Molybdenum sheets with two types of elongated coarse-grain structures (trade name: TEM) were developed by heavy-duty rolling and recrystallization treatment of sintered molybdenum bodies with 1mass% La₂O₃. One type of sheets has spindle-like grains (S-TEM), and the other has stacked, plate-like grains (P-TEM). Tensile tests were carried out on S-TEM and P-TEM at 1470K to 2070K in vacuum to investigate the effects of grain structure on tensile properties such as proof strength (σ_y), tensile strength (σ_m) and uniform elongation (δ_m) at high temperatures. The aspect ratio (L_TD/W, L_RD/W) of grains, i.e., ratio of grain length (L) to grain width (W) on the transverse plane and perpendicular plane to the rolling direction, were estimated as a parameter of grain structure. The following results were obtained.
(1) TEM with elongated coarse-grain structures (S-TEM and P-TEM) had a higher σ_y and σ_m than pure molybdenum and TZM with equiaxial-grain structures. At 2070K, the σ_y and σ_m of TEM were 2-3 times those of pure molybdenum.
(2) The σ_y and σ_m of TEM increased with increased L_TD/W, and strain hardening was difficult to perform with increased L_RD/W.
(3) Three distinct failure modes were found. The higher the test temperature, the smaller the reduction area in the case of S-TEM with small L_TD/W grains. In P-TEM with large LTD/W grains, the reduction was not dependent on temperature, although P-TEM indicated a larger reduction compared to S-TEM. In pure molybdenum and TZM, the higher the test temperature, the larger the reduction.