
428 Engineering Materials Technology
high temperatures result) since they do not remain hard at high temperatures.
An example of such a steel is BOl which has 0.90 per cent carbon, 0.50 per cent
tungsten, 0.50 per cent chromium and 1.0 per cent manganese. Such a material
is used for blanking dies, bending and forming dies, taps, etc. Because oil
quenching is used there is less distortion, cracking and dimensional change
than with water quenching. However, these changes are even further reduced
with air-hardening tool steels.
Air-hardening tool steels are used where toughness is the main requirement.
They are used for blanking dies, forming