Vliv současné dezoxidace oceli Al, Zr, KVZ a Ti na vlastnosti masivních odlitků

Influence of compound deoxidation of steel with Al, Zr, rare earth metals, and Ti on properties of heavy castings

journal article - other

en

Heavy steel castings deoxidized with aluminium are sometimes brittle intercrystalline failed during their service along primary grain boundaries what is initiated by aluminium nitrides and so called conchoidal fractures are formed. The tendency to forming the conchoidal fractures depends in particular on cooling rate (the casting modulus), aluminium and nitrogen contents in steel. During deoxidation, when manufacturing heavy castings, the elements with high affinity to nitrogen, zirconium or titanium, are added to steel that would decrease nitrogen activity by the bond on stable nitrides. The formation of stable nitrides should reduce the tendency of steel to the formation of conchoidal fractures. Deoxidation was thermodynamically analyzed at presence of the mentioned elements. For particular conditions a probable course of deoxidation was estimated at test castings. The deoxidation course was checked by microanalysis of deoxidation products (inclusions). For service and experimental castings the anticipated composition of inclusions was compared. It has been proved that in heavy castings with high aluminium contents in steel under studied conditions neither the addition of zirconium nor of titanium nor of rare earth metals will prevent the formation of conchoidal fractures.

U masivních ocelových odlitků dezoxidovaných hliníkem dochází někdy během provozu ke křehkému interkrystalickému porušení po hranicích primárních zrn iniciovaném nitridy hliníku, tzv. lasturové lomy. Náchylnost ke vzniku lasturových lomů závisí zejména na rychlosti chladnutí (modulu odlitku) a obsahům hliníku a dusíku v oceli. Během dezoxidace se při výrobě masivních odlitků přidávají do oceli prvky s vysokou afinitou k dusíku, zirkonium nebo titan, které mají snížit aktivitu dusíku vazbou na stabilní nitridy. Vznik stabilních nitridů zmenší sklon oceli ke vzniku lasturovému lomu. Byl proveden termodynamický rozbor dezoxidace za přítomnosti uvedených prvků. Pro konkrétní podmínky byl stanoven pravděpodobný průběh dezoxidace. Průběh dezoxidace byl kontrolován mikroanalýzou produktů dezoxidace (vměstků). U provozních a experimentálních odlitků bylo porovnáno předpokládané složení vměstků. Bylo prokázáno, že v masivních odlitcích ani přísada zirkonia, titanu ani KVZ nezabrání při vysokých obsazích hliníku v oceli za sledovaných podmínek vzniku lasturových lomů.

Heavy steel castings deoxidized with aluminium are sometimes brittle intercrystalline failed during their service along primary grain boundaries what is initiated by aluminium nitrides and so called conchoidal fractures are formed. The tendency to forming the conchoidal fractures depends in particular on cooling rate (the casting modulus), aluminium and nitrogen contents in steel. During deoxidation, when manufacturing heavy castings, the elements with high affinity to nitrogen, zirconium or titanium, are added to steel that would decrease nitrogen activity by the bond on stable nitrides. The formation of stable nitrides should reduce the tendency of steel to the formation of conchoidal fractures. Deoxidation was thermodynamically analyzed at presence of the mentioned elements. For particular conditions a probable course of deoxidation was estimated at test castings. The deoxidation course was checked by microanalysis of deoxidation products (inclusions). For service and experimental castings the anticipated composition of inclusions was compared. It has been proved that in heavy castings with high aluminium contents in steel under studied conditions neither the addition of zirconium nor of titanium nor of rare earth metals will prevent the formation of conchoidal fractures.

ocelové odlitky, dezoxidace, lasturové lomy

steel casting, deoxidation, conchoidal fractures

2012

03.04.2012

Polish Academy of Sciences

1897-3310

12

1

99–104

6