Under 669 is classed information on both ferrous and non-ferrous metallurgy, i.e. the production of metals from ores, including the metals themselves and their alloys from the technical point of view, and semi-finished metal and alloy products.
Fabricated metal articles, however, are classed elsewhere, e.g. under 671/673 and 683. Metallic building materials are classed under 691.7 (see related subjects below).
The properties of metallic materials are included in various sections of Class 5, e.g. 539.4 Strength, 539.5 Deform-ability, but testing and material defects come under 620.1, which includes metallography and grain structure.
BS 1000[669]:1986 history
1986BS 1000[669]:1986 Universal Decimal Classification - English full edition - Metallurgy