What is Ice Tempering (Eishärtung)?

Description

Ice tempering (Eishärtung) is a sub-zero hardening process used by German scissor manufacturers, particularly Jaguar of Solingen. Blades are cooled to sub-zero temperatures after quenching to convert retained austenite to martensite, improving hardness and dimensional stability.

What is Ice Tempering (Eishärtung)?

Ice tempering, known in German as Eishärtung (literally “ice hardening”), is a sub-zero cooling process applied to scissor blades after quenching. The hardened blades are cooled to temperatures well below 0°C to continue the martensite transformation that was incomplete at room temperature. This converts soft retained austenite into hard martensite, improving overall blade hardness, edge retention, and dimensional stability.

Why It Matters for Scissors

The Solingen scissor industry developed ice tempering as a standard process for premium blades, separate from but parallel to the Japanese cryogenic treatment tradition. Jaguar Solingen is the most prominent practitioner, marketing their sub-zero process under the Friodur brand name. The Friodur treatment is applied to their higher-tier scissors, including models made from their proprietary 4116 and 4034 modified steel compositions.

The metallurgical benefit is measurable. A blade quenched to room temperature from austenitizing may contain 10-20% retained austenite, depending on the steel composition. Ice tempering at -20°C to -40°C converts a portion of this — perhaps reducing retained austenite from 15% to 8-10%. Deeper cooling to -80°C can reduce it further to 3-5%. Each percentage point of retained austenite converted to martensite increases effective hardness by approximately 0.1-0.2 HRC.

Beyond hardness, dimensional stability is a practical concern for Solingen manufacturers who export worldwide. Scissors shipped to hot climates can experience slow retained austenite transformation during storage, causing microscopic dimensional changes that affect blade alignment. Ice tempering before final finishing eliminates this risk.

The German approach to sub-zero treatment tends to be less extreme than the Japanese deep cryogenic method. Where Japanese manufacturers may use liquid nitrogen at -196°C, German manufacturers more commonly use mechanical refrigeration or dry ice to reach -40°C to -80°C. This reflects different steel compositions — the German 4116-type steels have higher Ms/Mf temperatures than Japanese VG-10, requiring less extreme cooling for equivalent retained austenite conversion.

Technical Detail
The terminology difference between "ice tempering" and "cryogenic treatment" reflects both regional manufacturing traditions and genuine process variations: **German ice tempering (Eishärtung) process:** 1. Austenitize at 1,020-1,060°C (typical for 4116/4034 steels) 2. Quench — oil or plate quench to room temperature 3. Cool to sub-zero temperature: -20°C to -80°C, held for 1-4 hours 4. Warm slowly to room temperature 5. Temper at 150-200°C for 1-2 hours 6. Second temper (some manufacturers) at 150-180°C **Japanese cryogenic treatment process:** 1. Austenitize at 1,040-1,080°C (typical for VG-10) 2. Quench to room temperature 3. Cool to -80°C to -196°C, held for 1-24 hours 4. Warm slowly to room temperature 5. Temper at 150-200°C The steel composition drives the temperature requirement. German scissor steels: - **4116 (X50CrMoV15):** Ms ≈ 250°C, Mf ≈ -20°C to -40°C — moderate sub-zero cooling is sufficient - **4034 (X46Cr13):** Ms ≈ 270°C, Mf ≈ 0°C to -20°C — even mild cooling helps - **4034 modified with added Mo/V:** Ms ≈ 230°C, Mf ≈ -30°C to -50°C Compare to Japanese steels: - **VG-10:** Ms ≈ 180-200°C, Mf ≈ -50°C to -70°C — requires deeper cooling - **ZDP-189:** Ms ≈ 130-150°C, Mf ≈ below -100°C — requires deep cryogenic This explains why German manufacturers achieve good results at -40°C to -80°C, while Japanese manufacturers working with VG-10 need to go to -80°C or colder. **Jaguar's Friodur specifics:** Jaguar claims that Friodur treatment achieves: - Increased hardness of 1-2 HRC over non-cryo-treated blades - Improved corrosion resistance (likely due to more uniform martensite and fewer austenite pockets that corrode preferentially) - Better edge retention in salon conditions The Friodur branding is applied selectively — not all Jaguar scissors receive the treatment. The company's entry-level lines use standard heat treatment, while the Friodur designation indicates the additional sub-zero step. This mirrors the Japanese market where manufacturers differentiate product tiers partly through heat treatment sophistication. Other Solingen manufacturers including Tondeo and NTS use similar sub-zero processes without the Friodur brand name. The process is standard in the premium Solingen scissor segment, though specific temperatures and hold times are proprietary.

Sources

Frequently Asked Questions

Functionally similar but not identical. Ice tempering (Eishärtung) as practiced by German manufacturers like Jaguar typically uses temperatures around -20°C to -80°C. Japanese cryogenic treatment often goes deeper, to -80°C or even -196°C with liquid nitrogen. The metallurgical goal is the same — converting retained austenite to martensite — but the temperature ranges and terminology differ.

Friodur is Jaguar's proprietary name for their ice tempering treatment. The name comes from the Latin 'frigor' (cold) and 'durus' (hard). It is applied to their premium scissor lines and involves sub-zero cooling after quenching, followed by controlled tempering. Jaguar markets Friodur as producing superior edge retention and corrosion resistance.

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