Bars

Hot rolled, cold drawn or ground

The production route decides the tolerance, the surface and the price, and it is usually the thing a buyer under-specifies.

• Hot rolled, annealed and pickled — the widest tolerance and a matt scale-free surface. Correct where the bar will be fully machined anyway.
• Cold drawn — pulled through a die. Closer tolerance, brighter surface, higher strength through work hardening, lower ductility.
• Centreless ground — ground to a close diameter tolerance, typically h9 or h11, with a good surface. Specify this where the bar diameter is a functional dimension, such as a shaft running in a bearing.
• Peeled and polished — turned rather than drawn, which removes the decarburised surface layer. Used on larger diameters where drawing is impractical.

If you order “316 round bar 40 mm” without stating the route, you will get hot rolled, and the actual diameter may be a millimetre off nominal. That is correct to standard and useless if you needed a running fit.

Machinability and the free-cutting grades

Austenitic stainless work-hardens as it is cut, which makes it demanding to machine: it wants sharp tools, positive rake, rigid setups and a constant feed. Dwelling in the cut hardens the surface and destroys the next pass.

Where high volumes of turned parts are needed, SS 303 adds sulphur to break the chip and machines far faster than 304 — at the cost of corrosion resistance, so it should not be used in wet or chloride service. In brass, C360 free-cutting brass is the benchmark, and Type 1 and Type 2 free-cutting brasses cover the same territory. These are the grades behind most machined valve and fitting bodies.

The PH grades

17-4 PH and 15-5 PH are precipitation hardening martensitic stainless steels. They are supplied in the solution-annealed condition (Condition A) and then aged by the user to a designated condition — H900, H1025, H1150 and so on — where the number is the ageing temperature in Fahrenheit. Lower ageing temperatures give higher strength and lower toughness. Machine in Condition A and age afterwards, allowing for the small dimensional change on ageing. State the required condition on the order, because it determines the mechanical values on the certificate.

Copper busbar and electrical grades

Electrical conductivity is governed by purity and by temper. EC-grade copper busbar is supplied for switchgear and distribution, where conductivity is specified as a percentage of IACS. Hard temper gives strength for long unsupported spans; soft temper allows bending on site. Oxygen-free copper (C101) is used where the material will be brazed or used in a reducing atmosphere, since ETP copper suffers hydrogen embrittlement under those conditions.

Hex, square and flat

Hex bar is sized across flats and is the starting stock for fasteners and machined hex bodies. Square and flat bar cover structural and fabricated work. On flat bar, confirm whether the corners must be square or may be slightly radiused — rolled flat bar has a natural corner radius that occasionally matters at assembly.

What to tell us when you enquire

Grade and standard, section and size, production route and tolerance class, length, quantity, and any required condition or temper. For machined-part work, tell us the finished part diameter — we can often suggest a stock size that reduces the material you turn away.