Why Can the Same Grade Behave Differently in Different Delivery Conditions?

The properties of a material are not determined by its chemical composition alone. The heat treatment history that sets the microstructure, in other words the delivery condition, can make the same grade behave very differently.

Common delivery conditions

• Soft annealed (+A): Low hardness, easy machining. Tool steels are usually supplied in this condition; the working hardness is obtained later by heat treatment.
• Pre-hardened: Supplied within a defined hardness range; it can be machined and used without further heat treatment. Common for plastic mould steels (e.g. 1.2311, 1.2738).
• Quenched and tempered (+QT): A balance of strength and toughness after hardening and tempering. Values depend on the section size.
• Normalised (+N): Aims at a finer and more uniform structure.
• Solution treated / aged: In PH stainless steels and some nickel alloys, properties depend on the aged condition (e.g. H900, H1025, H1150 for 17-4 PH).

What changes?

• Hardness and strength
• Toughness and ductility
• Machinability and tool wear
• Dimensional change behaviour in subsequent heat treatment
• In some cases, corrosion behaviour

What to watch for in an order

• State the delivery condition with its code or a clear description (e.g. +A, +QT, H1025).
• Write the hardness or mechanical property requirement together with the relevant delivery condition.
• If pre-hardened material is required, state the hardness range.
• For values that depend on section size, clarify the size and the sampling location.

In requests without a stated delivery condition, the supplier may assume its own standard delivery condition. This can result in material that differs from what was expected.