CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 2
2.3.3 Manganese
Manganese is an austenite former, a deoxidizer, and a desulfurizer. In general, it is added
to austenitic stainless steel to assist in de-oxidation during melting, and to prevent iron sulphide
inclusions in order to avoid hot cracking. The manganese sulphides formed increases
machinability. However, it is a weak carbide former, and favorably effects forgeability and
weldability. The manganese sulphide inclusion acts as precursor site of pitting.
2.3.4 Molybdenum
Molybdenum increases the hardenability of austenitic stainless steel, particularly effective
in maintaining the hardenability between specified limits. It minimizes the susceptibility to temper
embrittlement, and is unique in the extent to which it increases the high temperature tensile, and
creep resistance of austenitic stainless steel. Apart from this, molybdenum is very effective in
stabilizing the passive film in presence of aggressive ions, and increases the pitting, intergranular
and crevice corrosion resistance of austenitic stainless steels.
2.3.5 Titanium
The main use of titanium as an alloying element in austenitic stainless steel is for
stabilization of carbides. It combines with carbon to form titanium carbide which is quite stable,
and hard to dissolve in austenite matrix. This tends to minimize the occurrence of intergranular
corrosion. Moreover, carbon preferentially combines with titanium than chromium preventing
depletion of chromium at the grain boundaries. Titanium also increases the hardness of austenitic
stainless steel.
2. 4 Microstructural properties of austenitic stainless steel
If properly processed austenitic stainless steels are truly single phase without carbides,
ferrite, and all alloying elements in solid solution. In single phase austenite the grains are
equiaxed, many of which contain annealing twins.