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Silicon in Steels
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- 2. Silicon Type Metalloid Melting Point1414 °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 SteelSteel 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 A1with increasing concentration; • Decreases the eutectoid C content with increasing concentration; Effect on Phase Transformation
- 5. • Slows downaustenite 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:
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- 11. Notable commercial Silicon Steels ExamplesComponents 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.