MATERIALS AND METALLURGY

 

TYPES OF STEEL

Mankind first learned to work with iron some 6,000 years ago, though it wouldn’t be until a few thousand years later when the ultra-common element was applied in its most important role: the production of steel. Steel is used in mechanical and electrical applications, heavy construction equipment, kitchen appliances and tools. With so much variety, it can be confusing to decide the type to use.

Steel is an iron alloy, meaning it’s primarily composed of iron and combined with one or more alloying metals to produce new materials with unique properties. There are four main classifications, but there are also multiple subgroups that serve different purposes. Its properties change depending on the elements iron is combined with as well as the methods used to heat and cool the metal.

Below, we explain the different kinds of steel and the purpose each type serves. We hope this information can help you make decisions about which type to use with clarity and confidence.

What Are the Different Types Of Steel?

Steel is classified by its composition: iron is fused with carbon and any number of other elements to achieve a specific end. The four main types are:

• Carbon steel
• Stainless steel
• Alloy steel
• Tool steel

1. Carbon Steel

All steel contains carbon, but carbon steel is unique for a notable absence of other elements in its makeup. Though it only contains 2% carbon or less by weight, its elemental nature makes carbon steel a strong, durable material that is ideal for numerous uses.

Carbon steel is sometimes confused with cast iron, though it must contain less than 2% carbon. Cast iron contains 2% to 3.5% carbon, giving it a rough texture and more brittle nature.

Even though carbon steel is composed of alloyed metals, it doesn’t have alloy classification because of the lack of other alloying elements in its composition. This simplicity contributes to carbon steel’s popularity — it accounts for about 90% of all steel production.

Types Of Carbon Steel

Below the 2% carbon threshold, carbon steel can be grouped into three categories: low, medium, and high carbon. Each type retains the inherent strength of carbon, but its useful purpose will change as the carbon content increases.

• Low carbon: This is the most common and the least expensive type. It’s easy to form due to its high ductility — its innate ability to be stretched under strain. Wires, bolts and pipes use this type of steel.
• Medium carbon: A carbon content between 0.31% and 0.60% gives this variety a higher strength and lower ductility than lower carbon varieties. Medium carbons are found in gears and railroad tracks.
• High carbon: The toughest variety is more than 0.61% carbon and is often used to produce brick nails and sharp cutting tools like trencher blades. They do not contain more than 2% carbon.

Carbon steel’s relative adaptability and low cost make it an ideal choice for a variety of construction projects, both large and small-scale.

2. Stainless Steel

This type is commonly known for its role in manufacturing medical equipment and appliances, but its range of use is far greater than just the gas range in your kitchen. Chromium is the alloy that sets stainless steel apart, lending the material its distinctive luster.

Chromium is more than a purely cosmetic addition, however: the element is oxidation-resistant and will increase the metal’s longevity by preventing it from rusting. Typically, stainless steel has a chromium content of more than 10.5% and sometimes contains up to 30% in certain applications.

Higher chromium content directly translates to a higher gloss when polished and has greater resistance to corrosion. Stainless steel is different from chrome when chromium is electroplated onto another metal to produce a tough, polished coating. The sheen in high-chromium stainless steel applications is less mirror-like due to the addition of other elements.

Types Of Stainless Steel

Kitchen, medical and automotive applications are common, but stainless steel is highly valued for other uses as well. It’s is grouped into four subcategories that each serve a different purpose.

• Martensitic alloys: Toughness is a hallmark of martensitic alloys, but they’re prone to corrosion. They’re formed by a rapid-cooling process that makes them ideal for heat treatment and are found in medical instruments, cutlery and pliers.
• Ferritic alloys: These are less-expensive steels with low amounts of carbon and nickel. Automotive applications are common final destinations for ferritic alloys because of their chromium-induced strength and sheen.
• Austenitic alloys: Austenitic alloys have higher chromium and nickel contents, improving their resistance to corrosion and causing them to become non-magnetic. They’re present in commercial kitchen appliances and are popular because they’re durable and easy to clean.
• Duplex alloys: A combination of austenitic and ferritic alloys results in a duplex alloy that inherits the properties of both while doubling strength. They’re also ductile and corrosion-resistant due to their fairly high chromium content.

Stainless steel variants, when used in the construction industry, are prized for their corrosion resistance and strength. They’re well-suited for a variety of building applications, as well as storage functions for hazardous construction materials.

3. Alloy Steel

The alloy type is iron fused with one of several other elements, each contributing its own unique attributes to the final product. It’s true that all steels are alloys, but carbon and chromium are specific alloys with names attributed to the type of metal they form.

Alloy steel as a grouping includes a diverse range of alloys with an equally diverse range of properties. Shipping containers use a complex alloy that combines multiple elements to produce a durable and lasting product. Silicon isn’t often thought of as a component of steel, but its magnetic properties make it a perfect component of most large machinery. Aluminum is versatile and used in revolutionary building materials that are both lightweight and extremely durable.

Some of the elements that combine with iron and carbon to produce alloys are also found in tool steels — cobalt, tungsten and molybdenum, for example, are ultra-hard metals that are desired for their impact resistance and cutting abilities.

Types Of Alloy Steel

The varied potential of alloy steel allows for intense customization for specific applications. However, because the secondary elements involved are not always easy to come by like carbon or chromium, certain alloys command a steep price.

Some of the most common alloys include:

• Aluminum: Lightweight, heat-resistant steel that’s ductile and easy to work with and is often used in hot exhaust systems and power generators.
• Copper: Corrosion-resistant steel that conducts heat very efficiently, making it a great choice for electrical wiring and industrial heat exchangers.
• Manganese: Impact-resistant steel that’s extremely tough. It can be found in bulletproof cabinets, anti-drill plates and high-strength safes.
• Molybdenum: Weldable, corrosion-resistant steel that performs under high pressure, making it well-suited for underwater construction or oil and gas pipelines.
• Silicon: Soft-natured steel that’s malleable and highly magnetic, and creates strong permanent magnets that are used in electrical transformers.
• Vanadium: High-impact steel that’s shock-absorbent and vibration-resistant, and often found in automotive parts like springs and shocks.

Their downright versatility makes alloys a common occurrence in many construction projects. Copper and aluminum alloy varieties are particularly popular for their low weight and heat working properties.

4. Tool Steel

Tool steels are up-front about their business: they’re used to tool manufacturing machinery. Tempering, the process of adding high heat, cooling quickly then heating again, creates tool steel that’s extremely hard and heat-resistant. They’re usually used in high-impact environments and are very abrasive.

Types of Tool Steel

Different types of tools require different types of tool steel in production. Tool steel is used in a variety of ways to best serve the production requirements of a particular tool. Added elements will determine which particular applications that it’s suited for.

• Air-hardening: The high chromium content in this steel allows it to be exposed to high temperatures without distorting.
• Water-hardening: This steel is water-quenched during use; it’s the most affordable tooling type and is used to make common tools.
• Oil-hardening: This oil-quenched steel is exceptionally wear-resistant from slipping, and is used to produce knives and shears.
• High-speed: High-speed steel is highly abrasive and impact-resistant. It’s found in drill bits and power saws.
• Hot-working: The name gives it away, but this steel can withstand extreme heat and is used in forging and casting.
• Shock-resisting: Small amounts of carbon, silicon and molybdenum harden this steel and suit it for punches and riveting tools.

These types can be further separated by the industry they’re used in, as well as their hardness and toughness.

What Are the Different Grades of Steel?

Steel is notably complicated due to its many properties and applications. Two comprehensive grading systems have been developed to accurately categorize a particular type, even within subgroups. These systems are standardized across industries so that material integrity can be insured. The two grading systems are:

• ASTM (American Society for Testing and Materials): Alphanumeric classification that denotes the steel’s overall categorization and specific attributes.
• SAE (Society of Automotive Engineers): Four-digit numerical classification that highlights steel type and carbon content along with the presence of other alloying elements.

You can find steel everywhere, materialized in different forms to suit various needs. It’s is an essential component of many building materials, home appliances and even tools used to make other tools. By combining the right elements, an exact steel match is available for almost any application.

Iron and carbon are proven versatile metals that are the building blocks of much of what we see in today’s modern cities, including transportation networks and telecommunications infrastructure. The usage of steel has a long history and will continue far into the future as new ways to combine elements are discovered.