A2		Technical Data
BS4659 BA2 is a cold work, air hardening tool steel, which  offers high surface hardness in hardening, good wear resistance, great through hardenability. A2 tool steel is also characterised by its high dimensional stability after hardening and tempering, high compression resistance and good resistance to tempering.

Forging:
Heat slowly and uniformly to 700°C. Forge within a range of 1050/1100°C, reheating if necessary. Cool  ver y slowly (preferably in a furnace) to avoid setting up stresses.  

Annealing:
Heat uniformly to 850°C, equalise, then furnace cool. (Hardness about 215 Brinell). Fully machined tools should be packed during annealing.

Stress Relieving:
If machining operations have been heavy or if the tool has an unbalanced section, remove stresses before hardening by heating up to 675°C, equalise, then cool in furnace to 500°C  before slowly cooling in air.

Hardening:
Pre heat to 600/700°C and thoroughly soak. Continue heating to the final hardening temperature of 950/980°C. Allow sufficient time for the component to be heated through. Quench in oil or cool in air.

Martempering:
Martempering is an alternative hardening procedure which may be used when suitable salt bath equipment is available.

Tempering:
Heat uniformly and thoroughly at the selected tempering temperatures and hold for at least one hour per inch of total thickness.

Hard Chromium Plating:
After hard chromium plating tempering of A2 tool steel is recommended at 180°C for 4 hours to avoid hydrogen embrittlement.  Tempering is to be performed immediately after chromium plating.

Welding:
Due to the high risk of crack formation welding of A2 tool steel should be avoided, if possible. When, howe ver welding is essential, the following serves as a guide:

A.  Welding of soft annealed A2 tool steel
·       Preheat to 300 - 500°C.
·       Weld at  300-500°C.
·       Immediately stress relieve.
Electrode: Cr-Mo alloy electrode for welding structural steel.

B.  Welding in connection with hardening of soft annealed A2 tool steel.
·       Heat to austenitizing temperature.
·       Cool to approx. 500°C.
·       Weld at approx. 500°C.
·       Cool to approx. 100°C in the same way as at normal hardening, then temper to desired hardness.
Electrode: Hard facing electrode.

C.  Repair welding of A2 tool steel in hardened and tempered condition.
·       Preheat to the tempering temperature (min. 200°C) previously used.
·       Weld at tempering temperature.
·       Heat immediately to tempering temperature, but max. 300°C. Soaking time 3 hours.
·       Cool in air to approx. 80°C.
·       Heat to tempering temperature. Soaking time 2 hours.
Electrode: Hard facing electrode.

Physical Properties:	Temperature:
	20°C	200°C	400°C
Density (Kg/dm³)	7.75	7.70	7.65
Coefficient of thermal expansion (per °C from 0°C)	-	11.6 x 10-6	11.3 x 10-6
Thermal conductivity (cal/cm.s °C)	62.4 x 10-3	64.8 x 10-3	68.4 x 10-3
Specific heat (cal/g °C)	0.110
Modulus of elasticity:
Kp/mm²	19 370	18 900	17 325
N/mm²	189 900	185 200	169 800