Peeled, turned, centreless-ground bar to ASTM A484 / ISO h9 tolerance for precision-machining feedstock
Cold-finished bar is the right feedstock when the downstream process is high-volume precision machining: CNC lathe production of valve trim, automated thread-rolling of stud bolts, Swiss-machined fittings, and any application where the supplier-supplied surface and dimensional tolerance must reach the machine spindle without intermediate roughing. The cold-finishing route (peeling, single-pass turning, then centreless grinding) removes the hot-roll oxide skin and the 0.5 to 1.5 mm decarburised surface zone, delivers an ISO h9 dimensional tolerance, and produces a Ra ≤ 1.6 μm surface finish straight from the supplier. Ferralium 255 (UNS S32550, EN 1.4507) cold-finished bar is supplied solution-annealed before the final cold-finish pass, so the as-supplied condition meets the 35 to 55% ferrite range per ASTM E562. Per-heat EN 10204 type 3.2 MTC. RFQ: info@torqbolt.com / WhatsApp +91-22-66157017.
| Diameter | Tolerance class | Surface Ra | Length |
|---|---|---|---|
| 3 mm to 25 mm | ISO h8 (peeled + ground) | ≤ 0.8 μm | up to 6 m |
| 25 mm to 80 mm | ISO h9 (peeled + turned) | ≤ 1.6 μm | up to 6 m |
| 80 mm to 200 mm | ISO h11 (peeled) | ≤ 3.2 μm | up to 6 m |
| Custom h7 / h6 | per drawing | per drawing | per drawing |
Hot-rolled bar arrives with mill scale, surface decarburisation, and ISO h11 to h13 dimensional tolerance, sufficient for general fabrication but not for precision machining feedstock. The cold-finishing route is: (1) end-pointing for centreless feed entry, (2) peeling to remove the oxide layer in a single chip pass, (3) optional turning to tighten the diameter tolerance, (4) centreless grinding to the final ISO h8 or h9 dimension. The resulting bar has a clean, dimensionally consistent OD that the customer's CNC lathe can pick up directly without a roughing pass.
