Selection of Tool Steel for Tube & Pipe Mill Rolls
Mill rolls are used to pierce, reduce, shape, and size seamless or welded tubes under combined mechanical loading and, in hot rolling, severe thermal cycling.
In hot rolling, surface temperatures can reach 650–700 °C, generating steep thermal gradients that lead to heat checking and surface cracking. At the same time, rolls are subjected to high Hertzian contact stress, cyclic subsurface shear, and continuous friction. As a result, the dominant failure modes are surface fatigue, spalling, and abrasive wear.
Key Selection Factors
Tool steel selection must be based on the dominant failure mechanism in the roll position.
Wear Resistance vs. Toughness
High hardness is required to resist abrasive wear and plastic deformation under contact pressure. However, increasing hardness and carbide content reduces toughness, thereby increasing the risk of spalling and brittle fracture under cyclic loading. In many mill applications, roll failure is more often caused by insufficient toughness than by wear.
Thermal Fatigue & Hot Hardness
In hot rolling, repeated heating and cooling cause thermal fatigue, leading to heat checking and crack propagation. The material must resist crack initiation while maintaining sufficient hot hardness to prevent surface softening and deformation. If hot hardness is insufficient, the roll surface deforms; if thermal fatigue resistance is inadequate, cracking and early failure occur.
Recommended Tool Steel Grades
AISI D2 Tool Steel |1.2379 | SKD11
D2 is suited for cold rolling and tube drawing, where abrasive wear is the primary concern and thermal effects are minimal. Its high chromium carbide content provides strong resistance to surface wear and dimensional loss. Under stable loading, it offers significantly longer service life than lower-alloy steels. However, due to limited toughness, it is not suitable for applications with impact loading, misalignment, or unstable operating conditions.
AISI A2 Tool Steel | 1.2363 | SKD12
A2 is used when the risk of spalling or cracking exceeds that of pure abrasive wear. It provides better toughness and resistance to crack propagation than D2 while maintaining adequate hardness for cold work rolls. It is commonly applied in backup roles or positions with fluctuating loads. The trade-off is reduced wear resistance compared to D2.
H13 Tool Steel Supplier | 1.2344 | SKD61
H13 is the preferred choice for hot-rolling and piercing applications where thermal fatigue is dominant. It resists heat checking and maintains structural stability under repeated thermal cycling. It is typically used at lower hardness levels to preserve toughness, ensuring resistance to cracking under combined thermal and mechanical loading.
Summary of Tool Steel Properties
| Grade | Hardness (HRC) | Primary Advantage | Typical Application |
| AISI D2 | 58–62 | High abrasion resistance | Cold rolling, tube drawing rolls |
| AISI A2 | 58–62 | Higher toughness and crack resistance | Backup rolls, unstable load zones |
| AISI H13 | 42–50 | Thermal fatigue resistance (heat checking) | Hot piercing, hot rolling rolls |