Influence of reverted austenite on fatigue life of 18 % nickel maraging steel

Abstract

AbstractMaraging steels containing 18 % nickel are based on a low‐carbon iron‐nickel‐cobalt‐molybdenum system. These steels demonstrate a remarkable combination of high strength and high toughness. To investigate the effect of overaging and resulting austenite reversion on the fatigue behavior of C250 maraging steel, specimens in the solution annealed state were overaged at 510 °C for various intervals, resulting in volume fractions of reverted austenite ranging from 2.6 % to 11.4 %. The staircase method was used to calculate the fatigue limit. S−N curves were generated by testing a minimum of four stress levels and at least three samples at each stress level. Basquin's equation was used to fit the experimental stress‐life data, and the Basquin exponent and fatigue strength coefficient were calculated. The presence of 2.6 % reverted austenite in the microstructure improved the fatigue limit and fatigue ratio, without significantly reducing tensile strength. The results can be interpreted in terms of reverted austenite having a crack blunting effect on the propagating cracks. A small amount of reverted austenite in the range of 2 %–3 % vol has a beneficial effect on the fatigue life.