Thermodynamic calculations for precipitation in maraging steels

Abstract

In the present work, thermodynamic calculations for several maraging systems have been carried out, and the results are compared with experimental data. The calculations were conducted using ThermoCalc. Excellent agreement is obtained between calculation and experimental measurements using mainly the atom probe. As a highlight, calculated equilibrium phases and their mole fractions in 1RK91 steel recently developed by Sandvik compare extremely well with atom probe microchemistry data, which showed the presence of copper rich particles, mixed Ni₃Al and Ni₃Ti, and molybdenum rich precipitates. Calculations also indicate the thermodynamic stability of μphase in the Fe–Ni–Mo and Fe–Ni–Co–Mo systems, Ni₃Al and Ni₃Ti in a chromium containing steel, and NiMn in a Fe–Ni–Mn system. However, it should be noted that thermodynamic calculations may only be used as a guideline for systems not in equilibrium.