Influence of long-lasting heat treatments on the structure and properties of the zirconium-steel bond

Abstract

The explosive welding technology is related to the dynamic impact of the clad onto base material. These results in significant microstructural changes of the bonded materials, the increase of internal stresses and the strain hardening of layers near the interface. In order to eliminate these unfavorable effects, it is advisable to carry out proper heat treatment. The paper presents the results of structural examinations and mechanical properties of bimetal zirconium - carbon steel, after long-lasting heat treatment. Bimetallic samples were annealed at 600oC for 1, 10, 100, 500, 1000 hours. Microscopic examination were used to the analysis of microstructural changes, whereas systematic microhardness measurements and static tensile test to evaluation of the mechanical properties. It was found that the temperature has a beneficial effect on the changes in the bond zone and for longer annealing times a systematic decrease of the strength properties of the tested bimetal was observed. However, essential for the clad mechanical properties changes were observed in carbon steel plate. After short annealing (times of 1h and 10h) only small microstructural changes due to processes of recovery and recrystallization were observed in layers near the interface. The increase of annealing time was conducive to grain growth and carbon diffusion in the interfacial layer from steel towards zirconium.