Production Method of FREE-CUTTING STEEL

FREE-CUTTING STEEL, also known as automatic machine steel or simply auto steel, is an alloy steel that incorporates one or more easily machinable elements such as sulfur, phosphorus, lead, calcium, selenium, and tellurium in a certain quantity to improve its machinability. The production method primarily involves the following steps:
I. Raw Material Preparation
Selection of Base Steel: Choose appropriate base steel, such as low-carbon steel or medium-carbon steel, based on the required mechanical and machinability properties.
Addition of Easily Machinable Elements: Determine the type and content of one or more easily machinable elements to be added based on production requirements. Common easily machinable elements include sulfur, phosphorus, lead, calcium, selenium, and tellurium.
II. Smelting and Casting
Smelting: Place the base steel and easily machinable elements into a smelting furnace for smelting to ensure uniform distribution of the elements.
Casting: After smelting, pour the molten steel into molds and let it cool to obtain billets of FREE-CUTTING STEEL.
III. Heat Treatment
Heating: Heat the billets to an appropriate temperature to eliminate internal stresses and improve structure.
Cooling: Select an appropriate cooling method, such as air cooling, water cooling, or oil cooling, based on the required performance requirements.
IV. Processing and Inspection
Processing: Perform cutting, grinding, and other processing on the billets to meet product requirements.
Inspection: Conduct quality inspections on the finished products, including chemical composition analysis, mechanical property testing, and machinability testing.
V. Classification and Applications
FREE-CUTTING STEEL can be classified into various types based on the different easily machinable elements it contains, such as sulfur-containing FREE-CUTTING STEEL, lead-containing FREE-CUTTING STEEL, and calcium-containing FREE-CUTTING STEEL. These different types of FREE-CUTTING STEEL have different machinability and mechanical properties and are suitable for different processing fields and applications.
Sulfur-containing FREE-CUTTING STEEL: Sulfur forms manganese sulfide inclusions with manganese and iron in steel. These inclusions disrupt the continuity of the matrix metal, promoting the formation of small and short curling radii of chips during cutting, which are easy to remove, reducing tool wear, lowering the roughness of the machined surface, and extending tool life.
Lead-containing FREE-CUTTING STEEL: Lead exists in steel in the form of fine metallic particles, uniformly distributed or attached around sulfides. Due to its low melting point, lead melts and seeps out during cutting, acting as a lubricant to reduce friction and improve machinability without affecting mechanical properties at room temperature.
Calcium-containing FREE-CUTTING STEEL: Calcium combines with aluminum and silicon in steel to form low-melting-point composite oxides (mainly CaO·Al2O3·SiO2). During high-speed cutting, calcium-based oxides adhere to the surface of the cutting tool to provide lubrication and reduce friction, thereby extending the tool's service life.
Additionally, elements such as selenium, tellurium, and bismuth can also be used in FREE-CUTTING STEEL to improve its machinability.
In summary, the production method of FREE-CUTTING STEEL includes raw material preparation, smelting and casting, heat treatment, processing and inspection, as well as classification and applications. Through reasonable formulation and process control, FREE-CUTTING STEEL with excellent machinability can be produced to meet various processing needs.