Selection of Tool Steel for Lamination Dies
Lamination dies are used to stamp thin electrical steel sheets for transformers, motors, and armatures. The process operates at room temperature and is entirely cold work.
During production, the die is subjected to high compressive loads and continuous cyclic impact from high-speed stamping. At the same time, repeated contact with thin sheet material causes progressive edge wear. The dominant failure modes are abrasive and adhesive (galling) wear, while thermal damage is not involved.
Because no elevated temperature is present, properties such as thermal fatigue resistance and hot hardness do not influence material selection.
Selection Factors
Tool steel selection for lamination dies is governed by the die edge’s actual failure mode. In most cases, the decision comes down to whether wear or chipping limits tool life.
Wear Resistance
When edge wear defines tool life, higher carbide content is required to maintain sharp cutting edges over long production runs. This improves resistance to abrasion from sheet material but increases brittleness.
Toughness
When edge chipping or cracking occurs before significant wear, higher toughness becomes necessary. Toughness governs resistance to impact-induced microfracture at the cutting edge, especially under high-speed or unstable stamping conditions.
Dimensional Stability
For dies with tight tolerances or complex geometries, distortion during heat treatment can be a practical limitation. Air-hardening steels are preferred where maintaining dimensional accuracy is critical.
Recommended Tool Steels
The following grades are selected based on which failure mechanism dominates in the application.
AISI D2 (High-Carbon, High-Chromium Steel)
D2 is used when wear is the primary limiting factor. Its high carbide volume provides strong resistance to edge wear, allowing stable performance in long production runs.
Its limitation is reduced toughness. When the die edge is thin, poorly supported, or exposed to impact variation, chipping may occur before wear becomes critical. Typical Hardness: 58–62 HRC
AISI A2 Tool Steel | 1.2363 | SKD12
A2 is selected when edge chipping limits tool life. It offers greater toughness than D2, reducing the risk of edge breakage under repeated impacts.
Wear resistance is lower than D2, so it is more suitable for moderate production volumes or conditions where stability is more important than maximum edge life. Typical Hardness: 56–60 HRC
AISI M2 Tool Steel | 1.3343 | SKH51
M2 is used in applications where standard cold-work steels wear too quickly. Its higher hardness and finer carbide distribution improve resistance to rapid edge wear, especially when stamping abrasive electrical steels.
Because of its lower toughness than A2, it requires a stable die design and sufficient support to prevent edge failure. Typical Hardness: 60–66 HRC
AISI L6 Tool Steel | 1.2714 | SKT4
L6 is applied when fracture or severe chipping is the dominant cause of tool failure. Its high toughness allows the die to withstand impact conditions that would cause brittle failure in higher-alloy steels.
This grade sacrifices wear resistance and is typically used only when D2 or A2 fails due to cracking. Typical Hardness: 52–58 HRC (for stamping applications)
Summary Table
| Tool Steel Grade | Typical Hardness | Primary Advantage | Best Use Case |
| AISI D2 | 58–62 HRC | High wear resistance | Long runs where edge wear dominates |
| AISI A2 | 56–60 HRC | Higher toughness | Chipping risk, unstable stamping conditions |
| AISI M2 | 60–66 HRC | Superior wear resistance at high hardness | Abrasive sheets, rapid edge wear |
| AISI L6 | 52–58 HRC | High impact resistance | Preventing cracking or edge breakage |