1. Limited hardenability during quenching
During quenching (rapid cooling from austenitizing temperature), the steel cannot form significant amounts of martensite (the hard, strong phase achieved in high-alloy steels). Instead, it primarily forms ferrite and pearlite, similar to normalization but with slightly finer grain structure due to faster cooling.
Little to no increase in hardness or strength is achieved compared to normalization. In most cases, quenching does not meaningfully improve tensile/yield strength beyond what normalization can achieve.
2. Tempering after quenching: Marginal effects
If quenching produced minor residual stresses or slight microstructural inhomogeneity, tempering could relieve these stresses, marginally improving toughness. However, this effect is negligible compared to the stress relief achieved by standard normalization.
Tempering may slightly reduce any minimal hardness gained from quenching, but since quenching itself does not significantly harden Q295GNH, the overall effect on mechanical properties is insignificant.
3. Potential drawbacks
Increased brittleness risk: Excessively rapid quenching (e.g., water cooling) may introduce thermal stress, leading to microcracks or reduced ductility, especially in thick sections.
Wasted energy: Quenching and tempering require more complex processing (higher temperatures, controlled cooling media) than normalization but provide no meaningful performance benefits for Q295GNH.
Corrosion resistance impact: Abnormal heat treatment (e.g., overheating during quenching) could disrupt the uniform distribution of alloying elements (Cu, Cr), impairing the formation of the protective oxide film critical for weathering resistance.
