Steel users everywhere are being benefited by the development of non-rusting stainless steel and this material has varying degrees of corrosion resistance, workability and tremendous strength. But there are some downfalls to the improved material, for instance, welding has become much more complicated in comparison to traditional carbon steel. You must now exercise more care with heating and cooling process and be sure to properly match filler materials with the material being welded…
Types of Stainless Steel:
There are five types of stainless steel, which are categorised based on their microstructure (microstructure in a key influencing factor in how strong the steel is going to be). Three out of the five steel types are most commonly found in fabrication shops:
- Austenitic stainless steel – the most commonly used material
- Martensitic stainless steel – used for hard facing and other high-wear applications
- Ferritic stainless steel – most commonly used for consumer products as it’s cheap to make
Each kind has it’s own benefits and difficulties when it comes to welding. The technique used to weld stainless steel is not all that different from that required to weld standard carbon steel, with two exceptions. Firstly, you must exercise more care and control with regard to heating and cooling stainless steel, and secondly, it’s more important to properly match filler metals with the material being welded.
Preparing to Weld:
As in any type of welding, it is very important to clean stainless steel before welding it. What you may not realise, however, is how important it is to only use the tools that you use on stainless steel, on stainless steel. Tools such as brushes should be kept separate for stainless steel projects because of how sensitive the material is to the presence of any carbon steel. The same is true of stainless hammers and clamps, because trace amounts of carbon steel can become embedded in stainless steel causing it to rust.
Similarly, grinding carbon steel in proximity to stainless steel can result in the same problems. Carbon steel dust that is suspended in the air can land on stainless steel and again lead to rusting. So it’s a good idea to keep carbon steel and stainless steel work areas totally separate.
The other important factor in preparing to weld stainless steel is making sure you have the proper filler material, which means you will need to be aware of exactly which type of base material you’re welding. There are, of course, situations where it is not as simple as this, like when you are doing on overlay, or joining dissimilar metals.
Austenitic Stainless Steel
Austenitic stainless steel are identified as the 300 series and are the most common type of stainless being used in fabrication shops. While these base materials do not require preheating, they do have a max.interpass temperature. Once the base metal reaches 350 degrees F, you’ll need to stop welding and let the material cool down.
Some of the 300 series stainless steels are referred to as fully austenitic. By using a low-heat-input process and by making welds that are convex you be be able to to prevent cracking. If you make a flat or concave weld on these materials, it will be more susceptible to cracking.
Ferritic Stainless Steel
Ferritic stainless steel is used largely in automotive applications. Ferritic stainless usually comes in thicknesses of ¼ inch or less, so most welding is done in a single pass, which is good because welding ferritic stainless steel have a maximum interpass temperature of 300 degrees F. and is most successful with low heat input.
At high heats ferritic stainless steel begins to experience grain growth and can quickly lose its strength. Aside from this, match the filler material grade to the base metal grade and your welds should turn out just fine.
Martensitic Stainless Steel
The martensitic types of stainless steel are used less for joining and more as overlays and for building up wear-resistant material and generally they have a minimum interpass temperature.
When welding martensitic stainless steel you’re likely to end up with cracks if you fail to hit an accurate preheat temperature and maintain the minimum interpass temperature the entire time you’re welding.
As with other stainless varieties, if you’re joining martensitic base metals you’ll probably have to use a filler metal with the same number.
Checking the Temperature
When you are welding stainless steel, it’s very important to monitor the temp for both the weld metal and the base metal. If you fail to stay within the specified temperature ranges, you’ll most likely experience some performance problems.
When you’re welding there are three ways you can check the steel’s temperature :
Electronic infrared thermometers
Electronic surface temperature probes
All in all, stainless steel in a nice material to work with. So long as you exercise care with your heating and cooling processes and be sure to properly match filler materials with the material being welded, you should get on just fine.
Written by: Bethany Pembrook