It is very important to be familiar with the physical property of metals. It’s just as important to know the terms and measurements used to identify them, as well. There are three classifications of common properties – all of which are used to define metal. They are:
- Absorption/Transmission of Energy
- Internal Structure
- Resistance to Stress
We’re going to go over these properties to show you what to look for when you’re preparing to weld and as you’re readying yourself to put arc to metal. Let’s dive in:
Absorption/Transmission of Energy
- Melting Point - The temperature where metal passes from a solid to a liquid.
- Weldability - If you’re looking for a very weldable metal, look no further than low carbon steel alloy. It has a high degree of weldability, for instance. Looking for a greater challenge? Cast iron is a great example of a metal with low weldability, so much so you have to preheat it before trying to join it.
- Volatility - Aluminum is a great example, which is why they require special push-pull guns to weld effectively on a commercial level.
- Electrical Conductivity Copper and aluminum are both great examples of metals with a lot of conductivity. What’s a metal with a lower conductivity? Anything with iron, for instance, because it has a higher melting point.
- Electrical Resistance Iron again shows a great deal of electrical resistance compared to some other metals.
- Thermal Conductivity – Literally a metal’s ability to carry heat.
- Coefficient of Thermal Expansion – This is basically the rate by which the substance expands when heat is applied or the amount of contraction when the substance cools.
- Hot Shortness – This refers to how brittle metal gets when it’s hot.
- Overheating – When your metal gets too hot and the properties of it get destroyed.
Internal Structure of Metals
- Specific Gravity – This would be a unit measurement based on the weight of column of material compared to the equal volume of water.
- Density – This is measured as the quantity per unit volume (pounds per cubic inch).
- Porosity – This is a metal that isn’t very compact in it’s properties.
- Plasticity – This is the ability of a material to deform without breaking. This is very important because strength, combined with the plasticity, is used in structural fabrication. Plasticity allows the overload to be redistributed into the structure. For a metal you would use in structural fabrication, low carbon steel is metal with a great deal of plasticity. When it comes to ones with low plasticity, look to metals with high carbon content like cast iron. They are typically more brittle. Higher percentage of manganese introduced to a carbon steel base alloy, the more plasticity exists.
- Strength – The ability of a metal to resist being deformed; Ultimate Tensile Strength.
- Toughness – Any material with a high degree of tensile strength would have a lot of toughness. The less tensile strength, the less tough.
- Impact Resistance – A metal’s ability to withstand the maximum welding gun load with it’s applied instantly.
- Brittleness – Anytime a material fails without warning, like when a small amount of amperage is applied and the metal fails would be considered a brittle piece.
- Hardness – A metal that can penetrate another material without fracturing.
- Malleability – Any metal that deforms without permanently without fracturing under compression.
- Elastic Limit – When the maximum load is applied to a material before it can return to it’s original shape.
- Yield Point – A point at which the metal has increased in length with no increase in the load. This term is expressed in pounds per square inch (psi) in low to medium carbon steels.
- Resilience – When the load is released and the material returns to its original shape (spring steel).
- Ductility – This is when a metal deforms permanently or is stretch but doesn’t fractured.
- Corrosion Resistance – A metal’s ability to not corrode from atmospheric or chemical liquid exposure. Stainless steel is a great example of a corrosion resistant metal. It’s why it’s used in everything from kitchen sinks to underground water pipes.
Welding today is equal parts craftsmanship, art, and science. With so many advanced welding processes to choose from, it’s vital for welders to understand and be able to determine their metal’s properties and choose the welding process that best suits it. Understanding how some metals react compared to others in certain conditions will really help in you deciding what metal and welding process fits your fabricating needs best.