What Red Hardness Really Means Skh51 Performance At Elevated Cutting Temperatures - China

SKH51 Red Hardness – Why Cutting Edges Stay Sharp At 600°C When a drill turns at 3000 RPM in a tough alloy steel, the cutting edge glows far above the temperatures where ordinary tool steels soften.

The property that keeps SKH51 cutting at these temperatures is red hardness (hot hardness) — and understanding it explains why SKH51 (equal to AISI M2, DIN 1.3343 and GB W6Mo5Cr4V2) remains the default choice for high-speed machining even in the carbide era.

The science behind SKH51 red hardness:

1 - Secondary hardening: during triple tempering at 550–580°C, fine Mo2C and VC carbides precipitate inside the martensite — a mechanism that actually raises hardness after tempering instead of reducing it.

2 - Tungsten-molybdenum carbides resist coarsening, so the tempered structure keeps HRC 63–65 even after reaching working temperatures near 600°C.

3 - Vanadium carbides (V 1.75–2.20%) are the hardest particles in the structure and directly resist abrasive wear on the cutting edge.

What red hardness means in practice:

- Drills and taps made from SKH51 keep their edge through long production runs without coolant breakdown failures.

- Reamers and countersinks maintain dimensional accuracy where softer steels would lose size within hours.

- Saw blades and milling cutters resist softening at the contact zone, so regrinding intervals stretch significantly longer.

- Compared with plain carbon tool steels (which soften below 200°C), SKH51 holds working hardness up to roughly three times higher temperature.

Conditions that protect red hardness in your tools:

- Quench within the recommended 1200–1240°C window; overheating dissolves too many carbides and destabilizes the structure.

- Always triple temper — a single temper leaves retained austenite that later transforms and distorts the edge.

- Avoid decarburization during your heat treatment; a decarburized skin loses hot hardness first and chips early.

Songshun supplies SKH51 in round bar dia 3–300mm, flat bar, plate and cut blocks, all annealed in-house to HB 255 max with full heat chemistry (C 0.80–0.90 / Cr 3.80–4.40 / Mo 4.50–5.50 / W 5.50–6.75 / V 1.75–2.20), mill certificates and UT reports included.

Tell us your workpiece material and cutting speeds — our engineers will confirm SKH51 is the right grade and quote your sizes within 12 hours.

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• Posted By: Dongguan Songshun Mould Steel Co., Ltd.

• Phone: 0086 0769 85475596

• Address: 1st Floor, No. 1, Dongda Fourth Street, Shatou Community, Chang'an Town, Dongguan , GuangDong , China

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• Business Description: Established in 2009,Songshun Steel supplies a wide range of carbon, alloy and tool steel products, including high speed tool steel, cold work tool steel, hot work tool steel, plastic mould steel, engineering steel and machine structural steel etc.
  
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