Engineering Steels - Bright Steels
Bright low carbon free cutting and
Commercial Quality Mild Steels
The bright low carbon free cutting steels XLCUT and XLCUTPb have been developed primarily for their excellent and consistent level of machinability.
These grades are therefore used where machining is the most important consideration, but high strength or the ability to withstand shock loading is not a requirement and welding will be minimal.
Both grades have high sulphur and increased manganese content to improve their machinability by the introduction of manganese sulphide (MnS) inclusions. These are distributed throughout the structure, promoting localised fracture in advance of the cutting tool. The swart produced is in the form of short chips, which exit the surface cleanly and do not wrap around the cutting tool, the result is an excellent surface finish.
Lead when added also acts as a chip former and lubricator for the cutting tool further improving machinability. While lead can cause some reduction in fatigue strength, ductility and toughness in the higher tensile steels, it has little or no effect on the mechanical properties of the low tensile grades such as XLCUTPb.
Weldability of both grades is reduced somewhat due to the high sulphur, with it's tendency towards brittleness when hot worked. This can be overcome however, by the use of suitable electrodes and correct welding technique.
The leaded grade has the additional problem of producing tox1c fumes during welding, which must be carried out in a well ventilated environment or otherwise avoided.
XCQ a commercial quality bright mild steel should be considered for those applications requiring more strength and/ or a better shock loading capability plus good weldability. This grade due to higher carbon and lower sulphur content has better strength with improved shock loading, welding and cold forming properties. Machinability while not as good as free cutting grades is reasonable, especially the cold drawn material.
To summarise: XCQ has higher strength and better shock loading capabilities than XLCUT or XLCUTPb, also much better weldability but lower machability.
Bright Steels - Technical Spec Sheets
AISI 1215 / XLCUT: Low Carbon Free Cutting Steel, with very good machinability but limited forming and welding properties. Will carburise, with a typical case hardness up to Rc60. End use: Lightly stressed parts.
AISI 12L14 / XLCUTPb: Low Carbon Leaded Free Cutting Steel, with excellent machinability, but limited forming and poor welding properties. End use: Lightly stressed parts.
AISI 1018 / XCQ: Low Carbon Commercial Quality Mild Steel, with excellent welding and forming properties plus good machinability. Will carburise, with a typical case hardness up to Rc60. End use: Light/medium stressed parts.