Sep 13 2012
Topics Covered
IntroductionChemical CompositionPhysical PropertiesMechanical PropertiesThermal PropertiesProcessing 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 in tungsten hot-work steels include tungsten, chromium, carbon, and vanadium. They 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 H21 tungsten hot-work tool steels. The tungsten content in this alloy provides hot strength at red heat.
Chemical Composition
The following table shows the chemical composition of H21 tools steels.
| Element |
Content (%) |
| C |
0.26-036 |
| Mn |
0.15-0.40 |
| Si |
0.15-0.50 |
| Cr |
3.00-3.75 |
| Ni |
0.3 |
| W |
8.50-10.00 |
| V |
0.30-0.60 |
| Cu |
0.25 |
| P |
0.03 |
| S |
0.03 |
Physical Properties
The physical properties of H21 tool steels are outlined in the following table.
| Properties |
Metric |
Imperial |
| Density |
8.19 g/cm3 |
0.296 lb/in3 |
| Melting point |
1432°C |
2610°F |
Mechanical Properties
The mechanical properties of H21steels are tabulated below.
| Properties |
Metric |
Imperial |
| Hardness, Rockwell C |
40.0 - 55.0 |
40.0 - 55.0 |
| Bulk modulus |
140 GPa |
20300 ksi |
| Shear modulus |
80.0 GPa |
11600 ksi |
| Poisson's ratio (25°C) |
0.27-0.30 |
0.27-0.30 |
| Elastic modulus |
190-210 GPa |
27557-30458 ksi |
Thermal Properties
The below table shows the thermal properties of H21 tool steels.
| Properties |
Metric |
Imperial |
| CTE, linear |
12.4 μm/m°C |
6.89 μin/in°F |
| Thermal conductivity |
27.0 W/mK |
187 BTU-in/hr-ft2°F |
Processing Properties
The following table provides the processing properties of H21 tool steels.
| Properties |
Metric |
Imperial |
| Processing temperature (tempering) |
595 - 675°C |
1100 - 1250°F |
| Processing temperature (tempering) |
1095 - 1205°C |
2003 - 2201°F |
| Annealing temperature (hardening) |
870 - 900°C |
1600 - 1650°F |
Other Designations
Other designations that are equivalent to AISI H21 tungsten hot-work tool steels include:
- DIN 1.2581
- JIS SKD5
- B.S. BH 21
- UNI X 28 W O9 KU
- ASTM A681
- FED QQ-T-570
- SAE J437
- SAE J438
- UNS T20821
- AFNOR Z 30 WCV 9
Fabrication and Heat Treatment
Machinability
The tungsten content in the H21 steels makes it difficult to machine in comparison to water hardening low alloy steels with 100% machinability while H21 is rated at 55%.
Forming
H21 steels can be formed using conventional methods.
Welding
H21 steels can be welded.
Heat Treatment
This process requires the H21 steels to be preheated to 816°C (1500°F) and then heated rapidly to 1177°C (2150°F). Then these steels should be held at the same temperature for 2 to 5 minutes and finally air cooled or oil quenched.
Forging
Forging of the H21 steels can be performed at 1150°C (2100°F) down to 927°C (1700°F) but not below 899°C (1650°F).
Cold Work
H21 steels can be cold-worked using conventional methods.
Annealing
Annealing should be performed at 885°C (1625°F) followed by slow furnace cooling at a temperature less than 4°C (40°F) per hour.
Tempering
Tempering of the H21 steels is performed at 593 to 677°C (1100 to 1250°F) to realize Rockwell C hardness of 54 to 36. A double tempering process is advisable and the parts should be maintained at same temperature for one hour.
Applications
The H21 tungsten hot-work tool steels are mainly used for hot-working dies and toolings, e.g., die casting, extrusion and hot-forming of parts.