Originally Posted by HuFlungDung  ....I do not think that any of the modified steels that have their composition adjusted for high machinability are recommended for welded construction. |
I have seen this stated in other threads/posts but I have never had problems welding leaded steel so I looked for some information. This is from;
www.key-to-steel.com
I put in the Bold Italic.
Free Machining Steels
The term free machining can apply to many metals but it is normally associated with steel and brass. Free machining is the property that makes machining easy because small cutting chips are formed. This characteristic is given to steel by sulfur and in some cases by lead. It is given to brass by lead.
Sulfur and lead are not considered alloying elements. In general, they are considered impurities in the steel. The specifications for steel show a maximum amount of sulfur as 0.040% with the actual sulfur content running lower, in the neighborhood of 0.030%. Lead is usually not mentioned in steel specifications since it is not expected and is considered a "tramp" element. Lead is sometimes purposely added to steel to give it free-machining properties.
Free-machining steels are usually specified for parts that require a considerable amount of machine tool work. The addition of the sulfur makes the steel easier to turn, drill, mill, etc., even though the hardness is the same as a steel of the same composition without the sulfur.
The sulfur content of free-machining steels will range from 0.07-0.12% as high as 0.24-0.33%. The amount of sulfur is specified in the AISI or other specifications for carbon steels. Sulfur is not added to any of the alloy steels. Leaded grades comparable to 12L14 and 11L18 are available.
Unless the correct welding procedure is used, the weld deposits on free-machining steel will always be porous and will not provide properties normally expected of a steel of the analysis but without the sulfur or lead.
The basis for establishing a welding procedure for free-machining steels is the same as that required for carbon steels of the same analysis. These steels usually run from 0.010% carbon to as high as 1.0% carbon. They may also contain manganese ranging from 0.30% to as high as 1.65%. Therefore, the procedure is based on these elements. If the steels are free-machining and contain a high percentage of sulfur the only change in procedure is to change to a low-hydrogen type weld deposit.
In the case of shielded metal arc welding this means the use of low-hydrogen type electrode of the E-XX15, E-XX16, or the E-XXX8 classification.
In the case of gas metal arc welding or flux-cored arc welding the same type of filler metal is specified as is normally used since these are no-hydrogen welding processes.
Submerged arc welding would not normally be used on free-machining steels. Gas tungsten arc welding is not normally used since free-machining steels are used in thicker sections which are not usually welded with the GTAW process.