CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 2
temperature, (c) higher intrinsic creep strength for lower stresses at elevated temperature (d) good
resistance to uniform corrosion and oxidation behaviour, and (e) economical from overall life
cycle cost [33,34]. However, austenitic steels possess low yield strength, and thus several process
are used to improve the yield strength, such as thermomechanical treatments, hardening with
nitrogen and precipitation hardening etc [35]. Apart from this, austenitic stainless steels are
susceptible to stress corrosion cracking in the presence of aggressive ions [15]. This type of failure
occurs under applied stress or as a result of residual stress in fabricated materials. Similarly,
localized corrosion along the grain boundaries can be a serious problem due to chromium
depletion, and formation of chromium carbide precipitates. Pitting and crevice corrosion are the
other localized corrosion type which occur in the environment containing halide ions [15].
2. 2 Fe-C equilibrium diagram and austenitic stainless steel
A study of the constitution and structure of all steels starts from Fe-C equilibrium diagram.
A portion of the Fe-C phase diagram is presented in Fig. 2.1 [15].
Fig. 2.1: Fe-C equilibrium phase diagram [15]