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Tolerances - Proposed New Standards for Stainless Steel Flat Products


There has been an attempt to produce worldwide standards for stainless steel flat products by ISO this has resulted in the following situation:

Comparison of EN and ISO Tolerance Standards for Stainless Steel Flat Products
EN Standard ISO Standard Current Status
EN 10258 ISO 9445 ISO Officially replaced EN standard August 2006
EN 10259 ISO 9445 ISO Officially replaced EN standard August 2006
EN 10048 ISO 9444 Awaiting deletion of stainless steels from scope of 10048. Can use ISO 9444 if agreed.
EN 10051 ISO 9445 Awaiting deletion of stainless steels from scope of 10048. Can use ISO 9444 if agreed.
EN 10029 ISO 18286 Awaiting deletion of stainless steels from scope of 10029. Can use ISO 18286 if agreed.

The main changes in the standards are summarised as follows:

Cold rolled wide strip and products cut from wide strip

The previous standard, BS EN 10259, has been ‘officially’ replaced at the end of August 2006 by BS EN ISO 9445. The new standard is formally applicable worldwide, rather than just within Europe. The technical content is very similar to BS 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 full summary of the standard can be found at Tolerances to ISO 9445.

Cold rolled narrow strip [rolled width < 600mm] and products cut from narrow strip

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

A full summary of the standard can be found at ISO 9445.

Hot rolled wide strip and products cut from it

These are currently officially covered by BS EN 10051, until the appropriate European standards committee releases stainless from the scope of BS 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 steels only. In EN 10051 there were 4 categories A – D of which B, C and D covered stainless steels. There were “base” tolerances for category A steels 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.

Thickness tolerances on typical examples
Thickness Width Grade EN 10051 ISO 9444
2.5 1500 1.4003 ±0.24 ±0.27
2.5 1500 1.4301(304) ±0.27 ±0.27
2.5 1500 1.4401(316) ±0.29 ±0.29
5 1500 1.4003 ±0.30 ±0.34
5 1500 1.4301(304) ±0.34 ±0.34
5 1500 1.4401(316) ±0.36 ±0.36
10 1500 1.4003 ±0.38 ±0.43
10 1500 1.4301(304) ±0.43 ±0.43
10 1500 1.4401(316) ±0.46 ±0.46

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.

A full summary of the standard can be found at ISO 9444.

Quarto Plate (Reversing Mill Plate)

This is currently covered by EN 10029 which was not primarily intended for stainless steels. 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.

A full summary of the standard can be found at ISO 18286.

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