Ferrite content is important for avoiding hot cracking during welding of austenitic stainless steels. Ferrite is also an important constituent in duplex stainless steels. Ferrite diagrams, also referred to as Constitution diagrams, are used to predict ferrite levels from the composition of austenite and ferrite stabilizing elements. Today, the WRC-92 diagram is widely used for duplex and austenitic stainless steels. The Schaeffler and Delong diagrams are the original methods for predicting the phase balances in austenitic stainless steel welds. A 'nickel equivalent' is calculated for the austenite stabilizing elements and a 'chromium equivalent' for the ferrite stabilizing elements. These are used as the axes for the diagrams. The nickel and chromium equivalent calculations are different for the three ferrite diagrams. The ferrite content in ferrite diagrams is based on thermodynamic stability and should therefore be seen as a guide, as differences to the actual ferrite in welds occur.
WRC-92
SCHAEFFLER
DELONG
Source: http://smt.sandvik.com/en/
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