Introduction
This article explains seamless brass square tubes for marine use and how to select grades. Brass is a family of copper-zinc alloys whose properties change with the copper-to-zinc ratio. The copper content, which ranges from about 57 percent to more than 95 percent, determines the color, strength, formability, corrosion resistance and cost of the alloy.
What Determines Brass Properties
Zinc is added to copper as a low-cost strengthening element. At low zinc levels the alloy is single-phase and very ductile; above about 37 percent zinc a second phase appears that raises strength and hot-workability but reduces cold formability. The zinc level also affects the corrosion behavior, and alloys with high zinc content are more susceptible to dezincification in chloride environments.
Common Brass Families
High-copper brasses such as C21000 and C22000 are used for jewelry, plaques and gilding metal; 70/30 cartridge brass C26000 is the deep-drawing standard; 60/40 Muntz metal C28000 is the hot-working grade; and leaded free-cutting grades such as C36000 are machined at high speed. Tin, lead, aluminum and arsenic additions create special brasses for particular duties.
| Grade | Cu % | Common Name | Main Use |
|---|---|---|---|
| C21000 | 94 - 96 | Gilding brass | Jewelry, plaques |
| C26000 | 68.5 - 71.5 | Cartridge brass | Deep drawing |
| C28000 | 59 - 63 | Muntz metal | Hot working, architecture |
| C36000 | 60 - 63 | Free-cutting brass | Machined parts |
Brass Versus Other Materials
Compared with copper, brass is stronger, harder and cheaper but less conductive. Compared with stainless steel, brass is easier to machine and form, conducts heat better and costs less, but it has lower strength and can dezincify in aggressive water. The comparison guides the selection of fittings, tubes and components for each service.
Products and Standards
Brass is produced as sheet, strip, rod, bar, wire, tube and forgings under standards such as ASTM B36, B134, B135, B16, B453 and B21. The Chinese equivalents are defined by GB/T 5231 and the product standards for each form.
Selection Guidance
Match the grade to the forming method, the corrosion environment and the cost target, and verify the composition and temper on the certificate. For decorative parts choose a high-copper grade; for machined fittings choose a free-cutting grade; for seawater choose a dezincification-resistant grade.
