Use of silicon in steel-making, whether as alloying element or deoxidizer; its effects on phase transformation and physical properties.

1. Silicon in
Steels
Erika Entico
MS MSE

2. Silicon
Type Metalloid
Melting Point 1414 °C
Lattice Type FCC (DC)
Density 2.390 g/cm3
Young’s Mod 130–188 GPa
• Alloying element (typically 0.2 ~
5.0%)
• α-Fe stabilizer – ferromagnetic;
• increases α-Fe hardness via solid
solution hardening;
• Improves electrical resistivity;
• Improves oxidation resistance;
• Deoxidizer (typically 0.15 ~ 0.3%,
fully killed)
• Higher affinity for O compared to
Fe or C

3. Plain Carbon Steel Steel with sufficient
Si content
• Sufficient Si in steel retards the
formation of γ-Fe within a smaller
range of C content; the so-called γ-
loop;
• α and σ phase fields become
continuous;
• Above a certain amount, γ-Fe
disappears and no phase
transformation occurs from the
melting point down to room temp;
Effect on Phase
Transformation

4. • Increases A1 with increasing
concentration;
• Decreases the eutectoid C content
with increasing concentration;
Effect on Phase
Transformation

5. • Slows down austenite
transformation into pearlite, bainite,
and martensite;
Effect on Phase
Transformation

6. Effect on Hardness
(Ferrite) and Ductility
• Significantly enhances ferritic steel
hardness thru solid solutions as Si
content is increased;
• However, Si also promotes
precipitation of graphite;

7. Effect on Hardenability
• Si alone has only moderate effect
on hardenability;

8. Effect on Hardenability
• Shifts the TTT curve to longer times but
has little effect on Ms;
• Makes austenitization difficult by
stabilizing the ferrite phase;

9. Effect on
Hardenability
• However, in combination with other
alloying elements such as Mn, Cr, and
Mo:

10. Effect on
Hardenability

11. Notable commercial Silicon
Steels
Examples Components
Electrical Steels Oriented 3.0 ~ 3.25 wt% Si
Non-oriented 0.5 ~ 3.25 wt% Si, max 0.5
wt% Al
Spring Steels 1080 (A228) (Piano wires) 0.7–1.0% C, 0.2–0.6% Mn,
0.1–0.3% Si
50CrV4 (EN 10277) 0.47–0.55% C, max. 1.10%
Mn, 0.90–1.20% Cr, 0.10–
0.20% V, max. 0.40% Si
9255 0.50–0.60% C, 0.70–0.95%
Mn, 1.80–2.20% Si
HSLA Steels 0.9 wt% max Si

12. References
 Oberg, E.; et al. (1996), Machinery's Handbook (25th ed.), Industrial Press Inc
 McMaster-Carr catalog (116th ed.), McMaster-Carr, p. 3662, retrieved 3
September 2010.
 Drumond, J.; et al. (2012), Effect of Silicon Content on the Microstructure and
Mechanical Properties of Dual-Phase Steels, Met. Microstruct. Anal.