Brass and gunmetal look similar but are made for different tasks. If you turn a bush from Ms58 where gunmetal belongs, you get wear. If you cold-bend Ms58, you get cracks. This article shows how the three alloys in our semi-finished product range differ.
Problem
The problem: same colour, different behaviour
Brass and gunmetal are both copper alloys. In the warehouse they lie side by side as round bars or tubes and at first glance differ only in shade. In the workshop, the differences then become clear: when turning, bending, brazing and in use as a bearing.
Frequent questions: can the bar be bent? Will the bush work without lubrication? May the part come into contact with drinking water? The answer depends on the alloy, not on the name “brass”.
Cause
The cause: zinc, tin and lead
Brass is copper with zinc. Ms58 (CuZn39Pb3, CW614N) also contains lead. The lead breaks the chip, which is why Ms58 is the reference material in machining tables. The same inclusions make the material brittle when cold: Ms58 can be hot-formed well but hardly cold-bent.
Ms63 (CuZn37, CW508L) has less zinc and no lead. It is very easy to cold-form, bend and braze. In return, the chip stays long and tough.
Gunmetal Rg7 (CuSn7Zn4Pb7, CC493K to EN 1982) is a tin bronze with zinc and lead, produced by centrifugal casting. Tin and lead give it good sliding and emergency running properties. It is resistant to water and seawater but not suitable for welding.
| Property | Ms58 (CuZn39Pb3) | Ms63 (CuZn37) | Gunmetal Rg7 |
|---|---|---|---|
| Tensile strength | about 380 N/mm² | 300 to 370 N/mm² depending on condition | about 240 N/mm² |
| Density | 8.4 kg/dm³ | 8.4 kg/dm³ | 8.8 kg/dm³ |
| Machining | excellent | moderate (long chips) | good |
| Cold bending | hardly (cracks) | very good | no (cast material) |
| Soldering / welding | easy to solder, weldable to a limited extent | very easy to solder | not weldable |
| Sliding, emergency running | – | – | very good |
| Lead above 0.1 % | yes | no | yes |
Standard values to EN 12164/12167, EN 1652 and EN 1982; the certificate of the respective delivery is binding.
Solution
The solution: choose by processing and use
Decide in two steps: first the processing, then the use. If you turn and cut threads, choose Ms58. If you bend, braze or deep-draw, take Ms63. If you need a plain bearing, a bush or a part for seawater, choose gunmetal.
- Turned and milled parts, parts with many threads, fittings: Ms58
- Bent visible and decorative parts, brazed joints, model making: Ms63
- Plain bearings, bushes, pump and valve parts, shipbuilding and hydraulic engineering: gunmetal Rg7
Remember: Never cold-bend Ms58. For bent brass parts, choose Ms63.
In practice
In practice: cutting, machining allowance and lead notice
As a cast material, gunmetal has a harder skin. Leave enough allowance when cutting to length; the skin is removed when the bearing bore is turned out. After heavy cold forming, Ms63 tends towards stress corrosion cracking – heavily formed parts are therefore stress-relief annealed.
Ms58 and gunmetal Rg7 contain more than 0.1% lead. In accordance with Art. 33 of the REACH Regulation, we point this out on the quotation, order confirmation, invoice and in the shop. Whether a leaded material is permitted for your application, for example in contact with drinking water or food, please check against the regulations that apply to you.
At a glance
- Define the processing: turning, bending, brazing or use as a bearing
- Describe the environment: water, seawater, lubrication
- Check the lead notice if regulations require lead-free materials
- With gunmetal, plan an allowance for the cast skin
Matching products
Frequently asked questions
Can I bend Ms58?
Hardly when cold: Ms58 cracks when cold-bent. For bent parts, Ms63 is the right material; Ms58, on the other hand, can be hot-formed well.
Why is gunmetal better than brass for bearings?
Thanks to tin and lead, gunmetal has very good sliding and emergency running properties. It tolerates poor lubrication better than brass and is resistant to water and seawater.
Which forms are available in gunmetal?
In our semi-finished product range, round bars and round tubes (hollow bars). We saw both to size; the configurator shows the available dimensions.
Is brass lead-free?
Not all brass. Ms58 (CuZn39Pb3) contains lead, Ms63 (CuZn37) does not. Gunmetal Rg7 also contains lead. We label leaded materials in accordance with REACH Art. 33.