H11 Hot Work Tool Steel Bars (AISI SAE Alloy Tool Die Steel)

Product Description

AISI H11 (classified under standard ASTM A681) is a 5% chromium hot-work tool steel engineered for structural stability, excellent red-hardness, and extreme toughness under cyclic thermal conditions.

Within the SAE/AISI classification system, H11 represents the ideal choice when a tool or component faces massive mechanical shock loads that would cause other hot-work steels (like H13) to crack or split catastrophically.

AISI H11 Chemical Composition (ASTM A681)

H11 utilizes a balanced carbon-to-chromium ratio paired with a low vanadium content. This prevents the formation of massive, coarse primary carbides, resulting in a highly uniform microstructure that yields exceptional fracture toughness.

Mechanical Properties & Design Attributes

• Resistance to Thermal Shock: The lower vanadium content maximizes structural ductility, allowing H11 to endure rapid water-cooling cycles or sudden surface temperature spikes without developing immediate heat checks.

• Deep Air-Hardening: Large cross-sectional bars harden uniformly from surface to core when quenched in moving air or pressurized gas, minimizing internal residual stresses.

• High Tensile Strength: Due to its excellent tempering response, H11 can be heat-treated to ultra-high tensile levels (over 1,500 MPa / 217 ksi) while maintaining enough structural yield to resist brittle failure.

Heat Treatment Standards for AISI H11

Proper thermal processing is critical to ensure that alloy carbides dissolve completely into the matrix without promoting grain boundary segregation.

1.Spheroidize Annealing:Delivered State.

Heat uniformly to 845C870C (1550F1600F). Cool slowly in the furnace at a rate of $\le$ 11C (20F) per hour down to 540C (1000F), then air cool. Maximum hardness: 229 HBW.

2.Stress Relieving:Post-Machining.

After heavy rough-machining, heat components to 650C675C (1200F1250F). Hold for 12 hours, then cool slowly in the furnace or in still air to eliminate machining stresses.

3.Two-Stage Preheating:Thermal Protection.

Slowly heat to 540C650C (1000F1200F) and equalize. Then ramp up to 840C870C (1550F1600F) to minimize the dwell time at higher austenitizing temperatures.

4.Austenitizing (Hardening):Carbide Solution.

Heat to 1000C1030C (1832F1886F). Soak for 15 to 30 minutes once the core temperature stabilizes.

5.Quenching:Transformation Control.

Quench in still air, pressurized nitrogen (vacuum furnace), or warm oil. For heavy cross-sections ($\ge$ 100mm), pressurized gas or interrupted oil quenching is required to ensure full martensitic transformation.

6.Double/Triple Tempering:Final Properties.

Temper immediately once the steel drops to 50C60C (120F140F). Bake twice for a minimum of 2 hours per cycle at 540C620C (1000F1150F). Typical working hardness ranges from 44 to 52 HRC.

Primary Applications of H11 Round Bars

Because of its balance of red hardness and impact energy absorption, AISI H11 bars are highly favored for:

• Structural Aerospace Components: Landing gear pillars, airframe structural brackets, and specialized high-tensile shafting where safety margins prohibit brittle materials.

• Heavy Hot-Forging Dies: Hammer die blocks and complex inserts subjected to intense impact forces.

• Helicopter Rotor Components: Highly stressed drive-train pins and structural fasteners.

• Hot Shear Tooling: Blades designed to cleanly clip hot steel billets or scrap profiles without fracturing along the cutting edge.