Hi YVAN

I believe your filler metal selection should be based on your service conditions.

Often 300 series fillers are used, because of their ease of use and availability. They are however prone to stress corrosion cracking, which is often the reason that ferritic stainless steels are used instead. If you have such an application, then obviously a 300 series filler is not a good idea.

At any rate, the filler you use will not really have a significant effect on the HAZ. Typically 409 suffers from excessive grain growth in the HAZ and is not generally welded in thicker sections. If you are making your heat exchangers from thin sheet, then 409 should be OK.

This alloy is mostly used in S/Steel automotive exhaust applications, which have rather thin wall thicknesses. (In the order of 1mm.)

Hope this helps.

Regards
Niekie Jooste
Fabristruct Solutions

Hi Ivan and Nikie:
I´m agree with Nikie´s answer but I want to say something that may create a little confusion about this field.
There are several filler metals among 300 series wich are not a good selection in order to make joints 409/409; I think Nikie knows it. For instance, ER308LSi will form martensite in the weld metal at dilutions values of 40% (tipical on thin walls or the first pass in a complete joint penetration); it reduce the ductility that is the Ivan´s concern. The ER309LSi (or any other 309) is more alloyed than ER308LSi and is able to avoid the martensite formation at this dilution levels producing a weld metal austenitic with almost 10-12% of ferrite no matter the chance in dilution below 40% approx.; then ER309LSi is a good choice from this point of view.

I hope this help.

Jorge Giraldo
Medellín, Colombia