1 ریخته گري (1) دانشکده مهندسي مواد و متالورژی دانشگاه علم و صنعت ایران فصل نهم فرآیندهای ذوب مهدی دیواندری ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384

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3 ریخته گري(آلومینیم) شمش ریزی شكل ریزی شمش ريختگي

The Big Picture

Ferrous Materials  Steels Steels are iron-carbon alloys that may contain other alloying elements. There are 1000s of alloys with different compositions and/or heat treatments. Low Alloy (<10 wt%) –Low Carbon (<0.25 wt%) –Medium Carbon (0.25 to 0.60 wt%) –High Carbon (0.60 to 1.4 wt%) High Alloy –Stainless Steel (> 11 wt% Cr) –Tool Steel Steels Low alloy Low Carbon Medium Carbon High Carbon High alloy Stainless Tool

Low Carbon Steel Plain carbon steels have very little additives (alloying elements) and small amounts of manganese. Most prevalent type of steel is low carbon steel (greatest quantity produced; least expensive). Low carbon not responsive to heat treatment; have to cold work. Weldable and machinable. High Strength, Low Alloy (HSLA) steel contains alloying elements (copper, vanadium, nickel and molybdenum) up to 10 wt %; they have higher strengths (than plain LC steels) and may be heat treated. ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384

Effects of Alloying Elements on Steel 7 Manganese contributes to strength and hardness; dependent upon the carbon content. Increasing the manganese content decreases ductility and weldability. Manganese has a significant effect on the hardenability of steel. Phosphorus increases strength and hardness and decreases ductility and notch impact toughness of steel. The adverse effects on ductility and toughness are greater in quenched and tempered higher-carbon steels. Sulfur decreases ductility and notch impact toughness especially in the transverse direction. Weldability decreases with increasing sulfur content. Sulfur is found primarily in the form of sulfide inclusions. Silicon is one of the principal deoxidizers used in steelmaking. Silicon is less effective than manganese in increasing as-rolled strength and hardness. In low- carbon steels, silicon is generally detrimental to surface quality. Copper in significant amounts is detrimental to hot-working steels. Copper can be detrimental to surface quality. Copper is beneficial to atmospheric corrosion resistance when present in amounts exceeding 0.20%. Nickel is a ferrite strengthener. Nickel does not form carbides in steel. It remains in solution in ferrite, strengthening and toughening the ferrite phase. Nickel increases the hardenability and impact strength of steels. Molybdenum increases the hardenability of steel. It enhances the creep strength of low-alloy steels at elevated temperatures.

ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384

Effect of Carbon content on Steel Hardness 9 Carbon wt % Nomenclature for steels (AISI/SAE) The first two digits indicate the major alloying metals in a steel, such as manganese, nickel- chromium, and chrome-molybdenum. xx is wt% C x 100 example: 1060 steel – plain carbon steel with 0.60 wt% C Carbon is the primary hardening element in steel. Hardness and tensile strength increase as carbon content increases up to about 0.85% C. Ductility and weldability decrease with increasing carbon. 10xxPlain Carbon steels 11xxResulfurized for machinablity 12xxResulfurized and rephosphorized Manganese 13xxMn xxMn Nickel 23xxNi xxNi 5.0 Nickel Chromium 31xxNi 1.25 Cr xxNi 1.75 Cr xxNi 3.50 Cr xxNi 3.00 Cr 0.77 Chromium Molybdenum 41xxCr Mo Nickel Chromium Molybdenum 43xxNi 1.82 Cr Mo xxNi 1.05 Cr 0.45 Mo 0.20 – xxNi 0.55 Cr 0.50 Mo 0.20 Nickel Molybdenum 46xxNi Mo xxNi 3.50 Mo 0.25 Chromium 50xxCr xxCr 0.80 – 1.05

10 Classification of Metal Alloys Metal Alloys Steels FerrousNonferrous Cast Irons <1.4wt%C3-4.5wt%C Steels <1.4 wt% C Cast Irons wt% C Fe 3 C cementite L  austenite  +L+L  +Fe 3 C  ferrite  +Fe 3 C  +  L+Fe 3 C  (Fe) C o, wt% C Eutectic: Eutectoid: °C 1148°C T(°C) microstructure: ferrite, graphite/cementite

Ferrous Steels Cast iron Grey White Nodular Malleable Compacted graphite 11

12 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Iron accounts for more than 95 wt% of the alloy material, while the main alloying elements are carbon (between wt%) and silicon (normally 1-3 wt%). From the iron-iron carbide phase diagram, cast iron has a eutectic point at 1153 °C and 4.2 wt% carbon. Since cast iron has roughly this composition, its melting temperature of 1150 to 1200 °C is about 300 °C lower than the melting point of pure iron. The most common cast iron types are: grey, white, nodular, malleable and compacted graphite. Ferrous Materials  Cast Irons

13 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Challenges of Molten Metal Hot metal readily forms oxides (dross or slag) Can be carried into the mold Can be controlled by pouring methods Control of temperature and atmosphere can slow creation of slag 1- پيشگيري 1-1- كنترل مواد شارژ 1-2- كنترل فرآيند ذوب كوره ها ساير تجهيزلت كنترل روش‍ 2- درمان 2-1- گاز زدايي 2-2- آخال زدايي

14 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Challenges of Molten Metal Dissolved gases Porosity Can be controlled by: Vacuum degassing Gas flushing “Killing” - Reacting trapped gas with material that will form buoyant compound that will float to surface Oxygen removed from copper by adding phosphorous Oxygen removed from steel by adding aluminum or silicon

15 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Challenges of Molten Metal Temperature Control Temp too Low Misruns Cold shuts Temp too High Excessive mold wear Higher reactivity of molten metal Penetration defects (excessive flash or entrapped sand)

Three Cast Structures of Solidified Metals FIGURE 5.8 Schematic illustration of three cast structures of metals solidified in a square mold: (a) pure metals; (b) solid-solution alloys; and (c) the structure obtained by heterogeneous nucleation of grains, using nucleating agents.

17 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Furnaces for Casting Processes Furnaces most commonly used in foundries: Cupolas Direct fuel ‑ fired furnaces Crucible furnaces Electric ‑ arc furnaces Induction furnaces

Cupolas Vertical cylindrical furnace equipped with tapping spout near base Used only for cast irons –Although other furnaces are also used, the largest tonnage of cast iron is melted in cupolas The "charge," consisting of iron, coke, flux, and possible alloying elements, is loaded through a charging door located less than halfway up height of cupola

Cupola furnace

Direct Fuel ‑ Fired Furnaces Small open ‑ hearth in which charge is heated by natural gas fuel burners located on side of furnace Furnace roof assists heating action by reflecting flame down against charge At bottom of hearth is a tap hole to release molten metal Generally used for nonferrous metals such as copper ‑ base alloys and aluminum

Crucible Furnaces Metal is melted without direct contact with burning fuel mixture Sometimes called indirect fuel ‑ fired furnaces Container (crucible) is made of refractory material or high ‑ temperature steel alloy Used for nonferrous metals such as bronze, brass, and alloys of zinc and aluminum Three types used in foundries: (a) lift ‑ out type, (b) stationary, (c) tilting

Crucible furnace

Three types of crucible furnaces: (a) lift ‑ out crucible, (b) stationary pot, from which molten metal must be ladled, and (c) tilting-pot furnace.

24 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Induction Furnaces Uses alternating current passing through a coil to develop magnetic field in metal Induced current causes rapid heating and melting Electromagnetic force field also causes mixing action in liquid metal Since metal does not contact heating elements, environment can be closely controlled to produce molten metals of high quality and purity Melting steel, cast iron, and aluminum alloys are common applications in foundry work

Electric Furnaces

26 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Charge is melted by heat generated from an electric arc High power consumption, but electric ‑ arc furnaces can be designed for high melting capacity Used primarily for melting steel Electric ‑ Arc Furnaces

27 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Ladles Moving molten metal from melting furnace to mold is sometimes done using crucibles More often, transfer is accomplished by ladles Two common types of ladles: (a) crane ladle, and (b) two ‑ man ladle.

28 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384

29 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Grain Structure in Casting Chill Zone – Rapid cooling near the surface creates many nucleation sites and many small, randomly oriented grains. Columnar Zone – Directionally oriented grains radiating inward from the surface of the part. Equiaxed Zone (not shown) – Randomly oriented, spherical crystals. (isotropic properties)

30 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Pouring Ladles

31 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Solidification Shrinkage

32 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384

33 ريخته گري ( 1)- دانشكده مهندسي مواد و متالورژي - دانشگاه علم و صنعت ایران 1384 Gate Filtering