MIG and TIG welding can be used to join austenitic stainless steels such as grade 304 stainless or grade 316 stainless to plain carbon steel. Weld methods that utilise filler material, such as MIG welding, are recommended for welding stainless steel to a different metal, such as plain carbon steel. The joint should be heat treated after welding to relieve any residual stress caused by the welding process.
Stainless steel can be welded only with care because of its susceptibility to oxidation and corrosion. Stainless steel should not be welded in an atmosphere containing more than 20% oxygen or it will oxidize and increase in size, causing cracking and failure at the joint.
Because stainless steel contains a large amount of iron, if too much heat is applied during the welding process, then ferrous (containing iron) metals will be converted into ferric (containing iron oxide) metals which can cause staining of the surface. This effect can be reduced by adding small amounts of nickel or copper to the stainless steel.
Welding stainless steel also causes some problems that need to be considered before you start. If water or any other liquid gets on the weld area, then it should be cleaned immediately to avoid rusting. Also, keep in mind that stainless steel is very sensitive to abrasives so if you use sand or stone to smooth surfaces before welding, then you should remove these materials before welding.
Stainless steel can be welded using shielded metal arc welding (MIG), gas tungsten arc welding (TIG), and stick welding, and the results will vary somewhat. Stick welding produces a heavy coat of oxide on the surface which prevents further oxidation. Thus, it is suitable for joining stainless steels that will not be exposed to oxygen or other corrosive gases.
Stainless steel cannot be joined by normal heat-treating methods such as quenching and tempering because the heat used in these processes would also affect the oxidized layer on the surface. However, if you grind off some of the oxide before welding, then heat-treat the joint afterward, you can get good strength and corrosion resistance from the weld.
The best way to join stainless steel is with a high-quality stainless steel braze. This material contains zinc or aluminum which are both reducing agents that will cause the iron in the stainless steel to become magnetically soft prior to melting. The brazing filler material should completely cover the surfaces to be joined, with no open seams or holes. It should also be of a thickness sufficient to produce a strong joint—usually about 0.005 inch or more.
Stainless steel should only be welded by a certified welder who has experience with this type of material.
Welding Rod or Wire Varieties When welding stainless steel, the usual guideline is to use either the same quality of welding rod, Tig Wire or Mig Wire, or a higher grade. So you could weld 304 stainless steel with 308 or 316 rod and wire, but not 316 with 308 rod and wire. The reason for this is that 304 is more resistant to corrosion than 316, so using lower-quality metal in 316 would cause it to corrode before 304. You should also avoid welding 310 stainless steel because it has too much iron in its structure to be welded without causing excessive heat damage.
Stainless Steel Welding Tips
Stainless steel can be difficult to weld because it tends to hold its heat longer than other metals, which can cause the surrounding material to melt or burn. To prevent this from happening, add some filler metal to the joint; this will reduce the heat exposure of the main body of the pipe or bar. Also, try to angle the hot metal away from sensitive areas like underneath appliances or inside walls. Finally, wear protective clothing and equipment when welding stainless steel.
Stainless steel is available in over 100 different grades with varying amounts of nickel and chromium. The two most common types are 304 and 316. 304 is less expensive but less resistant to corrosion than 316.
Welding is used to create several items of stainless steel equipment. In general, nickel austenitic alloys are superior for welding than other alloys, with Types 304 and 316 being the most often produced stainless steels worldwide. Nickel-based alloys can be hardened by heat treatment or precipitation hardening. The most common heat treatments are hardness increases due to a combination of carbon and nitrogen (forging and cutting tools) or chromium (wear resistance for machinery components). Precipitation hardening occurs when particles of carbides or nitrides form during cooling after welding.
Stainless steel is a generic name given to iron-chromium alloys that are resistant to corrosion by acids or bases. Stainless steels contain at least 10.5% chromium by weight. The two main types are type 410 and type 430. Type 410 has minimum contents of aluminum and silicon while type 430 has less silicon. Both types retain their toughness and ductility at high temperatures. Type 304 is an alloy similar to type 410 but with smaller amounts of aluminum and silicon. It can be used for cooking utensils because it is not as brittle as type 410 or 430 stainless steels.
Type 348 is an alloy similar to type 304 but with larger amounts of aluminum and silicon. This type of stainless steel is more resistant to corrosion than type 304 but is also more brittle.
MIG welding is the most often used method for welding carbon steel. Steel is composed mostly of iron and carbon, with trace quantities of other metals such as manganese, chromium, silicon, vanadium, and nickel. Low carbon steel is exceptionally easy to weld since it contains just 0.3 percent carbon. Medium carbon steel has between 1 and 3 percent carbon, while high-carbon steel has over 4 percent.
Carbon steels can also be welded by TIG (tungsten inert gas) or laser welding. These methods are usually only used on thinner materials that low carbon steel. Carbon steels contain a large amount of carbon which makes them resistant to heat and corrosion. This means they can be welded without worrying about damaging the surface quality of the metal. However, they cannot be melted by ordinary heating sources so special equipment is required for this type of welding.
Because of its excellent strength-to-weight ratio, low cost, and ease of fabrication, carbon steel is the most commonly used material in industrial applications. It can be used alone or in combination with other materials such as stainless steel, aluminum, and other carbon alloys.
Carbon steels contain between 0.3 and 1.5 percent carbon. The lower number is called low-carbon steel and is used for making tools and weapons while high-carbon steel is harder to work with but more resistant to corrosion and heat.