Cold working of metals

Vacancies and interstitials Cold working of metals At 7 < 0.4 7m solid-state diffusion is slow... 

Stress Relief A heat treatment process to reduce internal residual stress by heating to a desired temperature and holding for a suitable period of time, also known as a sub-critical anneal. Residual stresses can be induced by forging, casting, forming, welding or cold working of metal. 

Balance the stiffness relative stiffness, where each member carries its share of load, improves the strength (see Figure 9.47).Minimize expansion and contraction of structural members (creep-, thermal-, or stress- induced) select materials having similar coefficients of expansion Deformation and cold working of metals, especially those containing carbon and nitrogen, may promote preferential local attack at imperfection sites and increase the corrosion rate stress relief is indicated. 

Additions of selected alloying elements raise the recrystaUization temperature, extending to higher temperature regimes the tensile properties of the cold-worked molybdenum metal. The simultaneous additions of 0.5% titanium and 0.1% zirconium produce the TZM aUoy, which has a corresponding... 

Zirconium is a hard, shiny, ductile metal, similar to stainless steel in appearance. It can be hot-worked to form slabs, rods, and rounds from arc-melted ingot. Further cold-working of zirconium with intermediate annealings produces sheet, foil, bar wire, and tubing. Physical properties are given in Table 3. 

The body-centered-cuhic (bcc) metals and alloys are normally classified as undesirable for low temperature construction. This class includes Fe, the martensitic steels (low carbon and the 400-series stainless steels). Mo, and Nb. If not brittle at room temperature, these materials exhibit a ductile-to-brittle transition at low temperatures. Cold working of some steels, in particular, can induce the austenite-to-martensite transition. 

Cold Extrusion of Metals. See under Cold Working or Shaping of Metals... 

Adequate predictions of thermal conductivity for pure metals can be made by means of the Wiedemann-Franz law, which states that the ratio of the thermal conductivity to the product of the electrical conductivity and the absolute temperature is a constant. High-purity aluminum and copper exhibit peaks in thermal conductivity between 20 and 50 K, but these peaks are rapidly suppressed with increased impurity levels and cold work of the metal. The aluminum alloys Inconel, Monel, and stainless steel show a steady decrease in thermal conductivity with a decrease in temperature. This behavior makes these structural materials useful in any cryogenic service that requires low thermal conductivity over an extended temperature range. 

Cold working certain metals causes them to become harder and stronger. For example, if a wire made of iron is bent to make a kink in it, the wire will break at that point after flexing it a few times. When a wire made of copper is treated in this way, flexing it a few times causes the wire to bend in a new location beside the kink. The copper wire does not break, and this occurs because flexing the copper makes it harder and stronger. In other words, the metal has had its properties altered by cold working it. 

During cold working, polycrystaUine metals deform by mechanisms involving slip and, where slip is restricted, rotation of the individual grains. Both processes, of course, must satisfy the condition that the interfaces, along which the grains are connected. 

A metal, which, as the result of work in the cold, ie. at relatively low temperatures, has undergone permanent deformation, is said to be cold worked or work hardened. The properties of the metal, thus treated, are changed, and the amount of this change is a measure of the cause—the so-called cold work. A metal which has been completely annealed has, by definition, zero cold-work. 

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