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
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/053—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 30% but less than 40%
• • 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

Definitions

• This invention relates to corrosion resistant steel alloys and more particularly to a steel alloy especially well suited for fabricating parts which in addition to being resistant to corrosion in a medium containing sulfuric acid are also capable of sustaining stress in such a medium without cracking.
• a corrosion resistant alloy is generally identified as one which in a given medium will not lose metal or be penetrated at a rate greater than would be tolerable when fabricated into parts.
• a composition and parts made therefrom having a corrosion rate of about 0.005 inch penetration per year in 10% by weight boiling sulfuric acid are found in practice eminently well suited for use where resistance to hot sulfuric acid is required.
• the present invention stems from my discovery that when the elements nickel, chromium, molybdenum, copper and iron are combined in critically controlled proportions, a composition is provided which, in addition to being resistant to corrosion, is capable of sustaining stress in a medium containing sulfuric acid without cracking.
• an object of the present invention to provide a steel alloy having improved resistance to stress corrosion cracking. It is another object of this invention to provide such an alloy having improved stress corrosion resistance which is also hot workable, ductile, and easy to fabricate. It is a more specific object of this invention to provide such an alloy which is relatively inexpensive, which has a homogeneous austenitic microstructure after being hot worked or welded and which is completely free from stress corrosion cracking when immersed in a sul furic acid medium.
• my composition contains from about 0.025% to 0.035% nitrogen although as much as 0.05% or more nitrogen may be present, if desired.
• controlled amounts of titanium or columbium are included in my composition in order to stabilize the composition as an essentially homogeneous, austenitic alloy and to prevent the precipitation of chromium car bides, particularly when articles made from the composition are welded.
• up to 2% titanium or up to 1% columbium is present. I preferably utilize a minimum amount of titanium equal to four times the carbon content, while in the case of columbium, I preferably utilize a minimum amount equal to eight times the carbon content.
• columbium is accompanied by some tantalum and therefore, the percent stated for columbium is to be understood as including tantalum in the usual proportion.
• Additions of misch metal or boron improve the hot workability of my composition.
• An addition of misch metal in an amount suflicient to result in retention of from about 0.10% to 0.30% misch metal in the solidified metal provides improved hot workability Without adversely affecting the corrosion resistance of the alloy.
• the alloy contains from about 0.003% to 0.007% boron and best results are achieved with a boron content of from 0.003% to 0.005%.
• the remainder of the composition is essentially iron which is intended to include such impurities as are consistent with good commercial practice as well as such additional elements which are in keeping with good metallurgical practice and do not impair the desirable properties of the composition.
• manganese is included in an amount up to about 2% to prevent hot shortness.
• Silicon is included for the purpose of deoxidizing and cleaning the melt. When present in amounts above about 1%, silicon adversely affects the corrosion resistance and forgeability of the composition. Preferably, silicon is present in an amount ranging from about 0.40% to 0.75%.
• my preferred composition consists essentially of:
• Columbium is used in a minimum amount of 8 times the carbon contentand when titanium is included instead of coludmbium, a minimum of 4 times the carbon content is use Misch metal (primarily made up of cerium and 1antha num) or boron is included in the ranges indicated.
• my composition it is essential that the elements chromium, nickel, molybdenum and copper be present in the minimum amounts stated for the composition to have the required corrosion resistance, resistance to corrosion in sulfuric acid, resistance to pitting and the required freedom from stress corrosion cracking in sulfuric acid.
• Chromium may be present in my composition .in amounts ranging up to about 26%. Above about 26%, chromium causes the formation of an undesirable double phase microstructure. Thus, while the larger chromium contents tend to increase the general corrosion resistance of the composition, best results are achieved with chromium ranging from about 20% to 22%.
• molybdenum When molybdenum is present in an amount greater than 3%, there is an adverse effect upon the strength and the stress corrosion resistance of the composition because of .the formation of a sigma phase. Best results are achieved with a molybdenum content of from 2% to 2.5%.
• the nickel content must beat least 32.5% in order to achieve the desired freedom from stress corrosion cracking in sulfuric acid.
• nickel present in the stated amounts of from 32.5% to about the desired properties including freedom from stress corrosion cracking in sulfuric acid are achieved.
• Greater amounts of nickel than 35% have no beneficial eifect upon the resistance of my composition to corrosion and stress corrosion cracking in sulfuric acid and only add unnecessarily to its cost;
• each specimen and a nut was tightened on the bolt to maintain the specimen under stress in the shape of a U-bend.
• the concave inner surface of each specimen was thus placed under compression and the outside surface of the bend under tension, the highest stress occurring in the outer fibers.
• the specimens thus prepared and stressed were immersed in non-aerated, boiling 30 to 40% sulfuric acid.
• Example 1 was prepared having the following analysis:
• U-bend test specimens of this alloy were found to be entirely free of cracks after being kept in the boiling 30-40% sulfuric acid for 330 hours. It is to be noted that such U-bend specimens have a complex stress pattern varying from high to low stress levels and, having been cold worked, are ideally suited for testing the susceptibility of the alloy to stress corrosion cracking.
• Example 2 An alloy was prepared having the following analysis:
• Examplei-An alloy was prepared having the following analysis:
• Example 4.An alloy was prepared having the following analysis:
• the specimens formed from the alloys of Examples 1-4 each had a homogeneous, single phase austenitic microstructure.
• Articles made from my composition may be readily formed and when welded retain a homogeneous, single phase microstructure.
• this alloy is substantially identical to the alloys of Examples 1-4.
• One of the specimens was found cracked after only 24 hours in the boiling sulfuric acid While the last of the six specimens to crack did so in less than 135 hours. It may be noted that the cracks in each of these six specimens appeared on the outer surface, that under tension, apparently beginning at an edge slightly away from the center of the arc of the U-bend. No cracks were found on the inner, compression surface of the specimens.
• composition is suitable for use under conditions where it will be exposed to attack by a variety of corrosive agents, it is especially well suited for use where, among other things, it will be exposed to sulfuric acid.
• My composition is characterized by outstanding resistance to corrosion by sulfuric acid and is completely free from 1.
• a corrosion resistant austenitic steel alloy consisting essentially of in percent by weight:
• said alloy being characterized by freedom from stress corrosion cracking when under stress while exposed to sulfuric acid.
• a homogeneous corrosion resistant austenitic steel alloy consisting essentially of in percent by weight within the tolerances of good melting practice:
• colurnb-ium when present being in an amount equal to at least eight times the carbon content, the remainder being essentially iron, and said alloy being characterized by freedom from stress corrosion cracking when under stress while exposed to sulfuric acid.
• a homogeneous corrosion resistant austenitic steel alloy consisting essentially of in percent by weight within the tolerances of good melting pnactice:
• titanium when present being in an amount equal to at least four times the carbon content, the remainder being essentially iron, and said ⁇ alloy being characterized by freedom from stress corrosion cnacking when under stress while exposed to sulfuric acid.
• a homogeneous corrosion resistant austenitic steel alloy consisting essentially of in percent by weight within the tolenances of good melting practice:
• columbium when present being in an amount equal to at least eight timm the carbon content, the remainder being essentially iron, and said alloy being characterized by freedom from stress corrosion cracking when under stress while exposed to sulfuric acid.
• a homogeneous corrosion resistant austenitic steel alloy consisting essentially of in percent by weight within the tolerances of good melting practice:
• titanium when present being in an amount equal to at least four times the carbon content, the remainder being essentially iron, and said alloy being characterized by freedom from stress corrosion cracking when under stress While exposed to sulfuric acid.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Heat Treatment Of Steel (AREA)
• Treatment Of Steel In Its Molten State (AREA)

Priority Applications (4)

Applications Claiming Priority (1)

Publications (1)

Family

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Family Applications (1)

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Cited By (13)

Citations (7)

• 1962
  • 1962-01-03 US US164140A patent/US3168397A/en not_active Expired - Lifetime
  • 1962-11-19 GB GB43951/62A patent/GB990301A/en not_active Expired
  • 1962-12-10 DE DE19621302792 patent/DE1302792C2/de not_active Expired
  • 1962-12-20 CH CH1498062A patent/CH458756A/de unknown

Patent Citations (7)

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