Impact tensile behaviors of 9% nickel steel at low temperature

In order to prevent catastrophic failure of engineering structures in an aircraft crash, explosive or impulsive loading, fracture properties under dynamic loading conditions should be investigated. One major application is the integrity of liquefied natural gas (LNG) storage tanks. The investigation of effects of strain rate as well as tested temperature on the deformation behavior for it will be necessary. In this study, in order to clarify the strain rate effect on the deformation behavior of 9% nickel steel, tensile tests were performed in a strain rate range of 10−3 to 5×102 s−1 and at temperatures of 77 and 293 K. A drop weight testing apparatus was slightly modified to accommodate the application of the dynamic tensile load to specimens and instrumented to detect the applied dynamic load. The corresponding displacement was simultaneously measured by a laser displacement meter. Small-size specimens were used. The obtained results made clear a strain rate hardening behavior, especially distinct hardening trend over 1 s−1 order of strain rate in 9% Ni steel. The strain rate increase up to 5×102 s−1, produced an increase of about 20 and 33% in the yield strength at 77 and 293 K, respectively, as compared with ones at static conditions. However, the elongation of 9%Ni steel held to the static value even at the condition of 250 s−1, 77 K. At 77 K, a low-temperature hardening became significant, therefore the strain rate hardening effect appeared less as compared with the case at 293 K.