NEW.) Ver
saclay. Microstructure and properties of 18CuNMT drum steel after long term service
Q erreichen bei
x N iy A. Kielbus , A. Hernas, Silesian University of Technology Katowice, Poland,
Won RB
N Kun 1. Abstract
| heme Majority of the drums used in home power plants as well as heat and power-generating plants is
gd made from 18CuNMT steel and has already worked for over 150 thousand hours, some of them
Use- Versuch even 200 thousand hours. Long term service has influence on changes of material structure and its
smn fof. degradation. Decrease of toughness, bainite/pearlite regions degradation processes, copper particles
1) Gew% ist in ferrite and postbainite grains, high dislocation density we observed. After restorative heat
m der Boride treatment, some process occurred coagulation of carbides, decrease of density of dislocation pinned
(en, on copper particles, occurrence of polygonization processes. The results of research carried out
A des Comets show that the tested drum, withdrawn from service, could be still used. Application of the
Werkstoffbe- regenerative heat treatment would allow to extend its operation for further 40 000 hours.
5). Diese Be-
des Wolfram
IG) auf einen 2. Introduction
il eher Auf. ; In the present economic situation of the country an assessment of the condition of used
Pig dr boilers, the operation time of which has exceeded 100 000 and in some cases even 200 000 hours, is
ach abn very important, since it forms a basis for: Co N
a wo 9 prolongation of the operation time in the hitherto existing conditions,
mechs ¢ determining the scope of subsequent overhauls and possible modernisation’s.
a Thus, determining the usability of the above-mentioned boilers for further operation has a
technical and economical significance. Such an assessment is a necessity and simultaneously a
starting point for an appraisal of the condition of the boilers.
Majority of the drums used in home power plants as well as heat and power-generating plants
is made from 18CuNMT steel and has already worked for over 150 thousand hours. Hence, a
question arises: how long can they be safely used in real working conditions? In order to answer
this question an appraisal of the condition of the material they are made from is necessary. In
practice, an element loses its usability for further operation in the case of lacking safety reserve or
Ergestellt wer- when its further operation is not profitable (1).
fr Depending on the initial condition, technology, chemical constitution and service conditions,
Mai we the processes of material structure degradation leading to a decline of mechanical and functional
hmelzmetallur- properties take place at a different rate. It is quite natural that after 100 thousand hours of operation
a due microcracks of the drum’s welds and shell occur. In the first place, a decline of ductile properties
El occurs, which means increased susceptibility to brittle cracking (2).
großer Abküh-
mrfall gebracht 2. Material and Research Results and Their Analysis
Drum material made from 18CuNMT (DIN 17CuNiMo4) steel was subjected to research after
180 000 hours of service and after the application of regenerative heat treatment.
Long term service has a distinct influence on changes of the material structure and its
degradation. As a result of the research carried out the following phenomena were found in the
B4TiCVTE material (1,3,4):
¢ degradation of bainite/pearlite regions with a different degree of advancement (fig. 1, 2);
+ M;C and M,C; carbides precipitates at grain boundaries (fig. 1, 2), creating a characteristic
ars durch network at ferrite grain boundaries in material of high degradation (fig. 2);
» relatively high dislocation density in ferrite (fig. 3);
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