🔑 Prior Austenite Grain Size
The "hidden memory" of steel - affects hardenability, toughness, and final properties even after heat treatment.
⚡ Thermal + Transformational Stress
Two types of stresses during quenching: thermal (temperature gradient) and transformational (volume change). Both cause cracking.
🎲 Hardenability vs Hardness
Hardenability = depth of hardening. Hardness = surface hardness value. Different concepts!
💾 Process Memory of Steel
Steel "remembers" its thermal history - overheating, prior microstructure, and processing path affect final properties permanently.
⚖️ Strength–Toughness Trade-off
Higher strength usually means lower toughness. Bainite offers better balance than martensite.
🧪 Alloying Elements Role
Chromium - hardenability; Nickel - toughness; Molybdenum - temper embrittlement resistance; Silicon - deoxidizer but reduces toughness.