Abstract
An experimental investigation was made on the phenomenon of embrittlement during annealing encountered in the manufacturing process of aluminium-brass tubes. The tubes were hot-extruded, cold-drawn and then annealed at 400°C or 600°C by slow heating. The annealed tubes were very brittle. Metallurgical investigation on this tube revealed that a high level of internal stress prevailed in drawn tubes and the embrittlement was due to the formation of voids at original grain boundaries. Iso-thermal annealing test was made on the drawn tubes by very rapid heating in oil or salt bath at various temperature with variation of annealing time and the degree of embrittlement was measured. As the results of this test, it is inferred that the condition to cause embrittlement consists of the following three factors, (a) the materials with high internal stress (b) annealing in temperature range from 250°C to 400°C (c) keeping at the embrittling temperature range for more than a certain period. These three factors must be all satisfied to cause embrittlement. The experimental results have also shown that these characteristics are closely associated with that of intercrystalline brittle rupturing observed during creep or tensile test at elevated temperature.
