What is the heat treatment process?

flowchart LR
    A[Heat Treatment] --> B[Annealing\nsoften, relieve stress]
    A --> C[Normalising\nfiner structure, better strength]
    A --> D[Hardening\nquench → martensite]
    A --> E[Tempering\nhardness↔toughness]
    A --> F[Surface Hardening\nwear-resistant skin]

• Definition: controlled heating and cooling to change steel’s structure and properties without changing shape
• Main processes: annealing, normalising, hardening, tempering, surface hardening
• Annealing: heat + slow furnace cool → softens, relieves stress, refines grain
• Normalising: heat + air cool → finer, more uniform structure, better strength
• Hardening: rapid quench from austenitic range → carbon trapped as martensite (hard, brittle)
• Tempering: reheat hardened steel to lower temperature → trades hardness for toughness, relieves quench stress
• Surface hardening: carburising, nitriding, induction/flame → hard wear-resistant skin on tough core
• Prediction: TTT/CCT diagrams predict structure from cooling rate
• Regulatory context: IACS UR W7 §5.3, W8 §5.3, W27 §6 require properly constructed furnaces with temperature control and recording