1. 
   Sigma Phase
   Sigma is an iron-chromium (roughly 50-50) phase, which can form from ferrite in austenitic stainless steel weld metal at elevated temperatures ( approximately between 450 and 850oC). It, therefore, forms during high temperature service and its presence in the stainless steel is only apparent at room...
   Found op http://www.bocindustrial.co.uk/bocindustrial/technical/glossary/s.html
   
   
2. 
   sigma phase
   A hard, brittle, nonmagnetic intermediate phase with a tetragonal crystal structure, containing 30 atoms per unit cell, space group P4₂mnm, occurring in many binary and ternary alloys of the transition elements. The composition of this phase in the various systems is not the same and the ...
   Found op http://www.encyclo.co.uk/local/20742
   
   
3. 
   sigma phase
   A hard, brittle, nonmagnetic intermediate phase with a tetragonal crystal structure, containing 30 atoms per unit cell, space group P4₂mnm, occurring in many binary and ternary alloys of the transition elements. The composition of this phase in the various systems is not the same and the ...
   Found op http://www.encyclo.co.uk/local/21115
   
   

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