SAG Mill Liner Steel: Outlasting Hadfield by 1.5× in 70 Days
SAG mills do not give liner steel an easy time. Big balls, coarse feed, constant pounding — and at one copper mine in South China, the standard ZGMn13 Hadfield liners were losing the fight badly.
The mill in question: a φ28′ × 13′ (φ8.53 × 3.96 m) semi-autogenous mill, running a 140 t ball charge against ore with a hardness factor of 12–16. That is serious, high-energy duty.
The problem in numbers
Hadfield liners in this mill were failing in under two months. Some plates were down to roughly 10 cm of section after a single month. The mine’s SAG liner consumption ran to about 540 t per year — roughly ¥10.6 million in direct costs, before you count the downtime for relines.
When liner consumption is measured in hundreds of tonnes, the material decision is worth some engineering effort.
The replacement steel
The trial material was a medium-high carbon Cr-Ni-Mo bainitic low-alloy cast steel:
| Element / Property | Value |
|---|---|
| C | 0.69 % |
| Cr | 3.60 % |
| Ni | 0.70 % |
| Mo | 0.64 % |
| Micro-alloying | W, V traces |
| Microstructure | martensite + bainite + carbides |
| Hardness (cooling 2–12 °C/min) | HRC 52–62 |
The interesting property of this family is hardness stability across section thickness. Real SAG liners are heavy castings; a steel that only hardens in thin sections is useless here. This grade holds HRC 52–62 across a wide cooling-rate window, which is exactly what a large, irregular casting needs.
The result: 70 days, 910,000 tonnes
New steel liners and ordinary ZGMn13 liners were mixed in the same mill campaign — the fairest test a mine can run, because every liner position sees the same ore, the same balls, the same schedule.
| Metric | ZGMn13 Hadfield | Cr-Ni-Mo bainitic cast steel |
|---|---|---|
| Service life | < 2 months | 70 days continuous, still in service at inspection |
| Throughput in that period | — | 910,000 t of ore |
| Relative life | 1× | 1.5× or better |
After 70 days and 910,000 tonnes of ore, the bainitic steel liners were measured as still fit for service. Overall service life improvement over the incumbent liners came in at 1.5× or more.
Why not just use Hadfield in SAG mills?
Plenty of operations do, and it can work — with caveats. Hadfield steel needs impact to harden, and SAG mills supply plenty. The failure mode at this mine was not gradual wear but fracture. Under 140 t of ball charge, casting quality and toughness margins decide whether a plate survives. The bainitic grade’s martensite-bainite matrix takes impact and resists crack growth better than insufficiently-tough austenite in this duty.
Our practical take after looking at a lot of SAG liner failures: for mills above roughly 28 ft with hard ore, a engineered bainitic or medium-alloy steel will usually out-economize Hadfield even at a higher price per plate — the reline schedule relief alone often pays for it.
QM Mill Liners produces bainitic Cr-Ni-Mo cast steel liners for SAG mills up to this size class. Send your mill drawing, ball charge and ore hardness — we’ll quote both standard and upgraded options so you can see the cost-per-tonne math yourself.
FAQ
What liner steel is best for large SAG mills? There is no single answer, but for high-impact SAG duty on hard ore, bainitic and martensitic low-alloy cast steels in the HRC 50–62 range have displaced Hadfield in many mines. The 70-day trial above shows why.
How long do SAG mill liners last? Highly variable — from a few weeks for Hadfield in hard-ore large mills to several months for engineered alloy steels. Ball charge, feed size and ore hardness dominate.
Is bainitic cast steel more expensive than Hadfield? Per plate, yes. Per tonne of ore ground, often significantly cheaper. In this mine’s case, liner life of 1.5×+ against 540 t/yr of consumption made the upgrade an easy call.