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All You Need to Know About Steel Alloys

Author: Geym

Mar. 07, 2024

Mechanical Parts & Fabrication Services

If you’ve ever wondered what the most commonly used metal in the world is, you might be surprised (or unsurprised for that matter) to find out that it’s steel. Steel is strong and widely used. Many objects that you and I interact with on a regular basis are made of steel. Yet, with its popularity and applicability, many people are relatively unaware of steel’s various properties, intricacies, and uses. If that rings true for you, you'll likely find some interesting information in this post.  

The Origins of Today’s Steel Alloys

Steel was first made by mining iron ore from the ground, smelting the ore in a furnace to remove impurities, and adding carbon. Today’s steel-making process involves recycling existing steel. Whether it’s mined from the Earth or recycled, steel is a combination of iron and carbon.

As a 100% recyclable material, there is no limit to how many times steel can be reused and repurposed. According to the American Iron and Steel Institute,

“North American steelmaking furnaces consume nearly 70 million tons of domestic steel scrap in the production of new steel… By using steel scrap to make new steel, the North American steel industry conserves energy, emissions, raw materials, and natural resources.”

Plus, recycling steel does not result in a loss of quality or strength.  

Steel Groups: Stainless, Carbon, Tool, and Alloy

When you first try to understand steel, it’s easy to end up overwhelmed. And that’s partly because steel is made of four distinct groups. By understanding a bit about these groups, you’ll find the information about steel a bit more digestible. The four groups are stainless, carbon, tool, and alloy, and they are grouped based on chemical composition.

Stainless Steel

Stainless steel is known for being the most corrosion resistant of the four groups. Stainless steel typically includes chromium, nickel, or molybdenum, with these alloys making up around 11-30 percent of the steel.

Of the four steel groups, stainless steel is the most widely known. It is commonly used in food handling, food processing, medical instruments, hardware, and appliances.

Carbon Steel

Carbon steel and stainless steel have the same basic ingredients of iron and carbon, but where their composition differs is in alloy content. Carbon steel has under 10.5 percent alloy content. It’s common to see carbon steel broken down into three subcategories: low carbon steel (0.03-0.15% carbon), medium carbon steel (0.25%-0.50% carbon), and high carbon steel (0.55%-1.10% carbon).

As the percentage of carbon increases, the steel becomes harder and more difficult to bend or weld. Low carbon steels are more commonly used due to having lower production costs, greater ductility, and increased ease of use in manufacturing. Low carbon steels are more likely to deform under stress, while high carbon steels are more conducive to breaking under pressure. Low carbon steels are commonly used in auto body panels, bolts, fixtures, seamless tubes, and steel plate.   

Tool Steel

Tool steels have a carbon content between 0.5% and 1.5%. Tool steel contains other additives, including tungsten, chromium, vanadium, and molybdenum. Tool steels are known for their hardness and their ability to hold a cutting edge at elevated temperatures. This, combined with being resistant to wear and deformation, makes tool steel perfectly suited for use in machining and tool making.

Alloy Steel

If you’re being technical, steel that falls into any of these four group classifications is an alloy, but that’s not what I’m talking about right here. “Alloy steel” is different from “steel alloys.” So, what is alloy steel? Alloy steel is steel that includes about 5% alloying elements in its composition. These alloying elements can include manganese, chromium, vanadium, nickel, and tungsten. The addition of alloying elements increases overall machinability and corrosion resistance.

Alloy steel is most commonly used to manufacture pipes, especially pipes for energy-related applications. It’s also used in the manufacturing of heating elements in appliances like toasters, silverware, pots and pans, and corrosion-resistant containers.

I hope you have a better understanding of steel in general and the four groups steel is often broken into: stainless steel, carbon steel, tool steel, and alloy steel. If you’d like to learn more about stainless steel, feel free to download a free copy of our steel whitepaper:

Stainless steel, known primarily for its corrosion resistance, is used in a wide variety of applications. The diverse range of grades allows it to accommodate various applications across many different industries. However, having so many grades requires the know-how to select the appropriate one for the job.

Here are 7 things to consider when choosing a stainless steel grade:

  • Does it need to have good formability?
  • Does it need to be welded?
  • Does it need to be machined?
  • How much and what type of corrosion resistance is desired?
  • Does it need to be heat treated?
  • What are the strength requirements?
  • What are the typical applications?

Does the stainless steel need to have good formability?

If the application requires good formability, avoid the martensitic group of stainless steels. Try an austenitic grade such as 304 or a ferritic grade such as 430. Martensitic stainless steels like 410 tend to be brittle and are not readily formable. Austenitic stainless steels are usually the best choice when it comes to formable stainless steels.

Does the stainless steel need to be welded?

Welding stainless steel is very different than welding carbon steel, and can lead to problems such as intergranular corrosion, hot cracking and stress corrosion cracking. The most weldable stainless steels are typically in the austenitic group. When welding austenitic stainless steels, grades such as 304L or 347 should be used. Grade 304L has lower carbon while 347 has niobium stabilizers added to it which help to deter intergranular corrosion. Ferritic stainless steels such as grade 430 or grade 439 are also readily weldable, as are Duplex stainless steels. Martensitic stainless are generally not suitable for welding, however, some martensitic stainless steel grades with lower amounts of carbon can be welded. With precipitation hardened stainless steels, care should be taken to ensure that the original mechanical properties are not compromised during the welding process.

Does the stainless steel need to be machined?

If machining is required, special considerations must be accounted for when working with stainless steel. Most grades of stainless steel can be machined, however, stainless steel is very susceptible to work hardening. The machining process must be optimized to work at a rate that helps alleviate this issue, and the tools used for machining must also be kept in good working condition. Similar to carbon steels, sulfur can be added to increase machinability; grade 303 is an example of this. It is very similar to grade 304 except that sulfur has been added to it for machining purposes. Grade 416 is example of a ferritic stainless steel with added sulfur.

How much and what type of corrosion resistance is desired?

Stainless steel is usually chosen for its corrosion resistant properties, but it is important to know that different grades provide different amounts of corrosion resistance. Austenitic stainless steels generally provide the most corrosion resistance because of their high amounts of chromium. This makes grade 304 an excellent choice when corrosion resistance is important. Grade 316 is similar to grade 304, but it has molybdenum as part of its chemical makeup, further increasing its corrosion resistance. Ferritic stainless steels and martensitic are generally more affordable than austenitic stainless steel because they have less nickel and sometimes less chromium than austenitic stainless steels, which can result in a loss of corrosion resistance. Duplex stainless steels can be used to avoid the stress corrosion cracking associated with austenitic stainless steels.

Does the stainless steel need to be heat treated?

If the stainless steel is going to be subjected to heat treatment, it is important to know how the various grades of stainless steel can be affected. For the most part, austenitic stainless steels and ferritic stainless steels are non-hardenable when heat treated. The heat treatable stainless steels are typically martensitic or precipitation hardened. Examples of these are grade 440C and 17-4 PH, respectively.

What are the strength requirements of the stainless steel?

Very high strengths can be achieved with martensitic stainless steels, like grade 440C; and precipitation hardened stainless steels, like grades 17-4 PH and 15-5 PH. Austenitic stainless steels, such as grade 316, can provide high strengths as well, though not as high as the martensitic grades. Austenitic stainless steels also have more nickel than other stainless steels, so a grade like 316 will have greater toughness and ductility than ferritic and martensitic stainless steels. Duplex stainless steels can provide ferritic stainless steel properties while still maintaining a ductility and a toughness close to austenitic stainless steels.

Typical Applications

Sometimes the best way to find out what grade of stainless steel should be used is to see what has been used in the past. Here are some examples of where certain grades of stainless steel are used.

Ferritic Stainless Steels:

  • Grade 409: Automotive exhaust systems and heat exchangers
  • Grade 416: Axles, shafts, and fasteners
  • Grade 430: Food industry and appliances
  • Grade 439: Automotive exhaust systems components

Austenitic Stainless Steels:

  • Grade 303: Fasteners, fittings, gears
  • Grade 304: General purpose austenitic stainless steel
  • Grade 304L: Grade 304 applications that require welding
  • Grade 309: Applications involving elevated temperatures
  • Grade 316: Chemical applications
  • Grade 316L: Grade 316 applications that require welding

Martensitic Stainless Steels:

  • Grade 410: Generable purpose martensitic stainless steel
  • Grade 440C: Bearings, knives, and other wear resistant applications

Precipitation Hardened Stainless Steels:

  • 17-4 PH: Aerospace, nuclear, and chemical applications
  • 15-5 PH: Valves, fittings, and fasteners

Duplex stainless steels:

  • 2205: Heat exchangers and pressure vessels
  • 2507: Pressure vessels and desalination plants

Disclaimer: Please note this information is not to be used for design purposes, and in no event shall MSFFC be liable for any damages arising from the misuse of this information.

All You Need to Know About Steel Alloys

7 Things to Consider When Choosing a Stainless Steel Grade

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