A2 Steel

Heat treatment

Precaution needs to be taken while heat treating A2 to prevent decarburization.

Annealing

A2 should be protected and be heated uniformly to a temperature of 1560°F (850°C). Cooling the furnace at 20°F (10°C) per hour to a temperature of 1200°F (650°C) and cool further then in air.

Stress relieving

To relieve stress after rough machining, heat the work piece to a temperature of 1200°F (650°C) and hold for 2 hours. Cool in the furnace to a temperature of 930°F (500°C) and further cool in air after.

Hardening

Preheat the work piece to a temperature of 1200-1300°F (650-750°C), then rapidly heat to 1690-1780°F (925-970°C) and hold for 30 minutes until the part is uniformly heated through. Then cool to room temperature in dry mild air. To prevent decarburization and oxidation, parts should be protected.

Quenching media

Quenching should be done as quickly as possible. To avoid excessive distortion and/or quench cracking cooling has to be uniformly and at a sufficient cooling rate should be considered.

• Oil for small and simple parts
• Vacuum furnace with overpressure of gas at cooling
• Circulating air or atmosphere
• Martempering bath or fluidized bed at 360-430°F (180-220°C) or 840-1020°F (450-550°C) followed by cooling in air

Tempering

As soon as the parts have reached a temperature of about 150°F (66°C) after quenching, they should be tempered immediately. The normal tempering temperature for A2 is a range from 300-500°F (149-260°C). For tools subjected to shock for example, a double temper is recommended at a temperature of 900-1000°F (482-538°C), holding the temperature for 1 hour at least for small parts and 1 hour per inch (25.4 mm) of thickness for larger pieces.

For our tempering diagram, please click here.

Dimensional changes

A2 like other tool steels will hold its size best when quenched from the accurate hardening temperature. A2 will shrink after tempering if it is overheated and should not be hardened from a temperature above 1175° (968°C) and expands when tempered below 600°F (316°C).

Sub-zero treatment and aging

For maximum dimensional stability, parts should be treated at sub-zero and/or artificially aged.

Sub-zero treatment

Immediately after quenching, the work piece should be sub-zero treated to between -40 to -110°F (-40 to -80°C), soaking them for 2-3 hours following tempering or aging. Sub-zero treatment will increase the hardness of 154-160 BHN (1-3 HRC). Due to cracking, it is not advised to use this treatment for intricate shapes.

Aging

For aging, tempering after quenching is replaced by aging at 230-285°F (110-140°C), holding time 25-100 hours.

Surface treatment

To reduce friction and increase wear and corrosion resistance some cold work tool steels are surface treated, using nitrading, titanium nitrading or hard chrome plating.

Nitriding

Nitrading gives the surface of the material a hard layer with an excellent resistance to wear and galling. To suit the application, the thickness of the layer should be considered well.

Electrical Discharge Machining (EDM)

Performing EDM in the hardened and tempered condition, remove the recast layer completely by stoning and polishing. Then giving the tool another temper at approx. 50°F (25°C) below the prior tempering temperature and soak at this temperature for 2 hours.

Forging

Heat the parts uniformly to a temperature range of 1950-2050°F (1066-1121°C), forging should be avoided below the temperature of 1700°F (927°C). Reheat the material as often as necessary. To cool larger parts heat the furnace to about 1550°F (843°C), place the part in the furnace and soak at this temperature until the parts are uniformly heated throughout, then turn of the furnace and let the work pieces cool slowly in the furnace. Note that this is not an annealing, the parts should be annealed as described here in the section “Annealing” after the parts have cooled down from forging.

Welding

Good results can be achieved when welding tool steel, if the proper precautions are taken during welding (increased working temperature, joint preparation, choice of filler metals and the welding procedure). In the event that the parts are to be polished or photo-etched, it is necessary to work with a suitable electrode type of matching composition.