Introduction
AISI 439 stainless steel coil is a versatile and cost-effective, ferritic stainless steel designed for applications requiring good corrosion resistance in a variety of oxidizing environments. This titanium-stabilized, 18% chromium alloy offers several advantages over standard ferritic steels like 409L, making it a popular choice for applications where both affordability and performance are important.
Composition
The key elements in AISI 439 are:
Chromium (17.5% - 18.5%): Provides the foundation for overall corrosion resistance, particularly in oxidizing environments.
Titanium (stabilizer - typically around 0.5%): The addition of titanium helps prevent chromium carbide precipitation during exposure to high temperatures (typically in the range of 427°C to 816°C or 800°F to 1500°F). Chromium carbide precipitation can deplete chromium in grain boundaries, leading to intergranular corrosion (IGC).
Characteristics
Good Corrosion Resistance: AISI 439 offers superior corrosion resistance compared to standard ferritic stainless steels, particularly in environments with oxidizing agents like air, water, or mild chemicals. It can even compete with some austenitic grades (like 304L) in specific oxidizing environments.
Improved Resistance to Intergranular Corrosion (IGC): The key advantage of AISI 439 is its superior resistance to IGC compared to standard ferritic steels. This makes it ideal for applications involving exposure to elevated temperatures during service or welding.
Good Formability: AISI 439 exhibits good formability, allowing for shaping and drawing during fabrication. This characteristic makes it suitable for applications requiring moderate bending and forming.
Good Weldability: AISI 439 offers good weldability with minimal risk of weld decay due to the stabilizing effect of titanium. However, proper welding procedures are still recommended to maintain optimal corrosion resistance, especially in critical applications.
Strength and Hardness: While not the strongest stainless steel, 439 offers moderate strength and hardness compared to other ferritic grades. These properties can be further enhanced through cold working.
Magnetic: AISI 439 is magnetic in all conditions.
Uses
Due to its good corrosion resistance, improved IGC resistance, good formability, and affordability, AISI 439 stainless steel coil finds application in various industries, including:
Automotive Parts: Exhaust system components, particularly those exposed to high temperatures and oxidizing environments, can benefit from the IGC resistance and affordability of 439.
Appliance Parts: Certain appliance components exposed to moderate heat and oxidizing environments can utilize 439 due to its formability, corrosion resistance, and cost-effectiveness.
Chemical Processing Equipment: Tanks, vessels, and piping handling mild oxidizing chemicals at moderate temperatures can benefit from the combined corrosion resistance and IGC resistance of 439.
Architectural Applications: Building facades, railings, trim, and decorative elements in less aggressive environments can utilize 439 for its aesthetics, formability, corrosion resistance, and suitability for welding.
Heat Exchangers: Low-pressure heat exchangers operating in oxidizing environments can benefit from the affordability and IGC resistance of 439.
Product Specifications
| Specification | Description |
| Grades | 304. 304L, 316. 316L, 310S, 321. 410. 430. and more |
| Thickness | Ranges from 0.1mm to 20mm |
| Width | From 600mm to 1500mm, catering to specific project needs |
| Weight | Coils can be supplied in standard and custom weights, depending on customer requirements |
| Surface Finishes | 2B (mill finish), BA (bright annealed), No.4 (brushed), Mirror (reflective finish), and Satin (soft sheen finish) |
| Surface Treatments | Annealing, Pickling, Passivation, and Polishing for enhanced corrosion resistance and appearance |
Additional Points
AISI 439 comes in various standard specifications, such as ASTM A240/ASME SA240. ensuring consistent material properties.
Compared to higher-nickel austenitic stainless steels, 439 might not offer the same level of corrosion resistance in highly reducing environments or those containing chlorides.
When selecting between 439 and other stainless steel grades, consider the specific application's environment, temperature range, formability requirements, and budget. For superior corrosion resistance in chloride-containing environments, 316L might be a better choice.
