Stainless Steel Work Hardening: Causes and Machining Precautions
2025/9/25
Work hardening is a phenomenon where metal becomes harder when force is applied. In stainless steel (SUS), work hardening is a common issue during machining. The degree of work hardening depends on the stainless steel type.
This article explains which types of stainless steel are prone to work hardening, why it occurs, and how to address it during machining.
Types of Stainless Steel That Work Harden
Stainless steel (SUS) comes in many types, each with different physical properties. Some are prone to work hardening, while others are not.
Austenitic stainless steels are the most affected. They can harden significantly under stress, sometimes causing machining difficulties.
Type | Common Grade Example | Work Hardening |
|---|---|---|
Ferritic | SUS430 | Does not occur |
Martensitic | SUS410 | Does not occur |
Austenitic | SUS304, SUS316 | Occurs |
Austenitic-Ferritic | SUS329J1 | Occurs |
*For precipitation-hardening stainless steel (SUS 600 series), martensitic types do not experience work hardening.
Causes of Work Hardening
The tendency of austenitic stainless steel to work harden is linked to its crystal structure. This metal has a face centered cubic (FCC) crystal structure, which normally only exists at high temperatures. By adding chromium (Cr) and nickel (Ni) and then rapidly cooling it from a high heat state, manufacturers stabilize this FCC crystal structure at room temperature, where it would not naturally occur.
he FCC structure resists crystal movement, making deformation difficult. During machining, localized heat distorts the structure, transforming it into martensitic crystals, which are harder.
This hardened region, known as machining induced martensite, changes it from non-magnetic austenite to magnetic martensite.
Machining Precautions for Work-Hardened Stainless Steel
In addition to work hardening, the nickel (Ni) content makes the metal sticky, increasing the risk of it welding to the cutting tool. Austenitic steel generally has higher cutting resistance, requiring more force to shear the chips compared to other SUS types. Low thermal conductivity traps heat generated during machining on the cutting tool, shortening tool life.
During machining, the top 0.1–0.2 mm (0.004–0.008 in.) of the surface is most affected by work hardening. To manage this, avoid cutting in a way that only scrapes the hardened layer.
When machining austenitic stainless steel, it’s essential to choose the right tools and cutting conditions, and to position coolant so the cutting zone is properly cooled.
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