Cold-work tool steels which include D2, D3, D4, D5, and D7 steels are high-carbon, high-chromium steels. Apart from D3 steel all group D steels have 1% Mo and are air hardened. Type D3 steel is oil-quenched; though small sections can be gas quenched after austenitization using vacuum. As a result, tools made with type D3 steel tend to be brittle during hardening. Type D2 steel is the most commonly used steel among the group D steels. The D3 steels contain 1.5 to 2.35% of carbon and 12% of chromium.
Equivalent metals of D3 steel are:
- AFNOR Z 200 C 12
- DIN 1.2080
- UNI X 21O Cr 13 KU
- JIS SKD1
- B.S. BD 3
- ASTM A681
- FED QQ-T-570
- SAE J437
- SAE J438
- UNS T30403
- Annealing of D3 tool steel needs to be done in a controlled atmosphere furnace.
- D3 tool steels should be heated thoroughly to 871°C (1600°F) and cooled slowly at a rate of not more than -6°C (20°F) per hour, until the furnace is black.
- Then the material should be removed and air cooled.
- D3 tool steel requires hardening and tempering to achieve maximum properties.
- For maximum accuracy, the parts of D3 tool steel should be stress relieved after roughing operations.
- Stress should be relieved at 648°C (1200°F) for one hour and cooled slowly.
- Tempering The D3 tool steel should be cooled to room temperature and should be tempered immediately.
- The parts should be placed in the tempering furnace and increased slowly to the desired tempering temperature.
- D3 tool steel should be heated properly since it is very sensitive to overheating and if not heated maximum hardness cannot be achieved.
- The work should be directly placed in a furnace preheated to 954°C (1750°F) and soaked for 20-25 minutes, plus 5 minutes per inch of thickness, and then oil-quenched to harden it.
The following table shows the thermal properties of D3 steels:
|Thermal expansion 12 x 10-6/ºC||20-100||-|
Physical properties of D3 tool steels are given below:
|Density||7.7 x 1000 kg/m3||0.278 lb/in3|
The mechanical properties of D3 steels are tabulated below:
Tempering for 1 hour per inch of thickness is required:
|Izod impact unnotched||28.0 J||20.7 ft-lb|
|Elastic modulus||190-210 GPa||27557-30457 ksi|