Tolerance for Stainless Steel Flat Products

The previous standard, EN 10259, has been replaced by EN ISO 9445. The new standard is formally applicable worldwide, rather than just within Europe. The technical content is very similar to EN 10259 – in fact, there are a few small improvements made to the content - but an alternative thickness tolerance table is included, reflecting Japanese practice, with different rules about how close to the strip edge the thickness is measured. The demands of the two systems of measurement are almost identical, but the new document looks more complicated.

A further change is that the requirements for products produced from narrow strip, previously covered by EN 10258, are also included in this same standard, EN ISO 9445

These are currently officially covered by EN 10051, until the appropriate European standards committee releases stainless from the scope of EN 10051, so that we could use ISO 9444 instead. Here, too, supplier and customer may instead agree to use ISO 9444, which is specific to stainless, for dimensional tolerances.

One of the benefits of the new standard is that it is for stainless steel only. In EN 10051 there were 4 categories A - D of which B, C and D covered stainless steel. There were "base" tolerances for category A steel and then an increasing % was applied for categories B, C and D. In the ISO standard there are just 2 categories depending on Ni, Mo or N content. There are no rounding errors as there are no percentages. This also means that there is now no difference between ferritic and martensitic and non-Mo austenitics as there was in EN 10051

There are fewer thickness bands in the ISO standard reflecting the lower maximum rolled thickness of stainless steels compared to carbon and alloy steels.

Comparison of the thickness tolerances in the two standards indicates that the tolerances are similar for austenitic grades but looser for ferritic grades.

The main changes in the standards are summarised as follows:

The new standard also covers hot rolled narrow strip (rolled at < 600 mm).

Although the standard is clearly intended to cover continuously rolled material, there is a rather confusing reference to reversing mill or quarto plate. This product is intended to be covered by ISO 18286.

This is currently covered by EN 10029 which was not primarily intended for stainless steel. There are now no Classes A-D with varying amounts around the nominal thickness. The normal tolerance has a minimum thickness 0.3mm below nominal thickness which is similar to the Class B.

Tolerances now depend on plate width. In EN 10029 the plate width determined the maximum difference within a plate, which is now absent from the new standard.

Some thicknesses have tighter tolerances. For example, all thicknesses below 10mm are +1.15./-0.3. whereas EN 10029 had several thickness bands. 8mm plate was +1.40/-0.3.

Steel type does not affect thickness tolerance but it does affect flatness.

Width and length tolerances are dependent on the method of cutting, Sheared, plasma and water-jet cutting appear to be intended although the terms used are trimmed, flame-cut and abrasive-cut respectively.

One important change is that the standard appears to rule out ANY ground areas being under the minimum thickness. This is in contrast to EN 10029 which referred to EN 10163 which allowed ground areas below the minimum thickness.

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