As copper and nickel alloy with each other easily and have simple structures, the alloys are ductile and readily fabricated. Strength and hardness for each individual alloy is increased by cold working; they are not hardened by heat treatment. Joining of 90–10 (C70600) and 70–30 (C71500) is possible by both welding or brazing. They are both weldable by the majority of techniques, although autogenous (welding without weld consumables) or oxyacetylene methods are not recommended. The 70–30 rather than 90–10 weld consumables are normally preferred for both alloys and no after-welding heat treatment is required. They can also be welded directly to steel, providing a 65% nickel-copper weld consumable is used to avoid iron dilution effects. The C71640 alloy tends to be used as seamless tubing and expanded rather than welded into the tube plate. Brazing requires appropriate silver-base brazing alloys. However, great care must be taken to ensure that there are no stresses in the Cu–Ni being silver brazed, since any stress can cause intergranulary penetration of the brazing material, and severe stress cracking (see image). Thus, full annealing of any potential mechanical stress is necessary.