C71500 is a widely specified copper-nickel alloy (often called "70/30 copper-nickel" due to its approximate 70% copper and 30% nickel composition) and is classified under the Unified Numbering System (UNS) for metals and alloys. It is a high-performance alloy engineered to excel in harsh, corrosive environments-particularly those involving seawater, brackish water, or industrial fluids-and is valued for its superior corrosion resistance, mechanical strength, and resistance to erosion-corrosion (wear caused by fluid flow combined with corrosion).
Compared to lower-nickel copper-nickel alloys like C70600 (90/10 copper-nickel), C71500 offers enhanced durability in more aggressive conditions. Its key advantage lies in its ability to form a dense, stable oxide film on its surface when exposed to oxygen or moisture; this film self-heals if damaged, providing long-term protection against pitting, crevice corrosion, and stress corrosion cracking.
Typical applications include:
Marine engineering: Seawater cooling systems, ship hulls, propeller shafts, and offshore platform components.
Power generation: Condenser tubes and heat exchanger tubes in power plants (using seawater or industrial coolants).
Desalination plants: Tubing and membranes for saltwater purification.
Chemical processing: Equipment handling corrosive liquids (e.g., acids, alkalis) and high-temperature fluids.
It is also used in architectural applications for its sleek silvery appearance and resistance to atmospheric corrosion.
The chemical composition of C71500 is standardized by global bodies such as ASTM (American Society for Testing and Materials) and ISO, with strict limits on primary elements and trace impurities to ensure consistent performance. Below is the typical and standardized composition (by weight), as defined by ASTM B111 (for seamless tubes) and ASTM B466 (for welded tubes):
The 70% copper/30% nickel balance is the defining feature of C71500, as it directly contributes to the alloy's enhanced corrosion resistance compared to lower-nickel counterparts.
The hardness of C71500 depends primarily on its temper (heat treatment or cold-work state)-cold working increases hardness by introducing internal stresses, while annealing softens the alloy to improve formability. Hardness is typically measured using the Brinell Hardness Test (HB) or Rockwell Hardness Test (Rockwell B scale, HRB) for non-ferrous metals like copper-nickel alloys. Below are the typical hardness values for common tempers:
Annealing involves heating C71500 to ~650–750°C (1200–1380°F), holding it at that temperature to relieve internal stresses, and then cooling it slowly. This process maximizes ductility and formability, making it ideal for bending, welding, or shaping into tubes/parts.
Brinell Hardness (HB): ~70 – 90 HB (tested with a 500 kg load and 10 mm diameter steel ball).
Rockwell Hardness (HRB): ~60 – 80 HRB (a standard scale for measuring the hardness of soft-to-medium non-ferrous metals).
Cold working (e.g., rolling, drawing, or extrusion without subsequent annealing) strengthens C71500 by aligning metal grains and creating internal dislocations. Hardness increases with the degree of cold work, and common tempers include "1/4 Hard," "1/2 Hard," and "Full Hard":
1/4 Hard: ~90 – 110 HB / ~80 – 90 HRB
1/2 Hard: ~110 – 130 HB / ~90 – 100 HRB
Full Hard: ~130 – 150 HB / ~100 – 110 HRB
Cold-worked C71500 is used in applications requiring higher wear resistance or strength, such as fasteners, springs, or thin-gauge sheets for high-stress marine components.
