Stock standard is hard-chrome-plated bar in grade 280X which is a low-carbon micro-alloyed steel with analysis conforming both to 19MnVS6 in SS-EN 10267 and to S450J0 in SS-EN 10025-2 (SS2142). However, the analysis and processing are optimised such that the level of yield and tensile strength is 20 - 25 % higher than the standard grades mentioned. This improvement is attained without penalty in terms of weldability or machinability. The higher strength level offers the possibility to reduce the diameter of a piston rod without loss of performance which brings savings both in terms of weight as well as cost.
Chrome as such is characterised by excellent corrosion resistance. In spite of this, the corrosion resistance of hard-chrome bar is limited. The chrome layer is hard with considerable residual stresses which results in the formation of a network of fine micro-cracks. However, control of the plating process combined with judicious finishing allows the attainment of acceptable corrosion resistance, sufficient to withstand exposure in damp air or oxygenated water.
The diameter tolerance of Cromax 280X is f7 as defined in ISO 286 - 2. The surface finish expressed as Ra is 0.2 μm or finer. Straightness is ≤0.1 mm/0.5 m for diameters less than 30 mm and ≤0.1 mm/m for larger diameters. The thickness of the chrome layer is more than 20 μm and its hardness exceeds 850 HV0.1.
Tibnor can also supply induction-hardened hard-chrome bars as well as chrome-plated tubes.