Ledloy

Ledloy, a carbon steel with lead added to make the material machine better. Typical specification for 12L14 alloy is:

Carbon 0.15% max
Manganese: 0.85% to 1.15%
Phosphorus: 0.04% to 0.09%
Sulphor: 0.26% to 0.35%
Lead: 0.15% to 0.35%

Ledloy is a resulfurized and rephosphorized free machining grade of standard Carbon Steel

Here is an excerpt from a letter about CRS and warping problems that mentions Ledloy steel.

Earl Bower has raised a valid point concerning construction of parts from Cold Rolled Steel which needs to be addressed. He states that some time ago upon attempting to make a cross slide from CRS he had so much trouble form the steel warping tha he gave up and switched to cast iron. Veterans forgive me as you will already know all this.

Before I go into this let me state my qualifications to have an opinion! I began my career in machining as an apprentice in overhead line shaft driven production shops. I finished up as a Master Instrument Maker in controlled atmosphere clean room experimental shops engaged in the cutting edge of the business in charge of several large shops. I have run everything from a Derbyshire jewellers lathe to a twenty foot swing Sellers, multiple axis machining centers and every other kind of machine found in the business working in all metals, plastics, and ceramics that can be machined After firty seven years I retired to my own small basement shop, where I still pursue the trade and am still learning about it.

As to the warping problem, steel, just like wood, has a grain and a crystalline structure dictated by the ingredients of the alloy of the particular metal and the processes used in its manufacture. This structure can be readily observed under a metallurgical microscope. The warping problem occurs mostly when a smaller piece of CRS is cut from a large plate without regard to the grain. It doesn't matter if its sawn, sheared or flame cut, as the internal stresses in the plate will be released the minute the surface is broken by any kind of cut. Large cold rolled plates are notorious for this. Then the piece will twist in peculiar ways. The cure is quite simple. You take the piece to a Heat Treating shop and have them anneal it. You do not take your acetylene torch or propane torch to it, or shove it in your wife's oven.

Most sections of the country have heat treat shops which in my opinion are often a machinists best friend, they can usually be found in the yellow pages, and will carefully perform most processes for a very nominal fee. They use controlled atmosphere furnaces with precise time regulated temperature rise and fall parameters as specified for the particular alloy being treated, and are well worth the cost of their services. Needless to say, if you have a piece of steel of dubious origin, you should have this done before you make the first cut if you wish to avoid problems.

In my own experience the problem is rarely found when working from dimensional flats, squares or rounds, most such parts being made with no trouble. Only the large plates seem susceptible to it. You can also use Hot Rolled steel instead, which by the nature of its manufacture is already annealed. However, Hot Rolled is harder to work, and much more difficult to achieve a good finish on. Perusal of a good steel manufacturers catalog will reveal the characteristics of many alloys which are useable, many of them listed as free machining, which means they cut easily and are not plagued by stress problems. Steels such as David Smith's Ledloy or Stressfree are guaranteed free of internal stress and cut almost as easily as brass, but you pay for the privilege, and the usual common C1018 grade in flats has never given me much trouble, my own cross slide being made of C1018.