UNI 3245 Microscopic Examination of Ferrous Materials - Determination of Thickness of Austenic or Ferritic Steel Grains

In the UNI 3245 standard developed by the Italian Standardization Organization (UNI), a micrographic method is defined to determine the austenitic or ferritic grain size of steels. This standard provides the following methods for highlighting the grain and evaluating the average size of the resulting grain:

Counting method (Annex A)
Determination of grain size (Appendix B). Extracted from the standard NFA 04 102 Iron and steel products - Determination of ferritic or austenitic grain size of steels, published by the French Association for Standardization (AFNOR).
Determination of grain size (Appendix C). Extracted from the ASTM E112 standard test methods standard for determining the average grain size developed by the American Testing and Materials Association (ASTM).

These test methods cover the measurement of average grain size and are mainly applied to single-phase grain structures, but are also suitable for determining the average size of a given grain structure in a polyphase or multicomponent sample.

These test methods are used to determine the average grain size of samples with a unimodal distribution of grain areas, diameters, or lengths of intersection. These test methods do not include methods for characterizing the nature of these distributions.

These test methods deal only with the determination of planar grain size, that is, the characterization of two-dimensional grain partitions. Determination of spatial grain size, ie measuring the size of three-dimensional grains in the sample volume, is not within the scope of these test methods.

Briefly, this standard provides measurement procedures for determining the average grain size in metallic materials, and the procedures are geometrically based.

Ferritic steels are low-carbon stainless steels containing 11-30% chromium. All steels in this group are magnetic. Austenitic steels, on the other hand, are stainless steels containing a minimum of 11-26% chromium and 8-36% nickel in their alloy, and have high resistance to chemical corrosion and high temperatures. However, they are not magnetic.

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