Elevate Your Engineering with Aobo Steel’s 440C Stainless Steel

440C stainless steel overview

440C Stainless Steel is a type of steel classified under the American steel standard system, characterized by a chromium content ranging from 16% to 18%. Due to its exceptional corrosion resistance and toughness, 440C was initially widely used as a raw material for surgical instruments and in the shipbuilding industry. When the carbon content of 440C steel reaches 1.2%, its corrosion resistance is optimized.

Currently, 440C is extensively utilized in the high-end knife market, offering superior strength and sharpness compared to ATS-34. 440C’s weakness includes a gummy texture during grinding and rapid heat buildup. However, 440C is easier to grind than any carbon steel.

1. 440C Stainless Steel Chemical Composition

2. 440C Stainless Steel Performance and Properties

2.1 Hardness and Edge Retention

Thanks to its high carbon content and ability to be hardened, 440C achieves excellent hardness levels, often reaching around 58-60 HRC after proper heat treatment, such as austenitizing at around 1038°C, oil quenching, and tempering at around 204 °C. This high hardness translates directly to superior edge retention, making it a preferred choice for cutting tools.

2.2 Corrosion Resistance

The high chromium content gives 440C good corrosion resistance in mild environments. It can withstand exposure that would cause rust in lower chromium steels. However, for extreme conditions such as consistent exposure to marine or seawater, other grades may offer slightly better stain resistance.

2.3 Wear Resistance and Carbides

The high carbon content not only increases hardness but also boosts wear and abrasion resistance. This is partly due to the formation of hard chromium carbides within the steel’s structure during solidification. While these carbides enhance wear resistance, which is beneficial for cutting tools, their presence might be a factor to consider in specific high-stress bearing applications where alternative microstructures could offer advantages.

3. Processing and Handling

3.1 Heat Treatment Considerations

Achieving the optimal properties of 440C requires careful heat treatment.

• Hardening: Typically involves heating to a temperature of around 1010-1065°C (1850-1950°F), followed by quenching (often in oil or air).
• Tempering: Essential after hardening to relieve stress and achieve the target hardness. Tempering is typically performed at lower temperatures (e.g., 150-370°C or 300-700°F) to maintain high hardness. Tempering between 425-565°C (800-1050°F) is often avoided due to potential reduction in corrosion resistance and impact toughness.
• Atmosphere: Controlled atmospheres or vacuum furnaces are recommended during heat treatment to prevent decarburization, which is the loss of carbon from the surface.

3.2 Machinability

In its annealed (softened) state, 440C is machinable; however, its high carbon content makes it more difficult to machine than lower-carbon stainless steels. Free-machining variants, such as 440F, which contains sulfur, exist, offering easier machining but potentially sacrificing some toughness and corrosion resistance. Standard 440C requires sturdy tooling and appropriate speeds and feeds.