Abstract
Effects of Nb (niobium) contents and aging conditions on the strength and fatigue life of 18% Ni maraging steel commonly using in aircraft, space field, nuclear energy, and vehicle, etc. were investigated. Hardness value decreased about 3% for annealed specimens and increased about 60% for 1 h aged specimens. But the values of the other specimens aged 2 h or more showed almost the same. The yield strength was the highest about 1800 MPa in 0.06% Nb specimen having twice as much as the base metal specimen. Also, the elongation was the highest in 0.03% Nb specimen showing the same as base metal specimen. The higher aging temperature and the longer aging time, the fatigue life increased. On the other hand, the 0.03% Nb specimen showed the highest fatigue life which increased about 12% more than base metal specimen. 0.06% Nb specimen aged at 482 °C for 8 h simultaneously satisfied the 250 grade strength and 200 grade elongation having the most superior mechanical properties.
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