Phase composition and properties of maraging steels alloyed with molybdenum

Conclusions

• 1. The addition of 2–10% Mo to martensitic steels 13Cr−14Co−6Ni and 9Cr−14Co−6Ni increases the amount of retained austenite. Steels with 13 and 9% Cr become almost completely austenitic with 2 and 10% Mo respectively. Intermetallic phase of the Fe₂Mo type is formed, the temperature-time range in which it exists being considerably broader in steels with 13% Cr (at the same molybdenum concentration).

• 2. Raising the molybdenum content of the steels investigated increases the strength slightly and lowers the toughness after quenching due to formation of Fe₂Mo in grain boundaries.

• 3. Tempering of martensitic steels with 9% Cr at 500° leads to a substantial increase in strength, the effect increasing with the molybdenum content from 2 to 6% Mo. The increase in the strength of the steel with 9% Cr to 210 kg/mm² after tempering is evidently due to the formation of finely dispersed intermetallic R phase.

  Tempering at 500° does not induce any increase in the strength of steels with 13% Cr and 2–10% Mo, which have an austenitic structure.

• 4. Steels of the 9Cr−14Co−6Ni system alloyed with 2–6% Mo can be used as the basis for the development of high-strength corrosion resistant steels retaining their toughness at low temperatures.