Hardox, XAR, Corten, Domex, Strenx, Quard — brand grades with no product standard behind them. Issued by steel producers. 3 grades and 0 standards are documented so far; each grade links to a full data sheet and a graded cross-reference to the other systems.
Every other designation system on this site points at a document. S355J2 means EN 10025-2, with a published composition table, a published mechanical table and a stated test regime; any mill in the world can read it and any buyer can check a certificate against it. Hardox 450 means whatever SSAB's current datasheet says it means, and nothing else.
That is not a criticism of the product. Proprietary grades exist because the property being sold — abrasion resistance, formability at very high strength, atmospheric corrosion resistance — depends on things a composition table cannot capture: cleanliness, segregation control, through-thickness hardness uniformity, the exact rolling and quenching schedule. A standards committee cannot write those into a table that competing mills would all meet the same way, so the producer sells them under a brand and backs them with its own guarantee.
But it changes what a buyer is doing. With a standard grade you specify a document and inspect against it. With a proprietary grade you are buying from one supplier, against a datasheet that supplier can revise. There is no second source that is contractually the same material, and there is no independent arbiter if the plate underperforms.
The grades, and who owns them
Abrasion-resistant plate is the largest family. SSAB's Hardox (400, 450, 500, 550, 600, HiTuf, Extreme) is the reference brand; the competing ranges are ThyssenKrupp XAR, Dillinger Dillidur, ArcelorMittal Creusabro and Relia, NLMK Quard, SSAB Raex, voestalpine Durostat, Ancofer Abrazo and JFE Everhard. The generic American trade description for the same class is AR400 / AR450 / AR500.
High-strength structural plate: SSAB Strenx (formerly Weldox and Optim), Dillinger Dillimax, ArcelorMittal Amstrong, ThyssenKrupp XABO. Most of these can also be bought to EN 10025-6 as S690QL or S960QL, which is the usual escape route from single sourcing.
Cold-formable high-strength strip: SSAB Domex, now also sold as Strenx; the standard equivalent is EN 10149-2 S355MC to S700MC, and in this family the standard grade genuinely does cover it.
Weathering steel: Corten, originally a US Steel trademark and now used generically; the standard grades are EN 10025-5 S355J0WP and S355J2W, and ASTM A242, A588 and A606.
Tool steel: Böhler K110 / W302, Uddeholm Sverker / Orvar / Impax, Buderus Cryodur, ThyssenKrupp Thyrodur / Thyroplast. Here the standard grade almost always exists — K110 is 1.2379, Orvar is 1.2344 — and the brand buys remelting and cleanliness rather than a different analysis.
Why "or equivalent" fails on a proprietary grade
A specification that reads "Hardox 450 or equivalent" is the single most common cause of a wear-plate dispute, and the reason is that the word *equivalent* has no referent. There is no document that defines what Hardox 450 is, so there is nothing for a competing plate to be equivalent *to* — only a datasheet with a hardness range, an impact figure and a set of bending and welding recommendations, each of which a rival product may match on one line and miss on another.
In practice three different things get called equivalent:
Same hardness band. 425–475 HBW. This is what most "equivalent" offers mean, and it is the weakest claim — hardness predicts abrasive wear only within a given microstructure, and two plates at 450 HBW can differ substantially in service.
Same hardness and same impact energy. Adding a Charpy figure at −40 °C narrows it considerably and is the minimum a serious enquiry should ask for.
Same hardness, impact, thickness tolerance, flatness and bend radius. This is what the fabricator actually needs, because a plate that cracks when it is bent to the drawing radius is useless regardless of its hardness.
The way out is to specify properties, not brands: through-thickness hardness range, impact energy and temperature, maximum carbon equivalent, minimum bend radius at the ordered thickness, flatness and thickness tolerance class. A requirement written that way can be quoted by five mills and inspected on arrival.
Reading a proprietary-grade certificate
Certificates for brand grades are issued to EN 10204 3.1 like any other, but what they contain is set by the producer rather than by a product standard, so three checks are worth making.
Is the hardness measured, and where? Abrasion-resistant plate is sold on hardness, and the figure that matters is through-thickness, not surface. A surface reading on a quenched plate flatters it.
Is there an impact result, and at what temperature? Several AR brands quote typical rather than guaranteed impact values, and a typical value is not a requirement. If the plate will see impact at low temperature, the guarantee must be on the certificate.
What tolerance standard is cited? Dimensional requirements usually do come from a real standard — EN 10029 for thickness and flatness of hot-rolled plate, or ASTM A6 — and those references are worth confirming, because they are the only part of the order with independent backing.
The certificate will often also carry a standard grade alongside the brand: a Strenx 700 plate marked S690QL to EN 10025-6, for example. Where that dual marking exists, it is the standard grade that gives the buyer a second source.
When a standard grade will do instead
The proprietary premium is worth paying in some families and not in others, and the test is whether a standard grade covers the property being bought.
Abrasion-resistant plate: no standard exists. There is no EN or ASTM grade for 400–600 HBW wear plate. EN 10025-6 covers quenched and tempered structural plate by *strength*, not hardness, and stops well short. This family is genuinely proprietary and will stay that way.
High-strength structural plate: a standard exists and is widely used. EN 10025-6 S690QL, S890QL and S960QL are real grades with real tables, and most of the brand plate in this class is dual-certified to them. Specify the standard grade and let the mills compete.
Cold-formable strip: the standard grade is the normal purchase. EN 10149-2 S355MC through S700MC covers it fully; the brand adds consistency, not capability.
Weathering steel: the standard grade is the correct specification. Corten has become a generic word for a product that EN 10025-5 and ASTM A588 define properly.
Tool steel: the standard grade defines the analysis, the brand sells the cleanliness. Specify 1.2344 and then, where it matters, add the remelting and cleanliness requirement — which is exactly what NADCA #207 does for die casting steel.
Frequently asked questions
Is Hardox a grade of steel?
No — it is SSAB's registered trademark for a range of abrasion-resistant quenched and tempered plate. There is no standards document behind it; what Hardox 450 is, is defined by SSAB's current datasheet. That is normal for wear plate, because no EN or ASTM grade covers the 400–600 HBW class at all, but it means a buyer is specifying a supplier rather than a specification.
What does AR400 mean if it is not a standard?
It is a trade description: abrasion-resistant plate at a nominal 400 HBW hardness. No ASTM specification defines it, no composition is fixed, and two mills' AR400 can differ in analysis, impact energy, bend radius and thickness tolerance while both being correctly labelled. The number tells you the target hardness band and nothing more.
Why does "or equivalent" cause problems with brand grades?
Because there is no document the alternative can be equivalent to. In practice the word gets used for anything from "same hardness band" to "same hardness, impact energy, bend radius and tolerances", and those are very different promises. The fix is to specify the properties the application needs — through-thickness hardness range, impact energy and temperature, carbon equivalent, minimum bend radius, tolerance class — so that several mills can quote and the plate can be inspected on arrival.
Can I buy a standard grade instead of a proprietary one?
It depends on the family. For high-strength structural plate, yes — EN 10025-6 S690QL and S960QL are real grades and most brand plate is dual-certified to them. For cold-formable strip, yes — EN 10149-2 covers S355MC to S700MC. For weathering steel, yes — EN 10025-5 and ASTM A588. For abrasion-resistant wear plate, no: there is no standard grade in that class, which is why the brands own it.
Do proprietary grades come with a normal mill certificate?
Yes, usually EN 10204 3.1. What differs is that the requirements it is issued against come from the producer's datasheet rather than a product standard, so check three things: whether hardness is reported through-thickness rather than at the surface, whether the impact value is guaranteed or merely typical, and which dimensional standard is cited — EN 10029 or ASTM A6 are the usual ones and are the only independently backed part of the order.