OIL HARDENING TOOL STEEL, Carbon 0.85, Manganese 1.18, Silicon 0.26, Chromium 0.50, and
Tungsten 0.44 per cent.
HIGH CARBON HIGH CHROMIUM TOOL STEEL, Carbon 1.55, Manganese 0.27, Silicon 0.45,
Chromium 11.34, Vanadium 0.24, Molybdenum 0.53 per cent.
MOLYBDENUM HIGH SPEED STEEL, Carbon 0.80, Manganese 0.24, Silicon 0.29, Chromium 4.15,
Vanadium 1.89, Tungsten 6.64, and Molybdenum 4.94 per cent.
CHROMIUM MOLYBDENUM HOT WORK STEEL Carbon 0.38, Manganese 0.40, Molybdenum 1.35,
Nickel 0.30 per cent, Steel of the first analysis listed is usually referred to as plain carbon steel, and is
also frequently a water hardening or shallow hardening tool steel.
The next analysis is characteristic of Steels referred to as Oil Hardening, and differs from the first type
primarily in harden ability. This is the basic type of tool steel that I have used for over 30 years. Because
of its greater harden-ability, relatively large tools made of this steel can be hardened by an oil quench
rather than a water quench.
Tools made of the oil hardening tool steels do undergo as much size change and distortion during
hardening as those made from plain carbon steels.
STEELS OF THE THIRD ANALYSIS
Is referred to as a high carbon, high chromium steel or as an air hardening tool steel.
The last two steels are not used in the small shops, as they require special equipment to process them.
HOW HEATING CHANGES THE STRUCTURE OF TOOL STEEL
The first step in the heat treatment of steel is the heating. The purpose of the heating is to form austenite
and to dissolve carbon in the austenite. The solution of the carbon is necessary so in the second step of
heat treatment, when the transformation of austenite takes place, the steel will develop the desired
hardness.
You must remember that although a large amount of carbon is in the steel, it is not effective in
developing hardness unless it is first dissolved in the austenite. The hardness increases rapidly up to 60
Rc as the carbon increases to 0.40 to 0.70%. Above about 0.70 % carbon, the hardness remains
practically constant.
For maximum hardness in the steel, therefore, approximately 0.70 % of carbon must be dissolved in the
austenite. All of the steels being discussed except the chromium molybdenum hot work steel have
sufficient carbon in the analysis to attain a hardness of 65 Rc.