The surface of a nickel alloy bar decides how it looks, how it machines, and how it resists corrosion in service. Southerly Alloy supplies bars in the full range of surface conditions and finishing states, from hot-finished black bar to centreless-ground and mirror polish. This guide explains the common conditions and the steps that produce them.
Surface Conditions
| Condition | Description | Typical use |
|---|---|---|
| Black, hot-finished | As-rolled oxide surface, lowest cost | Rough machining, large sections |
| Bright | Smooth, light surface from cold drawing | Visible parts, light machining |
| Peeled, turned | Cut surface removes the outer layer | Better size control, cleaner base |
| Ground, centreless | Ground to tight tolerance, Ra ≤ 0.8 µm | Shafts, precision parts |
| Polished | Buffed bright surface | Decorative, clean-service parts |
| Mirror, No. 8 | < 0.05 µm, reflective | Hygienic, architectural |
| Pickled | Acid cleaned, scale free | Before further finishing |
| Brushed, satin, No. 4 | Directional texture | Architectural, handled parts |
| Bright annealed, BA | Shiny from controlled atmosphere | Corrosion-sensitive service |
| Sandblasted, bead-blasted | Matte, uniform roughness | Bonding, coating base |
| Passivated | Chemically stabilized surface | Corrosion resistance |
| Electropolished | Smooth, low-roughness, clean | Hygienic, high-purity service |
| 2B, 2D | Standard cold-rolled, matte | General supply |
Finishing Steps
Surface conditions are reached through a chain of finishing steps applied after the forming route:
- Turning and peeling remove the outer layer and scale.
- Centreless grinding holds tight diameter tolerance.
- Straightening removes bow for clean cutoff and machining.
- Polishing and buffing raise the surface to bright or mirror.
- Pickling strips scale in acid.
- Passivation stabilizes the chromium-rich layer.
- Electropolishing smooths and cleans the surface chemically.
- Shot peening and sandblasting set a matte, uniform texture.
- Burnishing, laser polishing, and chemical etching serve special surface needs.
- Plasma nitriding hardens the surface for wear service.
Choosing a Finish
Pick the finish from the service, not from habit. Black hot-finished bar suits rough machining where cost leads. Bright or peeled bar suits light machining and visible parts. Ground or mirror finishes suit shafts, seals, and hygienic duty. Our Bar Manufacturing Process guide explains how each finish follows from the forming route.
Bar Shapes and Conditions
Every surface condition is available across the bar shapes we supply. See Bars and rods by grade for the full catalogue, and our Heat Treatment Services guide for condition after heat treatment.
Frequently Asked Questions
How do peeled and ground bar differ in the shop?
Peeling cuts the outer layer on a lathe to reach size and a clean base. Grinding uses an abrasive wheel to hold a tight diameter and a low roughness.
Can you supply mirror-finish bar?
Yes. Mirror (No. 8) finishes are available on request, most often for architectural and hygienic service.
Is pickling required before passivation?
Pickling is the usual first step because it removes scale; passivation then stabilizes the surface chemically.
Are mill certificates provided?
Every heat travels with an EN 10204 3.1 mill certificate.
Request a Quote
Send the grade, shape, diameter, surface condition, and quantity. Southerly Alloy returns a quoted price, lead time, and the certificate package in one reply.