350 °C Aging: The Heat Treatment Step That Adds 45% Wear Life
Ask a foundry whether they water-toughen their manganese steel liners and the answer is always yes. Ask about the aging step afterward and you learn which foundries read the literature.
Here is what that missing hour in the furnace is worth — measured, not asserted.
The experiment
Researchers took a micro-alloyed Hadfield grade — ZGMn13MoCrTiRE: 13% Mn with Mo, Cr, Ti and rare-earth additions, a chemistry built for liners in low-impact duty — and ran a single-variable aging study after standard water toughening (1,080 °C × 3 h, water quench). Four aging temperatures, two hours each, air cooled: 150 / 250 / 350 / 450 °C.
The results form a clean curve with an unmistakable peak:
| Property | Water-toughened only | Aged at 350 °C × 2 h | Change |
|---|---|---|---|
| Tensile strength | 944.3 MPa | 1,004.1 MPa | +6.3% |
| Yield strength | 592.8 MPa | 647.3 MPa | +9.2% |
| Impact toughness | 150.3 J/cm² | 170.5 J/cm² | +13.4% |
| MLD-10 impact wear mass loss | 0.44 g | 0.24 g | −45.5% |
Every property peaked at 350 °C — strength, toughness, and wear resistance together, which is rare enough to be worth underlining. At 450 °C the story turns: second-phase carbides grow into needles along grain boundaries, stress concentrates at their tips, and every measured property falls back.
Why it works
Water-toughened austenite is a supersaturated solid solution — strong, tough, and carrying untapped dissolved alloy. Aging at 300–350 °C lets molybdenum-promoted carbides precipitate as fine, dispersed, spherical particles inside the grains. They pin dislocations. The matrix gets stronger; the surface resists gouging; and because the particles are round and inside the grains (not needled at the boundaries), nothing is given up in toughness.
The precipitation is why the strengthening and the toughening arrive together — and why the window matters. Same steel, 100 °C too hot, and the strengthening phase turns against you.
The field side: what an entire mine did with it
A large iron ore operation in North China — 14 ball mills, roughly 4,000 t of liner castings consumed yearly — built an entire heat-treatment discipline around this window. Their production schedule reads like a checklist of everything this site’s failure analyses recommend:
- Water-toughening cycles staged by casting thickness (35 mm plates and 390 mm crusher parts do not share a furnace program)
- Slow ramp 30–50 °C/h through the low-temperature range; equalization hold at 650–680 °C
- Quench at 1,060–1,090 °C, transfer to water in under one minute
- Then: aging at 300–350 °C for 6–8 h, furnace-cooled — dispersing carbides, relieving residual stress
- A standing ban on torch-cutting liners on site (local re-heating of a water-toughened plate embrittles the cut edge — see our failure guide)
The payoff, from their published liner records: ZGMn9Cr2 + rare-earth shell liners, quenched and aged, ran 10 months and 759,000 t of ore in a 3.6 × 4.5 m mill — against roughly 260,000 t for the plain ZGMn13 sets they replaced. Reported wear-resistance gain: 28–31% depending on the campaign report, with cost savings of about ¥560,000 for that campaign alone. We expand this story in our modified Hadfield case study.
What to ask your supplier
The process is cheap — a low-temperature furnace hold — which makes skipping it pure margin for a foundry and pure loss for you. Three questions separate the practitioners:
- “Do you age after water toughening, and at what temperature?” Acceptable answers center on 300–350 °C.
- “Show me the furnace chart.” Ramp rates and hold times are on the chart or they are not real.
- “What’s your transfer time to the quench tank?” Under two minutes is the discipline mark.
If you are running manganese liners in moderate-impact duty — where work-hardening alone never fully develops, as our Hadfield mechanics guide explains — this single process step is the cheapest available upgrade to the material you already know.
QM Mill Liners runs the quench-and-age route on all modified Hadfield liner orders and supplies furnace charts with the shipment. Send your current liner life and mill duty — we will quote the upgrade.
FAQ
What does aging do to Hadfield steel? Between 300–350 °C, dissolved alloy precipitates as fine dispersed carbides inside the grains, strengthening the matrix and improving wear resistance — measured +45.5% in impact wear tests — while impact toughness actually rises.
What temperature is best for aging manganese steel liners? 350 °C × 2 h in the controlled study; production schedules at the 14-mill operation use 300–350 °C × 6–8 h with furnace cooling. Above ~450 °C, boundary carbides needle out and properties decline.
Does aging replace water toughening? No — it follows it. Water toughening dissolves the as-cast carbide networks; aging then adds controlled precipitation strengthening. Skipping the first step leaves the brittle network (see our failure case), skipping the second leaves strength on the table.