Eyebolts DIN 580-case-hardened steel C15E zinc plated blue M24

Steel is an iron-carbon alloy with a maximum carbon content of 2% by mass. The steels achieve their intended physical and mechanical properties through various hardening, annealing and tempering processes. It is also possible to harden the edge zone by surface hardening, case hardening or nitriding. Well-known steel grades are structural steels, free-machining steels, case-hardening steels, nitriding steels, tempering steels, tool steels and stainless steels.

Blue galvanised finishes are produced either by electroplating in accordance with DIN EN ISO 4042 or by mechanical plating in accordance with DIN EN ISO 12683. For fasteners with a hardness exceeding 390 HV, there is a risk of hydrogen embrittlement during galvanising (electrolytic process). This necessitates specific measures (such as annealing), although these do not provide a 100 per cent guarantee against embrittlement.

According to the chemical composition, C15 (1.0401) is an unalloyed quality steel, C15E (1.1141) is an unalloyed stainless steel, with the difference being the permissible sulfur and phosphorus content. Both types of steel are classified as case-hardened steels depending on their intended use (carbon content less than 0.20%). The materials in this category are characterized in their initial state by good processing properties when machining and forming.