Grade Families and Hardness
AR400 and AR500 are commercial abrasion resistant designations widely used in North America and in export trade. The number reflects the nominal Brinell hardness of the quenched plate, so AR400 sits in the range of about 360 to 440 HBW and AR500 in the range of about 470 to 540 HBW. Hardness is measured on the plate surface according to ASTM E10. NM450 and NM500 are the Chinese designations from GB/T 24186, the standard for high strength abrasion resistant plate. NM360, NM400, NM450 and NM500 form a hardness series in which the number corresponds to the mid range of the specified surface hardness.
| Grade | Typical Surface Hardness HBW | Relative Wear Life |
| NM400 and AR400 | 360 to 440 | Reference |
| NM450 | 420 to 480 | Higher than NM400 |
| NM500 and AR500 | 470 to 540 | Highest of the series |
Composition and Toughness
These plates are low alloy steels with carbon typically between 0.20 and 0.35 percent, manganese up to about 1.60 percent and additions of chromium, molybdenum, nickel and boron to develop hardness. The plate is quenched directly from the rolling heat or from a reheat furnace, and it is usually supplied in the as quenched condition without tempering above 200 degrees Celsius so that hardness is preserved. Raising the hardness reduces ductility, so AR500 and NM500 need thicker support and more careful handling than AR400 and NM400. Where impact is severe, a lower hardness grade on a thicker section often outlasts a harder but more brittle plate.
Cutting and Forming
Wear plate can be cut by plasma, laser, water jet and abrasive saw. Thermal cutting creates a thin hardened zone along the cut edge, and on high hardness grades this edge should be ground back before welding to avoid cracking. Water jet cutting avoids the heat affected zone entirely and is preferred for intricate shapes in AR500. Cold forming is limited because the high hardness reduces ductility. Large radius bends may be made across the rolling direction with a generous bend radius, but tight bends should be avoided. Where a formed liner is required, a lower hardness grade or a thinner plate on a formed backing is the better solution.
Welding Practice
Wear plate is joined to structural steel backing in most applications. For NM400 and AR400 a low hydrogen consumable with light preheat is normally sufficient. For NM450, NM500 and AR500 the procedure should be qualified, with preheat in the range of 100 to 150 degrees Celsius, controlled heat input and avoidance of weld metal dilution from the hard plate. Butt joints between two wear plates should be minimised. Where they cannot be avoided, a matching or slightly softer filler is used and the joint is placed away from the highest abrasion zone.
Typical Applications
Truck tray liners and dump body floors.
Chute, hopper and transfer point liners.
Excavator and loader bucket wear strips.
Crusher feed plates and screen decks.
Conveyor skirt boards and impact bars.
Frequently Asked Questions
Q: Is AR400 the same as NM400?
They are different designations from different systems, but both describe a quenched abrasion resistant plate in the range of about 360 to 440 HBW and are treated as equivalent by many buyers.
Q: Which grade offers the longest wear life?
Within this series NM500 and AR500 give the longest life in sliding abrasion, provided the supporting structure and the cut edges are designed for the higher hardness.
Q: Can any of these plates be bent?
Limited cold forming is possible with a generous bend radius across the rolling direction, but neither the hardest grades nor thick plate should be formed tightly.
Q: How should wear plate be welded?
Use a qualified procedure with a low hydrogen consumable, light preheat, controlled heat input and grinding of thermally cut edges before welding.
Q: What thicknesses are available?
Wear resistant plate is commonly produced from 3 mm to 100 mm, with the 6 mm to 40 mm range being the most widely stocked for liners and truck bodies.