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20MnMoNi5-5 Steel
Steel name: 20MnMoNi5-5
Diagram No.: 5120
Type of diagram: CCT
DIN designation: 20MnMoNi5-5
Mat. No. (Wr. Nr.) designation: 1.6310
Chemical composition in weight %: 0.23% C, 0.25% Si, 1.38% Mn, 0.006% P, 0.013% S, 0.14% Cr, 0.51% Mo, 0.58% Ni, 0.12% Cu, 0.026% Al, 0.016% N
Steel group: Nuclear power station steels
Note: The austenitizing temperature for tempering should be between 870 and 910 °C. After water quenching, the material is tempered for 18 h between 630 and 680 °C.
The time-temperature-transformation diagram Fig. shows an extensive bainite range, whilst the ferrite and pearlite transformation is displaced to very long times. To attain the necessary toughness, the aim is a bainitic-martensitic transformation microstructure in this steel after water quenching. In the case of large wrought components, the cooling curves are displaced with increasing wall thickness from lower bainite with martensite via upper bainite to the start of the ferrite transformation.
After aging of the lower bainite, the light microscope shows a fine-grained microstructure
with numerous precipitates. In the extraction replica the form and distribution of the precipitates can be seen clearly at low magnification. In the thin foil it is seen that these precipitates form preferentially on the grain boundaries, but also to some extent within the grains. At higher magnifications the grain boundaries are seen to consist not only of normal high-angle boundaries. The extremely fine grain size (approx. 1 µm) is, mainly due to low-angle grain boundaries which have formed during aging by recovery of transformation-induced dislocations.
Reference: Not shown in this demo version.
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Time-temperature-transformation diagram for continuous cooling of the reactor pressure vessel steel 20MnMoNi5-5. Click the image to enlarge the diagram.
Disclaimer: The information and data presented herein are typical or average values and are not a guarantee of maximum or minimum values. Applications specifically suggested for material described herein are made solely for the purpose of illustration to enable the reader to make his own evaluation and are not intended as warranties, either express or implied, of fitness for these or other puposes. There is no representation that the recipient of this literature will receive updated editions as the become available.