The paper entitled "A mathematical model to predict delta-ferrite content in austenitic stainless steel weld metals" by Dr. Valiente has been published in the 09/10 issue of Welding in the World.
Here you have the summary:
This paper presents a mathematical model to forecast
the level of residual δ ferrite in terms of FN in austenitic stainless steel
welds at cooling rates between 10 ºC/s up to 103 ºC/s. With this
aim, two series of austenitic steel specimens were prepared using an electric arc
remelt furnace. Whilst the alloying level was kept constant at [Creq+Nieq]
=30% and [Creq+Nieq] =40%, the Creq/Nieq
ratio was gradually increased from 1.22 up to 2.00 in each series. For each
alloying level, a highly correlated polynomial function (FN vs. Creq/Nieq),
was found, being Creq and Nieq Hammar and Svensson’s
equivalents. These experimental results have led to the importance of [Creq+Nieq]
and (Creq/Nieq) variables in the forecast of the residual
ferrite content and a general expression including both variables is proposed.
FN=54.22-126.26(Creq+Nieq)+[-48.11+37.14(Creq+Nieq)](Creq+Nieq)+[-0.23+61.95(Creq+Nieq)](Creq+Nieq)^2 note that 0.2<(Creq+Nieq)<0.5 -(expressed in decimal form)
The proposed model is able to forecast the level of δ
ferrite with a mean error of +1.01 FN within a deviation of +/- 2.12 FN with 95%
probability by just considering the chemical composition of the alloy. This
level of error has been proved to be lower than DeLong’s and WRC-1988 diagrams
errors. Moreover, the proposed model has also been compared with WRC-1992
diagram and FNN-1999 neural network and it provides a more accurate FN forecast
within the range of compositions and cooling rates considered.