Direct answer: Mn13 jaw plates are cast austenitic manganese steel (nominally ~13% Mn, in the ASTM A128 family), not cut plate. As cast they sit near 200 HB and stay tough; under impact the working face work-hardens into roughly 450–550 HBW while the core stays austenitic. Mn13 suits standard quarry and aggregate feed. Mn18, Mn18Cr2 or Mn22 are specified for harder feed and for larger plates that flex under load, and an alloy or higher-chromium grade is the better start when the feed is fine and low-impact and the surface never hardens.
What Mn13 actually contains
Mn13 jaw plates are the default wear material for the fixed and movable jaws of jaw crushers, and the name carries real information: a manganese content around 13 percent in the Hadfield family of austenitic manganese steels, the same material family covered by ASTM A128. Mn13 is a family, not a single recipe. The nominal 13% manganese sits in a specification band, and the same family extends upward for heavier duty:
| Grade | Manganese | Carbon | Chromium | Typical use |
|---|---|---|---|---|
| Mn13 | ~11.5–14% | ~1.1–1.35% | — | Standard jaw plate duty |
| Mn13Cr2 | ~11.5–14% | ~1.1–1.35% | ~1.7–2.2% | Higher as-cast hardness, better sliding abrasion |
| Mn18 | ~17–19% | — | — | Heavier duty |
| Mn18Cr2 | ~17–19% | — | Chromium-bearing | Harder feed, large plates |
| Mn22 | ~21–23% | — | Chromium-bearing | Very heavy, high-impact duty |
Silicon sits around 0.3–1.0%, with sulphur and phosphorus held low. The chromium in the Mn13Cr2 form raises the as-cast hardness and improves resistance to sliding abrasion without giving up the toughness of the manganese family.
Ranges like these are published by most foundries, but they are typical bands, not a guarantee. The meaningful number is the melt chemistry of the actual heat, confirmed by a material certificate against the standard agreed for the order, an ASTM A128-series or GB equivalent.
Why it hardens where it is hit
As cast, and after the water-quench treatment that gives it a full austenitic structure, the plate is comparatively soft, which makes it ductile and tough enough to absorb the shock of a boulder landing on the jaw. Under repeated impact, the surface layer deforms and transforms: the austenite in the working face converts to a much harder martensite, while the core stays austenitic and tough.
| Condition | Typical hardness | What it means in service |
|---|---|---|
| As cast, after water quench | Around 200 HB | Ductile and tough; absorbs impact without cracking |
| Work-hardened surface layer | Roughly 450–550 HBW | Martensitic skin resists wear |
| Core | Stays austenitic | Retains the toughness reserve |
The plate effectively wears in a hardened skin and rests on a tough body, which is why a correctly loaded Mn13 jaw plate can outlast a harder-looking steel that starts hard but has no reserve of toughness. The same mechanism explains the limitation: without impact, the surface does not harden, and Mn13 in a low-impact, fine-feed duty can wear like a softer steel.
A jaw plate is a casting, not a cut piece
One distinction matters when buyers compare prices: a jaw plate is a casting, not a cut piece of plate. Mn13 steel is also supplied as rolled plate for liners and chutes, but crusher jaws are cast to the part geometry, tooth profile, mounting holes and all, through green sand, shell moulding or lost foam, depending on size and complexity.
A plate that is simply cut or machined from rolled Mn13 stock lacks the cast tooth geometry that makes the jaw bite, and its through-thickness properties are not the same as a casting poured for the part. The price comparison that matters is between castings of the same grade and review scope, not between a casting and a piece of stock steel. Ask what the plate was cast from and how it was made, not only what grade is stamped on it.
Mn13, Mn18Cr2 or Mn22: which duty needs which grade
Within the manganese family, the choice follows the loading:
| Duty | Typical grade | Why |
|---|---|---|
| Standard quarry and aggregate feed (granite, basalt, limestone), plates rigid enough to pass impact into the surface | Mn13 | Work-hardens under normal impact |
| Harder feed, larger plates that flex under load | Mn18, especially Mn18Cr2 | Higher as-cast hardness and better surface resistance, with a tough core |
| Very heavy, high-impact duty, large plates, very hard rock | Mn22 | Highest manganese content, usually with chromium |
| Fine, low-impact feed where the surface polishes instead of hardening | Alloy steel or a higher-chromium option | Needs initial hardness rather than work hardening |
The same part number can justify different grades in different pits, which is why a foundry that quotes a grade before asking about the feed is quoting on hope, not on data.
What the failure pattern tells you
Failure patterns decide whether the grade was right:
- Cracks through the plate. Usually oversized feed, tramp metal, or a plate that was not fully seated. A different grade will not cure it.
- Smooth, polished wear face in fine low-impact feed. The surface never hardened; an alloy steel or a higher-chromium option with more initial hardness can last longer.
- Uneven wear, one corner or one side fast. Feed distribution or jaw setting, not material.
Photographs of the worn plate with the running hours attached are the fastest diagnostic a foundry receives, and they are worth more than a verbal description of the failure.
Machine coverage
Jaw plates are produced to reference across the common jaw crusher ranges, the C-series and LT-class machines, the J and JM classes, Kue Ken and Terex Pegson machines, and the many PE and PEX models used across Asia and Latin America, as well as to drawing, 3D model or sample.
The part number cast on the back of the plate is the fastest reference; where it has worn away, a tape measure on the tooth profile and bolt pattern plus a photo of the mounting face is enough to match. Produced to reference means the geometry, bolt holes and tooth form are reproduced to the original part, with the grade and inspection scope confirmed in review. The machine name is the starting point, not the whole specification.
What to send for a quotation
For a reliable quotation, the foundry needs:
- The crusher model and part number, or a photo of the worn plate.
- The typical feed size and rock type.
- The closed-side setting.
- The current plate life in hours, and how the old plate failed.
- The quantity and delivery market.
With those facts DINGDAR confirms the grade, hardness and inspection scope before quoting, and replies with technical feedback within 12–24 hours. The fixed and movable jaw plates we cast, and the review process behind them, are laid out on the jaw crusher wear parts page; the material selection logic for the manganese family is covered in our guide to choosing jaw plate material.
Installation decides how much life you actually get
A jaw plate is clamped against the frame by wedges or bolts, and the fixing must hold the plate tight against its seat: a loose plate hammers, cracks from the back and wears its seat, regardless of grade.
Mn13 plates are generally fitted as cast or with light grinding on the mounting face. The jaw setting interacts with the plate profile: a worn tooth profile changes the crushing angle and the product shape long before the plate is thin. Checking the seat, the wedges and the setting at each change is cheap maintenance that shows up directly in plate life.
The certificate is what proves the grade
For Mn13 the meaningful evidence is the melt or heat analysis, which states the manganese, carbon and chromium actually poured against the agreed standard; a hardness figure on the as-cast or treated state; and a dimensional report on the tooth profile and the mounting face, because a plate that does not seat does not last.
Buyers who order Mn13 without specifying the standard or the records receive plates labelled Mn13. The certificate is what turns the label into a verifiable fact. Inspection scope is agreed in the review, so the records travel with the shipment rather than being requested after arrival.
Cost per ton, not cost per plate
Mn13 costs more than a plain carbon or low-alloy casting at the same weight, and it pays for itself only through longer life, which depends on the duty actually hardening the surface.
A plant that records tons crushed per set, and the failure mode at change-out, gets a simple cost per ton that settles the grade question faster than any brochure. Two plants crushing the same rock can legitimately see different economics for the same plate grade because their settings, feed and maintenance differ. That is why the data from your own plant is the deciding input, not a generic claim about life.
Summary
The short version: Mn13 jaw plates are cast, not cut; they harden where they are hit; Mn13 covers standard duty while Mn18 and alloy grades step in for harder feed; and a photo of the worn plate plus the machine reference beats a drawing request every time.
To start a review, send the part number, a photo of the worn plate, or the crusher model through the contact form, by email to [email protected], or on WhatsApp. The technical review confirms the grade and inspection scope within 12–24 hours, and the quotation is built on the confirmed facts.