E347 is preferred over E321 welding of SS321?

The selection of a specific welding electrode for welding stainless steel, such as SS321, depends on various factors including the application, welding process, and the desired properties of the weld joint.

E347 and E321 are both stainless steel welding electrodes, but they have different chemical compositions and are designed for different purposes:

Chemical composition of E321 and E347 is stated below

AWS Class	C	Cr	Ni	Mo	Mn	Si	P	S	Cu	Ti	Nb
ER321	0.08	18.5-20.5	9.0-10.5	0.75	1.0-2.5	0.30-0.65	0.003	0.003	0.75	9*C min/1.0 max.	–
ER347	0.08	19.0-21.5	9.0-11.0	0.75	1.0-2.5	0.30-0.65	0.003	0.003	0.75	–	9*C min/1.0 max.

Description and intended use of both as per ASME Section II part C

E347

The nominal composition (wt. %) of this classification is 20 Cr, 10 Ni, with Nb added as a stabilizer. The addition of niobium reduces the possibility of intergranular chromium carbide precipitation and thus susceptibility to intergranular corrosion. The filler metal of this classification is usually used for welding chromium-nickel stainless steel base metals of similar composition stabilized with either Nb or Ti. Although Nb is the stabilizing element usually specified in Type 347 alloys, it should be recognized that tantalum (Ta) is also present. Ta and Nb are almost equally effective in stabilizing carbon and in providing high-temperature strength. If dilution by the base metal produces a low ferrite or fully austenitic weld metal, the crack sensitivity of the weld may increase substantially.

E321

The nominal composition (wt. %) of this classification is 19.5 Cr, 9.5 Ni, with titanium added. The titanium acts in the same way as niobium in Type 347 in reducing intergranular chromium carbide precipitation and thus increasing resistance to intergranular corrosion. The filler metal of this classification is used for welding chromium nickel stainless steel base metals of similar composition, using an inert gas shielded process. It is not suitable for use with the submerged arc process because only a small portion of the titanium will be recovered in the weld metal.

Why E347 is over E321 in welding of SS321

As per stated chemical composition we have observed that the main difference between E321 and E347 is presence of different stabilizing elements i.e E321 is having Ti as stabilizing element where as E347 has Nb as stabilizing element.

Since E321 is having Ti as stabilizing element and in arc welding processes can’t be fully transferred through arc in weldment. So after welding the weldment will have stabilizing effect due to less Ti presence in weld metal.

To overcome this problem we need another stabilizing element which can be transferred through arc i.e. Nb, which is present in E347 welding electrode. So E347 is used for welding of SS321 material.

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