| Abstract | U ovom diplomskom radu je analiziran utjecaj različitih sastava uloška za izradu
taline, debljine stijenke odljevka i cijepljenja na mikrostrukturu sivog lijeva. Izrađene su 3
taline sivog lijeva gotovo istog kemijskog sastava. Korišteni su sljedeći udjeli sirovog željeza
(SŽ), čeličnog otpada (ČO), povratnog sivog lijeva (PSL) i SiC u ulošku: talina 1 (39,4 % SŽ,
10 % ČO, 49,2 % PSL, 0,6 % SiC), talina 2 (9,9 % SŽ, 38,8 % ČO, 47,9 % PSL, 1,6 % SiC) i
talina 3 (0 % SŽ, 0 % ČO, 99,2 % PSL, 0,06 % SiC). Od svake taline odlivena su 2 stepenasta
odljevka sa stijenkama debljina 5, 10, 20, 45 i 65 mm, jedan necijepljen i jedan cijepljen
(dodatak cjepiva u mlaz taline tijekom ulijevanja u kalup iznosio je 0,23 mas. %). Dobiveni
rezultati pokazuju da tip, veličina i raspodjela grafitnih listića u analiziranim stijenkama nisu
u značajnijoj mjeri ovisili o sastavu uloška. Debljina stijenke imala je veliki utjecaj na tip,
veličinu i raspodjelu grafitnih listića, izlučivanje karbida te strukturu metalne osnove. S
povećanjem debljine stijenke mijenja se tip grafitnih listića od D i E preko B do A tipa.
Karbidi su pronađeni u rubnom dijelu stijenke debljine 5 mm. Udio ferita u metalnoj osnovi
povećavao se sa smanjenjem brzine hlađenja te sa povećanjem udjela grafitnih listića D i E
tipa. Cijepljenjem je značajno smanjen udio karbida u rubnom dijelu stijenke debljine 5 mm.
U sredini stijenke debljine 5 mm te stijenkama debljine 10 do 65 mm cijepljenjem je povećan
udio grafitnih listića A tipa te su eliminirani grafitni listići B, D i E tipa ili je njihov udio
značajno smanjen (učinak ovisi o debljini stijenke). |
| Abstract (english) | The effect of different charge compositions for melt production, casting section
thickness and inoculation on the gray cast iron microstructure was analysed in this graduate
thesis. Three gray cast iron melts of almost the same chemical composition were made. The
following shares of pig iron (PI), steel scrap (SS), gray iron return (GIR) and SiC in charge
were used: melt 1 (39.4 % PI, 10 % SS, 49.2 % GIR, 0.6 % SiC), melt 2 (9.9 % PI, 38.8 %
SS, 47.9 % GIR, 1.6 % SiC) and melt 3 (0 % PI, 0 % SS, 99.2 % GIR, 0.06 % SiC). Two
stepped castings with walls thicknesses of 5, 10, 20, 45 and 65 mm are casted from each melt,
one uninoculated and one inoculated (the addition of inoculant in the melt stream during the
pouring in the mold was 0.23 wt.%). The obtained results show that the type, size and
distribution of graphite flakes in the analysed walls did not significantly depend on the
composition of the charge. The wall thickness had a great influence on the type, size and
distribution of graphite flakes, carbides precipitation and the structure of the metal matrix.
The type of graphite flakes is changed from D and E, over B to A type with increasing wall
thickness. Carbides were found in the edge part of the wall thickness of 5 mm. The percentage
of ferrite in the metal matrix increased with decreasing the cooling rate and with increasing
the proportion of graphite flakes D and E type. Inoculation significantly reduced the
proportion of carbides in the edge part of the wall thickness of 5 mm. In the middle of the
wall thickness of 5 mm and the walls thicknesses of 10 to 65 mm the inoculation resulted in
an increase in the proportion of graphite flakes A type. In addition, the graphite flakes B, D
and E types were eliminated or their proportion was significantly reduced (effect depends on
the wall thickness). |
