ZG70Cr3NiMo: One Steel, Ten Years of Trials, 30–60% Longer Liner Life
Some liner grades get one paper and a pat on the back. ZG70Cr3NiMo got a decade of attention from the same engineering team — a wear test, then a heat-treatment improvement, then a failure analysis of the weak link. That sequence, rare as it is, tells you more about a steel than any single trial.
The starting problem
At a major copper mine’s concentrator, large ball mills running wet grinding were eating ZGMn13 Hadfield liners. The classic complaint: after water toughening, thick manganese castings come out with toughness to spare but not enough hardness. In wet grinding — where ore slurry keeps stripping the surface — that combination wears fast.
Step 1: the steel
ZG70Cr3NiMo is a high-carbon alloy steel whose key trick is hardenability. The nickel and molybdenum let thick sections harden in still air — no oil, no water, no quench cracking risk in large castings. The base schedule:
- Hold 700 °C × 2 h (preheat/equalize)
- Austenitize 950 °C × 1.5 h, air quench
- Temper
Dynamic wear testing on an MLD-10 impact-abrasion rig set the baseline:
| Material | Wear loss (MLD-10, %) |
|---|---|
| ZGMn13 Hadfield | 5.35 |
| ZG70Cr3NiMo | 3.65–5.52 depending on condition |
Best-condition samples cut wear by roughly a third against Hadfield.
Step 2: fixing the heat treatment
Early production showed a real-world problem: air quenching left toughness inconsistent across heavy castings. The team’s process revision replaced plain air quenching with 950 °C sand-cooled slow quenching plus a 450 °C temper — and the result was ~50 HRC with uniform hardness through the section. Uniform is the operative word. A liner that is 50 HRC at the face and 40 HRC at the bolt boss wears unevenly and cracks at the soft spots.
Step 3: closing the loop on failure
Rather than declare victory, the team then analyzed failures of the lifter bars (压条) — the highest-stress liners in the set — and fed those findings back into casting and installation practice.
The bottom line
The grade went into service across three concentrators at the same copper group, with liner life improvements of 30–60% over the Hadfield baseline.
| Metric | Value |
|---|---|
| Wear loss vs Hadfield (MLD-10) | 3.65% vs 5.35% (best condition) |
| Production hardness | ~50 HRC, uniform through section |
| Field life gain, 3 plants | +30–60% |
| Heat treatment | air/sand hardening — suited to large castings |
What we take from it
Two things. First, air-hardening alloy steels are the right answer for large wet-grinding liners — you get hardness without quench-crack roulette. Second, a supplier who can talk about why a heat treatment was revised, and who analyzes its own failures, is worth more than one who only ships plates.
QM Mill Liners casts ZG70Cr3NiMo-class air-hardening alloy steel liners for wet ball mills. We run the sand-cooled quench plus temper route on heavy sections, and we’ll happily walk through the metallurgy before you buy. Mill drawing and current liner life get you a quote — start here.
FAQ
What does air-hardening mean for mill liners? The steel reaches full hardness by cooling in air or sand rather than oil or water. For heavy castings this avoids quench cracking and distortion, and gives more uniform properties through the section.
How much longer do alloy steel liners last than manganese steel in copper mills? In this program, 30–60% across three plants. Gains depend on how under-performing the incumbent Mn steel was; in fine-grinding chambers, alloy steels can do far better (see our ZGCr13SiMo case).
Is ZG70Cr3NiMo suitable for SAG mills? It belongs to the same alloy-steel family as the bainitic grades we run in SAG duty. The right choice depends on impact level — send us the duty data and we’ll match the grade.