Understanding Stainless Steel Grades: Which One is Right for You?

Why Understanding Stainless Steel Grades is Essential

When selecting stainless steel for a project, it’s critical to understand the different grades and types available. With each grade offering a distinct balance of corrosion resistance, strength, and performance, making the right choice ensures optimal durability and cost-efficiency.

Misunderstanding grades of stainless steel can lead to poor performance, costly repairs, or even failure in demanding applications.

This guide explains the types of stainless steel, popular grades, and how to choose the right option based on your environment and application.

Stainless Steel Grades Explained

A stainless steel grade refers to the specific chemical composition and mechanical properties of a stainless steel alloy. Grading systems classify stainless steels based on factors like:

• Corrosion resistance
• Chromium and nickel content
• Strength and hardness
• Applications and environments

Stainless steel grades are classified using various systems, depending on the country and application. At NeoNickel, we commonly use the SAE steel grading system, which is widely recognised for its clarity and practicality. The SAE system categorises stainless steel into several series based on composition and performance:

• Series 100 Steel: Basic carbon steels
• Series 200 Steel: Austenitic chromium-nickel-manganese alloys
• Series 300 Steel: Austenitic chromium-nickel alloys (e.g., grades 304, 316)
• Series 400 Steel: Ferritic and martensitic chromium alloys
• Series 500 Steel: Heat-resistant chromium alloys
• Series 600 Steel: Proprietary alloys (no longer graded by the SAE)
• Series 900 Steel: Austenitic chromium-molybdenum alloys

Understanding these series helps ensure you select the most suitable grade for your application. For example, Series 300 alloys, including 304 and 316, are ideal for environments requiring high corrosion resistance, while Series 400 alloys excel in strength and wear resistance.

The most common classifications include austenitic, ferritic, martensitic, and duplex stainless steels, each offering unique characteristics suited to different applications.

Types of Stainless Steel

Stainless steel is divided into four primary types, each with varying compositions and properties. Stainless steels are classified into four main types based on their microstructure, determined by their composition. Each type offers specific mechanical properties and corrosion resistance, making them suitable for various applications.

1. Austenitic Stainless Steel

Austenitic stainless steel is the most widely used type, offering outstanding corrosion resistance, excellent weldability, and ductility. Its high chromium and nickel content ensure superior performance in aggressive environments, such as those with moisture, chlorides, or chemicals.

Typical Composition:

• 16-26% chromium
• Up to 35% nickel

Applications:

• Food processing equipment
• Medical devices
• Chemical plants and tanks

Austenitic stainless steel is divided into three subgroups:

• Common chromium-nickel alloys
• Manganese-chromium-nickel-nitrogen alloys
• Speciality alloys for specific environments

High-Performance Consideration: Enhanced nickel content provides superior resistance to chloride-induced pitting and stress corrosion cracking, making it ideal for marine and chemical applications.

Common Austenitic Alloys we offer:

• AL-6XN®
• Alloy 310S
• 253 MA®
• Alloy RA 330®

2. Ferritic Stainless Steel

Ferritic stainless steels are known for their affordability, formability, and moderate corrosion resistance. They contain higher chromium content (10.5-27%) but no nickel, which reduces costs compared to austenitic grades. Although they are less resistant to corrosion, they perform well in indoor and decorative applications.

Typical Composition:

• 10.5-27% chromium
• 0% nickel

Applications:

• Automotive exhausts
• Kitchen sinks and appliances
• Heat exchangers

High-Performance Consideration: Ferritic grades are ideal for thin-sheet production and decorative uses due to their magnetic properties and ease of forming.

Common Ferritic Alloys:

• Grade 430
• Grade 409

3. Martensitic Stainless Steel

Martensitic stainless steels are known for their high strength, hardness, and wear resistance. They are typically used in applications that require mechanical performance, such as cutting tools and aerospace components. However, their corrosion resistance is lower than that of austenitic and duplex steels.

Typical Composition:

• 11.5-18% chromium
• 1.2% carbon

Applications:

• Surgical instruments
• Aerospace components
• Cutlery and valve parts

High-Performance Consideration: Tempered martensitic steels offer enhanced toughness and strength, making them suitable for high-stress environments.

Common Martensitic Alloys We Offer:

• AerMet® 100
• Alloy 13-8
• Alloy 17-4
• Alloy 410
• Greek Ascoloy®

4. Duplex Stainless Steel

Duplex stainless steels combine the best properties of both austenitic and ferritic steels, offering high strength and superior resistance to stress corrosion cracking and pitting. They are commonly used in marine, petrochemical, and offshore applications.

Typical Composition:

• 21-27% chromium
• 1.35-8% nickel
• 0.005-3% copper and molybdenum

Applications:

• Oil and gas pipelines
• Pressure vessels
• Heat exchangers

High-Performance Consideration: Duplex grades provide twice the yield strength of austenitic grades and are more resistant to chloride-induced corrosion.

Common Duplex Alloys We Offer:

• UNS S31803 / 2205
• UNS S32760
• ZERON® 100

Popular Grades of Stainless Steel and Their Properties

1. Grade 304 (Austenitic Stainless Steel)

The most widely used grade, 304 stainless steel offers excellent corrosion resistance and versatility, making it ideal for a broad range of applications.

• Composition: 18% chromium, 8% nickel
• Corrosion Resistance: High (general-purpose)
• Applications: Sinks, food equipment, chemical tanks
• Magnetism: Non-magnetic

2. Grade 316 (Austenitic Stainless Steel)

316 stainless steel is known for its superior resistance to chloride-induced corrosion, making it the top choice for marine and chemical applications.

• Composition: 16% chromium, 10% nickel, 2-3% molybdenum
• Corrosion Resistance: Very high (especially in chloride environments)
• Applications: Marine equipment, medical implants, offshore structures
• Magnetism: Non-magnetic

3. Grade 410 (Martensitic Stainless Steel)

With its high strength and wear resistance, 410 stainless steel is commonly used in applications that require toughness and mechanical performance.

• Composition: 12-13% chromium, 0.15% carbon
• Corrosion Resistance: Moderate
• Applications: Surgical instruments, cutlery, aerospace components
• Magnetism: Magnetic

4. Grade 430 (Ferritic Stainless Steel)

430 stainless steel is popular for its good corrosion resistance at an affordable cost. It is commonly used in decorative applications and kitchen appliances.

• Composition: 16-18% chromium
• Corrosion Resistance: Good (for indoor use)
• Applications: Automotive trim, kitchen appliances, decorative finishes
• Magnetism: Magnetic

Comparison Table of Stainless Steel Grades

Choosing the Right Stainless Steel Grade

1. Corrosion Resistance Requirements

If your application involves exposure to moisture, chlorides, or chemicals, opt for grades like 316 with superior corrosion resistance. For general indoor use, 304 or 430 may be sufficient.

2. Strength and Mechanical Performance

For applications requiring wear resistance and high strength, consider martensitic grades like 410 or duplex options for more demanding conditions.

3. Cost Considerations

Austenitic grades like 304 and 316 offer premium performance but come at a higher cost. Ferritic grades like 430 provide cost-effective solutions for less demanding environments.

Differences Between Stainless Steel Grades and Families

Austenitic vs. Ferritic Stainless Steel

• Austenitic: Non-magnetic, excellent corrosion resistance, more expensive
• Ferritic: Magnetic, good corrosion resistance, affordable

304 vs. 316 Stainless Steel

• 304: General-purpose, lower cost
• 316: Superior resistance to chlorides and harsh chemicals

What Grade of Stainless Steel Doesn’t Rust?

While stainless steel is known for its corrosion resistance, not all grades are equally resistant to rust. Grades that contain less chromium, such as ferritic (Series 400) and martensitic stainless steel, are more likely to rust in certain conditions. On the other hand, austenitic grades, like 304 and 316 stainless steel (Series 300), contain higher chromium and nickel levels, making them more resistant to rust and ideal for marine and chemical applications. In summary:

• More prone to rust: Ferritic and martensitic grades (Series 400)
• Highly resistant to rust: Austenitic grades (304, 316) due to higher chromium and nickel content

Selecting the Right Stainless Steel Grade

Choosing the right grade of stainless steel depends on environmental exposure, mechanical requirements, and budget considerations. 304 stainless steel is ideal for general applications, while 316 excels in marine and chemical settings. For strength and wear resistance, 410 or duplex stainless steels may be better options.

At NeoNickel, we offer a comprehensive selection of high-performance stainless steel alloys designed to meet the needs of industries across construction, automotive, medical, and more.

Contact us today for advice on selecting the right stainless steel grade for your project.

Related Resources:

Stainless Steels What is Stainless Steel & What is it Used For?