Selecting the hardness grade in Hardox wear-resistant steels

The choice between Hardox 450 and Hardox 500 depends on the wear mechanism acting on the component, not on the amount of wear it suffers. Where the damage comes from sliding abrasion, every point of hardness converts into service life in a nearly linear fashion. Where it comes from impact and gouging, beyond a certain threshold the plate cracks before it wears out, and the extra hardness produces no return.

Added to this is an effect that shows up in the workshop rather than in service: every step up in hardness widens the minimum bend radii, lowers the preheat threshold in welding and reduces the tolerance for process errors. A component in Hardox 500 costs more than one in Hardox 450 even at the same price per kilogram of plate.

This guide covers the selection parameters, the expected return on stepping up a grade and the implications for processing.

Surface hardness and structural properties

The most common misreading is to interpret the Brinell value as an index of structural strength. The two quantities are distinct: hardness measures the surface’s resistance to penetration, while yield strength marks the threshold beyond which the section deforms permanently.

Wear-resistant steels belong to the family of quenched and tempered grades, hardened and tempered to obtain a martensitic structure. Hardening is through-thickness, and the product guarantees assure at least 90% of the minimum surface hardness across the thickness. The component therefore keeps its properties even after wear has consumed the first millimetres — behaviour not obtainable with surface-only hardening.

Grade	Hardness	Prevailing function	Typical use
Hardox 450	425-475 HBW	Wear resistance with residual structural properties	Components that resist abrasion and carry load
Hardox 500	470-530 HBW	Specialised wear resistance	Liners and consumable elements applied to a load-bearing structure
Equivalent wear-resistant steels	Various classes	Wear resistance without extended product guarantees	Heavy-duty work on non-critical components

The 450 is the borderline case of the range, because it retains enough structural properties to act as a load-bearing element in many applications: tipper body walls, bucket structures, components that must both resist abrasion and carry load. From 500 upwards the function specialises, and the plate works as a liner applied to a structure whose load is carried by structural steel.

Ordering a wear-resistant grade for an element subject only to mechanical stress, with no exposure to abrasion, means paying for a performance the application does not use. In that case the correct reference is a high-yield structural steel, available among the quarto plates in S235, S275, S355 and Corten.

Wear mechanisms and the governing property

How the component wears out establishes which material property governs its life. The main mechanisms behave in opposite ways with respect to hardness.

Mechanism	Typical operating condition	Evidence on the part at end of life	Governing property	Direction of choice
Sliding abrasion	Fine, hard material flowing over the surface	Uniform thinning of the thickness	Hardness	Step up a grade
Impact and gouging	Large blocks falling and digging	Cracks from corners, holes and welds, with plenty of residual thickness	Toughness	Step down a grade or revise the geometry
Flow erosion	Suspended particles, slurries, pneumatic conveying	Varies with the angle of incidence	Hardness or toughness depending on the angle	Assess case by case

Sliding abrasion. Sand, crushed aggregates, slag, dry earth on hopper liners, tipper floors, chute plates, ducts for loose materials. The damage consists of the progressive removal of micro-volumes by particles harder than the steel, and the correlation between hardness and life is strong and essentially proportional. In these conditions the step up to 500 delivers as expected, and in particularly severe environments it makes sense to consider higher hardnesses.

Impact and gouging. Crusher feeds, screening grids, rock buckets, recycling plants with bulky, heterogeneous material. The prevailing damage is localised deformation with cracks propagating from the point of impact. The property governing life becomes toughness, which decreases as hardness increases. A plate that is too hard in a pure impact application breaks along the edges and around the holes before its sacrificial thickness is used up.

Erosion by particles in flow. Behaviour depends on the angle of incidence: at grazing incidence it approaches abrasion and rewards hardness; at perpendicular incidence it approaches impact and rewards toughness.

The operational criterion is to observe the replaced parts rather than the data sheets. A component that reaches end of life uniformly thinned indicates a need for more hardness. A component that reaches end of life cracked, with plenty of residual thickness, indicates the opposite — and replacing it with a harder grade makes the defect worse.

Return on the hardness step

The data published by the producer provide an order of magnitude usable in economic assessment, referred to abrasion conditions.

Increase over a 400 HBW wear-resistant steel	Indicative increase in service life
+50 HBW	30-40%
+100 HBW	80-100%

The values should be read as a trend across comparable applications, not as a guarantee transferable to any operating condition.

The economic comparison is made up of three items, in increasing order of weight:

1. Price delta per kilogram between the two grades — the smallest component.
2. Additional processing cost, less predictable and covered in the next section.
3. Cost of avoided downtime, which in most industrial applications dominates the calculation. Where replacing a liner means two days of stopped plant, doubling the replacement interval is worth far more than the list price difference.

The calculation flips for components that reach end of life for reasons unrelated to wear: scrapping of the surrounding structure, machine reconfiguration, plant obsolescence. Extending life beyond that threshold produces no return.

Verifying the correct grade starts from examining the worn part and the actual operating conditions. The available formats and processing options are listed on the page for Hardox wear-resistant steel plates; for an assessment of a specific application, contact the Solsider technical office.

Effects of hardness on processing

The difference between the grades shows up in the four operations a wear-resistant component goes through most often.

Operation	Hardox 450	Hardox 500	Operational note
Minimum internal bend radius	about 3 times the thickness	about 4 times the thickness	Values refer to bending transverse to the rolling direction
Preheat in welding	Needed from higher combined thicknesses	Lower threshold	Depends on the combined thickness of the joint
Filler material	Low hydrogen, strength below the base material	Same criterion	Deformation concentrates in the weld bead rather than the surrounding metal
Thermal cutting	Oxyfuel with preheat control	Tighter control	Risk of cold cracking along the edge
Drilling	Reduced speeds, sustained feed	Dedicated tooling	Preferable to cut holes in the cutting cycle

Bending. Beyond the minimum radius, two parameters change appreciably. The bending force grows in proportion to the yield strength, which on these steels far exceeds that of an S355. Springback is pronounced, which means the first bends of a series serve to calibrate the machine. Bending along the rolling direction requires wider radii than those shown in the table.

Welding. Both grades are weldable with ordinary processes. Heat input must be contained and interpass temperature kept low: excess heat locally tempers the martensitic structure and produces permanent softening of the heat-affected zone.

Thermal cutting. Oxyfuel is the usual process at these thicknesses. Selection criteria and consequences for the part are covered in the guide on selecting the thermal cutting process.

Thickness reduction at equal service life

There is a third option, rarely considered, which in several applications beats both initial alternatives. Replacing a structural steel with a wear-resistant one makes it possible to reduce the thickness while maintaining or improving service life, and the material saved converts into payload.

Thickness	Weight per square metre	Difference vs 10 mm
10 mm	78.5 kg	reference
8 mm	62.8 kg	-20%
6 mm	47.1 kg	-40%

On a tipper body with a total surface of twenty square metres, moving from 10 to 8 mm frees over three hundred kilograms, which become additional payload on every trip for the entire life of the vehicle. The comparison on real geometries and thicknesses can be set up with the section weight calculator.

The preliminary check concerns the structural function. Reducing thickness lowers the section’s moment of inertia and therefore its stiffness — an effect the higher yield strength of the wear-resistant grade only partly compensates. On walls stiffened by profiles the operation is almost always practicable; on wide unrestrained panels it must be verified, because the limit encountered first is elastic deformation, not strength.

Branded material and equivalent wear-resistant steels

The market offers wear-resistant plates from various producers with comparable nominal hardnesses and lower prices. The parameter to compare is the contractual guarantees that accompany the material.

Aspect	Branded material	Equivalent wear-resistant steel
Hardness through the thickness	Guaranteed at 90% of the minimum surface value	Not always declared
Dimensional tolerances	Tighter than the standard minimums	Per standard
Flatness and bending behaviour	Covered by guarantee	Varies between heats
Heat traceability	Complete	Depends on the supplier
Repeatability between supplies	High	To be verified

The value of these guarantees lies in repeatability: every plate behaves like the previous one, and the bending and welding parameters tuned once remain valid. For a fabricator producing the same component in series, predictability matters more than the price per kilogram.

The equivalent wear-resistant steel remains the reasonable choice for one-off non-critical parts, for simple geometries without tight bends, for applications where the component is oversized relative to the expected wear. In these conditions the weight of the documented guarantee diminishes.

The summary criterion is the consequence of error. Where a crack in bending or softening in welding stops a production line or compromises an installed component, the material guarantee is the cheapest item of the whole operation. Where the error costs one plate, the calculation may point elsewhere.

For hardnesses, formats and finishing operations such as bevelling, bending and rolling, the reference is the services page, or direct contact with the technical office.