Elevated-Temperature Properties of 1565ch Alloy Base Metal and Welded Joints Made by Friction Stir Welding

The mechanical properties and structure of sheets made of 1565ch alloy 1.2–5 mm thick and those of the weld produced by the friction stir welding were investigated at elevated and cryogenic temperatures. It was shown that the weld ductility is significantly higher than that of the base metal when the grain size in the weld metal is 5–8 μm and the test temperature is above 400°C. An increase in the test temperature leads to a decrease in strength properties and an increase in plasticity. The most significant changes begin at temperatures above 150°C. An increase in strength and ductility happens simultaneously with a decrease in the test temperature. When testing sheets of 1565ch alloy with a grain size of 15–40 μm, abrupt changes in deformation are observed at room temperature as well. They disappear however at the test temperature above 100–150°C. The obtained results allowed us to conclude that the grain refining (from 40 to 7 μm in the grain size) leads to a sequential transition from abrupt changes of the С type to the A type. It was stated that the temperature of the beginning of accumulative recrystallization in the weld metal with an average grain size of 5–8 μm is approximately 470–480°C, while in the base metal it is at the level of 540°C.