Selection of Tool Steel for Thread Rolling Dies

Thread rolling forms threads by plastic deformation, which subjects the dies to continuous high contact pressure and repeated loading. The process does not remove material, so stress accumulation at the die surface becomes the dominant factor.

During operation, dies are exposed to compressive stress, bending, and sliding contact. Friction can generate heat, particularly in cylindrical dies, but this is usually secondary. Under clean working conditions, abrasive wear is limited. Instead, failure is primarily driven by fatigue, which initiates microcracks at the thread crest and progresses into spalling and local breakdown. Once the crest geometry degrades, dimensional accuracy is quickly lost.

Selection Factors

Material selection for thread-rolling dies is governed by how the steel responds to repeated loading in stress-concentration zones rather than by static strength alone.

High compressive strength is required to prevent plastic deformation under radial pressure. However, the thread crest is highly sensitive to crack initiation. Without sufficient toughness, localized chipping or spalling occurs early in service.

Fatigue resistance governs service life. Materials that resist crack initiation and slow crack propagation maintain die integrity over longer production cycles.

The trade-off lies between toughness and wear resistance. For short or unstable runs, higher toughness reduces the risk of premature failure. For long-term, stable production, higher alloy content and carbide volume improve dimensional retention, even at the cost of reduced toughness.

Recommended Tool Steels

In industrial applications, the following grades are commonly used for flat and circular thread-rolling dies, depending on production conditions and stability requirements.

Summary Table