Heat Treatment — Normalising of Hypo-Eutectoid Steel Is this statement accurate: “In the normalising process, a hypo-eutectoid steel is heated 30–50° C above the upper critical temperature (A3) and then cooled in still air”?

Introduction / Context:
Normalising is a common heat treatment to refine grain size, homogenise microstructure, and improve mechanical properties prior to machining or service. It differs from full annealing mainly in the cooling stage and slightly in the austenitising temperature range.

Given Data / Assumptions:

• Material: hypo-eutectoid steel (less than 0.8% carbon).
• Temperature: 30–50° C above the upper critical temperature A3.
• Cooling medium: still air (not furnace cooling).

Concept / Approach:
For hypo-eutectoid steels, normalising involves heating above A3 to fully convert ferrite plus pearlite into austenite. Cooling in still air leads to a finer pearlitic structure than full annealing, which uses slower furnace cooling and typically yields coarser pearlite and greater softness. The specified temperature margin (30–50° C above A3) is standard to ensure full austenitisation without excessive grain growth.

Step-by-Step Solution:
Identify critical temperatures: A1 (eutectoid), A3 (upper critical for hypo-eutectoid steels).Heat to A3 + 30–50° C to obtain homogeneous austenite.Cool in still air to produce refined pearlite/ferrite, improving strength and machinability.Therefore, the statement aligns with normalising practice.

Verification / Alternative check:
Shop procedures and textbooks specify air cooling for normalising and furnace cooling for full anneal; this confirms the distinction.

Why Other Options Are Wrong:
“False” or “furnace cooling” contradicts the definition of normalising.Oil quenching is not part of normalising and would produce martensite, not normalised structure.Eutectoid steels use A1 as reference; the prompt explicitly names hypo-eutectoid steels.

Common Pitfalls:
Confusing normalising with annealing or normalising with hardening; cooling medium differentiates these processes.

Final Answer:
True