1. The NM and AR Grade Series
Wear resistant steel plates are grouped into the NM series, defined in the Chinese standard GB/T 24186, and the AR series, which follows common international hardness practice. The number in the grade is the nominal Brinell hardness: NM360 and NM400 cover the 360 and 400 HB levels, NM450 and AR450 the 450 level, and NM500 the 500 level. The plate is produced by quenching and tempering to a martensitic structure, which gives the high hardness that resists abrasive wear.
2. Hardness and Mechanical Properties
| Grade | Typical Hardness HB |
| NM360 | 320 - 400 |
| NM400 | 360 - 450 |
| NM450 | 410 - 480 |
| AR450 | 420 - 480 |
| NM500 | 450 - 540 |
In addition to the hardness, the plates carry defined tensile strength and elongation values, and the impact toughness is reported on the certificate. The exact values vary slightly between mills and thicknesses, so the certificate should always be checked against the order requirement.
3. Grade Selection
The grade is selected by the wear mechanism and the impact load. NM360 and NM400 are chosen for liners with moderate abrasion and some impact, where toughness matters as much as hardness. AR450 and NM450 give a balance of wear life and formability for chutes and hoppers, and NM500 is used for severe sliding abrasion where the material flow is fine and fast. For heavy impact, a thicker plate of the lower hardness grade is more reliable than a thin plate of the hardest grade.
4. Applications in Construction Machinery
Wear plates are the standard lining for the parts of construction machinery that contact abrasive material. Dump truck bodies are lined to protect the floor and walls, excavator buckets and loader buckets are fitted with wear plates on the cutting areas, and concrete mixer drums use wear resistant steel where the mix slides. Crushers, screens, hoppers and conveyor transfer points in aggregate plants are lined in the same way, and the plates are replaced when they wear to the minimum thickness.
5. Fabrication and Handling
The plates are cut with plasma or waterjet, welded with low hydrogen consumables and a preheat of 150 to 250°C, and handled with magnetic lifting equipment. The cut edges are ground before welding to remove the hardened zone, and the interpass temperature is controlled during multi pass welding. The plates are stored under cover to limit surface rust, and the surface is prepared before painting if a coating is required.
Frequently Asked Questions
Q: What does NM mean in NM400? NM is the prefix of the Chinese wear resistant plate designation in GB/T 24186, and the number is the nominal Brinell hardness of the grade.
Q: What is the hardness of AR450 plate? AR450 has a typical Brinell hardness of 420 to 480 HB, which suits chutes, hoppers and liners with moderate to severe abrasion.
Q: Which grade is best for an excavator bucket? The cutting edges and wear plates of buckets are commonly NM400 or NM450, with NM500 for severe abrasion and thicker plate for heavy impact.
Q: Can the plate be welded to mild steel? Yes, wear plates are welded to mild steel structures with low hydrogen consumables and a controlled preheat, and the weld should be placed away from the highest wear zone.
Q: How is the grade verified on delivery? The hardness is measured on the plate surface and the mechanical and chemical values are stated on the mill certificate, which should be checked against the order.