Last Updated on February 2021
Ferrous and non-ferrous are distinguished by the presence and absence of iron, respectively. This variation gives these metals very distinctive characteristics and properties. As such, ferrous and non-ferrous metals have unique industry applications.
As a welder, you must know how these metals interact with welding equipment and how they are used in the real world.
That said, this guide exists to provide you with an in-depth understanding of ferrous metals, non-ferrous metals, and their differences. With the knowledge, you can goforth and select the most appropriate use, and welding technique for a given metal.
Let’s dive in.
What are Ferrous Metals
The term “ferrous” is derived from the Latin word “Ferrum,” which means iron (Fe). As such, ferrous metals are those materials containing iron in relatively large quantities. Besides iron, ferrous metals may also contain other alloying elements.
Their use date back to 1,200 BC, where the production of iron became more commonplace; and as such, ushered in the Iron Age.
Iron is the most common metal on Earth, by mass. It is contained in Mars, soil, rocks, and the ground. It’s also found in stars as a by-product of nickel (Ni) decay.
The presence of iron (Fe) gives the ferrous metals unique characteristics and properties, such as ductility and high tensile strength. That, in turn, makes them valuable materials, particularly in the construction industry.
Carbon steel, for instance, is a popular ferrous metal and a staple in the metal building industry. Its properties make it ideal for constructing bridges, buildings, and other structures.
Most welding is carried out on ferrous metals – more so on steel, which is an iron-based alloy.
To that end, let’s get more familiar with iron.
Physical Properties of Iron
Iron has been proven to:
- Be brittle (when in pure form a.k.a. not alloyed)
- Be magnetic
- Have an average thermal conductivity
- Have a relatively average electrical conductivity
- Have a melting point of 15380°C
- Have a boiling point of 44280°C
- Have an average ductility
- Have a density of 7.87 g/cm³.
Fun fact: it takes up to 0.45J of the heat of energy to raise the temperature of a gram of iron by 10 °C.
Mechanical Properties of Iron
Iron is prone to corrosion when exposed to moist air/conditions. This condition is attributed to its high content in the carbon element. And as such, wrought iron which is over 99% pure iron is resistant to corrosion and rust.
To boost their rust resistance, some ferrous metals are coated with other elements to boost their rust resistance. For instance, stainless steel is more resistant to corrosion thanks to the chromium coating.
Chemically, iron is more reactive than silver but less reactive than magnesium. When added to hydrochloric acid, for instance, it produces a ferric chloride solution and hydrogen gas.
Generally, the characteristics and properties of ferrous metals can be changed by adding an alloy or by eta treatment. Their properties particularly change based on their respective carbon content. Carbon elements hold iron molecules in a crystal-like structure, making it harder. As such, ferrous metals are harder and less brittle.
Here are the various types of iron.
Types of Iron Metal
Iron (metal) can be classified as:
- Tool steel
- Carbon steel
- Cast iron
Types of Iron Alloys
Iron-based alloys include:
- White iron
- Gray cast iron
- Pig iron
- Alloy steel
- Alloy cast iron
- Carbon steel
- Malleable cast iron
- Chilled cast iron
- Nodular cast iron
- Wrought iron
The iron metal is extracted from iron ore rocks and minerals. These ores vary in color from yellow to dark gray to deep purple and rusty red.
Pig iron is mined from iron ore, a raw material used to make steel.
Production of Iron
As stated above, the metallic iron is obtained from iron ores. These ores exist in nature as oxides, with the most common being magnetite and hematite.
To produce iron, the said ore is charged into a blast furnace alongside coke and limestone. The latter element serves as a flux. Here, these raw materials are subjected to a blast of preheated air and rapid combustion to result in a chemical reaction – otherwise described as carburization and reduction of iron ore with coke.
The chemical reaction eliminates oxygen from the ore to yield pig iron. The pig iron then melts to form a relatively heavier liquid. Simultaneously, the limestone flux and coke ash combines with impurities present in the ore, and melts into a lighter liquid slag. The liquid slag floats on the molten pig iron, and the two materials are drawn off separately.
The pig iron produced in this process consists of 3.5% – 4.5% of the carbon element, which makes it highly brittle and inapplicable in most areas. It’s used to produce cast iron, steel iron, and wrought iron, as described below.
Cast iron (malleable, gray, and white)
Cast iron is a human-made iron alloy. It’s basically carbon steel that has more carbon added to it, in conjunction with sulfur, silicon, phosphorous, and manganese. Cast iron contains 1.7% – 4.5% of graphite or free carbon.
Given the high carbon content, cast iron is brittle (except for malleable cast iron.) It also has a relatively lower melting point compared to steel.
The production process of cast iron
Cast iron can be produced by melting pig iron in a cupola furnace, alongside limestone and coke. The resulting cast iron can then be poured into sand molds or alloy steel. Cast iron can either be gray, white, or malleable.
Gray cast iron (most common)
Gray cast iron is formed when the molten metal in the alloy is left to cool in the open air. Given the slow cooling rate, the chemical compounds of iron and carbon break into small graphite-flakes that are then scattered throughout the cast iron metal. The flakes result in a gray appearance, hence the name.
Gray cast iron is characterized by a low friction coefficient, making it ideal as a lubricant material. It also has good machinability and no ductility.
White cast iron
White cast iron is the opposite of gray cast iron. It’s formed when the molten cast iron poured in a sand mold or steel alloy cools at a faster rate. As such, iron and carbon remain in a chemically combined state. The amount of combined carbon in the white cast iron is in the range of 2.5% – 4.5% by weight.
When fracture, the metal is white, hence its name.
White cast iron is brittle and hard to machine. It’s also hard to weld following its poor ductile properties; as such, it has limited applications. Nonetheless, it’s used for inferior parts and castings. It also acts as a raw material in the production of malleable cast iron.
Difference between gray and white cast iron
Besides their difference in appearance, gray and white cast iron have different compositions. For instance, gray cast iron contains 1% – 3% of silicon, 2.5% – 4% of graphite carbon, with iron forming the remaining percentage. On its end, white cast iron consists of 0.5% – 3% of silicon, 1.7% – 4.5% of carbon, and can also contain small traces of sulfur, manganese, and phosphorous.
Malleable cast iron
Malleable cast iron is formed when white cast iron is heated at 760 – 927°C for around 150 hours in containers filled with hematite ore or iron scale. The heating process (otherwise referred to as annealing) forces some of the combined carbon to change into free or uncombined carbon. As a result, temper carbon is formed.
Temper carbon exists as small, rounded carbon particles that give the metal the ability to bend before breaking. Moreover, it can withstand shock better than its sister cast iron.
Malleable cast iron is characterized by high ductility/fluidity, toughness, strength, and shock resistance; in addition to good machinability. The metal has a higher tensile strength than gray cast iron.
Given its characteristics and properties, malleable cast iron is applicable in pipe fittings, hydraulic cylinders, valves, pipes, rails, and automobiles. It’s ideal for replacing forged steel or creating components used instead of parts whose intricate shapes lead to a forging problem.
Malleable cast iron can be welded and brazed. However, the welded part must be annealed.
Nodular cast iron
Nodular cast iron is formed when magnesium is added to the molten cast iron. Here, magnesium converts the graphite carbon from flakes to spheroidal or nodular form. As such, the tensile strength of the metal increases while its brittleness decreases.
Note, castings made of nodal cast iron can replace steel.
Chilled cast iron
Chilled cast iron is one produced with quick cooling. All cast irons are chilled up to a limited depth of 2mm when pouring the molten metal into various molds. However, the casting can be intentionally chilled to provide the needed hardness to withstand wear and friction.
Chilled cast iron is widely used in stamping dies, crushing rolls railway, wheel cam followers, and gray cast iron.
Use of cast iron
Cast iron can make:
- Water pipes
- Transmission housing
- Stove castings
- Machine tools parts and castings
- Automotive parts such as gearbox cases, pistons, cylinder blocks, and engine blocks
For a deeper dive on metal Casting [Read Our Full Guide]
Properties of cast iron
Cast iron has:
- specific gravity of 7.6
- A Brinell hardness number of 300 – 600 (for alloyed cast iron) and 150 – 200 (for non-alloyed cast iron)
- A tensile strength of 344,750 – 689,500 kPa (for alloys) and 172,375 – 344,750 kPa (for non-alloys)
- A high compressive strength (often 4X its tensile strength)
- A good wear resistance
- A high rigidity
- A fair corrosion resistance
Welding capabilities of cast iron
Cast iron can be brazed/bronze welded, gas or arc welded, machined, or hardened. They are:
- Low cost
- Excellent machinability
- Good casting properties
- High compressive strength
- Excellent wear resistance
Limitations of cast iron
Cast iron cannot be worked on when cold. As such, it must be preheated before welding. It is also highly brittle with low tensile strength.
Wrought iron is almost pure iron. It contains 99% iron whereas slag, sulfur, phosphorous, manganese, carbon, and silicon form the remaining 1%.
Wrought iron is made from pig iron. During its manufacture, some slag is mixed with the pig iron to yield a metal that’s resistant to oxidation and corrosion.
As its name suggests, it has sufficient fluidity to allow cold and hot deformation.
The metal is easy to plate, machine, form, and gas or arc weld.
Its use; however, has declined since the late 19th century as wrought iron is replaced by mild steel, which is easier to obtain.
How wrought iron is made
As noted above, wrought iron is made from pig iron in a puddling furnace. The pig iron is mixed with slag to produce a fibrous structure. As such, the long threads of iron combine with long stringers of slag. The resulting metal is press-squeezed and rolled into billets.
When the thin layer of slag is separated, the result is a metal with high corrosion resistance, oxidation resistance, shock absorbance, and fatigue resistance.
Wrought iron contains up to 0.08% of carbon. Given its low composition in additives, wrought iron has a woody or stringy appearance.
Wrought iron properties
Wrought iron has the following properties:
- The specific gravity of 7.7
- High ductility
- High corrosion resistance
- A melting point of 1510°C
- Tensile strength of 35,000 psi
- A Brinell hardness number of 105
- It also cannot be hardened or tempered like steel.
As mentioned earlier, the use of wrought iron has declined over the years. However, some items were traditionally made of wrought iron; they include:
- Nuts & bolts
- Barbed wire
- Farm implements
- Porch railings
- Railway couplings
- Water and steam pipes
- Ornamental ironworks
Welding capabilities of wrought iron
Wrought iron can be plated, machined, easily formed, and arc or gas welded. Its billets can be reheated to create any of the items listed under its uses.
Limitations of wrought iron
Wrought iron is low in hardness and fatigue strength.
Ingot iron contains 99.85% iron making it the most commercially pure iron in the current market.
It’s easy to form, and its properties mirror those of carbon steel. The only difference is, in iron, the carbon content is considered an impurity, whereas, in steel, carbon compounds are alloying elements.
Ingot iron is used for enameled and galvanized sheets.
Steel ferrous metals
Ferrous metals (including cast iron, wrought iron, and steel) contains chemical mixtures and compounds of carbon, iron, and other elements (in small quantities). And the classification of metal as cast iron or steel solely depends on the amount of carbon contained herewith.
For instance, cast iron contains carbon content in excess f 1.7% – distributed as graphite, nodular form, or free carbon – throughout the metal.
Steel is the most common metal in the welding planet. It occurs ina myriad of varieties, all with different mechanical and physical properties. These varieties include:
Stainless steel is produced by coating an iron and carbon-based alloy with (1% – 30%) chromium. The coating serves to increase the corrosion resistance of the metal.
Stainless steel includes:
Austenitic stainless steel that’s corrosion-resistant, ductile, tough, strong, with low thermal conductivity.
Martensitic stainless steel is high in carbon, and as such, it is subject to cracking.
Ferritic stainless steel is high in chromium, low in carbon, and less ductile.
Steel alloys exist in many varieties based on their constituents. Alloying elements include nickel, molybdenum, manganese, and chromium.
Steel carbons consist of iron, carbon, and small traces of other elements. They are rated based on the quantities of carbon in the metal. Their classes include low (.05% to .3% carbon), medium (.30 – .50% carbon) and high carbon (.5 – 1% carbon) steels.
Uses of Ferrous Metals
Ferrous metals are sturdy and robust, and as such, they can make:
- Railroad tracks
- Domestic and commercial tools
- Shipping containers
- Industrial piping
What are Non-Ferrous Metals?
Non-ferrous metals are those metals that do not contain iron – or that contain iron in small traces. Non-ferrous metals have been in use since 5000 BC. Then, copper was used in the manufacture of jewelry and pottery.
Some of the most used non-ferrous metals include copper, lead, zinc, titanium, nickel, and aluminum. Rare and precious metals such as mercury, platinum, tungsten, gold, and silver are non-ferrous metals, too.
Applications of Non-Ferrous Metals
Non-ferrous metals are characterized by:
- High malleability
- High conductivity
- Low weight
- High resistance to corrosion
- No oxidation
- Low tensile and compressive strength
Since these metals are void of iron, they are relatively more resistant to corrosion than ferrous metals.
Properties of Non-Ferrous Metals
Non-ferrous metals are ideal for various applications; for instance, being lightweight makes them the best option when building aircraft and other welding industries. Their non-magnetic nature makes them suitable for use in cases where magnetic properties are undesirable. Think of wiring applications. Similarly, their malleability nature makes them ideal for use in parts of varying shapes.
In summary, non-ferrous metals make:
- Outdoor signs
- Liquid pipes
- Electrical components/wiring applications
Non-ferrous metals are rare compared to their ferrous counterparts, which makes them more costly. As a result, the recycling scrap metals industry is booming – as major players seek to extract non-ferrous metals. As such, copper is the third most recycled material in the world.
Here’s an outlook of how ferrous metals differ from non-ferrous metals.
Ferrous vs. Non-Ferrous Metals: What’s the Difference
Here are some of the properties that differentiate ferrous from non-ferrous metals.
Iron (Fe) is naturally magnetic; as such, any metals comprising metallic iron or its alloys will have magnetic characteristics. As a result, ferrous metals are magnetic, whereas non-ferrous metals are non-magnetic.
To that end, you can sort between these two classes of metals with a magnet.
Iron is magnetic due to its polar molecular construction. See, the electrons in the atomic ring are aligned unsymmetrically. Thus, when the iron is in close range with a magnetic field, its electrons are pulled to one side (of the atomic ring) with ease.
Non-ferrous metals are the complete opposite. As such, they are attracted to a magnetic field only when an electric current runs through them. See, the electric field will polarize the electrons, make them temporary magnetic.
In other words, electrons in an atom have a south and a north pole – just like a magnet. So in non-ferrous metals, their electrons are aligned in pairs, with their poles pointing in the opposite direction. This alignment causes the “poles” to cancel each other’s magnetic characteristics. In ferrous metals, however, the electrons have their poles pointing in the same direction, which results in a net magnetic effect.
Oxidation is a chemical process in which an atom loses electrons.
Given its polarity, iron is likely to lose electrons to other polar elements like water. This loss in electrons occurs at the anode. Here, iron reacts with other materials to form different compounds. For example, when iron reacts with water and oxygen, it losses three electrons to form hydrated iron (III) oxide, better know as rust. Rust is weak and flaky and thus does not protect the underlying ferrous metal from more corrosive processes.
Of course, there are exceptions. For instance, stainless steel is resistant to corrosion due to its chromium coating. Similarly, wrought iron is resistant to corrosion; due to its high purity.
Non-ferrous metals do not contain iron; thus, they do not undergo oxidation. When non-ferrous metals react with water and oxygen, for instance; they form oxide layers that firmly adhere to the metal surface. These oxide layers act as impervious barriers – protecting the metal from corrosion.
Given their corrosion-resistant nature, non-ferrous metals are ideal for highly-corrosive environments, such as sewage pipes.
For more an in depth look into metal rust and how to prevent it using hosehold spray paint, [Read Our Full Guide]
When it comes to tensile strength, ferrous metals have capacities that surpass those of non-ferrous metals, by far. Steel, for instance, is considered one of the strongest materials in the construction industry for structural design.
There exist some high-strength non-ferrous metals, but few (if any) can compare to iron-based alloys. Besides, these high-strength metals are expensive due to their scarcity.
Here’s how various metals fair when it comes to tensile strength.
|Element||Metal type||Young’s Modulus (GPa)||Yield Strength (MPa)||Ultimate Strength (MPa)|
Besides their properties, ferrous and non-ferrous metals differ in their availability. While ferrous metals are widely available, non-ferrous metals are scarce, which makes them more expensive. Given their availability, ferrous metals are more recyclable than their counterparts. However, the recycling of spare parts to obtain non-ferrous material is booming.
Welding Techniques for Ferrous and Non-Ferrous Metals
Welding techniques and challenges vary from one metal to the next.
When welding cast iron, for instance, welders must be cautious of any potential cracking. Welding cast steel, on its end, is relatively easy; however, the steel tends to stretch when heated and can fracture or distort the structure in the process.
When welding nickel, magnesium, copper, and their alloys, it’s best to use an inert-gas-shielded-arc welding method. That is even more crucial for magnesium as it burns rather quickly when exposed to oxygen and heat.
Therefore, you should study the metal at hand, learn its properties and whatnot – and determine the most suitable technique for it.
Metals are grouped into ferrous and non-ferrous. However, the difference in this classification goes deeper than the presence or absence of iron. These metals differ in terms of tensile strength, oxidation, and magnetism. That, in turn, affects their weldability and applicability. The two classes also differ in their availability, which affects their prices.