Guide to Ferrous Metals

Picture of rusty iron chain. Photo courtesy of Artem Beliaikin // Unsplash

Ferrous metals commonly used in countless applications, from construction, machinery, and transportation to manufacturing and infrastructure. Chosen for their incredible strength, durability, and magnetic properties, ferrous metals have played a big role in the development of the world as we know it, and will continue to be present in daily life well into the future.

What Are Ferrous Metals?

Ferrous metals contain iron as their primary component. In fact, the word “ferrous” comes from the Latin “ferrum” meaning “iron.” (Iron is also the element listed on the Periodic Table as “Fe.”)

Types of Ferrous Metals

There are five types of ferrous metals: carbon steel, alloy steel, cast iron, wrought iron, and stainless steel.

Carbon Steel

The most common type of ferrous metal, carbon steel is an alloy of iron, carbon, and other elements, like copper, manganese, and silicon. Carbon steel is widely used due to its high strength, weldability, and relatively low cost.

Carbon steel is further divided into four types: low, mild, medium, and high carbon steel.

Low-carbon steel (0.15% carbon maximum) is highly ductile and malleable. It is easy to bend, roll form, weld, and machine. It is often used in sheet metal applications where high strength is not critical.
Mild carbon steel (between 0.15% to 0.29% carbon) is similar to low carbon steel in that it is highly malleable with high ductility, but it is somewhat stronger.
Medium carbon steel (between 0.30% and 0.59% carbon) has higher strength and hardness but less ductility than low or mild-carbon steel. It is often found in rails, crankshafts, and gears, where higher strength and wear resistance is required.
High-carbon steel (between 0.60% and 1.70% carbon) is strong and hard but has less ductility than low-carbon steel. Since high-carbon steels offer high strength, hardness, and wear resistance, it is often used in knives, chisels, and other applications where wear resistance and hardness are critical.

Alloy Steel

Alloy steels are made by adding elements like copper, nickel, and silicon to steel to enhance its mechanical properties. This may provide corrosion resistance or higher strength and ductility at elevated temperatures.

Alloy steels are classified based on the amount and type of additional elements they contain.

Low-alloy steel contains only small amounts of alloying elements (less than 5%) to enhance desired properties without drastically increasing cost.
High-alloy steel contains higher amounts of alloying elements and is typically used in specific applications where properties like corrosion resistance or high strength at high operating temperatures are required.
Tool steels are designed for making cutting instruments with high degrees of hardness and wear resistance.

Stainless Steel

Stainless steel is a versatile and durable alloy made by combining iron, carbon (often at slightly reduced levels), and chromium (10% minimum) along with some other elements, typically nickel and manganese. There are several different types and grades of stainless steel but all have varying degrees of high corrosion resistance, high strength, and ductility, which makes them well-suited for a wide variety of applications.

Cast Iron

Cast iron is iron alloyed with carbon (between 2% and 4%), silicon (between 0.9% and 2.8%), and other elements, including manganese, sulfur, and phosphorus (in small traces). Cast iron is brittle but offers good wear resistance due to its hardness.

Wrought Iron

Wrought iron is an alloy of highly refined iron and carbon (typically 0.08%). Slag is minutely and uniformly distributed throughout, which gives it its characteristic grainy texture.

Though traditional wrought iron production is in decline, wrought iron is still widely used in many decorative applications today for its strength and high degree of malleability. Many modern wrought iron products are made from mild steel that resembles traditional wrought iron.

Properties of Ferrous Metals

Before discussing the properties of ferrous metals, it is important to first understand what “properties” refer to when discussing metals. The Webster’s Dictionary describes a “property” as “a quality or trait belonging to and especially peculiar to an individual or thing.” Let's examine the specific properties of ferrous metals.

Magnetic Properties

Ferrous metals are usually magnetic. The only exception is when the ferrous metal is alloyed with other elements that make it non-magnetic, such as in the case of austenitic stainless steel.

Mechanical Properties

Ferrous metals have high tensile strength (the capability to withstand being pulled apart) with a high degree of ductility (although this varies greatly depending on the specific type and grade of the material). This is one of the main reasons why steel is common in such a wide array of applications.

Corrosion Resistance

Ferrous metals tend to rust easily, due to the high capacity for oxidation inherent in carbon steel alloys. However, stainless steels offer a high degree of corrosion resistance, even at elevated temperatures.

Density and Weight

Ferrous materials have a higher density (mass in proportion to weight) than most other materials and are therefore heavier, which makes them suitable for applications that require high strength and load-bearing capability.

Pros and Cons of Working with Ferrous Metals

There are many advantages, as well as disadvantages, to working with ferrous metals.

Pros

High strength and durability make steel and other ferrous metals ideal for situations that require them to hold up under load or pressure.
Weldable and machineable, which makes ferrous metals relatively easy to cut, bend, shape, form fabricate, and weld into a variety of sizes, shapes, and applications across a broad spectrum of industries, including building and bridge construction, pipelines, automotive, residential, decorative, and tools and equipment.
Corrosion resistant. Many ferrous metals (stainless steel in particular) offer high degrees of corrosion resistance, which makes them well-suited for hot and harsh environments.

Cons

Weight. Ferrous metals are dense and heavy. Equipment like cranes or forklifts may be necessary to move large pieces.
Heat. High heat is necessary to form, cut, and weld ferrous metals, which increases risk exposure.
Cost of equipment. Expensive, specialized equipment may be necessary to cut, bend, form, machine, and weld ferrous metals. The larger and heavier the pieces, the more expensive the equipment required.

How Ferrous Metals are Used

Probably the biggest reason that ferrous metals (especially steel) are the most commonly used materials in manufacturing and construction is their versatility. It would be hard to go through the day and not use something made of or made by ferrous metals.

The Construction Industry

Ferrous metals are used in framing residential and office buildings, bridges, and structures of all shapes and designs. Ferrous metals make it possible to build buildings of tremendous size, where construction with other types of materials (stone or wood) would be impractical.

Transportation and the Automotive Industry

Ferrous metals are common in automotive applications, often forming the chassis and many individual components within cars and trucks, including gears, axles, rotors, and brakes.

Ferrous metals are also a vital component of our modern infrastructure, forming the foundation of railways and bridge systems all over the world.

Machinery and Tools

Consider all the tools that would not be possible without ferrous metals. Tool steel offers such high strength and durability that it can form saw blades, drill bits, and cutting tools to process a wide range of other materials, including other types and grades of steel.

Household Appliances

Ferrous metals are present in homes all over the world in ovens, washing machines, toasters, pots and pans, and eating utensils. Electronics and appliances also contain many ferrous metals, both in the frames and in some of the internal components.

Processing and Manufacturing Ferrous Metals

The process of extracting iron ore from the ground, refining it into raw material, alloying it with other materials, and shaping it into the desired product involves several steps.

Mining and Extraction

First, the iron ore is mined, either in an open pit or using an underground method. It is then shipped to a processing plant, where it is crushed and ground into fine particulate. It is separated from other particles by magnetic separation or flotation. The iron ore is then formed into pellets or some sort of solid form, where it can be moved to the next stage for further refining.

Smelting and Refining

The next phase of material production is smelting the iron ore, which involves a blast furnace using coke (a form of carbon) and limestone. The coke adds carbon to the iron ore, creating steel, while the limestone helps to remove impurities, often referred to as slag.

The raw iron ore is then taken to the refining process, where the metal is purified through smelting to achieve the desired quality and properties. This process involves placing the “pig iron” into a furnace to reduce the carbon content and adjust the composition by adding alloying elements to create various grades of steel.

Casting

The casting process involves pouring the molten metal into a mold and allowing it to cool and harden into the desired shape. Many automotive parts and machinery components are made this way. Casting offers cost-effective design flexibility and is widely used in production.

Forging and Rolling

Of course, not all ferrous metals are used in casts. Forging is used to compress and deform the metal into the desired shape, while I-beams, channels, angles, pipes, plate, and tubing are made by rolling. The metal is heated to a transition temperature and fed through rollers of various configurations to obtain the desired size, shape, and thickness.

Both forging and rolling are possible with the use of heat as well as at or near room temperature in processes known as “cold rolling” or “cold forming.” The absence of heat makes the material less malleable and harder to shape, but it is possible to form materials at tighter dimensional tolerances and improve surface finish.

Heat Treatment

Heat treatment is a critical step in the production of ferrous metals. By heating and cooling the material at controlled rates, heat treatment alters the granular microstructure of the metal, which has a tremendous impact on things like hardness, ductility, and strength.

The production of ferrous metals uses several different heat-treating techniques.

Annealing

Annealing involves heating the metal to a specific temperature and cooling it slowly to relieve internal stress, which greatly increases ductility.

Quenching

Quenching is almost the exact opposite of annealing. It involves heating and cooling the metal rapidly, usually in water, oil, or a solution to increase the hardness, but it also reduces the metal’s ductility and toughness. (This is a common technique blacksmiths use to make knives.)

Tempering

Tempering is often used just after quenching to restore some of the hardened metal’s ductility. The metal is heated to a much lower temperature and cooled in a slower, more controlled manner.

Case Hardening

Case hardening involves adding carbon to the surface of the metal, which creates a hard outer layer while maintaining a tough inner core. (A great example of this is the making of katana swords. The swords use high carbon for the outer edge but preserve a strong core. The characteristic, curved shape of the katana is the result of the different types of steel being cooled at different rates.)

Recycling Ferrous Metals

One of the advantages of ferrous metals is their recyclability. They can be used again without a reduction in qualities like strength and durability.

A great example of this is the aftermath of the 9/11 attacks. Much of the resulting scrap iron generated after the towers collapsed was moved to a scrap yard on Staten Island. Northrup Gruman used approximately 7.5 tons of scrap from the fallen towers to build the amphibious vessel the USS New York. The steel was presented as a gift to the US Navy by the City of New York. The ship represents the largest functional item made from World Trade Center scrap metal.

Importance of Recycling

Recycling is an important part of meeting the world's demand for steel and ferrous metal products because it is cheaper and more environmentally friendly than mining new steel. Recycling also reduces the amount of waste piled up in landfills, dumps, scrap yards, and recycling centers throughout the world.

Process of Recycling Ferrous Metals

There are several steps in recycling ferrous metals:

Collecting — The metal may be brought to a station or center by truck, by railway, or using other transport methods. Many centers allow anyone to dump scrap metal and pay them the market rate.

Sorting — Scrap metal is usually sorted with the use of magnets to separate ferrous from non-ferrous metals.

Processing — The scrap metal is often shredded, cut, or compacted into smaller parts, which makes it easier to handle and melt.

Melting — The metal is heated to a molten state in a furnace.

Purifying — The molten scrap iron is subjected to the same processing as in the initial production. The metal must be heated and any residual contaminants removed.

Solidifying — The scrap metal is forged, cast, or rolled into the desired size and shape.

Making New Items from Scrap Iron

It's also worth noting that ferrous metals can be easily repurposed into useful items instead of being recycled. For example, old car springs can become wedges or knives. Old tractor seats can become decorative bar stools. Sheet metal, in the hands of a skilled craftsman, can become ornate sculptures.

Safety Precautions

Working with ferrous metals involves risks that should be understood before work begins.

Handling and Storage

Never handle ferrous metals with bare hands due to the tendency of ferrous metals to rust. Burrs from cutting and sawing may result in deep cuts to the hands and fingers. Always use sturdy canvas or leather work gloves.

Protective Gear and Equipment

Always wear the following PPE (personal protective equipment) when working with ferrous metals:

Safety glasses with side shields
Steel toed boots
Cotton or denim long-sleeve shirt or welding jacket — never polyester
Work/welding gloves appropriate for the activity
Face shield if grinding or operating chop saws

Welding and Cutting Safety

Welding operations have a unique set of risks, which are possible to mitigate with the use of these items:

Welding helmet with appropriate shade lens
Safety glasses with side shields
Welding jacket or leather welding sleeves or apron
Sturdy welding gloves
Steel-toed boots
Torch goggles, dark shade (#5) glasses, or face shield for oxy-acetylene cutting, welding, or brazing

FAQ

What are ferrous metals and how are they different from non-ferrous metals?

Ferrous metals contain iron, whereas non-ferrous metals (like aluminum, copper, and titanium) do not.

What are the main types of ferrous metals used in industrial applications?

The most common ferrous metal in use today is carbon steel, available as low, medium, mild, and tool steel. Stainless steel is also widely used.

What are the advantages of using ferrous metals in construction and manufacturing?

Ferrous metals have several advantages over other types of metal. For one thing, ferrous metals offer high strength and load bearing (weight and pressure) at a relatively low cost.

Second, ferrous metals are relatively easy to cut, bend, forge, and weld into all sorts of complex shapes, structures, and designs.

What are the environmental implications of recycling ferrous metals?

Recycling ferrous materials greatly reduces the need to mine iron ore from the ground. Less mining means fewer open pit mines and a smaller carbon footprint to meet global ferrous metal needs. Recycling materials also means fewer stockpiles in scrap yards.

Featured photo courtesy of Miguel Á. Padriñán // Pexels