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Structure and fracture of medium carbon microalloyed steel

Struktura i lom u srednjeugljeničnim mikrolegiranim čelicima

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2013
4606.pdf (148.6Mb)
Authors
Glišić, Dragomir
Contributors
Radović, Nenad
Cvijović, Zorica
Rakin, Marko
Grabulov, Vencislav
Doctoral thesis (Published version)
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Abstract
Two medium carbon vanadium microalloyed foring steels with different content of carbon and titanium were investigated. Broad goals were to examine transformational behavior of the steels on continuous cooling at still air directly from austenitisation temperatures, to determine optimal regime to produce predominantly acicular ferrite structure and to examine it both by means of mechanical behavior and fracture properties at liquid nitrogen temperature. Main goal was to establish micromehanism of cleavage fracture of the steels with predominantly acicular ferrite structure, and to measure critical parameters of cleavage fracture – critical fracture stress and effective fracture surface energy. The influence of vanadium and nitrogen on microstructure and mechanical properties of medium-carbon steels has been studied by means of metallography and mechanical testing. Vanadium addition to the low nitrogen steel suppresses the formation of ferrite-pearlite following the low reheating tempera...tures and microstructure consists of bainitic sheaves. For high reheating temperatures, dominantly acicular ferrite structure in both the low nitrogen and the high nitrogen vanadium steels is obtained. The results suggest that vanadium in solid solution promotes the formation of bainite, whereas the effect of nitrogen is related to the precipitation of VN particles in austenite with high potency for intragranular nucleation of acicular ferrite and to the precipitation of V(C,N) particles in ferrite with high potency for precipitation strengthening. Addition of both vanadium and nitrogen considerably increases the strength level. The aim of this work was to establish deformation behaviour of two vanadium microalloyed medium carbon steels with different contents of carbon and titanium by tensile testing at 77 K. Samples were reheated at 1250°C/30 min and continuously cooled at still air. Beside acicular ferrite as dominant morphology in both microstructures, the steel with lower content of carbon and negligible amount of titanium contains considerable fraction of grain boundary ferrite and pearlite...

U radu su ispitivanana dva srednjeugljenična čelika za kovanje, mikrolegirana vanadijumom, koji se međusobno razlikuju po sadržaju titana i ugljenika. V– mikrolegirani čelik sadrži 0,26%C, označen je kao „V19“, i Ti–V– mikrolegirani čelik mikrolegiran je titanom i sadrži 0,31%C, označen kao „TiV22“. Cilj rada bio je da se ispitaju transformacione karakteristike srednjeugljeničnih mikrolegiranih čelika pri kontinuiranom hlađenju na vazduhu, direktno sa temperature austenitizacije, da se odrede uslovi postizanja strukture acikularnog ferita i da se odrede kritični parametri loma cepanjem na temperaturi tečnog azota za ovu strukturu. Čelici su isporučeni kao toplovaljane šipke. Analizom mikrostruktura koje su postignute pri kontinuiranom hlađenju na mirnom vazduhu, direktno sa različitih temperatura austenitizacije, određen je termički režim pripreme uzoraka za ispitivanje. Pripremljeni uzorci čelika sa strukturom acikularnog ferita ispitivani su na temperaturi tečnog azota jednoosnim zat...ezanjem i savijanjem u četiri tačke. Za ispitivanje savijanjem u četiri tačke korišćene su epruvete sa zarezom po Grifitsu i Ovenu. Temperatura tečnog azota odabrana je radi ispitivanja u uslovima potpuno krtog loma i određivanja kritičnog napona loma. Određivanje kritičnog napona loma obuhvata fraktografiju i modelovanje savijanja u četiri tačke metodom konačnih elemenata. Rezultati jednoosnog zateznog ispitivanja na temperaturi tečnog azota poslužili su kao ulazni podaci za modelovanje. Modelovanjem je izračunata raspodela napona i deformacija u uzorku, u trenutku loma, pri savijanju u četiri tačke. U opsegu temperatura austenitizacije između 850°C i 1300°C, za pripremu uzoraka za ispittivanje izabrana je temperatura od 1250°C. Nakon hlađenja na mirnom vazduhu sa 1250°C, struktura čelika legiranog vanadijumom i sa nižim sadržajem ugljenika (čelik V19) sastoji se od ferita, perlita i acikularnog ferita, dok se struktura čelika legiranog titanom i vanadijumom, sa višim sadržajem ugljenika (čelik TiV22), pretežno sastoji od acikularnog ferita...

Keywords:
Medium carbon microalloyed steels / forging steels / acicular ferrite / cleavage fracture / brittle fracture / fracture micromechanism / critical fracture stress / Средњеугљенични микролегирани челици / ацикуларни ферит / крти лом / лом цепањем / микромеханизам лома / критичан напон лома
Source:
2013
Publisher:
  • Univerzitet u Beogradu, Tehnološko-metalurški fakultet
Funding / projects:
  • Micromechanical criteria of damage and fracture (RS-174004)
[ Google Scholar ]
Handle
https://hdl.handle.net/21.15107/rcub_technorep_4609
URI
http://eteze.bg.ac.rs/application/showtheses?thesesId=820
https://fedorabg.bg.ac.rs/fedora/get/o:7165/bdef:Content/download
http://vbs.rs/scripts/cobiss?command=DISPLAY&base=70036&RID=44711951
http://TechnoRep.tmf.bg.ac.rs/handle/123456789/4609
Collections
  • Doktorske disertacije (TMF)
Institution/Community
Tehnološko-metalurški fakultet
TY  - THES
AU  - Glišić, Dragomir
PY  - 2013
UR  - http://eteze.bg.ac.rs/application/showtheses?thesesId=820
UR  - https://fedorabg.bg.ac.rs/fedora/get/o:7165/bdef:Content/download
UR  - http://vbs.rs/scripts/cobiss?command=DISPLAY&base=70036&RID=44711951
UR  - http://TechnoRep.tmf.bg.ac.rs/handle/123456789/4609
AB  - Two medium carbon vanadium microalloyed foring steels with different content of carbon and titanium were investigated. Broad goals were to examine transformational behavior of the steels on continuous cooling at still air directly from austenitisation temperatures, to determine optimal regime to produce predominantly acicular ferrite structure and to examine it both by means of mechanical behavior and fracture properties at liquid nitrogen temperature. Main goal was to establish micromehanism of cleavage fracture of the steels with predominantly acicular ferrite structure, and to measure critical parameters of cleavage fracture – critical fracture stress and effective fracture surface energy. The influence of vanadium and nitrogen on microstructure and mechanical properties of medium-carbon steels has been studied by means of metallography and mechanical testing. Vanadium addition to the low nitrogen steel suppresses the formation of ferrite-pearlite following the low reheating temperatures and microstructure consists of bainitic sheaves. For high reheating temperatures, dominantly acicular ferrite structure in both the low nitrogen and the high nitrogen vanadium steels is obtained. The results suggest that vanadium in solid solution promotes the formation of bainite, whereas the effect of nitrogen is related to the precipitation of VN particles in austenite with high potency for intragranular nucleation of acicular ferrite and to the precipitation of V(C,N) particles in ferrite with high potency for precipitation strengthening. Addition of both vanadium and nitrogen considerably increases the strength level. The aim of this work was to establish deformation behaviour of two vanadium microalloyed medium carbon steels with different contents of carbon and titanium by tensile testing at 77 K. Samples were reheated at 1250°C/30 min and continuously cooled at still air. Beside acicular ferrite as dominant morphology in both microstructures, the steel with lower content of carbon and negligible amount of titanium contains considerable fraction of grain boundary ferrite and pearlite...
AB  - U radu su ispitivanana dva srednjeugljenična čelika za kovanje, mikrolegirana vanadijumom, koji se međusobno razlikuju po sadržaju titana i ugljenika. V– mikrolegirani čelik sadrži 0,26%C, označen je kao „V19“, i Ti–V– mikrolegirani čelik mikrolegiran je titanom i sadrži 0,31%C, označen kao „TiV22“. Cilj rada bio je da se ispitaju transformacione karakteristike srednjeugljeničnih mikrolegiranih čelika pri kontinuiranom hlađenju na vazduhu, direktno sa temperature austenitizacije, da se odrede uslovi postizanja strukture acikularnog ferita i da se odrede kritični parametri loma cepanjem na temperaturi tečnog azota za ovu strukturu. Čelici su isporučeni kao toplovaljane šipke. Analizom mikrostruktura koje su postignute pri kontinuiranom hlađenju na mirnom vazduhu, direktno sa različitih temperatura austenitizacije, određen je termički režim pripreme uzoraka za ispitivanje. Pripremljeni uzorci čelika sa strukturom acikularnog ferita ispitivani su na temperaturi tečnog azota jednoosnim zatezanjem i savijanjem u četiri tačke. Za ispitivanje savijanjem u četiri tačke korišćene su epruvete sa zarezom po Grifitsu i Ovenu. Temperatura tečnog azota odabrana je radi ispitivanja u uslovima potpuno krtog loma i određivanja kritičnog napona loma. Određivanje kritičnog napona loma obuhvata fraktografiju i modelovanje savijanja u četiri tačke metodom konačnih elemenata. Rezultati jednoosnog zateznog ispitivanja na temperaturi tečnog azota poslužili su kao ulazni podaci za modelovanje. Modelovanjem je izračunata raspodela napona i deformacija u uzorku, u trenutku loma, pri savijanju u četiri tačke. U opsegu temperatura austenitizacije između 850°C i 1300°C, za pripremu uzoraka za ispittivanje izabrana je temperatura od 1250°C. Nakon hlađenja na mirnom vazduhu sa 1250°C, struktura čelika legiranog vanadijumom i sa nižim sadržajem ugljenika (čelik V19) sastoji se od ferita, perlita i acikularnog ferita, dok se struktura čelika legiranog titanom i vanadijumom, sa višim sadržajem ugljenika (čelik TiV22), pretežno sastoji od acikularnog ferita...
PB  - Univerzitet u Beogradu, Tehnološko-metalurški fakultet
T1  - Structure and fracture of medium carbon microalloyed steel
T1  - Struktura i lom u srednjeugljeničnim mikrolegiranim čelicima
UR  - https://hdl.handle.net/21.15107/rcub_technorep_4609
ER  - 
@phdthesis{
author = "Glišić, Dragomir",
year = "2013",
abstract = "Two medium carbon vanadium microalloyed foring steels with different content of carbon and titanium were investigated. Broad goals were to examine transformational behavior of the steels on continuous cooling at still air directly from austenitisation temperatures, to determine optimal regime to produce predominantly acicular ferrite structure and to examine it both by means of mechanical behavior and fracture properties at liquid nitrogen temperature. Main goal was to establish micromehanism of cleavage fracture of the steels with predominantly acicular ferrite structure, and to measure critical parameters of cleavage fracture – critical fracture stress and effective fracture surface energy. The influence of vanadium and nitrogen on microstructure and mechanical properties of medium-carbon steels has been studied by means of metallography and mechanical testing. Vanadium addition to the low nitrogen steel suppresses the formation of ferrite-pearlite following the low reheating temperatures and microstructure consists of bainitic sheaves. For high reheating temperatures, dominantly acicular ferrite structure in both the low nitrogen and the high nitrogen vanadium steels is obtained. The results suggest that vanadium in solid solution promotes the formation of bainite, whereas the effect of nitrogen is related to the precipitation of VN particles in austenite with high potency for intragranular nucleation of acicular ferrite and to the precipitation of V(C,N) particles in ferrite with high potency for precipitation strengthening. Addition of both vanadium and nitrogen considerably increases the strength level. The aim of this work was to establish deformation behaviour of two vanadium microalloyed medium carbon steels with different contents of carbon and titanium by tensile testing at 77 K. Samples were reheated at 1250°C/30 min and continuously cooled at still air. Beside acicular ferrite as dominant morphology in both microstructures, the steel with lower content of carbon and negligible amount of titanium contains considerable fraction of grain boundary ferrite and pearlite..., U radu su ispitivanana dva srednjeugljenična čelika za kovanje, mikrolegirana vanadijumom, koji se međusobno razlikuju po sadržaju titana i ugljenika. V– mikrolegirani čelik sadrži 0,26%C, označen je kao „V19“, i Ti–V– mikrolegirani čelik mikrolegiran je titanom i sadrži 0,31%C, označen kao „TiV22“. Cilj rada bio je da se ispitaju transformacione karakteristike srednjeugljeničnih mikrolegiranih čelika pri kontinuiranom hlađenju na vazduhu, direktno sa temperature austenitizacije, da se odrede uslovi postizanja strukture acikularnog ferita i da se odrede kritični parametri loma cepanjem na temperaturi tečnog azota za ovu strukturu. Čelici su isporučeni kao toplovaljane šipke. Analizom mikrostruktura koje su postignute pri kontinuiranom hlađenju na mirnom vazduhu, direktno sa različitih temperatura austenitizacije, određen je termički režim pripreme uzoraka za ispitivanje. Pripremljeni uzorci čelika sa strukturom acikularnog ferita ispitivani su na temperaturi tečnog azota jednoosnim zatezanjem i savijanjem u četiri tačke. Za ispitivanje savijanjem u četiri tačke korišćene su epruvete sa zarezom po Grifitsu i Ovenu. Temperatura tečnog azota odabrana je radi ispitivanja u uslovima potpuno krtog loma i određivanja kritičnog napona loma. Određivanje kritičnog napona loma obuhvata fraktografiju i modelovanje savijanja u četiri tačke metodom konačnih elemenata. Rezultati jednoosnog zateznog ispitivanja na temperaturi tečnog azota poslužili su kao ulazni podaci za modelovanje. Modelovanjem je izračunata raspodela napona i deformacija u uzorku, u trenutku loma, pri savijanju u četiri tačke. U opsegu temperatura austenitizacije između 850°C i 1300°C, za pripremu uzoraka za ispittivanje izabrana je temperatura od 1250°C. Nakon hlađenja na mirnom vazduhu sa 1250°C, struktura čelika legiranog vanadijumom i sa nižim sadržajem ugljenika (čelik V19) sastoji se od ferita, perlita i acikularnog ferita, dok se struktura čelika legiranog titanom i vanadijumom, sa višim sadržajem ugljenika (čelik TiV22), pretežno sastoji od acikularnog ferita...",
publisher = "Univerzitet u Beogradu, Tehnološko-metalurški fakultet",
title = "Structure and fracture of medium carbon microalloyed steel, Struktura i lom u srednjeugljeničnim mikrolegiranim čelicima",
url = "https://hdl.handle.net/21.15107/rcub_technorep_4609"
}
Glišić, D.. (2013). Structure and fracture of medium carbon microalloyed steel. 
Univerzitet u Beogradu, Tehnološko-metalurški fakultet..
https://hdl.handle.net/21.15107/rcub_technorep_4609
Glišić D. Structure and fracture of medium carbon microalloyed steel. 2013;.
https://hdl.handle.net/21.15107/rcub_technorep_4609 .
Glišić, Dragomir, "Structure and fracture of medium carbon microalloyed steel" (2013),
https://hdl.handle.net/21.15107/rcub_technorep_4609 .

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