relates to brazeable ferritic stainless steels and is particularly useful for ferritic stainless steel articles which are joined by brazing.
  • Ferritic stainless steels possess excellent mechanical properties and oxidation and general corrosion resistance at elevated temperatures. These steels are ideal for use as the structural members of heat exchangers, exhaust systems, chemical process vessels and the like which are exposed to high temperatures and stresses and corrosive environments. Fabrication of these articles frequently requires the joining of the ferritic stainless steel with either itself or with another dissimilar metal at sufficiently high temperatures for the joining method to be effective. Also, generally speaking, the steel must be joined in a temperature range exceeding the anticipated service temperature.
  • Brazing is a widely practised method of joining metals involving temperatures of from 427°C (800°F) to the 1093°C-1149°C (2000°F-2100°F) range which are above the melting point of the brazing filler material but below the melting point of the base metal being joined.
  • temperatures of from 427°C (800°F) to the 1093°C-1149°C (2000°F-2100°F) range which are above the melting point of the brazing filler material but below the melting point of the base metal being joined.
  • the temperature of the brazing filler material is about the melting point, it becomes molten and wets the surface of the steel, and then flows by capillary action to fill a joint. Bonding results from the intimate contact produced by the dissolution of a small amount of the base metal in the molten filler metal.
  • Ferritic stainless steels to be joined at high temperatures contain low levels of carbon and small amounts of stabilizing elements for combining with carbon and nitrogen to maintain the ferritic phase and to maintain the oxidation and corrosion resistance of the steel.
  • Stabilizing elements such as titanium, niobium or tantalum react with the carbon and nitrogen to prevent the formation and precipitation of chromium carbides and nitrides at grain boundaries and the simultaneous depletion of chromium in the surrounding areas. Stabilizing elements must be added in amounts exceeding the theoretical requirement to assure complete stabilization of carbon and nitrogen. Titanium has been the preferred stabilizing element because of its very strong affinity for carbon and nitrogen, its low atomic weight and its availability. Other stabilizing agents including niobium and tantalum have not been favoured because they are more expensive and less effective on a weight basis than titanium and also because they are accompanied by a tendency toward weld cracking problems.
  • Titanium stabilized ferritic steels known in the prior art cannot be readily brazed with filler materials such as oxygen-free copper and nickel base alloys. These steels form a non-wettable surface film which prevents proper bonding between the ferritic stainless steel base metal and the brazing filler material even when furance brazing under vacuum or in an inert atmosphere.
  • the oxygen-free copper as a high temperature brazing filler metal does not penetrate this surface film.
  • Nickel alloy high temperature brazing filler metals usually contain boron and silicon additions to penetrate the surface film. Although the steel wettability is improved, these nickel base materials will also penetrate the grain boundaries thereby causing intergranular attack of the base metal.
  • brazing operations are not aided by increased temperatures or by increased brazing times because the high temperature range is beginning to affect the grain size of the steel and prolonged time tends to increase film resistance.
  • brazing with copper is impossible and brazing with nickel base metals is not consistent enough to be of practical value from a quality assurance viewpoint.
  • copper clad ferritic stainless steels are used in brazing applications when the brazing temperature is to reach 1093°C-1149°C (2000°F-2100°F). In this process, the copper cladding is brazed rather than the steel.
  • the present invention relates to a stabilized ferritic stainless steel composition which is wettable by conventional brazing materials used at temperatures of from 1093°C-1149°C (2000°F-2100°F) in furnace brazing practices.
  • the present invention provides a ferritic stainless steel containing, by weight, 10.5% to 13.5% chromium, up to 0.03% carbon, up to 0.05% nitrogen, up to 0.10% aluminium, up to 0.12% titanium and at least one other stabilizing element selected from niobium and tantalum in accordance with the relationship: the balance being iron optionally including up to 1.25% molybdenum, up to 1 % manganese and up to 1 % silicon and incidental impurities.
  • Preferred nitrogen and aluminium levels are up to 0.03% and up to 0.020% respectively.
  • niobium, tantalum and titanium in accordance with this stabilization relationship are sufficient to effectively stabilize the interstitial elements in the steel without forming a non-wettable surface film.
  • the niobium and tantalum are present as additions to the melt. Where niobium is a stabilising element, it may preferably be present in an amount up to 1.0%. When tantalum is a stabilizing element, it may preferably be present in an amount up to 1.8%. Titanium may be present in the scrap feed or added to the melt. The titanium is responsible for the nature of the film which becomes non-wettable when titanium is present in amounts greater than about 0.12%.
  • titanium compounds stable at brazing temperatures such as Ti0 2 , TiS and TiN are permitted to form.
  • oxygen, sulphur and nitrogen have an undesirable effect on other steel qualties and generally they will be kept as low as possible.
  • the titanium is preferably present in an amount up to 0.01 % by weight and, most preferably, up to 0.005%.
  • the steel may also contain up to 0.1 % aluminium, up to 1.25% molybdenum, up to 1% manganese and up to 1% silicon to enhance its mechanical and corrosion properties. Articles of this composition are wettable by fillers such as copper, nickel and their alloys and can be successfully furnace brazed according to conventional practices.
  • titanium is tolerated in controlled amounts, i.e. from at least 0.001 % up to 0.12%, to prevent weld cracking while maintaining reasonable wettability during brazing operations. Larger amounts of titanium render the steel unbrazeable for practical purposes.
  • Laboratory heats Nos. 1-6 and 14-16 are alloys in accordance with the present invention; laboratory heats 7-13 and the commercial heats A and B are included for purposes of comparison.
  • the test generally consisted of placing a brazing filler material on each specimen and heating the specimens and filler materials to the melting point of the filler material.
  • the wettability of the specimens were evaluated according to the parameter "d 2 /h", where "d” is the average diameter of the drop in inches which formed on the surface of the specimen and "h” is the height of the drop in inches, wettability being proportional to the area covered by the drop and inversely proportional to the height of the drop.
  • the furnace was evacuated cold, heated to 565°C (1050°F) held at a vacuum of one micron (133.3 Pa) or less while heating to 649°C (1200°F), pressurized with nitrogen to 1500 microns (2.10 5 Pa) and heated to the brazing temperature.
  • the furnace was evacuated cold, heated to 565°C (1050°F), held at a vacuum of one micron (133.3 Pa) or less while heating to 649°C (1200°F), pressurized with dry hydrogen (having a dew point of less than -62°C 4-80°F) to a pressure of 300,000 microns (4.10' Pa) and heated to the brazing temperature.
  • the wettability ratings (d 2 /h) of the specimens are shown in Table II. The letter "C" indicates that the specimen was completely wetted.
  • the wettability of the laboratory melted compositions can be compared with each other and with the prior art compositions of Heats A and B to determine the adverse effects of titanium.
  • the prior art compositions are clearly non-wettable.
  • the stabilized compositions of Heats 1-4 and 14-16 contain up to 0.005 wt% of titanium and exhibit superior wettability under all atmospheres.
  • the effect of increasing amounts of titanium is most clearly shown by the compositions of Heats 5-7.
  • the composition of Heat 5 contains 0.008 wt% titanium and has superior wettability characteristics under all atmospheres.
  • the composition of Heat 6 contains 0.11 wt% titanium and has improived wettability characteristics under inert gas and vacuum atmospheres, however the adverse effect of titanium is evident in a reducing atmosphere.
  • Heats 7-13 contain large amounts of titanium and have no better wettability characteristics than do the prior art compositions.
  • Figures 1 and 2 are the perspective and top views, respectively, of a brazing table supporting the specimens identified in Tables I and II.
  • Specimens A and B are the commercial steels and illustrate the problem where the filler material does not wet the surface beyond the periphery of the molten drop.
  • specimens 7, 8, 9 and 10 are also not wetted by the filler material.
  • Specimens 1, 2, 3 and 4 are completely wetted by the oxygen-free copper.
  • Specimens 5 and 6 although containing increasing titanium concentrations of 0.008% and 0.11 % respectively, are clearly wetted by the copper beyond the periphery of the molten drop.
  • the prior art compositions were not tested but they would have a rating approximating those of Heats 7 and 9 respectively in view of their titanium contents.
  • the compositions of Heats 3, 5 and 14-16 all contain less than .01 wt% titanium and have superior wettability characteristics.
  • the composition of Heat 6 contains 0.11 wt% titanium and has superior wettability characteristics in comparison to the other compositions containing 0.18 wt% (Heat 12) or more titanium (Heats 7 and 9).

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Ceramic Products (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Laminated Bodies (AREA)
  • Catalysts (AREA)
EP81303337A 1980-08-08 1981-07-21 Brazeable ferritic stainless steel, method of using same and article formed therefrom Expired EP0049033B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US17632480A 1980-08-08 1980-08-08
US176324 1980-08-08

Publications (2)

Publication Number Publication Date
EP0049033A1 EP0049033A1 (en) 1982-04-07
EP0049033B1 true EP0049033B1 (en) 1985-11-21

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EP81303337A Expired EP0049033B1 (en) 1980-08-08 1981-07-21 Brazeable ferritic stainless steel, method of using same and article formed therefrom

Country Status (9)

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EP (1) EP0049033B1 (enrdf_load_stackoverflow)
JP (1) JPS5760056A (enrdf_load_stackoverflow)
AT (1) ATA345281A (enrdf_load_stackoverflow)
AU (1) AU7317081A (enrdf_load_stackoverflow)
BR (1) BR8105025A (enrdf_load_stackoverflow)
CA (1) CA1181267A (enrdf_load_stackoverflow)
DE (1) DE3172977D1 (enrdf_load_stackoverflow)
ES (1) ES504584A0 (enrdf_load_stackoverflow)
ZA (1) ZA814922B (enrdf_load_stackoverflow)

Families Citing this family (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6029449A (ja) * 1983-07-27 1985-02-14 Mitsubishi Heavy Ind Ltd 高クロム耐熱鋳鍛鋼
DE3480602D1 (de) * 1983-12-12 1990-01-04 Armco Advanced Materials Warmfester ferritischer stahl.
US4834808A (en) * 1987-09-08 1989-05-30 Allegheny Ludlum Corporation Producing a weldable, ferritic stainless steel strip
DE69500714T2 (de) * 1994-04-21 1998-03-26 Kawasaki Steel Co Heissgewalzter ferritischer Stahl für eine Kraftfahrzeug-Abgasanlage
KR101261192B1 (ko) 2006-05-09 2013-05-09 닛폰 스틸 앤드 스미킨 스테인레스 스틸 코포레이션 내간극 부식성이 우수한 페라이트계 스테인리스 강
JP5390175B2 (ja) * 2007-12-28 2014-01-15 新日鐵住金ステンレス株式会社 ろう付け性に優れたフェライト系ステンレス鋼
JP5788946B2 (ja) * 2007-12-28 2015-10-07 新日鐵住金ステンレス株式会社 ろう付け性に優れたろう付け接合により組み立てられる部材用フェライト系ステンレス鋼
JP5264199B2 (ja) * 2008-01-28 2013-08-14 日新製鋼株式会社 フェライト系ステンレス鋼を用いたｅｇｒクーラー
JP5420292B2 (ja) * 2008-05-12 2014-02-19 日新製鋼株式会社 フェライト系ステンレス鋼
JP5462583B2 (ja) * 2008-10-24 2014-04-02 新日鐵住金ステンレス株式会社 Ｅｇｒクーラ用フェライト系ステンレス鋼板
MX348600B (es) 2011-08-18 2017-06-21 Unitload Pty Ltd Estructura de soporte de carga.
JP6270821B2 (ja) 2013-03-29 2018-01-31 新日鐵住金ステンレス株式会社 ろう付け性に優れたフェライト系ステンレス鋼板、熱交換器、熱交換器用フェライト系ステンレス鋼板、フェライト系ステンレス鋼、燃料供給系部材用フェライト系ステンレス鋼、及び燃料供給系部品
WO2022265639A1 (en) 2021-06-17 2022-12-22 Cummins Inc. Steel alloy and method of manufacture exhibiting enhanced combination of high temperature strength, oxidation resistance, and thermal conductivity

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3000729A (en) * 1959-12-03 1961-09-19 Armco Steel Corp Stainless steel
US3389991A (en) * 1964-12-23 1968-06-25 Armco Steel Corp Stainless steel and method
DE1783136C2 (de) * 1965-10-22 1975-10-02 Stahlwerke Suedwestfalen Ag, 5930 Huettental-Geisweid Verwendung eines gut zerspanbaren, nichtrostenden magnetisch weichen Chromtstahles für Magnetventile
JPS5432409B2 (enrdf_load_stackoverflow) * 1973-11-21 1979-10-15
US3997373A (en) * 1975-01-13 1976-12-14 Allegheny Ludlum Industries, Inc. Ferritic stainless steel having high anisotropy

Also Published As

Publication number Publication date
EP0049033A1 (en) 1982-04-07
CA1181267A (en) 1985-01-22
BR8105025A (pt) 1982-04-20
DE3172977D1 (en) 1986-01-02
AU7317081A (en) 1982-02-11
ZA814922B (en) 1982-07-28
ES8302116A1 (es) 1983-01-01
ES504584A0 (es) 1983-01-01
JPS5760056A (en) 1982-04-10
ATA345281A (de) 1983-12-15
JPH034617B2 (enrdf_load_stackoverflow) 1991-01-23

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