When sourcing alloy steel round bars for mechanical parts, gear and shaft manufacturing, buyers frequently confuse black hot‑rolled bar and peeled (turned) bright bar. Misunderstanding surface conditions may lead to wrong dimension expectation, extra machining cost or claim risk.
Black Hot‑Rolled Bar (Black Bar)
Black bar is hot‑rolled & annealed (HR+A) raw bar without further surface machining.
- Surface: covered with mill oxide scale, minor rolling marks are acceptable
- Dimension: follow hot‑rolling tolerance, e.g. Dia 31mm ±0.2 mm
- Advantage: lower unit cost, suitable for heavy stock‑removal forging or full turning process
- Note: oxide scale and decarburized layer exist on outer surface.
Peeled / Turned Bright Bar
Peeled bar is processed by peeling lathe from original hot‑rolled black bar.
- Surface: clean bright metallic finish, oxide scale fully removed
- Important reminder: Peeling will remove material layer. If you start from Dia31mm black bar, final peeled diameter will be smaller than original 31 mm. Do not expect peeled dimension equal to hot‑rolled blank dimension.
- Tolerance: tighter dimensional accuracy compared with hot‑rolled black bar
- Advantage: less machining allowance for customers, saving tool wear and processing time.
Cost Gap Reference
Normal peeling processing cost creates price gap around 1.2‑1.7 USD/kg equivalent. Much larger price difference usually comes from extra grinding, straightening, full UT inspection or mill original bright bar, not only simple peeling work.
Which one you should choose
- Select black bar: for forging, heavy‑cut machining project, cost‑sensitive order
- Select peeled bar: for semi‑finished components, limited machining allowance requirement
