ISO 643:2019 pdf free

ISO 643:2019 pdf free.Steels – Micrographic determination of the apparent grain size
If the order, or the International Standard defining the product, does not specify the number of specimens and the point at which they are to be taken from the product, these are left to the manufacturer,although it has been shown that precision of grain size determination increases the higher the number of specimens assessed. Therefore, it is recommended that two or more sections be assessed. Care shall be taken to ensure that the specimens are representative of the bulk of the product (i.e. avoid heavily deformed material such as that found at the extreme end of certain products or where shearing has been used to remove the specimen, etc.). The specimens shall be polished in accordance with the usual methods.
Unless otherwise stated by the product standard or by agreement with the customer, the polished face of the specimen shall be longitudinal, i.e. parallel to the principal axis of deformation in wrought products. Measurements of the grain size on a transverse plane will be biased if the grain shape is not equiaxial.
This is a method specifically for case-hardening steels and shows up austenitic grain boundaries formed during carburization of these steels. It is not usually suitable for revealing grains actually formed during other heat treatments.
NOTE The “mock carburizing” procedure can also be used. The specimen is subjected to the same thermal treatment but without a carbon-rich atmosphere. It is then heat-treated as the product would be treated. The Bechet- Beaujard reagent is used to reveal the grain boundaries, see 6.3.2.
The specimens shall be free from any trace of decarburization or of surface oxidation. Any prior treatment, either cold, hot, mechanical, etc, may have an effect on the shape of the grain obtained; the product specification shall state the treatments to be carried out before determination in cases where it is advisable to take into account these considerations.
After carburizing, the specimen must be cooled at a rate slow enough to precipitate cementite at the grain boundaries in the hypereutectoid surface region of the carburized specimen.ISO 643 pdf free download.