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Learn about the different types and compositions of steels and cast irons, their applications, and the effects of carbon and alloying elements on their properties. Discover the processes of hot rolling and the heat treatment of steels.
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Materials Applications Chapter 13
The Big Picture c13f01
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
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.
Hot Rolling • Hot rolling is a hot metalworking process where large pieces of metal (slabs or billets), are heated above their recrystallization temperature (1/3 Tm< Hot roll <1/2 Tm) and then deformed between rollers to form thinner cross sections. • Hot rolling produces thinner cross sections than cold rolling processes with the same number of stages. • Hot rolling, due to recrystallization, will reduce the average grain size of a metal while maintaining an equiaxed microstructure where as cold rolling will produce a hardened microstructure.
Effects of Alloying Elements on Steel • 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.
Medium Carbon Steel • These alloys may be (heat treated) austenitized, quenched and then tempered to improve mechanical properties (tempered martensite). • Cr, Ni, Moimprove the heat treating capacity of plain medium carbon steels. High Carbon Steel • These steels alloyed with Cr, V, W, Mo are used in blade applications and tools.
Classification of Metal Alloys Steels Cast Irons <1.4wt%C 3-4.5wt%C microstructure: ferrite, T(°C) graphite/cementite 1600 d L 1400 g +L g L+Fe3C 1200 1148°C austenite Eutectic: 4.30 1000 g a +Fe3C + Fe C 800 a g 3 727°C ferrite Eutectoid: cementite a +Fe3C 600 0.76 400 0 1 2 3 4 5 6 6.7 (Fe) Co, wt% C Metal Alloys Ferrous Nonferrous Steels Cast Irons <1.4wt%C 3-4.5 wt%C 15
Ferrous Materials Cast Irons • Iron accounts for more than 95 wt% of the alloy material, while the main alloying elements are carbon (between 2.1- 4.5 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.
Cast iron coated with durable porcelain enamel distributes heat slowly and evenly. Cast Iron • Wide range of applications (including pipes, machine and car parts, such as cylinder heads, blocks and gearbox cases) due to: • low melting point, • good fluidity, • relatively easy to cast, • excellent machinability, • resistance to deformation • wear resistance • Cast iron tends to be brittle, except for malleable cast irons, so shaping these by deformation is very difficult.
Grey Cast Iron Grey cast iron is named after its grey fractured surface that occurs when the graphitic flakes deflect a passing crack and initiate many new cracks as the material breaks. • graphite flakes surrounded by a-ferrite or pearlite matrix • weak & brittle in tension (the graphite flake tips are sharp; act as stress raisers) • stronger in compression • excellent vibrational dampening • wear resistant • Carbon content: 3.0 – 4.0 wt% • Silicon content: 1.0 – 3.0 wt % • Modifying silicon content and cooling rate affects microstructure. • Casting shrinkage is low grey grey
Nodular (Ductile) Cast Iron Adding Mg and/or Cerium to grey iron before casting produces a distinctly different microstructure and mechanical properties. • graphite forms nodules not flakes • Normally a pearlite matrix • Photo (nodular) shows ferrite matrix that was heat treated for several hours at 700˚C. • Castings are stronger and much more ductile than grey iron. grey nodular nodular
White Cast Iron White cast iron is named after its white surface when fractured due to its carbide impurities that allow cracks to pass straight through; the crystalline fractures are shiny compared to the dull gray fractures of graphite irons. • < 1 wt% Si, rapid cooling rates • pearlite + most of the carbon forms cementite, not graphite. • very hard and brittle; • thickness may result in nonuniform microstructure from variable cooling; white iron develops from faster cooling; slower cooling rate yields grey iron. • limited applications; used as intermediate to produce malleable cast iron.
white iron nodular Malleable Cast Iron • Malleable cast iron formed by heat treating white iron at 800-900ºC for a prolonged period causes decomposition of cementite into graphite. • graphite forms clusters or rosettes that are surrounded by a ferrite or pearlite matrix. • reasonably strong and ductile (malleable) • Carbon content: 2.3 – 2.7 wt% • Silicon content: 1.0 – 1.75 wt % malleable malleable
Fe-C True Equilibrium Diagram • Graphite formation promoted by • Si > 1 wt% • slow cooling • Cementite decomposes to ferrite + graphite Fe3C 3 Fe () + C (graphite)
Variety of Cast Iron Microstructures Gf , graphite flake Gr , graphite rosettes Gn, graphite nodules P, pearlite = a + cementite a, ferrite
Compact Graphite Iron (CGI) • CGI graphite occurs as blunt flakes or with a worm-like shape (vermicular). • Microstructure and properties are a cross between gray and ductile iron. • Production requires other alloying elements to minimize the sharp edges and formation of spheroidal graphite. • CGI retains much of the castability of gray iron, but has a higher tensile strength and some ductility. • Its matrix structure can be adjusted by alloying or heat treatment. • relatively high thermal conductivity • good resistance to thermal shock • lower oxidation at elevated temperatures • Carbon content: 3.1 – 4.0 wt% • Silicon content: 1.7 – 3.00 wt % CGI CGI
Stainless steel • Stainless steels - A group of ferrous alloys that contain at least 11% Cr, providing extraordinary corrosion resistance. • Categories of stainless steels: • Ferritic Stainless Steels • Martensitic Stainless Steels • Austenitic Stainless Steels • Precipitation-Hardening (PH) Stainless Steels • Duplex Stainless Steels
Ferrous Alloys Limitations Strengths • Relatively high densities • Relatively low electrical conductivities • Generally poor corrosion resistance • Inexpensive • Abundant supply of iron ore • Many applications due to wide range of material properties. http://www.nickelinstitute.org/index.cfm?ci_id=8&la_id=1 stainless steel videos
The name Cronidur is derived from the blade itself which is made from a single piece of Cronidur 30 steel. Used in the aerospace industry, this steel is designed to repel corrosion under the most extreme conditions and retain hardness without being brittle. • Each knife is precision forged using Zwilling’s Sigmaforge process resulting in an exceptionally hard yet flexible blade. • Zwilling’s Fridour ice-hardening technique results in a harder, sharper blade that is corrosion resistant and highly elastic. • Precise lasers are used to ensure each blade’s edge is at the optimal cutting angle for maximum sharpness. • Partnered with renowned Italian architect Matteo Thun to develop the design of the knife. • A curved and recessed bolster provides a seamless transition from handle to blade and supports the thumb for better balance and safety. • The ergonomic handle is made of full-linen Micarta—a composite with the grained look of wood and the longevity of plastic. • Made in Germany by Zwilling J.A. Henckels since 1731.
Nonferrous Metals • Al Alloys -low r: 2.7 g/cm3 -Cu, Mg, Si, Mn, Zn additions -solid solution or precipitation strengthened (structural aircraft parts & packaging) NonFerrous • Mg Alloys r -very low : 1.7g/cm3 Alloys -ignites easily - aircraft, missiles • Ti Alloys • Refractory metals -relativelylowr:4.5g/cm3 -high melting T’s (7.9 g/cm3 for steel) • Noble metals -Nb, Mo, W, Ta -Ag, Au, Pt -reactiveathighT’s - oxidation/corrosion resistant - space application • Cu Alloys Brass:Zn is a substitutional impurity (costume jewelry, coins, corrosion resistant) Bronze : Sn, Al, Si, Ni are substitutionalimpurities Cu-Be : precipitation hardened for strength (bushings, landing gear)
Copper • It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable making it difficult to machine. • Copper is the standard benchmark for electrical conductivity. It conducts electrical current better than any other metal except silver. • Copper is routinely refined to 99.98% purity before it is acceptable for many electrical applications. • Building construction accounts for more than 40% of all copper use. The average single-family home contains the following amounts of copper: 195 pounds - building wire 151 pounds - plumbing tube, fillings, valves 24 pounds - plumbers' brass goods 47 pounds - built-in appliances 12 pounds - builders hardware 10 pounds - other wire and tube
Copper Facts • Copper is the oldest metal, dating back more than 10,000 years. A copper pendant discovered in what is now northern Iraq dates to roughly 8700 B.C. • The boilers on Robert Fulton's steamboats were made from copper. • Archeologists have recovered a portion of a water plumbing system from the Pyramid of Cheops in Egypt. The copper tubing used was found in serviceable condition after more than 5,000 years. • Copper cookware is the most highly regarded by chefs around the world. Its noted advantages - high heat transfer (the highest of any material used in cooking) plus uniform heating (no hot spots). • Brasses and Bronzes are probably the most well-known families of copper-base alloys. Brasses are mainly copper and zinc. Bronzes are mainly copper along with alloying elements such as tin, aluminum, silicon or beryllium. • Other copper alloy families include copper-nickels and nickel silvers. Copper Development Association (CDA) recognizes more than 400 copper-base alloys in current use.
c13f06 • The US penny contains only 2.6% copper. In 1982, the U.S. Mint converted production of the 95% copper coin to a predominantly zinc alloy, but coated it with copper to preserve its appearance. • The U.S. nickel is actually 75% copper. The dime, quarter, and half dollar coins contain 91.67% copper and the Susan B. Anthony dollar is 87.5% copper. • The various Euro coins are Cu-Ni, Cu-Zn-Ni or Cu-Al-Zn-Sn alloys.
Brass • Brass is the most common copper alloy (zinc is the substitutional impurity). • Brass has higher ductility than copper or zinc. The relatively low melting point of brass (900 to 940°C, depending on composition) and its flow characteristics make it a relatively easy material to cast. • By varying the proportions of copper and zinc, the properties of the brass can be changed, allowing hard and soft brasses. • Some of the common brasses are yellow, naval and cartridge. • Brass is frequently used to make musical instruments (good ductility and acoustic properties).
Bronze • Copper alloys containing tin, (lead), aluminum, silicon and nickel are classified as bronzes. • Stronger than brasses with good corrosion and tensile properties; can be cast, hot worked and cold worked. • Wide range of applications: ancient Chinese cast artifacts, skateboard ball bearings, surgical and dental instruments.
Beryllium copper • Beryllium copper is ductile, weldable and machinable. It is resistant to non-oxidizing acids (hydrochloric acid or carbonic acid), to abrasive wear and to galling (surface damage caused by sliding solids). • It can be heat-treated to improve its strength, durability and electrical conductivity. • Beryllium copper is used in springs, load cells and other parts that must retain their shapes while subjected to repeated stress and strain. • Due to its electrical conductivity, it is used in low-current contacts for batteries and electrical connectors. • High strength beryllium copper alloys contain up to 2.7% of beryllium (cast), or 1.6-2% of beryllium with about 0.3% cobalt (wrought). The high mechanical strength is achieved by precipitation hardening or age hardening. The thermal conductivity of these alloys lies between steels and aluminum. The cast alloys are frequently used as material for injection molds. • Other applications include jet aircraft landing gear bearings and bushings and percussion instruments.
Aluminum • Aluminum is a relatively light metal compared to steel, nickel, brass and copper. Aluminum is easily machinable and can have a wide variety of surface finishes. It also has good electrical and thermal conductivities and is highly reflective to heat and light. • Aluminum is a versatile metal and can be cast in many forms. It can be rolled, stamped, drawn, spun, roll-formed, hammered and forged. The metal can be extruded into a variety of shapes, and can be milled, and bored in the machining process. Aluminum can be riveted, welded, brazed, or resin bonded. For most applications, aluminum needs no protective coating as it can be finished to look good, however it is often anodized to improve color and strength. • Another important characteristic is specific strength; where the specific strength is a material's strength (force per unit area at failure) divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio. Materials with high specific strengths are widely used in aerospace applications where weight savings are worth the higher material cost. Titanium, magnesium and carbon fiber-epoxy (composites) are widely used in these applications for this reason.
Alloy Designation System • Aluminum alloys are classified as either cast or wrought. • Composition is designated by a 4 digit number that specifies the major alloying element. http://www.alcotec.com/us/en/solutions/-Understanding-the-Aluminum-Alloy-Designation-System.cfm
Temper Designations • F As fabricated. Applies to products in which no thermal treatments or strain-hardening methods are used to shaped the product. • H Strain-hardened (wrought products only). Applies to products that have their strength increased by strain-hardening, with or without additional thermal treatments to produce a reduction in strength. • H1 Strain-hardened only. Applies to products which are strain-hardened to achieve the strength desired without additional thermal treatment. • OAnnealed, recrystallized (wrought products only). Applies to wrought alloys which are annealed to obtain the softest temper, and to cast alloys which are annealed to improve ductility and dimensional stability. • T Thermally treated to produce stable tempers other than F, O or H. Applies to products which are thermally treated, with or without additional strain-hardening, to produce stable tempers. • T3Solution heat-treated and then cold worked. Applies to alloys which are cold worked to improve strength after solution heat treatment, or in which the effect of cold work in flattening or straightening is significant in mechanical property limits. http://www.efunda.com/materials/alloys/aluminum/temper.cfm
c13tf07 Composed of three interlocking nonstick layers for superior durability, the anodized aluminum pans are engineered to stand years of daily use and dishwasher cleaning. Safe for use on both gas and electric stovetops (and oven safe to 500ºF), they conduct heat exceptionally well while resisting stains and scratches. The triple-riveted ergonomic handles stay cool to the touch. Innovative cookware is made in Ohio by Calphalon - Made in the USA. CALPHALON 8-Piece Non-Stick Cookware Set 8 pc. cookware set includes an 8" omelette pan, a 10" omelette pan, a 1 qt. sauce pan with cover, a 2 qt. saucepan with cover, and a 6 qt. stock pot with cover. Features non-stick interior, hard anodized aluminum exterior with 2-coat system, contoured, riveted silicone and stainless steel handles, tempered glass dome covers.
Titanium • Titanium is very reactive, and because of this it is often used for alloying and deoxidizing other metals. Titanium is a more powerful deoxidizer of steel than silicon or manganese. • Titanium is 40% lighter than steel and 60% heavier than aluminum. This combination of high strength and low weight makes titanium a very useful structural metal. • Titanium also features excellent corrosion resistance, which stems from a thin oxide surface film that protects it from atmospheric and ocean conditions as well as a wide variety of chemicals. • Pure titanium melts at 1670oC and has a density of 4.51 g/cm3. Good for use in components that operate at elevated temperatures, especially where large strength to weight ratios are required. • Titanium can catch fire and cause severe damage in circumstances where it rubs against other metals at elevated temperatures. This is what limits its application in the harsh environment of aeroengines, to regions where the temperature does not exceed 400oC. http://www.msm.cam.ac.uk/phase-trans/2004/titanium/titanium.html
Titanium-2 • Titanium is rather difficult to fabricate because of its susceptibility to oxygen, nitrogen, and hydrogen impurities that cause the titanium to become more brittle. • Elevated temperature processing must be used under special conditions to avoid diffusion of these gasses into the titanium. • Commercially produced titanium products are made in the following mill wrought forms; plate, tubing, sheet, wire, extrusions, and forgings. • Titanium can also be cast, but must be done in a vacuum furnace because of titanium's reactive nature. • Because of its high strength to weight ratio and excellent corrosion resistance, titanium is used in a variety of applications: aircraft, sporting equipment, chemical processing, desalination, power generation equipment, valve and pump parts, marine hardware and prosthetic devices.
Nickel • Nickel-containing materials are used in buildings and infrastructure, chemical production, communications, energy supply (batteries: NiCd, Ni-metal hydrides), environmental protection, food preparation, water treatment and travel. • Nickel Catalyst for Fuel Cells: Nickel-cobalt is seen as a low-cost substitute for platinum catalysts. • Shape Memory Alloys: Stainless steel may soon provide a low-cost alternative to alloys that snap back to original form but are too expensive for widespread use. • Two-thirds of all nickel produced goes into stainless steel, to promote a stable, ductile, austenitic structure as well as contribute to corrosion resistance. • Key attributes: high melting point of 1453°C • forms an adherent oxide film • resists corrosion by alkalis • forms alloys readily, both as solute and solvent • readily deposited by electroplating Liquid natural gas storage tank
http://www.nickelinstitute.org/8/index1.shtml Nickel-2 Stainless steel roofing on the Thames Barrier
