It is my understanding that using the Delong (FN) diagram involves the nickel and chromium equivalents from the Weld Metal analysis, not base and filler seperate. This results in a WRC Ferrite Number (FN). The acceptable(FN)is usually specified by job/service specifications and manipulated by controling dilution in the weld or by using a different filler which will result in lower or higher nickel and/or chromium equivalents. Refer to Tech.  Report  (Publication 50-A) by Teledyne McKay for a fairly good explaination of FERRITE.

Hope this helps some.

JVB,

When using the schaeffler diagram for estimating microstructure of stainless steel weld metal, it is easier to take a proposed weld filler metal and see if the predicted microstructure is acceptable, than to identify an acceptable microstructure, and predict an acceptable weld metal.  For instance, you are proposing a fillet weld.  If you assume that during welding, you will be melting the same amount of both types of base metal, admixture of the two base metals would be 50:50. Next what you need to determine, is what kind of dilution you will be getting from your proposed weld.  You do not say which welding process you are using, so I will use submerged arc welding for this illustration.  Lets assume you are getting 60% dilution.  This means that the weld metal will be made up of 60% of the 50:50 base metal mix, and 40% of the weld filler material. Once all your variables are determined.  Plot each base metal and the filler metal on the diagram. Draw a line between the two base metal plot points.  Plot a point half way along the line, and this will be the chemistry of the base metals contribution to the weld.  (or you can use the arithmetical averages of the Cr and Ni equivalents and plot this point).  Next, draw a line between the base metal combination point, and the filler metal point.  Plot a point on the line at the 60:40 ratio of filler to base metal. (or you can calculate this also)  This is the composition of your weld metal.  Once you find this, you generally want your weld metal to be in the A+F region of the diagram.  Other regions can be acceptable under the right circumstances, but you want to stay away from the A+M+F region.

After writing all of this, I see that ARMOX 440T is a low alloy steel.  Much of what you decide to use will depend on the welding process you are using, and the welding perameters that affect the dilution percentages, but the most common weld wire to weld low alloy steel to austenitic stainless steel is 309.  If you have high dilution from the base metal, you may experience problems even with this, and could use type 310.  The most difficult part is getting an accurate estimate of the correct percentages to plug in to the diagram.  If it is a critical application, you may want to cross section a weld so that this can be measured.

This info is kind of generic, but I hope it helps you out.

G Roberts

There is a good diagram on the internet at:-

http://www.avestapolarit.com/upload/steel_properties/Schaeffler_large.jpg


Regards

John  www.gowelding.com

From the Oak Ridge Nation Laboratory are some online calculations for Ferrite number Predictions using both Function Fit and a Neural Network models.

http://engm01.ms.ornl.gov/index.html

The process that GRoberts suggested is a good approach, through a little tedious.  If you have the talents a simple spreadsheet where one inputs the base and filler metal compositions, the dilution rate of each would help.  The spreadsheet helps significantly when designing thick section, multi-pass welds.  Another application of this spreadsheet is when one changes the filler materials through the weld to get the correct corrosion, wear etc. properties on the inside or outside surfaces.