The supply condition drastically alters the microstructure and, consequently, the mechanical properties of 42CrMo.
Annealed (+A): The steel is heated and slowly cooled to produce a soft, coarse microstructure (pearlite and ferrite). This maximizes machinability and ductility but offers low strength.
Typical Hardness: 180 - 220 HBW
Tensile Strength: ~650 - 800 MPa
Purpose: Ideal for extensive machining prior to final heat treatment by the customer.
Quenched and Tempered (+QT): As described above, this involves austenitizing, rapid quenching (in oil), and tempering. This produces a fine, strong microstructure (tempered martensite/bainite).
Typical Hardness: 270 - 320 HBW (adjustable via tempering)
High Strength and Good Toughness: See table in Q7.
Purpose: Supplied ready for final machining/grinding and use in high-stress applications.
Normalized (+N): Heated to austenitizing temperature and air-cooled. Provides a finer grain structure than annealed, with slightly higher strength, but properties are inferior to +QT.
Hot-rolled (+HR) or Black: As-rolled from high temperature, with a decarburized surface scale. Properties are non-uniform and not guaranteed for critical use; it often requires further processing.