Forging, Heat Treatment and Forming
What the domain tests
Forging, Heat Treatment and Forming tests how heat changes metal, how to forge and bend safely, and how to select annealing, normalizing, hardening and tempering treatments. You must link treatment to properties.
Core rules
- Forging is hot deformation above the recrystallization temperature. Heat the metal evenly to a suitable colour, forge within the plastic range, and avoid burning or overheating.
- Annealing softens, relieves stress and improves machinability; normalizing refines grain structure; hardening forms martensite by rapid quenching; tempering reduces brittleness after hardening.
- Carbon content controls response: low-carbon steel does not harden much; medium- and high-carbon steels respond. Quench medium depends on steel: water for simple carbon steels, oil for alloy tool steels.
- Temper after hardening. Temper colours indicate temperature ranges: pale straw for cutting tools, blue for springs.
- Use tongs, face shields and dry floors; confine hot work away from flammables.
Worked example
A 0.7% carbon cold chisel is heated to about 780–800°C (cherry red), quenched in water, then tempered. The cutting edge is polished and reheated until a straw colour appears, then quenched again. This leaves the edge hard and wear-resistant while the body is less brittle. If the whole chisel were left fully hard, it could shatter under hammering.
Traps
Do not quench high-carbon steel and skip tempering. Do not judge temperature only by colour in poor light. Overheating causes grain growth and decarburization; underheating gives incomplete hardening. Never forge or heat galvanized metal without fume control.