Regarding anchor bolt manufacturing, S-1 refers to a section in the ASTM F1554 Specification. The current version is F1554-07a. Under the Supplementary Requirements, section S-1 reads;
“The material described in this section is intended for welding. This supplemental section, by chemical composition restrictions and by a carbon equivalent formula, provides assurance of weldability.”
F1554 allows for three grades of steel round bar: A-36, Grade 55, and A-105. The S-1 section of the supplement is titled, Grade 55 Bars and Anchor Bolts, and as it implies covers only Grade 55 steel. As far as we know, all A-36 steel is weldable. A-105, as a heat treated product is not recommended for welding, as the heat generated during the welding process may compromise the strength of the bolt.
In researching the S-1 Weldability supplement, metallurgists have indicated the likelihood is very high that a batch (known as a HEAT) of grade 55 round bar will be weldable regardless if it shows the S-1 supplement on the mill certification or not. What the S-1 designation does is remove any possibility of any problems with welding.
That possibility only exists due to the steel being recycled. Prior to recycling, steel was made from virgin minerals and the results would be fairly predictable. With the advent of the recycling Mini-Mills a new set of variables was introduced. The raw product is scrap steel that has very little traceability and no indication of mineral content. Often it is not the first time those minerals are being recycled. Along the way each piece of scrap picked up some sort of variation in its mineral composition. Among metallurgists the unwanted minerals are referred to as “tramp elements.”
Once the scrap is reduced to liquid, it can be analyzed. The metallurgist will be looking to make steel to the required specification, such as A-36, A-529, A-572, Grade 55, etc. Through the chemical analysis, what needs to be added to produce the desired results can be determined. In some cases, the heat is deemed to be unusable for any structural steel purpose. These rejected heats get formed in billets, eventually becoming rebar.
If the heat is closed enough to the acceptable range for the desired product, the metallurgist will introduce any additional elements to fine-tune the mineral content. In the case of Grade 55 steel being weldable, what he is looking at is an equation that shows a “Carbon Equivalent” or CE. The CE, which is expressed as a percent will insure proper balance of the alloys present to allow for the steel to be weldable. What the carbon equivalent is mainly protecting against that the steel becomes too hard and the possibility that upon welding hydrogen induced cracking could occur.