Q: We have to weld repair the vanes of a sea water pump impeller and would like to get some advice or procedure regarding this weld. The impeller is made of A743CD-4MCu stainless steel.

The thickness of the vanes ranges from 6 mm to 12 mm (0.236 in. to 0.472 in.)

The intention of welding is to reattach the salvaged pieces of the vanes after removing the damaged areas.

We anticipate that we may not have enough of the salvaged vanes, so we may just weld build up to recreate the vane or we may decide to weld a piece of 316L plate to the stub.

Can this material be readily welded to 316L stainless steel plate? And, what is the rod/procedure/precaution?

What is the rod/procedure/precaution for welding in same material: A743CD-4MCu?

A: Within the specification for CD4MCu casting, the nitrogen level is a variable and not specified in the ASTM A351 specification that will determine its weldability.

Low nitrogen levels will lead to excessive ferrite in the heat affected zone (HAZ) producing reduced ductility, toughness, and corrosion resistance.

Therefore the first step in your repair should be to do a nitrogen analysis on the impeller that you intend on repairing.

The level of nitrogen will indicate the post weld heat treatment that may be necessary.

An analysis that shows 0.18 percent nitrogen indicates a level of nitrogen that could be welded without requiring a post weld solution anneal heat treatment for the impeller.

Analysis values below 0.14 percent of nitrogen would indicate that a post weld solution anneal to restore the HAZ properties would be required.

As far as the appropriate material to add back in for the material that broke off, the 316L material will be much lower in strength and would not have the same corrosion properties as the CD4MCu.

A material that would match better that you could add back in would be Ferralium 255. That would offer comparable strength and corrosion properties.

The filler metal to use would be the ER2594 also known as Zeron 100X.

That filler material could be used to build up the casting in lightly worn areas, as well as to join the Ferralium 255 to the CD4MCu in the replacement scenario.

If the 316L material is chosen as a suitable replacement blade material despite miss-match in properties, a 316L filler would be an acceptable filler selection.

This column is sponsored by Penton and the Lincoln Electric Co., Cleveland. Dave Barton is a senior welding engineer in the Application Engineering Group of The Lincoln Electric Co. He oversees welding procedure development for both new technology and existing products, performs failure analyses for customers, and serves as a consultant on welding application problems. Barton has been with Lincoln Electric for 21 years. Send your questions for Mr. Barton in care of WDF by e-mail to: askdav@penton.com.

Send us your questions.

For answers to more of your questions, visit our online discussion forums at www.weldingdesign.com