439 stainless steel

2025-05-30

What is 439 stainless steel?

439 stainless steel is a ferritic stainless steel mainly composed of iron, chromium and a small amount of titanium. It belongs to the 400 series stainless steel and features excellent corrosion resistance and good formability. Due to the presence of the stabilizing element titanium (Ti) in its chemical composition, 439 stainless steel performs particularly well in terms of weldability and resistance to intergranular corrosion.

The chemical composition of 439 stainless steel

The main chemical components of 439 stainless steel are as follows:
Chromium (Cr) : Approximately 17%-19%, providing excellent corrosion resistance.
Iron (Fe) : The main component.
Titanium (Ti) : A small amount of titanium is added to enhance welding performance and prevent intergranular corrosion.
Carbon (C) : It has a relatively low content, generally less than 0.03%, to ensure the material's toughness and corrosion resistance.

The characteristics of 439 stainless steel

1. Strong corrosion resistance
Due to its high chromium content, 439 stainless steel has excellent corrosion resistance in many environments, especially in humid conditions or weakly acidic conditions.
2. Excellent welding performance
After adding titanium, 439 stainless steel can effectively prevent intergranular corrosion during the welding process, making it an ideal choice for applications that require welding.
3. Low coefficient of thermal expansion
Compared with austenitic stainless steel, 439 stainless steel has a lower coefficient of thermal expansion, thus it performs more stably and is less prone to deformation in high-temperature environments.
4. Good processing performance
439 stainless steel has excellent cold working properties and is suitable for forming processes such as stamping and drawing.
5. Magnetic properties
As a ferritic stainless steel, 439 stainless steel is magnetic, which makes it very useful in certain special applications.

The application fields of 439 stainless steel

Due to its excellent performance, 439 stainless steel is widely used in the following fields:
1. Automotive industry
439 stainless steel is often used in components of automotive exhaust systems, such as mufflers and exhaust pipes. This is because it has excellent corrosion resistance and oxidation resistance in high-temperature environments.
2. Household appliances
In the home appliance industry, 439 stainless steel is used to manufacture components such as the inner drum of washing machines and the inner tank of water heaters, mainly taking advantage of its corrosion resistance and high strength.
3. Architectural decoration
Due to its attractive appearance and corrosion resistance, 439 stainless steel is also used in building decoration materials, such as roof and wall decorative panels.
4. Food processing equipment
439 stainless steel is used in the food industry to manufacture food processing equipment and storage containers, ensuring food safety and extending the service life of the equipment.

A comparison between 439 stainless steel and other stainless steels

Compared with the common 304 austenitic stainless steel, although 439 stainless steel has slightly inferior corrosion resistance, it performs more stably in high-temperature environments and has a lower cost. In addition, compared with 430 stainless steel, 439 has stronger weldability and resistance to intergranular corrosion due to the addition of titanium.

What surface treatment processes can 439 stainless steel undergo

Mechanical surface treatment
(1) Grinding
Process: Use a grinding wheel or abrasive belt to grind and obtain a uniform matte surface.
Features: Improves surface flatness, suitable for subsequent coating or welding.
Application: Automotive exhaust pipes, structural components of industrial equipment.
(2) Polishing
Mirror Polish:
Gradually use polishing wheels from coarse to fine (#180→#2000) to achieve high reflectivity.
The difficulty lies in that ferrite has a relatively low hardness and is prone to scratches, so the pressure needs to be controlled.
Hairline/Brushed:
Unidirectional wire drawing forms straight lines, and commonly uses #180-#400 mesh sand belts.
Application: Elevator decoration, home appliance panels (such as the back of gas stoves).
(3) Sandblasting (Sandblasting)
Process: High-speed injection of alumina or glass beads is used to form a uniform frosted surface.
Advantages: Enhance coating adhesion and hide scratches.
Subdivision type:
Dry sandblasting: Roughness is controllable (Ra 1.5-6.3μm).
Wet sandblasting: Reduces dust and makes the surface finer.
Application: Building curtain walls, inner walls of chemical equipment.

Chemical surface treatment
(1) Pickling & Passivation
Technology:
Pickling: A mixture of hydrofluoric acid and nitric acid (HF+HNO₃) is used to remove the oxide scale.
Passivation: Treatment with nitric acid (HNO₃) or citric acid to form a chromium oxide film.
Key points:
The titanium stabilizing element of 439 May affect the passivation effect, and the acid concentration needs to be optimized.
After treatment, thorough rinsing is required to prevent local corrosion caused by titanium residue.
Application: Food processing equipment, medical devices (must comply with FDA standards).
(2) Electropolishing
Process: Pass an electric current through a phosphoric acid + sulfuric acid electrolyte to selectively dissolve the microscopic protrusions on the surface.
Advantages:
Reduce surface roughness (Ra can reach 0.1μm) and enhance corrosion resistance.
It can remove processing stress and is suitable for precision parts.
Limitations: High cost, suitable for small or high value-added products (such as semiconductor equipment components).

Coating treatment
(1) PVD coating (Physical Vapor Deposition
Process: Ion plating of titanium, chromium and other metal layers in a vacuum environment.
Effect: Decorative surfaces in gold, black, etc., while enhancing wear resistance.
Application: High-end kitchenware and bathroom hardware.
(2) Electroplating
Optional coatings: nickel, chromium (pre-nickel plating is required first to improve adhesion).
Note: The expansion coefficients of the ferrite substrate and the coating differ greatly, making it prone to peeling off. Therefore, the process must be strictly controlled.

Special texture processing
(1) Chemical Etching
Process: Engraving patterns through a mask + acidic etching solution (such as FeCl₃).
Application: Decorative panels, brand signs.
(2) Laser Engraving
Advantages: High-precision marking of serial numbers and logos, contactless and non-deforming.