Topics CoveredIntroductionChemical CompositionPhysical PropertiesMechanical PropertiesThermal PropertiesOther DesignationsFabrication and Heat Treatment Heat Treatment Forging Annealing TemperingApplications
Cold-work tool steels include the high-carbon, high-chromium steels or group D steels. These steels are designated as group D steels and consist of D2, D3, D4, D5, and D7 steels. These steels contain 1.5 to 2.35% of carbon and 12% of chromium. Except type D3 steel, all the other group D steels include 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 tends to be brittle during hardening. Type D2 steel is the most commonly used steel among the group D steels.
The following table shows the chemical composition of D2 tool steels.
||1.40 – 1.60|
||11.00 – 13.00|
||0.70 – 1.20|
The physical properties of D2 tool steels are outlined in the following table.
||7.7 x 1000 kg/m3
The mechanical properties of D2 steels are tabulated below:
|Hardness, Knoop (converted from Rockwell C hardness)
|Hardness, Rockwell C
|Izod impact unnotched
The following table shows the thermal properties of D2 steels.
||10.4 x 10-6/ºC
Equivalent materials to D2 tool steels are:
- DIN 1.2379
- NI KU
- B.S. BD 2
- ASTM A681
- FED QQ-T-570
- SAE J437
- SAE J438
- UNS T30402
Fabrication and Heat Treatment
D2 steels should be preheated very slowly to 815ºC (1500ºF) and then temperature can be increased to 1010ºC (1850ºF). They are then held at 1010ºC (1850ºF) for 20 to 45 minutes and air cooled (air quenched).
Forging of D2 steels can be done from 1065ºC (1950ºF) down to 954ºC (1750ºF). Do not forge below 926ºC (1700ºF).
Annealing of D2 steels should be done at 871 to 898ºC (1600 to 1650ºF) followed by slow furnace cooling at 4.4ºC (40ºF) per hour or less.
D2 steels can be tempered at 204ºC (400ºF) for achieving Rockwell C hardness of 61 and at 537ºC (1000ºF) for a Rockwell C hardness of 54.
D2 tool steels are used for long run tooling applications, where wear resistance is important, such as blanking or forming dies and thread rolling dies.