Ferrite
BCC ironSoft matrix in low-carbon steels; ductile, magnetic, limited strength.
What holds Acier together is not the nickname. Formula Fe–C (±Mn, Si, Cr…), density 7.85 g/cm³.
Meters are atlas-relative. Grades are the SKUs buyers write.
Phases
Pearlite
Fe3C + ferrite lamellaeThe classic strengthening mix in medium-carbon steels after slow cool.
Austenite
FCC ironHigh-temperature phase; retained in some stainless and TRIP steels.
Martensite
BCT supersaturatedQuench product; hard, needs tempering for toughness.
Cementite
Fe3CHard carbide that pins dislocations; too much makes steel brittle.
Inclusions
MnS, oxidesNon-metallic particles that start fatigue cracks if not controlled.
Jauges relatives
Strength88
Strength is an editorial 0–100 mark relative to the other 31 materials in this atlas — not a laboratory certificate.
Heat envelope72
Heat envelope is an editorial 0–100 mark relative to the other 31 materials in this atlas — not a laboratory certificate.
Fire behaviour84
Fire behaviour is an editorial 0–100 mark relative to the other 31 materials in this atlas — not a laboratory certificate.
Insulation8
Insulation is an editorial 0–100 mark relative to the other 31 materials in this atlas — not a laboratory certificate.
Workability80
Workability is an editorial 0–100 mark relative to the other 31 materials in this atlas — not a laboratory certificate.
Circularity64
Circularity is an editorial 0–100 mark relative to the other 31 materials in this atlas — not a laboratory certificate.
Nuances
S235 / A36
Mild structuralMild structural
S355
Higher-yield structuralHigher-yield structural
1045
Medium carbonMedium carbon
DP600 / DP800
Dual-phase AHSSDual-phase AHSS
Corten / weathering
Patina steelPatina steel
Liaisons
Metallic bonding
Delocalised electrons give ductility and electrical conductivity.
Fe–C interstitial
Carbon in octahedral sites hardens iron far more than its weight share suggests.
Grain boundaries
Hall–Petch strengthening: finer grains raise yield without losing much toughness.
Precipitates
Carbides and copper-rich clusters pin dislocations in HSLA and ageing grades.
Change the grade, the coating or the moisture and you have a different material with the same English name.
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