Cold-work tool steels are steels with a high carbon content and relatively low amounts of chromium, molybdenum, tungsten and manganese. These steels, in the annealed state, have carbide and ferrite, mainly Fe3C, in addition carbide formers. These steels are inexpensive compared to other steels and resist deformation during heat treatment.
Cold-work tool steels can be used between 205 and 260°C (400 to 500°F) as they have low softening resistance at elevated temperatures due to insufficient alloy content. However, hardenability of the cold-work steels is improved upon addition of alloys and thus allowing oil quenching with less distortion when compared to the water-hardening steel tools.
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. Type D2 steel is the most commonly used steel among the group D 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.
The key properties of group D steels are the following:
- High resistance to softening at high temperatures
- Excellent wear resistance (especially type D7 steel, which has the highest carbon and vanadium contents)
- Susceptibility to edge brittleness (especially D3, D4, and D7 type steels as they contain carbides in large quantities)
The following table shows the composition limits of high-carbon, high-chromium cold-work steels.
|High-carbon, high-chromium cold-work steels|
aAll the steels (except group W) contain 0.25 max Cu, 0.03 max P, and 0.03 max S; Group W contains 0.20 max Cu, 0.025 max P, and 0.025 max S. Where mentioned, sulfur can be increased from 0.06 to 0.15% to enhance machinability of group A, D, H, M, and T steels.
The major applications of the high-carbon, high-chromium cold-work steels are the following:
|Press forming dies
||Dies for cutting laminations
||Molds for wire cutting|
|Forming and banding rolls
||Molds for shaping wheels|
||Molds for rolling cutters|
||Thread rolling dies
||Blanking dies |