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The effect of ageing on the mechanical and impact properties of non-quenched and tempered steel wire strengthened by cold forming to an area reduction of 25.5% was investigated by tensile testing, charpy impact tests and scanning electronic microscopy. It was found that when the specimen was aged at 300 °C for 2 h, its tensile strength, yield strength, elongation and impact absorption energy increased by 10.8, 18.1, 44.8 and 19.6%, respectively. In addition the ductile-brittle transition temperature decreased by 5 °C. These improved properties are attributed to the decreasing dislocation density, the formation of sub-grains in a stable condition and the uniform dispersion of a fine precipitation phase during the ageing treatment.

The grain size variation in a gradient surface produced by a punching and recovery process on a Cu-30Ni alloy has been observed by atomic force microscopy. The friction characteristics of the gradient surface in a 3.5 wt% NaCl solution were investigated using a micro-indenter probe, a pin-on-disc type tribometer, a strain sensor and an optical microscope. The results showed that the hardness and grain size can be well represented by the Hall–Petch relationship when the gain size is more than 30 nm. The wear rate, friction coefficient and adhesive force all increase depth below the surface. These variations are attributed to a gradual increasing grain size with depth. The morphologies of the worn track were also studied to understand further the corrosive wear behaviour of gradient surfaces.