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Steel Sections Illustration by Jock Dempsey

Commercial Forms of Steel:

Hot and Cold Roll steel

HR bar: Any steel, alloy, low carbon or high that is rolled at the mill and left with the scaled finish and in the "as rolled" condition (not heat treated) is "hot roll steel",HR Steel or HR bar. In the past "mild steel" HR bar was SAE 1018-1020 but today common HR mild steel is structural grade ASTM A36 or similar.

CF bar: The general term for steels that are otherwise finished are "CF" for cold finished. CF steels include cold drawn steels, centerless ground and "pickled and cold rolled steel" and sheared and edge rolled steel. Most steel service centers use the CF as a general indication of the steel's finish as their inventory often varies between different processing methods.

Which cold finish makes a great deal of difference to many end users. The different methods determine the temper condition and the preciseness of the product.

Cold Drawn: For nearly 100 years (~1880 to ~1975) cold drawn was the standard of excellence in precision mild steel, usually SAE 1018-1020. Annealed and then drawn through precision dies it was true to square and held a tolerance of +.000/-.005" (+0.0/-0.13mm) or better (usually better). Cold drawn steel was usually sufficiently precision to make shafts to fit standard bearings, keys for shafts, shims and manufacture all types of items that needed a smooth clean surface and good dimensional control of the raw material. The drawing process requires very good quality steel properly annealed and descaled before drawing. This usualy assures that cold drawn is a better grade of steel. Most small square stock is cold drawn but other types are replacing this under the "CF" designation that does NOT mean the same thing.

Pickled and cold rolled is steel that is rolled just a tad oversize, descaled with acid or water blast and cold rolled to the finished dimensions. In the past this was the same grade of SAE steel as cold drawn and the process used on rectangulars and flats that could not be drawn through dies. It started in the annealed condition and the end product was hard to distinguish from cold drawn. Today however this steel is often A36 structural grade that is cold rolled immediately from the hot roll after spray quenching to remove the scale. The quality of the steel is not as good, finish is not as good, and the temper is usually harder than cold drawn.

Sheared and rolled from plate starts as HR plate that has been rolled to its final thickness dimension at a black heat. This leaves a fine finish and a hard temper. The sheet is then sheared, further work hardening it as well as twisting and bending it. The final stage is straightening and edge rolling which work hardens the product more. The shearing does not produce square edges. The edge and corner rolling attempts to correct this but in the process often creates edge folds and cold shuts. This product is MUCH inferior to cold drawn and is often substituted for both cold drawn and hot rolled flats. The squareness and tolerances are not suitable for key stock or precision applications. The hard temper from work hardening has much more spring back than other steels, ESPECIALLY hot roll and requires different bending jigs than other steels.

I had a supplier substitute sheared and edge rolled 3/16" x 2" for hot roll or the same dimensions. I had built numerous bending jigs based on hot roll from the same supplier just a few weeks prior. The temper of the sheared product was so hard that you could bend a 6" radius and it sprung back to nearly straight. The hot roll only sprung back about 1/4". Just enough to get it off the jig.

Centerless ground is round bar that is sized by grinding on rolls. It is not as straight or as precision as cold drawn round bar which is often used as-is for small and large shafting. The finish is smooth but produced by grinding so that it is not the same as cold drawn. Most centerless ground stock is too high a carbon material to be cold drawn and the process is usually applied to tool steels and drill rod. However, there ARE low carbon centerless ground products AND precision centerless ground products such as stainless ball slide ways. In most cases you need to know which product and the tolerances for your application.

Your steel supplier will generally sell you any one of the four under the CF designation. However, to the end user the difference in products MAY be critical. If you are hot forging the entirety of a piece the original condition is not a concern. But if you are forging part of a bar such as for a picket you will want a hot rolled bar that has a similar finish to the hot forged section. If you are cold bending on jigs or in a press the as delivered temper is critical. Steel Sections Illustration by Jock Dempsey

Shapes and Sizes

Shape forms in steel are becoming more and more limited over time. Most books include shapes like octagon, V-bar, half rounds and round edge flats which are no longer available along with many of the more unusual shapes such as heavy T's. I recently reviewed a new book on welding that included all the shapes available in the early 20th century that were no longer available by the 1970's. I wondered where the author had been for past 30 or 40 years.

The range of sizes is also becoming more limited as our industrial society in North America declines. Most steel catalogs listed HR bar rounds and squares in 1/16" increments from 3/16" up to about an inch and then in 1/8" increments up to 2". Since the early 1970's 1/4" and smaller HR bar and the odd 1/16" increments have not been available. If you needed these sizes you were forced to purchase the more expensive cold drawn bar. The only reason these sizes are still available in CF bar is that they are used for shafting keys and as material to feed a few automatic machines.

Odd size HR bar such as 7/16" square can be ordered from mills if you have time to wait and can afford to purchase the rolling of an entire billet. In the late 1970's I placed an order for 7/16" square from a local mill. The 4,000 feet of bar showed up some three years later!

References and Links


Copyright © 2004 Jock Dempsey, www.anvilfire.com

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