Heat Treatment-ASM Metals HandBook Volume 4 | Steel | Physical Sciences

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Heat Treatment-ASM Metals HandBook Volume 4
  against any alleged infringement of letters patent, copyright, or trademark, or as a defense against liability for suchinfringement.Comments, criticisms, and suggestions are invited, and should be forwarded to ASM International. Library    of    Congress   Cataloging-in-Publication   Data   (for    Print    Volume) ASM Handbook !evised vol. # Metals Handbook. $itle proper has changed with v. % ASM Handbook&'repared under the direction of the ASM International Handbook Committee. Includes bibliographies and inde(es. Contents% v. . Heat$reating.). Metals*Handbooks, manuals, etc. I. ASM International. Handbook Committee. II. $itle% ASM Handbook.$A +.M - ) /0.)1/ *))+IS23 *45)5*-5*-SA3 0 *5+4/'rinted in the 6nited States of America Principles   of    Heat   Treating   of    Steels $orsten 7ricsson, 8ink9ping Institute of $echnology, Sweden Introduction A S$778 is usually defined as an alloy of iron and carbon with the carbon content between a few hundreds of a percentup to about 0 wt:. ;ther alloying elements can amount in total to about + wt: in low*alloy steels and higher in morehighly alloyed steels such as tool steels and stainless steels. Steels can e(hibit a wide variety of properties depending oncomposition as well as the phases and microconstituents present, which in turn depend on the heat treatment. Insubse<uent articles in this Section, various types of heat treatment are described in detail. In this article, an outline of the physical metallurgy associated with heat treating of steels will be given and some important =tools= will be introduced.>eliberately no microstructures are shown as a well*illustrated article e(ists in =Microstructures, 'rocessing, and'roperties of Steels,= by ?. @rauss in  Properties   and    Selection:    Irons,   Steels,   and     High-Performance    Alloys,  olume ) of   ASM     Handbook  . A companion article that emphasiBes information systems for predicting microstructures and hardnessesof <uenched steels follows see the article=uantitative 'rediction of $ransformation Hardening in Steels= in thisolume#. The   Fe-C   Phase   Diagram $he basis for the understanding of the heat treatment of steels is the De*C phase diagram Dig. )#. 2ecause it is welle(plained in earlier volumes of  ASM     Handbook  , formerly  Metals    Handbook   !ef ), 0, -#, and in many elementaryte(tbooks, it will be treated very briefly here. Digure ) actually shows two diagramsE the stable iron*graphite diagramdashed lines# and the metastable De*De - C diagram. $he stable condition usually takes a very long time to develop,especially in the low*temperature and low*carbon range, and therefore the metastable diagram is of more interest. $he De*C diagram shows which phases are to be e(pected at e<uilibrium or metastable e<uilibrium# for different combinations of carbon concentration and temperature. $able ) provides a summary of important metallurgical phases andmicroconstituents. Fe distinguish at the low*carbon end ferrite G*iron#, which can at most dissolve .04 wt: C at 505C )- ) D# and austenite *iron#, which can dissolve 0.)) wt: C at )) 4 C 04 D#. At the carbon*rich side we findcementite De - C#. ;f less interest, e(cept for highly alloyed steels, is the J*ferrite e(isting at the highest temperatures.2etween the single*phase fields are found regions with mi(tures of two phases, such as ferrite K cementite, austenite Kcementite, and ferrite K austenite. At the highest temperatures, the li<uid phase field can be found and below this are thetwo phase fields li<uid K austenite, li<uid K cementite, and li<uid K J*ferrite. In heat treating of steels, the li<uid phase is  always avoided. Some important boundaries at single*phase fields have been given special names that facilitate thediscussion. $hese include% ã A ) , the so*called eutectoid temperature, which is the minimum temperature for austenite ã A - , the lower*temperature boundary of the austenite region at low carbon contents, that is, the & K G boundary ã A cm , the counterpart boundary for high carbon contents, that is, the & K De - C boundary Sometimes the letters c, e, or r are included. !elevant definitions of terms associated with phase transformations of steelscan be found in $able 0 as well as the ?lossary of $erms in this olume and !ef -. $he carbon content at which theminimum austenite temperature is attained is called the eutectoid carbon content .55 wt: C#. $he ferrite*cementite phase mi(ture of this composition formed during cooling has a characteristic appearance and is called pearlite and can betreated as a microstructural entity or microconstituent. It is an aggregate of alternating ferrite and cementite lamellae thatdegenerates =spheroidiBes= or =coarsens=# into cementite particles dispersed with a ferrite matri( after e(tended holdingclose to A ) . Table   1   Important   metallurgical   phases   and   microconstituents Phase   (microconstituent) Derrite G*iron#bJ*ferrite J*iron#bAustenite *iron#f Cementite De - C#C?raphite'earliteMartensiteb2ainite. Table      Definitions   of    transformation   temperatures   in   iron   and   steels   See the ?lossary of $erms in this olume for additional terminology. Transformation   temperature!  $he temperature at which a change in phase occurs. $he term is sometimes used to denote the limiting temperature of a transformation range. $he following symbols are used for iron and steels.  Only 2 pages have been converted.Please go to htt p s://d o cs.zo n e and Sign Up to convert all pages.
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