H11 TOOL STEEL | 1.2343 | skd6

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H11 tool steel is an air-cooling hardening hot work tool steel known for its excellent toughness, thermal strength, fatigue performance, and wear resistance at medium temperatures. Additionally, it retains some toughness in the quenched state and demonstrates strong resistance to thermal fatigue. When air-quenched at lower austenitizing temperatures, it exhibits minimal heat treatment deformation and a low tendency to form oxide skin.

Moreover, it can effectively resist the erosion of molten aluminum. As a result, H11 tool steel is commonly used to manufacture aluminum die-casting molds, hot extrusion tools, press forging dies, and plastic molds.

The designation for this steel is H11 in the U.S. ASTM A681 system. Similarly, other national standards use comparable designations, such as ISO X37CrMoV5-1, Japan/JIS SKD6, USA/UNS T20811, Germany/DIN X38CrMoV5-1, Germany/W-Nr. 1.2343, and Czech Republic (CSN) 19552. 

1. Applications

H11 tool steel is widely used in industries where tools must withstand both high heat and mechanical stress. Its excellent thermal stability, toughness, and wear resistance suit various demanding applications.

  • Die Casting Dies: H11 is commonly used for casting aluminum, zinc, and magnesium due to its high thermal stability and toughness, ensuring durability in extreme conditions.
  • Forging Dies: Because it can resist bending at high temperatures, H11 is a preferred choice for forging dies and hot-forming tools, maintaining strength under intense pressure.
  • Extrusion Tools: This steel is ideal for extrusion dies used in metal and plastic processing. It offers excellent wear resistance and can perform under high-temperature conditions.
  • Hot Shear Blades: Thanks to its superior heat and wear resistance, H11 is perfect for manufacturing blades that cut hot metals efficiently and maintain their sharpness.
  • Aerospace Components: H11 is also utilized in critical aerospace parts such as landing gear, where strength, fatigue resistance, and reliability are essential.

2. Chemical composition

The effectiveness of H11 tool steel in high-temperature applications is largely determined by the precise percentages of its key alloying elements:

Element

Symbol

Typical Range (Weight %)

Key Characteristics & Noted Values

Carbon

C

0.33 – 0.43

Essential for hardness. You’ll often see analyses around 0.35% to 0.38%. Some specifications narrow this to 0.35-0.42% or 0.38-0.43%.

Manganese

Mn

0.20 – 0.50

Contributes to strength and hardenability. Typical values are around 0.30%; the range 0.25-0.50% is also common.

Silicon

Si

0.80 – 1.20

Aids in deoxidation and improves strength. A typical value is 1.00%. (Note: A Low-Si H11 variant exists with Si around 0.3%).

Chromium

Cr

4.75 – 5.50

The defining element for H11, providing hot strength and oxidation resistance. Often referred to as a “5% Chromium” steel. Typical: 5.00%.

Molybdenum

Mo

1.10 – 1.60

Crucial for maintaining strength and hardness at elevated temperatures (hot hardness) and tempering resistance. Typical: 1.30% or 1.50%. (One source notes 1.10-1.50%).

Vanadium

V

0.30 – 0.50

Enhances wear resistance, particularly at high temperatures, by forming hard carbides. Typical: 0.40% or 0.50%. (Some specialized analyses may show V up to 0.90%-1.00%).

H11 Tool Steel
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3. H11 Tool Steel Properties

Its unique combination of properties makes it exceptionally suited for a wide array of demanding hot-work and high-strength tooling applications.

Key Property of H11 Tool Steel

Performance Details & Benefits for Your Factory Operations

Ultrahigh Strength

Following appropriate heat treatment, H11 tool steel achieves remarkable strength. You can typically expect a 0.2% yield strength greater than 1380 MPa (200 ksi), with ultimate tensile strength potentially exceeding 2070 MPa (300 ksi). This is vital for tools under extreme stress.

Hot Hardness & Tempering Resistance

H11 is a secondary hardening steel, meaning it excels at retaining its hardness and structural stability at elevated service temperatures. It’s typically tempered above its secondary hardening peak (around 510°C / 950°F) and strongly resists softening up to approximately 540°C (1000°F). It can maintain a hardness of about 50 HRC even after extended periods at 500-550°C.

Deep Air Hardenability

A significant advantage of H11 tool steel is its ability to harden uniformly through large cross-sections simply by air cooling. This air hardening characteristic minimizes residual stresses and distortion during the heat treatment process, ensuring dimensional stability for your tools.

Good Toughness

H11 tool steel provides a commendable balance of impact strength and overall toughness. Compared to some higher alloy H-series steels, it offers better resistance to brittle fracture, which is crucial for tool longevity and safety.

Wear Resistance

This steel offers good inherent wear resistance, further enhanced by elements like Vanadium, which helps resist washing or erosive wear. For applications demanding superior surface durability, H11’s wear resistance can be significantly boosted through surface nitriding, often achieving surface hardness levels above 1000 HV.

Fatigue Resistance

In applications involving cyclic loading, H11 tool steel demonstrates good resistance to fatigue cracking. This property is essential for tools subjected to repetitive stress, contributing to a longer operational life.

Elevated Temperature Service

H11 is engineered for applications that require consistent strength and property stability at high temperatures, performing reliably up to approximately 540°C (1000°F).

Weldability

From a practical standpoint, H11 tool steel is considered readily weldable, provided that appropriate pre-heating, interpass temperature control, and post-weld heat treatment procedures are followed to maintain its integrity.

Machinability

In its annealed condition, H11 tool steel offers good machinability, generally rated around 70% of a standard 1% carbon steel. This allows for efficient shaping and preparation of your tools before heat treatment.

Corrosion & Oxidation Resistance

H11 provides better-than-average resistance to corrosion and oxidation. The presence of Silicon, for instance, improves its oxidation resistance at temperatures up to 800°C (1475°F). However, for prolonged high-temperature service, appropriate surface protection is still advisable.

Thermal Properties

The thermal characteristics of H11 tool steel include acceptable thermal conductivity and a relatively low coefficient of thermal expansion. These are beneficial for tooling that experiences significant thermal cycling, helping to maintain dimensional accuracy and reduce thermal fatigue.

 

4. H11 Tool Steel Heat Treatment

Precise H11 tool steel heat treatment is crucial for achieving its optimal performance as a 5% chromium hot-work die steel and ultrahigh-strength steel, similar to H11 Modified and H13. This process tunes the microstructure for demanding factory tooling. This guide details the key heat treatment operations for H11, ensuring maximum durability and efficiency.

4.1 Austenitizing

Austenitizing, the primary hardening step for H11 tool steel, involves heating to transform its structure into austenite. This allows uniform conversion and dissolution of alloying elements and carbides.

  • Preheating: Preheating H11 to 760-815 °C (1400-1500 °F) before austenitizing is recommended to minimize thermal shock and cracking, especially for this high-alloy material.

  • Austenitizing Temperatures & Holding Times:

Steel TypeAustenitizing Temperature RangeTypical Austenitizing Temp. (for air cooling)Recommended Holding Time

H11

995 to 1025 °C (1825 to 1875 °F)

–

20 minutes + 5 minutes per 25 mm (1 inch) of thickness

H11 Mod/H13

(Similar to H11)

Around 1010 °C (1850 °F)

(Follow general H11 guideline)

Holding at the austenitizing temperature ensures uniform transformation and dissolution.

4.2 Quenching

After austenitizing, H11 steel is rapidly cooled (quenched) to form hard martensite.

  • Air Hardening Advantage: H11 is an air-hardening steel, providing uniform hardening through large sections with minimal residual stress and dimensional change. Air cooling is the standard and preferred method for H11 tool steel heat treatment.

  • Oil Quenching: While air cooling is standard, oil quenching from 995 °C (1825 °F) is a possible alternative for H11.

  • Critical Note: Hot-work steels like H11 must never be water quenched, as this can lead to cracking.

4.3 Tempering

After hardening, tempering H11 tool steel by reheating to a lower temperature is crucial for improving toughness, relieving stress, and stabilizing properties.

  • Secondary Hardening: H11 is a secondary hardening steel. Its optimum properties develop when tempered above the secondary hardening peak (around 510 °C / 950 °F), where hardness can increase or be maintained.

  • Tempering Temperatures and Effects:

Steel TypeTempering Temperature(s)Key Benefits & Considerations

H11

Above 510 °C (950 °F)

Develops optimum properties; significant stress relief; stabilizes for use up to ~55 °C (100 °F) below tempering temperature.

H11

150 °C (300 °F) and 205 °C (400 °F)

Lower temperature tempering options.

H11 Mod

510 °C (950 °F) and 540 °C (1000 °F)

Typical ranges for achieving desired performance.

  • Double Tempering: A common and recommended practice for H11 tool steel heat treatment is double tempering (e.g., 2 hours at temperature, cool, then another 2 hours at temperature) to ensure complete transformation and property refinement.

4.4 Annealing

Annealing softens H11 tool steel, improves machinability, and relieves internal stresses, typically after hot working or welding.

  • Post-Forging/Welding Care: After forging or welding, H11 parts require slow cooling and then full annealing to prevent stress cracking.

  • Annealing Parameters:

ProcessTemperature RangeCooling RateNotes

H11 Annealing

845-900°C (1550-1650°F)

Slow: 22-40°C/h (40-70°F/h)

Spheroidizing annealing is a specific type to improve machinability.

DH31-S (similar)

820-870°C

Slow cooling

(Comparable to SKD61, an H11 equivalent)

4.5 Other Important H11 Heat Treatment Considerations

  • Normalizing: This process is generally not recommended for H11 or H13 tool steels due to the high risk of cracking, especially with surface decarburization.

  • Stress-Relief Heat Treating: While stress relief can be achieved below Ac1, the high tempering temperatures (above 510 °C / 950 °F) used for H11 provide substantial stress relief.

  • Cryogenic Treatment: Sub-zero treatment (e.g., -73°C / -100°F) can reduce retained austenite, but H11’s high tempering temperatures usually make it unnecessary for achieving maximum secondary hardening response.

  • Surface Protection: Protecting H11 surfaces from oxidation and decarburization during high-temperature treatments, such as austenitizing and annealing, is vital. This is often achieved using controlled atmospheres, vacuum furnaces, or salt baths.

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