Beta-quenching of zircaloy cladding tubes in intermediate or final size - methods to improve corrosion and mechanical properties

Three batches of Zicaloy-2 tubing were beta-quenched prior to the final cold-rolling, cold rolled 80 percent, and annealed at 475 to 575 degree C. A fourth batch was /beta/-quenched in the final size. Beta-quenching instead of an intermediate or the final anneal results in significant stuctural changes. In high-pressure steam at 475 degree C such /beta/-quenching has a dramatic beneficial effect on the corrosion resistance. The short term strength as measured in tension and burst testing is improved by /beta/-quenching of hollows or finished tubes, whereas such treatment results in a slight drop in ductility, especially for tubing /beta/107 -quenched in the final size. The 400 degree celluis transverse creep strength is increased by the introduction of /beta/-quenching prior to the final cold-rolling. The improvement is caused mainly by small second-phase particles, formed during /beta/-quenching, which give rise to precipitation hardening. 5 refs