Hot Forging (鍛造)

Description

Hot forging shapes scissor blades from heated steel billets for superior grain structure and strength. Learn why forged scissors outperform stamped and cast alternatives.

Hot Forging (鍛造 / tanzō)

Quick look

  • Process: Steel heated to ~1,100 °C and shaped under drop hammer dies or hydraulic presses.
  • Key benefit: Refines and aligns grain structure, producing denser, stronger metal than casting or stamping.
  • Cost position: Premium — slower cycle times, higher energy use, skilled operators required.
  • Where used: Japanese artisan workshops (Seki, Sakai, Tsubame-Sanjo), premium German manufacturers (Solingen).

Why it matters

Hot forging is the method closest to traditional bladesmithing. When steel is heated past its recrystallisation temperature and struck repeatedly, the internal grain structure compresses and realigns along the shape of the blank. The result is a piece of metal that is measurably stronger and more fatigue-resistant than the same alloy in cast or stamped form.

For professional scissors, that translates into blades that hold an edge longer, flex without cracking, and respond more predictably to sharpening — because the grain flows with the blade geometry rather than cutting across it.

Connection to Japanese sword forging (日本刀鍛造)

The scissor forging tradition in Seki City and Sakai descends directly from centuries of Japanese sword making (日本刀鍛造 / nihontō tanzō). The same principles apply: repeated heating and hammering expel impurities, close internal voids, and create a layered grain that resists fracture. Modern scissor forges have traded charcoal hearths for induction furnaces and hand hammers for precision drop hammers, but the metallurgical logic is unchanged.

How it works in practice

  1. Billet preparation: A rod or bar of scissor steel (VG-10, ATS-314, SUS440C, cobalt alloy, etc.) is cut to the approximate weight of the finished blank.
  2. Heating: The billet enters an induction or gas furnace and reaches forging temperature — typically 1,050-1,150 °C, where the steel glows bright orange-red.
  3. Die forging: The hot billet is placed between matched dies and struck by a drop hammer or squeezed by a hydraulic press. Multiple strikes progressively shape the rough scissor profile.
  4. Trimming: Flash (excess metal squeezed out at die edges) is trimmed while the blank is still warm.
  5. Normalising: The blank is allowed to air-cool slowly to relieve internal stresses before moving on to heat treatment.

Trade-offs

  • Pros: Superior grain structure, highest fatigue strength, best edge stability, honoured craft lineage.
  • Cons: Slow production, expensive tooling, requires experienced operators, limited to relatively simple shapes (complex handle designs may need secondary machining).

What to ask a manufacturer

If a brand claims “hand-forged” or “forged blades,” ask whether the entire blank is forged or only the blade portion. Some manufacturers forge only the cutting blade and weld it to a stamped or cast handle — which is a legitimate technique (two-piece welding) but different from a fully forged shear.

Sources

  1. S2 Hasami — Production Flow (Japanese)
  2. Manufacturing Regions — Seki City
Related processes: Cold Stamping Investment Casting Heat Treatment

Related Manufacturing processes