Overview and Standard Basis
CuZn31Si1 is a silicon brass, designated CW708R in the European system and known as UNS C69800 in the American system. The silicon addition distinguishes it from conventional copper-zinc alloys: it raises strength and improves resistance to wear and seizure, which is why the grade is a long-standing choice for bearing and bushing components that run against steel shafts.
Product standards for the grade are EN 12164, which covers copper alloy rod for free machining purposes, and EN 12167, which covers copper alloy profiles and bars. The alloy is classified as non-hardenable, meaning that strength is obtained only by cold forming rather than by quenching and tempering or by precipitation treatment. That single fact shapes how the material is ordered, machined and used.
Composition and Strengthening Mechanism
| Element | Typical range |
|---|---|
| Copper | 66.0 to 70.0 % |
| Silicon | 0.8 to 1.5 % |
| Lead | restricted to low level |
| Zinc | remainder |
| UNS equivalent | C69800 |
Because the alloy does not respond to heat treatment, the delivered temper depends on the amount of cold reduction applied during drawing. A hard drawn rod is stronger and less ductile than a soft annealed one, and the correct temper is selected by matching the drawing requirement to the service load rather than by assuming a default condition.
Mechanical Behaviour and Wear Performance
In the drawn condition, silicon brass of this type is supplied with tensile strength typically in the region of 440 MPa and above, with 0.2 % proof stress around 230 MPa and above. The figures vary with temper and section, so the requirement should be stated against the governing standard for the specific product form.
The property that earns the grade its place is wear resistance. Silicon brass runs against steel with a low tendency to gall or seize, which allows plain bearings and bushes to operate without continuous lubrication in some designs, and it resists the adhesive wear that damages softer bearing materials. Hardness is moderate by comparison with hardened steel, so the shaft is normally the harder member of the pair and should be finished to a suitable surface roughness to protect the bush.
Applications: Bearings, Bushes and Gears
Plain bearings, wrapped bushes, thrust washers, slide plates, worm wheels and low-speed gears are the main uses. The grade also appears in valve components, wear strips and general machined parts where a combination of strength, corrosion resistance and low friction is needed. Because it contains no significant lead addition, it is often selected where a lower-lead material is preferred for the application.
Typical service conditions are moderate load at moderate sliding speed with adequate heat dissipation. Where load or speed rises beyond the capability of a plain bearing, the design change should be a different bearing system rather than a different temper of the same alloy, since temper adjustment cannot compensate for a fundamentally overloaded contact.
Machining, Forming and Assembly
The alloy machines readily at conventional cutting speeds, producing a controlled chip, though tool geometry and cutting parameters should be set for a material that is tougher than free-cutting leaded brass. Cold forming, including bending, swaging and heading, is practical within the limits of the selected temper, and annealing restores ductility where a component requires several forming steps.
Assembly by press fitting, adhesive bonding or mechanical fastening is straightforward. Welding and brazing of high-zinc brasses calls for care because of the zinc content, and where a joint is unavoidable the procedure should be qualified on the actual grade rather than transferred from a different alloy.
Frequently Asked Questions
Q: What is CuZn31Si1 used for?
A: It is mainly used for bearings, bushes, thrust washers and wear-resistant machine parts where low friction against steel and good load capacity are required.
Q: Can this alloy be hardened by heat treatment?
A: No. It is a non-hardenable alloy, so its strength depends on cold working during drawing or forming, and the temper must be specified accordingly.
Q: Which standard governs the supply?
A: EN 12164 covers rod for free machining purposes and EN 12167 covers profiles and bars. The requirement for mechanical properties should be quoted against the standard for the product form ordered.
Q: How does silicon change the properties?
A: Silicon increases strength and wear resistance relative to plain brass and improves the way the alloy behaves against a steel counterface, which is why it is used in bearing applications.
Q: Does the alloy contain lead?
A: Lead content is restricted to a low level compared with free-cutting leaded brass, which is one reason the grade is chosen where a reduced-lead material is preferred.
