Heterogenita kontinuálně lité ocelové bramy krátce před průvalem

Heterogeneity of Continuously Cast Steel Slab Shortly Before Breakout

conference paper

en

The paper presents heterogeneous chemical composition of the steel slab, which was determined during short-time operation of continuous casting machine after flying tundish change. Before this exchange the steel A was cast (0.41 wt.% C and 0.95 wt.% Cr), shortly after the exchange continuous casting of the steel B (0.17 wt.% C and 0.70 wt.% Cr) started. After 20 minutes the continuous casting machine automatically stopped, because in the straightening zone, between the 7th and the 8th segment a breakout had occurred. Part of the slab was taken from the place of breakout for more precise determination of the position of breakout. It served also for taking the test samples for analysis of local chemical composition. It was expected that basic information on chemical heterogeneity of both steels A and B will be obtained, as well as information on exchange of mass between these two steels, which occurred some 20 minutes before stopping of the continuous casting machine. The reason was that structural state of both steels contained at the moment of breakout both solid and liquid phases. Intermixing zone enabled comparatively rapid mixing of masses of both steels A and B. Apart from obtaining basic experimental concept of chemical heterogeneity of continuous cast slab connected with breakout it was expected that it would be possible to make a semi quantitative evaluation of the extent of mixing of both melts A and B in this very short time interval.

V příspěvku je prezentováno heterogenní chemické složení ocelové bramy jehož ustavení nastalo během krátkodobého chodu licího stroje pro plynulé lití po letmé výměně mezipánve. Před výměnou se odlévala ocel A( 0,41 hm.% C a 0,95 hm.% Cr) krátce po výměně pak pokračovalo plynulé lití oceli B ( 0,17 hm.% C a 0,70 hm.% Cr). Po 20 minutách se licí stroj automaticky zastavil, neboť v oblasti rovnání bramy mezi 7. a 8. segmentem došlo k průvalu. Z místa průvalu byla odebrána část bramy k upřesnění polohy průvalu. Z ní byly odebrány zkušební vzorky k analýze lokálního chemického složení. Očekávalo se, že se získají základní informace o chemické heterogenitě obou ocelí A a B a také informace o výměně hmoty mezi oběma ocelemi, ke které docházelo 20 min před zastavením stroje. Strukturní stav obou ocelí zahrnoval totiž v okamžiku průvalu jak pevnou tak kapalnou fázi. Směsná zóna umožňovala relativně dosti rychlé promíchávaní hmot obou ocelí A a B. Kromě získání základní experimentální představy o chemické heterogenitě plynule lité bramy spojené s průvalem se očekávalo, že bude možno semikvantitativně posoudit rozsah promíšení obou taveb A a B v tomto krátkém časovém intervalu.

The paper presents heterogeneous chemical composition of the steel slab, which was determined during short-time operation of continuous casting machine after flying tundish change. Before this exchange the steel A was cast (0.41 wt.% C and 0.95 wt.% Cr), shortly after the exchange continuous casting of the steel B (0.17 wt.% C and 0.70 wt.% Cr) started. After 20 minutes the continuous casting machine automatically stopped, because in the straightening zone, between the 7th and the 8th segment a breakout had occurred. Part of the slab was taken from the place of breakout for more precise determination of the position of breakout. It served also for taking the test samples for analysis of local chemical composition. It was expected that basic information on chemical heterogeneity of both steels A and B will be obtained, as well as information on exchange of mass between these two steels, which occurred some 20 minutes before stopping of the continuous casting machine. The reason was that structural state of both steels contained at the moment of breakout both solid and liquid phases. Intermixing zone enabled comparatively rapid mixing of masses of both steels A and B. Apart from obtaining basic experimental concept of chemical heterogeneity of continuous cast slab connected with breakout it was expected that it would be possible to make a semi quantitative evaluation of the extent of mixing of both melts A and B in this very short time interval.

kontinuální lití, chemické složení, heterogenita, průval

concast slab, chemical composition, heterogeneity, breakout

2012

23.05.2012

Tanger

Ostrava

978-80-87294-29-1

Metal 2012 Conference proceedings abstracts, CD-ROM

1

148–153

6