ALLOYS POURED IN THE FOUNDRY

Transcription

1 ALLOYS POURED IN THE FOUNDRY I. What is the difference between an alloy and metal? A. Metal: A chemical element such as iron, aluminum, copper etc. B. Alloy: A substance having metallic properties and composed of two or more chemical elements of which at least one is metal. Examples of alloys are cast iron, carbon steel, aluminum-silicon, brass, and bronze. II. Foundries are generally categorized by the type of alloy poured A. Ferrous Alloys: Those alloys in which the predominant metal is iron. These foundries include those which pour cast irons, carbon steels and high alloy steels. B. Nonferrous Alloys: Those alloys which contain very little, if any, iron. These foundries include those which pour aluminum, copper and magnesium alloys. C. Specialty Alloys: These alloys usually are not classified as ferrous or nonferrous. These foundries pour titanium, cobalt and the "super" alloys. Sometimes the highalloy steels are placed in this category. III. The Nonferrous Alloys A. Light Alloys: 1. Family of Aluminum Alloys: a) 1XX.X - Aluminum--99% minimum and greater b) 2XX.X - Copper--major alloying element c) 3XX.X - Silicon--major alloying element with copper and/or magnesium added. Most commonly poured aluminum alloy d) 4XX.X - Silicon--major alloying element e) 5XX.X - Magnesium--major alloying element f) 7XX.X - Zinc--major alloying element g) 8XX.X - Tin--major alloying element h) 9XX.X - Other major alloying elements i) 6XX.X - Unused series 1

2 2. Family of Magnesium Alloys: a) (Magnesium - Aluminum)--Magnesium predominant metal (90%) b) (Magnesium - Aluminum - Zinc)--Magnesium predominant metal (88% ) with aluminum second and then zinc c) (Magnesium - Aluminum - Zinc - Manganese)--Magnesium predominant metal with aluminum second, zinc third and traces of manganese d) (Magnesium - Zinc - Thorium)--Magnesium predominant metal followed by zinc and thorium e) (Magnesium - Thorium - Zinc)--Magnesium predominant metal followed by zinc, thorium, rare earths and zirconium f) (Magnesium - Rare Earths - also at times, Thorium, Zinc or Zirconium or combinations of them)--magnesium predominant metal followed by a rare earth such as cerium 3. Family of Zinc Aluminum Alloys: a) ZA 8 - Zinc predominant metal with 8% Aluminum, 3% Copper and trace of Magnesium b) ZA11 - Zinc predominant metal with 11% Aluminum, 1.75% Copper and trace of Magnesium c) AZ12 - Zinc predominant metal with 12% Aluminum d) AZ27 - Zinc predominant metal with 27% aluminum, 2% Copper and trace of Magnesium e) These alloys also known as ILZRO (International Lead Zinc Research Organization) ILZRO12, etc. 4. Some foundries pour pure aluminum or magnesium 2

3 B. Copper Base Alloys 1. Brass - Zinc is the major alloying element and is broken into four major families a) Copper-Tin-Zinc alloys (red, semi-red, yellow brasses) b) Manganese Bronze alloys (high strength yellow brasses) c) Leaded Manganese Bronze alloys (leaded, high strength yellow brasses) d) Copper-Zinc-Silicon alloys (silicon brasses and bronzes) 2. Bronzes - Copper alloys in which zinc or nickel are not the major alloying element and broken into four major families a) Copper-Tin alloys (tin bronzes) b) Copper-Tin-Lead alloys (leaded and high-leaded tin bronzes) c) Copper-Tin-Nickel alloys (nickel-tin bronzes) d) Copper-Aluminum alloys (aluminum bronzes) 3. Numbering System a) A new numbering system has been instituted as follows 1) Brasses - C8XXXX 2) Bronze C95XXX 3) Copper-Nickel-Iron (Cupro Nickel) C96XXX 4) Copper-Nickel-Zinc (Nickel Silver) C97XXX 5) Copper-Lead (Leaded Coppers) C98XXX 6) Special Alloys C99XXX 7) Monel (Copper-Nickel alloy) 62-65% Nickel, 29-32% Copper, % Silicon, % Iron, 0.5-1% Manganese, % Carbon 4. Some foundries pour pure copper 3

4 IV. In some cases the High Alloy Steels are considered Nonferrous Alloys V. Ferrous Alloys A. Steels - Iron is the major constituent with low carbon and other elements. (1.8% or less Carbon levels) 1. Low carbon steels - less than 0.20% Carbon 2. Medium carbon steels % Carbon 3. High carbon steels - more than 0.50% Carbon 4. High alloy steels - alloys of iron and carbon that have over 8% alloy content. Stainless and Heat Resistant Steels are examples. a. 16 Standard Grades of Corrosion Resistant Steels b. 12 Standard Grades of Heat Resistant Steels 5. Low alloy steels - alloys of iron and carbon that have 8% or less alloy content. Can be heat treated to higher levels of hardness and strength in a given cross section. a. Common alloying elements include: Manganese, Chromium, Molybdenum, Nickel, Silicon, Copper and Vanadium 6. Hadfield's manganese steel % Manganese a. Outstanding wear resistance b. Commercially unmachinable B. Cast Irons - Iron is the major constituent with carbon levels of 1.8% and above with other alloying elements. 1. Gray Cast Iron a. Typical Composition: C % Si % Mn % S % P % b. Graphite (carbon) comes out of solution as flakes c. Properties 1) Outstanding compressive strength 2) Poor ductility 3) Excellent machinability 4) Hardness can be varied 5) Excellent damping capacity (absorb energy due to vibrations) 4

5 2. Malleable Iron a. Typical composition: C % Si % Mn % S P % b. Solidifies as "white iron" (massive carbides & pearlite) c. Heat treated d. Properties 1) Workable (has ductility) 2) Good strength 3) Pearlitic-Harder, more wear resistant 4) Ferritic-Softer, more ductile 3. Ductile Iron a. Typical composition: C % Si % Mn % S 0.03% minimum P 0.10% maximum b. Base iron treated with Magnesium or Rare Earth 1) Graphite comes out in nodular (round) shape 2) Very low sulfurs required to produce ductile iron c. Properties 1) Good ductility 2) Machinability better than gray iron 3) Gives engineering advantages of steel and malleable iron 4) Properties can be varied by changing matrix a) Alloying b) Heat treating 4. Compacted Graphite a. A ductile iron to which titanium is added b. Changes nodules to short "pudgy" shapes c. Properties between gray and ductile iron 5. Austempered Ductile iron a. Ductile iron to which molybdenum is added b. Heat treated which gives it work hardening characteristics c. Uses: gears, agricultural implements 5

6 VI. Terms Used When Dealing With Alloys A. Ferrous alloys (CI-Cast Iron), (DI-Ductile Iron), (MI-Malleable Iron), (ST-Steel) 1. Inoculation (CI & DI) - addition to molten cast irons designed to form nuclei for graphite to form on 2. Treatment (DI) - addition of magnesium or rare earths to base iron to cause graphite to form nodules 3. Nodulizer (DI) - material, such as magnesium, added to base iron to form nodules 4. In-mold treatment (DI) - nodulizing material is placed in the mold's gating system 5. In-mold inoculation (DI & CI) - inoculant placed in bottom of sprue or gating system 6. Stream additions (DI & CI) - inoculant added to stream of metal when it leaves furnace and in some cases from transfer ladle to pouring ladle. 7. Hard Iron (MI) - Malleable iron before it is heat treated 8. Soft Iron (MI) - Malleable iron after it is heat treated 9. Killed Steel (ST) - Steel deoxidized with a strong deoxidizer such as aluminum or silicon 10. Rimmed Steel (ST) - A low carbon steel 11. Carbon Boil (ST) - Oxygen blown into to molten steel, while in the furnace, to reduce carbon levels 12. Blocked Heat - Same "killed steel" 13. Pig Iron (CI, DI, MI) - Cast iron poured into "pigs" used in melting of cast irons and usually used to raise carbon levels 14. Spiegeleisen (CI, MI, ST) - A high manganese pig iron (16-23%Mn) 15. Silvery pig (CI, DI, MI) - A high silicon pig iron (8-22% Si) 16. Ferroalloys (CI, DI, MI) - Normally used as inoculants. 17. Deoxidizer (ST) - Added to molten steel after carbon boil to drive out oxygen. Usually aluminum or silicon 6

7 18. Slag (CI, DI, MI, ST) - Contains the impurities produced during melting. In steel melting, it also plays an important role in controlling the chemistry of the melt. 19. Dross (DI) - The "slag" formed after treatment. Usually very high in magnesium oxide. 20. Pearlite (GI, DI, MI) - Matrix around graphite in cast irons made up of alternate layers of ferrite, which is soft and Iron Carbide, which is hard. 21. Ferrite (GI, DI, MI) - Matrix around graphite in cast iron which is soft. Solution of Carbon and Alpha Iron 22. Chill (GI, DI, MI) - Iron-carbide (cementite) which is very hard. Usually found on external edges of cast iron castings due to rapid solidification 23. Graphitizers (GI, DI, MI) - Elements added to cast irons to help carbon come out of the liquid solution. 24. Carbide Stabilizers (GI, DI, MI) - Elements in cast irons which tend to help keep carbon in solution with the liquid iron. 25. Austenite (GI, DI, MI, ST) - a metal solution of carbon dissolved in Gamma Iron. B. Nonferrous Alloys - (Al - Aluminum) (CU - Copper base) 1. Degas (Al, Cu) - Removing gasses from molten metal. In aluminum alloys the gas is hydrogen and in copper base alloys it is oxygen. 2. Deoxidize (Cu)-removing oxygen from copper base alloys. 3. Grain refining (Al) - Addition of titanium/boron to molten aluminum to cause many fine grains to develop upon solidification. 4. Modification (Al) - Addition of strontium or sodium to Aluminum Silicon alloys which "rounds off" sharp corners on silicon crystals which form on solidification. Increases ductility 5. Vacuum or Reduced Pressure Test (Al, Cu) - Method of testing gas content of liquid metal before pouring. 6. Thermal Analysis (Al) - Method of checking the amount of grain refining accomplished in grain refining process. 7. Dross (Al, Cu) - The impurities formed during the melting of nonferrous alloys. 7

8 8. Primary Ingot - Nonferrous alloys or metals which are not adulterated with reclaimed metal scrap and used for melting. 9. Secondary Ingot - Nonferrous alloys produced from recovered scrap by remelting and used for melting stock in the foundry. C. General Terms (all alloys) 1. Eutectic - A point in the chemical composition of an alloy where it solidifies and acts as a pure metal 2. Eutectoid - A point in the chemical composition of carbon steels where it solidifies and acts as a pure metal. In carbon steels this point is 0.80% Carbon 3. Hypereutectic - Any composition of an alloy which is to the right or above the eutectic point. 4. Hypoeutectic - Any composition of an alloy which is to the left or below the eutectic point. 5. Hypereutectoid - Same as hypereutectic except used in carbon steel alloys 6. Hypoeutectoid - Same as hypoeutectic except used in carbon steel alloys. 7. Dendrite - Solidified metal characterized by a treelike pattern of growth. 8. Crystallization - Formation of crystals by the atoms assuming definite positions when the metal solidifies. 9. Machinability - The ease with which an alloy can be machined. 10. Weldability - The ease with which an alloy can be welded. 11. Ingot - Nonferrous alloy of specific chemical composition cast to a convenient size and used for melting. 12. Superheat - Any increment of temperature above the melting point of the alloy or metal. 8