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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
  • B22F5/008—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product of engine cylinder parts or of piston parts other than piston rings
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
  • C22C33/0278—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5%
  • C22C33/0285—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements with at least one alloying element having a minimum content above 5% with Cr, Co, or Ni having a minimum content higher than 5%
• • 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
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • 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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • 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
• • 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
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/56—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.7% by weight of carbon
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L3/00—Lift-valve, i.e. cut-off apparatus with closure members having at least a component of their opening and closing motion perpendicular to the closing faces; Parts or accessories thereof
  • F01L3/02—Selecting particular materials for valve-members or valve-seats; Valve-members or valve-seats composed of two or more materials
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L2301/00—Using particular materials

Definitions

• This invention relates to an acid corrosion resistant and wear resistant austenitic iron-base alloy that possesses excellent resistance to sulfuric acid and is superior to high speed steels for many applications where both sulfuric acid corrosion and wear occur simultaneously.
• This invention further relates to such a corrosion resistant alloy useful for making valve seat inserts used in internal combustion engines an with exhaust gas recirculation (EGR) system.
• EGR exhaust gas recirculation
• modified M2 tool steel and Silichrome XB are two common material choices for making diesel engine intake valve seat inserts.
• modified M2 tool steel comprises 1.2-1.5 wt% carbon, 0.3-0.5 wt% silicon, 0.3-0.6 wt% manganese, 6.0-7.0 wt% molybdenum, 3.5-4.3 wt% chromium, 5.0-6.0 wt% tungsten, up to 1.0 wt% nickel, and the balance being iron.
• Modified Silichrome XB contains 1.3-1.8 wt% carbon, 1.9-2.6 wt% silicon, 0.2-0.6 wt% manganese, 19.0-21.0 wt% chromium, 1.0-1.6 wt% nickel, and the balance being iron.
• Another common iron-base alloy for intake valve seat inserts contains 1.8-2.3 wt% carbon, 1.8-2.1 wt% silicon, 0.2-0.6 wt% manganese, 2.0-2.5 wt% molybdenum, 33.0-35.0 wt% chromium, up to 1.0 wt% nickel, and the balance being substantially iron.
• U.S. Patent No. 6,916,444 discloses an iron-base alloy containing a large amount of residual austenite for intake valve seat insert material. This alloy contains 2.0-4.0% carbon, 3.0-9.0% chromium, 0.0-4.0% manganese, 5.0-15.0% molybdenum, 0.0-6.0% tungsten, 0.0-6.0% vanadium, 0.0-4.0 niobium, 7.0-15.0 % nickel, 0.0-6.0 % cobalt, and the balance being iron with impurities.
• U.S. Patent No. 6,436,338 discloses a corrosion resistant iron-base alloy for diesel engine valve seat insert applications.
• the alloy is composed of carbon 1.1-1.4%, chromium 11-14.5%, molybdenum 4.75-6.25%, tungsten 3.5-4.5%, cobalt 0-3%, niobium 1.5-2.5%, vanadium 1-1.75%, copper 0-2.5%, silicon 0-1 %, nickel 0-0.8%, iron being the balance with impurities.
• U.S. Patent No. 6,866,816 discloses an austenitic type iron-base alloy with good corrosion resistance.
• the chemical composition of the alloy is 0.7-2.4% carbon, 1.5-4.0% silicon, 5.0-9.0% chromium, less than 6.0% manganese, 5.0-20.0% molybdenum and tungsten, the total of vanadium and niobium 0-4.0%, titanium 0-1.5%, aluminum 0.01-0.5%, nickel 12.0-25.0%, copper 0-3.0%, and at least 45.0% iron.
• carbon 0.7-2.4% carbon
• silicon 5.0-9.0%
• chromium less than 6.0%
• manganese 5.0-20.0%
• molybdenum and tungsten the total of vanadium and niobium 0-4.0%
• titanium 0-1.5% aluminum 0.01-0.5%
• nickel 12.0-25.0% nickel 12.0-25.0%
• copper 0-3.0% copper 0-3.0%
• at least 45.0% iron iron.
• more severe corrosion conditions in some engines with high sulfur fuel and high humidity demands materials with corrosion resistance much better than the above iron-base alloys.
• High carbon and high chromium type nickel-base alloys normally do not exhibit good wear resistance under intake valve seat insert working conditions due to lack of combustion deposits and insufficient amount of metal oxides to protect the valve seat insert from direct metal-to-metal wear.
• Eatonite 2 is one example of the nickel-base alloys used for making exhaust valve seat inserts, which contains 2.0-2.8 wt% carbon, up to 1.0 wt% silicon, 27.0-31.0 wt% chromium, 14.0-16.0 wt% tungsten, up to 8.0 wt% iron, and the balance being essentially nickel. Eatonite is a trademark of Eaton Corporation.
• Several similar nickel-base alloys with added iron and/or cobalt are also available for exhaust valve seat inserts.
• U.S. Patent No. 6,200,688 discloses high silicon and high iron-type nickel-base alloy used as material for valve seat inserts. These nickel-base alloys may possibly be used in EGR engines only when the wear rate of intake insert is moderate.
• Tribaloy® T400 contains 2.0-2.6 wt% silicon, 7.5-8.5 wt% chromium, 26.5-29.5 wt% molybdenum, up to 0.08 wt% carbon, up to 1.50 wt% nickel, up to 1.5 wt% iron, and the balance being essentially cobalt.
• Stellite® 3 contains 2.3-2.7 wt% carbon, 11.0-14.0 wt% tungsten, 29.0-32.0 wt% chromium, up to 3.0 wt% nickel, up to 3.0 wt% iron, and the balance being cobalt.
• the above cobalt-base alloys possess both excellent corrosion and wear resistance. However, the cost of these cobalt-base alloys only allows these alloys to be used in limited applications. ( ® Registered Trademarks of Deloro Stellite Company Inc.) Austenitic iron-base valve alloys or valve facing alloys may also be classified-into the same group of materials.
• 4,122,817 discloses an austenitic iron-base alloy with good wear resistance, PbO corrosion and oxidation resistance.
• the alloy contains 1.4-2.0 wt% carbon, 4.0-6.0 wt% molybdenum, 0.1 to 1.0 wt% silicon, 8.0-13.0 wt% nickel, 20.0-26.0 wt% chromium, 0-3.0 wt% manganese, with the balance being iron.
• 4,929,419 discloses a heat, corrosion and wear resistant austenitic steel for internal combustion exhaust valves, which contains 0.35-1.5 wt% carbon, 3.0-10.0 wt% manganese, 18.0-28.0 wt% chromium, 3.0-10.0 wt% nickel, up to 2.0 wt% silicon, up to 0.1 wt% phosphorus, up to 0.05 wt% sulfur, up to 10.0 wt% molybdenum, up to 4.0 wt% vanadium, up to 8.0 wt% tungsten, up to 1.0 wt% niobium, up to 0.03 wt% boron, and the balance being essentially iron.
• the present invention is an alloy with the following composition: Element wt. % Carbon 1.8-2.8 Silicon 0.5-3.5 Chromium 12.0-22.0 Molybdenum and tungsten combined 2.0-16.0 Nickel 12.0-25.0 Niobium and vanadium combined 0.05-4.0 Titanium 0-1.0 Aluminum 0.01-0.2 Copper 0.05-3.0 Iron and impurities Balance
• metal components are either made of the alloy, such as by casting, or by the powder metallurgy method by forming from a powder and sintering. Furthermore, the alloy can be used to hardface the components as the protective coating.
• Alloys with excellent corrosion resistance under static immersion type test may perform poorly under cyclic heating corrosion because of different corrosion behaviors at high temperature and the possible influence of oxidation to the corrosion process.
• the high temperature cyclic corrosion tester provides a tool to study corrosion behavior with the influence of oxidation under high temperature condition.
• a number of alloy elements can affect corrosion and hardness of the alloy, where it is preferred to have a minimum hardness of 34.0 HRC in order to achieve good wear resistance in the inventive austenitic alloy.
• the austenitic alloy can become too brittle when the hardness of the alloy exceeds 54.0 HRC due to formation of intermetallic compounds like sigma phase from excessive amount of alloy elements.
• the hardness of the current inventive alloy can reach to the hardness of the alloy disclosed in U.S. Patent No. 6,866,816 when carbon is between 2.3-2.7 wt%, chromium 16.0-20.0 wt%, silicon 0.5-3.0 wt%, a combination of tungsten and molybdenum 3.0-7.0 wt% (preferably all tungsten), nickel 14.0-18.0 wt%, copper 1.0-2.0 wt%, vanadium 0.02-3.0 wt%, niobium 0.02-3.0 wt% (with the combination of vanadium and niobium being 0.05-4.0 wt%), aluminum 0.03-0.06 wt%, and the balance being iron with other inevitable impurities.
• the iron content will be at least 50 wt%.
• Ring samples with 45 mm outer diameter, 32 mm inner diameter and 5 mm thickness were used as hardness samples and the hardness values of all samples were obtained using a Rockwell C hardness tester.
• a high temperature cyclic corrosion tester was built to simulate sulfuric acid corrosion at high temperature.
• the new corrosion tester provides a better corrosion measurement method than the traditional static immersion corrosion test, as both oxidation and high temperature are also important factors contributing to the corrosion process in the intake insert working environment.
• the high temperature cyclic corrosion test rig is composed of a heating coil, an air cylinder, a sample with its holder, a control unit, and an acid solution container.
• the air cylinder lifts the sample up into the heating coil to heat the specimen.
• the sample is held inside the coil for about 22 seconds so that the specimen temperature reaches about 300 °F.
• the air cylinder moves the heated sample down into the sulfuric acid solution container, and the cycle continues to repeat. All acid solution left on the sample is vaporized when the sample is heated inside the heating coil. Therefore both corrosion and oxidation occur in this process, which is closer to the actual insert corrosion in EGR equipped engines than the static acid immersion test. Corrosion also occurs when the heated specimen is pushed into the sulfuric acid solution container.
• the testing time is one hour.
• the sample dimensions are 6.35 mm in diameter and 31.75 mm in length. About 12.7 mm length of the sample is immersed into the solution. 0.25 vol. %, 0.50 vol. %, and 1.0 vol. % sulfuric acid solutions are used for each sample.
• a precision balance is used to measure the weight of each sample before and after the test. The precision of the balance is 0.0001 gram.
• the corrosion weight loss is the weight difference of a sample before and after the corrosion test. The lower the corrosion weight loss the higher the corrosion resistance of an alloy sample. From actual engine with EGR corrosion tests, the composition of the invention alloy is such as to produce a corrosion weight loss preferably less than 5.0 mg, 10.0 mg, and 18 mg in 0.25, 0.5, and 1.0 vol.
• Samples 1-7 contain carbon contents from 1.2 to 2.7 wt% with silicon 1.0 wt%, chromium 18.0 wt%, tungsten 7.0 wt%, nickel 16 wt%, vanadium 1.0 wt%, niobium 1.0 wt%, aluminum 0.04 wt%, copper 1.5 wt%, and the balance is iron with other impurities associated with casting raw materials. Hardness increases rapidly with carbon content increasing from 1.2 to 2.2 wt% and then slowly increases with further carbon content. Carbon content in the inventive alloy needs to be at least 1.8 or higher in order to achieve required hardness because the hardness of sample alloys with 1.2 and 1.4 wt% carbon is only 29.0 and 30.4 HRC.
• the carbon content of the alloy is more than 2.8 wt%, shrinkage will become a major problem for insert-type ring shaped castings. Therefore, the carbon content is defined to be within the range of from 1.8 to 2.8 wt% for good hardness and casting properties, and preferably in the range of 2.3-2.7 wt%.
• Samples 8-15 contain chromium from 10.0 to 25.0 wt% with carbon 2.5 wt%, silicon 1.0 wt%, tungsten 7.0 wt%, nickel 16 wt%, vanadium 1.0 wt%, niobium 1.0 wt%, aluminum 0.04 wt%, copper 1.5 wt%, and the balance is iron with other impurities associated with casting raw materials.
• These different chromium contents containing samples illustrate the effects of chromium on hardness and corrosion resistance. Lower chromium containing alloy gives lower corrosion resistance while alloys with higher chromium contents have lower hardness.
• chromium content in the inventive alloy is defined to be within 12.0 to 22.0 wt%, preferably 16.0 to 20.0 wt%, for the balance of good corrosion resistance and adequate hardness. While sample 15 has adequate hardness, it is expected that it will have too high of a wear rate.
• Samples 16-20 contain tungsten and/or molybdenum from 0 to 15.0 wt% with carbon 2.5 wt%, silicon 1.0-2.0 wt%, chromium 18.0 wt%, nickel 16.0-25.0 wt%, vanadium 1.0-2.0 wt%, niobium 1.0 wt%, aluminum 0.04 wt%, copper 1.5 wt%, and the balance is iron with other impurities associated with casting raw materials.
• tungsten and/or molybdenum from 0 to 15.0 wt% with carbon 2.5 wt%, silicon 1.0-2.0 wt%, chromium 18.0 wt%, nickel 16.0-25.0 wt%, vanadium 1.0-2.0 wt%, niobium 1.0 wt%, aluminum 0.04 wt%, copper 1.5 wt%, and the balance is iron with other impurities associated with casting raw materials.
• molybdenum and/or tungsten content it is not necessary to use high molybdenum and/or tungsten content for better corrosion or higher hardness in the inventive alloy. Similar to high speed steels, addition of molybdenum or tungsten improves hot hardness of the inventive alloy, which is important from the designed application view as the intake insert working temperature can reach 700 °F.
• the combined molybdenum and tungsten content is defined to be within 2.0 to 16.0 wt%, preferably 3.0 to 15.0 wt%. In some alloys the tungsten will be between about 3.0 and about 7.0 wt%, and may contain no molybdenum.
• the combination of molybdenum and tungsten will be between 10.0 and 16.0 wt%, with the molybdenum preferably 12.0 to 15.0 wt% and no tungsten. Excessive amount of tungsten or molybdenum causes a brittleness problem for castings made from the inventive alloy.
• Samples 6, 21, and 23 contain nickel from 12.0 to 25.0 wt% with carbon 2.5 wt%, silicon 1.0 wt%, chromium 18.0 wt%, tungsten 7.0 wt%, vanadium 1.0 wt%, niobium 1.0 wt%, aluminum 0.04 wt%, copper 1.5 wt%, and the balance is iron with other impurities associated with casting raw materials.
• Nickel has a positive contribution to the corrosion resistance of the alloy. First, there is a minimum amount of nickel required in order to form stable austenite in the alloy. Second, higher nickel content improves corrosion resistance of the alloy in all acid concentrations tested. However the improvement is at the expense of lower hardness and therefore lower wear resistance. Therefore, the nickel content is defined to be within the range of 12.0 to 25.0 wt%, preferably 14.0 to 18.0 wt%.
• Vanadium and niobium are strong MC carbide type forming alloy elements. A small addition of vanadium and niobium helps to improve corrosion resistance of the alloy. Too much vanadium or niobium decreases the hardness of the alloy. Samples 5 and 24 contain vanadium from 1.0 to 3.0 wt% with carbon 2.5 wt%, silicon 1.0 wt%, chromium 18.0 wt%, tungsten 7.0 wt%, niobium 1.0 wt%, aluminum 0.04 wt%, copper 1.5 wt%, and the balance is iron with other impurities associated with casting raw materials. From the corrosion and hardness test results, vanadium content should be in the range of 0.02 to 3.0 wt%. Similarly, niobium content is between 0.02 to 3.0 wt%. The combined vanadium and niobium content should be between 0.05 and 4.0 wt%, preferably between 1.5 and 2.5 wt%
• Samples 6 and 25 contain silicon from 1.0 to 3.0 wt% with carbon 2.5 wt%, chromium 18.0 wt%, tungsten 7.0 wt%, nickel 16 wt%, vanadium 1.0 wt%, niobium 1.0 wt%, aluminum 0.04 wt%, copper 1.5 wt%, and the balance is iron with other impurities associated with casting raw materials. Silicon has deoxidizing and desulfurizing effects during alloy melting process. Silicon also has the effect of improving fluidity. However, the main reasons for using silicon in the inventive alloy are that silicon can also improve corrosion and wear resistance of the alloys. Increasing silicon content from 1.0 to 3.0 wt% improves corrosion resistance of the inventive alloy.
• the Si content is less than 0.5%, the effects on wear and corrosion are not achieved. If the Si content is more than 3.5 wt%, especially in the high-carbon austenitic alloy, excessive amount of silicon provides a too brittle alloy. Higher amount of silicon also decreases the hardness of the inventive alloy. Therefore, the silicon content is defined to be within the range of 0.5 to 3.5 wt%, preferably 0.5 to 3.0 wt%, and more preferably 0.5 and 1.5 wt%.
• the range of copper in the alloy is defined to be within 0.05 to 3.0 wt%, preferably 1.0 to 2.0 wt%.
• Manganese also has deoxidizing and desulfurizing effects to molten metals. However, manganese can deteriorate corrosion resistance if its content is too high. Therefore, the manganese range is defined to be less than 1.5 wt%, preferably 0.2 to 0.6 wt%.
• the range for aluminum is between about 0.01 and about 0.2 wt%, preferably between about 0.03 and about 0.06 wt%.
• the range for titanium is between about zero and about 1 wt%, preferably between about 0.02 wt% and about 0.06 wt%.
• alloys of the present invention are capable of being incorporated in the form of a variety of embodiments, only a few of which have been illustrated and described.
• the invention may be embodied in other forms without departing from its spirit or essential characteristics. It should be appreciated that the addition of some other ingredients, process steps, materials or components not specifically included will have an adverse impact on the present invention.
• the best mode of the invention may, therefore, exclude ingredients, process steps, materials or components other than those listed above for inclusion or use in the invention.
• the described embodiments are considered in all respects only as illustrative and not restrictive, and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

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