What Is Wear Resistant Steel Sheet
A wear resistant steel sheet is a low-carbon structural plate that has been quenched and tempered to reach high surface hardness while retaining enough toughness for impact service. In the NM series produced to GB/T 24186-2009, the grades NM400, NM450, NM500, NM550 and NM600 are named after their nominal Brinell hardness level, covering roughly 360 HBW up to 640 HBW. Because hardness directly controls abrasive wear resistance, these plates are specified where components slide, scrape or impact against rock, ore, sand and other hard materials.
NM Grade Overview and Hardness
The NM series covers a stepped range of guaranteed hardness, so engineers can match the grade to the severity of the wear duty:
NM400 - 360-440 HBW; general wear service, dump truck bodies, chutes and hoppers.
NM450 - 420-480 HBW; stronger abrasion resistance with balanced toughness for impact areas.
NM500 - 470-540 HBW; high abrasion service such as bucket liners and crusher feeds.
NM550 - 530-580 HBW; severe sliding abrasion with limited impact.
NM600 - 570-640 HBW; extreme wear applications where maximum surface hardness is required.
All grades are delivered in the quenched and tempered condition, which creates a hardened microstructure through the full plate thickness rather than only at the surface.
Why Dump Trucks Use Wear Resistant Sheet
Mining and quarry dump trucks work against constant sliding and impact abrasion. Fitting NM400 to NM600 sheet to the body floor, side walls, front bulkhead and tail areas delivers three measurable benefits:
Longer service life - hardened surfaces resist gouging, scratching and deformation between maintenance intervals.
Lower dead weight - the same wear life can be reached with a thinner plate, allowing more payload per cycle.
Lower operating cost - fewer liner replacements reduce downtime and spare-part expense.
Cutting, Forming and Welding
Wear resistant sheet is normally processed with plasma or laser cutting, and thick sections may require preheating before thermal cutting to avoid edge hardening cracks. For welded assemblies, low-hydrogen filler metal and controlled preheat and interpass temperatures are essential; the heat-affected zone loses some hardness, so weld seams should be positioned away from the highest-wear surfaces wherever possible. Forming in the transverse direction is preferred, and the minimum bend radius increases with plate hardness and thickness.
Supply Formats and Tolerances
NM series sheet is supplied in thicknesses from about 6 mm to 80 mm, widths up to 2500 mm and lengths up to 12000 mm, with mill edge or cut edge options. Dimensional tolerances follow GB/T 709 for hot-rolled plate. Surfaces can be delivered as-rolled, shot blasted, or with a removable protective primer. Each plate is marked with the grade, heat number, dimensions and the applicable standard for full traceability.
Frequently Asked Questions
Q: What hardness does NM400 guarantee?
NM400 is guaranteed to 360-440 HBW per GB/T 24186-2009, with typical yield strength around 900 MPa in thin sections.
Q: Can NM500 plates be welded to structural steel frames?
Yes, but low-hydrogen consumables, preheating and controlled interpass temperature are required to prevent hydrogen cracking in the hardened base material.
Q: What is the difference between NM and AR wear grades?
NM is the Chinese designation per GB/T 24186, while AR400 and AR500 are the widely used export names; both describe quenched and tempered plates with similar hardness ranges.
Q: Which grade is best for dump truck floors?
NM400 or NM450 is the common choice for floors and side liners, balancing wear resistance, weldability and cost; NM500 is used where abrasion is severe and impact is limited.
Q: Do wear plates need preheating before cutting?
Thick sections above roughly 20 mm generally benefit from preheating to 100-150 °C before thermal cutting to reduce the risk of edge cracking.
Q: How is wear life measured?
Wear life is usually assessed by the ASTM G65 dry sand/rubber wheel test, with lower volume loss in cubic millimetres indicating better abrasion resistance.