What is Annealing?

Description

Annealing is a heat treatment process where steel is heated to 800-870°C then slowly cooled to soften it for machining and shaping. It produces the lowest hardness state of the steel and is reversed by later quenching during the hardening process.

What is Annealing?

Annealing is a heat treatment process where steel is heated to 800-870°C and then slowly cooled — typically in the furnace — to produce the softest possible microstructure. This makes the steel easy to machine, grind, drill, and shape into blade profiles before the hardening heat treatment that gives the blade its final properties.

Why It Matters for Scissors

Scissor blades require extensive machining before hardening: cutting the blank, drilling the pivot hole, rough grinding the blade profile, and shaping the finger rings. All of these operations are dramatically easier — and produce better results — when performed on soft, annealed steel.

Proterial specifies a delivery hardness of HBW 272 maximum (approximately HRC 26) for their GIN-series scissor steels in the annealed condition. At this hardness, standard tooling can cut and shape the steel efficiently. Attempting to machine hardened steel at HRC 58-62 would destroy cutting tools rapidly and introduce heat damage to the blade.

The annealing process also homogenizes the microstructure, breaking up any banding or segregation from the original steel production. This produces more uniform properties throughout the blade after final heat treatment — meaning consistent hardness from heel to tip and from spine to edge.

Technical Detail
Full annealing of scissor steels involves heating to just above the upper critical temperature (Ac3) — typically 800-870°C depending on the alloy — holding for sufficient time to fully austenitize, then cooling very slowly (usually 10-30°C per hour) through the transformation range. The slow cooling allows the austenite to transform completely into a mixture of ferrite and spheroidized carbides, rather than the pearlite lamellae that would form at faster cooling rates. Spheroidized annealing, where carbides form into rounded particles rather than plates, produces the best machinability and is preferred for scissor steel processing. Proterial publishes the following annealing specifications for their scissor-grade steels: - **GIN-1 (Silver-1):** 840-870°C, slow cool, HBW ≤ 262 - **GIN-3 (Silver-3):** 800-850°C, slow cool, HBW ≤ 255 - **GIN-5 (Silver-5):** 830-870°C, slow cool, HBW ≤ 272 - **ZDP-189:** 830-870°C, slow cool, HBW ≤ 280 Takefu Special Steel similarly specifies annealing at 830-880°C for VG-10 with furnace cooling to below 600°C before air cooling to room temperature. It is critical that annealing is performed in a controlled atmosphere or vacuum to prevent decarburization — the loss of carbon from the steel surface. Decarburized steel will not achieve full hardness after quenching, producing a soft surface layer that quickly dulls. While subsequent grinding removes some surface material, excessive decarburization during annealing can extend deeper than the grinding allowance. Some manufacturers use subcritical annealing (heating to just below the lower critical temperature, around 700-750°C) as a faster alternative. This does not fully austenitize the steel but softens it sufficiently for most machining operations while reducing furnace time and energy consumption.

Sources

Frequently Asked Questions

Steel arrives from the mill in a relatively hard state. Annealing softens it to allow cutting, drilling, grinding, and shaping of the blade profile without excessive tool wear or cracking.

No. Annealing is completely reversed during the subsequent quenching step. The final hardness depends on the austenitizing temperature and quench, not the annealed starting condition.

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