Structure Formed in Two-Phase (α plus γ) Field and Mechanical Properties of a Cryogenic Alloy 10N7

The effect of different types of structures produced by quenching from the intercritical temperature range on the strength, plasticity, and impact toughness of the Fe-6.9Ni-0.1C alloy has been studied. Two structures-ferrite + globular cementite and lath martensite-have been used as the initial state. The rate of heating into the two-phase (alpha + gamma) field has been selected such that four morphological types of two-phase structures, namely, ferritic-martensitic (Widmanstatten or globular) and duplex (lamellar or lamellar-globular), could be formed in a single alloy as a result of partial alpha -> gamma and gamma -> alpha transformations. It has been found that the mechanical properties of the alloy depend on the type of the initial structure and on the rate and temperature of heating to the intercritical temperature range. It has been shown that the alloy with a Widmanstatten ferritic-martensitic structure has a more favorable combination of the strength and plasticity properties than the alloy with a globular structure. The alloy with a lamellar duplex structure offers a much higher level of the impact toughness, plasticity, and strength at low temperatures than the alloy with a Widmanstatten ferritic-martensitic structure.