Ch4 alloys heat threatment

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Chapter 4Metal Alloys: Structure and

Strengthening by Heat Treatment


Gear Teeth Cross-section

Figure 4.1 Cross-section of gear teeth showing induction-hardenedsurfaces. Source: Courtesy of TOCCO Div., Park-Ohio Industries, Inc.


Chapter 4 Topics

Figure 4.2 Outline of topics described in Chapter 4.


Two Phase Systems

Figure 4.3 (a) Schematic illustration of grains, grain boundaries, and particles dispersedthroughout the structure of a two-phase system, such as a lead-copper alloy. The grainsrepresent lead in solid solution in copper, and the particles are lead as a second phase.(b) Schematic illustration of a two-phase system consisting of two sets of grains: darkand light. The dark and the light grains have separate compositions and properties.


Cooling of Metals

Figure 4.4 (a) Cooling curve for the solidification of pure metals. Note that freezingtakes place at a constant temperature; during freezing, the latent heat ofsolidification is given off. (b) Change in density during the cooling of pure metals.


Phase Diagram for Nickel-copper Alloy System

Figure 4.5 Phase diagram for nickel-copper alloy system obtained at a slow rate ofsolidification. Note that pure nickel and pure copper each has one freezing ormelting temperature. The top circle on the right depicts the nucleation of crystals.The second circle shows the formation of dendrites (see Section 10.2). The bottomcircle shows the solidified alloy with grain boundaries.


Mechanical Properties of Copper Alloys

Figure 4.6 Mechanical properties of copper-nickel and copper-zincalloys as a function of their composition. The curves for zinc are short,because zinc has a maximum solid solubility of 40% in copper.


Lead-tin Phase Diagram

Figure 4.7 The lead-tin phase diagram. Note that the composition of eutecticpoint for this alloy is 61.9% Sn – 38.1% Pb. A composition either lower orhigher than this ratio will have a higher liquidus temperature.


Iron-iron Carbide Phase Diagram

Figure 4.8 The iron-iron carbide phase diagram. Because ofthe importance of steel as an engineering material, thisdiagram is one of the most important of all phase diagrams.


Unit Cells

Figure 4.9 The unit cells for (a) austenite, (b) ferrite, and (c) martensite. The effectof percentage of carbon (by weight) on the lattice dimensions for martensite isshown in (d). Note the interstitial position of the carbon atoms (see Fig. 1.9). Alsonote, the increase in dimension c with increasing carbon content: this effect causesthe unit cell of martensite to be in the shape of a rectangular prism.


Microstructures for an Iron-Carbon Alloy

Figure 4.10 Schematic illustration ofthe microstructures for an iron-carbon alloy of eutectoidcomposition (0.77% carbon) aboveand below the eutectoid temperatureof 727°C (1341°F).


Microstructure of Steel Formed from Eutectoid Composition

Figure 4.11 Microstructure of pearlite in 1080 steel formed from austeniteof a eutectoid composition. In this lamellar structure, the lighter regionsare ferrite, and the darker regions are carbide. Magnification: 2500x.


Iron-Carbon Phase Diagram with Graphite

Figure 4.12 Phase diagram for the iron-carbon system with graphite (instead ofcementite) as the stable phase. Note that this figure is an extended version of Fig. 4.8.


Microstructure for Cast Irons

Figure 4.13 Microstructure for cast irons. Magnification: 100x. (a) Ferritic gray ironwith graphite flakes. (b) Ferritic ductile iron (nodular iron) with graphite in nodularform. (c) Ferritic malleable iron. This cast iron solidified as white cast iron with thecarbon present as cementite and was heat treated to graphitize the carbon.


Microstructure of Eutectoid Steel

Figure 4.14Microstructure of eutectoidsteel. Spheroidite isformed by tempering thesteel at 700°C (1292°F).Magnification: 1000x.


Martensite

Figure 4.15 (a) Hardness of martensite as a function of carbon content. (b)Micrograph of martensite containing 0.8% carbon. The gray plate-like regions aremartensite; they have the same composition as the original austenite (whiteregions). Magnification: 1000x.


Hardness of Tempered Martensite

Figure 4.16 Hardness of tempered martensite as a function oftempering time for the 1080 steel quenched to 65 HRC. Hardnessdecreases because the carbide particles coalesce and grow in size,thereby increasing the interparticle distance of the softer ferrite.


Time-temperature-

transformationdiagrams

Figure 4.17 (a) Austenite-to-pearlite transformationof iron-carbon alloy as afunction of time andtemperature. (b)Isothermal transformationdiagram obtained from (a)for a transformationtemperature of 675°C(1274°F). (c)Microstructures obtainedfor a eutectoid iron-carbonalloy as a function ofcooling rate.


Hardness and Toughness in Steel as a Function of Carbide Shape

Figure 4.18 (a) and (b) Hardness and (c) toughness for annealed plain-carbon steel as afunction of a carbide shape. Carbides in the pearlite are lamellar. Fine pearlite is obtainedby increasing the cooling rate. The spheroidite structure has sphere-like carbide particles.


Mechanical Properties of Steel as a Function ofComposition and Microstructure

Figure 4.19 Mechanical properties of annealed steels as a function of composition andmicrostructure. Note in (a) the increase in hardness and strength and in (b) the decreasein ductility and toughness with increasing amounts of pearlite and iron carbide.


End-QuenchHardenability

Test

Figure 4.20 (a) End-quench test and coolingrate. (b) Hardenabilitycurves for five differentsteels, as obtained from theend-quench test. Smallvariations in compositioncan change the shape ofthese curves. Each curve isactually a band, and itsexact determination isimportant in the heattreatment of metals forbetter control of properties.


Phase Diagram for Aluminum-copper Alloyand Obtained Microstructures

Figure 4.21 (a) Phase diagram for the aluminum-copper alloy system.(b) Various microstructures obtained during the age-hardening process.


Effect of Time and Temperature on Yield Stress

Figure 4.22 The effect of again time and temperature on the yieldstress of 2014-T4 aluminum alloy. Note that, for eachtemperature, there is an optimal aging time for maximum strength.


Outline of Heat Treatment Processes for Surface Hardening


Outline of Heat Treatment Processes for Surface Hardening, con’t.


Heat-treating Temperature Ranges for Plain-Carbon Steels

Figure 4.23 Heat-treating temperature ranges for plain-carbonsteels, as indicated on the iron-iron carbide phase diagram.


Hardness of Steel as a Function of Carbon Content

Figure 4.24 Hardness of steels in the quenched andnormalized conditions as a function of carbon content.


Mechanical Properties of Steel as a Function ofTempering Temperature

Figure 4.25 Mechanicalproperties of oil-quenched 4340 steel asa function of temperingtemperature.