Annealing, normalising, stress relief

Last updated 2026-09-24 · route revision 2

These routes are not about hardness but about structure: getting the metal ready to cut, evening it out after forging, or taking stress out after welding.

Normalising

We heat above the critical point and cool in still air. Normalising evens out the structure of rolled stock and forgings and removes uneven grain; it is often placed before machining so the part cuts cleanly.

Annealing

Full annealing is cooled with the furnace down to 500 °C - slowly, or there is no point. It lowers hardness for cutting: 40Kh settles to 180–220 HB after annealing, and tool grade U8 to 170–207 HB.

Spheroidise annealing is a separate matter for ShKh15 and 9KhS: cooling with the furnace at about 20 °C/h gives a granular pearlite that is kind to both the cutter and the later quench. We will not take bearing-grade ShKh15 for quenching without that preparation.

Stress relief

After welding and rough machining we soak the part at 600–650 °C with the furnace: the stress leaves while hardness and size barely move. It is cheap insurance against distortion on the finishing cut.

Normalising and annealing need a smaller allowance, 0.2–0.3 mm per side, and stress relief 0.1–0.2 mm. The full allowance table is on the preparation page.