JIS SKT4 Hot Die Steel Round Bar

Product Description

Technical Specifications for SKT4 Round Bars

1. Chemical Composition (JIS G4404)

The standard chemistry ensures that large-diameter round bars achieve uniform mechanical properties from the outer skin to the center core:

2. Physical Properties

• Density: $7.85 \text{ g/cm}^3$

• Thermal Conductivity (at 20°C): $36.0 \text{ W/(m}\cdot\text{K)}$

• Modulus of Elasticity: $215 \text{ GPa}$

Why Use the Round Bar Form?

Round bars are primarily used when the final component shares a circular geometry. This minimizes material waste and machining time compared to cutting shapes out of large rectangular blocks. Typical round bar applications include:

• Forging Rolls & Mandrels: High-stress cylindrical components used in rotary forging or tube piercing.

• Press Ejector Pins & Punch Holders: Machined round inserts designed to handle punishing, high-velocity cyclic stress.

• Die Inserts: Circular pockets machined into larger die holders are frequently filled with SKT4 inserts to handle localized high wear and impact.

Supply Condition & Processing Notes

Surface & Delivery Status

SKT4 round bars are typically supplied in the following states:

• Black Forged/Rolled: Raw mill finish with an oxide scale layer; requires rough machining.

• Peeled/Turned: Surface scale removed to close dimensional tolerances, revealing a bright steel finish ready for precise tool-making.

• Annealed: Delivered at a maximum hardness of 248 HBW to allow for high-speed machining and drilling before heat treatment.

Ultrasonic Testing (UT)

Because hot-work round bars face severe shock loads during operation, premier suppliers subject large-diameter SKT4 bars to Ultrasonic Testing (typically per SEP 1921 Class C/c or D/d standards). This guarantees the core is free of internal micro-cracks, gas pockets, or structural porosity that could cause sudden catastrophic tool failure under the hammer.