ENJaw Plate Materials: Mn13 vs Mn18 vs Mn22 Compared
Mn13, Mn18 and Mn22 compared: how work hardening decides jaw plate life, which grade fits which feed, and the cost per tonne numbers behind the choice.
Manganese grade is not a spec detail; it is the cost per tonne, because two plants crushing the same granite can see jaw plate life differ by a factor of two on the choice between Mn13, Mn18 and Mn22.
The three grades in one table
| Mn13 | Mn18 | Mn22 | |
|---|---|---|---|
| Manganese content | ~12–14% | ~16–19% | ~20–24% |
| As-cast hardness | HB ~200–230 | HB ~200–230 | HB ~200–230 |
| Work-hardening response | Moderate | Strong | Strongest |
| Surface hardness in service | ~HB 350–400 | ~HB 450–500 | ~HB 500–550 |
| Best-fit feed | Medium abrasive, low impact | Hard abrasive granite, basalt | Extreme impact plus hard feed |
| Relative price index | 1.0 | 1.15 | 1.3 |
All three are austenitic manganese steels in the Hadfield family. The alloy percentages move and the crystal structure does not, which is why the as-cast plate is soft by design in every grade: the surface the chamber needs is manufactured later, by the rock.
Each grade has a personality. Mn13 is the veteran: the cheapest casting, the most forgiving under shock, and the one that renews its surface fastest per strike, which is why it survives abusive feeds that crack higher grades. Mn18 is the workhorse most hard-rock quarries end up buying: close to the toughness of Mn13 with a stronger hardening response on abrasive feed. Mn22 is the specialist; the extra alloy buys surface hardness for feeds that combine high impact with high abrasion, and it asks for a feed that actually delivers both.
Work hardening, explained properly
Austenitic manganese steel leaves the foundry at roughly HB 200, soft enough to machine and far too soft to crush rock. The answer is in the crystal structure. Under impact, the surface layer transforms to hard martensite; each strike deepens the transformed zone until the working face sits several hundred HB points above the casting beneath it. A jaw plate is therefore a composite the machine makes itself: tough, soft interior, hard skin.
The consequence buyers miss: a jaw plate that never sees real impact never hardens, and wears like aluminium. Cushion the feed with fines or sticky material ahead of the plates and even the costliest grade polishes away at close to its as-cast hardness. Work hardening is bought with strikes, which is why a full chamber, real lumps and no pre-screened cushion deliver the catalogue life on any grade.
The mechanism was patented by Robert Hadfield in 1882 and has outlived every challenger for crushing duty. Carbon around 1.1–1.4% and the manganese that names each grade hold the structure austenitic at room temperature, which is what lets the surface transform under strain instead of in a furnace. Ordinary steels take their hardness at the foundry and lose it only to wear; a jaw plate takes its hardness at the quarry face and renews it with every tonne.
Matching the grade to the feed
The grade is chosen by the feed, and the feed is described by three numbers: compressive strength, abrasiveness, and how much uncrushable material arrives mixed in. The common cases, in the terms a quarry or recycling site actually uses:
- Granite around 200 MPa: Mn18. Hardness response enough for the abrasion, toughness enough for the nips.
- Demolition concrete with rebar tramp: Mn13 is fine; the plate deforms rather than shatters, and the cheaper grade forgives the abuse.
- Quartzite and river gravel, angular and abrasive: Mn18, moving to Mn22 where impact is heavy and plate life is short anyway.
- Soft limestone under 150 MPa that never tramps: Mn13 saves money; the feed is too gentle to wake up a higher grade.
A jaw plate overspecified for its feed earns nothing extra, because hardening follows impact energy, not the alloy content printed on the certificate. Two feed details move the decision as much as the rock does. Feed lump size sets impact energy, which is why primaries often justify a grade that secondaries on the same rock do not. And clay or fines that cushion the chamber suppress hardening on every grade, which is why a washing stage upstream can outperform a metallurgy upgrade.
The cost-per-tonne comparison
Market windows below are for a jaw plate set on a mid-size crusher, quoted for comparison only; real numbers move with the casting market and the chamber size. The feed is granite, and tonnes are per set before final replacement.
| Grade | Plate set, market window | Expected tonnes per set | Cost per 1,000 t |
|---|---|---|---|
| Mn13 | $3,800 | ~55,000 t | $69 |
| Mn18 | $4,400 | ~110,000 t | $40 |
| Mn22 | $5,100 | ~130,000 t | $39 |
The table's message: the expensive grade is the one that does not match the feed. On this granite window Mn13 halves its own life and loses badly; Mn22 buys almost nothing over Mn18 because the nips, not the abrasion, set the failure. Two costs sit outside the table: the change-out itself, which costs the same hours on any grade and therefore favours the longer-lived one, and the risk of an early crack, which favours the tougher one. Where the feed carries uncrushable shocks, the ranking flips toward toughness.
One refinement: plates are reversible, and the mid-life turn at 50% wear applies on every grade, so the tonnes-per-set figures assume the turn is taken. What the buyer controls is not only the grade but the wear log. Two operations on the same rock, one logging tonnes per set and one guessing, diverge within a year; the one that logs buys the grade the rock actually wants, which is worth more than any price negotiation on the casting itself.
The costly grade is not the one with the highest number. It is the one that does not match the feed.
Common questions
Can a higher manganese grade ever be the wrong choice?
Yes, twice over. A jaw plate harder than its duty needs costs more up front and work-hardens no better, because hardening is driven by impact energy rather than alloy content. The extra alloying also trims as-cast toughness slightly, which matters on feeds that hammer. Move up a grade when impact and abrasion both rise, not because a bigger number feels safer.
Why did new plates wear fast without hardening?
Almost always a cushioned feed. Sand, fines or sticky material packed against the liners means the surface is ground rather than struck, so it never transforms to martensite and stays near its as-cast hardness of about HB 200. Clean the feed, keep the chamber full, and read the wear face: a polished plate means grinding, a dimpled plate means hardening is working.
How is the grade of a delivered plate verified?
Ask for the mill certificate with the shipment; it lists chemistry against a heat number. A spectrometer check on arrival costs little and catches substitutions before the plates go in. The as-cast surface should read around HB 200–230; a plate delivered much harder than that has been heat treated into something the chamber will crack early.
The grade decision sits inside the wider parts picture. Part names and intervals are mapped in jaw crusher parts: names, functions and life, the failure patterns behind premature wear are in the five failures that stop a plant, and the machines that carry the plates are on the jaw crusher range page. Send a feed sample and a worn plate photo through the contact page, and SUHMAN answers the grade question against the rock, not against a catalogue.
