High-Toughness Tool Steels for Cracking and Fracture Resistance
High-toughness tool steels are used when cracking, chipping, or sudden fracture are the primary failure modes. In these applications, the tool usually breaks before it wears out, so the material must absorb impact loads, resist stress concentrations, and slow crack growth.
High-Toughness Tool Steels Available from Aobo Steel
Aobo Steel supplies high-toughness tool steel round bar and flat bar for impact tools, shear blades, forming dies, hot-work tooling, and fracture-sensitive industrial applications.
S7 | 1.2355
Best general-purpose shock-resisting tool steel for impact, chipping, and fracture problems.
S1 | 1.2550
Shock-loaded tool steel for moderate hot hardness, hot punching, hot shearing, and selected impact tools.
L6 Tool Steel
Nickel-enhanced toughness direction for heavy shearing, forming, and shock-loaded machine parts.
H11 Tool Steel
Hot work steel for tools that crack under heat, pressure, and repeated thermal cycling.
H13 | 1.2344 | SKD61
Balanced hot work steel for forging, extrusion, die casting, and hot punches.
High-toughness tool steels usually have lower or moderate carbon content and fewer large primary carbides than high-wear cold work steels. This improves fracture resistance, but it also limits maximum hardness and abrasive wear resistance.
Why Toughness Matters in Cracking and Fracture Failure
Cracking often starts from sharp corners, impact-loaded edges, holes, notches, or areas exposed to repeated thermal cycling.
In high-carbon, high-chromium steels, large carbides improve abrasive wear resistance but can also serve as crack initiation sites. This is why grades such as D2 and D3 are strong choices for wear, but not always the best choice for heavy impact or sudden fracture.
High-toughness tool steels use a different balance. They reduce carbide-related brittleness and rely more on matrix strength, ductility, and shock resistance.
High Toughness Tool Steel Selection Table
| Failure / Working Condition | Recommended Grades | Why These Grades Fit |
|---|---|---|
| Repeated impact at room temperature | S7, S5, S1 | S-series steels are designed for shock resistance. S7 gives the best general balance, S5 suits severe battering tools, and S1 is useful when some hot hardness is also needed. |
| Punches, chisels, and impact tools breaking in service | S7, S1, S5 | These grades absorb impact better than high-carbon wear steels and reduce the risk of sudden fracture. |
| Heavy shearing or forming with edge chipping | S7, L6, H11 | S7 gives high shock resistance, L6 adds nickel-enhanced toughness, and H11 is useful when the load is combined with heat. |
| Hot punching, hot shearing, or moderate hot impact | S1, S7, H11, H13 | These grades keep better toughness under elevated temperature than ordinary cold work steels. |
| Hot forging, extrusion, die casting, or thermal fatigue cracking | H11, H13 | H-series hot work steels combine toughness, hot strength, and resistance to heat checking. |
| Heavy-duty machine parts under shock load | L6, S7, H11 | These grades offer better fracture resistance than high-wear cold work steels while keeping useful strength and hardenability. |
| Simple striking tools, hand tools, or cold chisels | W1, W2, S1 | W-series steels can form a hard surface with a tougher core in shallow-hardening applications; S1 gives better shock resistance. |
Grade Direction
| Grade | Selection Direction |
|---|---|
| S7 | Best general-purpose shock-resisting tool steel for impact, chipping, and fracture problems. Good choice for punches, chisels, shear blades, and forming tools. |
| S1 | Suitable for shock-loaded tools that may see moderately elevated temperature, such as hot punching or hot shearing tools. |
| S5 | Better for severe battering and pneumatic impact tools where shock resistance is more important than wear resistance. |
| L6 | Useful when better toughness is needed, but the application still requires more wear resistance and hardenability than many S-series grades. |
| H11 | Better for hot work tools that crack under heat, pressure, and repeated thermal cycling. |
| H13 | More balanced hot work choice for forging, extrusion, die casting, and hot punches where toughness and hot strength are both required. |
| W1 / W2 | Suitable for simpler tools where shallow hardening can provide a hard working surface with a tougher core. |
When Not to Choose High-Toughness Tool Steels
High-toughness tool steels are not the best choice when abrasive wear is the main failure mode.
If the tool loses size, edge sharpness, or service life mainly due to wear rather than cracking, high-wear cold-work steels are usually better. D2, D3, and D6 are typical choices for severe abrasive wear.
High-toughness tool steels are also not ideal when the working hardness must stay above 60 HRC. Most toughness-oriented grades are selected for fracture resistance rather than maximum hardness.
For high-speed cutting, toughness alone is not enough. The steel must be selected for hot hardness and red hardness instead.
For cracking and fracture problems, toughness should be the first selection factor. For severe abrasive wear, high-wear cold-work steels are usually the better direction.
Need Bulk High-Toughness Tool Steel Supply?
Aobo Steel supplies S7, S1, L6, H11, H13 and other high-toughness tool steel round bar and flat bar for bulk industrial orders. Send your required grade, size, quantity, and application.