Transcript Slide 1

IMPURITIES IN STEEL
• SULPHUR, PHOSPHEROUS, SILICON,
MANGANESE
• PROPERTIES DEPEND ON THE WAY BY WHICH
THESE IMOURITIES ARE DIDTRIBUTED
• EVEN DISTRIBUTION PREFERRED TO CORED
• CORING CONCENTRATES IMPURITIES
Sulphur & Phosphorus segregate and precipitate at grain boundaries---- coring.
Silicon & Manganese evenly distributed (Even 0.3% effect is
minimum)
Si- imparts fluidity, upto 0.3%- [In HCS, kept lower (decomposes to
graphite)]
Mn- soluble in Austenite and Ferrite Mn3C. Increases ‘depth’ of
hardening, improves strength & toughness, max 0.3%
Sulphur- Forms brittle
FeS
Solubility 0.03%,
Precipitates at
boundaries; Iron Sulphide
brittle and makes steel
not suitable for cold
working. Difficult to
reduce below 0.05%.
Excess Mn as MnS
nullifies the effect.
MnS globules
Isolated .
Insoluble and
mostly removed
as slag during
processing
P – max 1% hardening effect.
(0.05% general).
[More- brittle
phosphide forms]
• Nitrogen-forms nitrides during
manufacture.
• Makes steel not suitable for cold
working. (Fe4N brittle).
• Possible to bring to very low (0.002%),
with good processes.