AISI A2 Tool Steel

A2 Tool Steel (UNS T30102) - Air-Hardening

Forging

A2 tool steels are forged between 1093°C to 913°C (2000°F to 1675°F). These tool steels should not be forged below 899°C (1650°F).

Annealing

Annealing must be performed after hot working and before re-hardening.
Heat at a rate not exceeding 400°F per hour (222°C per hour) to 1550°F (843°C), and hold at temperature for 1 hour per inch (25.4mm) of maximum thickness; 2 hours minimum.

Then cool slowly with the furnace at a rate not exceeding 50°F per hour (28°C per hour) to 1000°F (538°C). Continue cooling to ambient temperature in the furnace or in air. The resultant hardness should be a maximum of 235 HBW.

Hardening

Critical Temperature: Ac1: 1460°F (793°C)

Preheating: 1200–1380°F (650°C-750°C). Tool wrap will have to be used when placing the knife in the furnace at the start of preheat. Anti-scaling paint like Condursal will not withstand the low temperatures and as such can only be used if the knife is placed in the furnace after it has reached a nominal 650°C

Preheating of complicated parts: Heat at a rate not exceeding 400°F per hour (222°C per hour) to 1150-1250°F (621-677°C) and equalize.

Preheating step 2: Heat slowly to 788°C (1450°F) and this is followed by increasing too the high heat.

Austenitizing (High Heat): Heat slowly from the preheat temperature to 1760°F (960°C) Soak for 30 to 45 minutes for the first inch (25.4 mm) of thickness.

Quenching: Air, plate quench or interrupted oil to 150-125°F(66-51°C).
For the oil quench, quench until black, about 900°F (482°C), then cool in still air to 150-125°F(66-51°C).

CCT Graph

Tempering: Temper immediately after quenching. Hold at temperature for 1 hour per inch (25.4 mm) of thickness, 2 hours minimum, then air cool to ambient temperature. The typical tempering range is 350 to 500°F (177 to 260°C).

177°C (350°F) for Rockwell C 62
538°C (1000°F) for Rockwell C 56

Cryogenic Treatment:

Pieces requiring maximum dimensional stability should be sub-zero and/or artificially aged as volume changes may arise in the course of time. This applies, for example, to measuring tools like gauges and certain structural components.

Immediately after quenching, the piece should be cooled to sub-zero temperatures between –40°F and –110°F (–40°C and –80°C) followed by tempering.
Sub-zero cooling for 2–3 hours will provide a hardness increase of 1–3 HRC. Avoid intricate shapes as there is a risk of cracking.

Alternatively, sub-zero treatment can be done between first and second tempers.

This will have less effect, but safer with respect to risk cracking.