- Published 15 Nov 2024
- Last Modified 15 Nov 2024
- 6 min
Understanding and Using Stainless Steel
Beneath stainless steel’s slick appearance is a host of manufacturing advantages. Learn more about what stainless steel is, how it’s made, the various stainless steel grades explained and their uses.
Reviewed by David Carmichael, Solution Engineer (October 2024)
We know stainless steel for its slick appearance, but just what is it, and what are the main uses of stainless steel? This guide will help to explain stainless steel uses and properties, and to understand what are the 3 grades of stainless steel.
What is Stainless Steel?
All steels are alloys (mixtures) of iron and carbon, with other elements added to tailor properties. Stainless steel has a high chromium content: at least 10.5%.
What are the properties of stainless steel?
The chromium gives superior corrosion resistance, stainless steel’s chief advantage. It also has high recyclability and heat resistance, good strength and durability, and a shiny appearance (which lasts long with easy cleaning).
Why does stainless steel not rust?
Rust, a type of corrosion, is the oxidation of iron with oxygen. Stainless steel is pre-oxidised with its chromium oxide shell, which continually self-replenishes through oxidation with oxygen in air or water. This protects the metal underneath. Stainless steel can indeed rust under certain conditions, though, such as insufficient water drainage or airflow.
What is the most common use for stainless steel? Common uses of stainless steel include:
- Surgical tools and operating tables
- Cutlery and cookware
- Sinks and food preparation surfaces
- Exhaust systems
- Cosmetic trimming for buildings and vehicles
What Metals is Stainless Steel Made of?
Stainless steel has a high proportion of chromium, 10.5% to 30%, in its iron and carbon base. The more chromium, the greater the corrosion resistance. Stainless steel may also feature other elements (in smaller amounts) to further tailor material properties:
- Nickel: Improves strength and ductility and helps prevent corrosion from some substances.
- Manganese: A nickel substitute that sacrifices corrosion resistance and ductility for lower costs.
- Molybdenum: Prevents corrosion from acids and increases high-temperature strength.
How is Stainless Steel Made?
The stainless steel manufacturing process involves:
- Melting: An electric furnace heats and melts the ingredient materials (often scrap, i.e. recycled metal) for several hours.
- Carbon Removal: Processes of injecting argon or oxygen gas reduce the material’s carbon content, which is essential for increasing the chromium proportion.
- Tuning: Manufacturers stir the material and finetune its chemistry and temperature, often involving sampling and testing to get the right balance.
- Forming: The foundry initially shapes molten material into slabs, rods (round or square), or tubes.
- Hot and Cold Rolling: The manufacturer then repeatedly rolls the material above (hot rolling) and later below (cold rolling) its recrystallisation temperature to fine-tune its shape.
- Heat Treatment or Annealing: Controlled heating and cooling cycles relieve internal stress and soften the stainless steel.
- Pickling: Acid baths or oxygen-free heating and cooling remove scale accumulated from all these processes. This guarantees stainless steel’s shine and corrosion resistance.
- Cutting: The material is cut into useful shapes, such as stainless bars, stainless sheet, and stainless tubes. This involves blades or dies, or even plasma cutting for intricate shapes.
- Finishing: Surface treatments finalise the material’s appearance and remove remaining impurities.
Stainless Steel Grades and Uses
What are the 4 types of stainless steel? Stainless steel is categorised by the grains of its microstructure: either austenitic, ferritic, martensitic, or duplex (ferritic-austenitic hybrid) patterns. These types fall into numerical stainless steel grades like 300, 200, 400, and 2000.
300 Series: Austenitics
The most prevalent type of stainless steel in industry, 300 series austenitics have 16% to 21% chromium and they rely on 6% to 26% nickel for strength, ductility, and further corrosion resistance.
Comparing 304 vs 316 stainless steel, two of the most common of these grades, 316 contains molybdenum and thus resists corrosion better than 304 in acidic environments. Both have high weldability and formability, making them industrially versatile. They are also both fit for medical and surgical products and food and beverage applications.
200 Series: Austenitics with Manganese
These have 15% to 19% chromium and use manganese together with nitrogen in place of nickel. Industries developed them due to nickel shortages following World War II, and they continue to be less expensive than 300 grades due to reduced nickel. 200 series austenitics have greater strength, hardness, and toughness than the 300 series but have lower ductility and formability.
They share many applications with the 300 series, such as washing machine drums, food and beverage equipment, and home water tanks.
400 Series: Ferritics
Ferritic stainless steels have the highest chromium content: 10.5% to 30%. They thus have the highest corrosion resistance. They also have good ductility, resist cracking in high-stress corrosive environments, and are magnetic. They have widespread use in parts for vehicles and industrial machinery. They’re also used in furnaces, heat exchangers, and exhaust systems.
400 Series: Martensitics
The 400 series also includes martensitic steel, which has a relatively low chromium content at 11.5% to 17% (giving it less corrosion resistance) and the most carbon of stainless steels: 0.1% or more. The carbon increases its strength and makes these steels suitable for high-stress, potentially corrosive applications like in compressors, turbines, pumps, and cutting tools.
2000 Series: Duplex
Duplex stainless steels have a microstructure exhibiting ferritic and austenitic properties. They have a high chromium content at 21% to 26%, up to 5% molybdenum content, and low nickel content. They also have high strength and corrosion resistance and avoid the high costs of nickel-containing steels.
These steels are suited for intense industrial processes like chemical and oil processing, pulp and paper production, pressure vessels, and high-chlorine environments.
Comparing Grades
All these stainless steel grades and types might be confusing, so this table gives a general comparison of them:
Type | Corrosion Resistance | Strength | Ductility | Weldability | Cost |
|---|---|---|---|---|---|
300 Austenitics | High | Medium | High | High | High |
200 Austenitics | Medium | High | Low | Medium | Low |
400 Ferritics | Medium | Medium | Medium | Low | Low |
400 Martensitics | Medium | High | Low | Low | Low |
2000 Duplex | High | High | Medium | Medium | Low |
Stainless Steel Advantages
Stainless steel properties give the metal great advantages over others:
- Corrosion Resistance: The chromium oxide outer layer prevents corrosion, such as rust, thus avoiding reduced structural integrity.
- Appearance: The outer layer also has a slick, shiny appearance, making it sought after for appliances and the exteriors of homes, vehicles, and buildings.
- Cleanability: The oxide’s imperviousness also makes it easily cleanable, making it great for the food and medical industries, which have high sanitisation needs.
- Recyclability: Stainless steel has green advantages with its near-100% recyclability, so stainless products are often made from recycled material.
- Heat Resistance: In high-temperature environments, stainless steel resists oxidation and extreme temperatures and prevents flame growth, making it good for automotive exhaust systems.
Stainless steel isn’t always the best choice, though. Considering stainless steel vs steel, i.e. mild steel / carbon steel, stainless steel has lower strength and durability and is generally more expensive. Comparing alloy vs stainless steel, alloy steel (steels featuring other prominent alloyed elements besides chromium) has a superior strength-to-weight ratio and better machinability.
RS carries an assortment of stainless steel rods and bars, plus other metal materials to fulfil all your structural needs.
