Hitachi Aogami Blue 2 Stainless San Mai

Hitachi Aogami Blue 2 Stainless San Mai

Aogami 2, also known as Blue 2 or Ao-Ko II, is a Hitachi-produced high carbon steel famed for its use in premium kitchen knives. Renowned for its pure alloy composition with phosphorus at less than 0.025% and sulfur below 0.004%, this steel offers a fine balance between toughness and wear resistance.

Though slightly tougher than its counterpart, Aogami 1, it maintains excellent wear resistance, especially noticeable in its performance at hardness levels of 63HRC and above.

This steel is supplied cold rolled and annealed, offering a smooth surface free of decarburization or pitting. It is soft and easily cut, ground, drilled, and filed. Once polished, etch in hydrochloric and ferric acid to bring out the intricate Damascus pattern.

If you do not micro-texture (hammer while cold or hot) to disrupt the pattern, you will achieve straight, clean layers.

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Composition

Blue Paper 2 Core:

• Carbon – 1.10-1.20%
• Chromium – 0.20-0.50%
• Tungsten – 1.00-1.50%
• Manganese – 0.20-0.40%
• Phosphorus – ≤ 0.03%
• Sulfur – ≤ 0.004%

Stainless Steel Cladding

Performance Characteristics

Toughness: 6/10 – Medium to high toughness, suitable for a wide range of blade styles and sizes. While not as tough as some tool steels, its cladding enhances its durability.

Edge Retention: 7/10 – Superior edge retention due to its high carbon and tungsten content, allowing for excellent sharpness and stability.

Corrosion Resistance: 6/10 – The stainless cladding provides protection against rust, while the high-carbon core requires maintenance to prevent patina or corrosion.

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Recommended Heat Treatment

1. Coat Blade: Use an anti-scale compound or seal in double-crimped 321 or 309 grade stainless steel tool wrap.
2. Austenitize: Heat to 800-830°C and hold for 10 minutes.
3. Quench: Use oil or air quenching to ensure proper hardness.
4. Temper: Temper at 150-200°C for 2 hours, twice, to achieve the desired hardness and relieve internal stresses.

As-Quenched Hardness (Approximate)

• After quenching from 800-830°C: 63-65HRC

Recommended Working Hardness

60-62HRC – Ideal for balancing edge retention and toughness, making it suitable for high-performance applications.

NOTE

To prevent delamination of the core, a low and long stress-relief temper (~100°C for 2+ hours) is recommended after your primary tempering process. This step ensures a more stable and durable blade.