The electrodes of this group are used for welding stainless steels. Stainless steels are used in cases where corrosion resistance and resistance to high temperatures are required. 3xx and 4xx series are among the most widely used stainless steels.
Series 3 stainless steels with chromium and nickel alloy elements have austenitic structure and are not harden able. Series 3 stainless steels are non-magnetic and do not absorb magnets, which are called non-magnetic steels. Series 4 steels have a chromium alloy element and have a ferrite or martensitic structure. These steels have magnetic properties and are attracted to magnets.
The corrosion resistance of stainless steels is due to the presence of a thin, continuous and stable layer of chromium oxide and nickel oxide that protect the metal surface in many corrosive environments. This property is only seen in steels with more than 10% chromium, and if the amount of chromium in the steel is less than this amount, this surface layer will not be formed. The main groups of these steels are martensitic stainless steels, ferritic stainless steels and austenitic stainless steels.
- Martensitic stainless steels are essentially plain chrome steels containing 11.5-18% chromium. Martensitic stainless steels are magnetic, easy to cut, tough and resistant to corrosion in air and some chemicals.
- Ferritic stainless steels are also simple chrome steels and contain 14-27% chromium. These steels are magnetic and have less carbon and more chromium than martensite. They also have better corrosion resistance and machinability than martensitic type and are therefore widely used in the construction of chemical and food tanks.
- Austenitic stainless steels are chromium-nickel (300) or chromium-nickel-manganese (200). These categories are non-magnetic under irradiated conditions, but the use of cold work to improve mechanical properties may give them slightly magnetic properties. Austenitic stainless steels have the highest strength at high temperatures and are resistant to scaling. Austenitic steels are usually more resistant to corrosion than ferritic and martensitic steels.
Electrodes for welding stainless steels in the manual method are often rutile and base. Electrodes related to this category have a wide variety of properties that should be selected depending on the type and environment of application of the structure or part. For example, for the application of austenitic 316 and L316 stainless steels in acidic environments, rutile electrodes with low carbon steel core wire containing nickel, chromium, and molybdenum are recommended.
The main difference between electrodes and stainless steel wires is in the coating used in these electrodes. Each coating used for stainless steel electrodes has its own unique properties, which are mostly related to the welding state and fluidity of the weld metal. Several types of coatings are used to make these electrodes, which will be discussed in more detail below:
- Type 15 coating: This type of coating is alkaline and is designed for DC + polarity. The produced slag is lighter than the other two types and is used for all welding situations.
- Type 16 coating: This type of coating is a rutile base type that can be used for both AC and DC polarity and is usually used for all welding situations. This type of coating increases the ability to withstand hot cracks and creates a stable arch. Low spraying and easy arc formation are other features of electrodes with this coating.
- Type 17 coating: This type of coating, in addition to rutile, also contains silicon oxide, which adds silicon to the coating, increases the fluidity of the molten pool. This coating can also be used in both AC and DC polarity. One of the main features of this coating is to increase the fluidity of stainless steels, which have less fluidity compared to carbon steels. Due to the widespread use of stainless steels, stainless steel electrodes are used in most industries for welding stainless steels. Choosing the right welding electrode depends on the material and application environment of the part.
Special Stainless-steel Electrodes:
- Welding of heterogeneous metals: E307, E312 and E309LMo electrodes are used for welding heterogeneous metals.
- Intermediate layer in surface hardening process: E307 and E312 electrodes are used as special intermediate layer in surface hardening process in special conditions.
- Welding of high temperature resistant alloys: Electrodes E308H, E347, E309 and E310 are used for welding of high temperature resistant alloys.
- Duplex welding: E2209 and E2594 electrodes are used for welding two-phase steels