Reasons for occurrence of brittleness in ferrite-austenite stainless steels

Conclusions

• 1. In ferrite-austenite steels of type ÉI811 and ÉP53, containing more than 0.4–0.6% titanium, when heated over the range 400–600°C, aging occurs (in the ferrite) and leads to an increase in strength and a decline in plasticity.

• 2. Aging of steels with a ferrite structure, as opposed to a martensite one, is characterized by extremely uneven distribution of the particles of precipitated phase. At the initial aging stages the new phase is formed predominantly along the grain boundaries. Uneven distribution of the new phase particles along the boundaries and in the body of the grain together with the presence of larger precipitations along the boundaries are the main reasons for embrittlement of ferrite-austenite stainless steels.

• 3. The phase precipitated during aging has a cubic structure, most likely of the type CsCl with a parameter equal to twice the matrix parameter (5.73 A) coinciding crystallographically with the matrix lattice.