Asm Comp Tt Stainless Steel

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Curso de tratamiento térmico de aceros inoxidables
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  . . : . ( , . _  j . . . .. / HOME STUDY AND EXTENSION COURSES AMERICAN SOCIETY FOR METALS onstitution and I Ieat Treatment of StaiIlless Steels by Paul G. Nel s on, B.S. The Budd Company Philadelphia, Pa. .. :. .  : Course 10 Lesson, TestIS Course 41 Lesson, Test 14 METALS ENGINEERING INSTITUTE METALS PARK, OHIO ~ I -   .   -   - . -- -- .    :.::: ~   '.   ... . - ,:: . '';~\. ~ < ;: ':> -'<~: :~7   - : .n: ' :~::  :: ';· :  :~';:~~ ~: ~ :t~,{ ~~~ . . iron-cemenlte phase diagram, fig. 14:1. form to the gamma ( ) ) or face-centered This diagram shows that on heating from cubic form at the A3 temperature. On room temperature iron transforms from further heating to , the . A4 temperature the alpha (ex) or body-center  ed cubic~ , , . the gamma form transforms   to the delta - -- j-. o I EU1[CTO O PER C(NT CARBON [UTECTIC ~ ~ HYPO (UttCTO O ----1 f r---  '''[II[U1[C'01O& ,= .. HYPO (UT[GTIC ~+~ H'''[''[U1[(;TIC 1 0 , l--- STEELS _ CAST '''ONS _ ~~~a~· ~ ~w~~ ~ {j P .... 1'£.unCTIC nil ...... [UT[CTIC 2040 1. w IRON C RBIDE ' ,c ~  TYPICAL . ANN[ALED J 4 IC ROSTRUCTUR S Fig. 14:1. Th e Ir o n- Ce mentit e Phase Diag ram : The critical pOints (or pure iron are shown on the left. Changes appear as lines pro greS S ing to the ri~ht as carbon is anded. Note the location of the A, critical li ne and the influ e nce of carb on on the delta (,q fi eld. Mel.l EnRineerinr. In s lit ute- .  - ;::-::: :.. :.~ .. , . .. . t  . .-S   ~ I \ 1 , ,   : J  , -' ' ã '.' - ... ' : .. - .. ' CONSTITUTION AND HEAT TREA TMENTOF- STAINLESS STEELS , , - By Paul O. Nelson, B c S   ~ ~ : .. . Iron has been alloyed with practi cally every mown' element in an effort ' to improve Its . corr.osion resistance. The discovery that relatively large additions of chromium (about 12% or more) markedly improved the corrosion re- _ sistance of iron under atmospheric conditions resuited in the development of the group of modern ' 3Jloys popularly termed stainless steels.' The classi fication stainless is not a precise one but rather a relative one, because all of these alloys will corrode under certain conditions. Howe ver, this in no way re duces the industrial importance of these alloys. They do have outstanding corro sion re s istance in a wide variety of en vironments, Under normal atmospheric co nditi o ns co rrosive attack is so little on man y of the stainless steei alloys that t is easy to unde rstand why they have been te rmed ã stainless .' Th e development of stainless st ee ls cann ot be attributed to anyon e individual but mu st be shar ed by a number of investigators, Th e production of low car bon fe rr oc hr o mium and chromium me tai by aluminothermic reduction was ce rt ainly a tr e mendous f ac tor. This process, developed by Goldschmidt in 1895, is stilI' in use today. Later, using Goldschmidt chromium, Guillet produced all thr ee of the present-day important cl asses of stainless st e el-martensitic, f err i tic , and aus te nitic- and examined them m etal lur gic ally and me chanica lly. _ s :. ~ His d1scoveri/ls were complemented by Monnarti~ V{hose : observatiims of fac- - tors affecting the corrosive behaviorof these - alloys were not fully appreCiated until mo o e modern theories of corrosion we re de'leloped. -_ . CONSTITUTION The three important classes of stainless steel which have been developed ha ve been classified according to their microstructure as follows : 1. Martensitic 2. Ferritic 3. Austenitic A newcomer Into the stainless steel family is a type of alloy known as pre Cipitation-hardening stalnless steel. These alloys will also be discussed. Each of these classes contains a minimum of 12 per cent chromium, that amount being necess a ry to obtain the unique pas s ivity or stainless character possessed' by these alloys. The baiance of the co mposition has been modified with other alloying elements to obtain the characteristic microstructure and desired mechanical properties. Iron-Chromium Phase Diagram To better understand the phase re lationshi ps In Iro n-ch r omium alloys, it is h. elpful to' refer once again to the This material may not be reproduced n whole or n part n any form whats oeve r. ~ Fully protected  by co pyright '. \ . . ; ;.' . - _. __ _--   - --- - .. ---   _ .. _.-  ; ~ l:\ ~ ~ . . ,,' - . ~ , -   ~ : :: : {~ ~ 71~k:f ~~ ~~: ~F   ~~,· ;~~:, :?o.,;~; ~~ ~~~~ ~ ; ~: _ · \~ : , - , , :,   'j~oT ?:;   ~. form smaller and smaller gaIIUll,;lloops .. those ' of ,' chromium. These , elements .   ãã   -   \ . as seen in Fig. 14:4. lower :' ~   'and ' ralse ' A/. ' When Aa Is ' lowered 5ufflciently   ~ oiily' austenite . ,, ~ . , ã , ã l .. ~ There are , other alloying addltions ~ exists even at room temperature. 'When ' which tend to stabilize ferrite because A. Is raised sufficlently,- ferrite dls- . they form carbides and thus reduce the appears entirely so that only austenite . ' austenite-forming effect of carbon. How- is present when the , melting point is ever before discussing them further it , reached . The effect  of carbon in raising will be well to consider the alloying A. ' and lowering ' A ~   , is shown in , elements which have ~ffects opposite to Fig. 14:5. It will be 'noted that   the 100 . ~ - . LL o I O -   3200 2800 2400 2000 16 ~= -01200 - O Cl E 800 400 , . > o Alpha  o E Ol (f) 20 40. 60 Chromium-Per Cen t Fig. 14 :3. Ph ase Diagram for Carbon-Free Iron-Chromium Alloys _ t  h E n~i n e eri ng nst tut  80 1 00 I , I· l ) ... . I .
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