In this Komacut guide, we’ll look at the different types of stainless steel. We’ll explain what the main families of stainless steel are and look in detail at some of the common grades used in manufacturing. We’ll also look at where different types of steel are used and how to choose the right steel for your project.

Stainless steel is the name given to steels that are made with chromium as an alloy at a minimum concentration of 10.5%.  Chromium adds corrosion resistance, strength and toughness, and is what makes stainless steel what it is.

Stainless steel is also alloyed with other elements to create different variants; the amount of chromium can also be altered as can the amounts of additional alloying elements.

There can also be secondary processing, such as annealing or heat treatments, to enhance certain physical properties.

Key Takeaways

• There are a total of five families of stainless steel which are organized primarily by the different alloys and percentage of chromium
• The most commonly used grade of stainless steel is grade 304, which has very good corrosion resistance and formability.
• Generally, the selection of grade is going to be down to the mechanical performance (strength) or biocompatability

Table of Contents

• Introduction
• Key Takeaways
• The Stainless Steel Grading System
• The Stainless Steel Material Families
• Shared Characteristics of All Stainless Steels
• Stainless Steels Commonly Used in Fabrication
• How to Select the Right Material Grade
• The Best Grades By Requirement
• Summary

The Stainless Steel Grading System

The different grades of stainless steel are classified according to a numbering system created by SAE International. The numbering system features three numbers and sometimes, letters added at the end.

The first number indicates the family to which each steel type belongs:

Some stainless steel grades include letter suffixes to indicate specific modifications:

• L – Low carbon (e.g., 304L): Improved weldability and resistance to intergranular corrosion.
• H – High carbon (e.g., 304H): Increased strength at high temperatures.
• N – Nitrogen added (e.g., 304N): Improved strength and resistance to pitting.
• F, Ti, Nb, etc. – Added elements for improved machining, stabilization, or strength.

Duplex and precipitation-hardened stainless steels often follow alternative or proprietary naming conventions. For example:

• UNS (Unified Numbering System): e.g., S31803 (Duplex)
• EN / DIN (European): e.g., 1.4462
• GB/T (China): e.g., 022Cr19Ni10

Here are some answers to some of the questions commonly asked about the stainless steel grade identification system:

What are the differences between grades?

Different grades of stainless steel are classified according to which alloying elements are used and the concentration of each element. Variation creates grades of stainless steel with widely varying physical properties.

Individual grades are also subject to modifications to enhance certain characteristics. Grade 420 is heat treated, for example, to create stainless steels with much higher strength and hardness.

What is 301 vs 304?

Stainless steel 301 has a higher carbon content than stainless steel 304 but is made with less chromium and nickel. 304 is much more corrosion resistant, while 301 will undergo “work hardening,” which means the material will become stronger as it is worked or formed. This is why 301 is used in applications that require good structural strength (automotive, for example).

What does the L mean in 304L (304 vs 304L)?

The L in 304L indicates that the metal is a type of 304 stainless steel that has been made with a lower carbon content. This will make the material slightly weaker, but more weldable.

The Stainless Steel Material Families

Stainless steel is a ferrous alloy that contains chromium at a minimum concentration of 10.5%. The primary role of chromium is making stainless steel corrosion resistant, to improve strength and durability and to improve at high temperatures.

There are five main families of stainless steel, which we’ll explore here.

Austenitic

Austenitic stainless steel is the most commonly used group of stainless steels. They are identified by a 200 or 300 series designation (e.g. 201, 304, 316…). What does that number signify? Hint:

Composition

• Austenitic stainless steels are made with at least 16% chromium. T
• he most common types of austenitic stainless steel are also made with nickel (at least 6%).
• It can also be made with manganese and nitrogen as alloy elements.

Physical Characteristics

• The main strengths of austenitic stainless steel are excellent corrosion resistance,
• high ductility
• high formability
• good weldability

Disadvantages

• Lower hardness
• Lower wear resistance
• Higher cost

Ferritic

Ferritic stainless steel is made with widely varying amounts of chromium and either very small amounts of nickel or no nickel. The amount of chromium used varies between 10.5% and 30%. Ferritic stainless steels are also made with a higher carbon content than austenitic stainless steels and are hardened by cold working.

The main strengths of ferritic stainless steel are good corrosion resistance, good performance at high temperatures, magnetism and lower cost. Weaknesses are lower toughness, reduced ductility, reduced weldability and lower performance in saltwater environments.

Ferritic stainless steels are identified by a 400 series designation (e.g. 420, 430…)

Martensitic

Martensitic stainless steel is made with 12% - 18% chromium and, in some cases, with small amounts of other alloying elements. They are also hardened by heat treating and cold working.

There are many different types of martensitic stainless steels, and the different types offer a wide range of different properties.

The different types are grouped into four main categories. The basic category is made with chromium and offers very good wear resistance. Nickel is added in the next type to increase corrosion resistance and hardness. Martensitic hardening and precipitation hardening is used in the next type to increase strength and toughness. In the fourth type, niobium, vanadium, boron and cobalt are added to increase strength and creep resistance.

Martensitic stainless steels are also identified by a 400 series designation.

Duplex

Duplex stainless steels are made with a mixed microstructure of austenite and ferrite. They also have a high chromium content (19 – 32%), contain up to 5% molybdenum and only have small amounts of nickel.

Duplex stainless steels are mainly produced for their exceptional corrosion resistance (especially to pitting and stress corrosion cracking) and high strength. They also have good weldability and are cost effective. The main weaknesses are brittleness at very low temperatures (below -50°C) and risk of sigma phase formation.

Precipitation Hardened

Precipitation hardened stainless steel is stainless steel that undergoes a heat treatment process called precipitation hardening.

Precipitation hardening significantly increases the strength of the material. Precipitation hardened stainless steels are typically 3 - 4 times harder than basic austenitic stainless steels. Besides being extra high strength, these steels are also highly corrosion resistant. The main disadvantage is the higher cost.

The three types of precipitation hardened stainless steel are:

• Martensitic precipitation hardened
• Semi-austenitic precipitation hardened
• Austenitic precipitation hardened

Shared Characteristics of All Stainless Steels

There are certain positive characteristics that all stainless steels possess when compared to alternative metals.

All stainless steels have good:

• Corrosion resistance: The chromium in stainless steel forms a passive oxide layer on the surface of the material, protecting it from corrosion.
• Strength and durability: All stainless steels have very high tensile strength and excellent wear resistance. Some grades of stainless steel have the highest tensile and yield strengths of all manufacturing metals.
• Hygienic properties: Stainless steel is highly cleanable, making it suitable for food-grade applications.
• Temperature resistance: Stainless steels perform well in high-temperature environments.
• Aesthetic appeal: Stainless steel has a nice appearance. It is often used in architectural applications and in jewelry.
• Recyclability: 100% recyclable, with quality retained.

Stainless Steels Commonly Used in Fabrication

In this section, we’ll look at some of the grades of stainless steel most commonly used in manufacturing.

2) SS304

Composition:

• Chromium: 18–20%
• Nickel: 8–10.5%
• Carbon, manganese, silicon in small amounts
• Traces of phosphorus and sulfur
• Variants may include nitrogen for increased strength

Mechanical Characteristics:

• Moderate strength
• Excellent corrosion resistance
• Higher strength possible with nitrogen-alloyed variants

Processing Characteristics:

• Good machinability
• Excellent formability
• Suitable for welding and polishing

Performance & Applications:

• Highly corrosion-resistant in a wide range of environments
• Hygienic and easy to clean
• Widely used in food, beverage, and chemical processing industries
• Common in brewing equipment, dairies, sinks, water tanks, and kitchen appliances

Standards & Grades:

• Often available in 304L (low carbon) variant for improved weldability

4) SS316

Composition:

• Chromium: 16–18%
• Nickel: 10–14%
• Molybdenum: 2–3%
• Small amounts of carbon, manganese, and silicon
• Traces of phosphorus and sulfur

Mechanical Characteristics:

• Enhanced corrosion resistance, especially in chloride or acidic environments
• Good mechanical strength and durability

Processing Characteristics:

• Good machinability
• Excellent weldability
• Suitable for sheet metal bending and fabrication

Performance & Applications:

• Outstanding corrosion resistance, particularly in marine and chemical settings
• Commonly used in harsh environments or where hygiene is critical
• Applications include exhaust manifolds, heat exchangers, valves, pumps, chemical process equipment, sterile storage tanks, and even jewelry

Standards & Grades:

• Often available in SS316L (low carbon variant) for improved weldability in corrosive conditions

Ferritic

6) SS420

Composition:

• Chromium: 12–14%
• Small amounts of carbon, manganese, and silicon
• Traces of phosphorus and sulfur
• Higher carbon content improves wear resistance

Mechanical Characteristics:

• High hardness
• Good wear resistance
• Limited corrosion resistance compared to austenitic grades

Processing Characteristics:

• Excellent machinability
• Can be hardened by heat treatment

Performance & Applications:

• Suitable for applications requiring high wear resistance and moderate corrosion protection
• Common in cutlery, surgical instruments, scissors, and blades
• Not typically used for food-grade applications due to limited corrosion resistance

Standards & Grades:

• Classified as a martensitic stainless steel; various hardness levels achievable depending on carbon content and heat treatment

Summary Table

Here’s a summary of the stainless steel grades discussed above:

How to Select the Right Material Grade

In this section, we’ll look at the most important things to consider when you’re choosing a grade of stainless steel.

The most important factors that determine any choice of material are:

• 1. How it will be used
• 2. How it will be fabricated
• 3. Project cost sensitivity

How it Will Be Used

• Corrosion resistance – Different grades of stainless steel vary significantly in the level of corrosion resistance they offer. Austenitic and duplex alloys such as 304, 304L, 316 and 316L are usually best.
• High temperature resistance – Grades with high chromium, silicon, nitrogen and rare earth elements are usually more heat resistant. Austenitic grades, such as 310, are often the best choice.
• Low temperature resistance- Austenitic steel grades are also ideal for low-temperature or cryogenic environments. Common grades for low-temperature environments include 304, 304LN, 310 and 316.
• High strength needed – alloys which allow for work hardening (such as 301) are excellent for these types of applications as strength will increase dramatically after processing
• Spring / Flex required – the 200 series stainless steels are often used for applications (even as actual springs) which require more flex
• Shafts / Axles – 420 and 430 are often used in these applications due to the high machinability (even if it is costly) and the excellent stiffness, which means minimal flex in an axle

How it Will be Fabricated

• Welding – L-variants of stainless alloys offer improved weldability due to the lower levels of carbon
• Forming – avoid very high hardness steels (e.g. duplex)
• Sheet metal fabrication – series 300 stainless steels are preferred due to ease of cutting and CNC bending

Cost vs Performance Sensitivity

• Low Cost Needed – 301 and 200 series stainless are a good option
• All around performance – 304 is one of the most common stainless grades for a reason; it has a good mix of cost, corrosion resistance andstrength

What Factors Inform Your Decision?

Here are the elements to consider when you’re making your decision:

• Strength and durability requirements - You should accurately ascertain what tensile strength, yield strength and hardness requirements your component needs to meet and choose a material that at least meets your minimum requirements.
• Budget constraints – Select a material that meets your requirements within the production budget.
• Processing requirements – You need to understand exactly what fabrication processes your part will need to go through and choose a material that matches your requirements. This is often a good thing to discuss with your manufacturer.
• Corrosion resistance – Different grades of stainless steel vary significantly in the level of corrosion resistance they offer. Austenitic and duplex alloys such as 304, 304L, 316 and 316L are usually best. You should accurately ascertain what exposure your component will experience.
• High temperature resistance – Grades with high chromium, silicon, nitrogen and rare earth elements are usually more heat resistant. Austenitic grades, such as 310, are often the best choice.
• Low temperature resistance - Austenitic steel grades are also ideal for low-temperature or cryogenic environments. Common grades for low-temperature environments include 304, 304LN, 310 and 316.

The Best Grades By Requirement

Here’s a simple table to identify good grades for particular requirements.

Summary

Stainless steel is a far more diverse material than is widely known, filling a huge range of manufacturing roles. It is used in everything from low-end products to advanced engineering applications in fields such as aerospace. In many cases, it is not clear what the best choice of material is.

All stainless steels offer good corrosion resistance, strength and hardness. It’s important, however, to make a refined choice when you choose a type for a manufacturing project. The differences between grades vary widely, even within family groups. There are also sub-grades to consider for each grade.