Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C37/00—Cast-iron alloys
  • C22C37/06—Cast-iron alloys containing chromium
• • 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
  • C22C38/36—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.7% by weight of carbon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C37/00—Cast-iron alloys
  • C22C37/06—Cast-iron alloys containing chromium
  • C22C37/08—Cast-iron alloys containing chromium with nickel

Definitions

• the present invention relates to a ferrochromium alloy and more particularly to an erosion and corrosion resistant ferrochromium alloy.
• the present invention is designed for use in thn formation of parts for lining pumps, pipes, nozzles, mixers and similar devices which, in service, can be subjected to mixtures containing a corrosive fluid and abrasive particles.
• Typical applications for such parts include flue gas desulphurization, in which the parts are exposed to sulphuric acid and limestone, and fertiliser production, in which the parts are exposed to phosphoric acid, nitric acid and gypsum.
• An object of the present invention is to provide a ferrochromium alloy which has improved erosion and corrosion resistance compared with the alloys disclosed in the Abex U.S. patents.
• the present invention is based on the realization that by increasing both the chromium and carbon concentrations of alloys of the type disclosed in the Abex U.S. patents it is possible to increase the volume fraction of the chromium carbide phase, and thereby improve the wear resistance characteristics of the ferrochromium alloys, while maintaining the matrix at a chromium concentration which is at a level that will not lead to the formation of significant amounts of sigma phase. It can be appreciated that by improving the wear resistance of the ferrochromium alloys, in view of the mechanism by which erosion and corrosion occurs, as noted above, it is possible to realize an improvement in the erosion and corrosion resistance of the ferrochromium alloys.
• an erosion and corrosion resistant ferrochromium alloy comprising the following composition, in wt. %.
• micro-alloying elements selected from the group consisting of titanium, zirconium, niobium, boron, vanadium and tungsten, and balance, iron and incidental impurities, with a microstructure comprising eutectic chromium carbides in a matrix comprising one or more of ferrite, retained austenite and martensite, as herein defined.
• ferrous is herein understood to mean body-centred cubic iron (in the alpha and/or delta forms) containing a solid solution of chromium.
• the ternA"austenite is herein understood to mean face-centred cubic iron containing solid solutions of carbon ajtd chromium.
• austenite is herein understood to mean a transformation product of austenite.
• the matrix contains a 25-35 wt. % solid solution of chromium.
• the microstructure further comprises one of primary chromium carbides, primary ferrite or primary austenite in the matrix.
• the preferred amount in wt %. of the elements chromium, carbon, manganese, silicon, molybdenum, nickel and copper is as follows:
• the matrix contains a 29-32 wt. % solid solution of chromium.
• increasing both the chromium and carbon contents of the ferrochromium alloy above the levels disclosed in the Abex U.S. patents permits the formation of a greater volume fraction of hard carbides to enhance wear resistance. More specifically, and preferably, a stoichiometric balance in the increase in chromium and carbon contents permits the formation of a greater volume fraction of chromium carbides without increasing the chromium content of the matrix to a critical level above which sigma phase embrittlement occurs.
• The_ alloy of the present invention has a diff-arent microstructure to that of the alloys disclosed in the Abex U.S. patents. The difference is illustrated in the accompanying figures which comprise photocopies of photomicrographs of an alloy disclosed in the Abex U.S. patents and preferred alloys of the present invention.
• Figure 1 shows the microstructure of an Abex alloy which comprises 28.4% chromium, 1.94% carbon, 0.97% manganese, 1.48% silicon, 2.10% molybdenum, 2.01% nickel and 1.49% copper, the balance substantially iron.
• the microstructure consists of primary austenite dendrites (50% volume) and a eutectic structure comprising eutectic carbides in a matrix of eutectic ferrite, retained austenite and martensite.
• Figure 2 shows the microstructure of one preferred alloy of the present invention which comprises 35.8% chromium, 1.94% carbon, 0.96% manganese, 1.48% silicon, 1.94% carbon, 0.96% manganese, 1.48% silicon, 2.06% molybdenum, 2.04% nickel, 1.48% copper, the balance substantially iron.
• the microstructure is hypereutectic with primary ferrite dendrites (20% volume) and a eutectic structure comprising finely dispersed eutectic carbides in a matrix of eutectic ferrite. It is noted that when compared with the microstructure of the Abex U.S.
• the microstructure of Figure 2 reflects that there is a reduced volume of primary dendrites and an increased volume of the eutectic matrix and since the eutectic matrix has a relatively high proportion of carbides there is an overall increase in the volume fraction of hard carbides in the alloy when compared with the Abex alloy. It is noted that the foregoing phenomenon is also apparent to a greater extent from a comparison of the microstructures shown in Figs. 3 to 5 and Fig. 1.
• Figure 3 shows the microstructure of another preferred alloy of the present invention which comprises 40.0% chromium, 1.92% carbon, 0.96% manganese, 1.59% silicon, 1.95% molybdenum, 1.95% nickel, 1.48% copper, the balance substantially iron.
• the microstructure consists of eutectic carbides in a matrix of eutectic ferrite.
• Figure 4 shows the microstructure of another preferred alloy of the present invention which comprises 40.0% chromium, 2.30% carbon, 2.77% manganese, 1.51% silicon, 2.04% molybdenum, 1.88% nickel, 1.43% copper, the balance substantially iron.
• the microstructure is hypereutectic with primary M 7 C 3 carbides and a eutectic structure comprising eutectic carbides in a matrix of eutectic ferrite.
• Figure 5 shows the micr structure of another preferred alloy of the present invention which comprises 43% chromium, 2.02% carbon, 0.92 manganese, 1.44% silicon, 1.88% molybdenum, 1.92% nickel, 1.2% copper, the balance substantially iron.
• the microstructure in this case is hypereutectic with trace amounts of primary M C carbides and a eutectic structure comprising eutectic carbides in a matrix of eutectic ferrite.
• any suitable conventional casting and heat treatment technology may be used to produce the alloys of the present invention.
• the alloys are formed by casting and then heat treating at a temperature in the range of 600 to 1000°C followed by air cooling.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)
• Materials For Medical Uses (AREA)
• Soft Magnetic Materials (AREA)
• Powder Metallurgy (AREA)
• Heat Treatment Of Articles (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Braking Arrangements (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)
• Chemically Coating (AREA)
• Electrolytic Production Of Metals (AREA)
• Hard Magnetic Materials (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Physical Vapour Deposition (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Earth Drilling (AREA)

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Publications (1)

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Cited By (6)

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Citations (5)

• 1990
  • 1990-08-03 EP EP90911863A patent/EP0438560B1/de not_active Expired - Lifetime
  • 1990-08-03 ES ES90911863T patent/ES2087159T3/es not_active Expired - Lifetime
  • 1990-08-03 KR KR1019910700327A patent/KR940003890B1/ko not_active IP Right Cessation
  • 1990-08-03 DE DE69026701T patent/DE69026701T2/de not_active Expired - Lifetime
  • 1990-08-03 HU HU906124A patent/HU212085B/hu unknown
  • 1990-08-03 WO PCT/AU1990/000331 patent/WO1991002101A1/en active IP Right Grant
  • 1990-08-03 AT AT90911863T patent/ATE137274T1/de active
  • 1990-08-03 CA CA002037921A patent/CA2037921C/en not_active Expired - Lifetime
  • 1990-08-04 CN CN90107369A patent/CN1029692C/zh not_active Expired - Lifetime
  • 1990-08-18 TW TW079106940A patent/TW208044B/zh active
• 1998
  • 1998-06-22 HK HK98106026A patent/HK1006859A1/xx not_active IP Right Cessation

Patent Citations (5)

Non-Patent Citations (2)

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