342 Prakt. Met. Sonderband 30 (1999) 
Sv,/Vvy, Figs.2e and f. With further increasing time of annealing intensive coarsening of the 
structure by coalescence and rounding of the boundaries decreases the effect of the change of the 
phase composition. 
Since the conversion of d-ferrite to y, at 900°C results in only 70 % of the 3—y, transformation 
product at 1050°C the material is still far from equilibrium when this transformation is complete. 
The material can achieve equilibrium only by the formation of more c-phase. During the early stage 
of annealing, the rate of its precipitation was also retarded (see Table 1 and Fig.4a), but after an 
incubation period of 5 minutes, a great continuous increase was observed. Thus, after 60 and 120 
minutes the amount of & transformed to o-phase was 68.9 % and 71.3%, respectively. The 
precipitation of o-phase begins in the ferrite lamellas, which are chromium and molybdenum rich, 
Fig.lc. Other nucleation sites, although not frequently observed, are the new migrating Ö/y2v 
boundaries. At later stages, when the precipitation of c-phase was more intensive the majority of 
particles are found to nucleate within ferrite matrix. The increase in fineness of o particles could 
have been due to accelerated nucleation. As a result, the highest value of Sy, exhibited at the end of 
exposure period is greater by a factor 1.73 than after 30 minutes, Fig.2g. However, it should be 
noted that the values of Sys /Vve are very similar, due to the high amount of o-phase, Fig.2h. 
4.Conclusion 
The results of microstructural analysis indicate that the LF structure of a cast 22/7/2 Cu-bearing 
grade DSS solidified at moderate high cooling rate is very sensitive to the short-time annealing at 
elevated temperature. The extent and kinetics of isothermal 3-ferrite decomposition vary with 
annealing temperature. The process kinetics are much faster at 900°C than at 1050 and 1150°C. 
With increasing time of annealing, the fraction of transformed 8-ferrite increases rapidly due to the 
simultaneous precipitation of secondary austenite (y2) and c-phase and reaches a maximum of about 
30vol.% after 120 minutes of annealing. The formation of y, occurs at the 8/y boundaries by 
epitaxial growth or cellular precipitation, and, further, by intragranular precipitation within ferrite 
matrix, resulting in a very large increase of Sv, and Sv,/Vvy. After prolonged annealing these 
parameters reflect the kinetics and intensity of the structure coarsening by coalescence and rounding 
of the boundaries. Nucleation of o-phase occurs during the later stages of 3-ferrite transformation. 
At 1050 and 1150°C the kinetics of precipitation are somewhat slower, because the c-phase 
precipitation is negligible or does not detect, so that the amount of retained 8-ferrite is for 17 and 
19vol.%, respactively, higher than after annealing at lower temperature. Namely, when the material 
is annealed at 1150°C, only the y, formation and coarsening processes occur. 
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