Page 291 - Handbook of Materials Failure Analysis

5 Material and Experiment 287

1200

True stress (MPa) 800 Room temp.

400
–20 °C
–600 °C
–1000 °C
0
0.0 0.2 0.4 0.6 0.8
True plastic strain
FIGURE 12.1
True stress versus true plastic strain curve of the material DIN 22NiMOCr3-7 at various
temperatures.

at coalescence) are shown in Table 12.3. The 1T CT and SEB specimen has a thick-
ness B of 25 mm, width W of 50 mm, and initial crack length “a” of 26.1 mm. The
geometry, dimensions, loading and support conditions of the 1T SEB and 1T CT
specimens are shown in Figure 12.2a and b, respectively. The specimens are 20%
side-grooved and the a/W (initial crack length to width ratio) ratio is 0.52.
A dissimilar weld joint has been prepared between two pieces of ferritic and aus-
tenitic pipes (of 332 mm outer diameter and 29 mm thickness). The ferritic steel is
DIN 20MnMoNi55 (similar to A508 Cl.3) and the austenitic steel is DIN 1.4550. The
ferritic steel is an optimized reactor pressure vessel steel material. It has a bainitic
structure at room temperature. From the metallographic examination of cross-
sections of the deformed tensile specimens, it was observed that voids usually form

Table 12.3 Material Properties of DIN 22NiMoCr3-7 Pressure Vessel Steel

Rousselier’s Void Parameters
Parameters Initial Void Volume Final Void Char. E
Constants
Void
Length
Model D σ k (MPa) Volume Fraction at Volume Parameter (Young’s ν (Poisson’s
Fraction
Coalescence
Fraction
Mod. in
C length
2
GPa)
Ratio)
(mm )
f 0
f c
f f
Value 2 445 0.0003 0.05 0.3 0.05 210 0.3