Tool Steel Grades for Punches and Dies
October 11, 2018There’s something about tool steel grades, especially when they’re used in punches and dies. The metals feel incredibly dense. Way back at the milling plant, a suitable steel alloy has been selected. It’s a coarse-grained material with a ready to adapt microcrystalline structure. Beyond the fabrication process, the tool grade steel is heat treated and tempered, until it emerges ready for its heavy impact duties.
Tool Grade Steel Doesn’t Deform
Using logical reasoning, the steel used to make a tool must be harder and more deform-resistant than the workpiece it’ll eventually be used upon. More than this, the punch or die components must last for hundreds, perhaps even thousands of impact-stressed operations. They can’t crack, can’t deform, and they cannot exhibit any signs of chipping. Beating back the effects of wear and tear, and those effects are extraordinarily heavy in this application area, the versatile tool steel maintains an uncompromised operating edge.
Tools Steel Qualities
Tool materials need to be durable and fatigue-resistant. A cold worked, air hardened tool steel will pull its weight, but then so does a wear resistant steel alloy. The cold worked feature partners with the hardenability ratio to ensure chip indefatigability. Then it’s the wear resistance attribute that prevents a sharp-edged punch or die from losing its well-defined edges. Since the milling facility has provided a suitable coarse-grained steel alloy, let’s head for the heat treatment plant to see how the hardenability process is shaping up.
The Tool Steel Grade Table
Exotic tooling alloys have technical labels like Cryodur and Thermodur. They’re placed in the first column of punch and die grading tables, which allocate the following properties to each tool alloy:
- Hardness ratio
- Toughness
- Shock resistance strength
- High-carbide rating
The labels continue, with technical tags like D-2, 0-1, and A-2 dominating the grading pack.
Incorporating Alloying Additives
Tungsten or vanadium, chromium or molybdenum, the alloying elements occupy prime space inside the steel grain. The heat treated metal goes through a phase change, a transformative process that converts the austenite metal into hardened martensite. Still very much a ferrous-heavy metal, the two phases represent different granular configurations. Now it’s the carbon content that diffuses until the thermal energy produces hardened carbides. From here, there’s still the quenching operation to pass through. Cold water mediums are often replaced here, perhaps by oil or a brine solution.
The milling factory sends billets of steel to the heat treatment factory, the carbon diffuses while the carbides form, and the quench stage locks those tool-centric features in place. However, the work isn’t done just yet, not until the tempering stage is over. The tool steel is brittle. The ultra-hard alloy needs to be tempered, injected with much-needed resilience.
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