Dynamic Fabrication specializes in stainless steel welding. DFI is certified to weld all metals. Stainless steels or, more precisely, corrosion-resisting steels are a family of iron-base alloys having excellent resistance to corrosion. These steels do not rust and strongly resist attack by a great many liquids, gases, and chemicals. Many of the stainless steels have good low-temperature toughness and ductility. Most of them exhibit good strength properties and resistance to scaling at high temperatures.
Stainless Steel Welding Overview
Stainless steel is a fascinating metal to weld. I have spent many years welding different grades of stainless steel. Needless to say I have picked up a few tricks along the way to make the process a little bit easier and of course to produce better welds. All stainless steels contain iron as the main element and chromium in amounts ranging from about 11% to 30%. Chromium provides the basic corrosion resistance to stainless steels. There are about 15 types of straight chromium stainless steels.
Stainless steel is a fascinating metal to weld. I have spent many years welding different grades of stainless steel. Needless to say I have picked up a few tricks along the way to make the process a little bit easier and of course to produce better welds.
Welding stainless can be difficult if you don’t know what you are doing. It reacts to excessive heat by warping and distorting once it cools. Everything shows up in stainless. What I mean by that is if you weld with too much heat you can see it by the heat marks left in the metal along with any distortion. It also scratches very easily so you must take care when welding on a metal table.
Stainless Steel Welding Techniques
Stainless steels can be welded using several different procedures such as shielded metal arc welding, gas tungsten arc welding, and gas metal arc welding.
These steels are slightly more difficult to weld than mild carbon steels. The physical properties of stainless steel are 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 the similar welding characteristics and are grouped according to the metallurgical structure with respect to welding.
One of the best things to do when welding stainless is to use a heat sink such as brass or aluminum. I usually clamp a piece of 3/8 brass behind the seam of the weld. This absorbs the heat and also prevents any burn through. The trick with stainless is to put as little heat into it as possible, especially with thin material. It’s worth the extra time to make sure you have the heat sinks in place before beginning your weld. This allows you to actually weld the entire seam without interruption.
Have you ever noticed that when you get to the end of the weld and you pull the heat off it always tends to turn a dark gray. That’s because you are carrying all the heat with you and by the time you get to the end it’s at its hottest point. A little trick that I discovered on accident is when you get to the end of the weld and you take your foot off the pedal. Wait until the weld pool solidifies and then touch the tungsten to the metal and hold it there till your gas stops flowing. You’ll notice that the color will come back to the weld. Depending on how long you touch the tungsten to the end of the weld. You can actually get that nice salmon color back. You can only do this with a setup that uses a foot pedal. If you are using a dry rig system where you have to use a lift arc this is not possible.
I have built many stainless steel tables for commercial kitchens. We would add hat channels to give the table more stiffness. Any welding would be done on the channels and not the actual table. This keeps it looking clean.
Lets say you had a 5 sided box as a base. The bottom was open and you wanted to weld a pipe in the center of it. No matter how small you kept the welds, the base would still warp and twist from the heat. This depends on the material thickness. I am talking about 14 gauge material. You have to have a frame to keep the base from warping. I have tried several different methods using heat sinks and clamps but they have all produced some amount of distortion. The best way was to add either a few channels underneath or an actual frame with angle iron.
Stainless Steel Welding Procedures
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, the 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 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 dry area. These electrode coatings, of low hydrogen type, are 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 welding process. The spray transfer mode is used for flat position welding and this requires the use of argon for shielding with 2% or 5% oxygen or special mixtures. The oxygen helps producing better wetting action on the edges of the weld. The short-circuiting transfer can also be used on thinner materials. In this case, CO2 shielding or the 25% CO2 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 CO2-argon mixture should not be used.
For all welding operations, the weld area should be cleaned and free from all foreign material, oil, paint, dirt, etc. The welding arc should be as short as possible when using any of the arc processes.
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