The effects of tungsten contents (2-5 w/o) on tensile properties and impact toughnesses in stainless Fe-Cr-Ni-W maraging steels with varying heat treatments were investigated. Precipitates formed in solution treatment condition was identified and was related to mechanical properties.
It was found that yield strength and reduction of area of the stainless Fe-Cr-Ni-W maraging steels were very sensitive to the heat treatment conditions. The yield strength decreased with increasing solution treatment temperatures, but reduction of area increased with the increasing solution treatment temperatures. When solution treatment temperature increased above the critical temperature, yield and reduction of area strength remained constant. The results were associated with the solvus temperature of precipitates formed during the solution treatment.
Impact energies were found to be also sensitive to the solubility of the precipitate formed in the austenite. When solution treatment temperature was below the critical temperature, impact energies rapidly increased with increasing solution treatment temperature. However, impact energies remained constant with increasing solution treatment temperature at above the solvus temperature. The results were related to the solvus temperature of $Fe_2W$ precipitate formed in the austenite. It was observed that the solvus temperature of the $Fe_2W$ precipitate in austenite increased with increasing tungsten contents.
The precipitates formed during heat treatments were identified by transmission electron microscopy. The major strengthing precipitate formed during the aging treatment of stainless Fe-Cr-Ni-W maraging steels was orthorhombic A(=Fe, Cr and Ni)$_3$W. It was observed that hexagonal $Fe_2W$ precipitate was formed during the solution treatment. The orientation relationship of the precipitates and matrix were identified by electron diffraction spot pattern analyses. The orientation relationships of $Fe_2W$ was ${011}_{α'}, // ($\bar{1}$2$\bar{1}$0)_{Fe_2W'}, <1$\bar{1}1>_{α'}, // [0001]_{Fe_2W'}$, while that of $A_3W$ was ${110}_{α'}, // (010)_{A_3W'}, <1$\bar{1}1>_{α'}// [100]_{A_3W'}$.
