Material number and steel name

The material number is the unique number of a steel to EN 10027-2, for example 1.7225. The first digit stands for steel, the next two for the steel group, and the last two are sequential: 1.72 for chromium-molybdenum steels, 1.65 for nickel-chromium-molybdenum steels, 1.45 for stainless steels, 2.4 for nickel alloys, 3.7 for titanium. The steel name to EN 10027-1, on the other hand, describes the composition: 42CrMo4 means 0.42% carbon, chromium and molybdenum as alloying elements, and a chromium content of around 1%. Both designations refer to the same steel.

American and other designations

ASTM and ASME do not designate the steel but the grade of the finished fastener: B7 to ASTM A193 is a quenched and tempered chromium-molybdenum steel of the 42CrMo4 type with specified properties, L7 to ASTM A320 is the same type of steel with low-temperature impact testing. UNS numbers such as S31803 (duplex 1.4462) or N07718 (Alloy 718) identify materials internationally. AISI 4140 is the American equivalent of 42CrMo4.

Why RS Randack needs both

A drawing stating “10.9” without a material leaves the choice of material open; a drawing stating “1.7225” without a property class leaves the heat treatment open. Ideally, both should be stated in the enquiry, together with the test standard. If only one is given, RS Randack proposes the appropriate addition and states it in the quotation. The marking on the part later shows the material in abbreviated form, for example RS 6580 with the batch.