Relationship between the Torsion or Bending Creep Strength and the Tension Creep Strength of 13%Cr Steel

Abstract

In order to find the correlation of the torsion or bending creep strength with the tensile creep strength for hardened and tempered 13%Cr steel, creep tests in tension, torsion and pure bending have been made at temperatures 400°C and 500°C. And then, these experimental results were compared with the analytical results by calculation based on von Mises or Tresca criterion. The tensile creep tests were conducted on 8mmφ cylindrical specimens, the torsion creep tests on 10mmφ/8.5mmφ thin-walled and 8mmφ solid cylindrical specimens, and the bending creep tests with 6mmt×10mm plate specimens. The apparatus employed in the torsion or bending creep tests were made in our laboratory. The creep test continued altogether for 400 hours. The results obtained can be summarized as follows:(1) The ratio of the shear creep strength to the tensile creep strength of 13%Cr steel corresponding to a mean creep rate of 0.2 or 1.0 per cent per 1000 hours for 300 to 400 hours is respectively 0.48 for 400°C, and 0.43, 0.46 for 500°C. On the other hand, the ratio derieved from the calculations due to von Mises or Tresca criterion is respectively 0.48 and 0.43 for 400°C, and 0.51, 0.45 for 500°C.(2) The ratio of the torsion creep strength of solid cylindrical specimen to the tensile creep strength for same creep rates is respectively 0.68, 0.70 for 400°C and for 500°C, 0.49, 0.50.(3) The ratio of the bending creep strength to the tensile creep strength for same creep rates is respectively 1.37, 1.55 for 400°C, and 1.47, 1.35 for 500°C, while the ratios obtained by calculation are 1.29 for 400°C and 1.34 for 500°C.