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Surface Finish

Surface Finish

While cold drawn bars retain some of the surface imperfections of hot rolled bars, especially seams, small pits, etc., which are not always detected in normal inspection, this product does have a measurable degree of smoothness. The normal cold drawn finish, while it can be plated*, is not recommended for this purpose as imperfections will be evident after plating. Special preparation of cold drawn bars is necessary to improve their suitability for plating.

Turned and polished bars, which have had the surface metal removed, have a smooth surface and can be easily plated.

Ground and polished bars have the highest degree of smoothness and offer a beautifully decorative surface after plating.

Standard "As Drawn" Finish

Cold drawing produces a clean, smooth, bright, uniform surface that minimizes or eliminates further operations by the user to improve the surface. In addition to finish, cold drawn bars are accurate in size and straight-which means they work smoothly in the collets of screw machines. The process also raises tensile and yield strengths, increases hardness and improves machinability.

Turned Finish

Turning is a process of machining bars to a desired size. The removal of the bar's surface layer generally eliminates decarburization, seams, slivers and other surface imperfections. The finished bar can be machined with relative freedom from warpage.

All hot rolled and cold drawn bars have a decarburized outer layer which is low in, or possibly without, carbon content. This condition is due to the prolonged heating at high temperatures used in hot rolling. Because this surface layer of metal is removed, turned bars are especially suited for induction hardening.

Turned bars are usually polished following machining. This leaves a smooth, shiny surface which has a better appearance than is possible in cold drawn bars.

Precision Ground Finish

When an application requires an improved surface finish and closer tolerances than that provided by either cold drawing or turning, ground bars may be specified.

They give the user closer accuracy, maximum smoothness of surface and an improved surface appearance. Removal of the decarburized surface may also be specified, particularly for small size rounds for which turning is not available.

Grinding does not materially cold work the bar, so its metallurgical characteristics are not altered. It is important for the user to distinguish whether the ground bar is to be cold drawn and ground, or turned and ground. Ground bars also are usually polished to give added luster to the finish.

Precision Polished Finish

All cold finished round bars, whether cold drawn, turned, and with or without grinding, are polished as an integral part of the cold finishing process unless specified not polished. Steel bars can be ordered rough turned (not polished) at a reduction in price by sacrificing finish and tolerances (double those of turned and polished).

The polishing operation gives a far smoother, brighter, and more metallic looking bar.

Surface Ratings

The degree of smoothness of the cold finished bars can be measured, as with a Profilometer. Measurement of the surface smoothness is checked in a longitudinal direction and measured in micro-inches (millionths of an inch). Typical measurements of surface roughness follow:

* Reference should be made to the AISI Steel Products Manual, March 1985, page 112.