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11.07.2009 07:20 - Thermal Metastability in Heating and Cooling of Some Austenitic Ferrous Alloys—Theoretical Foundations
Автор: bogomil Категория: Технологии   
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Последна промяна: 11.07.2009 18:11


Met. Phys. Adv. Tech., 2001, Vol. 19, pp. 517-532 
Reprints available directly from the publisher 
Photocopying permitted by license only      

                    © 2001 ΟΡA
(Overseas Publishers Association)               N.V.             Published by license under                      the Gordon and Breach Science
                      Publishers imprint.

PHASE TRANSFORMATIONS

Thermal Metastability in Heating and Cooling of Some Austenitic
Ferrous Alloys—Theoretical Foundations  B. Kolev Institute for Metal Science, Bulgarian Academy of Sciences, 67 "Shipchenski Prohod"Str., 1574 Sofia, Bulgaria, home  adress1797 Sofia; E-mail: b.v.kolev@abv.bg

According to the hypothesis suggested the basic processes, namely solid phase reactions caused by ageing of homogenised and quenched austenitic (A) alloys of Fe—Cr—Mn—C and Fe—Mn—(Cr)—C systems with and without nitrogen, are determined by the rate of supersaturation of the solid solution with C, N, C+N and by their interaction with the available "substitutes" (carbide- and nitride-forming elements) depending on their quantity, affinity and diffusion coefficient as well as on their influence in relation to equilibrium curves of the state diagrams—polythermal cross-sections.
(Received June 26, 1998) 1. INTRODUCTION A theory about structural processes caused by heating and cooling (ageing) of homogenised and quenched austenitic alloys of the Fe—Cr-Mn—C system with and without nitrogen is absent in the literature sources to date. The experimental data concern nitrided stainless forgec steels containing less than 0.1% C and more than 14-16% Cr [1, 2, 7] Examinations were conducted after plastic deformation [1, 2, 7]. Th< mechanism of the process is not clear yet. The structural change! caused by ageing of homogenised and quenched alloys of the abov< mentioned systems containing 0.3-4% C, 0-30% Cr by Mn from 7-10% up to 22-30% without overequilibrium nitrogen contents, an considered in experimental and theoretical works. The purpose of the present work is to sum up the former experi mental and theoretical material produced by the author and formulate j hypothesis (theory) of the structural processes caused by "ageing" of pre liminarily homogenised and quenched austenitic alloys of the abov< mentioned systems.
Figure 1. Structure diagram of Fe-Cr-Mn-C-N system, 1150°C, 6 hours, H2, 0.9-19% Μη [1, 6-8].


2. SUMMARIZED RESULTS AND DISCUSSION The hypothesis is based on the studies made during 1975-1997 for the following groups of alloys: a)          Fe-Cr-Mn-C-N respectively Fe-Cr-Mn-N systems (stainless
steels): C = 0.05-2.8%; Si = 0.6-2.5%; Mn = 5-15%; Cr = 7-23%; Ν =
=0.15-1.325%; S, P



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Автор: bogomil
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