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Stainless Steel Round Bar Machined EN 1.4418
1.4418 is a martensitic stainless steel which combines very high strength and hardness with good corrosion resistance equivalent to the austenitic types, 1.4301 and 1.4307. Otherwise, the usual situation is that the high strength of martensitic steels is achieved at the expense of the anti-corrosion properties. The steel contains about 16% chromium together with 5% nickel and 1% molybdenum. Furthermore, and at variance with other martensitic stainless steels, its carbon content is low. The bars in stock are in the quenched-and-tempered condition with minimum tensile strength 900 MPa and typical hardness 300 HB.
Ground round bars in 1.4418 are standardised in EN 10088-3 and the heat-treatment condition is designated “+QT 900”. This standard covers cold-finished round bars with diameters up to 250 mm even though it is normally only smaller dimensions that are available in ground execution. However, Tibnor’s extensive programme encompasses diameters up to and including 125 mm.
In spite of its high strength, 1.4418 is characterised by good resistance to corrosion in neutral water both indoors and outdoors. The steel also exhibits immunity from atmospheric corrosion. The comparatively good corrosion properties in combination with higher strength render 1.4418 as an attractive alternative for machine components exposed to corrosive environments such as pump parts, axles and in the energy segment (water power, offshore).
Cold forming of 1.4418 is quite difficult because of the high strength. On the other hand, the low carbon content means that for a martensitic steel, it is quite easy to weld. In parity with the high hardness, machining of 1.4418 can be quite difficult but working is always facilitated through bespoke tooling. However, in reality, 1.4418 is no more difficult to machine than quenched-and-tempered carbon steels with the same hardness.
The surface finish of ground bars of 1.4418 as stocked is 2G as defined in EN 10088-3. Grinding is carried after hot-rolled bars have been quenched and tempered, pickled as needed and the surface pre-processed through either cold drawing or peeling. This procedure eliminates any remaining surface defects. The diameter tolerance of ground bars is h9 as stipulated in ISO 286 - 2 which is a zero-minus tolerance. In other words, the actual diameter is marginally less than the nominal one. In addition, ground bars of stainless steel are very straight (height of arc less than 0.001 x length) with fine surface (Ra <1µm).