Delayed Failure and Precipitation Behavior in Maraging Steels

Abstract

The relationship between delayed failure occurring in air environment and precipitation behaviors was studied on maraging steels by sustained load test and electrical resistivity measurement.The formation of low temperature precipitates associated with the presence of titanium was found to have a close relation to the delayed failure occurring on cobalt free maraging steels containing titanium as a main hardening element. In case of 18% Ni maraging steels, the delayed failure in air environment was scarcely affected by the precipitation of Mo rich low temperature precipitates which played an important role in the hardening at low temperature aging, but the delayed failure began to be markedly revealed depending on the titanium content, when titanium was added in the 186/ Ni maraging steels. It was estimated from the activation energies that the delayed failure of 18% Ni maraging steels was also significantly affected by the formation of the low temperature precipitates relevant to titanium.Since it is assumed that the delayed failure is controlled by interaction between dislocation motion cutting the coherent precipitates and hydrogen introduced by dissociation of water adsorbed on the steel surface, the reason why the delayed failure does not occur by the formation of Mo low temperature precipitates only would be that Mo rich low temperature precipitates do not promote the dissociation of water adsorbed on the steel surface unlike the low temperature precipitates relevant to titanium.(Received December 20, 1986) -Keywords: cobalt free maraging steel, 18% nickel maraging steel, delayed failure, sustained load test, activation energy, electrical resistivity, effect of isothermal aging, effect of isochronal aging

Structural Transformations Influence on Mechanical-and-Physical and Chemical Properties of Fe-Cr-Co Alloys in Heating

“…Such properties are common for maraging steels at standard rate testing of mechanical properties, while under static loading conditions it is often susceptible to grain-boundary cracking or stress corrosion. Fe-Cr-Ni-based maraging steels have been more studied [1][2][3][4][5][6] at the present time. Fe-Cr-Co-based steels could replace Fe-Cr-Ni-maraging steels in some applications, due to its high-temperature stability.…”