1.
: Typically increases both tensile strength (by 5–10%) and yield strength (by 3–7%) compared to the as-rolled state. This is due to grain refinement and the formation of a more uniform ferrite-pearlite structure, which enhances interatomic bonding and resistance to deformation.
: Slightly reduces tensile and yield strength (by 2–5%) as the process softens the material by relieving internal stresses and coarsening pearlite lamellae marginally, prioritizing ductility over strength.
: Has minimal impact on strength, as it focuses on reducing residual stresses without altering the primary microstructure.
2.
: Improves elongation by 1–3% (e.g., from 22% to 24–25% in some cases). The refined, uniform grain structure allows greater plastic deformation before fracture, as fine grains distribute stress more evenly.
: Significantly enhances ductility (elongation increases by 3–5%) by softening the steel and reducing grain-boundary restrictions, making it more malleable for forming processes.
Rapid Cooling (Post-Normalization): May slightly reduce ductility if cooling is too fast, as it can introduce minor microstructural inhomogeneity (though this effect is limited in Q295GNH due to low hardenability).
3.
: Markedly improves impact toughness (e.g., Charpy V-notch energy increases by 15–25%). Fine-grained microstructure and uniform phase distribution reduce stress concentration, allowing the material to absorb more energy during impact before fracturing.
: Improves toughness moderately (5–10% increase) by relieving internal stresses that could act as fracture initiation points, though its effect is less pronounced than normalization.
Slow Cooling (Post-Normalization): Degrades toughness by promoting coarse grain growth and uneven pearlite formation, which create brittle zones prone to crack propagation.
4.
: Increases hardness slightly (by 5–10 HB) due to finer pearlite and grain refinement, which enhance resistance to indentation.
: Reduces hardness (by 10–15 HB) as the material softens, making it easier to machine or weld.
: Has negligible effect on hardness, as it does not alter the microstructure's phase composition.
5.
: Enhances weathering corrosion resistance indirectly. By homogenizing the distribution of alloying elements (Cu, Cr, Ni), it promotes the formation of a denser, more uniform protective oxide film on the surface, slowing down corrosion.
: Can diminish corrosion resistance if microstructural inhomogeneity occurs (e.g., segregation of alloy elements), as it creates localized areas more susceptible to corrosion.
