Selection of Tool Steel for Cold-Work Dies and Punches
Cold-work dies, and punches are used in operations such as blanking, shearing, bending, drawing, and extrusion, in which deformation occurs below the material’s recrystallization temperature. Although the process is performed at relatively low temperatures, localized heating at the tool surface can reach around 200°C due to plastic deformation and friction.
In these applications, thermal effects are secondary. Tool failure is primarily driven by mechanical loading, including very high compressive stresses—up to 2413 MPa (350 ksi) in forward extrusion—combined with repeated impact and sliding contact. As a result, the dominant failure modes are abrasive wear, adhesive wear (galling), edge chipping, and fatigue cracking. Material selection must therefore be based on the primary failure mechanism rather than general hardness requirements.
Selection Factors
Tool steel selection for cold-work applications is defined by the relationship between wear resistance and toughness.
Higher hardness improves resistance to abrasion and plastic deformation but reduces toughness, increasing the risk of chipping or brittle fracture under impact or stress concentration. The correct balance depends on how the tool fails in service:
- Applications dominated by sliding contact and long production runs require higher wear resistance
- Applications involving impact, interruption, or stress concentration require higher toughness
For tools with complex geometries or tight dimensional tolerances, the heat-treatment response becomes a practical constraint. Air-hardening steels are preferred in these cases because they reduce the risk of distortion and cracking compared to liquid quenching.
Hardness should not be maximized without considering the failure mode. It must be selected to control either wear or fracture, depending on which limits tool life.
Recommended Tool Steels
AISI A2 Tool Steel | 1.2363 | SKD12
A2 is suitable for applications where neither severe wear nor heavy impact dominates. It is commonly used in medium-run forming and blanking operations where a compromise between wear resistance and toughness is required.
Its air-hardening characteristic minimizes distortion during heat treatment, making it appropriate for tools with tighter dimensional requirements. At 58–62 HRC, A2 provides moderate wear resistance with significantly better toughness than high-carbon, high-chromium steels.
A2 is often selected when D2 provides excessive brittleness, but higher wear resistance than O1 is still required.
AISI D2 Tool Steel |1.2379 | SKD11
D2 is selected when abrasive wear is the primary limiting factor. Its high carbon and chromium content produce a large volume of hard carbides, giving strong resistance to wear and plastic deformation.
It performs well in long-run blanking, deep drawing, and other high-friction operations. However, its low toughness makes it unsuitable for applications involving impact loading or sharp stress concentrations. Edge chipping is a common failure mode if applied outside its suitable range.
D2 should be avoided in punch applications or under interrupted cutting conditions where the risk of fracture is high.
AISI O1 Tool Steel | 1.2510 | SKS3
O1 is used in short-run or less demanding applications where cost and machinability are prioritized over tool life and dimensional stability.
It provides adequate wear resistance and toughness for simple geometries and moderate loads, typically at 58–60 HRC. However, oil quenching increases the risk of distortion and cracking compared to air-hardening steels, limiting its use in precision tooling.
O1 is generally not suitable for long production runs or applications where dimensional accuracy after heat treatment is critical.
S7 (Shock-Resisting Tool Steel)
S7 is selected when fracture or breakage is the primary risk of failure. Its lower carbon content allows it to maintain high toughness and resistance to cracking under repeated impact.
It is commonly used for heavy-duty punches, shear blades, and tools subjected to cyclic shock loading. Typical hardness is 54–58 HRC, which is intentionally lower to improve impact resistance.
S7 should be used where other steels fail by chipping or catastrophic fracture. It is not suitable for high-wear applications unless wear is secondary to impact.
M2 (Molybdenum High-Speed Steel)
M2 is used in severe cold-work conditions where both compressive strength and wear resistance are required, such as cold extrusion punches.
Its high alloy content provides strong resistance to deformation and abrasion at high hardness levels (60–65 HRC). For cold-work applications, heat treatment is often adjusted to achieve a slightly lower hardness to improve toughness and reduce the risk of fracture.
M2 is typically applied where tool failure carries a high cost and standard cold-work steels cannot provide sufficient strength or wear resistance.
Summary Table
| Tool Steel Grade | Typical Hardness | Primary Advantage | Ideal Application |
| A2 | 58–62 HRC | Balanced wear resistance and toughness | General forming & blanking |
| D2 | 58–62 HRC | High wear resistance and compressive strength | Long-run production & deep drawing |
| O1 | 58–60 HRC | Low cost and good machinability | Short-run dies & simple tools |
| S7 | 54–58 HRC | High impact resistance | Heavy-duty punches & shear blades |
| M2 | 60–65 HRC | High strength and wear resistance | Cold extrusion & high-stress tooling |