Grade H21 is a high-performance tungsten-based hot-work tool steel designed for extremely high-temperature applications. It belongs to the H-series tungsten hot-work steels (H20–H26) and is known for its excellent heat resistance, thermal fatigue resistance, and red-hardness. H21 is capable of maintaining its hardness, strength, and dimensional stability at temperatures much higher than chromium-molybdenum grades like H11 and H13. Because of this, it is chosen for tooling exposed to continuous high heat, flame contact, rapid thermal cycling, or abrasive hot-working operations.

Key Properties of H21 Tool Steel

1. Outstanding High-Temperature Strength

H21 maintains hardness and structural stability at temperatures up to 650–700°C, making it suitable for extreme hot-working conditions.

2. Excellent Red-Hardness

The tungsten-rich composition retains hardness even under direct flame, hot metal flow, or prolonged heating.

3. Superior Thermal Fatigue & Fire Crack Resistance

H21 withstands repeated heating and cooling cycles without cracking—ideal for tools subjected to flame or molten material.

4. Good Abrasion Resistance at High Heat

The carbides formed by tungsten and chromium provide strong wear resistance even at elevated temperatures.

5. High Toughness (Compared to Other Tungsten Grades)

While harder and more heat-resistant than H13, H21 retains reasonable toughness, reducing the risk of catastrophic tool failure.

6. Good Hardening Ability

Typical working hardness after heat treatment: 45 – 55 HRC (depending on application).

Common Applications

H21 is widely used in industries requiring tooling that survives extreme heat exposure, including steel mills, foundries, forging shops, and aerospace manufacturing.

Typical applications:
1. Hot shear blades
2. Hot extrusion tooling
3. Drop forging dies & inserts
4. Punches for hot punching applications
5. Furnace tooling (fixtures, bars, rollers)
6. Mandrels and hot forming tools
7. Tools exposed directly to flame or molten metal
8. High-temperature wear plates and guide rails
9. Cutting tools for hot steel or billets

Summary

Grade H21 is an ultra-high-performance hot-work tool steel built for extreme temperatures and severe thermal shock environments. Its tungsten-based alloy system provides unmatched red-hardness, wear resistance, and heat stability beyond what H11 or H13 can offer. For operations involving continuous high heat, flame contact, or hot metal forming, H21 is one of the most reliable and durable steels available.