| The effect of Ni-content(8.3∼12 wt%) on the tensile properties and work hardening behavior between 20℃ and -196℃, formability and weldability was studied on Type 304 stainless steel used for the membrane of LNG storage tank. At room temperature, the hardening and ductility indices (such as tensile strength, strain hardening exponent and elongation) were increased and formability was improved by decreasing the Ni-content. When the Ni-content is less than 10 wt.%, lower yield point is observed at temperatures lower than -60℃. It is due to the dynamic strain softening or transformation plasticity, which accompanies the rapid increase in the amount of strain induced martensite(α`) at low strains. Dynamic strain softening or transformation plasticity is not observed when only E-martensitic transformation occurs at low strains. Regardless of the Ni-content in the Type 304 stainless steel, no cracks were observed during the fabrication of the LNG storage tank membrane since the stain level of the maximum deformed area was the half of forming limit curve. During the gas-tungsten-arc welding, the variation of Ni-content did not affect the penetration characteristics of the Type 304 stainless steel. |
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