Determine the Non-Metallic Inclusions on Metallic Materials

Nonmetallic inclusions are compound materials embedded within steel during the manufacturing process.

Inclusions have a different chemical origin and give various mechanical properties to steel, such as corrosion resistance, machinability, toughness, and formability.


As a general rule, the fewer or less severe the inclusions, the higher the steel quality. Consequently, analyzing and documenting nonmetallic inclusions is crucial for steel quality control.



There are a number of microscopic test methods that have been developed to determine the non-metallic inclusion content of wrought steel.  For each method, inclusions are assigned to a category based on similarities in morphology, and not necessarily on their chemical identity.


The most common microscopic inclusion ratings performed for steel in the US are ASTM E45 Methods A and E, also referred as JK inclusion rating.  These methods place inclusions into one of several composition-related categories (Type A – Sulfides, Type B – Aluminates, Type C – Silicates, Type D – Globular Oxides).  These types of inclusions are referred to as “indigenous inclusions”.  The microscopic methods are not intended for assessing the content of “exogenous inclusions” (those from entrapped slag or refractories).  Microanalytical techniques such as energy dispersive X-ray spectroscopy (EDS) may be used to aid in determining the nature of the inclusion.


Materials with very low inclusion contents may be more accurately rated by automatic image analysis, which permits more precise microscopic ratings.


Common inclusion rating specifications are:


  • ASTM E45, Methods A, C, D, E – Standard Test Methods for Determining Inclusion Content of Steel.
  • ISO 4967 – Steel — Determination of content of non-metallic inclusions
  • ASTM E1245 – Standard Practice for Determining the Inclusion or Second-Phase Constituent Content of Metals by Automated Image Analysis.
  • ASTM E3 – Guide for Preparation of Metallographic Specimens.
  • SAE J422 – Recommended Practice for Determination of Inclusions is Steel.


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