Washers without chamfer DIN 125-1-A-steel 140 HV burnished 21

The combination of strength classes for flat washers with those for bolts and nuts is governed by ISO 898-3:2018, Table 1. Washers with a hardness of 140 HV are suitable for applications with unhardened bolts up to strength class 5.8 and nuts up to class 5. Applications involving bolts of strength class 6.8 and nuts of class 6 must be checked during installation. Combinations with higher strength classes must not be used.

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.

Blackening is carried out in accordance with DIN 50938. Due to the thinness of the conversion coating – approximately one micrometre – the workpieces retain their dimensional stability to a large extent. Blackened fasteners offer only very limited protection against corrosion. Consequently, this process involves the constant-climate condensation test in accordance with DIN EN ISO 6270-2-CH, as well as the acetic acid and oxalic acid tests.