W.Nr. 55NiCrMoV7 Hot Die Steel Bars

Product Description

Overview of W.Nr. 1.2714 (55NiCrMoV7)

W.Nr. 1.2714 (standardized as 55NiCrMoV7) is a premium, heavy-duty nickel-chromium-molybdenum-vanadium alloy hot-work tool steel. Known for its exceptional toughness, deep hardenability, and excellent resistance to thermal shock, it is the global industry standard for high-stress hot forging applications.

Here is a breakdown of its technical profile, equivalent international grades, mechanical properties, and typical applications.

International Equivalent Grades

Because of its widespread global use, this grade is cross-referenced across several international standards:

Chemical Composition (Typical Weight %)

The specific blend of alloying elements gives 55NiCrMoV7 its unique balance of core toughness and hot hardness:

• Carbon (C): 0.50% – 0.60% (Provides high baseline hardness and strength)

• Nickel (Ni): 1.50% – 1.80% (Ensures extreme toughness and deep through-hardening)

• Chromium (Cr): 1.00% – 1.30% (Improves wear resistance and high-temperature strength)

• Molybdenum (Mo): 0.40% – 0.60% (Reduces temper brittleness, increases hot yield strength)

• Vanadium (V): 0.07% – 0.15% (Refines grain structure, enhances thermal fatigue resistance)

Key Performance Properties

• Deep Through-Hardening: The high nickel and molybdenum content ensures uniform hardness from the surface to the core, even in very large cross-sections (e.g., massive die blocks).

• High Impact Toughness: Excellent resistance to brittle fracturing under heavy impact loads (hammer forging).

• Thermal Shock Resistance: Highly resistant to heat checking (cracking caused by rapid cycles of heating and cooling).

• Excellent Machinability: In its soft-annealed state, it machines predictably and takes an excellent surface polish.

Typical Applications

55NiCrMoV7 hot die steel bars are primarily used where tooling is subject to high dynamic stresses, heavy impact, and elevated operating temperatures:

• Forging Dies: Die blocks for drop hammers, mechanical forging presses, and upsetting dies.

• Molds: Heavy-duty plastic injection molds or die casting dies requiring high core strength.

• Hot Shears: Blades for hot shearing steel billets and bars.

• Extrusion Tooling: Die holders, bolster plates, and dummy blocks for aluminum and copper extrusion.

• Punching Tools: Hot punching dies and piercing mandrels.

Heat Treatment Guidelines

Annealing

• Temperature: 650°C to 700°C

• Process: Controlled slow cooling in a furnace (10°C to 20°C per hour) down to approx. 600°C, followed by air cooling.

• Delivered Hardness: Max 248 HBW (Soft Annealed).

Hardening

• Preheating: Slow preheat to 600°C – 650°C, followed by a second stage at 800°C.

• Austenitizing Temperature: 830°C to 870°C

• Quenching Medium: Oil, polymer, or warm bath ($450^\circ\text{C} - 500^\circ\text{C}$). Large sections may utilize forced air or polymer to minimize distortion.

Tempering

• Temperature: 530°C to 650°C (depending on the desired final working hardness).

• Requirement: Double tempering is highly recommended. Cool to room temperature between tempers.

• Typical Working Hardness: Usually targeted between 38 to 44 HRC for hammers, and 44 to 50 HRC for mechanical press dies.