Stainless Steel: Types and Characteristics

Stainless steel is one of the most versatile and widely used metals in machining and manufacturing. Its properties depend on alloying elements and heat treatment, which alter its crystal structure and result in distinct grades with different strengths, corrosion resistance, and applications.

Understanding the main types of stainless steel helps in selecting the right material for each application. Stainless steels are primarily classified into martensitic, ferritic, austenitic, and precipitation hardening types.

Representative Types of Stainless Steel

Martensitic Stainless Steel

Martensitic stainless steels contain higher carbon content and are typically hardened and tempered. They offer:

• High strength, wear resistance, and toughness

• Lower corrosion resistance than other stainless steels (11–18% chromium)

• Magnetic properties

Because of their strength and durability, martensitic grades are often used in shafts, bearings, and mechanical parts. However, untreated martensitic steels are brittle, so most undergo quenching and tempering to enhance their properties.

Common grades include SUS403, SUS410, and SUS440.

Ferritic Stainless Steel

Ferritic stainless steels are chromium-based, with added elements like molybdenum or copper. Their characteristics include:

• Better formability, weldability, and corrosion resistance than martensitic types

• Lower strength compared to other stainless steels

• Magnetic properties

Due to their stable crystal structure, they do not harden through heat treatment.

At around 475°C (887°F), prolonged exposure can cause embrittlement, requiring heat treatment for recovery. While ferritic steels have less corrosion resistance than austenitic steels, they resist stress corrosion cracking since they contain little to no nickel.

SUS444, an ultra-low carbon and nitrogen ferritic stainless steel, offers improved corrosion resistance and is well-suited for chloride environments such as coastal or industrial areas.

Common grades include SUS430 and SUS444.

Austenitic Stainless Steel

Austenitic stainless steels are the most widely used type, known for:

• Excellent corrosion resistance (best among stainless steels)

• Good ductility, toughness, and weldability

• Suitability for press forming and cold working

• Non-magnetic properties (though may become slightly magnetic after processing)

They are commonly used in automotive parts, nuclear power equipment, and scientific instruments.

Key Grades:

• SUS303: easiest to machine

• SUS304: superior corrosion resistance and weldability

• SUS316: improved version of SUS304 with added molybdenum for enhanced corrosion resistance

Work hardening can transform austenite into martensite during machining, increasing hardness and machinability difficulty. This transformation is known as strain-induced martensite, which reduces corrosion resistance and introduces magnetic properties. Austenitic stainless steels have a higher cost due to nickel content.

It is also important to note that when austenitic stainless steels are exposed to temperatures between 600-900°C (1112-1652°F) for extended periods of time, they may experience reduced corrosion resistance, embrittlement, and stress corrosion cracking in chloride environments (coastal areas, industrial settings, etc).

Common grades include SUS303, SUS304, and SUS316.

Precipitation Hardening Stainless Steel

Precipitation hardening stainless steels have enhanced strength through specialized heat treatment. They provide

• High strength (comparable to quenched and tempered martensitic steels)

• Good corrosion resistance (better than martensitic and ferritic, but below austenitic)

• Balance of strength and corrosion resistance ideal for aircraft, rockets, and engine components

Due to the high cost of raw materials and the complexity of manufacturing, they are among the most expensive stainless steels.

Common grades include SUS630 and SUS660.

Key Takeaways

• Martensitic stainless steels: High strength, lower corrosion resistance, magnetic.

• Ferritic stainless steels: Good corrosion resistance and formability, lower strength, magnetic.

• Austenitic stainless steels: Best corrosion resistance, high ductility, weldable, non-magnetic, higher cost.

• Precipitation hardening stainless steels: High strength with good corrosion resistance, premium cost.

Step Up Your Project with Yumoto Electric

Yumoto Electric delivers high-quality components fast, worldwide. We provide precision machining for a wide range of metals using milling, turning, and specialized metal processing. We have experience with over 200 materials including aluminum alloys, stainless steel, molybdenum, and titanium. 

If you’re unsure about material selection or machining methods, we offer complimentary consultations to help optimize your design and production. For any questions, please feel free to contact us.