Keep these 6 Keys to Using Free Machining (12XX) Steels in mind:
- These steels are not generally sold for applications requiring high standards of strength, hardness or other related properties. Applications where vibratory, torsional or alternating stresses approach the grades’ static limits are NOT recommended.
- These steels are frequently case hardened or carburized in order to achieve desired surface hardness.
- When cold drawn, these steels can be notch sensitive. Highly polished fatigue specimens may achieve expected endurance values, but poor surface finish, tool marks, or sharp corners in the design may cause lower than expected performance.
- These grades have relatively low impact strength at reduced temperatures and should not be used for sub-zero impact applications.
- These steels are not recommended for applications where severe cold work follows machining. Crimping, staking and swaging may be performed, especially in non-renitrogenized grades. But severe crimping, cold metal movement, and bending may not be satisfactory in these grades.
- The addition of Lead or Bismuth does not alter the mechanical properties in tension. 12L14 and 1215 of same nominal size and process will be indistinguishable by hardness or tensile testing.
Free Machining Steels in the 12XX series- 12L14, 1215, etc., are selected in order to reduce the time needed to make large volumes of complex parts. This reduces the cost per part. The usual application is one where bulk and shape (mass and geometry) are the chief requirements. The factors that make these steels highly machinable also influence behavior of the products in service. Designers and engineers should keep the above 6 Keys in mind when considering the material for an application.