Vpliv mikrolegirnih elementov na rast zrn v avstenitnem nerjavnem jeklu

magistrsko delo

Samo Tome (Author), Aleš Nagode (Mentor), Jaka Burja (Co-mentor)

Abstract

Raziskovali smo vpliv mikrolegirnih elementov niobija, titana, itrija in cirkonija na rast kristalnih zrn v avstenitnem nerjavnem jeklu AISI 304 pri temperaturah žarjenja od 1050 °C do 1200 °C ter časih žarjenja od 0 do 8 ur. Velikost kristalnih zrn je bila ocenjena pod svetlobnim mikroskopom s primerjalno metodo po standardu ASTM E112, izmerili smo delež delta ferita, in naredili mikrostrukturno analizo z vrstičnim elektronskim mikroskopom (SEM), opremljenim z energijskim disperzijskim spektrometrom rentgenskih žarkov (EDS) za analizo kemijske sestave vključkov in izločkov, ter izmerili trdoto po Brinellu. Rast kristalnih zrn med žarjenjem je najbolj zaviral titan, vendar le do temperature 1100 °C. Vpliv cirkonija na rast kristalnih zrn je nekoliko manjši kot vpliv titana, večjo učinkovitost pa je cirkonij imel pri višjih temperaturah (do 1150 °C). Itrij je bil edini mikrolegirni element, ki je vplival na velikost kristalnih zrn pri žarjenju na 1200 °C, torej šele ko so bila kristalna zrna že bolj groba. Niobij je imel vpliv samo pri temperaturi žarjenja 1050 °C, pri kateri je rahlo upočasnil rast kristalnih zrn in povišal trdoto zaradi tvorbe Nb(C, N). Za opis rasti kristalnih zrn jekla AISI 304 smo izdelali model na osnovi Sellars-Whitemanove enačbe Arrheniusovega tipa. Uporabili smo tudi model, ki opisuje trdoto v odvisnosti od velikosti kristalnih zrn, ki temelji na modificirani Hall-Petch enačbi. Pri obeh modelih smo imeli dobro ujemanje izmerjenih in izračunanih vrednosti. Temperatura žarjenja je vplivala tudi na delež delta ferita. Z višjo temperaturo se je delež delta ferita zmanjševal. Njen vpliv je bil večji pri krajših časih žarjenja.

Keywords

avstenitno nerjavno jeklo;mikrolegiranje;velikost kristalnih zrn;vključki;izločki;pripenjanje mej kristalnih zrn;

Data

Language:	Slovenian
Year of publishing:	2020
Typology:	2.09 - Master's Thesis
Organization:	UL NTF - Faculty of Natural Sciences and Engineering
Publisher:	[S. Tome]
UDC:	669
COBISS:	31501059
Views:	457
Downloads:	224
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	English
Secondary title:	effect of microalloying elements on grain growth in austenitic stainless steel
Secondary abstract:	The influence of microalloy elements niobium, titanium, yttrium and zirconium on the growth of crystal grains in austenitic stainless steel AISI 304 at annealing temperatures from 1050 ° C to 1200 °C and annealing times from 0 to 8 hours was investigated. The grain size was assessed under a light microscope using the ASTM E112 comparative method, the delta ferrite content was measured and Brinell hardness and microstructural analysis was performed using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) for chemical analysis of inclusions and precipitates. Titanium was the most effective microalloy element at inhibiting grain growth during annealing, but only up to the temperature of 1100 °C. The effect of zirconium on grain growth is slightly smaller than that of titanium, however, it was more effective at higher temperatures (up to 1150 °C). Yttrium was the only microalloy element that affected the size of the crystal grains when annealed at 1200 °C, i.e. when the crystal grains were already coarse. Niobium only had an effect at an annealing temperature of 1050 °C where it slightly slowed the growth of crystal grains and increased hardness due to the formation of Nb(C, N). To describe grain growth in AISI 304 steel, we developed a model based on the Sellars Whiteman Arrhenius-type equation and used a model based on the modified Hall-Petch equation that describes hardness as a function of crystal grain size. In both models, we had a good match between the measured and calculated values. The annealing temperature also affected the delta ferrite content. With higher temperatures, the proportion of delta ferrite decreased. Its effect was greater at shorter annealing times.
Secondary keywords:	austenitic stainless steel;microalloying;grain size;inclusions;precipitations;grain boundary pinning;
Type (COBISS):	Master's thesis/paper
Study programme:	0
Embargo end date (OpenAIRE):	1970-01-01
Thesis comment:	Univ. v Ljubljani, Naravoslovnotehniška fak., Odd. za materiale in metalurgijo
Pages:	XVI, 53 f.
ID:	12040817