Sep 18 2012
Topics Covered
IntroductionChemical CompositionPhysical PropertiesMechanical PropertiesThermal PropertiesOther DesignationsFabrication and Heat Treatment Machinability Forming Welding Heat Treatment Forging Cold Work Annealing TemperingApplications
Introduction
Tungsten hot-work steels are of different types, namely, H21 to H26 types. These steels have similar characteristics to that of high-speed steels. The primary alloying elements of tungsten hot-work steels include tungsten, chromium, carbon, and vanadium. The tungsten hot-work steels are resistant to distortion when they are air-hardened, and have higher hardening temperature when compared to chromium hot-work steels. Breakage of the tungsten hot-work steels can be reduced if they are preheated to operating temperature before use. Thermal shock resistance and toughness of these steels can be improved by reducing the carbon content.
The following datasheet will provide details of H26 tungsten hot-work tool steels. This alloy has higher tungsten content and good resistance to softening when used in high temperature applications.
Chemical Composition
The following table shows the chemical composition of H26 tool steels.
| Element |
Content (%) |
| C |
0.45-0.55 |
| Mn |
0.15-0.40 |
| Si |
0.15-0.40 |
| Cr |
3.75-4.50 |
| Ni |
0.3 |
| W |
17.25-19.00 |
| V |
0.75-1.25 |
| Cu |
0.25 |
| P |
0.03 |
| S |
0.03 |
Physical Properties
The physical properties of H26 tool steels are outlined in the following table.
| Properties |
Conditions |
| T (°C) |
Treatment |
| Density |
8.67 x 1000 kg/m3 |
25 |
- |
Mechanical Properties
The mechanical properties of H26 tool steels are tabulated below.
| Properties |
Conditions |
| T (°C) |
Treatment |
| Poisson's ratio |
0.27-0.30 |
25 |
- |
| Elastic modulus |
27557-30458 ksi |
25 |
- |
Thermal Properties
The table below shows the thermal properties of H26 tool steels.
| Properties |
Conditions |
| T (°C) |
Treatment |
| Thermal expansion |
12.4 x 10-6/ºC |
20-540 |
- |
Other Designations
Other designations that are equivalent to AISI H26 tungsten hot-work tool steels include:
- ASTM A681
- FED QQ-T-570
- UNS T20826
Fabrication and Heat Treatment
Machinability
The machinability of H26 tool steels is medium, and rates at 60% in comparisons to the W tool steels group which is rated at 100%.
Forming
H26 steels can be formed using conventional methods.
Welding
H26 tool steels can be welded.
Heat Treatment
This process requires the H26 steels to be preheated to 871°C (1600°F) and then heated rapidly to 1218°C (2225°F). Then they should be held at the same temperature for 2 to 5 minutes and finally air cooled, oil or salt bath quenched.
Forging
Forging of the H26 steels can be performed at 1150°C (2100°F) down to 968°C (1775°F) but not below 954°C (1750°F).
Cold Work
H26 tools steels can be cold-worked using conventional methods.
Annealing
Annealing can be performed at 885°C (1625°F) followed by slow cooling process at a temperature of 4°C (40°F) per hour.
Tempering
Tempering of H26 steels is performed at 566 to 677°C (1050 to 1250°F) to realize Rockwell C hardness of 58 to 43. A double tempering process can also be performed for better results.
Applications
H26 tungsten hot-work tool steels are applied in areas of hot-forming temperatures including hot-extrusion or forming dies.