Why Wear Governs Equipment Life
In bulk material handling, wear is the most common reason a component is taken out of service. Chutes, hoppers, truck trays, bucket lips, crusher liners, screen decks, fan housings and conveyor transfer points are all replaced on a wear cycle rather than on a structural fatigue cycle. The cost of wear is not only the replacement plate: it includes welding labour, production downtime, and the risk that a thinned component fails and damages the equipment behind it.
Because the wear rate depends on the combination of abrasive material, contact pressure, sliding speed, impact angle and moisture, there is no single best plate. The engineering task is to identify which mechanism dominates in each location and then choose a hardness level, a thickness and a steel structure that resists that mechanism.
Wear Mechanisms in Abrasion Resistant Plate
Standard terminology, such as the classification of wear in ASTM G40, distinguishes several mechanisms that frequently act together:
Abrasive wear: hard particles or hard counterfaces cut or plough the surface. It dominates in chutes, hoppers and slurry lines and is the mechanism that abrasion resistant plate is designed for.
Adhesive wear: asperities weld and tear under high contact pressure, producing material transfer. It appears in sliding contacts with insufficient lubrication.
Erosion wear: a stream of particles strikes the surface at an angle. Low-angle impact produces cutting, high-angle impact produces deformation and cracking.
Impact wear: repeated or single high-energy blows deform and eventually crack the surface, which is where toughness, not hardness, decides life.
Corrosion and corrosion-erosion wear: chemical attack removes the protective layer and accelerates mechanical loss, typical of wet coal, salt and fertilizer handling.
Contact fatigue wear: cyclic rolling or sliding contact generates subsurface cracks that spall out, common in crusher rolls and rail wheels.
In most mining and quarrying equipment, abrasive wear accounts for the largest share of failures, with erosion and impact wear increasing in importance in crusher feed zones, transfer chutes and truck tray corners where the material stream strikes the steel directly.
How Abrasion Resistant Plate Resists Wear
Abrasion resistant plate is a low-alloy, quenched and tempered steel whose microstructure is predominantly martensitic, giving a hard surface that resists indentation and cutting by abrasive particles. Hardness is the primary design parameter, expressed in Brinell units, because the wear rate of a steel against a harder abrasive drops as the surface hardness of the steel approaches and exceeds the hardness of the abrasive. Silica sand, a common constituent of mined material, sits around 600-800 HV, which explains why plate in the 400-500 HBW range performs so much better than ordinary structural steel at roughly 150 HBW.
| Grade designation | Nominal Brinell hardness | Typical application |
|---|---|---|
| NM360 | 360 HBW nominal | General chute liners and low-severity handling |
| NM400 | 360-440 HBW | Hoppers, buckets, truck trays, conveyor skirts |
| NM450 | 420-480 HBW | Crusher feed chutes, screen decks, loader buckets |
| NM500 | 470-530 HBW | High-severity impact plus sliding wear zones |
| NM550 and NM600 | Higher nominal hardness | Extreme abrasion with limited impact, such as specific liner inserts |
Hardness in this family is specified and verified in accordance with the GB/T 24186 wear resistant steel plate standard, which defines the grades, hardness ranges, mechanical property requirements and test methods, with Brinell hardness determined to the GB/T 231.1 method. Abrasive wear resistance is assessed separately, because hardness alone does not capture the effect of hard second-phase particles, work hardening or microstructure. Laboratory comparison uses the dry sand rubber wheel test of ASTM G65, the wet variant of ASTM G105 and equivalent domestic wear test methods, in which a specimen is pressed against a rotating wheel with a controlled abrasive feed and the volume loss is measured.
Balancing Hardness, Toughness and Thickness
Hardness and toughness pull in opposite directions. A harder plate resists scratching but tolerates less deformation before cracking, so a 500 HBW plate used in a zone of heavy impact will crack and spall while surviving far longer in a sliding wear zone. The practical rules that guide selection are:
Sliding abrasive wear with fine particles and no heavy impact: choose the highest hardness the fabrication shop can weld and form reliably.
Direct impact from large lumps: step down one hardness level or increase thickness, and prefer grades with controlled impact energy and a low inclusion content.
High-angle erosion: consider thickness and support geometry before hardness, because the material loss is driven by velocity and particle size.
Corrosive slurries: select low-carbon, low-sulphur plate with a controlled hardness ceiling, since a hard, crack-sensitive surface loses material faster in a corrosive medium.
Large flat areas: bolt or plug-weld liners in removable panels so that worn areas can be replaced without cutting out structural steel.
Supply, Fabrication and Quality Control
Abrasion resistant plate is supplied quenched and tempered, with hardness stated as a range rather than a single figure and verified on the delivered plate. Thickness is commonly available from 3 mm to 100 mm, with widths up to about 3200 mm, and cut-to-size or profile-cut parts are normally supplied because thermal cutting and the subsequent edge preparation are better controlled at the plate producer than in a busy maintenance workshop.
Welding follows low-hydrogen practice with preheat on thick sections and a controlled heat input, since overheating the heat-affected zone softens it and creates a soft, fast-wearing band beside the weld. Hardfacing overlays are used where the wear rate justifies the extra cost, and manganese steel is preferred where impact dominates. Forming hot is not permitted, and cold bending requires radii large enough to avoid surface cracking in the martensitic structure.
Material verification on delivery should confirm the grade, the hardness range by Brinell testing, the thickness and flatness tolerances, the surface condition, and the inspection certificate to EN 10204 with the heat number traceable to the plate marking.
Frequently Asked Questions
Q: What is the most common cause of wear in abrasion resistant steel?
A: Abrasive wear, in which hard particles cut and plough the surface. It dominates in chutes, hoppers and bulk handling equipment.
Q: Is higher hardness always better for wear plate?
A: No. In impact zones a very hard plate can crack or spall, so hardness must be balanced against toughness and thickness.
Q: Which standard covers wear resistant steel plate grades?
A: GB/T 24186 defines the NM series grades, their hardness ranges and mechanical requirements, with Brinell hardness tested to the GB/T 231.1 method.
Q: What hardness does NM400 have?
A: NM400 is typically supplied in the 360-440 HBW range, with the actual result stated on the inspection certificate.
Q: How is wear resistance measured in a laboratory?
A: By controlled abrasion tests such as the dry sand rubber wheel method of ASTM G65 or its wet counterpart ASTM G105, which measure volume loss under a defined abrasive feed.
Q: Why does welding soften wear plate?
A: Excessive heat input tempers the martensitic structure near the weld, creating a softer band that wears faster than the parent plate, so heat input limits are part of the welding procedure.
