Work hardening softening

Bai [48] presents a linear stability analysis of plastic shear deformation. This involves the relationship between competing effects of work hardening, thermal softening, and thermal conduction. If the flow stress is given by Tq, and work hardening and thermal softening in the initial state are represented... 

Demonstrations Take a strip — 0.25 mm X 1 cm X 15 cm of cold-rolled (work-hardened) brass and bend it (on edge) on the overhead until permanent deformation takes place. Anneal brass strip at bright red head for — 0.5 min to soften it. After cooling replace on overhead and show that permanent deformation takes place at a much smaller deflection than before. This illustrates the importance of large Uy in springs. 

All the stainless steels can be machined in the softened states, but they may present some problems unless the correct techniques are adopted. This is especially so with the austenitic grades where the extreme ductility minimises chip breaking and the work hardening may cause difficulties unless modest cuts are made. The free-cutting grades (those with high sulphur contents or selenium additions) are much easier to machine, but it must be remembered that they have somewhat reduced corrosion resistance, ductility and weldability compared to their normal counterparts. Detailed machining instructions are readily available from steel suppliers. 

Annealing. This softens work-hardened and heat-treated alloys, relieves stress, and stabilizes properties and dimensions. 

Tellurium increases softening temperature of work-hardened copper. 

A. Aluminum. Aluminum (mp 660°C), is a light, soft metal with fair resistance to corrosion by laboratory fumes except hydrogen halide vapor. It has excellent electrical and thermal conductivity. Many aluminum alloys are used some may be softened by heating to 550°C and quenching in water. The metal subsequently work-hardens or hardens upon standing for a few hours (that is, 24 ST and 14 ST alloys), and all aluminum alloys are easily machined. These alloys... 

Recrystallization (or anneal) Used for non-ferrous or work hardened metals, to soften and remove strain hardening. 

In contrast to metals, polymers do not work-harden because no new obstacles are created when the molecules slide past each other. Heat generated during deformation causes a local increase in temperature, further easing plastic deformation. This results in a local softening of the material, similar to a metal with an apparent yield point (see section 6.4.3). Only if the plastic strain becomes larger does some hardening occur because the molecules become aligned in the direction of the applied stress. 

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