Lec ture 2 8: inc lusion sourc es and control
Why inclus ion control i s necessary
Sources of inclusion formation
Control of inclusio ns
Key words: Inclusion in steel, inclu sion engin eering, clean steel
Why inclu sion c ontrol is ne cessar y?
Impact pro perties are a dversely affe cted with an increase in v olume fractio n of inclu sion a s well as
incl usion length; sp herica l inclu sions are bet ter. Britt le inclusions or inclu sions that have low bon d
strengt h with the m a t r i x break up during early strai ning an d create voids at t he incl usion/ matrix
interface.
Hot fat igue s trength of high strengt h steel is reduc ed by s urface and subsu rface inclusi ons those have
lower expansi on coeffic ient than ste el
The hot workability of steel is affected by the low deformability of inclusions
Anis otropy of a prop erty i s cause d by orientat ion of elongated inclusion s along the d irection of working.
Macro incl usions of sul phides are desirabl e for better steel mach ining properties .
In v iew of the above , cont rol of inc lusion in steel is necessary. It must be ment ioned a nd as pointed out
earlier (see A. iv), macro- inc lusion s are harm ful and they must be co ntroll ed.
Sou rces of i nclu sion form ation
Incl usions can fo rm either (a) during transfer of molten steel from one reactor t o o t he r or (b) duri ng
solidification of steel (lecture 27) or during solid s tate processing by any of the following me chanisms:
i. Rea ction betw een rejected solute elements during solidi fication, for ex ample, rea ction
between sulphur and manganese, and betw een oxy gen and al uminium etc.
ii. Mechan ical and chem ical er osion of refract ory and other materials.
iii. Oxygen picku p by teeming stream and co nsequent oxide f ormatio n.
iv. Chemical reactions.
Incl usions produced by mechani sm (i) are called endogenous, where as mechanis ms ii and i ii pro duce
exogeno us inc lusions . Incl usions can form duri ng
Docsity.com
