SS444 Round Bars / AISI 444 Rods / SAE 444 Stainless Steel Bar

Product Description

AISI 444 Stainless Steel (Ferritic)

AISI 444 (UNS S44400) is a low-carbon, low-nitrogen, ferritic stainless steel stabilized with molybdenum, titanium, and/or niobium. It is often referred to as the "ferritic equivalent" to Grade 316, offering similar corrosion resistance without the high nickel content, making it more price-stable.

Because it is a dual-stabilized ferritic steel, it is exceptionally resistant to Stress Corrosion Cracking (SCC), a common failure point for austenitic steels like 304 and 316.

International Designations & Equivalents

AISI 444 is widely recognized for its high molybdenum content ($2\%$), which provides superior pitting resistance.

Typical Chemical Composition

The addition of Molybdenum and Titanium/Niobium is critical for its performance in aggressive environments.

• Chromium (Cr): 17.5% – 19.5%

• Molybdenum (Mo): 1.75% – 2.50%

• Carbon (C): $\le$ 0.025%

• Nitrogen (N): $\le$ 0.035%

• Stabilizers (Ti + Nb): $0.20\% + 4 \times (C+N) \min$

Mechanical Properties (Annealed Condition)

Unlike the 420 series, Grade 444 cannot be hardened by heat treatment. It is typically supplied in the annealed condition.

Key Performance Attributes

• Resistance to SCC: Being ferritic, AISI 444 is virtually immune to chloride-induced stress corrosion cracking, making it a superior choice over Grade 316 in hot water applications.

• Pitting Resistance: The PREN (Pitting Resistance Equivalent Number) of AISI 444 is approximately 23–25, which is comparable to Grade 316.

• Thermal Expansion: It has a lower coefficient of thermal expansion than austenitic steels, which reduces thermal fatigue in applications involving temperature cycling.

• Magnetic: Like all ferritic steels, AISI 444 is ferromagnetic.

Common Applications

AISI 444 round bars and rods are frequently used in environments where chloride levels or temperature fluctuations are high:

1. Hot Water Tanks & Heat Exchangers: Due to its immunity to SCC and excellent thermal conductivity.

2. Solar Collectors: Used for framing and fluid handling where long-term durability is required.

3. Food Processing Equipment: Particularly for components exposed to salty or acidic food products (e.g., vinegar or brine).

4. Automotive Exhaust Systems: Specifically for components that require high-temperature oxidation resistance.

5. Water Treatment Facilities: For shafts and fittings in desalination or waste-water management.

Fabrication Notes

• Welding: AISI 444 is weldable using standard techniques, provided the carbon and nitrogen pickup is minimized. Using Grade 316L or 444 filler metal is common. The titanium/niobium stabilization prevents sensitization and intergranular corrosion in the heat-affected zone (HAZ).

• Machinability: It machines similarly to Grade 316 but with less work-hardening. Rigid setups and sharp tools are recommended to manage the "gummy" nature typical of high-chromium ferritics.

• Bending/Forming: It has good ductility but a higher yield-to-tensile ratio than 304, meaning it requires slightly more power to deform and exhibits more spring-back.