These steels arc slightly more difficult to weld than mild carbon steels.
The physical properties of stainless steel arc different from mild steel and this makes it weld differently.
These differences are :
- Lower melting temperature.
- Lower coefficient of thermal conductivity.
- Higher coefficient of thermal expansion.
- Higher electrical resistance.
The properties are not the same for all stainless steels, but they are the same for those having the same microstructure.
Regarding this, stainless steels from the same metallurgical class have similar welding characteristics and are grouped according to the metallurgical structure with respect to welding.
When stainless steel welding use a heat sink such as brass or aluminum. This absorbs the heat and also prevents any burn through.
When we get to the end of the weld and pull the heat off it always tends to turn a dark gray. That’s because we are carrying all the heat with us and by the time we get to the end, it’s at its hottest point.
Wait until the weld pool solidifies and then touch the tungsten to the metal and hold it there till our gas stops flowing. We’ll notice that the color will come back to the weld. Depending on how long we touch the tungsten to the end of the weld.
We can actually get that nice salmon color back. We would add hat channels to give the stainless steel tables more stiffness. Any stainless steel welding or any welding would be done on the channels and not the actual table. This keeps it looking clean.
Stainless Steel Welding Process:
- For shielded metal arc welding. there are two basic types of electrode coatings. These are the lime type indicated by the suffix 15 and the titanium type designated by the suffix 16.
- The lime-type electrodes are used only with direct current electrode positive (reverse polarity).
- The titanium-coated electrode with the suffix 16 can be used with alternating current and with direct current electrode positive.
- Both coatings are of the low-hydrogen type and both are used in all positions. However, type 16 is smoother, has more welder appeal, and operates better in the flat position.
- The lime-type electrodes are more crack resistant and are slightly better for out-of-position stainless steel welding.
- The width of weaving should be limited to two-and-one-half (2.5) times the diameter of the electrode core wire.
- Covered electrodes for shielded metal arc welding must be stored at normal room temperatures in a dry area. These electrode coatings, of low hydrogen type, arc susceptible to moisture pickup.
- Once the electrode box has been opened, the electrodes should be kept in a dry box until used.
- The gas tungsten arc welding process is widely used for thinner sections of stainless steel. The 2% tungsten is recommended and the electrode should be ground to a taper.
- Argon is normally used for gas shielding; however, argon-helium mixtures are sometimes used for automatic applications.
- The gas metal arc welding process is widely used for thicker materials since it is a faster stainless steel welding process.
- The spray transfer mode is used for flat position stainless steel welding and this requires the use of argon for shielding with 2% or 5% oxygen or special mixtures.
- The oxygen helps in producing better wetting action on the edges of the weld.
- The short-circuiting transfer can also be used on thinner materials. In this case, C02 shielding or the 25% C02 plus 75% argon mixture is used.
- The argon-oxygen mixture can also be used with small-diameter electrode wires.
- With extra low-carbon electrode wires and CO2 shielding, the amount of carbon pickup will increase slightly. This should be related to the service life of the weldment.
- If corrosion resistance is a major factor, the CO2 gas or the C02 -argon mixture should not be used.
- For all stainless steel welding operations, the weld area should be cleaned and free from all foreign materials, oils, paints, din, etc.
- The stainless steel welding arc should be as short as possible when using any of the arc processes.