Linsen-Blechschrauben Bund u. Spitz DIN 968C-St znb C4,8x16

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.

A further development of Form H are Pozidriv (PZ) screws, standardized in ISO 8764 (blades) and DIN 7962 (Phillips). With the Pozidriv screws, the flanks of the screw head run parallel to each other in the depth of the screw head. Due to the more precise fit, the direction of force is precisely determined and higher torques are possible because the cam-out effect is prevented.

Case hardening is used to impart significantly greater hardness to the surface layer of steel workpieces and to improve their mechanical properties. Case-hardened workpieces are characterised by increased wear resistance, a tough core and enhanced fatigue strength.