What the pin has to do
A roller-chain pin does two jobs at once, and they pull in opposite directions. It is the bearing surface of every joint: the bush rotates on it each time the chain articulates round a sprocket, so its surface has to resist wear. And it is a structural member carrying the full chain tension in shear and bending, plus whatever shock the drive throws at it, so its body has to resist breaking. Hard surfaces resist wear; tough cores resist cracking. How a pin is heat-treated is a decision about which of those two to favour, and that decision shows up years later as the way the chain eventually fails.
Case-hardening: hard skin, tough core
Case-hardening (carburising and similar surface treatments) hardens the outer layer of the pin and leaves the core softer and tougher. The hard case takes the sliding wear against the bush; the ductile core absorbs shock without cracking. It is the conventional route for general roller chain because most drives are lubricated, moderately loaded and expected to wear out, and a case-hardened pin wears slowly and predictably as long as it is oiled.
Its limit is that it is a wear solution. Once the case is worn through, usually because the joint ran dry or full of grit, the softer core underneath wears fast and elongation runs away. And under repeated overload the pin can crack from the surface inward, because a hard case is also a brittle case.
Through-hardening: uniform strength, all the way in
Through-hardening heats and quenches the whole pin so that its hardness, and therefore its strength, is uniform through the full cross-section, not concentrated in a skin. There is no soft core to expose and no hard–soft boundary for a crack to follow. The result is a pin that resists shock loading and fatigue far better, which is why it is the construction chosen for the drives that break chain rather than wear it: presses, shredders, granulators, heavy bucket elevators and shock-loaded conveyor drives.
On MAXTOP HV chain the V in the size code denotes through-hardened pins, paired with heavier plates; the range runs 60HV to 200HV with ultimate strengths from 5,100 to 51,000 kgf. See the HV range page for the full table. Welded steel mill chain uses letter codes for the same idea: R for heat-treated pins, X for induction-hardened pins, H for all parts heat-treated, detailed on the welded steel page.
What through-hardening does not do. It does not stop wear. The pin and bush are still a sliding joint, and a through-hardened chain run dry elongates like any other. Strength buys resistance to breaking; lubrication buys resistance to wearing. They are different purchases.
Read the failure, then choose the pin
| What you see | What it means | The fix |
|---|---|---|
| Chain elongated to 1.5–2%, sprockets hooking, no broken parts | Worn out: lubrication, alignment or contamination | Fix the cause; a stronger pin will not help. See lubrication. |
| Chain elongated far earlier than expected, joints stiff or seized | Case worn through or joint run dry / full of grit | Lubricate, seal or move to self-lube; check the environment |
| Broken or turned pins, cracked plates, little elongation | Overload, shock or fatigue: a load problem | Through-hardened pins and heavier plates: HV chain, or a larger pitch |
| Both: elongated and breaking | Two problems; the wear may have caused the breakage (chain climbing teeth) | Fix lubrication and sprockets first, then reassess load. See the fault finder |
The rule of thumb: wear points to lubrication, breakage points to load. Fitting stronger chain to a wear problem wastes money and changes nothing; fitting more lubrication to a load problem delays the next breakage by a week.
Where HV fits
HV chain follows standard ANSI pitches and roller diameters, so it is normally the answer when a drive keeps breaking chain but upsizing the pitch would mean new sprockets, guards and centres. It adds capacity at the same pitch. It is supplied to order (contact us for the current lead time), and we will confirm sprocket compatibility on your drive before you commit. If you send a photo of the failed part, we will also tell you if HV is not the answer.
Common questions
What does through-hardened pin mean on a chain?
The pin is hardened uniformly through its full cross-section rather than only at the surface. That gives it consistent strength all the way through, which raises the chain's resistance to shock loading and fatigue on heavily loaded drives. On MAXTOP HV chain the V in the size code denotes through-hardened pins.
Is a through-hardened pin always better?
No. It is better at resisting breakage, not wear. The pin and bush still form the same sliding joint, so a chain that is elongating rather than breaking will elongate just the same. Fix lubrication, alignment or contamination first; upgrade the pin construction when the failure is cracked plates, broken or turned pins.
How do I tell whether my chain is wearing out or breaking?
Measure it. A chain that has reached 1.5–2% elongation has worn out, and wear almost always comes back to lubrication. A chain that fails well before that with broken pins, cracked plates or fatigue marks has been overloaded or shock-loaded. Our fault-finding guide walks through the signs.
Breaking pins?Send a photo of the failure and the drive details and we'll say whether HV solves it before you spend.
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