Dave Barton

askdav@penton.com

Q: We are welding 304 stainless steel tanks with a 308L stainless welding wire and noticed that magnets stick to the weld wire and, after welding, will grab slightly at the weld joints. Why does this happen?

A: Austenitic stainless material can be differentiated easily by its non-magentic properties when compared to carbon steel. In addition, in some applications stainless material is chosen for its non-magnetic properties. There are two factors involved in your situation.

First, 308L weld metal normally contains a small amount of ferrite in the austenitic matrix to prevent hot cracking. Ferrite is ferro-magnetic, which explains why the magnet is slightly attracted.

The 308L stainless welding wire is different. After annealing the rod stock to produce it, no ferrite is left in the wire. Annealing causes all ferrite to transform to austenite. The wire is, however, cold worked during drawing. The cold work causes transformation of some of the austenite into martensite. Martensite also is ferro-magnetic. Melting the wire eliminates the martensite, so the weld metal contains no martensite unless you cold work it. All this means that there is some ferrite is present in the resultant weld that makes it slightly ferro-magnetic which is why the magnet sticks ony slightly to the finished weld.

Q: We have some parts that resemble a tile that are gas-tungsten arc (GTAW) welded to a 304L auger flighting. The tiles consist of a cast 17-4Ph stainless steel holder with a soldered wear plate. Our current welding procedure calls for GTAW, using 1/16-inch diameter ER630 filler material and straight polarity DC 130-150 amps at 18-20 volts. We are getting the breakage at the soldered connection with the tiles adjacent to the weld. We believe there is too much heat being added during the welding of the tile assemblies. Do you have any suggestions how we can eliminate this failure?

A: I suggest you attach the tiles using gas-metal arc (GMAW) short circuiting transfer instead of GTAW. This process will greatly reduce the heat input.

Q: I am working on a project that requires welding of a longitudinal butt weld of a 0.024-inch-stainless 430 steel roll cylinder. After welding, we will final form the cylinder. Are there any common problems with this material?

A: Yes. The problem with 430 is that it contains small amounts of free carbon that produce martensite in the heat-affected zone. You will not be able to form the steel after welding unless you post-weld heat-treat at about 1400 F. for a few minutes. If you want formability as welded, and corrosion resistance at least as good as 430, consider 439 stainless or 444 which is even more corrosion resistant.

Q: If a welder is certified for a welding process using ATSM A36 base material, does this automatically qualify him for using ASTM A572 Grade 50 base material for the same process?

A: Check Table 4.11 "Welding Personnel Performance Essential Variable Changes Requiring Re-qualification" of AWS D1.1 - 2004 Structural Welding Code — Steel. This table states that the group number of the steel (listed in Table 3.1 titled "Prequalified Base Metal — Filler Metal Combinations for Matching Strength") is not a factor that requires re-qualification.

If you are using shielded-metal arc welding (SMAW), then you need to be concerned with the F-number listed in Table 4.12 titled "Electrode Classification Group." If a welder is qualified to use an electrode with an F-number lower than the one that will be used to weld ASTM A572 Grade 50, that welder will have to re-qualify for that job.