Page 118 - Steam Turbines Design, Applications, and Rerating

Rotors for Reaction Turbines 99

5.2 Materials for Solid Rotors
Experienced manufacturers often use St 460 TS and 461 TS steels for
solid rotors. The mechanical properties of these steels and their
behavior over longer periods have been under research for many
years. Basic mechanical fracture investigations have given informa-
tion on crack strength, crack propagation velocity, as well as the
whole field of brittle fracture behavior. The chemical analysis and
mechanical properties of rotor materials St 460 TS and St 461 TS are
given in Table 5.1.
Figure 5.10 shows the stressing of the rotor of Figure 5.6 when the
maximum temperature difference occurs between the rotor surface
and the axis. The same comparative stress, resulting from the centrifu-
gal and thermal stresses, prevails along a given line.

TABLE 5.1 Composition and Properties of Steels
for Solid Rotors
St 460 TS St 461 TS
Chemical composition in %
C 0.17 ÷ 0.25
Mn 0.30 ÷ 0.50
Cr 1.20 ÷ 1.50
Ni Max. 0.60/0.50 ÷ 0.80
Mo 0.70 ÷ 1.20
V 0.25 ÷ 0.35
Mechanical properties, kgf/mm 2
Fracture point at 20°C σ B 70 ÷ 85
Yield point at 20°C σ S Min. 60
Resistance to fatigue Min.
5
σ B /10 h 350°C 44
400°C 32
450°C 22
500°C 13
550°C 7
These materials correspond to DIN specification 21 CrMoV 511.
SOURCE: Asea Brown-Boveri, Baden, Switzerland

Figure 5.10 Stressing a solid rotor during start-up will yield the same comparative
stresses along a given line. (Asea Brown-Boveri, Baden, Switzerland)