Effect of Aging Conditions on Mechanical Properties of Fe-Ni-1.8Ti Maraging Steels

Abstract

Tensile properties and resistivity changes during isothermal aging have been investigated for Fe-10Ni-1.8Ti, Fe-15Ni-1.8Ti and Fe-20Ni-1.8Ti maraging steels. In order to investigate the effect of strain rate on elongation, a crosshead speed has been varied from 0.005 to 10 mm /min.
Two stage precipitation appears in the resistivity curves of the maraging steels. Embrittlement caused by the decrease in strain rate is found in the maraging steels containing fine and coherent precipitates, formed in the first precipitation stage. Brittle fracture irrespective of strain rate is also found in the Fe-10Ni-1.8Ti and Fe-15Ni-1.8Ti maraging steels strengthened fully by the first precipitation stage. When the second precipitation stage progresses, elongation increases with the decrease in tensile strength. The embrittlement caused by the decrease in strain rate is not found in the maraging steels containing precipitates formed in the second precipitation stage. It is considered that slip bands produced in plastic deformation are less intense in the maraging steels containing precipitates which are difficult to be cut by movement of dislocations.