What is AISI H12 Steel

AISI H12 hot work tool steel is one of the most widely used grades in the tool steel family, known for its outstanding combination of toughness, heat resistance, and wear strength. As industries continue to demand stronger and more durable materials for die casting, forging, and extrusion, AISI H12 remains a preferred choice among engineers and toolmakers worldwide.

In this article, we will explore in detail what AISI H12 steel is, its chemical composition, mechanical properties, heat treatment process, typical industrial applications, and why SAKYSTEEL is one of the most trusted suppliers of H12 hot work tool steel.

1. Introduction to AISI H12 Steel

AISI H12 is a chromium-based hot work tool steel belonging to the H-series of steels, which includes grades like H10, H11, and H13. These steels are primarily used for tooling applications that involve exposure to high temperatures and mechanical stress.

The designation “H” refers to “Hot Work,” indicating that AISI H12 is designed to retain hardness and strength even when used at elevated temperatures. This grade offers excellent resistance to thermal fatigue cracking, oxidation, and softening under prolonged heat exposure.

AISI H12 is standardized under several equivalent designations:

  • AISI H12 / UNS T20812

  • Werkstoff Nr. 1.2605

  • DIN X35CrW5 / X35CrMoV5-1

  • JIS SKD6

Because of its combination of hardness, toughness, and resistance to heat checking, AISI H12 is ideal for heavy-duty tools, hot dies, and extrusion molds.

2. Chemical Composition of AISI H12

The performance of AISI H12 steel is largely defined by its carefully balanced chemical composition. The presence of chromium, molybdenum, and tungsten provides high-temperature strength and oxidation resistance, while carbon ensures hardenability and wear resistance.

Element Content (%)
Carbon (C) 0.35 – 0.45
Chromium (Cr) 4.75 – 5.50
Molybdenum (Mo) 1.10 – 1.75
Tungsten (W) 1.00 – 1.75
Vanadium (V) 0.20 – 0.60
Silicon (Si) 0.80 – 1.20
Manganese (Mn) 0.25 – 0.50
Nickel (Ni) ≤ 0.3
Sulfur (S) + Phosphorus (P) ≤ 0.03

This composition provides a well-balanced microstructure that supports both thermal and mechanical stability. The chromium content enhances corrosion resistance and hardness retention, while tungsten and molybdenum strengthen the steel at elevated temperatures.

3. Mechanical Properties of AISI H12

The mechanical performance of AISI H12 makes it suitable for operations involving high pressure and temperature cycles. The typical mechanical properties after heat treatment are as follows:

Property Typical Value
Hardness (Annealed) ≤ 229 HB
Hardness (Hardened & Tempered) 44 – 52 HRC
Tensile Strength 1500 – 1900 MPa
Yield Strength 1200 MPa (approx.)
Elongation 10 – 15%
Impact Toughness Excellent at high temperature

AISI H12 combines high hot strength with toughness, which minimizes the risk of cracking during die-casting or forging operations. This property set allows the steel to perform well under repeated thermal cycling.

4. Heat Treatment Process

Proper heat treatment is essential for optimizing the mechanical performance of AISI H12. The standard heat treatment process includes the following steps:

Annealing

  • Heat to 850–900°C.

  • Hold for 2–4 hours depending on section size.

  • Cool slowly in the furnace to 600°C, then in air.

  • Result: Soft structure with hardness ≤ 229 HB for machining.

Preheating

  • Preheat gradually in two stages: first to 450–500°C, then to 850–900°C.

Hardening

  • Austenitize at 1000–1050°C.

  • Hold for sufficient time (20–30 minutes).

  • Quench in air, oil, or salt bath at 550°C.

  • Result: Hardness up to 52 HRC.

Tempering

  • Temper immediately after hardening.

  • Typical tempering temperature: 500–650°C.

  • Double tempering is recommended for improved toughness.

After tempering, the final hardness can be controlled according to the desired application — generally between 44 to 52 HRC.

5. Advantages of AISI H12 Steel

AISI H12 is highly valued for its well-balanced properties. Below are the major advantages that make it a reliable material for industrial tooling:

  1. High Thermal Fatigue Resistance
    Resists cracking under repeated heating and cooling cycles.

  2. Excellent Toughness
    Maintains impact strength even under high stress and temperature.

  3. Good Dimensional Stability
    Minimal distortion during heat treatment ensures precision in tooling.

  4. Resistance to Softening
    Retains hardness at elevated service temperatures up to 600°C.

  5. Good Wear Resistance
    Suitable for abrasive environments like extrusion dies and forging hammers.

  6. Machinability and Polishability
    AISI H12 offers moderate machinability and can achieve a fine surface finish.

These features make AISI H12 one of the most cost-effective choices for heavy-duty hot work tooling.

6. Industrial Applications

AISI H12 is used in a wide range of industrial applications that require high heat resistance and toughness. Common applications include:

1. Die Casting Tools

  • Pressure die casting dies

  • Die inserts

  • Core pins and sleeves

2. Forging Dies

  • Drop forge dies

  • Hot press dies

  • Upsetting tools

3. Extrusion Dies

  • Aluminum extrusion dies

  • Copper and magnesium die tools

4. Plastic Molds and Hot Runners

  • Plastic injection mold cores

  • Runner systems for high-temperature plastics

5. Aerospace and Automotive Components

  • Turbine blades and nozzle parts

  • Engine valve seats and high-heat inserts

6. Hot Shear Blades and Punches

  • Cutting blades for high-temperature materials

  • Piercing tools for hot steel processing

The broad usability of AISI H12 across multiple industries demonstrates its performance reliability and long service life.

7. Comparison: AISI H12 vs AISI H13 vs H11

While AISI H13 and H11 are also popular hot work steels, H12 offers a distinct balance of strength and toughness.

Property AISI H11 AISI H12 AISI H13
Carbon (C) 0.35 0.40 0.40
Chromium (Cr) 5.25 5.25 5.25
Molybdenum (Mo) 1.25 1.25 1.35
Tungsten (W) — 1.50 —
Hot Strength Good Excellent Very Good
Thermal Fatigue Moderate Excellent Excellent
Wear Resistance Moderate High Very High

AISI H12 provides superior hot strength and resistance to cracking compared with H11, while maintaining better toughness than H13 in certain applications. This makes it particularly suitable for heavy-duty forging dies and extrusion molds.

8. Machining and Welding Considerations

Machining

AISI H12 should be machined in its annealed condition. Its machinability rating is approximately 75% of that of AISI 4140 steel. Using carbide tools and maintaining proper cooling conditions are essential for extended tool life.

Welding

Welding is possible with preheating (250–350°C) and post-weld tempering to avoid cracking. Recommended filler materials are of similar composition to the base metal.

Surface Treatment

For longer service life, surface treatments like nitriding or PVD coating can be applied. Nitrided AISI H12 surfaces exhibit improved hardness and wear resistance without loss of core toughness.

9. Supply Forms and Sizes

SAKYSTEEL supplies AISI H12 hot work tool steel in various forms and sizes, including:

  • Round bars

  • Flat bars

  • Plates and blocks

  • Forged billets

  • Pre-machined dies

All materials are supplied with EN 10204 3.1 Mill Test Certificates, confirming chemical composition and mechanical performance. Custom cutting, precision machining, and heat treatment services are also available according to client specifications.

10. Quality Assurance and Standards

At SAKYSTEEL, all AISI H12 materials are produced in accordance with international standards such as:

  • ASTM A681 – Tool Steels Alloy

  • DIN EN ISO 4957 – Tool Steels

  • JIS G4404 – Alloy Tool Steels

Every batch undergoes strict quality control, including ultrasonic testing, hardness inspection, and metallographic analysis to ensure defect-free performance.

11. Tips for Optimal Tool Life

To achieve the best tool life from AISI H12 components:

  1. Use proper preheating before operation.

  2. Avoid excessive temperature fluctuations.

  3. Perform double tempering for enhanced toughness.

  4. Apply nitriding for extended surface hardness.

  5. Maintain consistent lubrication in hot applications.

Following these guidelines ensures maximum service life, reduced downtime, and cost savings for industrial users.

12. Conclusion

AISI H12 is a high-performance hot work tool steel that delivers exceptional toughness, heat resistance, and dimensional stability in extreme industrial environments. Its balanced alloy composition and superior resistance to thermal fatigue make it a preferred material for forging, die casting, and extrusion tooling.

With years of manufacturing and export experience, SAKYSTEEL provides high-quality AISI H12 steel products that meet international standards and customer-specific requirements. Whether you need forged blocks, precision-cut plates, or ready-to-machine bars, SAKYSTEEL ensures reliable quality, timely delivery, and professional technical support.

Post time: Oct-28-2025