Page 10 - Stainless Steel Solutions

JOINING

Welding guidelines

Welding Stainless Steel
There are a number of variables to remember when welding stainless steel.
A few of the most important are:
1. Make sure the base metal and filler metal are clean

2. Minimize the heat input whenever possible
3. Use the correct filler metal
4. Fill the crater upon weld completion
5. Avoid sensitization (overheating the base material)

1. Make sure the base metal and filler metal are clean
Surface contamination can create problems when welding stainless steels. The base materials should be
clean and degreased to remove any contamination. Dirt, grease, grinding dust, paint, markers, bending
lubricants and moisture all contain compounds that will be dissociated by the heat of the arc. Carbon and
hydrogen can be released in this way and absorbed by the puddle.
Wire brushes should have stainless bristles, and only grinding and cutting wheels or other abrasives reserved
for stainless steel should be used on any weld or base metal. Using a grinder first on carbon steel and then
on stainless can contaminate the stainless with carbon-containing particles. This can cause a decrease in
corrosion resistance, cracking or porosity.
Use an appropriate solvent to remove any grease and oil from the base metal. The surface should be wiped
with a clean rag until there are no traces of dirt. Wire should not be left unprotected on a wire feeder for
JOINING extended periods of time. Dirt, grease and oil in the shop atmosphere can settle on the wire and cause
possible contamination of the weld. Use a wire pad to remove surface contamination.
When making multi-pass welds, the residual oxidation and slag islands from the last pass should be
removed, before any additional passes are completed. Use a grinding wheel that is new or has been used
only on stainless. If you are using a pneumatic grinder, make sure the exhaust stream is free from
lubricating oil. Use solvent to clean between passes.
Filler wire should not have dirt or drawing lubricants on its surface as these contaminants, too, are
introduced into the puddle. These materials can also affect the stability of the arc by interfering with
current transfer in the contact tip. This can cause instability in the arc and possible defects in the
deposited weld metal.
2. Minimize the heat input whenever possible
When welding stainless steel, it is critical to control the heat input. High heat inputs can cause cracking,
distortion, loss of strength and loss of corrosion resistance. Because of the high alloy content of stainless
steel, the thermal conductivity of the material is about 20-30% less than carbon steels and the expansion
rate when heated is three to four times greater than mild steel. Because of this, frequent tacking is
recommended in order to provide sufficient joint constraint. This means that less heat is dissipated into
the surrounding plate, so the weld zone stays hotter longer.

When welding stainless steel, it is good practice to use a low heat input process, such as short-arc, pulsed
spray, or low current spray transfer, depending on the material thickness. Short-arc and pulsed spray reduce
the voltage and current in comparison to spray transfer and are recommended for thinner material. Reduced
heat inputs also reduce the dilution of the weld metal with base metal and minimize the chances for carbide
precipitation.
Shielding gases can also affect the heat input of the process. For low current short arc transfer, gas blends
with high helium content are sometimes used. Helium is added to increase the arc energy by increasing the
operating voltage required. This ensures that there is adequate energy to provide good fusion.

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