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The respective cross-sectional area and cold work index were then calculated for each percentage deformation

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The respective cross-sectional area and cold work index were then calculated for each percentage deformation. The hardness of the copper sample was also calculated at each reduction. A graphical presentation of hardness versus cold work index was plotted which clearly showed a sharp increase of hardness with an initial increase in cold work index.

Experiment two examined how annealing times and annealing temperature affected the hardness of copper. Each of the six specimens of commercially pure copper was subjected to different amounts of annealing subsequent to cold rolling. For a copper sample annealed at 0 C for 0 minutes, the measured hardness was 156.6HRB (Bendrich, pp178-256). The hardness decreased as time and temperature were increased.

The hardness of a sample annealed at 800C for 120 minutes was 69.7HRB, which in essence approved that cold working a metal, increases its hardness. Again the more the metal was annealed and the higher the temperature, the more the grain growth continued, and the softer the metal became. The observation was made in that, the crystallization temperature of the metal affects how much the grain growth will be.

Rockwell Hardness Tester was used to determine the hardness of a specimen of commercially pure copper that has been annealed at 800 C for 120 minutes. A rolling machine was used to reduce the thickness of the sample by 5%, 10%, 20%, 40%, 60% and 80%. The percentage of cold work was calculated by the bellow formula.

The work table 1 shows the calculated values for the dimensions of sample copper at each percentage reduction in width. It also includes the cross-sectional area, the percentage cold work as well as the hardness for each percentage reduction.

Hardness by definition is ‘a measure of a material’s resistance to localized plastic deformation’ (Callister pp234-318).