Selection of Tool Steel for Shear Blades and Slitter Knives
Shear blades and slitter knives are used to cut metal sheets, strips, and coils under high load and repeated cycles. Because failure initiates at the cutting edge, edge stability directly determines tool life.
During operation, the edge is subjected to compressive penetration forces, localized plastic deformation, and continuous sliding contact with the workpiece. Repeated loading further accelerates fatigue at the edge. In high-speed slitting, factors such as strip tension, misalignment, and vibration exacerbate these conditions.
In practice, tool life is typically limited by edge wear, micro-chipping, or adhesion rather than a single dominant mechanism. Material selection should therefore focus on maintaining a stable cutting edge under real operating conditions, not on maximizing hardness alone.
Selection Factors
Wear Resistance vs Edge Stability
Wear resistance is primarily provided by hard carbides, which reduce abrasive wear at the cutting edge. Increasing carbide content improves wear resistance but reduces toughness.
In shear and slitting operations, this trade-off is critical. Excessive wear resistance often leads to unstable edges and micro-chipping under minor disturbances. The objective is not maximum wear resistance, but controlled wear with stable edge behavior.
Toughness and Resistance to Chipping
The cutting edge operates under non-uniform and often unstable loading conditions. Variations in material thickness, alignment, or cutting clearance can generate localized stress concentrations.
If toughness is insufficient, small edge defects quickly develop into chipping or cracking. Once initiated, failure progresses rapidly and tool life becomes unpredictable. In such cases, improving toughness is more effective than increasing hardness.
Hardness and Edge Retention
Higher hardness improves resistance to plastic deformation and slows edge rounding. However, increasing hardness reduces the material’s ability to absorb stress.
In stable cutting conditions, higher hardness can extend tool life. In less controlled environments, slightly lower hardness improves edge stability and reduces the risk of brittle failure. The target hardness level maintains edge integrity under actual operating conditions.
Material Being Cut
The workpiece determines the dominant failure mode. Higher-strength materials increase cutting forces and accelerate both wear and edge stress. Stainless steels introduce adhesion and unstable cutting behavior, while softer materials may reduce wear but increase the risk of material transfer.
Selection should therefore be based on the primary problem observed in production—whether it is wear, chipping, or adhesion—rather than on material classification alone.
Cutting Conditions and Stability
Machine condition directly affects tool performance. Alignment accuracy, blade clearance, cutting speed, and vibration determine whether the loading is stable.
In stable systems, wear-resistant grades can achieve long service life. In unstable conditions, the same materials often fail due to edge chipping. In these cases, selecting a tougher grade provides more reliable performance. Ignoring process stability is one of the most common causes of incorrect material selection.
Recommended Tool Steels
AISI D2 (1.2379 / SKD11)
D2 provides high wear resistance and good dimensional stability, making it suitable for high-volume production under stable cutting conditions.
Its limitation is reduced toughness due to high carbide content. Under misalignment or fluctuating loads, edge chipping becomes a common failure mode.
AISI D3 (1.2080 / SKD1)
D3 offers higher wear resistance than D2 and performs well in applications dominated by abrasive wear and long production runs.
However, its lower toughness requires stable operating conditions. Under uneven loading, edge failure occurs quickly.
AISI A2 (1.2363 / SKD12)
A2 provides a balanced combination of wear resistance and toughness. It performs more reliably than D2 in applications where cutting conditions are not fully controlled.
Although its wear resistance is lower, its improved edge stability often results in more predictable tool life.
AISI S7 (1.2355)
S7 is designed for high toughness and impact resistance. It is suitable for heavy-duty shearing, thicker materials, and conditions where shock or misalignment cannot be avoided.
Its lower wear resistance is offset by strong resistance to edge fracture, making it a reliable choice in demanding mechanical environments.
Practical Selection Logic
Material selection should be based on the dominant failure mode observed in production. When wear limits tool life, higher wear-resistant grades such as D2 or D3 are appropriate. When edge chipping or fracture occurs, tougher materials such as A2 or S7 perform better.
Process stability should guide the final decision. Stable systems allow optimization for wear resistance, while unstable conditions require prioritizing toughness. Most selection errors stem from focusing on hardness or theoretical properties rather than actual working conditions.
Conclusion
The performance of shear blades and slitter knives depends on maintaining a stable cutting edge under repeated loading.
Effective material selection requires identifying the dominant failure mode and matching material properties to real operating conditions. Balancing wear resistance and toughness leads to more predictable performance, longer tool life, and lower overall production cost.