Cold Rolled SS Sheet Coil Strips Grade 347 Used In Strong Oxidizing Acid Environment

Chemical Composition and Principle:

Basic Composition: Similar to 304 stainless steel, containing approximately 18% chromium and 9% nickel.

Key Stabilizing Element: Niobium (Nb) is added, with a niobium content at least 10 times the carbon content (usually expressed as Nb ≥ 10 × C). Sometimes a small amount of tantalum (Ta) is also added.

Role of Niobium: Similar to titanium (Ti) in 321. At high temperatures (sensitization range of 450°C - 850°C), niobium preferentially combines with carbon to form stable niobium carbide (NbC), thus preventing chromium depletion at grain boundaries caused by carbon combining with chromium, fundamentally immune to intergranular corrosion.

Key Differences from 321 (Titanium Stabilized):

Stronger Carbon Fixation Capacity: Niobium has a stronger and more stable carbon-binding capacity than titanium.

Better High-Temperature Performance: Niobium carbide is less prone to aggregation and growth at high temperatures. Therefore, 347 exhibits better microstructure stability and higher strength retention during long-term high-temperature service (e.g., above 600°C).

Improved weldability: The addition of niobium has minimal impact on the fluidity of the weld pool, resulting in excellent weldability.

Surface quality and machinability: The absence of titanium avoids titanium oxide inclusions, leading to superior surface finish and polishing properties, and facilitating cold forming.

Key properties:

Excellent resistance to intergranular corrosion: Stable performance after welding or high-temperature sensitization.

Excellent high-temperature strength: Superior creep strength and resistance to creep in environments above 500°C compared to 321 and 304.

Good corrosion resistance: Superior corrosion resistance to strong oxidizing acids (such as nitric acid) compared to 321 and 304.

Good weldability and formability.