316L stainless steel is selected for its corrosion resistance, but weld metal solidification cracking remains a risk when delta ferrite content is too low. The Schaeffler diagram and its successor, the WRC-1992 diagram, are the standard tools for predicting ferrite number from weld metal composition.
The WRC-1992 diagram improves accuracy for austenitic and duplex stainless steels. It uses chromium and nickel equivalents calculated from the weld deposit analysis, not the base metal alone. A target ferrite number of 3-8 FN is commonly specified to balance crack resistance and corrosion performance.
Key points for welding engineers:
? Always verify the filler metal composition against the WRC-1992 diagram before production.
? Dilution from the base metal can shift ferrite content significantly, especially on thin-gauge or multi-pass welds.
? Magnetic ferrite measurements (e.g., Feritscope) provide a quick shop-floor check but require calibration against the diagram prediction.
? Excessive ferrite (above 10 FN) can reduce corrosion resistance in highly oxidizing environments.
Controlling delta ferrite is not just a paperwork exercise. It directly affects weld integrity and service life.
Source: AWS A5.4/A5.4M
How do you manage ferrite control on your projects?