Abstract
To clarify the effects of grain size and carbon content on the ductility of molybdenum, the variations in ductility with grain size were investigated on the three grades of 1 mmφ wire specimens by means of tensile tests at 25° and −76°C. The results are as follows: (1) Low carbon specimens ((Remark: Graphics omitted.) ppm) were extremely low in ductility due to an intergranular brittleness when the average grain diameter in the transverse cross section of the specimen (\bardT) was larger than about 0.04mm, though the specimen showed a large ductility when \bardT was smaller than 0.04 mm. (2) At −76°C, the ductility of medium carbon specimens (C=80 ppm) increased with increasing \bardT when \bardT was larger than about 0.08 mm. (3) In high carbon specimens (C=210 ppm) the ductility increased nearly linearly with increasing \bardT−1⁄2. (4) When \bardT was larger than about 0.04mm, both the medium and high carbon specimens were more ductile than the low carbon specimen. The most ductile was the medium carbon specimen which was free from the intergranular brittleness and also from coarse carbides. (5) When \bardT was smaller than 0.04 mm, the ductility of the low carbon specimen was as large as, or slightly larger than, that of the high carbon specimen. However, it could not be concluded whether carbon increases or lowers the ductility in an equiaxed fine grained molybdenum because of a uniaxed recrystallized structure of the low carbon specimen.
