Of the copper-base alloy materials used for diaphragms and bellows, brass, phosphor bronze, and beryllium copper are most common. Historically, the most widely used material for bellows is cartridge brass because in its annealed condition it lends itself to deep drawing. Phosphor bronze is more corrosion-resistant than brass and slightly stronger. Both brass and phosphor acquire their hardness and strength by cold-working. On the other hand, a newer alloy, beryllium copper, is heat-treatable to a considerably higher tensile strength and is the preferred material for diaphragms. The one property that is common to all copper alloys is their resistance to embrittlement at temperatures as low as – 300°F or lower. For this reasons they are sometimes used in place of steel for subzero environments. On the other hand, the elastic limit of most copper alloys decreases rapidly at temperatures as low as 300°F.