Welding is a complicated process that combines the science of electricity (aside from oxyfuel welding), heat, metallurgy, different states of matter, and oxidation. This also means there are many complications that can arise which can lead to weld failure. One way to reduce the risk is by selecting a metal that is easily weldable and does not require many extra pre-weld and post-weld operations to prevent weld failure. Below are some of the best metals for welding.
Low Carbon Mild Steel
Low carbon mild steel is one of the most, if not the most weldable metal. This is due to several different factors. One reason for its excellent weldability is the fact that it has historically been very commonly used in numerous applications. The historic abundance and demand for low carbon steel has led to scientists and engineers developing ways to weld it. Developments include patented electrical arc waveforms, special filler material chemical compositions, and top-of-the-line welding power sources to weld low carbon steel. All of this enables welders to make satisfactory carbon steel welds with relative ease.
Another reason that low carbon steel is so weldable is because it is more ductile than other types of steel. This is because it has very low amounts of carbon and only trace amounts of other alloying elements. This prevents the formation of brittle microstructures such as martensite. All of this eliminates the risks of certain types of weld failures, such as hydrogen cracking. As the amount of carbon increases, so does the difficulty of making a satisfactory weld.
While it can be trickier than low carbon steel, aluminum can be welded without much difficulty as long as you have the proper knowledge and techniques. One concern when welding aluminum is making sure that the proper grade is selected. Grades in the 1XXX series can be welded without much extra effort needed. Grades in the 6XXX series can be welded, but proper filler material and welding operation must be used to aid in crack prevention. Aluminum in the 2XXX series is typically not weldable at all, although a few grades in this series can be welded with proper filler material and technique.
One other consideration when welding aluminum is material strength. Some aluminum alloys, such as those with a T6 designation, have been artificially aged to increase the strength. This means that they have been heated to a certain temperature for a specific amount of time so that intermetallic precipitates are the proper size and shape to increase the strength of the aluminum. When these grades of aluminum are welded, the intermetallic precipitates change their form, and it is common for the strength of the aluminum to be reduced greatly. To return these welded aluminum alloys back to their original strength, they must be artificially aged again by means of a heat treatment process.
Stainless steel is a metal that can also be welded readily when proper technique is used and adequate knowledge is applied. Many stainless steels, known for their corrosion resistance, can be welded despite their complex chemical composition. The most important consideration when welding a stainless steel is to know what grade is being welded. There are three major types of stainless steel: austenitic, ferritic, and martensitic. Many ferritic stainless steels are very weldable. Austenitic stainless steels can be weldable as well. Martensitic stainless steels are generally more difficult due to their high hardness and their propensity to crack.
A major consideration when welding stainless steels is intergranular corrosion. When stainless steels are subjected high temperature environments, like those that occur during welding, the chromium can be susceptible to joining with the carbon within the steel. This formation of chromium carbide prevents the ability of the chromium to combine with oxygen. Therefore no chromium oxide layer is formed, and the oxygen is free to combine with the iron in stainless steel, contributing to corrosion. There are a couple of methods available that can prevent this. Using a grade stabilized with titanium or niobium such as Grade 321 can prevent intergranular corrosion as the titanium is more likely to form with the carbon atoms before the chromium. Another way to prevent intergranular corrosion is through the use of low carbon stainless steels. These simply do not offer enough carbon to stop the formation of a protective chromium oxide layer.
While there are exceptions, welding tends to get more complicated with other types of metals. The welding of titanium will typically require extra equipment or shielding to prevent it from being oxidized. High carbon steels will generally require preheat and post-weld heat treatment to avoid cracking. Some super alloys can only be welded in a vacuum. Every metal that is going to be welded should be researched on an individual basis to ensure that welding methods exist to make a successful weld.
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