Industrial context
Measuring ferrite content in austenitic molten zone

A specification may ask for a prediction diagram to be used when selecting a filler material. In this case, a filler is selected to produce "so much" ferrite according to "such-and-such" diagram, given "such-and-such" dilution.

After measurement, the actual content may not be as expected. The diagrams allow for a margin of error in prediction, while the method of deposition and welding conditions influence residual ferrite content (influence of arc voltage in submerged...