These micrographs show the effects of cold work and annealing at various temperatures. After a material has been cold worked, the grains change shape; since these samples were cold rolled, the grains elongated. A bunch of samples were rolled and then placed in a heat treating oven to anneal. We heat treated them for the same time, but varied temperature.
During the heat treatment, the samples go through three stages: recovery, recrystalization and grain growth. Recovery shows very little change. Recrystalizaton is marked by the larger grains being taken over by new, smaller grains. Grain growth begins once the grains begin to expand in size (after all the old grains are gone). All of these samples experienced 60% cold work and then a 30 minute anneal. The material was cartridge brass: 70%Cu, 30%Zn. All Photos were taken by Kathy Rohr and the samples prepared by the Monday Spring 2003 Lab.
Our starting samples:
A final point: As the annealing temperature increases, the hardness of the material decreases. Below is a plot of Temperature vs. Rockwell F Hardness.