There are a plethora of metals and alloys. Steel, in particular, has different types and grades of alloys. Their properties vary due to different compositions, so their weldability is also diverse. Different steel types behave differently to welding. As steel is one of the most widely used metals; what type of steel can be welded is crucial knowledge that every welder should know.
While pretty much every type of steel can be welded with precautions and preemptive measures, low-carbon steels are the best for welding. Their properties are suitable for welding and show no tendency of post-welding cold cracking.
As I’ve said above, there are a lot of steels and their alloys that a welder has to come across in his line of work. So, good command in different steel types and their properties related to welding is the precursor to being the best at welding. And that is exactly what I will be teaching you in this article. Without further ado, let’s get right to it.
Different Steel Types And Their Weldability
There are so many different types of steel depending on the type and percentage of compounds and the manufacturing process. Each type has varying properties which determine its weldability. Let’s have a look at steel types and how well they can be welded with modern welding techniques.
Carbon steel is iron, carbon, and manganese. The variation depends on the amount of carbon and manganese, which brings us to the following varieties:
Low Carbon Steel
Low carbon steels contain 0.1-0.3% carbon and about 0.4% manganese. These types of steel have pretty good weldability. Carbon content between 0.12-0.25% is best for welding. Steels with more carbon than the upper extreme are prone to cracking. Also, if the carbon amount is below 0.12%, it can cause porosity.
Low carbon steels can be welded using any welding type as long as the impurities are low. They are used in construction and bridge parts, pipes, drink cans etc.
Medium Carbon Steel
In medium carbon steels, the carbon and manganese amounts are 0.3-0.6% and 0.6-1.6%, respectively. Although they are stronger, the higher carbon content makes them susceptible to cracking; hence medium carbon steels are difficult to weld.
The low hydrogen process is the welding of choice for these types of steel. Automobile industries extensively use medium carbon steels to make axles, crankshafts, shafts, couplings, gears etc.
High Carbon Steel
High carbon steels have 0.3-0.9% manganese and 0.6-1% carbon. They are stronger than the previous two. But due to being too hard, high carbon steels are difficult to weld because they crack easily. Fillers with low hydrogen content and a low hydrogen welding process are necessary to weld these steels.
Due to their extreme hardness and strength, high carbon steels are used to make cutting and masonry tools.
Carbon-manganese Steel (CMn)
Manganese-carbon steels have carbon content up to 0.5% and manganese up to 1.7%. They are weldable but may require prior measures like preheating, heat input control, etc. Manganese steels are used for making mining products like rock crushers, cement mixers, tractor parts, etc.
Stainless steel has 1.2% carbon or less and approximately 11% chromium. This composition makes stainless steel rust and heat resistant. There are three main types of stainless with differing welding properties. Let’s take a look:
Austenitic Stainless Steel
Austenitic stainless steels have 16-26% chromium, about 22% nickel, and a low amount of carbon. They have improved properties such as corrosion resistance, high strength, etc. Austenitic steels are the best among stainless steels for welding as they require no heat treatment post or before welding.
Martensitic Stainless Steel
Martensitic stainless steels have around 12-18% chromium, a high carbon percentage, and little to no nickel. These alloys have better wear resistance, fatigue resistance, and strength than austenitic steel, but they are more prone to corrosion.
When martensitic steel cools, it becomes brittle and cracks. It is the reason these types of steel are not good for welding. You can weld them with some precautions, though.
Ferritic Stainless Steel
Ferritic stainless steel has more than 12% chromium and different chemical composition and molecular structure. They are brittle and have low corrosion resistance. At high temperatures, rapid gain growth results in brittle HAZ. That’s why ferritic steels are not good for welding. However, if the workpiece has a thickness less than 6mm thickness, you can weld it.
Tools steel has 2.5% carbon content. As more carbon means poor weldability, you can realize these steels are not good for welding.
Alloy steels are iron, carbon, and various elements like chromium, manganese, cobalt, nickel, tungsten, etc. These steels have enhanced hardness hence poor weldability. When welding them, factors like preheat, cooling rate, post-weld treatment need to be kept under observation.
Nickel steel contains around 3% nickel. The range is usually 1-3%. In terms of weldability, nickel steels behave the same as carbon steel. More nickel means increased hardenability and decreased weldability. You can weld nickel steel carefully by the low hydrogen welding process. Nickel steels with more than 5% nickel content are not weldable.
They are nearly impossible to weld without cracking. Even with low nickel steels, using a low hydrogen process and controlled hydrogen fillers is mandatory.
Types Of Metals That Can Be Welded
Welding is a very old and widely used method of joining metals. You can weld every metal to a certain extent, but not all metals respond the same to welding. Understanding various metals and their weldability is the key to becoming a proficient welder.
Welding is about extreme heat. Different metals react differently to a temperature which I’m sure you already have some idea of. Also, different welding types are meant for different metals. Here are the metals that you can weld:
Steel is one of the most common metals in the world. It is not an element; steel is an alloy of iron. Carbon is mixed with iron to variable percentages to improve its physical properties. A high carbon percentage means a stronger alloy.
Steel is a very versatile metal. You can do any welding with steel. The welding area must be clean and free from gaseous contaminants as steel is highly prone to rust from oxygen.
- Stainless Steel
Stainless steel is the superior version of steel. Besides carbon, stainless steel has chromium, nickel, molybdenum to enhance its properties than that steel. Stainless steel is corrosion-resistant, unlike steel.
Stainless steel is great for welding as well. MIG, SMAW, and TIG welding is the best suitable welding type.
Copper is a popular metal for welding thanks to its excellent heat and electricity conductivity, wear and corrosion resistance, etc. There are various copper alloys like nickel-silver alloy, silicon bronze alloy, brass, copper-tin alloy, etc. All of the alloys are used for welding as well.
The best welding type for copper and its alloys is GMAW and GTAW. You can also perform Stick welding but the resultant quality is not up to the mark. Joint design should be according to the copper alloy and the welding type. The weld area has to be clean from dirt, dust, etc.
Aluminum has similar properties to stainless steel, it is corrosion resistant and lighter, both pure and alloys are used for welding. GMAW, GTAW, and stick welding are used for aluminum. TIG welding is the preferable method, however.
Welding magnesium is not as easy as welding other metals due to being highly flammable. But it’s doable nonetheless. You can weld magnesium in the same way as aluminum. Aerospace engineering companies extensively use magnesium for manufacturing different parts of airplanes and spacecraft.
Airplane parts are very expensive so replacing them is not economical. So, most of the time, welding magnesium is necessary to repair various parts rather than joining two parts. The first thing to know when welding magnesium is the type of alloy and its properties.
TIG welding is the welding of choice for magnesium. Aircraft are delicate and require top-notch weld quality and superior finish, which only TIG welding can provide. In fact, an aircraft corporation invented TIG welding around 1940 to weld on magnesium and aluminum.
You can weld nickels by any arc welding technique. Nickel alloys can also be joined by TIG, MIG, and stick welding. There are several types of nickel alloys such as 141, 61, 190, 60, etc. Nickel alloys usually don’t require post-weld heat treatment but may need thermal treatment to relieve stress and for precipitation hardening.
- Cast iron
Welding cast iron is problematic, but it’s possible. The problem is due to its high carbon percentage. The carbon accumulates into the weld and can crack the joint post welding.
But you can weld cast iron with some precautions. You have to correctly identify the alloy, properly clean the cast and use a suitable temperature and technique. Stick welding is the most efficient method to weld cast iron.
Lead is not suitable for arc welding. Gas welding or oxy-fuel welding is the preferable method to weld lead. Commonly oxyacetylene, oxyhydrogen, and natural oxygen is used for welding lead. The joint types are the same as arc welding like butt, lap, edge, etc.
Determinants Of Weldability Of Steel
Steels and other metals have similar factors that affect their weldability, but steels have three distinct metrics that determine their weldability. These metrics are known as failure modes. The three failure modes are:
- Cold Cracking
Cold cracking or hydrogen-induced cold cracking is one of the key failure modes that indicate the weldability of steel. This characteristic is prevalent in high-carbon steel. When welding such steels, the adjacent heat-affected zone (HAZ) hardens due to the extreme temperature and cracks when the metal cools off.
To understand this, you have to realize hardenability. Hardenability and hardness are not the same things. Hardenability is a factor that determines the ease of making martensitic steel. You can find details of hardenability here.
Hardenability and weldability are inversely proportional. More carbon means more susceptibility to cold cracking but better hardenability, meaning better suited to form martensite.
- Lamellar Tearing
Lamellar tearing only occurs in rolled steel plates. When you weld two rolled steel sheets together, shrinkage and tearing take place along the length of the sheets. This is lamellar tearing. It occurs due to the presence of sulfur in the metal.
The occurrence of lamellar tearing has been mitigated by limiting the inclusion of sulfur and adding other elements. You can find more about lamellar tearing here.
- Spot Weld Peeling Test
Spot welding high strength low alloy (HSLA) steel can be problematic due to the excessive hardenability. The spot weld peel test gives you an idea that your welding is of the correct size, shape, etc. There’s an excellent article about the spot weld peel test that you can find here.
What Determines The Weldability Of A Metal?
Besides the failure modes of steels, a few factors affect the weldability of any metal, including steels. Here are the factors:
Type of welding: There are many different types of welding apart from the four popular welding methods. Not all of the mare is suitable for all types of metals. For example, stick welding is best suitable for steel, and TIG welding is best for magnesium and aluminum.
A metal might seem poorly weldable when using one technique but shows an excellent result when you resort to another type of welding.
Joint Shape: Joint design is a pivotal component of welding. It varies for different welding materials as well as welding types. TIG and stick welding are the two most common welding processes in pipe welding.
When welding pipes using stick welding, the landing area needs to be happy, and the gap should be narrow. The design is quite the opposite when using TIG welding for welding pipes. The landing area must be like a knife-edge with a slightly wider gap.
Thermal Conductivity: Extreme heat melts the base metal in welding, and filler metal fills the gap. When it cools down, fusion occurs between the two parts, forming a joint. So as you can understand, thermal conductivity is a big issue. Low thermal conducting metals usually have better weldability.
Coefficient of Thermal Expansion: The coefficient of thermal expansion determines how much a metal expands when it’s subjected to increased temperature. When welding dissimilar metals, both metals’ coefficient of thermal expansion has to be close to each other. If there is too much difference, cracks can occur after cooling.
Melting Point: The two workpieces melt a fuse with each other after cooling. The metals need to reach a specific temperature for melting, known as the melting point. Low to medium melting point is better for welding, and a high melting point can make a metal poorly weldable.
Electrical Resistance: Electrical resistance is inversely proportional to weldability. Metals with high electrical resistance require high electricity to reach the melting point, meaning they have poor weldability.
How Can You Improve Weldability?
An optimum weld quality depends on various measures and precautions. These very measures can be the determinant of the weldability of any metal. If you properly follow them, the resultant welding will be top-notch. If not, you will experience degraded weldability. Here is how you can improve the weldability of metals:
Proper Shielding Gas
The welding area must be protected from gasses in the atmosphere during welding. There are different shielding gasses available for different grades of metals and welding techniques. Argon, helium, or a combination of both are the most common. It’s important to have a clear conception of shielding gas for proper welding.
Right Welding Process
All metals don’t respond the same to a specific welding technique. It’s the reason why there are so many welding types. Welding involves differing temperatures, pressure, amperage, etc., that are specified for certain types of metals and alloys. So picking the right welding process is compulsory for optimum quality welding.
Right Filler Metal
Filler metal holds the two base metals together. Using the right filler metal depends on various factors. But one thing is for sure is that there is no alternative to knowing the ins and outs of filler metals if you want to improve weldability.
There are some precautions like preheating, using low hydrogen techniques, etc. As there are countless grades of metals, such associated techniques are also endless. You have to have proper knowledge of their better welding performance.
Steel is perhaps the most common metal in the welding sector. Even 5th graders know that different metals have different properties, but the sheer number of variations steels have is a whole another chapter. And this is a chapter that every welder should ace.
For that I have provided this detailed guide on the weldability of various types of steels and metals in general. So, I believe this write-up was able to shed some light on what type of steel can be welded and be of help to all of you.