70/30 cartridge brass for deep drawing, tubes and pressings

Because small-arms cartridge cases have been deep drawn from it for well over a century. A case is drawn from a flat cup in several stages, with anneals in between, and the brass has to stretch evenly through each stage without splitting at the mouth. Few other copper alloys at a similar price will take that much cold work. The name stuck, and today it covers the alloy whether it ends up in ammunition, a radiator tank or a lamp holder.

A lot, as long as you anneal between heavy reductions. In the annealed condition 70/30 can be drawn, spun, stretched and coined. As it is worked it hardens steadily, and the tensile strength roughly doubles from the soft to the fully hard condition. Once it reaches the hardness your process cannot handle, an intermediate anneal restores the ductility.

For deep drawing, grain size matters as much as tensile strength. Coarse grains leave an orange-peel surface on the drawn part, while very fine grains make the strip stiffer to form. EN 1652 deals with this by offering grain-size-controlled tempers alongside the tensile tempers, so a press shop can order to the finish it needs. For flat stock in this grade see our brass sheets and strips page.

Three systems turn up on Indian drawings. IS 410 uses letter codes: O for annealed, then HA, HB, HD, HE and HS as the strip gets progressively harder, with HS the spring-hard end. ASTM uses H01 (quarter hard), H02 (half hard), H04 (hard) and so on up to the spring tempers. EN 1652 states the minimum tensile strength directly, so R350 means at least 350 N/mm².

These are not exact equivalents of each other. If a drawing quotes one system and your old supplier used another, send us both and we will match the tensile range rather than the label.

Plain 70/30 can lose zinc in some waters, a form of corrosion called dezincification. Adding a small amount of arsenic, around 0.02 to 0.08 percent, largely stops it. That variant is UNS C26130, known in Britain as CZ126 and in Indian and European standards as CuZn30As. It is the 70/30 most often used in condensers, evaporators and the juice heaters covered on our sugar mill quality brass tube page.

Note that ASTM B111, the American condenser tube standard, does not list 70/30 at all. Arsenical 70/30 tubes are normally ordered to IS 1545, BS 2871 Part 3 or EN 12451.

Cold-worked 70/30 that still holds residual stress can crack if it meets ammonia or ammonium compounds, even in small amounts. The old name is season cracking, from cartridge cases that split in storage during the monsoon. Today it shows up in drawn parts stored near fertiliser, in cattle sheds, or in heat exchangers where ammonia is present in the process.

The fix is a low-temperature stress-relief anneal after forming, which removes most of the locked-in stress without softening the part much. If your parts will see ammonia, mention it at enquiry and we will talk about tempers before you order.

Compared with 63/37 brass, 70/30 is more ductile, a little more corrosion resistant and dearer. Compared with 60/40 it is far better cold and much worse hot, since it does not have the beta phase that makes Muntz metal forge so easily. It machines poorly, with a machinability rating of about 30 against 100 for free-cutting brass, so turned parts are rarely made from it.

Tell us the form, the standard you are buying to and the temper. For strip, give width, thickness and whether you need slit edges or mill edges. For tube, give OD, wall thickness or SWG, length and whether the ends must be annealed for expanding into a tube plate. If the part is deep drawn, mention the draw depth and blank diameter so we can check the temper with you before cutting.

Each lot is supplied with a test certificate from a Government-recognised test house showing copper, lead and iron against the standard, which is the quickest way to confirm you have genuine 70/30 and not a lower-copper brass sold under the same name.