The processing of fibre-reinforced plastics requires hardenable, corrosion-resistant tool steels with a high carbide content, approx. 13 to 20 % Chromium, additions of Molybdenum, Tungsten and Vanadium and a hardness of 50 to over 60 HRC. In High-Nitrogen Steels, Carbon is partially replaced by Nitrogen to achieve a hardness of approx. 58 HRC with the best corrosion resistance.
This group of steels is specially designed for use as corrosion-resistant tool steels in plastics processing when corrosion and wear resistance are of primary importance, as is the case, for example, when processing fibre-reinforced and heavily filled, aggressive plastics. Experience shows that corrosion-resistant tool steels with hardnesses of over 50 HRC are then required. Under particularly critical operating conditions, however, steels with a higher carbide content and hardnesses above 60 HRC are often essential.
Steels in this product group are usually selected hardenable, martensitic stainless steels with approx. 13 to 20 % Cr , alloyed with Mo , W and V and a C content of approx. 0.40 to over 2%.
In general, the production of these steels with regard to purity, homogeneity and analytical balance takes special account of the needs of plastics processing with regard to polishability and corrosion resistance, and high-purity steels are frequently produced by remelting processes, e.g. electroslag (ESR), or extremely homogeneous, high-alloy steels are produced by powder metallurgy.
A special category of hardenable corrosion resistant steels are High Nitrogen Steels (HNS). In such steels the high Carbon (C)- content present usually in steels of this group is reduced and part of the Carbon is replaced by Nitrogen(N). This results in a hardness of approx. 58 HRC together with the best corrosion resistance and optimum homogeneity and prevents the excessive bonding of Chromium in the form of carbides. Usually remelting of this steel takes place in the special Pressure Electroslag Remelting Process (PESR).