TY  - JOUR
AU  - Timotijević, Milica
AU  - Erić Cekić, Olivera
AU  - Rajnović, Dragan
AU  - Dojčinović, Marina
AU  - Janjatović, Petar
PY  - 2022
UR  - http://TechnoRep.tmf.bg.ac.rs/handle/123456789/6320
AB  - In this work, the heat-resistant cast steel HP40Nb alloy, produced in the form of a centrifugally cast tube, which failed after 11.4 years service is investigated. The microstructure is examined using a scanning electron microscope (SEM), while the phases observed are analysed using an energy dispersive X-ray analyser system (EDS). Additionally, fractography is performed on the fractured surface of failed specimens. Mechanical properties of the tube are evaluated by using tensile and Charpy impact testing at room temperature (298 K). Main results indicate that the failed tube microstructure consists of an austenitic matrix and a continuous network of primary eutectic carbides of two types: one rich in Nb (bright particles), and one rich in Cr (dark particles). These carbides are NbC and complex M7C3 (M = Cr, Ni, Fe) type. The brittle intergranular fracture mode is explained by the presence of massive precipitation and coarsening of intergranular carbides at grain boundaries. Lower tensile properties of the in-service exposed tube might be correlated to the morphological, chemical, and distribution changes of precipitates during service at high temperature. Decreased values of hardness can be attributed to increase in grain size, as well as due to the decomposition of Cr-carbide during the heat treatment at temperatures above 1073 K.
AB  - U ovom radu је ispitivana legura od livenog čelika HP40Nb otpornog na toplotu, proizvedena u obliku centrifugalno livene cevi, koja je otkazala posle 11,4 godina eksploatacije. Mikrostruktura je ispitivana primenom skenirajućeg elektronskog mikroskopa SEM, dok su uočene faze analizirane korišćenjem sistema energetski disperzivnog rendgenskog analizatora (EDS). Dodatno, fraktografija je urađena na površini loma oštećenih uzoraka. Mehanička svojstva su procenjena ispitivanjem na zatezanje i ispitivanjem energije udara po Šarpiju na sobnoj temperaturi (298 K). Glavni rezultati su pokazali da se mikrostruktura oštećene cevi sastoji od austenitne osnove i neprekidne mreže primarnih eutektičkih karbida dva tipa: jednog bogatog Nb (svetle čestice) i jednog bogatog Cr (tamne čestice). Oba karbida su tipa NbC i složeni M7C3 (M = Cr, Ni, Fe). Mehanizam krtog intergranularnog loma objašnjen je prisustvom masivnog taloženja grubih intergranularnih karbida na granicama zrna. Niža zatezna svojstva cevi izložene eksploataciji mogu biti u korelaciji sa morfološkim, hemijskim i distributivnim promenama taloga tokom eksploatacije na visokoj temperaturi. Smanjenje vrednosti tvrdoće može se pripisati povećanju veličine zrna kao i razlaganju Cr-karbida tokom termičke obrade na temperaturama iznad 1073 K.
PB  - Society for Structural Integrity and Life (DIVK)
T2  - Structural Integrity and Life
T1  - Microstructure evolution and mechanical properties degradation of HPNB alloy after an eleven-year service
T1  - Mikrostrukturni razvoj i degradacija mehaničkih svojstava legure HPNB posle jedanaest godina eksploatacije
EP  - 304
IS  - 3
SP  - 299
VL  - 22
UR  - https://hdl.handle.net/21.15107/rcub_technorep_6320
ER  - 

@article{
author = "Timotijević, Milica and Erić Cekić, Olivera and Rajnović, Dragan and Dojčinović, Marina and Janjatović, Petar",
year = "2022",
abstract = "In this work, the heat-resistant cast steel HP40Nb alloy, produced in the form of a centrifugally cast tube, which failed after 11.4 years service is investigated. The microstructure is examined using a scanning electron microscope (SEM), while the phases observed are analysed using an energy dispersive X-ray analyser system (EDS). Additionally, fractography is performed on the fractured surface of failed specimens. Mechanical properties of the tube are evaluated by using tensile and Charpy impact testing at room temperature (298 K). Main results indicate that the failed tube microstructure consists of an austenitic matrix and a continuous network of primary eutectic carbides of two types: one rich in Nb (bright particles), and one rich in Cr (dark particles). These carbides are NbC and complex M7C3 (M = Cr, Ni, Fe) type. The brittle intergranular fracture mode is explained by the presence of massive precipitation and coarsening of intergranular carbides at grain boundaries. Lower tensile properties of the in-service exposed tube might be correlated to the morphological, chemical, and distribution changes of precipitates during service at high temperature. Decreased values of hardness can be attributed to increase in grain size, as well as due to the decomposition of Cr-carbide during the heat treatment at temperatures above 1073 K., U ovom radu је ispitivana legura od livenog čelika HP40Nb otpornog na toplotu, proizvedena u obliku centrifugalno livene cevi, koja je otkazala posle 11,4 godina eksploatacije. Mikrostruktura je ispitivana primenom skenirajućeg elektronskog mikroskopa SEM, dok su uočene faze analizirane korišćenjem sistema energetski disperzivnog rendgenskog analizatora (EDS). Dodatno, fraktografija je urađena na površini loma oštećenih uzoraka. Mehanička svojstva su procenjena ispitivanjem na zatezanje i ispitivanjem energije udara po Šarpiju na sobnoj temperaturi (298 K). Glavni rezultati su pokazali da se mikrostruktura oštećene cevi sastoji od austenitne osnove i neprekidne mreže primarnih eutektičkih karbida dva tipa: jednog bogatog Nb (svetle čestice) i jednog bogatog Cr (tamne čestice). Oba karbida su tipa NbC i složeni M7C3 (M = Cr, Ni, Fe). Mehanizam krtog intergranularnog loma objašnjen je prisustvom masivnog taloženja grubih intergranularnih karbida na granicama zrna. Niža zatezna svojstva cevi izložene eksploataciji mogu biti u korelaciji sa morfološkim, hemijskim i distributivnim promenama taloga tokom eksploatacije na visokoj temperaturi. Smanjenje vrednosti tvrdoće može se pripisati povećanju veličine zrna kao i razlaganju Cr-karbida tokom termičke obrade na temperaturama iznad 1073 K.",
publisher = "Society for Structural Integrity and Life (DIVK)",
journal = "Structural Integrity and Life",
title = "Microstructure evolution and mechanical properties degradation of HPNB alloy after an eleven-year service, Mikrostrukturni razvoj i degradacija mehaničkih svojstava legure HPNB posle jedanaest godina eksploatacije",
pages = "304-299",
number = "3",
volume = "22",
url = "https://hdl.handle.net/21.15107/rcub_technorep_6320"
}

Timotijević, M., Erić Cekić, O., Rajnović, D., Dojčinović, M.,& Janjatović, P.. (2022). Microstructure evolution and mechanical properties degradation of HPNB alloy after an eleven-year service. in Structural Integrity and Life
Society for Structural Integrity and Life (DIVK)., 22(3), 299-304.
https://hdl.handle.net/21.15107/rcub_technorep_6320

Timotijević M, Erić Cekić O, Rajnović D, Dojčinović M, Janjatović P. Microstructure evolution and mechanical properties degradation of HPNB alloy after an eleven-year service. in Structural Integrity and Life. 2022;22(3):299-304.
https://hdl.handle.net/21.15107/rcub_technorep_6320 .

Timotijević, Milica, Erić Cekić, Olivera, Rajnović, Dragan, Dojčinović, Marina, Janjatović, Petar, "Microstructure evolution and mechanical properties degradation of HPNB alloy after an eleven-year service" in Structural Integrity and Life, 22, no. 3 (2022):299-304,
https://hdl.handle.net/21.15107/rcub_technorep_6320 .