1. Effects of Heating Temperature
(a) Optimal (850–1050°C)
Microstructure: Uniform austenite (soft, ductile, ideal for deformation).
Properties: Easy to forge/roll; post-cooling ferrite-pearlite microstructure ensures balanced strength (≥345 MPa) and toughness. Cr/Cu dissolves evenly, preserving weather resistance.
(b) Undertemperature (<850°C)
Microstructure: Incomplete austenitization (residual hard ferrite/pearlite).
Properties: Poor workability (prone to cracking); uneven strength/toughness.
(c) Overheating (>1050°C)
Microstructure: Coarse austenite; Cr/Cu segregates at grain boundaries.
Properties: Reduced toughness (coarse grains); uneven patina formation (weakened weather resistance); surface scale/decarburization.
2. Effects of Cooling Rate
(a) Slow (Air/Furnace Cooling – Standard)
Microstructure: Fine ferrite-pearlite.
Properties: Balanced strength/ductility (elongation ≥20%); high toughness; even Cr/Cu distribution (consistent weather resistance).
(b) Medium (Forced Air)
Microstructure: Ferrite-bainite (finer grains).
Properties: Higher strength (400–450 MPa); slightly lower ductility; toughness retained.
(c) Rapid (Water Quenching – Rarely Used)
Microstructure: Brittle martensite.
Properties: Extreme hardness but near-zero ductility (prone to cracking); poor weldability; stress corrosion risk.
