Choosing a cold heading die material is one of the few decisions that locks in everything downstream: hit rate, tolerance drift, regrind interval and scrap rate. Pick too soft and the bore washes out in a week. Pick too hard and the nib chips on the first slug. This guide compares the three families we actually run in production, tungsten carbide, high-speed steel and powder metallurgy steel, and shows how we narrow the choice down from a part drawing.
A heading die is not a cutting tool. There is no clean, continuous chip. It takes a short, violent load cycle at 60 to 300 blows per minute, and most of the damage happens inside a few milliseconds.
Three loads arrive at the same time:
Hardness on its own answers none of this. What decides die life is the balance between hardness, transverse rupture strength and fatigue resistance, matched to your hit count.
Tungsten carbide (硬质合金) is what most of our production dies are made from, and for high-volume screw and bolt work it is still the default. Hardness sits at HRA 88 to 93 after HIP sintering, roughly HRC 70 equivalent, and it holds that hardness at temperatures where HSS has already softened.
Cobalt is the binder. It buys toughness and gives up wear resistance.
| Cobalt | Hardness (HRA) | Behaviour | When we specify it |
|---|---|---|---|
| 6% | 92-93 | Highest wear resistance, most brittle | Fine detail work, thin nibs, stable presses |
| 10% | 90-91 | General purpose balance | Standard screw and bolt dies, the majority of orders |
| 15% | 88-89 | Absorbs misalignment and shock | Headers with imperfect punch alignment, thick-wall nuts |
| 20-25% | 86-88 | Maximum toughness, faster wear | Stainless and high-alloy heading, heavy impact |
Carbide does not wear out gradually. It chips at an edge, or it ring-cracks through the wall. A chip almost always traces back to one of three causes: insufficient shrink-ring interference, a sharp internal corner that should have been radiused, or a slug that was cut off-square and entered the die off-axis. Changing the grade will not fix any of them, and that is why we ask for the heading machine model before quoting a carbide die.
HSS sits between carbide and conventional tool steel. It survives shock that would crack a carbide nib, and it can be reground several times, which matters when a die costs more in downtime than in carbide.
In practice HSS pays for itself on two kinds of job: small batches where the carbide tooling cost cannot be amortised, and awkward geometries where a carbide nib would have unsupported thin sections.
PM steel is atomised, then HIP consolidated, so the carbide particles are uniform and there is no segregation. The result behaves closer to carbide in wear while keeping steel-level toughness and machinability.
It is the right answer when a customer wants carbide-level die life but the geometry is too intricate to press and sinter economically, or when the press is old enough that alignment cannot be guaranteed. Typical grades run HRC 64 to 67 with a very fine, even carbide distribution.
| Property | Tungsten carbide | HSS | PM steel |
|---|---|---|---|
| Hardness | HRA 88-93 | HRC 62-68 | HRC 64-67 |
| Wear resistance | Excellent | Moderate | Very good |
| Shock resistance | Low to moderate | Excellent | Good |
| Regrindable | Limited | Yes, several times | Yes |
| Typical life | 500K-1M+ hits | 80K-300K hits | 200K-500K hits |
| Tooling cost | Highest | Lowest | Mid |
We do not start from a material list. We start from the part and work backwards. These five answers usually settle it:
| What you see | Usual cause | Response |
|---|---|---|
| Corner chipping | Impact load, sharp internal radius | Raise cobalt, add radius, check cut-off squareness |
| Bore bell-mouthing | Abrasive wear at entry | Harder grade, entry chamfer revision, coating |
| Longitudinal crack | Insufficient shrink-ring interference | Recalculate casing fit, not a material change |
| Galling on the bore | Lubricant film failure | Surface finish, polishing direction, lubricant review |
| Size drift before wear-out | Thermal growth or casing relaxation | Cooling check, casing material review |
Notice that two of those five are not material problems at all. Replacing the grade is the most expensive way to discover that the casing fit was wrong.
We make the full set, not just the insert: die nib or insert, shrink ring or casing, punch, and the closing ring where the design needs one. Nibs and casings are matched and shipped as a pair, because a replacement nib dropped into a worn casing will crack. For the wider product range see cold heading dies and split dies, and for the deformation limits that sit behind material choice, read the extrusion ratio limits.
Give us the drawing, the wire grade, the machine model and the annual volume. We will come back with a recommended grade, an interference calculation for the casing, and a hit-life estimate you can compare against your current tool. Precision requirements are covered in our die precision grades.