Schaeffler Diagram Calculator (Cr and Ni equivalent)

The Schaeffler diagram, in the modified version with DeLong's ferrite number (FN) lines, predicts the microstructure of stainless steel weld metal from its chemical composition. It applies to the as-solidified metal, with no heat treatment.

Chromium promotes ferrite and nickel promotes austenite. The other elements count with their equivalent weight, using the same formulas printed on the diagram:

Cr eq = %Cr + %Mo + 1.5 × %Si + 0.5 × %Nb

Ni eq = %Ni + 0.5 × %Mn + 30 × (%C + %N)

In a dissimilar joint, such as carbon steel to stainless steel, the weld is a mix of both base metals and the filler metal. Pick the three materials, set the dilution and see where the weld point lands.

Base metal 1

Material

C %N %Si %Mn %Cr %Ni %Mo %Nb %

Base metal 2

Material

C %N %Si %Mn %Cr %Ni %Mo %Nb %

Filler metal

Material

C %N %Si %Mn %Cr %Ni %Mo %Nb %

Dilution: How much of the weld metal comes from the base metals. In manual welding it is usually between 20 and 40 % (the root pass can exceed that); measure it on a macro section when you need the real value.Share of base metal 1 in the mix: 50 % when both sides of the joint melt equally.

● BM1 and ● BM2 base metals,◆ mix of the base metals,■ filler and● weld at the chosen dilution. The black points and labels belong to the original figure.

How to read the result

The weld point sits on the line joining the base metal mix to the filler metal. The higher the dilution, the closer it lands to the mix. That is why, in a carbon steel to austenitic stainless joint, the filler must be more highly alloyed than the stainless base metal, such as ER309L: it offsets the carbon steel dilution and keeps the weld in a ferrite range that reduces the risk of solidification cracking without falling into the martensite region.

The typical material values are nominal reference compositions. For a qualification or a failure analysis, use the composition from the material and filler metal certificates.